@c Copyright (C) 1988-2014 Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @ignore @c man begin INCLUDE @include gcc-vers.texi @c man end @c man begin COPYRIGHT Copyright @copyright{} 1988-2014 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License'' and ``Funding Free Software'', the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. @c man end @c Set file name and title for the man page. @setfilename gcc @settitle GNU project C and C++ compiler @c man begin SYNOPSIS gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} Only the most useful options are listed here; see below for the remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. @c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for @file{gcc}, @file{cpp}, @file{as}, @file{ld}, @file{binutils} and @file{gdb}. @c man end @c man begin BUGS For instructions on reporting bugs, see @w{@value{BUGURL}}. @c man end @c man begin AUTHOR See the Info entry for @command{gcc}, or @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, for contributors to GCC@. @c man end @end ignore @node Invoking GCC @chapter GCC Command Options @cindex GCC command options @cindex command options @cindex options, GCC command @c man begin DESCRIPTION When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The ``overall options'' allow you to stop this process at an intermediate stage. For example, the @option{-c} option says not to run the linker. Then the output consists of object files output by the assembler. Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them. @cindex C compilation options Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages. @cindex C++ compilation options @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special options for compiling C++ programs. @cindex grouping options @cindex options, grouping The @command{gcc} program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d -v}}. @cindex order of options @cindex options, order You can mix options and other arguments. For the most part, the order you use doesn't matter. Order does matter when you use several options of the same kind; for example, if you specify @option{-L} more than once, the directories are searched in the order specified. Also, the placement of the @option{-l} option is significant. Many options have long names starting with @samp{-f} or with @samp{-W}---for example, @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of these have both positive and negative forms; the negative form of @option{-ffoo} is @option{-fno-foo}. This manual documents only one of these two forms, whichever one is not the default. @c man end @xref{Option Index}, for an index to GCC's options. @menu * Option Summary:: Brief list of all options, without explanations. * Overall Options:: Controlling the kind of output: an executable, object files, assembler files, or preprocessed source. * Invoking G++:: Compiling C++ programs. * C Dialect Options:: Controlling the variant of C language compiled. * C++ Dialect Options:: Variations on C++. * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C and Objective-C++. * Language Independent Options:: Controlling how diagnostics should be formatted. * Warning Options:: How picky should the compiler be? * Debugging Options:: Symbol tables, measurements, and debugging dumps. * Optimize Options:: How much optimization? * Preprocessor Options:: Controlling header files and macro definitions. Also, getting dependency information for Make. * Assembler Options:: Passing options to the assembler. * Link Options:: Specifying libraries and so on. * Directory Options:: Where to find header files and libraries. Where to find the compiler executable files. * Spec Files:: How to pass switches to sub-processes. * Target Options:: Running a cross-compiler, or an old version of GCC. * Submodel Options:: Specifying minor hardware or convention variations, such as 68010 vs 68020. * Code Gen Options:: Specifying conventions for function calls, data layout and register usage. * Environment Variables:: Env vars that affect GCC. * Precompiled Headers:: Compiling a header once, and using it many times. @end menu @c man begin OPTIONS @node Option Summary @section Option Summary Here is a summary of all the options, grouped by type. Explanations are in the following sections. @table @emph @item Overall Options @xref{Overall Options,,Options Controlling the Kind of Output}. @gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol -pipe -pass-exit-codes @gol -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol --version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} @item C Language Options @xref{C Dialect Options,,Options Controlling C Dialect}. @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol -fno-asm -fno-builtin -fno-builtin-@var{function} @gol -fhosted -ffreestanding -fopenmp -fopenmp-simd -fms-extensions @gol -fplan9-extensions -trigraphs -traditional -traditional-cpp @gol -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol -fsigned-bitfields -fsigned-char @gol -funsigned-bitfields -funsigned-char} @item C++ Language Options @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol -fconstexpr-depth=@var{n} -ffriend-injection @gol -fno-elide-constructors @gol -fno-enforce-eh-specs @gol -ffor-scope -fno-for-scope -fno-gnu-keywords @gol -fno-implicit-templates @gol -fno-implicit-inline-templates @gol -fno-implement-inlines -fms-extensions @gol -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol -fno-optional-diags -fpermissive @gol -fno-pretty-templates @gol -frepo -fno-rtti -fstats -ftemplate-backtrace-limit=@var{n} @gol -ftemplate-depth=@var{n} @gol -fno-threadsafe-statics -fuse-cxa-atexit @gol -fno-weak -nostdinc++ @gol -fvisibility-inlines-hidden @gol -fvtable-verify=@var{std|preinit|none} @gol -fvtv-counts -fvtv-debug @gol -fvisibility-ms-compat @gol -fext-numeric-literals @gol -Wabi=@var{n} -Wconversion-null -Wctor-dtor-privacy @gol -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol -Wnoexcept -Wnon-virtual-dtor -Wreorder @gol -Weffc++ -Wstrict-null-sentinel @gol -Wno-non-template-friend -Wold-style-cast @gol -Woverloaded-virtual -Wno-pmf-conversions @gol -Wsign-promo} @item Objective-C and Objective-C++ Language Options @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling Objective-C and Objective-C++ Dialects}. @gccoptlist{-fconstant-string-class=@var{class-name} @gol -fgnu-runtime -fnext-runtime @gol -fno-nil-receivers @gol -fobjc-abi-version=@var{n} @gol -fobjc-call-cxx-cdtors @gol -fobjc-direct-dispatch @gol -fobjc-exceptions @gol -fobjc-gc @gol -fobjc-nilcheck @gol -fobjc-std=objc1 @gol -fno-local-ivars @gol -fivar-visibility=@var{public|protected|private|package} @gol -freplace-objc-classes @gol -fzero-link @gol -gen-decls @gol -Wassign-intercept @gol -Wno-protocol -Wselector @gol -Wstrict-selector-match @gol -Wundeclared-selector} @item Language Independent Options @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. @gccoptlist{-fmessage-length=@var{n} @gol -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol -fno-diagnostics-show-option -fno-diagnostics-show-caret} @item Warning Options @xref{Warning Options,,Options to Request or Suppress Warnings}. @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol -pedantic-errors @gol -w -Wextra -Wall -Waddress -Waggregate-return @gol -Waggressive-loop-optimizations -Warray-bounds @gol -Wbool-compare @gol -Wno-attributes -Wno-builtin-macro-redefined @gol -Wc90-c99-compat -Wc99-c11-compat @gol -Wc++-compat -Wc++11-compat -Wcast-align -Wcast-qual @gol -Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported @gol -Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp @gol -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol -Wdisabled-optimization -Wno-discarded-qualifiers @gol -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol -Wno-endif-labels -Werror -Werror=* @gol -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol -Wformat-security -Wformat-signedness -Wformat-y2k @gol -Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol -Wignored-qualifiers -Wincompatible-pointer-types @gol -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol -Winit-self -Winline -Wno-int-conversion @gol -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol -Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol -Wmain -Wmaybe-uninitialized -Wmemset-transposed-args -Wmissing-braces @gol -Wmissing-field-initializers -Wmissing-include-dirs @gol -Wno-multichar -Wnonnull -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol -Wodr -Wno-overflow -Wopenmp-simd @gol -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol -Wpointer-arith -Wno-pointer-to-int-cast @gol -Wredundant-decls -Wno-return-local-addr @gol -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol -Wshift-count-negative -Wshift-count-overflow @gol -Wsign-compare -Wsign-conversion -Wfloat-conversion @gol -Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol -Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol -Wsuggest-final-types @gol -Wsuggest-final-methods @gol -Wmissing-format-attribute @gol -Wswitch -Wswitch-default -Wswitch-enum -Wswitch-bool -Wsync-nand @gol -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol -Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol -Wunsuffixed-float-constants -Wunused -Wunused-function @gol -Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol -Wno-unused-result -Wunused-value @gol -Wunused-variable @gol -Wunused-but-set-parameter -Wunused-but-set-variable @gol -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol -Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant} @item C and Objective-C-only Warning Options @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol -Wold-style-declaration -Wold-style-definition @gol -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol -Wdeclaration-after-statement -Wpointer-sign} @item Debugging Options @xref{Debugging Options,,Options for Debugging Your Program or GCC}. @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol -fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol -fasan-shadow-offset=@var{number} -fsanitize-undefined-trap-on-error @gol -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol -fdisable-ipa-@var{pass_name} @gol -fdisable-rtl-@var{pass_name} @gol -fdisable-rtl-@var{pass-name}=@var{range-list} @gol -fdisable-tree-@var{pass_name} @gol -fdisable-tree-@var{pass-name}=@var{range-list} @gol -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol -fdump-translation-unit@r{[}-@var{n}@r{]} @gol -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol -fdump-passes @gol -fdump-statistics @gol -fdump-tree-all @gol -fdump-tree-original@r{[}-@var{n}@r{]} @gol -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol -fdump-tree-cfg -fdump-tree-alias @gol -fdump-tree-ch @gol -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol -fdump-tree-gimple@r{[}-raw@r{]} @gol -fdump-tree-dom@r{[}-@var{n}@r{]} @gol -fdump-tree-dse@r{[}-@var{n}@r{]} @gol -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol -fdump-tree-nrv -fdump-tree-vect @gol -fdump-tree-sink @gol -fdump-tree-sra@r{[}-@var{n}@r{]} @gol -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol -fdump-tree-fre@r{[}-@var{n}@r{]} @gol -fdump-tree-vtable-verify @gol -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol -fdump-final-insns=@var{file} @gol -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol -feliminate-unused-debug-symbols -femit-class-debug-always @gol -fenable-@var{kind}-@var{pass} @gol -fenable-@var{kind}-@var{pass}=@var{range-list} @gol -fdebug-types-section -fmem-report-wpa @gol -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol -fopt-info @gol -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol -frandom-seed=@var{number} -fsched-verbose=@var{n} @gol -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol -fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol -fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol -ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol -gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol -fdebug-prefix-map=@var{old}=@var{new} @gol -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol -print-multi-directory -print-multi-lib -print-multi-os-directory @gol -print-prog-name=@var{program} -print-search-dirs -Q @gol -print-sysroot -print-sysroot-headers-suffix @gol -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} @item Optimization Options @xref{Optimize Options,,Options that Control Optimization}. @gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol -falign-jumps[=@var{n}] @gol -falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol -fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol -fauto-inc-dec -fbranch-probabilities @gol -fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol -fbtr-bb-exclusive -fcaller-saves @gol -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol -fcompare-elim -fcprop-registers -fcrossjumping @gol -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol -fcx-limited-range @gol -fdata-sections -fdce -fdelayed-branch @gol -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fdse @gol -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol -fif-conversion2 -findirect-inlining @gol -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol -finline-small-functions -fipa-cp -fipa-cp-clone @gol -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf @gol -fira-algorithm=@var{algorithm} @gol -fira-region=@var{region} -fira-hoist-pressure @gol -fira-loop-pressure -fno-ira-share-save-slots @gol -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol -fivopts -fkeep-inline-functions -fkeep-static-consts -flive-range-shrinkage @gol -floop-block -floop-interchange -floop-strip-mine -floop-nest-optimize @gol -floop-parallelize-all -flra-remat -flto -flto-compression-level @gol -flto-partition=@var{alg} -flto-report -flto-report-wpa -fmerge-all-constants @gol -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol -fmove-loop-invariants -fno-branch-count-reg @gol -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol -fomit-frame-pointer -foptimize-sibling-calls @gol -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol -fprefetch-loop-arrays -fprofile-report @gol -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol -fprofile-generate=@var{path} @gol -fprofile-use -fprofile-use=@var{path} -fprofile-values -fprofile-reorder-functions @gol -freciprocal-math -free -frename-registers -fschedule-fusion -freorder-blocks @gol -freorder-blocks-and-partition -freorder-functions @gol -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol -frounding-math -fsched2-use-superblocks -fsched-pressure @gol -fsched-spec-load -fsched-spec-load-dangerous @gol -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol -fsched-group-heuristic -fsched-critical-path-heuristic @gol -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol -fschedule-insns -fschedule-insns2 -fsection-anchors @gol -fselective-scheduling -fselective-scheduling2 @gol -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol -fsemantic-interposition @gol -fshrink-wrap -fsignaling-nans -fsingle-precision-constant @gol -fsplit-ivs-in-unroller -fsplit-wide-types -fssa-phiopt -fstack-protector @gol -fstack-protector-all -fstack-protector-strong -fstrict-aliasing @gol -fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp @gol -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol -ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol -ftree-loop-if-convert-stores -ftree-loop-im @gol -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol -ftree-loop-vectorize @gol -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol -ftree-switch-conversion -ftree-tail-merge -ftree-ter @gol -ftree-vectorize -ftree-vrp @gol -funit-at-a-time -funroll-all-loops -funroll-loops @gol -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol -fuse-caller-save -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol -fweb -fwhole-program -fwpa -fuse-ld=@var{linker} -fuse-linker-plugin @gol --param @var{name}=@var{value} -O -O0 -O1 -O2 -O3 -Os -Ofast -Og} @item Preprocessor Options @xref{Preprocessor Options,,Options Controlling the Preprocessor}. @gccoptlist{-A@var{question}=@var{answer} @gol -A-@var{question}@r{[}=@var{answer}@r{]} @gol -C -dD -dI -dM -dN @gol -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol -idirafter @var{dir} @gol -include @var{file} -imacros @var{file} @gol -iprefix @var{file} -iwithprefix @var{dir} @gol -iwithprefixbefore @var{dir} -isystem @var{dir} @gol -imultilib @var{dir} -isysroot @var{dir} @gol -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol -P -fdebug-cpp -ftrack-macro-expansion -fworking-directory @gol -remap -trigraphs -undef -U@var{macro} @gol -Wp,@var{option} -Xpreprocessor @var{option} -no-integrated-cpp} @item Assembler Option @xref{Assembler Options,,Passing Options to the Assembler}. @gccoptlist{-Wa,@var{option} -Xassembler @var{option}} @item Linker Options @xref{Link Options,,Options for Linking}. @gccoptlist{@var{object-file-name} -l@var{library} @gol -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol -s -static -static-libgcc -static-libstdc++ @gol -static-libasan -static-libtsan -static-liblsan -static-libubsan @gol -shared -shared-libgcc -symbolic @gol -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol -u @var{symbol} -z @var{keyword}} @item Directory Options @xref{Directory Options,,Options for Directory Search}. @gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol -iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol --sysroot=@var{dir} --no-sysroot-suffix} @item Machine Dependent Options @xref{Submodel Options,,Hardware Models and Configurations}. @c This list is ordered alphanumerically by subsection name. @c Try and put the significant identifier (CPU or system) first, @c so users have a clue at guessing where the ones they want will be. @emph{AArch64 Options} @gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol -mgeneral-regs-only @gol -mcmodel=tiny -mcmodel=small -mcmodel=large @gol -mstrict-align @gol -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol -mtls-dialect=desc -mtls-dialect=traditional @gol -mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol -march=@var{name} -mcpu=@var{name} -mtune=@var{name}} @emph{Adapteva Epiphany Options} @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol -mround-nearest -mlong-calls -mshort-calls -msmall16 @gol -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol -msplit-vecmove-early -m1reg-@var{reg}} @emph{ARC Options} @gccoptlist{-mbarrel-shifter @gol -mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol -mea -mno-mpy -mmul32x16 -mmul64 @gol -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol -mepilogue-cfi -mlong-calls -mmedium-calls -msdata @gol -mucb-mcount -mvolatile-cache @gol -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol -mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol -mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol -mtune=@var{cpu} -mmultcost=@var{num} -munalign-prob-threshold=@var{probability}} @emph{ARM Options} @gccoptlist{-mapcs-frame -mno-apcs-frame @gol -mabi=@var{name} @gol -mapcs-stack-check -mno-apcs-stack-check @gol -mapcs-float -mno-apcs-float @gol -mapcs-reentrant -mno-apcs-reentrant @gol -msched-prolog -mno-sched-prolog @gol -mlittle-endian -mbig-endian @gol -mfloat-abi=@var{name} @gol -mfp16-format=@var{name} -mthumb-interwork -mno-thumb-interwork @gol -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol -mstructure-size-boundary=@var{n} @gol -mabort-on-noreturn @gol -mlong-calls -mno-long-calls @gol -msingle-pic-base -mno-single-pic-base @gol -mpic-register=@var{reg} @gol -mnop-fun-dllimport @gol -mpoke-function-name @gol -mthumb -marm @gol -mtpcs-frame -mtpcs-leaf-frame @gol -mcaller-super-interworking -mcallee-super-interworking @gol -mtp=@var{name} -mtls-dialect=@var{dialect} @gol -mword-relocations @gol -mfix-cortex-m3-ldrd @gol -munaligned-access @gol -mneon-for-64bits @gol -mslow-flash-data @gol -masm-syntax-unified @gol -mrestrict-it} @emph{AVR Options} @gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol -mcall-prologues -mint8 -mno-interrupts -mrelax @gol -mstrict-X -mtiny-stack -Waddr-space-convert} @emph{Blackfin Options} @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol -mno-id-shared-library -mshared-library-id=@var{n} @gol -mleaf-id-shared-library -mno-leaf-id-shared-library @gol -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol -micplb} @emph{C6X Options} @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol -msim -msdata=@var{sdata-type}} @emph{CRIS Options} @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol -mstack-align -mdata-align -mconst-align @gol -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol -melf -maout -melinux -mlinux -sim -sim2 @gol -mmul-bug-workaround -mno-mul-bug-workaround} @emph{CR16 Options} @gccoptlist{-mmac @gol -mcr16cplus -mcr16c @gol -msim -mint32 -mbit-ops -mdata-model=@var{model}} @emph{Darwin Options} @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol -arch_only -bind_at_load -bundle -bundle_loader @gol -client_name -compatibility_version -current_version @gol -dead_strip @gol -dependency-file -dylib_file -dylinker_install_name @gol -dynamic -dynamiclib -exported_symbols_list @gol -filelist -flat_namespace -force_cpusubtype_ALL @gol -force_flat_namespace -headerpad_max_install_names @gol -iframework @gol -image_base -init -install_name -keep_private_externs @gol -multi_module -multiply_defined -multiply_defined_unused @gol -noall_load -no_dead_strip_inits_and_terms @gol -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol -pagezero_size -prebind -prebind_all_twolevel_modules @gol -private_bundle -read_only_relocs -sectalign @gol -sectobjectsymbols -whyload -seg1addr @gol -sectcreate -sectobjectsymbols -sectorder @gol -segaddr -segs_read_only_addr -segs_read_write_addr @gol -seg_addr_table -seg_addr_table_filename -seglinkedit @gol -segprot -segs_read_only_addr -segs_read_write_addr @gol -single_module -static -sub_library -sub_umbrella @gol -twolevel_namespace -umbrella -undefined @gol -unexported_symbols_list -weak_reference_mismatches @gol -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol -mkernel -mone-byte-bool} @emph{DEC Alpha Options} @gccoptlist{-mno-fp-regs -msoft-float @gol -mieee -mieee-with-inexact -mieee-conformant @gol -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol -mtrap-precision=@var{mode} -mbuild-constants @gol -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol -mbwx -mmax -mfix -mcix @gol -mfloat-vax -mfloat-ieee @gol -mexplicit-relocs -msmall-data -mlarge-data @gol -msmall-text -mlarge-text @gol -mmemory-latency=@var{time}} @emph{FR30 Options} @gccoptlist{-msmall-model -mno-lsim} @emph{FRV Options} @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol -mhard-float -msoft-float @gol -malloc-cc -mfixed-cc -mdword -mno-dword @gol -mdouble -mno-double @gol -mmedia -mno-media -mmuladd -mno-muladd @gol -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol -mlinked-fp -mlong-calls -malign-labels @gol -mlibrary-pic -macc-4 -macc-8 @gol -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol -moptimize-membar -mno-optimize-membar @gol -mscc -mno-scc -mcond-exec -mno-cond-exec @gol -mvliw-branch -mno-vliw-branch @gol -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol -mno-nested-cond-exec -mtomcat-stats @gol -mTLS -mtls @gol -mcpu=@var{cpu}} @emph{GNU/Linux Options} @gccoptlist{-mglibc -muclibc -mbionic -mandroid @gol -tno-android-cc -tno-android-ld} @emph{H8/300 Options} @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} @emph{HPPA Options} @gccoptlist{-march=@var{architecture-type} @gol -mdisable-fpregs -mdisable-indexing @gol -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol -mfixed-range=@var{register-range} @gol -mjump-in-delay -mlinker-opt -mlong-calls @gol -mlong-load-store -mno-disable-fpregs @gol -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol -mno-jump-in-delay -mno-long-load-store @gol -mno-portable-runtime -mno-soft-float @gol -mno-space-regs -msoft-float -mpa-risc-1-0 @gol -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol -munix=@var{unix-std} -nolibdld -static -threads} @emph{i386 and x86-64 Options} @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol -mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol -mfpmath=@var{unit} @gol -masm=@var{dialect} -mno-fancy-math-387 @gol -mno-fp-ret-in-387 -msoft-float @gol -mno-wide-multiply -mrtd -malign-double @gol -mpreferred-stack-boundary=@var{num} @gol -mincoming-stack-boundary=@var{num} @gol -mcld -mcx16 -msahf -mmovbe -mcrc32 @gol -mrecip -mrecip=@var{opt} @gol -mvzeroupper -mprefer-avx128 @gol -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -msha @gol -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mprefetchwt1 @gol -mclflushopt -mxsavec -mxsaves @gol -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mthreads @gol -mno-align-stringops -minline-all-stringops @gol -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol -mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol -mregparm=@var{num} -msseregparm @gol -mveclibabi=@var{type} -mvect8-ret-in-mem @gol -mpc32 -mpc64 -mpc80 -mstackrealign @gol -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol -m32 -m64 -mx32 -m16 -mlarge-data-threshold=@var{num} @gol -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol -mstack-protector-guard=@var{guard}} @emph{i386 and x86-64 Windows Options} @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol -mnop-fun-dllimport -mthread @gol -municode -mwin32 -mwindows -fno-set-stack-executable} @emph{IA-64 Options} @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol -mconstant-gp -mauto-pic -mfused-madd @gol -minline-float-divide-min-latency @gol -minline-float-divide-max-throughput @gol -mno-inline-float-divide @gol -minline-int-divide-min-latency @gol -minline-int-divide-max-throughput @gol -mno-inline-int-divide @gol -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol -mno-inline-sqrt @gol -mdwarf2-asm -mearly-stop-bits @gol -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol -mtune=@var{cpu-type} -milp32 -mlp64 @gol -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol -msched-spec-ldc -msched-spec-control-ldc @gol -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} @emph{LM32 Options} @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol -msign-extend-enabled -muser-enabled} @emph{M32R/D Options} @gccoptlist{-m32r2 -m32rx -m32r @gol -mdebug @gol -malign-loops -mno-align-loops @gol -missue-rate=@var{number} @gol -mbranch-cost=@var{number} @gol -mmodel=@var{code-size-model-type} @gol -msdata=@var{sdata-type} @gol -mno-flush-func -mflush-func=@var{name} @gol -mno-flush-trap -mflush-trap=@var{number} @gol -G @var{num}} @emph{M32C Options} @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} @emph{M680x0 Options} @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol -malign-int -mstrict-align -msep-data -mno-sep-data @gol -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol -mxgot -mno-xgot} @emph{MCore Options} @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} @emph{MeP Options} @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol -mtiny=@var{n}} @emph{MicroBlaze Options} @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}} @emph{MIPS Options} @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol -mips64 -mips64r2 -mips64r3 -mips64r5 @gol -mips16 -mno-mips16 -mflip-mips16 @gol -minterlink-compressed -mno-interlink-compressed @gol -minterlink-mips16 -mno-interlink-mips16 @gol -mabi=@var{abi} -mabicalls -mno-abicalls @gol -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol -mno-float -msingle-float -mdouble-float @gol -modd-spreg -mno-odd-spreg @gol -mabs=@var{mode} -mnan=@var{encoding} @gol -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol -mmcu -mmno-mcu @gol -meva -mno-eva @gol -mvirt -mno-virt @gol -mxpa -mno-xpa @gol -mmicromips -mno-micromips @gol -mfpu=@var{fpu-type} @gol -msmartmips -mno-smartmips @gol -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol -mlong64 -mlong32 -msym32 -mno-sym32 @gol -G@var{num} -mlocal-sdata -mno-local-sdata @gol -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol -membedded-data -mno-embedded-data @gol -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol -mcode-readable=@var{setting} @gol -msplit-addresses -mno-split-addresses @gol -mexplicit-relocs -mno-explicit-relocs @gol -mcheck-zero-division -mno-check-zero-division @gol -mdivide-traps -mdivide-breaks @gol -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol -mfix-24k -mno-fix-24k @gol -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol -mfix-vr4120 -mno-fix-vr4120 @gol -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol -mflush-func=@var{func} -mno-flush-func @gol -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol -mfp-exceptions -mno-fp-exceptions @gol -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address} @emph{MMIX Options} @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol -mno-base-addresses -msingle-exit -mno-single-exit} @emph{MN10300 Options} @gccoptlist{-mmult-bug -mno-mult-bug @gol -mno-am33 -mam33 -mam33-2 -mam34 @gol -mtune=@var{cpu-type} @gol -mreturn-pointer-on-d0 @gol -mno-crt0 -mrelax -mliw -msetlb} @emph{Moxie Options} @gccoptlist{-meb -mel -mno-crt0} @emph{MSP430 Options} @gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol -mhwmult= -minrt} @emph{NDS32 Options} @gccoptlist{-mbig-endian -mlittle-endian @gol -mreduced-regs -mfull-regs @gol -mcmov -mno-cmov @gol -mperf-ext -mno-perf-ext @gol -mv3push -mno-v3push @gol -m16bit -mno-16bit @gol -mgp-direct -mno-gp-direct @gol -misr-vector-size=@var{num} @gol -mcache-block-size=@var{num} @gol -march=@var{arch} @gol -mforce-fp-as-gp -mforbid-fp-as-gp @gol -mex9 -mctor-dtor -mrelax} @emph{Nios II Options} @gccoptlist{-G @var{num} -mgpopt -mno-gpopt -mel -meb @gol -mno-bypass-cache -mbypass-cache @gol -mno-cache-volatile -mcache-volatile @gol -mno-fast-sw-div -mfast-sw-div @gol -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol -mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol -mcustom-fpu-cfg=@var{name} @gol -mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name}} @emph{PDP-11 Options} @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol -mint16 -mno-int32 -mfloat32 -mno-float64 @gol -mfloat64 -mno-float32 -mabshi -mno-abshi @gol -mbranch-expensive -mbranch-cheap @gol -munix-asm -mdec-asm} @emph{picoChip Options} @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol -msymbol-as-address -mno-inefficient-warnings} @emph{PowerPC Options} See RS/6000 and PowerPC Options. @emph{RL78 Options} @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=rl78 @gol -m64bit-doubles -m32bit-doubles} @emph{RS/6000 and PowerPC Options} @gccoptlist{-mcpu=@var{cpu-type} @gol -mtune=@var{cpu-type} @gol -mcmodel=@var{code-model} @gol -mpowerpc64 @gol -maltivec -mno-altivec @gol -mpowerpc-gpopt -mno-powerpc-gpopt @gol -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol -mfprnd -mno-fprnd @gol -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol -malign-power -malign-natural @gol -msoft-float -mhard-float -mmultiple -mno-multiple @gol -msingle-float -mdouble-float -msimple-fpu @gol -mstring -mno-string -mupdate -mno-update @gol -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol -mstrict-align -mno-strict-align -mrelocatable @gol -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol -mprioritize-restricted-insns=@var{priority} @gol -msched-costly-dep=@var{dependence_type} @gol -minsert-sched-nops=@var{scheme} @gol -mcall-sysv -mcall-netbsd @gol -maix-struct-return -msvr4-struct-return @gol -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol -mblock-move-inline-limit=@var{num} @gol -misel -mno-isel @gol -misel=yes -misel=no @gol -mspe -mno-spe @gol -mspe=yes -mspe=no @gol -mpaired @gol -mgen-cell-microcode -mwarn-cell-microcode @gol -mvrsave -mno-vrsave @gol -mmulhw -mno-mulhw @gol -mdlmzb -mno-dlmzb @gol -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol -mprototype -mno-prototype @gol -msim -mmvme -mads -myellowknife -memb -msdata @gol -msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol -mno-recip-precision @gol -mveclibabi=@var{type} -mfriz -mno-friz @gol -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol -msave-toc-indirect -mno-save-toc-indirect @gol -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol -mcrypto -mno-crypto -mdirect-move -mno-direct-move @gol -mquad-memory -mno-quad-memory @gol -mquad-memory-atomic -mno-quad-memory-atomic @gol -mcompat-align-parm -mno-compat-align-parm} @emph{RX Options} @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol -mcpu=@gol -mbig-endian-data -mlittle-endian-data @gol -msmall-data @gol -msim -mno-sim@gol -mas100-syntax -mno-as100-syntax@gol -mrelax@gol -mmax-constant-size=@gol -mint-register=@gol -mpid@gol -mno-warn-multiple-fast-interrupts@gol -msave-acc-in-interrupts} @emph{S/390 and zSeries Options} @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol -mlong-double-64 -mlong-double-128 @gol -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol -mhotpatch[=@var{halfwords}] -mno-hotpatch} @emph{Score Options} @gccoptlist{-meb -mel @gol -mnhwloop @gol -muls @gol -mmac @gol -mscore5 -mscore5u -mscore7 -mscore7d} @emph{SH Options} @gccoptlist{-m1 -m2 -m2e @gol -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol -m3 -m3e @gol -m4-nofpu -m4-single-only -m4-single -m4 @gol -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol -m5-64media -m5-64media-nofpu @gol -m5-32media -m5-32media-nofpu @gol -m5-compact -m5-compact-nofpu @gol -mb -ml -mdalign -mrelax @gol -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol -mspace -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol -maccumulate-outgoing-args -minvalid-symbols @gol -matomic-model=@var{atomic-model} @gol -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol -mpretend-cmove -mtas} @emph{Solaris 2 Options} @gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol -pthreads -pthread} @emph{SPARC Options} @gccoptlist{-mcpu=@var{cpu-type} @gol -mtune=@var{cpu-type} @gol -mcmodel=@var{code-model} @gol -mmemory-model=@var{mem-model} @gol -m32 -m64 -mapp-regs -mno-app-regs @gol -mfaster-structs -mno-faster-structs -mflat -mno-flat @gol -mfpu -mno-fpu -mhard-float -msoft-float @gol -mhard-quad-float -msoft-quad-float @gol -mstack-bias -mno-stack-bias @gol -munaligned-doubles -mno-unaligned-doubles @gol -muser-mode -mno-user-mode @gol -mv8plus -mno-v8plus -mvis -mno-vis @gol -mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol -mcbcond -mno-cbcond @gol -mfmaf -mno-fmaf -mpopc -mno-popc @gol -mfix-at697f -mfix-ut699} @emph{SPU Options} @gccoptlist{-mwarn-reloc -merror-reloc @gol -msafe-dma -munsafe-dma @gol -mbranch-hints @gol -msmall-mem -mlarge-mem -mstdmain @gol -mfixed-range=@var{register-range} @gol -mea32 -mea64 @gol -maddress-space-conversion -mno-address-space-conversion @gol -mcache-size=@var{cache-size} @gol -matomic-updates -mno-atomic-updates} @emph{System V Options} @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} @emph{TILE-Gx Options} @gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol -mcmodel=@var{code-model}} @emph{TILEPro Options} @gccoptlist{-mcpu=@var{cpu} -m32} @emph{V850 Options} @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol -mprolog-function -mno-prolog-function -mspace @gol -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol -mapp-regs -mno-app-regs @gol -mdisable-callt -mno-disable-callt @gol -mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol -mv850e -mv850 -mv850e3v5 @gol -mloop @gol -mrelax @gol -mlong-jumps @gol -msoft-float @gol -mhard-float @gol -mgcc-abi @gol -mrh850-abi @gol -mbig-switch} @emph{VAX Options} @gccoptlist{-mg -mgnu -munix} @emph{VMS Options} @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol -mpointer-size=@var{size}} @emph{VxWorks Options} @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol -Xbind-lazy -Xbind-now} @emph{x86-64 Options} See i386 and x86-64 Options. @emph{Xstormy16 Options} @gccoptlist{-msim} @emph{Xtensa Options} @gccoptlist{-mconst16 -mno-const16 @gol -mfused-madd -mno-fused-madd @gol -mforce-no-pic @gol -mserialize-volatile -mno-serialize-volatile @gol -mtext-section-literals -mno-text-section-literals @gol -mtarget-align -mno-target-align @gol -mlongcalls -mno-longcalls} @emph{zSeries Options} See S/390 and zSeries Options. @item Code Generation Options @xref{Code Gen Options,,Options for Code Generation Conventions}. @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol -ffixed-@var{reg} -fexceptions @gol -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol -fasynchronous-unwind-tables @gol -fno-gnu-unique @gol -finhibit-size-directive -finstrument-functions @gol -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol -fno-common -fno-ident @gol -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol -fno-jump-tables @gol -frecord-gcc-switches @gol -freg-struct-return -fshort-enums @gol -fshort-double -fshort-wchar @gol -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol -fno-stack-limit -fsplit-stack @gol -fleading-underscore -ftls-model=@var{model} @gol -fstack-reuse=@var{reuse_level} @gol -ftrapv -fwrapv -fbounds-check @gol -fvisibility -fstrict-volatile-bitfields -fsync-libcalls} @end table @node Overall Options @section Options Controlling the Kind of Output Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file. @cindex file name suffix For any given input file, the file name suffix determines what kind of compilation is done: @table @gcctabopt @item @var{file}.c C source code that must be preprocessed. @item @var{file}.i C source code that should not be preprocessed. @item @var{file}.ii C++ source code that should not be preprocessed. @item @var{file}.m Objective-C source code. Note that you must link with the @file{libobjc} library to make an Objective-C program work. @item @var{file}.mi Objective-C source code that should not be preprocessed. @item @var{file}.mm @itemx @var{file}.M Objective-C++ source code. Note that you must link with the @file{libobjc} library to make an Objective-C++ program work. Note that @samp{.M} refers to a literal capital M@. @item @var{file}.mii Objective-C++ source code that should not be preprocessed. @item @var{file}.h C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via the @option{-fdump-ada-spec} switch). @item @var{file}.cc @itemx @var{file}.cp @itemx @var{file}.cxx @itemx @var{file}.cpp @itemx @var{file}.CPP @itemx @var{file}.c++ @itemx @var{file}.C C++ source code that must be preprocessed. Note that in @samp{.cxx}, the last two letters must both be literally @samp{x}. Likewise, @samp{.C} refers to a literal capital C@. @item @var{file}.mm @itemx @var{file}.M Objective-C++ source code that must be preprocessed. @item @var{file}.mii Objective-C++ source code that should not be preprocessed. @item @var{file}.hh @itemx @var{file}.H @itemx @var{file}.hp @itemx @var{file}.hxx @itemx @var{file}.hpp @itemx @var{file}.HPP @itemx @var{file}.h++ @itemx @var{file}.tcc C++ header file to be turned into a precompiled header or Ada spec. @item @var{file}.f @itemx @var{file}.for @itemx @var{file}.ftn Fixed form Fortran source code that should not be preprocessed. @item @var{file}.F @itemx @var{file}.FOR @itemx @var{file}.fpp @itemx @var{file}.FPP @itemx @var{file}.FTN Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor). @item @var{file}.f90 @itemx @var{file}.f95 @itemx @var{file}.f03 @itemx @var{file}.f08 Free form Fortran source code that should not be preprocessed. @item @var{file}.F90 @itemx @var{file}.F95 @itemx @var{file}.F03 @itemx @var{file}.F08 Free form Fortran source code that must be preprocessed (with the traditional preprocessor). @item @var{file}.go Go source code. @c FIXME: Descriptions of Java file types. @c @var{file}.java @c @var{file}.class @c @var{file}.zip @c @var{file}.jar @item @var{file}.ads Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called @dfn{specs}. @item @var{file}.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called @dfn{bodies}. @c GCC also knows about some suffixes for languages not yet included: @c Pascal: @c @var{file}.p @c @var{file}.pas @c Ratfor: @c @var{file}.r @item @var{file}.s Assembler code. @item @var{file}.S @itemx @var{file}.sx Assembler code that must be preprocessed. @item @var{other} An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. @end table @opindex x You can specify the input language explicitly with the @option{-x} option: @table @gcctabopt @item -x @var{language} Specify explicitly the @var{language} for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next @option{-x} option. Possible values for @var{language} are: @smallexample c c-header cpp-output c++ c++-header c++-cpp-output objective-c objective-c-header objective-c-cpp-output objective-c++ objective-c++-header objective-c++-cpp-output assembler assembler-with-cpp ada f77 f77-cpp-input f95 f95-cpp-input go java @end smallexample @item -x none Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if @option{-x} has not been used at all). @item -pass-exit-codes @opindex pass-exit-codes Normally the @command{gcc} program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify @option{-pass-exit-codes}, the @command{gcc} program instead returns with the numerically highest error produced by any phase returning an error indication. The C, C++, and Fortran front ends return 4 if an internal compiler error is encountered. @end table If you only want some of the stages of compilation, you can use @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and one of the options @option{-c}, @option{-S}, or @option{-E} to say where @command{gcc} is to stop. Note that some combinations (for example, @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. @table @gcctabopt @item -c @opindex c Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file. By default, the object file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. Unrecognized input files, not requiring compilation or assembly, are ignored. @item -S @opindex S Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified. By default, the assembler file name for a source file is made by replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. Input files that don't require compilation are ignored. @item -E @opindex E Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output. Input files that don't require preprocessing are ignored. @cindex output file option @item -o @var{file} @opindex o Place output in file @var{file}. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code. If @option{-o} is not specified, the default is to put an executable file in @file{a.out}, the object file for @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its assembler file in @file{@var{source}.s}, a precompiled header file in @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on standard output. @item -v @opindex v Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper. @item -### @opindex ### Like @option{-v} except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or @code{./-_}. This is useful for shell scripts to capture the driver-generated command lines. @item -pipe @opindex pipe Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble. @item --help @opindex help Print (on the standard output) a description of the command-line options understood by @command{gcc}. If the @option{-v} option is also specified then @option{--help} is also passed on to the various processes invoked by @command{gcc}, so that they can display the command-line options they accept. If the @option{-Wextra} option has also been specified (prior to the @option{--help} option), then command-line options that have no documentation associated with them are also displayed. @item --target-help @opindex target-help Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target-specific information may also be printed. @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes: @table @asis @item @samp{optimizers} Display all of the optimization options supported by the compiler. @item @samp{warnings} Display all of the options controlling warning messages produced by the compiler. @item @samp{target} Display target-specific options. Unlike the @option{--target-help} option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended @option{--help=} syntax. @item @samp{params} Display the values recognized by the @option{--param} option. @item @var{language} Display the options supported for @var{language}, where @var{language} is the name of one of the languages supported in this version of GCC@. @item @samp{common} Display the options that are common to all languages. @end table These are the supported qualifiers: @table @asis @item @samp{undocumented} Display only those options that are undocumented. @item @samp{joined} Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: @samp{--help=target}. @item @samp{separate} Display options taking an argument that appears as a separate word following the original option, such as: @samp{-o output-file}. @end table Thus for example to display all the undocumented target-specific switches supported by the compiler, use: @smallexample --help=target,undocumented @end smallexample The sense of a qualifier can be inverted by prefixing it with the @samp{^} character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use: @smallexample --help=warnings,^joined,^undocumented @end smallexample The argument to @option{--help=} should not consist solely of inverted qualifiers. Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is @var{target}. For example, to display all the target-specific optimization options, use: @smallexample --help=target,optimizers @end smallexample The @option{--help=} option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed. If the @option{-Q} option appears on the command line before the @option{--help=} option, then the descriptive text displayed by @option{--help=} is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the @option{--help=} option is used). Here is a truncated example from the ARM port of @command{gcc}: @smallexample % gcc -Q -mabi=2 --help=target -c The following options are target specific: -mabi= 2 -mabort-on-noreturn [disabled] -mapcs [disabled] @end smallexample The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at @option{-O2} by using: @smallexample -Q -O2 --help=optimizers @end smallexample Alternatively you can discover which binary optimizations are enabled by @option{-O3} by using: @smallexample gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts diff /tmp/O2-opts /tmp/O3-opts | grep enabled @end smallexample @item -no-canonical-prefixes @opindex no-canonical-prefixes Do not expand any symbolic links, resolve references to @samp{/../} or @samp{/./}, or make the path absolute when generating a relative prefix. @item --version @opindex version Display the version number and copyrights of the invoked GCC@. @item -wrapper @opindex wrapper Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list. @smallexample gcc -c t.c -wrapper gdb,--args @end smallexample @noindent This invokes all subprograms of @command{gcc} under @samp{gdb --args}, thus the invocation of @command{cc1} is @samp{gdb --args cc1 @dots{}}. @item -fplugin=@var{name}.so @opindex fplugin Load the plugin code in file @var{name}.so, assumed to be a shared object to be dlopen'd by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). Each plugin should define the callback functions specified in the Plugins API. @item -fplugin-arg-@var{name}-@var{key}=@var{value} @opindex fplugin-arg Define an argument called @var{key} with a value of @var{value} for the plugin called @var{name}. @item -fdump-ada-spec@r{[}-slim@r{]} @opindex fdump-ada-spec For C and C++ source and include files, generate corresponding Ada specs. @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, GNAT User's Guide}, which provides detailed documentation on this feature. @item -fada-spec-parent=@var{unit} @opindex fada-spec-parent In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate Ada specs as child units of parent @var{unit}. @item -fdump-go-spec=@var{file} @opindex fdump-go-spec For input files in any language, generate corresponding Go declarations in @var{file}. This generates Go @code{const}, @code{type}, @code{var}, and @code{func} declarations which may be a useful way to start writing a Go interface to code written in some other language. @include @value{srcdir}/../libiberty/at-file.texi @end table @node Invoking G++ @section Compiling C++ Programs @cindex suffixes for C++ source @cindex C++ source file suffixes C++ source files conventionally use one of the suffixes @samp{.C}, @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, @samp{.H}, or (for shared template code) @samp{.tcc}; and preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name @command{gcc}). @findex g++ @findex c++ However, the use of @command{gcc} does not add the C++ library. @command{g++} is a program that calls GCC and automatically specifies linking against the C++ library. It treats @samp{.c}, @samp{.h} and @samp{.i} files as C++ source files instead of C source files unless @option{-x} is used. This program is also useful when precompiling a C header file with a @samp{.h} extension for use in C++ compilations. On many systems, @command{g++} is also installed with the name @command{c++}. @cindex invoking @command{g++} When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. @xref{C Dialect Options,,Options Controlling C Dialect}, for explanations of options for languages related to C@. @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for explanations of options that are meaningful only for C++ programs. @node C Dialect Options @section Options Controlling C Dialect @cindex dialect options @cindex language dialect options @cindex options, dialect The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts: @table @gcctabopt @cindex ANSI support @cindex ISO support @item -ansi @opindex ansi In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is equivalent to @option{-std=c++98}. This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the @code{asm} and @code{typeof} keywords, and predefined macros such as @code{unix} and @code{vax} that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style @samp{//} comments as well as the @code{inline} keyword. The alternate keywords @code{__asm__}, @code{__extension__}, @code{__inline__} and @code{__typeof__} continue to work despite @option{-ansi}. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with @option{-ansi}. Alternate predefined macros such as @code{__unix__} and @code{__vax__} are also available, with or without @option{-ansi}. The @option{-ansi} option does not cause non-ISO programs to be rejected gratuitously. For that, @option{-Wpedantic} is required in addition to @option{-ansi}. @xref{Warning Options}. The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesn't call for; this is to avoid interfering with any programs that might use these names for other things. Functions that are normally built in but do not have semantics defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in functions when @option{-ansi} is used. @xref{Other Builtins,,Other built-in functions provided by GCC}, for details of the functions affected. @item -std= @opindex std Determine the language standard. @xref{Standards,,Language Standards Supported by GCC}, for details of these standard versions. This option is currently only supported when compiling C or C++. The compiler can accept several base standards, such as @samp{c90} or @samp{c++98}, and GNU dialects of those standards, such as @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, @option{-std=c90} turns off certain features of GCC that are incompatible with ISO C90, such as the @code{asm} and @code{typeof} keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a @code{?:} expression. On the other hand, when a GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by @option{-Wpedantic} to identify which features are GNU extensions given that version of the standard. For example @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} comments, while @option{-std=gnu99 -Wpedantic} does not. A value for this option must be provided; possible values are @table @samp @item c90 @itemx c89 @itemx iso9899:1990 Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as @option{-ansi} for C code. @item iso9899:199409 ISO C90 as modified in amendment 1. @item c99 @itemx c9x @itemx iso9899:1999 @itemx iso9899:199x ISO C99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). See @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The names @samp{c9x} and @samp{iso9899:199x} are deprecated. @item c11 @itemx c1x @itemx iso9899:2011 ISO C11, the 2011 revision of the ISO C standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name @samp{c1x} is deprecated. @item gnu90 @itemx gnu89 GNU dialect of ISO C90 (including some C99 features). @item gnu99 @itemx gnu9x GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated. @item gnu11 @itemx gnu1x GNU dialect of ISO C11. This is the default for C code. The name @samp{gnu1x} is deprecated. @item c++98 @itemx c++03 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports. Same as @option{-ansi} for C++ code. @item gnu++98 @itemx gnu++03 GNU dialect of @option{-std=c++98}. This is the default for C++ code. @item c++11 @itemx c++0x The 2011 ISO C++ standard plus amendments. The name @samp{c++0x} is deprecated. @item gnu++11 @itemx gnu++0x GNU dialect of @option{-std=c++11}. The name @samp{gnu++0x} is deprecated. @item c++14 @itemx c++1y The 2014 ISO C++ standard plus amendments. The name @samp{c++1y} is deprecated. @item gnu++14 @itemx gnu++1y GNU dialect of @option{-std=c++14}. The name @samp{gnu++1y} is deprecated. @item c++1z The next revision of the ISO C++ standard, tentatively planned for 2017. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. @item gnu++1z GNU dialect of @option{-std=c++1z}. Support is highly experimental, and will almost certainly change in incompatible ways in future releases. @end table @item -fgnu89-inline @opindex fgnu89-inline The option @option{-fgnu89-inline} tells GCC to use the traditional GNU semantics for @code{inline} functions when in C99 mode. @xref{Inline,,An Inline Function is As Fast As a Macro}. This option is accepted and ignored by GCC versions 4.1.3 up to but not including 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in C99 mode. Using this option is roughly equivalent to adding the @code{gnu_inline} function attribute to all inline functions (@pxref{Function Attributes}). The option @option{-fno-gnu89-inline} explicitly tells GCC to use the C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option was first supported in GCC 4.3. This option is not supported in @option{-std=c90} or @option{-std=gnu90} mode. The preprocessor macros @code{__GNUC_GNU_INLINE__} and @code{__GNUC_STDC_INLINE__} may be used to check which semantics are in effect for @code{inline} functions. @xref{Common Predefined Macros,,,cpp,The C Preprocessor}. @item -aux-info @var{filename} @opindex aux-info Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C@. Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or @samp{O} for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (@samp{C} or @samp{F}, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration. @item -fallow-parameterless-variadic-functions @opindex fallow-parameterless-variadic-functions Accept variadic functions without named parameters. Although it is possible to define such a function, this is not very useful as it is not possible to read the arguments. This is only supported for C as this construct is allowed by C++. @item -fno-asm @opindex fno-asm Do not recognize @code{asm}, @code{inline} or @code{typeof} as a keyword, so that code can use these words as identifiers. You can use the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} instead. @option{-ansi} implies @option{-fno-asm}. In C++, this switch only affects the @code{typeof} keyword, since @code{asm} and @code{inline} are standard keywords. You may want to use the @option{-fno-gnu-keywords} flag instead, which has the same effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this switch only affects the @code{asm} and @code{typeof} keywords, since @code{inline} is a standard keyword in ISO C99. @item -fno-builtin @itemx -fno-builtin-@var{function} @opindex fno-builtin @cindex built-in functions Don't recognize built-in functions that do not begin with @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in functions provided by GCC}, for details of the functions affected, including those which are not built-in functions when @option{-ansi} or @option{-std} options for strict ISO C conformance are used because they do not have an ISO standard meaning. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to @code{alloca} may become single instructions which adjust the stack directly, and calls to @code{memcpy} may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with @option{-Wformat} for bad calls to @code{printf} when @code{printf} is built in and @code{strlen} is known not to modify global memory. With the @option{-fno-builtin-@var{function}} option only the built-in function @var{function} is disabled. @var{function} must not begin with @samp{__builtin_}. If a function is named that is not built-in in this version of GCC, this option is ignored. There is no corresponding @option{-fbuiltin-@var{function}} option; if you wish to enable built-in functions selectively when using @option{-fno-builtin} or @option{-ffreestanding}, you may define macros such as: @smallexample #define abs(n) __builtin_abs ((n)) #define strcpy(d, s) __builtin_strcpy ((d), (s)) @end smallexample @item -fhosted @opindex fhosted @cindex hosted environment Assert that compilation targets a hosted environment. This implies @option{-fbuiltin}. A hosted environment is one in which the entire standard library is available, and in which @code{main} has a return type of @code{int}. Examples are nearly everything except a kernel. This is equivalent to @option{-fno-freestanding}. @item -ffreestanding @opindex ffreestanding @cindex hosted environment Assert that compilation targets a freestanding environment. This implies @option{-fno-builtin}. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at @code{main}. The most obvious example is an OS kernel. This is equivalent to @option{-fno-hosted}. @xref{Standards,,Language Standards Supported by GCC}, for details of freestanding and hosted environments. @item -fopenmp @opindex fopenmp @cindex OpenMP parallel Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v4.0 @w{@uref{http://www.openmp.org/}}. This option implies @option{-pthread}, and thus is only supported on targets that have support for @option{-pthread}. @option{-fopenmp} implies @option{-fopenmp-simd}. @item -fopenmp-simd @opindex fopenmp-simd @cindex OpenMP SIMD @cindex SIMD Enable handling of OpenMP's SIMD directives with @code{#pragma omp} in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives are ignored. @item -fcilkplus @opindex fcilkplus @cindex Enable Cilk Plus Enable the usage of Cilk Plus language extension features for C/C++. When the option @option{-fcilkplus} is specified, enable the usage of the Cilk Plus Language extension features for C/C++. The present implementation follows ABI version 1.2. This is an experimental feature that is only partially complete, and whose interface may change in future versions of GCC as the official specification changes. Currently, all features but @code{_Cilk_for} have been implemented. @item -fgnu-tm @opindex fgnu-tm When the option @option{-fgnu-tm} is specified, the compiler generates code for the Linux variant of Intel's current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of GCC, as the official specification changes. Please note that not all architectures are supported for this feature. For more information on GCC's support for transactional memory, @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU Transactional Memory Library}. Note that the transactional memory feature is not supported with non-call exceptions (@option{-fnon-call-exceptions}). @item -fms-extensions @opindex fms-extensions Accept some non-standard constructs used in Microsoft header files. In C++ code, this allows member names in structures to be similar to previous types declarations. @smallexample typedef int UOW; struct ABC @{ UOW UOW; @}; @end smallexample Some cases of unnamed fields in structures and unions are only accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union fields within structs/unions}, for details. Note that this option is off for all targets but i?86 and x86_64 targets using ms-abi. @item -fplan9-extensions Accept some non-standard constructs used in Plan 9 code. This enables @option{-fms-extensions}, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. @xref{Unnamed Fields,,Unnamed struct/union fields within structs/unions}, for details. This is only supported for C, not C++. @item -trigraphs @opindex trigraphs Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} options for strict ISO C conformance) implies @option{-trigraphs}. @cindex traditional C language @cindex C language, traditional @item -traditional @itemx -traditional-cpp @opindex traditional-cpp @opindex traditional Formerly, these options caused GCC to attempt to emulate a pre-standard C compiler. They are now only supported with the @option{-E} switch. The preprocessor continues to support a pre-standard mode. See the GNU CPP manual for details. @item -fcond-mismatch @opindex fcond-mismatch Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++. @item -flax-vector-conversions @opindex flax-vector-conversions Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code. @item -funsigned-char @opindex funsigned-char Let the type @code{char} be unsigned, like @code{unsigned char}. Each kind of machine has a default for what @code{char} should be. It is either like @code{unsigned char} by default or like @code{signed char} by default. Ideally, a portable program should always use @code{signed char} or @code{unsigned char} when it depends on the signedness of an object. But many programs have been written to use plain @code{char} and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default. The type @code{char} is always a distinct type from each of @code{signed char} or @code{unsigned char}, even though its behavior is always just like one of those two. @item -fsigned-char @opindex fsigned-char Let the type @code{char} be signed, like @code{signed char}. Note that this is equivalent to @option{-fno-unsigned-char}, which is the negative form of @option{-funsigned-char}. Likewise, the option @option{-fno-signed-char} is equivalent to @option{-funsigned-char}. @item -fsigned-bitfields @itemx -funsigned-bitfields @itemx -fno-signed-bitfields @itemx -fno-unsigned-bitfields @opindex fsigned-bitfields @opindex funsigned-bitfields @opindex fno-signed-bitfields @opindex fno-unsigned-bitfields These options control whether a bit-field is signed or unsigned, when the declaration does not use either @code{signed} or @code{unsigned}. By default, such a bit-field is signed, because this is consistent: the basic integer types such as @code{int} are signed types. @end table @node C++ Dialect Options @section Options Controlling C++ Dialect @cindex compiler options, C++ @cindex C++ options, command-line @cindex options, C++ This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file @code{firstClass.C} like this: @smallexample g++ -g -frepo -O -c firstClass.C @end smallexample @noindent In this example, only @option{-frepo} is an option meant only for C++ programs; you can use the other options with any language supported by GCC@. Here is a list of options that are @emph{only} for compiling C++ programs: @table @gcctabopt @item -fabi-version=@var{n} @opindex fabi-version Use version @var{n} of the C++ ABI@. The default is version 0. Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed. Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9. Version 3 corrects an error in mangling a constant address as a template argument. Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types. Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter. Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and --, and a class scope function used as a template argument. Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope. Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers. See also @option{-Wabi}. @item -fabi-compat-version=@var{n} @opindex fabi-compat-version Starting with GCC 4.5, on targets that support strong aliases, G++ works around mangling changes by creating an alias with the correct mangled name when defining a symbol with an incorrect mangled name. This switch specifies which ABI version to use for the alias. With @option{-fabi-version=0} (the default), this defaults to 2. If another ABI version is explicitly selected, this defaults to 0. The compatibility version is also set by @option{-Wabi=@var{n}}. @item -fno-access-control @opindex fno-access-control Turn off all access checking. This switch is mainly useful for working around bugs in the access control code. @item -fcheck-new @opindex fcheck-new Check that the pointer returned by @code{operator new} is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that @code{operator new} only returns @code{0} if it is declared @samp{throw()}, in which case the compiler always checks the return value even without this option. In all other cases, when @code{operator new} has a non-empty exception specification, memory exhaustion is signalled by throwing @code{std::bad_alloc}. See also @samp{new (nothrow)}. @item -fconstexpr-depth=@var{n} @opindex fconstexpr-depth Set the maximum nested evaluation depth for C++11 constexpr functions to @var{n}. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512. @item -fdeduce-init-list @opindex fdeduce-init-list Enable deduction of a template type parameter as @code{std::initializer_list} from a brace-enclosed initializer list, i.e.@: @smallexample template auto forward(T t) -> decltype (realfn (t)) @{ return realfn (t); @} void f() @{ forward(@{1,2@}); // call forward> @} @end smallexample This deduction was implemented as a possible extension to the originally proposed semantics for the C++11 standard, but was not part of the final standard, so it is disabled by default. This option is deprecated, and may be removed in a future version of G++. @item -ffriend-injection @opindex ffriend-injection Inject friend functions into the enclosing namespace, so that they are visible outside the scope of the class in which they are declared. Friend functions were documented to work this way in the old Annotated C++ Reference Manual, and versions of G++ before 4.1 always worked that way. However, in ISO C++ a friend function that is not declared in an enclosing scope can only be found using argument dependent lookup. This option causes friends to be injected as they were in earlier releases. This option is for compatibility, and may be removed in a future release of G++. @item -fno-elide-constructors @opindex fno-elide-constructors The C++ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. @item -fno-enforce-eh-specs @opindex fno-enforce-eh-specs Don't generate code to check for violation of exception specifications at run time. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining @samp{NDEBUG}. This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an unexpected exception results in undefined behavior at run time. @item -fextern-tls-init @itemx -fno-extern-tls-init @opindex fextern-tls-init @opindex fno-extern-tls-init The C++11 and OpenMP standards allow @samp{thread_local} and @samp{threadprivate} variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the use is in a different translation unit there is significant overhead even if the variable doesn't actually need dynamic initialization. If the programmer can be sure that no use of the variable in a non-defining TU needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TU will be executed before any uses in another TU), they can avoid this overhead with the @option{-fno-extern-tls-init} option. On targets that support symbol aliases, the default is @option{-fextern-tls-init}. On targets that do not support symbol aliases, the default is @option{-fno-extern-tls-init}. @item -ffor-scope @itemx -fno-for-scope @opindex ffor-scope @opindex fno-for-scope If @option{-ffor-scope} is specified, the scope of variables declared in a @i{for-init-statement} is limited to the @samp{for} loop itself, as specified by the C++ standard. If @option{-fno-for-scope} is specified, the scope of variables declared in a @i{for-init-statement} extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of C++. If neither flag is given, the default is to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior. @item -fno-gnu-keywords @opindex fno-gnu-keywords Do not recognize @code{typeof} as a keyword, so that code can use this word as an identifier. You can use the keyword @code{__typeof__} instead. @option{-ansi} implies @option{-fno-gnu-keywords}. @item -fno-implicit-templates @opindex fno-implicit-templates Never emit code for non-inline templates that are instantiated implicitly (i.e.@: by use); only emit code for explicit instantiations. @xref{Template Instantiation}, for more information. @item -fno-implicit-inline-templates @opindex fno-implicit-inline-templates Don't emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization need the same set of explicit instantiations. @item -fno-implement-inlines @opindex fno-implement-inlines To save space, do not emit out-of-line copies of inline functions controlled by @samp{#pragma implementation}. This causes linker errors if these functions are not inlined everywhere they are called. @item -fms-extensions @opindex fms-extensions Disable Wpedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax. @item -fno-nonansi-builtins @opindex fno-nonansi-builtins Disable built-in declarations of functions that are not mandated by ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, @code{index}, @code{bzero}, @code{conjf}, and other related functions. @item -fnothrow-opt @opindex fnothrow-opt Treat a @code{throw()} exception specification as if it were a @code{noexcept} specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to @code{terminate} rather than @code{unexpected}. @item -fno-operator-names @opindex fno-operator-names Do not treat the operator name keywords @code{and}, @code{bitand}, @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as synonyms as keywords. @item -fno-optional-diags @opindex fno-optional-diags Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class. @item -fpermissive @opindex fpermissive Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using @option{-fpermissive} allows some nonconforming code to compile. @item -fno-pretty-templates @opindex fno-pretty-templates When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. @code{void f(T) [with T = int]} rather than @code{void f(int)}) so that it's clear which template is involved. When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, you can use @option{-fno-pretty-templates} to disable them. @item -frepo @opindex frepo Enable automatic template instantiation at link time. This option also implies @option{-fno-implicit-templates}. @xref{Template Instantiation}, for more information. @item -fno-rtti @opindex fno-rtti Disable generation of information about every class with virtual functions for use by the C++ run-time type identification features (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The @samp{dynamic_cast} operator can still be used for casts that do not require run-time type information, i.e.@: casts to @code{void *} or to unambiguous base classes. @item -fstats @opindex fstats Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team. @item -fstrict-enums @opindex fstrict-enums Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the C++ standard; basically, a value that can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value to the enumerated type. @item -ftemplate-backtrace-limit=@var{n} @opindex ftemplate-backtrace-limit Set the maximum number of template instantiation notes for a single warning or error to @var{n}. The default value is 10. @item -ftemplate-depth=@var{n} @opindex ftemplate-depth Set the maximum instantiation depth for template classes to @var{n}. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations. @item -fno-threadsafe-statics @opindex fno-threadsafe-statics Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe. @item -fuse-cxa-atexit @opindex fuse-cxa-atexit Register destructors for objects with static storage duration with the @code{__cxa_atexit} function rather than the @code{atexit} function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports @code{__cxa_atexit}. @item -fno-use-cxa-get-exception-ptr @opindex fno-use-cxa-get-exception-ptr Don't use the @code{__cxa_get_exception_ptr} runtime routine. This causes @code{std::uncaught_exception} to be incorrect, but is necessary if the runtime routine is not available. @item -fvisibility-inlines-hidden @opindex fvisibility-inlines-hidden This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions are taken in different shared objects. The effect of this is that GCC may, effectively, mark inline methods with @code{__attribute__ ((visibility ("hidden")))} so that they do not appear in the export table of a DSO and do not require a PLT indirection when used within the DSO@. Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when the library makes heavy use of templates. The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object. You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect. Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. @xref{Template Instantiation}. @item -fvisibility-ms-compat @opindex fvisibility-ms-compat This flag attempts to use visibility settings to make GCC's C++ linkage model compatible with that of Microsoft Visual Studio. The flag makes these changes to GCC's linkage model: @enumerate @item It sets the default visibility to @code{hidden}, like @option{-fvisibility=hidden}. @item Types, but not their members, are not hidden by default. @item The One Definition Rule is relaxed for types without explicit visibility specifications that are defined in more than one shared object: those declarations are permitted if they are permitted when this option is not used. @end enumerate In new code it is better to use @option{-fvisibility=hidden} and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior. Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently. @item -fvtable-verify=@var{std|preinit|none} @opindex fvtable-verify Turn on (or off, if using @option{-fvtable-verify=none}) the security feature that verifies at runtime, for every virtual call that is made, that the vtable pointer through which the call is made is valid for the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected (at runtime), an error is reported and execution of the program is immediately halted. This option causes runtime data structures to be built, at program start up, for verifying the vtable pointers. The options @code{std} and @code{preinit} control the timing of when these data structures are built. In both cases the data structures are built before execution reaches 'main'. The @option{-fvtable-verify=std} causes these data structure to be built after the shared libraries have been loaded and initialized. @option{-fvtable-verify=preinit} causes them to be built before the shared libraries have been loaded and initialized. If this option appears multiple times in the compiler line, with different values specified, 'none' will take highest priority over both 'std' and 'preinit'; 'preinit' will take priority over 'std'. @item -fvtv-debug @opindex (fvtv-debug) Causes debug versions of the runtime functions for the vtable verification feature to be called. This assumes the @option{-fvtable-verify=std} or @option{-fvtable-verify=preinit} has been used. This flag will also cause the compiler to keep track of which vtable pointers it found for each class, and record that information in the file ``vtv_set_ptr_data.log'', in the dump file directory on the user's machine. Note: This feature APPENDS data to the log file. If you want a fresh log file, be sure to delete any existing one. @item -fvtv-counts @opindex fvtv-counts This is a debugging flag. When used in conjunction with @option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this causes the compiler to keep track of the total number of virtual calls it encountered and the number of verifications it inserted. It also counts the number of calls to certain runtime library functions that it inserts. This information, for each compilation unit, is written to a file named ``vtv_count_data.log'', in the dump_file directory on the user's machine. It also counts the size of the vtable pointer sets for each class, and writes this information to ``vtv_class_set_sizes.log'' in the same directory. Note: This feature APPENDS data to the log files. To get a fresh log files, be sure to delete any existing ones. @item -fno-weak @opindex fno-weak Do not use weak symbol support, even if it is provided by the linker. By default, G++ uses weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it results in inferior code and has no benefits. This option may be removed in a future release of G++. @item -nostdinc++ @opindex nostdinc++ Do not search for header files in the standard directories specific to C++, but do still search the other standard directories. (This option is used when building the C++ library.) @end table In addition, these optimization, warning, and code generation options have meanings only for C++ programs: @table @gcctabopt @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} @opindex Wabi @opindex Wno-abi When an explicit @option{-fabi-version=@var{n}} option is used, causes G++ to warn when it generates code that is probably not compatible with the vendor-neutral C++ ABI@. Since G++ now defaults to @option{-fabi-version=0}, @option{-Wabi} has no effect unless either an older ABI version is selected (with @option{-fabi-version=@var{n}}) or an older compatibility version is selected (with @option{-Wabi=@var{n}} or @option{-fabi-compat-version=@var{n}}). Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated is compatible. You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers. @option{-Wabi} can also be used with an explicit version number to warn about compatibility with a particular @option{-fabi-version} level, e.g. @option{-Wabi=2} to warn about changes relative to @option{-fabi-version=2}. Specifying a version number also sets @option{-fabi-compat-version=@var{n}}. The known incompatibilities in @option{-fabi-version=2} (which was the default from GCC 3.4 to 4.9) include: @itemize @bullet @item A template with a non-type template parameter of reference type was mangled incorrectly: @smallexample extern int N; template struct S @{@}; void n (S) @{2@} @end smallexample This was fixed in @option{-fabi-version=3}. @item SIMD vector types declared using @code{__attribute ((vector_size))} were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes. The mangling was changed in @option{-fabi-version=4}. @item @code{__attribute ((const))} and @code{noreturn} were mangled as type qualifiers, and @code{decltype} of a plain declaration was folded away. These mangling issues were fixed in @option{-fabi-version=5}. @item Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing @samp{va_arg} to complain. On most targets this does not actually affect the parameter passing ABI, as there is no way to pass an argument smaller than @samp{int}. Also, the ABI changed the mangling of template argument packs, @code{const_cast}, @code{static_cast}, prefix increment/decrement, and a class scope function used as a template argument. These issues were corrected in @option{-fabi-version=6}. @item Lambdas in default argument scope were mangled incorrectly, and the ABI changed the mangling of nullptr_t. These issues were corrected in @option{-fabi-version=7}. @item When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate. This was fixed in @option{-fabi-version=8}. @end itemize It also warns about psABI-related changes. The known psABI changes at this point include: @itemize @bullet @item For SysV/x86-64, unions with @code{long double} members are passed in memory as specified in psABI. For example: @smallexample union U @{ long double ld; int i; @}; @end smallexample @noindent @code{union U} is always passed in memory. @end itemize @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} @opindex Wctor-dtor-privacy @opindex Wno-ctor-dtor-privacy Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Also warn if there are no non-private methods, and there's at least one private member function that isn't a constructor or destructor. @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} @opindex Wdelete-non-virtual-dtor @opindex Wno-delete-non-virtual-dtor Warn when @samp{delete} is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by @option{-Wall}. @item -Wliteral-suffix @r{(C++ and Objective-C++ only)} @opindex Wliteral-suffix @opindex Wno-literal-suffix Warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, GCC treats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from @code{}. For example: @smallexample #define __STDC_FORMAT_MACROS #include #include int main() @{ int64_t i64 = 123; printf("My int64: %"PRId64"\n", i64); @} @end smallexample In this case, @code{PRId64} is treated as a separate preprocessing token. This warning is enabled by default. @item -Wnarrowing @r{(C++ and Objective-C++ only)} @opindex Wnarrowing @opindex Wno-narrowing Warn when a narrowing conversion prohibited by C++11 occurs within @samp{@{ @}}, e.g. @smallexample int i = @{ 2.2 @}; // error: narrowing from double to int @end smallexample This flag is included in @option{-Wall} and @option{-Wc++11-compat}. With @option{-std=c++11}, @option{-Wno-narrowing} suppresses for non-constants the diagnostic required by the standard. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in SFINAE context. @item -Wnoexcept @r{(C++ and Objective-C++ only)} @opindex Wnoexcept @opindex Wno-noexcept Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. @samp{throw()} or @samp{noexcept}) but is known by the compiler to never throw an exception. @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} @opindex Wnon-virtual-dtor @opindex Wno-non-virtual-dtor Warn when a class has virtual functions and an accessible non-virtual destructor itself or in an accessible polymorphic base class, in which case it is possible but unsafe to delete an instance of a derived class through a pointer to the class itself or base class. This warning is automatically enabled if @option{-Weffc++} is specified. @item -Wreorder @r{(C++ and Objective-C++ only)} @opindex Wreorder @opindex Wno-reorder @cindex reordering, warning @cindex warning for reordering of member initializers Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance: @smallexample struct A @{ int i; int j; A(): j (0), i (1) @{ @} @}; @end smallexample @noindent The compiler rearranges the member initializers for @samp{i} and @samp{j} to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by @option{-Wall}. @item -fext-numeric-literals @r{(C++ and Objective-C++ only)} @opindex fext-numeric-literals @opindex fno-ext-numeric-literals Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU extensions. When this option is turned off these suffixes are treated as C++11 user-defined literal numeric suffixes. This is on by default for all pre-C++11 dialects and all GNU dialects: @option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, @option{-std=gnu++14}. This option is off by default for ISO C++11 onwards (@option{-std=c++11}, ...). @end table The following @option{-W@dots{}} options are not affected by @option{-Wall}. @table @gcctabopt @item -Weffc++ @r{(C++ and Objective-C++ only)} @opindex Weffc++ @opindex Wno-effc++ Warn about violations of the following style guidelines from Scott Meyers' @cite{Effective C++} series of books: @itemize @bullet @item Define a copy constructor and an assignment operator for classes with dynamically-allocated memory. @item Prefer initialization to assignment in constructors. @item Have @code{operator=} return a reference to @code{*this}. @item Don't try to return a reference when you must return an object. @item Distinguish between prefix and postfix forms of increment and decrement operators. @item Never overload @code{&&}, @code{||}, or @code{,}. @end itemize This option also enables @option{-Wnon-virtual-dtor}, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non-polymorphic bases classes too. When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use @samp{grep -v} to filter out those warnings. @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} @opindex Wstrict-null-sentinel @opindex Wno-strict-null-sentinel Warn about the use of an uncasted @code{NULL} as sentinel. When compiling only with GCC this is a valid sentinel, as @code{NULL} is defined to @code{__null}. Although it is a null pointer constant rather than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers. @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} @opindex Wno-non-template-friend @opindex Wnon-template-friend Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., @samp{friend foo(int)}), the C++ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, @option{-Wnon-template-friend} allows the compiler to check existing code for potential trouble spots and is on by default. This new compiler behavior can be turned off with @option{-Wno-non-template-friend}, which keeps the conformant compiler code but disables the helpful warning. @item -Wold-style-cast @r{(C++ and Objective-C++ only)} @opindex Wold-style-cast @opindex Wno-old-style-cast Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts (@samp{dynamic_cast}, @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to unintended effects and much easier to search for. @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} @opindex Woverloaded-virtual @opindex Wno-overloaded-virtual @cindex overloaded virtual function, warning @cindex warning for overloaded virtual function Warn when a function declaration hides virtual functions from a base class. For example, in: @smallexample struct A @{ virtual void f(); @}; struct B: public A @{ void f(int); @}; @end smallexample the @code{A} class version of @code{f} is hidden in @code{B}, and code like: @smallexample B* b; b->f(); @end smallexample @noindent fails to compile. @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} @opindex Wno-pmf-conversions @opindex Wpmf-conversions Disable the diagnostic for converting a bound pointer to member function to a plain pointer. @item -Wsign-promo @r{(C++ and Objective-C++ only)} @opindex Wsign-promo @opindex Wno-sign-promo Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ tried to preserve unsignedness, but the standard mandates the current behavior. @end table @node Objective-C and Objective-C++ Dialect Options @section Options Controlling Objective-C and Objective-C++ Dialects @cindex compiler options, Objective-C and Objective-C++ @cindex Objective-C and Objective-C++ options, command-line @cindex options, Objective-C and Objective-C++ (NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. @xref{Standards,,Language Standards Supported by GCC}, for references.) This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For example, you might compile a file @code{some_class.m} like this: @smallexample gcc -g -fgnu-runtime -O -c some_class.m @end smallexample @noindent In this example, @option{-fgnu-runtime} is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC@. Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., @option{-Wtraditional}). Similarly, Objective-C++ compilations may use C++-specific options (e.g., @option{-Wabi}). Here is a list of options that are @emph{only} for compiling Objective-C and Objective-C++ programs: @table @gcctabopt @item -fconstant-string-class=@var{class-name} @opindex fconstant-string-class Use @var{class-name} as the name of the class to instantiate for each literal string specified with the syntax @code{@@"@dots{}"}. The default class name is @code{NXConstantString} if the GNU runtime is being used, and @code{NSConstantString} if the NeXT runtime is being used (see below). The @option{-fconstant-cfstrings} option, if also present, overrides the @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals to be laid out as constant CoreFoundation strings. @item -fgnu-runtime @opindex fgnu-runtime Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems. @item -fnext-runtime @opindex fnext-runtime Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X@. The macro @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is used. @item -fno-nil-receivers @opindex fno-nil-receivers Assume that all Objective-C message dispatches (@code{[receiver message:arg]}) in this translation unit ensure that the receiver is not @code{nil}. This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1. @item -fobjc-abi-version=@var{n} @opindex fobjc-abi-version Use version @var{n} of the Objective-C ABI for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) ABI without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines. @item -fobjc-call-cxx-cdtors @opindex fobjc-call-cxx-cdtors For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial default constructor. If so, synthesize a special @code{- (id) .cxx_construct} instance method which runs non-trivial default constructors on any such instance variables, in order, and then return @code{self}. Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and if so, synthesize a special @code{- (void) .cxx_destruct} method which runs all such default destructors, in reverse order. The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods are invoked by the runtime immediately after a new object instance is allocated; the @code{- (void) .cxx_destruct} methods are invoked immediately before the runtime deallocates an object instance. As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} methods. @item -fobjc-direct-dispatch @opindex fobjc-direct-dispatch Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page. @item -fobjc-exceptions @opindex fobjc-exceptions Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++ and Java. This option is required to use the Objective-C keywords @code{@@try}, @code{@@throw}, @code{@@catch}, @code{@@finally} and @code{@@synchronized}. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier). @item -fobjc-gc @opindex fobjc-gc Enable garbage collection (GC) in Objective-C and Objective-C++ programs. This option is only available with the NeXT runtime; the GNU runtime has a different garbage collection implementation that does not require special compiler flags. @item -fobjc-nilcheck @opindex fobjc-nilcheck For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using @option{-fno-objc-nilcheck}. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used. @item -fobjc-std=objc1 @opindex fobjc-std Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0. This only affects the Objective-C additions to the C/C++ language; it does not affect conformance to C/C++ standards, which is controlled by the separate C/C++ dialect option flags. When this option is used with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not recognized by GCC 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC@. @item -freplace-objc-classes @opindex freplace-objc-classes Emit a special marker instructing @command{ld(1)} not to statically link in the resulting object file, and allow @command{dyld(1)} to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later. @item -fzero-link @opindex fzero-link When compiling for the NeXT runtime, the compiler ordinarily replaces calls to @code{objc_getClass("@dots{}")} (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the @option{-fzero-link} flag suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} regardless of command-line options. @item -fno-local-ivars @opindex fno-local-ivars @opindex flocal-ivars By default instance variables in Objective-C can be accessed as if they were local variables from within the methods of the class they're declared in. This can lead to shadowing between instance variables and other variables declared either locally inside a class method or globally with the same name. Specifying the @option{-fno-local-ivars} flag disables this behavior thus avoiding variable shadowing issues. @item -fivar-visibility=@var{public|protected|private|package} @opindex fivar-visibility Set the default instance variable visibility to the specified option so that instance variables declared outside the scope of any access modifier directives default to the specified visibility. @item -gen-decls @opindex gen-decls Dump interface declarations for all classes seen in the source file to a file named @file{@var{sourcename}.decl}. @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} @opindex Wassign-intercept @opindex Wno-assign-intercept Warn whenever an Objective-C assignment is being intercepted by the garbage collector. @item -Wno-protocol @r{(Objective-C and Objective-C++ only)} @opindex Wno-protocol @opindex Wprotocol If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the @option{-Wno-protocol} option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them. @item -Wselector @r{(Objective-C and Objective-C++ only)} @opindex Wselector @opindex Wno-selector Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a @code{@@selector(@dots{})} expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the @option{-fsyntax-only} option is being used. @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} @opindex Wstrict-selector-match @opindex Wno-strict-selector-match Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type @code{id} or @code{Class}. When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment. @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} @opindex Wundeclared-selector @opindex Wno-undeclared-selector Warn if a @code{@@selector(@dots{})} expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the @code{@@selector(@dots{})} expression, either explicitly in an @code{@@interface} or @code{@@protocol} declaration, or implicitly in an @code{@@implementation} section. This option always performs its checks as soon as a @code{@@selector(@dots{})} expression is found, while @option{-Wselector} only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used. @item -print-objc-runtime-info @opindex print-objc-runtime-info Generate C header describing the largest structure that is passed by value, if any. @end table @node Language Independent Options @section Options to Control Diagnostic Messages Formatting @cindex options to control diagnostics formatting @cindex diagnostic messages @cindex message formatting Traditionally, diagnostic messages have been formatted irrespective of the output device's aspect (e.g.@: its width, @dots{}). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g.@: how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options. @table @gcctabopt @item -fmessage-length=@var{n} @opindex fmessage-length Try to format error messages so that they fit on lines of about @var{n} characters. If @var{n} is zero, then no line-wrapping will be done; each error message will appear on a single line. This is the default for all front ends. @item -fdiagnostics-show-location=once @opindex fdiagnostics-show-location Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information @emph{once}; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior. @item -fdiagnostics-show-location=every-line Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line. @item -fdiagnostics-color[=@var{WHEN}] @itemx -fno-diagnostics-color @opindex fdiagnostics-color @cindex highlight, color, colour @vindex GCC_COLORS @r{environment variable} Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. The default depends on how the compiler has been configured, it can be any of the above @var{WHEN} options or also @samp{never} if @env{GCC_COLORS} environment variable isn't present in the environment, and @samp{auto} otherwise. @samp{auto} means to use color only when the standard error is a terminal. The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are aliases for @option{-fdiagnostics-color=always} and @option{-fdiagnostics-color=never}, respectively. The colors are defined by the environment variable @env{GCC_COLORS}. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include @samp{1} for bold, @samp{4} for underline, @samp{5} for blink, @samp{7} for inverse, @samp{39} for default foreground color, @samp{30} to @samp{37} for foreground colors, @samp{90} to @samp{97} for 16-color mode foreground colors, @samp{38;5;0} to @samp{38;5;255} for 88-color and 256-color modes foreground colors, @samp{49} for default background color, @samp{40} to @samp{47} for background colors, @samp{100} to @samp{107} for 16-color mode background colors, and @samp{48;5;0} to @samp{48;5;255} for 88-color and 256-color modes background colors. The default @env{GCC_COLORS} is @samp{error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01} where @samp{01;31} is bold red, @samp{01;35} is bold magenta, @samp{01;36} is bold cyan, @samp{01;32} is bold green and @samp{01} is bold. Setting @env{GCC_COLORS} to the empty string disables colors. Supported capabilities are as follows. @table @code @item error= @vindex error GCC_COLORS @r{capability} SGR substring for error: markers. @item warning= @vindex warning GCC_COLORS @r{capability} SGR substring for warning: markers. @item note= @vindex note GCC_COLORS @r{capability} SGR substring for note: markers. @item caret= @vindex caret GCC_COLORS @r{capability} SGR substring for caret line. @item locus= @vindex locus GCC_COLORS @r{capability} SGR substring for location information, @samp{file:line} or @samp{file:line:column} etc. @item quote= @vindex quote GCC_COLORS @r{capability} SGR substring for information printed within quotes. @end table @item -fno-diagnostics-show-option @opindex fno-diagnostics-show-option @opindex fdiagnostics-show-option By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). Specifying the @option{-fno-diagnostics-show-option} flag suppresses that behavior. @item -fno-diagnostics-show-caret @opindex fno-diagnostics-show-caret @opindex fdiagnostics-show-caret By default, each diagnostic emitted includes the original source line and a caret '^' indicating the column. This option suppresses this information. @end table @node Warning Options @section Options to Request or Suppress Warnings @cindex options to control warnings @cindex warning messages @cindex messages, warning @cindex suppressing warnings Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error. The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC@. @table @gcctabopt @cindex syntax checking @item -fsyntax-only @opindex fsyntax-only Check the code for syntax errors, but don't do anything beyond that. @item -fmax-errors=@var{n} @opindex fmax-errors Limits the maximum number of error messages to @var{n}, at which point GCC bails out rather than attempting to continue processing the source code. If @var{n} is 0 (the default), there is no limit on the number of error messages produced. If @option{-Wfatal-errors} is also specified, then @option{-Wfatal-errors} takes precedence over this option. @item -w @opindex w Inhibit all warning messages. @item -Werror @opindex Werror @opindex Wno-error Make all warnings into errors. @item -Werror= @opindex Werror= @opindex Wno-error= Make the specified warning into an error. The specifier for a warning is appended; for example @option{-Werror=switch} turns the warnings controlled by @option{-Wswitch} into errors. This switch takes a negative form, to be used to negate @option{-Werror} for specific warnings; for example @option{-Wno-error=switch} makes @option{-Wswitch} warnings not be errors, even when @option{-Werror} is in effect. The warning message for each controllable warning includes the option that controls the warning. That option can then be used with @option{-Werror=} and @option{-Wno-error=} as described above. (Printing of the option in the warning message can be disabled using the @option{-fno-diagnostics-show-option} flag.) Note that specifying @option{-Werror=}@var{foo} automatically implies @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not imply anything. @item -Wfatal-errors @opindex Wfatal-errors @opindex Wno-fatal-errors This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages. @end table You can request many specific warnings with options beginning with @samp{-W}, for example @option{-Wimplicit} to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning @samp{-Wno-} to turn off warnings; for example, @option{-Wno-implicit}. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect Options}. Some options, such as @option{-Wall} and @option{-Wextra}, turn on other options, such as @option{-Wunused}, which may turn on further options, such as @option{-Wunused-value}. The combined effect of positive and negative forms is that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect as if they appeared at the end of the command-line. When an unrecognized warning option is requested (e.g., @option{-Wunknown-warning}), GCC emits a diagnostic stating that the option is not recognized. However, if the @option{-Wno-} form is used, the behavior is slightly different: no diagnostic is produced for @option{-Wno-unknown-warning} unless other diagnostics are being produced. This allows the use of new @option{-Wno-} options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present. @table @gcctabopt @item -Wpedantic @itemx -pedantic @opindex pedantic @opindex Wpedantic Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any @option{-std} option used. Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require @option{-ansi} or a @option{-std} option specifying the required version of ISO C)@. However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected. @option{-Wpedantic} does not cause warning messages for use of the alternate keywords whose names begin and end with @samp{__}. Pedantic warnings are also disabled in the expression that follows @code{__extension__}. However, only system header files should use these escape routes; application programs should avoid them. @xref{Alternate Keywords}. Some users try to use @option{-Wpedantic} to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not all---only those for which ISO C @emph{requires} a diagnostic, and some others for which diagnostics have been added. A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from @option{-Wpedantic}. We don't have plans to support such a feature in the near future. Where the standard specified with @option{-std} represents a GNU extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a corresponding @dfn{base standard}, the version of ISO C on which the GNU extended dialect is based. Warnings from @option{-Wpedantic} are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.) @item -pedantic-errors @opindex pedantic-errors Give an error whenever the @dfn{base standard} (see @option{-Wpedantic}) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent compilation of programs that are valid according to the standard. This is not equivalent to @option{-Werror=pedantic}, since there are errors enabled by this option and not enabled by the latter and vice versa. @item -Wall @opindex Wall @opindex Wno-all This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect Options}. @option{-Wall} turns on the following warning flags: @gccoptlist{-Waddress @gol -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol -Wc++11-compat @gol -Wchar-subscripts @gol -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol -Wimplicit-int @r{(C and Objective-C only)} @gol -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol -Wcomment @gol -Wformat @gol -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol -Wmaybe-uninitialized @gol -Wmissing-braces @r{(only for C/ObjC)} @gol -Wnonnull @gol -Wopenmp-simd @gol -Wparentheses @gol -Wpointer-sign @gol -Wreorder @gol -Wreturn-type @gol -Wsequence-point @gol -Wsign-compare @r{(only in C++)} @gol -Wstrict-aliasing @gol -Wstrict-overflow=1 @gol -Wswitch @gol -Wtrigraphs @gol -Wuninitialized @gol -Wunknown-pragmas @gol -Wunused-function @gol -Wunused-label @gol -Wunused-value @gol -Wunused-variable @gol -Wvolatile-register-var @gol } Note that some warning flags are not implied by @option{-Wall}. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by @option{-Wextra} but many of them must be enabled individually. @item -Wextra @opindex W @opindex Wextra @opindex Wno-extra This enables some extra warning flags that are not enabled by @option{-Wall}. (This option used to be called @option{-W}. The older name is still supported, but the newer name is more descriptive.) @gccoptlist{-Wclobbered @gol -Wempty-body @gol -Wignored-qualifiers @gol -Wmissing-field-initializers @gol -Wmissing-parameter-type @r{(C only)} @gol -Wold-style-declaration @r{(C only)} @gol -Woverride-init @gol -Wsign-compare @gol -Wtype-limits @gol -Wuninitialized @gol -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol } The option @option{-Wextra} also prints warning messages for the following cases: @itemize @bullet @item A pointer is compared against integer zero with @samp{<}, @samp{<=}, @samp{>}, or @samp{>=}. @item (C++ only) An enumerator and a non-enumerator both appear in a conditional expression. @item (C++ only) Ambiguous virtual bases. @item (C++ only) Subscripting an array that has been declared @samp{register}. @item (C++ only) Taking the address of a variable that has been declared @samp{register}. @item (C++ only) A base class is not initialized in a derived class's copy constructor. @end itemize @item -Wchar-subscripts @opindex Wchar-subscripts @opindex Wno-char-subscripts Warn if an array subscript has type @code{char}. This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by @option{-Wall}. @item -Wcomment @opindex Wcomment @opindex Wno-comment Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} comment, or whenever a Backslash-Newline appears in a @samp{//} comment. This warning is enabled by @option{-Wall}. @item -Wno-coverage-mismatch @opindex Wno-coverage-mismatch Warn if feedback profiles do not match when using the @option{-fprofile-use} option. If a source file is changed between compiling with @option{-fprofile-gen} and with @option{-fprofile-use}, the files with the profile feedback can fail to match the source file and GCC cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. @option{-Wno-coverage-mismatch} can be used to disable the warning or @option{-Wno-error=coverage-mismatch} can be used to disable the error. Disabling the error for this warning can result in poorly optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended. @item -Wno-cpp @r{(C, Objective-C, C++, Objective-C++ and Fortran only)} Suppress warning messages emitted by @code{#warning} directives. @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} @opindex Wdouble-promotion @opindex Wno-double-promotion Give a warning when a value of type @code{float} is implicitly promoted to @code{double}. CPUs with a 32-bit ``single-precision'' floating-point unit implement @code{float} in hardware, but emulate @code{double} in software. On such a machine, doing computations using @code{double} values is much more expensive because of the overhead required for software emulation. It is easy to accidentally do computations with @code{double} because floating-point literals are implicitly of type @code{double}. For example, in: @smallexample @group float area(float radius) @{ return 3.14159 * radius * radius; @} @end group @end smallexample the compiler performs the entire computation with @code{double} because the floating-point literal is a @code{double}. @item -Wformat @itemx -Wformat=@var{n} @opindex Wformat @opindex Wno-format @opindex ffreestanding @opindex fno-builtin @opindex Wformat= Check calls to @code{printf} and @code{scanf}, etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes (@pxref{Function Attributes}), in the @code{printf}, @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, not in the C standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks of functions without the attribute specified are disabled by @option{-ffreestanding} or @option{-fno-builtin}. The formats are checked against the format features supported by GNU libc version 2.2. These include all ISO C90 and C99 features, as well as features from the Single Unix Specification and some BSD and GNU extensions. Other library implementations may not support all these features; GCC does not support warning about features that go beyond a particular library's limitations. However, if @option{-Wpedantic} is used with @option{-Wformat}, warnings are given about format features not in the selected standard version (but not for @code{strfmon} formats, since those are not in any version of the C standard). @xref{C Dialect Options,,Options Controlling C Dialect}. @table @gcctabopt @item -Wformat=1 @itemx -Wformat @opindex Wformat @opindex Wformat=1 Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and @option{-Wno-format} is equivalent to @option{-Wformat=0}. Since @option{-Wformat} also checks for null format arguments for several functions, @option{-Wformat} also implies @option{-Wnonnull}. Some aspects of this level of format checking can be disabled by the options: @option{-Wno-format-contains-nul}, @option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. @option{-Wformat} is enabled by @option{-Wall}. @item -Wno-format-contains-nul @opindex Wno-format-contains-nul @opindex Wformat-contains-nul If @option{-Wformat} is specified, do not warn about format strings that contain NUL bytes. @item -Wno-format-extra-args @opindex Wno-format-extra-args @opindex Wformat-extra-args If @option{-Wformat} is specified, do not warn about excess arguments to a @code{printf} or @code{scanf} format function. The C standard specifies that such arguments are ignored. Where the unused arguments lie between used arguments that are specified with @samp{$} operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to @code{va_arg} to skip the unused arguments. However, in the case of @code{scanf} formats, this option suppresses the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed. @item -Wno-format-zero-length @opindex Wno-format-zero-length @opindex Wformat-zero-length If @option{-Wformat} is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed. @item -Wformat=2 @opindex Wformat=2 Enable @option{-Wformat} plus additional format checks. Currently equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security -Wformat-signedness -Wformat-y2k}. @item -Wformat-nonliteral @opindex Wformat-nonliteral @opindex Wno-format-nonliteral If @option{-Wformat} is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a @code{va_list}. @item -Wformat-security @opindex Wformat-security @opindex Wno-format-security If @option{-Wformat} is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to @code{printf} and @code{scanf} functions where the format string is not a string literal and there are no format arguments, as in @code{printf (foo);}. This may be a security hole if the format string came from untrusted input and contains @samp{%n}. (This is currently a subset of what @option{-Wformat-nonliteral} warns about, but in future warnings may be added to @option{-Wformat-security} that are not included in @option{-Wformat-nonliteral}.) @item -Wformat-signedness @opindex Wformat-signedness @opindex Wno-format-signedness If @option{-Wformat} is specified, also warn if the format string requires an unsigned argument and the argument is signed and vice versa. @item -Wformat-y2k @opindex Wformat-y2k @opindex Wno-format-y2k If @option{-Wformat} is specified, also warn about @code{strftime} formats that may yield only a two-digit year. @end table @item -Wnonnull @opindex Wnonnull @opindex Wno-nonnull Warn about passing a null pointer for arguments marked as requiring a non-null value by the @code{nonnull} function attribute. @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It can be disabled with the @option{-Wno-nonnull} option. @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} @opindex Winit-self @opindex Wno-init-self Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the @option{-Wuninitialized} option. For example, GCC warns about @code{i} being uninitialized in the following snippet only when @option{-Winit-self} has been specified: @smallexample @group int f() @{ int i = i; return i; @} @end group @end smallexample This warning is enabled by @option{-Wall} in C++. @item -Wimplicit-int @r{(C and Objective-C only)} @opindex Wimplicit-int @opindex Wno-implicit-int Warn when a declaration does not specify a type. This warning is enabled by @option{-Wall}. @item -Wimplicit-function-declaration @r{(C and Objective-C only)} @opindex Wimplicit-function-declaration @opindex Wno-implicit-function-declaration Give a warning whenever a function is used before being declared. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is enabled by default and it is made into an error by @option{-pedantic-errors}. This warning is also enabled by @option{-Wall}. @item -Wimplicit @r{(C and Objective-C only)} @opindex Wimplicit @opindex Wno-implicit Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. This warning is enabled by @option{-Wall}. @item -Wignored-qualifiers @r{(C and C++ only)} @opindex Wignored-qualifiers @opindex Wno-ignored-qualifiers Warn if the return type of a function has a type qualifier such as @code{const}. For ISO C such a type qualifier has no effect, since the value returned by a function is not an lvalue. For C++, the warning is only emitted for scalar types or @code{void}. ISO C prohibits qualified @code{void} return types on function definitions, so such return types always receive a warning even without this option. This warning is also enabled by @option{-Wextra}. @item -Wmain @opindex Wmain @opindex Wno-main Warn if the type of @samp{main} is suspicious. @samp{main} should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in C++ and is enabled by either @option{-Wall} or @option{-Wpedantic}. @item -Wmissing-braces @opindex Wmissing-braces @opindex Wno-missing-braces Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for @samp{a} is not fully bracketed, but that for @samp{b} is fully bracketed. This warning is enabled by @option{-Wall} in C. @smallexample int a[2][2] = @{ 0, 1, 2, 3 @}; int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; @end smallexample This warning is enabled by @option{-Wall}. @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)} @opindex Wmissing-include-dirs @opindex Wno-missing-include-dirs Warn if a user-supplied include directory does not exist. @item -Wparentheses @opindex Wparentheses @opindex Wno-parentheses Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about. Also warn if a comparison like @samp{x<=y<=z} appears; this is equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different interpretation from that of ordinary mathematical notation. Also warn about constructions where there may be confusion to which @code{if} statement an @code{else} branch belongs. Here is an example of such a case: @smallexample @group @{ if (a) if (b) foo (); else bar (); @} @end group @end smallexample In C/C++, every @code{else} branch belongs to the innermost possible @code{if} statement, which in this example is @code{if (b)}. This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, GCC issues a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost @code{if} statement so there is no way the @code{else} can belong to the enclosing @code{if}. The resulting code looks like this: @smallexample @group @{ if (a) @{ if (b) foo (); else bar (); @} @} @end group @end smallexample Also warn for dangerous uses of the GNU extension to @code{?:} with omitted middle operand. When the condition in the @code{?}: operator is a boolean expression, the omitted value is always 1. Often programmers expect it to be a value computed inside the conditional expression instead. This warning is enabled by @option{-Wall}. @item -Wsequence-point @opindex Wsequence-point @opindex Wno-sequence-point Warn about code that may have undefined semantics because of violations of sequence point rules in the C and C++ standards. The C and C++ standards define the order in which expressions in a C/C++ program are evaluated in terms of @dfn{sequence points}, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap. It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that ``Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.''. If a program breaks these rules, the results on any particular implementation are entirely unpredictable. Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs. The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the GCC readings page, at @uref{http://gcc.gnu.org/@/readings.html}. This warning is enabled by @option{-Wall} for C and C++. @item -Wno-return-local-addr @opindex Wno-return-local-addr @opindex Wreturn-local-addr Do not warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope after the function returns. @item -Wreturn-type @opindex Wreturn-type @opindex Wno-return-type Warn whenever a function is defined with a return type that defaults to @code{int}. Also warn about any @code{return} statement with no return value in a function whose return type is not @code{void} (falling off the end of the function body is considered returning without a value), and about a @code{return} statement with an expression in a function whose return type is @code{void}. For C++, a function without return type always produces a diagnostic message, even when @option{-Wno-return-type} is specified. The only exceptions are @samp{main} and functions defined in system headers. This warning is enabled by @option{-Wall}. @item -Wshift-count-negative @opindex Wshift-count-negative @opindex Wno-shift-count-negative Warn if shift count is negative. This warning is enabled by default. @item -Wshift-count-overflow @opindex Wshift-count-overflow @opindex Wno-shift-count-overflow Warn if shift count >= width of type. This warning is enabled by default. @item -Wswitch @opindex Wswitch @opindex Wno-switch Warn whenever a @code{switch} statement has an index of enumerated type and lacks a @code{case} for one or more of the named codes of that enumeration. (The presence of a @code{default} label prevents this warning.) @code{case} labels outside the enumeration range also provoke warnings when this option is used (even if there is a @code{default} label). This warning is enabled by @option{-Wall}. @item -Wswitch-default @opindex Wswitch-default @opindex Wno-switch-default Warn whenever a @code{switch} statement does not have a @code{default} case. @item -Wswitch-enum @opindex Wswitch-enum @opindex Wno-switch-enum Warn whenever a @code{switch} statement has an index of enumerated type and lacks a @code{case} for one or more of the named codes of that enumeration. @code{case} labels outside the enumeration range also provoke warnings when this option is used. The only difference between @option{-Wswitch} and this option is that this option gives a warning about an omitted enumeration code even if there is a @code{default} label. @item -Wswitch-bool @opindex Wswitch-bool @opindex Wno-switch-bool Warn whenever a @code{switch} statement has an index of boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than @code{bool}. For example: @smallexample @group switch ((int) (a == 4)) @{ @dots{} @} @end group @end smallexample This warning is enabled by default for C and C++ programs. @item -Wsync-nand @r{(C and C++ only)} @opindex Wsync-nand @opindex Wno-sync-nand Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} built-in functions are used. These functions changed semantics in GCC 4.4. @item -Wtrigraphs @opindex Wtrigraphs @opindex Wno-trigraphs Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). This warning is enabled by @option{-Wall}. @item -Wunused-but-set-parameter @opindex Wunused-but-set-parameter @opindex Wno-unused-but-set-parameter Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration). To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). This warning is also enabled by @option{-Wunused} together with @option{-Wextra}. @item -Wunused-but-set-variable @opindex Wunused-but-set-variable @opindex Wno-unused-but-set-variable Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by @option{-Wall}. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). This warning is also enabled by @option{-Wunused}, which is enabled by @option{-Wall}. @item -Wunused-function @opindex Wunused-function @opindex Wno-unused-function Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by @option{-Wall}. @item -Wunused-label @opindex Wunused-label @opindex Wno-unused-label Warn whenever a label is declared but not used. This warning is enabled by @option{-Wall}. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} @opindex Wunused-local-typedefs Warn when a typedef locally defined in a function is not used. This warning is enabled by @option{-Wall}. @item -Wunused-parameter @opindex Wunused-parameter @opindex Wno-unused-parameter Warn whenever a function parameter is unused aside from its declaration. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wno-unused-result @opindex Wunused-result @opindex Wno-unused-result Do not warn if a caller of a function marked with attribute @code{warn_unused_result} (@pxref{Function Attributes}) does not use its return value. The default is @option{-Wunused-result}. @item -Wunused-variable @opindex Wunused-variable @opindex Wno-unused-variable Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by @option{-Wall}. To suppress this warning use the @samp{unused} attribute (@pxref{Variable Attributes}). @item -Wunused-value @opindex Wunused-value @opindex Wno-unused-value Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to @samp{void}. This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as @samp{x[i,j]} causes a warning, while @samp{x[(void)i,j]} does not. This warning is enabled by @option{-Wall}. @item -Wunused @opindex Wunused @opindex Wno-unused All the above @option{-Wunused} options combined. In order to get a warning about an unused function parameter, you must either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies @option{-Wunused}), or separately specify @option{-Wunused-parameter}. @item -Wuninitialized @opindex Wuninitialized @opindex Wno-uninitialized Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a @code{setjmp} call. In C++, warn if a non-static reference or non-static @samp{const} member appears in a class without constructors. If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the @option{-Winit-self} option. These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They do not occur for variables or elements declared @code{volatile}. Because these warnings depend on optimization, the exact variables or elements for which there are warnings depends on the precise optimization options and version of GCC used. Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed. @item -Wmaybe-uninitialized @opindex Wmaybe-uninitialized @opindex Wno-maybe-uninitialized For an automatic variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths for which the variable is not initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. These warnings are made optional because GCC is not smart enough to see all the reasons why the code might be correct in spite of appearing to have an error. Here is one example of how this can happen: @smallexample @group @{ int x; switch (y) @{ case 1: x = 1; break; case 2: x = 4; break; case 3: x = 5; @} foo (x); @} @end group @end smallexample @noindent If the value of @code{y} is always 1, 2 or 3, then @code{x} is always initialized, but GCC doesn't know this. To suppress the warning, you need to provide a default case with assert(0) or similar code. @cindex @code{longjmp} warnings This option also warns when a non-volatile automatic variable might be changed by a call to @code{longjmp}. These warnings as well are possible only in optimizing compilation. The compiler sees only the calls to @code{setjmp}. It cannot know where @code{longjmp} will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because @code{longjmp} cannot in fact be called at the place that would cause a problem. Some spurious warnings can be avoided if you declare all the functions you use that never return as @code{noreturn}. @xref{Function Attributes}. This warning is enabled by @option{-Wall} or @option{-Wextra}. @item -Wunknown-pragmas @opindex Wunknown-pragmas @opindex Wno-unknown-pragmas @cindex warning for unknown pragmas @cindex unknown pragmas, warning @cindex pragmas, warning of unknown Warn when a @code{#pragma} directive is encountered that is not understood by GCC@. If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This is not the case if the warnings are only enabled by the @option{-Wall} command-line option. @item -Wno-pragmas @opindex Wno-pragmas @opindex Wpragmas Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also @option{-Wunknown-pragmas}. @item -Wstrict-aliasing @opindex Wstrict-aliasing @opindex Wno-strict-aliasing This option is only active when @option{-fstrict-aliasing} is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in @option{-Wall}. It is equivalent to @option{-Wstrict-aliasing=3} @item -Wstrict-aliasing=n @opindex Wstrict-aliasing=n This option is only active when @option{-fstrict-aliasing} is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way @option{-O} works. @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only. Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only. Level 3 (default for @option{-Wstrict-aliasing}): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: @code{*(int*)&some_float}. If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types. @item -Wstrict-overflow @itemx -Wstrict-overflow=@var{n} @opindex Wstrict-overflow @opindex Wno-strict-overflow This option is only active when @option{-fstrict-overflow} is active. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level. An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all. @table @gcctabopt @item -Wstrict-overflow=1 Warn about cases that are both questionable and easy to avoid. For example, with @option{-fstrict-overflow}, the compiler simplifies @code{x + 1 > x} to @code{1}. This level of @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels are not, and must be explicitly requested. @item -Wstrict-overflow=2 Also warn about other cases where a comparison is simplified to a constant. For example: @code{abs (x) >= 0}. This can only be simplified when @option{-fstrict-overflow} is in effect, because @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than zero. @option{-Wstrict-overflow} (with no level) is the same as @option{-Wstrict-overflow=2}. @item -Wstrict-overflow=3 Also warn about other cases where a comparison is simplified. For example: @code{x + 1 > 1} is simplified to @code{x > 0}. @item -Wstrict-overflow=4 Also warn about other simplifications not covered by the above cases. For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. @item -Wstrict-overflow=5 Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: @code{x + 2 > y} is simplified to @code{x + 1 >= y}. This is reported only at the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives. @end table @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @opindex Wsuggest-attribute= @opindex Wno-suggest-attribute= Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below. @table @gcctabopt @item -Wsuggest-attribute=pure @itemx -Wsuggest-attribute=const @itemx -Wsuggest-attribute=noreturn @opindex Wsuggest-attribute=pure @opindex Wno-suggest-attribute=pure @opindex Wsuggest-attribute=const @opindex Wno-suggest-attribute=const @opindex Wsuggest-attribute=noreturn @opindex Wno-suggest-attribute=noreturn Warn about functions that might be candidates for attributes @code{pure}, @code{const} or @code{noreturn}. The compiler only warns for functions visible in other compilation units or (in the case of @code{pure} and @code{const}) if it cannot prove that the function returns normally. A function returns normally if it doesn't contain an infinite loop or return abnormally by throwing, calling @code{abort()} or trapping. This analysis requires option @option{-fipa-pure-const}, which is enabled by default at @option{-O} and higher. Higher optimization levels improve the accuracy of the analysis. @item -Wsuggest-attribute=format @itemx -Wmissing-format-attribute @opindex Wsuggest-attribute=format @opindex Wmissing-format-attribute @opindex Wno-suggest-attribute=format @opindex Wno-missing-format-attribute @opindex Wformat @opindex Wno-format Warn about function pointers that might be candidates for @code{format} attributes. Note these are only possible candidates, not absolute ones. GCC guesses that function pointers with @code{format} attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding @code{format} attribute in the resulting type. I.e.@: the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a @code{format} attribute to avoid the warning. GCC also warns about function definitions that might be candidates for @code{format} attributes. Again, these are only possible candidates. GCC guesses that @code{format} attributes might be appropriate for any function that calls a function like @code{vprintf} or @code{vscanf}, but this might not always be the case, and some functions for which @code{format} attributes are appropriate may not be detected. @end table @item -Wsuggest-final-types @opindex Wno-suggest-final-types @opindex Wsuggest-final-types Warn about types with virtual methods where code quality would be improved if the type was declared with C++11 final specifier, or, if possible, declared in anonymous namespace. This allows GCC to devritualize more aggressively the polymorphic calls. This warning is more effective with link time optimization, where the information about the class hiearchy graph is more complete. @item -Wsuggest-final-methods @opindex Wno-suggest-final-methods @opindex Wsuggest-final-methods Warn about virtual methods where code quality would be improved if the method was declared with C++11 final specifier, or, if possible, its type was declared in the anonymous namespace or with final specifier. This warning is more effective with link time optimization, where the information about the class hiearchy graph is more complete. It is recommended to first consider suggestins of @option{-Wsuggest-final-types} and then rebuild with new annotations. @item -Warray-bounds @opindex Wno-array-bounds @opindex Warray-bounds This option is only active when @option{-ftree-vrp} is active (default for @option{-O2} and above). It warns about subscripts to arrays that are always out of bounds. This warning is enabled by @option{-Wall}. @item -Wbool-compare @opindex Wno-bool-compare @opindex Wbool-compare Warn about boolean expression compared with an integer value different from @code{true}/@code{false}. For instance, the following comparison is always false: @smallexample int n = 5; @dots{} if ((n > 1) == 2) @{ @dots{} @} @end smallexample This warning is enabled by @option{-Wall}. @item -Wno-discarded-qualifiers @r{(C and Objective-C only)} @opindex Wno-discarded-qualifiers @opindex Wdiscarded-qualifiers Do not warn if type qualifiers on pointers are being discarded. Typically, the compiler will warn if a @code{const char *} variable is passed to a function that takes @code{char *} parameter. This option can be used to suppress such a warning. @item -Wno-incompatible-pointer-types @r{(C and Objective-C only)} @opindex Wno-incompatible-pointer-types @opindex Wincompatible-pointer-types Do not warn when there is a conversion between pointers that have incompatible types. This warning is for cases not covered by @option{-Wno-pointer-sign}, which warns for pointer argument passing or assignment with different signedness @item -Wno-int-conversion @r{(C and Objective-C only)} @opindex Wno-int-conversion @opindex Wint-conversion Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions the warnings @option{-Wno-int-to-pointer-cast} and @option{-Wno-pointer-to-int-cast} may be used. @item -Wno-div-by-zero @opindex Wno-div-by-zero @opindex Wdiv-by-zero Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs. @item -Wsystem-headers @opindex Wsystem-headers @opindex Wno-system-headers @cindex warnings from system headers @cindex system headers, warnings from Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command-line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using @option{-Wall} in conjunction with this option does @emph{not} warn about unknown pragmas in system headers---for that, @option{-Wunknown-pragmas} must also be used. @item -Wtrampolines @opindex Wtrampolines @opindex Wno-trampolines Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and thus requires the stack to be made executable in order for the program to work properly. @item -Wfloat-equal @opindex Wfloat-equal @opindex Wno-float-equal Warn if floating-point values are used in equality comparisons. The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but that's a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken. @item -Wtraditional @r{(C and Objective-C only)} @opindex Wtraditional @opindex Wno-traditional Warn about certain constructs that behave differently in traditional and ISO C@. Also warn about ISO C constructs that have no traditional C equivalent, and/or problematic constructs that should be avoided. @itemize @bullet @item Macro parameters that appear within string literals in the macro body. In traditional C macro replacement takes place within string literals, but in ISO C it does not. @item In traditional C, some preprocessor directives did not exist. Traditional preprocessors only considered a line to be a directive if the @samp{#} appeared in column 1 on the line. Therefore @option{-Wtraditional} warns about directives that traditional C understands but ignores because the @samp{#} does not appear as the first character on the line. It also suggests you hide directives like @samp{#pragma} not understood by traditional C by indenting them. Some traditional implementations do not recognize @samp{#elif}, so this option suggests avoiding it altogether. @item A function-like macro that appears without arguments. @item The unary plus operator. @item The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point constant suffixes. (Traditional C does support the @samp{L} suffix on integer constants.) Note, these suffixes appear in macros defined in the system headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{}. Use of these macros in user code might normally lead to spurious warnings, however GCC's integrated preprocessor has enough context to avoid warning in these cases. @item A function declared external in one block and then used after the end of the block. @item A @code{switch} statement has an operand of type @code{long}. @item A non-@code{static} function declaration follows a @code{static} one. This construct is not accepted by some traditional C compilers. @item The ISO type of an integer constant has a different width or signedness from its traditional type. This warning is only issued if the base of the constant is ten. I.e.@: hexadecimal or octal values, which typically represent bit patterns, are not warned about. @item Usage of ISO string concatenation is detected. @item Initialization of automatic aggregates. @item Identifier conflicts with labels. Traditional C lacks a separate namespace for labels. @item Initialization of unions. If the initializer is zero, the warning is omitted. This is done under the assumption that the zero initializer in user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing initializer warnings and relies on default initialization to zero in the traditional C case. @item Conversions by prototypes between fixed/floating-point values and vice versa. The absence of these prototypes when compiling with traditional C causes serious problems. This is a subset of the possible conversion warnings; for the full set use @option{-Wtraditional-conversion}. @item Use of ISO C style function definitions. This warning intentionally is @emph{not} issued for prototype declarations or variadic functions because these ISO C features appear in your code when using libiberty's traditional C compatibility macros, @code{PARAMS} and @code{VPARAMS}. This warning is also bypassed for nested functions because that feature is already a GCC extension and thus not relevant to traditional C compatibility. @end itemize @item -Wtraditional-conversion @r{(C and Objective-C only)} @opindex Wtraditional-conversion @opindex Wno-traditional-conversion Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion. @item -Wdeclaration-after-statement @r{(C and Objective-C only)} @opindex Wdeclaration-after-statement @opindex Wno-declaration-after-statement Warn when a declaration is found after a statement in a block. This construct, known from C++, was introduced with ISO C99 and is by default allowed in GCC@. It is not supported by ISO C90 and was not supported by GCC versions before GCC 3.0. @xref{Mixed Declarations}. @item -Wundef @opindex Wundef @opindex Wno-undef Warn if an undefined identifier is evaluated in an @samp{#if} directive. @item -Wno-endif-labels @opindex Wno-endif-labels @opindex Wendif-labels Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text. @item -Wshadow @opindex Wshadow @opindex Wno-shadow Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum. @item -Wno-shadow-ivar @r{(Objective-C only)} @opindex Wno-shadow-ivar @opindex Wshadow-ivar Do not warn whenever a local variable shadows an instance variable in an Objective-C method. @item -Wlarger-than=@var{len} @opindex Wlarger-than=@var{len} @opindex Wlarger-than-@var{len} Warn whenever an object of larger than @var{len} bytes is defined. @item -Wframe-larger-than=@var{len} @opindex Wframe-larger-than Warn if the size of a function frame is larger than @var{len} bytes. The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be somewhat greater than @var{len} even if you do not get a warning. In addition, any space allocated via @code{alloca}, variable-length arrays, or related constructs is not included by the compiler when determining whether or not to issue a warning. @item -Wno-free-nonheap-object @opindex Wno-free-nonheap-object @opindex Wfree-nonheap-object Do not warn when attempting to free an object that was not allocated on the heap. @item -Wstack-usage=@var{len} @opindex Wstack-usage Warn if the stack usage of a function might be larger than @var{len} bytes. The computation done to determine the stack usage is conservative. Any space allocated via @code{alloca}, variable-length arrays, or related constructs is included by the compiler when determining whether or not to issue a warning. The message is in keeping with the output of @option{-fstack-usage}. @itemize @item If the stack usage is fully static but exceeds the specified amount, it's: @smallexample warning: stack usage is 1120 bytes @end smallexample @item If the stack usage is (partly) dynamic but bounded, it's: @smallexample warning: stack usage might be 1648 bytes @end smallexample @item If the stack usage is (partly) dynamic and not bounded, it's: @smallexample warning: stack usage might be unbounded @end smallexample @end itemize @item -Wunsafe-loop-optimizations @opindex Wunsafe-loop-optimizations @opindex Wno-unsafe-loop-optimizations Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the loop indices. With @option{-funsafe-loop-optimizations} warn if the compiler makes such assumptions. @item -Wno-pedantic-ms-format @r{(MinGW targets only)} @opindex Wno-pedantic-ms-format @opindex Wpedantic-ms-format When used in combination with @option{-Wformat} and @option{-pedantic} without GNU extensions, this option disables the warnings about non-ISO @code{printf} / @code{scanf} format width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, which depend on the MS runtime. @item -Wpointer-arith @opindex Wpointer-arith @opindex Wno-pointer-arith Warn about anything that depends on the ``size of'' a function type or of @code{void}. GNU C assigns these types a size of 1, for convenience in calculations with @code{void *} pointers and pointers to functions. In C++, warn also when an arithmetic operation involves @code{NULL}. This warning is also enabled by @option{-Wpedantic}. @item -Wtype-limits @opindex Wtype-limits @opindex Wno-type-limits Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is compared against zero with @samp{<} or @samp{>=}. This warning is also enabled by @option{-Wextra}. @item -Wbad-function-cast @r{(C and Objective-C only)} @opindex Wbad-function-cast @opindex Wno-bad-function-cast Warn whenever a function call is cast to a non-matching type. For example, warn if @code{int malloc()} is cast to @code{anything *}. @item -Wc90-c99-compat @r{(C and Objective-C only)} @opindex Wc90-c99-compat @opindex Wno-c90-c99-compat Warn about features not present in ISO C90, but present in ISO C99. For instance, warn about use of variable length arrays, @code{long long} type, @code{bool} type, compound literals, designated initializers, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows @code{__extension__}. @item -Wc99-c11-compat @r{(C and Objective-C only)} @opindex Wc99-c11-compat @opindex Wno-c99-c11-compat Warn about features not present in ISO C99, but present in ISO C11. For instance, warn about use of anonymous structures and unions, @code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier, @code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows @code{__extension__}. @item -Wc++-compat @r{(C and Objective-C only)} Warn about ISO C constructs that are outside of the common subset of ISO C and ISO C++, e.g.@: request for implicit conversion from @code{void *} to a pointer to non-@code{void} type. @item -Wc++11-compat @r{(C++ and Objective-C++ only)} Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is enabled by @option{-Wall}. @item -Wcast-qual @opindex Wcast-qual @opindex Wno-cast-qual Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a @code{const char *} is cast to an ordinary @code{char *}. Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting @code{char **} to @code{const char **} is unsafe, as in this example: @smallexample /* p is char ** value. */ const char **q = (const char **) p; /* Assignment of readonly string to const char * is OK. */ *q = "string"; /* Now char** pointer points to read-only memory. */ **p = 'b'; @end smallexample @item -Wcast-align @opindex Wcast-align @opindex Wno-cast-align Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a @code{char *} is cast to an @code{int *} on machines where integers can only be accessed at two- or four-byte boundaries. @item -Wwrite-strings @opindex Wwrite-strings @opindex Wno-write-strings When compiling C, give string constants the type @code{const char[@var{length}]} so that copying the address of one into a non-@code{const} @code{char *} pointer produces a warning. These warnings help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using @code{const} in declarations and prototypes. Otherwise, it is just a nuisance. This is why we did not make @option{-Wall} request these warnings. When compiling C++, warn about the deprecated conversion from string literals to @code{char *}. This warning is enabled by default for C++ programs. @item -Wclobbered @opindex Wclobbered @opindex Wno-clobbered Warn for variables that might be changed by @samp{longjmp} or @samp{vfork}. This warning is also enabled by @option{-Wextra}. @item -Wconditionally-supported @r{(C++ and Objective-C++ only)} @opindex Wconditionally-supported @opindex Wno-conditionally-supported Warn for conditionally-supported (C++11 [intro.defs]) constructs. @item -Wconversion @opindex Wconversion @opindex Wno-conversion Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like @code{abs (x)} when @code{x} is @code{double}; conversions between signed and unsigned, like @code{unsigned ui = -1}; and conversions to smaller types, like @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not changed by the conversion like in @code{abs (2.0)}. Warnings about conversions between signed and unsigned integers can be disabled by using @option{-Wno-sign-conversion}. For C++, also warn for confusing overload resolution for user-defined conversions; and conversions that never use a type conversion operator: conversions to @code{void}, the same type, a base class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in C++ unless @option{-Wsign-conversion} is explicitly enabled. @item -Wno-conversion-null @r{(C++ and Objective-C++ only)} @opindex Wconversion-null @opindex Wno-conversion-null Do not warn for conversions between @code{NULL} and non-pointer types. @option{-Wconversion-null} is enabled by default. @item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} @opindex Wzero-as-null-pointer-constant @opindex Wno-zero-as-null-pointer-constant Warn when a literal '0' is used as null pointer constant. This can be useful to facilitate the conversion to @code{nullptr} in C++11. @item -Wdate-time @opindex Wdate-time @opindex Wno-date-time Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__} are encountered as they might prevent bit-wise-identical reproducible compilations. @item -Wdelete-incomplete @r{(C++ and Objective-C++ only)} @opindex Wdelete-incomplete @opindex Wno-delete-incomplete Warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default. @item -Wuseless-cast @r{(C++ and Objective-C++ only)} @opindex Wuseless-cast @opindex Wno-useless-cast Warn when an expression is casted to its own type. @item -Wempty-body @opindex Wempty-body @opindex Wno-empty-body Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do while} statement. This warning is also enabled by @option{-Wextra}. @item -Wenum-compare @opindex Wenum-compare @opindex Wno-enum-compare Warn about a comparison between values of different enumerated types. In C++ enumeral mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by @option{-Wall}. @item -Wjump-misses-init @r{(C, Objective-C only)} @opindex Wjump-misses-init @opindex Wno-jump-misses-init Warn if a @code{goto} statement or a @code{switch} statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in C++ this sort of branch is an error in any case. @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It can be disabled with the @option{-Wno-jump-misses-init} option. @item -Wsign-compare @opindex Wsign-compare @opindex Wno-sign-compare @cindex warning for comparison of signed and unsigned values @cindex comparison of signed and unsigned values, warning @cindex signed and unsigned values, comparison warning Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by @option{-Wextra}; to get the other warnings of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}. @item -Wsign-conversion @opindex Wsign-conversion @opindex Wno-sign-conversion Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this option is enabled also by @option{-Wconversion}. @item -Wfloat-conversion @opindex Wfloat-conversion @opindex Wno-float-conversion Warn for implicit conversions that reduce the precision of a real value. This includes conversions from real to integer, and from higher precision real to lower precision real values. This option is also enabled by @option{-Wconversion}. @item -Wsizeof-pointer-memaccess @opindex Wsizeof-pointer-memaccess @opindex Wno-sizeof-pointer-memaccess Warn for suspicious length parameters to certain string and memory built-in functions if the argument uses @code{sizeof}. This warning warns e.g.@: about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array, but a pointer, and suggests a possible fix, or about @code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by @option{-Wall}. @item -Wsizeof-array-argument @opindex Wsizeof-array-argument @opindex Wno-sizeof-array-argument Warn when the @code{sizeof} operator is applied to a parameter that is declared as an array in a function definition. This warning is enabled by default for C and C++ programs. @item -Wmemset-transposed-args @opindex Wmemset-transposed-args @opindex Wno-memset-transposed-args Warn for suspicious calls to the @code{memset} built-in function, if the second argument is not zero and the third argument is zero. This warns e.g.@ about @code{memset (buf, sizeof buf, 0)} where most probably @code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostics is only emitted if the third argument is literal zero, if it is some expression that is folded to zero, or e.g. a cast of zero to some type etc., it is far less likely that user has mistakenly exchanged the arguments and no warning is emitted. This warning is enabled by @option{-Wall}. @item -Waddress @opindex Waddress @opindex Wno-address Warn about suspicious uses of memory addresses. These include using the address of a function in a conditional expression, such as @code{void func(void); if (func)}, and comparisons against the memory address of a string literal, such as @code{if (x == "abc")}. Such uses typically indicate a programmer error: the address of a function always evaluates to true, so their use in a conditional usually indicate that the programmer forgot the parentheses in a function call; and comparisons against string literals result in unspecified behavior and are not portable in C, so they usually indicate that the programmer intended to use @code{strcmp}. This warning is enabled by @option{-Wall}. @item -Wlogical-op @opindex Wlogical-op @opindex Wno-logical-op Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. @item -Wlogical-not-parentheses @opindex Wlogical-not-parentheses @opindex Wno-logical-not-parentheses Warn about logical not used on the left hand side operand of a comparison. This option does not warn if the RHS operand is of a boolean type. Its purpose is to detect suspicious code like the following: @smallexample int a; @dots{} if (!a > 1) @{ @dots{} @} @end smallexample It is possible to suppress the warning by wrapping the LHS into parentheses: @smallexample if ((!a) > 1) @{ @dots{} @} @end smallexample This warning is enabled by @option{-Wall}. @item -Waggregate-return @opindex Waggregate-return @opindex Wno-aggregate-return Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.) @item -Wno-aggressive-loop-optimizations @opindex Wno-aggressive-loop-optimizations @opindex Waggressive-loop-optimizations Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations. @item -Wno-attributes @opindex Wno-attributes @opindex Wattributes Do not warn if an unexpected @code{__attribute__} is used, such as unrecognized attributes, function attributes applied to variables, etc. This does not stop errors for incorrect use of supported attributes. @item -Wno-builtin-macro-redefined @opindex Wno-builtin-macro-redefined @opindex Wbuiltin-macro-redefined Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. @item -Wstrict-prototypes @r{(C and Objective-C only)} @opindex Wstrict-prototypes @opindex Wno-strict-prototypes Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.) @item -Wold-style-declaration @r{(C and Objective-C only)} @opindex Wold-style-declaration @opindex Wno-old-style-declaration Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like @code{static} are not the first things in a declaration. This warning is also enabled by @option{-Wextra}. @item -Wold-style-definition @r{(C and Objective-C only)} @opindex Wold-style-definition @opindex Wno-old-style-definition Warn if an old-style function definition is used. A warning is given even if there is a previous prototype. @item -Wmissing-parameter-type @r{(C and Objective-C only)} @opindex Wmissing-parameter-type @opindex Wno-missing-parameter-type A function parameter is declared without a type specifier in K&R-style functions: @smallexample void foo(bar) @{ @} @end smallexample This warning is also enabled by @option{-Wextra}. @item -Wmissing-prototypes @r{(C and Objective-C only)} @opindex Wmissing-prototypes @opindex Wno-missing-prototypes Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for C++ because all function declarations provide prototypes and a non-matching declaration will declare an overload rather than conflict with an earlier declaration. Use @option{-Wmissing-declarations} to detect missing declarations in C++. @item -Wmissing-declarations @opindex Wmissing-declarations @opindex Wno-missing-declarations Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use @option{-Wmissing-prototypes} to detect missing prototypes. In C++, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces. @item -Wmissing-field-initializers @opindex Wmissing-field-initializers @opindex Wno-missing-field-initializers @opindex W @opindex Wextra @opindex Wno-extra Warn if a structure's initializer has some fields missing. For example, the following code causes such a warning, because @code{x.h} is implicitly zero: @smallexample struct s @{ int f, g, h; @}; struct s x = @{ 3, 4 @}; @end smallexample This option does not warn about designated initializers, so the following modification does not trigger a warning: @smallexample struct s @{ int f, g, h; @}; struct s x = @{ .f = 3, .g = 4 @}; @end smallexample In C++ this option does not warn either about the empty @{ @} initializer, for example: @smallexample struct s @{ int f, g, h; @}; s x = @{ @}; @end smallexample This warning is included in @option{-Wextra}. To get other @option{-Wextra} warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. @item -Wno-multichar @opindex Wno-multichar @opindex Wmultichar Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. Usually they indicate a typo in the user's code, as they have implementation-defined values, and should not be used in portable code. @item -Wnormalized@r{[}=@r{<}none@r{|}id@r{|}nfc@r{|}nfkc@r{>]} @opindex Wnormalized= @opindex Wnormalized @opindex Wno-normalized @cindex NFC @cindex NFKC @cindex character set, input normalization In ISO C and ISO C++, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic ASCII character set are used, you can have two different character sequences that look the same. To avoid confusion, the ISO 10646 standard sets out some @dfn{normalization rules} which when applied ensure that two sequences that look the same are turned into the same sequence. GCC can warn you if you are using identifiers that have not been normalized; this option controls that warning. There are four levels of warning supported by GCC@. The default is @option{-Wnormalized=nfc}, which warns about any identifier that is not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the recommended form for most uses. It is equivalent to @option{-Wnormalized}. Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++ that, when turned into NFC, are not allowed in identifiers. That is, there's no way to use these symbols in portable ISO C or C++ and have all your identifiers in NFC@. @option{-Wnormalized=id} suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default. You can switch the warning off for all characters by writing @option{-Wnormalized=none} or @option{-Wno-normalized}. You should only do this if you are using some other normalization scheme (like ``D''), because otherwise you can easily create bugs that are literally impossible to see. Some characters in ISO 10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL LETTER N'', displays just like a regular @code{n} that has been placed in a superscript. ISO 10646 defines the @dfn{NFKC} normalization scheme to convert all these into a standard form as well, and GCC warns if your code is not in NFKC if you use @option{-Wnormalized=nfkc}. This warning is comparable to warning about every identifier that contains the letter O because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment cannot be fixed to display these characters distinctly. @item -Wno-deprecated @opindex Wno-deprecated @opindex Wdeprecated Do not warn about usage of deprecated features. @xref{Deprecated Features}. @item -Wno-deprecated-declarations @opindex Wno-deprecated-declarations @opindex Wdeprecated-declarations Do not warn about uses of functions (@pxref{Function Attributes}), variables (@pxref{Variable Attributes}), and types (@pxref{Type Attributes}) marked as deprecated by using the @code{deprecated} attribute. @item -Wno-overflow @opindex Wno-overflow @opindex Woverflow Do not warn about compile-time overflow in constant expressions. @item -Wno-odr @opindex Wno-odr @opindex Wodr Warn about One Definition Rule violations during link-time optimization. Requires @option{-flto-odr-type-merging} to be enabled. Enabled by default. @item -Wopenmp-simd @opindex Wopenm-simd Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus simd directive set by user. The @option{-fsimd-cost-model=unlimited} can be used to relax the cost model. @item -Woverride-init @r{(C and Objective-C only)} @opindex Woverride-init @opindex Wno-override-init @opindex W @opindex Wextra @opindex Wno-extra Warn if an initialized field without side effects is overridden when using designated initializers (@pxref{Designated Inits, , Designated Initializers}). This warning is included in @option{-Wextra}. To get other @option{-Wextra} warnings without this one, use @option{-Wextra -Wno-override-init}. @item -Wpacked @opindex Wpacked @opindex Wno-packed Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable @code{f.x} in @code{struct bar} is misaligned even though @code{struct bar} does not itself have the packed attribute: @smallexample @group struct foo @{ int x; char a, b, c, d; @} __attribute__((packed)); struct bar @{ char z; struct foo f; @}; @end group @end smallexample @item -Wpacked-bitfield-compat @opindex Wpacked-bitfield-compat @opindex Wno-packed-bitfield-compat The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout. GCC informs you when the offset of such a field has changed in GCC 4.4. For example there is no longer a 4-bit padding between field @code{a} and @code{b} in this structure: @smallexample struct foo @{ char a:4; char b:8; @} __attribute__ ((packed)); @end smallexample This warning is enabled by default. Use @option{-Wno-packed-bitfield-compat} to disable this warning. @item -Wpadded @opindex Wpadded @opindex Wno-padded Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller. @item -Wredundant-decls @opindex Wredundant-decls @opindex Wno-redundant-decls Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing. @item -Wnested-externs @r{(C and Objective-C only)} @opindex Wnested-externs @opindex Wno-nested-externs Warn if an @code{extern} declaration is encountered within a function. @item -Wno-inherited-variadic-ctor @opindex Winherited-variadic-ctor @opindex Wno-inherited-variadic-ctor Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not inherited. @item -Winline @opindex Winline @opindex Wno-inline Warn if a function that is declared as inline cannot be inlined. Even with this option, the compiler does not warn about failures to inline functions declared in system headers. The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by @option{-Winline} to appear or disappear. @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} @opindex Wno-invalid-offsetof @opindex Winvalid-offsetof Suppress warnings from applying the @samp{offsetof} macro to a non-POD type. According to the 2014 ISO C++ standard, applying @samp{offsetof} to a non-standard-layout type is undefined. In existing C++ implementations, however, @samp{offsetof} typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it. The restrictions on @samp{offsetof} may be relaxed in a future version of the C++ standard. @item -Wno-int-to-pointer-cast @opindex Wno-int-to-pointer-cast @opindex Wint-to-pointer-cast Suppress warnings from casts to pointer type of an integer of a different size. In C++, casting to a pointer type of smaller size is an error. @option{Wint-to-pointer-cast} is enabled by default. @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} @opindex Wno-pointer-to-int-cast @opindex Wpointer-to-int-cast Suppress warnings from casts from a pointer to an integer type of a different size. @item -Winvalid-pch @opindex Winvalid-pch @opindex Wno-invalid-pch Warn if a precompiled header (@pxref{Precompiled Headers}) is found in the search path but can't be used. @item -Wlong-long @opindex Wlong-long @opindex Wno-long-long Warn if @samp{long long} type is used. This is enabled by either @option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 modes. To inhibit the warning messages, use @option{-Wno-long-long}. @item -Wvariadic-macros @opindex Wvariadic-macros @opindex Wno-variadic-macros Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is used in ISO C99 mode. This is enabled by either @option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning messages, use @option{-Wno-variadic-macros}. @item -Wvarargs @opindex Wvarargs @opindex Wno-varargs Warn upon questionable usage of the macros used to handle variable arguments like @samp{va_start}. This is default. To inhibit the warning messages, use @option{-Wno-varargs}. @item -Wvector-operation-performance @opindex Wvector-operation-performance @opindex Wno-vector-operation-performance Warn if vector operation is not implemented via SIMD capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented @code{piecewise}, which means that the scalar operation is performed on every vector element; @code{in parallel}, which means that the vector operation is implemented using scalars of wider type, which normally is more performance efficient; and @code{as a single scalar}, which means that vector fits into a scalar type. @item -Wno-virtual-move-assign @opindex Wvirtual-move-assign @opindex Wno-virtual-move-assign Suppress warnings about inheriting from a virtual base with a non-trivial C++11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one path, it will be moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this warning can be disabled. @item -Wvla @opindex Wvla @opindex Wno-vla Warn if variable length array is used in the code. @option{-Wno-vla} prevents the @option{-Wpedantic} warning of the variable length array. @item -Wvolatile-register-var @opindex Wvolatile-register-var @opindex Wno-volatile-register-var Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is enabled by @option{-Wall}. @item -Wdisabled-optimization @opindex Wdisabled-optimization @opindex Wno-disabled-optimization Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCC's optimizers are unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC refuses to optimize programs when the optimization itself is likely to take inordinate amounts of time. @item -Wpointer-sign @r{(C and Objective-C only)} @opindex Wpointer-sign @opindex Wno-pointer-sign Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C@. It is implied by @option{-Wall} and by @option{-Wpedantic}, which can be disabled with @option{-Wno-pointer-sign}. @item -Wstack-protector @opindex Wstack-protector @opindex Wno-stack-protector This option is only active when @option{-fstack-protector} is active. It warns about functions that are not protected against stack smashing. @item -Woverlength-strings @opindex Woverlength-strings @opindex Wno-overlength-strings Warn about string constants that are longer than the ``minimum maximum'' length specified in the C standard. Modern compilers generally allow string constants that are much longer than the standard's minimum limit, but very portable programs should avoid using longer strings. The limit applies @emph{after} string constant concatenation, and does not count the trailing NUL@. In C90, the limit was 509 characters; in C99, it was raised to 4095. C++98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in C++@. This option is implied by @option{-Wpedantic}, and can be disabled with @option{-Wno-overlength-strings}. @item -Wunsuffixed-float-constants @r{(C and Objective-C only)} @opindex Wunsuffixed-float-constants Issue a warning for any floating constant that does not have a suffix. When used together with @option{-Wsystem-headers} it warns about such constants in system header files. This can be useful when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma from the decimal floating-point extension to C99. @item -Wno-designated-init @r{(C and Objective-C only)} Suppress warnings when a positional initializer is used to initialize a structure that has been marked with the @code{designated_init} attribute. @end table @node Debugging Options @section Options for Debugging Your Program or GCC @cindex options, debugging @cindex debugging information options GCC has various special options that are used for debugging either your program or GCC: @table @gcctabopt @item -g @opindex g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging information. On most systems that use stabs format, @option{-g} enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below). GCC allows you to use @option{-g} with @option{-O}. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops. Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs. The following options are useful when GCC is generated with the capability for more than one debugging format. @item -gsplit-dwarf @opindex gsplit-dwarf Separate as much dwarf debugging information as possible into a separate output file with the extension .dwo. This option allows the build system to avoid linking files with debug information. To be useful, this option requires a debugger capable of reading .dwo files. @item -ggdb @opindex ggdb Produce debugging information for use by GDB@. This means to use the most expressive format available (DWARF 2, stabs, or the native format if neither of those are supported), including GDB extensions if at all possible. @item -gpubnames @opindex gpubnames Generate dwarf .debug_pubnames and .debug_pubtypes sections. @item -ggnu-pubnames @opindex ggnu-pubnames Generate .debug_pubnames and .debug_pubtypes sections in a format suitable for conversion into a GDB@ index. This option is only useful with a linker that can produce GDB@ index version 7. @item -gstabs @opindex gstabs Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. On MIPS, Alpha and System V Release 4 systems this option produces stabs debugging output that is not understood by DBX or SDB@. On System V Release 4 systems this option requires the GNU assembler. @item -feliminate-unused-debug-symbols @opindex feliminate-unused-debug-symbols Produce debugging information in stabs format (if that is supported), for only symbols that are actually used. @item -femit-class-debug-always Instead of emitting debugging information for a C++ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are unable to handle the way GCC normally emits debugging information for classes because using this option increases the size of debugging information by as much as a factor of two. @item -fdebug-types-section @opindex fdebug-types-section @opindex fno-debug-types-section When using DWARF Version 4 or higher, type DIEs can be put into their own @code{.debug_types} section instead of making them part of the @code{.debug_info} section. It is more efficient to put them in a separate comdat sections since the linker can then remove duplicates. But not all DWARF consumers support @code{.debug_types} sections yet and on some objects @code{.debug_types} produces larger instead of smaller debugging information. @item -gstabs+ @opindex gstabs+ Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB)@. The use of these extensions is likely to make other debuggers crash or refuse to read the program. @item -gcoff @opindex gcoff Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4. @item -gxcoff @opindex gxcoff Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems. @item -gxcoff+ @opindex gxcoff+ Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB)@. The use of these extensions is likely to make other debuggers crash or refuse to read the program, and may cause assemblers other than the GNU assembler (GAS) to fail with an error. @item -gdwarf-@var{version} @opindex gdwarf-@var{version} Produce debugging information in DWARF format (if that is supported). The value of @var{version} may be either 2, 3 or 4; the default version for most targets is 4. Note that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables. Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} for maximum benefit. @item -grecord-gcc-switches @opindex grecord-gcc-switches This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in DWARF debugging information. The options are concatenated with spaces separating them from each other and from the compiler version. See also @option{-frecord-gcc-switches} for another way of storing compiler options into the object file. This is the default. @item -gno-record-gcc-switches @opindex gno-record-gcc-switches Disallow appending command-line options to the DW_AT_producer attribute in DWARF debugging information. @item -gstrict-dwarf @opindex gstrict-dwarf Disallow using extensions of later DWARF standard version than selected with @option{-gdwarf-@var{version}}. On most targets using non-conflicting DWARF extensions from later standard versions is allowed. @item -gno-strict-dwarf @opindex gno-strict-dwarf Allow using extensions of later DWARF standard version than selected with @option{-gdwarf-@var{version}}. @item -gz@r{[}=@var{type}@r{]} @opindex gz Produce compressed debug sections in DWARF format, if that is supported. If @var{type} is not given, the default type depends on the capabilities of the assembler and linker used. @var{type} may be one of @option{none} (don't compress debug sections), @option{zlib} (use zlib compression in ELF gABI format), or @option{zlib-gnu} (use zlib compression in traditional GNU format). If the linker doesn't support writing compressed debug sections, the option is rejected. Otherwise, if the assembler does not support them, @option{-gz} is silently ignored when producing object files. @item -gvms @opindex gvms Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUG on Alpha/VMS systems. @item -g@var{level} @itemx -ggdb@var{level} @itemx -gstabs@var{level} @itemx -gcoff@var{level} @itemx -gxcoff@var{level} @itemx -gvms@var{level} Request debugging information and also use @var{level} to specify how much information. The default level is 2. Level 0 produces no debug information at all. Thus, @option{-g0} negates @option{-g}. Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables. Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use @option{-g3}. @option{-gdwarf-2} does not accept a concatenated debug level, because GCC used to support an option @option{-gdwarf} that meant to generate debug information in version 1 of the DWARF format (which is very different from version 2), and it would have been too confusing. That debug format is long obsolete, but the option cannot be changed now. Instead use an additional @option{-g@var{level}} option to change the debug level for DWARF. @item -gtoggle @opindex gtoggle Turn off generation of debug info, if leaving out this option generates it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter; it takes effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with @option{-fcompare-debug}. @item -fsanitize=address @opindex fsanitize=address Enable AddressSanitizer, a fast memory error detector. Memory access instructions will be instrumented to detect out-of-bounds and use-after-free bugs. See @uref{http://code.google.com/p/address-sanitizer/} for more details. The run-time behavior can be influenced using the @env{ASAN_OPTIONS} environment variable; see @url{https://code.google.com/p/address-sanitizer/wiki/Flags#Run-time_flags} for a list of supported options. @item -fsanitize=kernel-address @opindex fsanitize=kernel-address Enable AddressSanitizer for Linux kernel. See @uref{http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel} for more details. @item -fsanitize=thread @opindex fsanitize=thread Enable ThreadSanitizer, a fast data race detector. Memory access instructions will be instrumented to detect data race bugs. See @uref{http://code.google.com/p/thread-sanitizer/} for more details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS} environment variable; see @url{https://code.google.com/p/thread-sanitizer/wiki/Flags} for a list of supported options. @item -fsanitize=leak @opindex fsanitize=leak Enable LeakSanitizer, a memory leak detector. This option only matters for linking of executables and if neither @option{-fsanitize=address} nor @option{-fsanitize=thread} is used. In that case it will link the executable against a library that overrides @code{malloc} and other allocator functions. See @uref{https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer} for more details. The run-time behavior can be influenced using the @env{LSAN_OPTIONS} environment variable. @item -fsanitize=undefined @opindex fsanitize=undefined Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations will be instrumented to detect undefined behavior at runtime. Current suboptions are: @table @gcctabopt @item -fsanitize=shift @opindex fsanitize=shift This option enables checking that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and C++, as well as between ISO C90 and C99, etc. @item -fsanitize=integer-divide-by-zero @opindex fsanitize=integer-divide-by-zero Detect integer division by zero as well as @code{INT_MIN / -1} division. @item -fsanitize=unreachable @opindex fsanitize=unreachable With this option, the compiler will turn the @code{__builtin_unreachable} call into a diagnostics message call instead. When reaching the @code{__builtin_unreachable} call, the behavior is undefined. @item -fsanitize=vla-bound @opindex fsanitize=vla-bound This option instructs the compiler to check that the size of a variable length array is positive. This option does not have any effect in @option{-std=c++14} mode, as the standard requires the exception be thrown instead. @item -fsanitize=null @opindex fsanitize=null This option enables pointer checking. Particularly, the application built with this option turned on will issue an error message when it tries to dereference a NULL pointer, or if a reference (possibly an rvalue reference) is bound to a NULL pointer, or if a method is invoked on an object pointed by a NULL pointer. @item -fsanitize=return @opindex fsanitize=return This option enables return statement checking. Programs built with this option turned on will issue an error message when the end of a non-void function is reached without actually returning a value. This option works in C++ only. @item -fsanitize=signed-integer-overflow @opindex fsanitize=signed-integer-overflow This option enables signed integer overflow checking. We check that the result of @code{+}, @code{*}, and both unary and binary @code{-} does not overflow in the signed arithmetics. Note, integer promotion rules must be taken into account. That is, the following is not an overflow: @smallexample signed char a = SCHAR_MAX; a++; @end smallexample @item -fsanitize=bounds @opindex fsanitize=bounds This option enables instrumentation of array bounds. Various out of bounds accesses are detected. Flexible array members and initializers of variables with static storage are not instrumented. @item -fsanitize=alignment @opindex fsanitize=alignment This option enables checking of alignment of pointers when they are dereferenced, or when a reference is bound to insufficiently aligned target, or when a method or constructor is invoked on insufficiently aligned object. @item -fsanitize=object-size @opindex fsanitize=object-size This option enables instrumentation of memory references using the @code{__builtin_object_size} function. Various out of bounds pointer accesses are detected. @item -fsanitize=float-divide-by-zero @opindex fsanitize=float-divide-by-zero Detect floating-point division by zero. Unlike other similar options, @option{-fsanitize=float-divide-by-zero} is not enabled by @option{-fsanitize=undefined}, since floating-point division by zero can be a legitimate way of obtaining infinities and NaNs. @item -fsanitize=float-cast-overflow @opindex fsanitize=float-cast-overflow This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow. This option does not work well with @code{FE_INVALID} exceptions enabled. @item -fsanitize=nonnull-attribute @opindex fsanitize=nonnull-attribute This option enables instrumentation of calls, checking whether null values are not passed to arguments marked as requiring a non-null value by the @code{nonnull} function attribute. @item -fsanitize=returns-nonnull-attribute @opindex fsanitize=returns-nonnull-attribute This option enables instrumentation of return statements in functions marked with @code{returns_nonnull} function attribute, to detect returning of null values from such functions. @item -fsanitize=bool @opindex fsanitize=bool This option enables instrumentation of loads from bool. If a value other than 0/1 is loaded, a run-time error is issued. @item -fsanitize=enum @opindex fsanitize=enum This option enables instrumentation of loads from an enum type. If a value outside the range of values for the enum type is loaded, a run-time error is issued. @end table While @option{-ftrapv} causes traps for signed overflows to be emitted, @option{-fsanitize=undefined} gives a diagnostic message. This currently works only for the C family of languages. @item -fasan-shadow-offset=@var{number} @opindex fasan-shadow-offset This option forces GCC to use custom shadow offset in AddressSanitizer checks. It is useful for experimenting with different shadow memory layouts in Kernel AddressSanitizer. @item -fsanitize-recover@r{[}=@var{opts}@r{]} @opindex fsanitize-recover @opindex fno-sanitize-recover @option{-fsanitize-recover=} controls error recovery mode for sanitizers mentioned in comma-separated list of @var{opts}. Enabling this option for a sanitizer component would cause it to attempt to continue running the program as if no error happened. This means multiple runtime errors can be reported in a single program run, and the exit code of the program may indicate success even when errors have been reported. The @option{-fno-sanitize-recover=} can be used to alter this behavior, only the first detected error will be reported and program will exit after that with non-zero exit code. Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}), @option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero} and @option{-fsanitize=kernel-address}. For these sanitizers error recovery is turned on by default. Syntax without explicit @var{opts} parameter is deprecated. It is equivalent to @option{-fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero,kernel-address}. Similarly @option{-fno-sanitize-recover} is equivalent to @option{-fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero,kernel-address}. @item -fsanitize-undefined-trap-on-error @opindex fsanitize-undefined-trap-on-error The @option{-fsanitize-undefined-trap-on-error} instructs the compiler to report undefined behavior using @code{__builtin_trap ()} rather than a @code{libubsan} library routine. The advantage of this is that the @code{libubsan} library is not needed and will not be linked in, so this is usable even for use in freestanding environments. @item -fdump-final-insns@r{[}=@var{file}@r{]} @opindex fdump-final-insns Dump the final internal representation (RTL) to @var{file}. If the optional argument is omitted (or if @var{file} is @code{.}), the name of the dump file is determined by appending @code{.gkd} to the compilation output file name. @item -fcompare-debug@r{[}=@var{opts}@r{]} @opindex fcompare-debug @opindex fno-compare-debug If no error occurs during compilation, run the compiler a second time, adding @var{opts} and @option{-fcompare-debug-second} to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ. If the equal sign is omitted, the default @option{-gtoggle} is used. The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty and nonzero, implicitly enables @option{-fcompare-debug}. If @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, then it is used for @var{opts}, otherwise the default @option{-gtoggle} is used. @option{-fcompare-debug=}, with the equal sign but without @var{opts}, is equivalent to @option{-fno-compare-debug}, which disables the dumping of the final representation and the second compilation, preventing even @env{GCC_COMPARE_DEBUG} from taking effect. To verify full coverage during @option{-fcompare-debug} testing, set @env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden}, which GCC rejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug not overridden} will do. @item -fcompare-debug-second @opindex fcompare-debug-second This option is implicitly passed to the compiler for the second compilation requested by @option{-fcompare-debug}, along with options to silence warnings, and omitting other options that would cause side-effect compiler outputs to files or to the standard output. Dump files and preserved temporary files are renamed so as to contain the @code{.gk} additional extension during the second compilation, to avoid overwriting those generated by the first. When this option is passed to the compiler driver, it causes the @emph{first} compilation to be skipped, which makes it useful for little other than debugging the compiler proper. @item -feliminate-dwarf2-dups @opindex feliminate-dwarf2-dups Compress DWARF 2 debugging information by eliminating duplicated information about each symbol. This option only makes sense when generating DWARF 2 debugging information with @option{-gdwarf-2}. @item -femit-struct-debug-baseonly @opindex femit-struct-debug-baseonly Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct is defined. This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See @option{-femit-struct-debug-reduced} for a less aggressive option. See @option{-femit-struct-debug-detailed} for more detailed control. This option works only with DWARF 2. @item -femit-struct-debug-reduced @opindex femit-struct-debug-reduced Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type is defined, unless the struct is a template or defined in a system header. This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See @option{-femit-struct-debug-baseonly} for a more aggressive option. See @option{-femit-struct-debug-detailed} for more detailed control. This option works only with DWARF 2. @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same program. This option is a detailed version of @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, which serves for most needs. A specification has the syntax@* [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) The optional first word limits the specification to structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is @samp{struct one direct; struct two * indirect;}. The optional second word limits the specification to ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). Generic structs are a bit complicated to explain. For C++, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but @option{-femit-struct-debug-detailed} does not yet implement them. The third word specifies the source files for those structs for which the compiler should emit debug information. The values @samp{none} and @samp{any} have the normal meaning. The value @samp{base} means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling @file{foo.c}, debug information is generated for types declared in that file and @file{foo.h}, but not other header files. The value @samp{sys} means those types satisfying @samp{base} or declared in system or compiler headers. You may need to experiment to determine the best settings for your application. The default is @option{-femit-struct-debug-detailed=all}. This option works only with DWARF 2. @item -fno-merge-debug-strings @opindex fmerge-debug-strings @opindex fno-merge-debug-strings Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default. @item -fdebug-prefix-map=@var{old}=@var{new} @opindex fdebug-prefix-map When compiling files in directory @file{@var{old}}, record debugging information describing them as in @file{@var{new}} instead. @item -fno-dwarf2-cfi-asm @opindex fdwarf2-cfi-asm @opindex fno-dwarf2-cfi-asm Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section instead of using GAS @code{.cfi_*} directives. @cindex @command{prof} @item -p @opindex p Generate extra code to write profile information suitable for the analysis program @command{prof}. You must use this option when compiling the source files you want data about, and you must also use it when linking. @cindex @command{gprof} @item -pg @opindex pg Generate extra code to write profile information suitable for the analysis program @command{gprof}. You must use this option when compiling the source files you want data about, and you must also use it when linking. @item -Q @opindex Q Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes. @item -ftime-report @opindex ftime-report Makes the compiler print some statistics about the time consumed by each pass when it finishes. @item -fmem-report @opindex fmem-report Makes the compiler print some statistics about permanent memory allocation when it finishes. @item -fmem-report-wpa @opindex fmem-report-wpa Makes the compiler print some statistics about permanent memory allocation for the WPA phase only. @item -fpre-ipa-mem-report @opindex fpre-ipa-mem-report @item -fpost-ipa-mem-report @opindex fpost-ipa-mem-report Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization. @item -fprofile-report @opindex fprofile-report Makes the compiler print some statistics about consistency of the (estimated) profile and effect of individual passes. @item -fstack-usage @opindex fstack-usage Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields: @itemize @item The name of the function. @item A number of bytes. @item One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. @end itemize The qualifier @code{static} means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack adjustments are otherwise made in the function. The second field is this fixed number of bytes. The qualifier @code{dynamic} means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the function, for example to push/pop arguments around function calls. If the qualifier @code{bounded} is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only represents the bounded part. @item -fprofile-arcs @opindex fprofile-arcs Add code so that program flow @dfn{arcs} are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. When the compiled program exits it saves this data to a file called @file{@var{auxname}.gcda} for each source file. The data may be used for profile-directed optimizations (@option{-fbranch-probabilities}), or for test coverage analysis (@option{-ftest-coverage}). Each object file's @var{auxname} is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). @xref{Cross-profiling}. @cindex @command{gcov} @item --coverage @opindex coverage This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for @option{-fprofile-arcs} @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when linking). See the documentation for those options for more details. @itemize @item Compile the source files with @option{-fprofile-arcs} plus optimization and code generation options. For test coverage analysis, use the additional @option{-ftest-coverage} option. You do not need to profile every source file in a program. @item Link your object files with @option{-lgcov} or @option{-fprofile-arcs} (the latter implies the former). @item Run the program on a representative workload to generate the arc profile information. This may be repeated any number of times. You can run concurrent instances of your program, and provided that the file system supports locking, the data files will be correctly updated. Also @code{fork} calls are detected and correctly handled (double counting will not happen). @item For profile-directed optimizations, compile the source files again with the same optimization and code generation options plus @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that Control Optimization}). @item For test coverage analysis, use @command{gcov} to produce human readable information from the @file{.gcno} and @file{.gcda} files. Refer to the @command{gcov} documentation for further information. @end itemize With @option{-fprofile-arcs}, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code. @need 2000 @item -ftest-coverage @opindex ftest-coverage Produce a notes file that the @command{gcov} code-coverage utility (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to show program coverage. Each source file's note file is called @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option above for a description of @var{auxname} and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize. @item -fdbg-cnt-list @opindex fdbg-cnt-list Print the name and the counter upper bound for all debug counters. @item -fdbg-cnt=@var{counter-value-list} @opindex fdbg-cnt Set the internal debug counter upper bound. @var{counter-value-list} is a comma-separated list of @var{name}:@var{value} pairs which sets the upper bound of each debug counter @var{name} to @var{value}. All debug counters have the initial upper bound of @code{UINT_MAX}; thus @code{dbg_cnt()} returns true always unless the upper bound is set by this option. For example, with @option{-fdbg-cnt=dce:10,tail_call:0}, @code{dbg_cnt(dce)} returns true only for first 10 invocations. @item -fenable-@var{kind}-@var{pass} @itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} @opindex fdisable- @opindex fenable- This is a set of options that are used to explicitly disable/enable optimization passes. These options are intended for use for debugging GCC. Compiler users should use regular options for enabling/disabling passes instead. @table @gcctabopt @item -fdisable-ipa-@var{pass} Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. @item -fdisable-rtl-@var{pass} @itemx -fdisable-rtl-@var{pass}=@var{range-list} Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. @var{range-list} is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon. The range is inclusive in both ends. If the range is trivial, the number pair can be simplified as a single number. If the function's call graph node's @var{uid} falls within one of the specified ranges, the @var{pass} is disabled for that function. The @var{uid} is shown in the function header of a dump file, and the pass names can be dumped by using option @option{-fdump-passes}. @item -fdisable-tree-@var{pass} @itemx -fdisable-tree-@var{pass}=@var{range-list} Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of option arguments. @item -fenable-ipa-@var{pass} Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. @item -fenable-rtl-@var{pass} @itemx -fenable-rtl-@var{pass}=@var{range-list} Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument description and examples. @item -fenable-tree-@var{pass} @itemx -fenable-tree-@var{pass}=@var{range-list} Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of option arguments. @end table Here are some examples showing uses of these options. @smallexample # disable ccp1 for all functions -fdisable-tree-ccp1 # disable complete unroll for function whose cgraph node uid is 1 -fenable-tree-cunroll=1 # disable gcse2 for functions at the following ranges [1,1], # [300,400], and [400,1000] # disable gcse2 for functions foo and foo2 -fdisable-rtl-gcse2=foo,foo2 # disable early inlining -fdisable-tree-einline # disable ipa inlining -fdisable-ipa-inline # enable tree full unroll -fenable-tree-unroll @end smallexample @item -d@var{letters} @itemx -fdump-rtl-@var{pass} @itemx -fdump-rtl-@var{pass}=@var{filename} @opindex d @opindex fdump-rtl-@var{pass} Says to make debugging dumps during compilation at times specified by @var{letters}. This is used for debugging the RTL-based passes of the compiler. The file names for most of the dumps are made by appending a pass number and a word to the @var{dumpname}, and the files are created in the directory of the output file. In case of @option{=@var{filename}} option, the dump is output on the given file instead of the pass numbered dump files. Note that the pass number is computed statically as passes get registered into the pass manager. Thus the numbering is not related to the dynamic order of execution of passes. In particular, a pass installed by a plugin could have a number over 200 even if it executed quite early. @var{dumpname} is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. These switches may have different effects when @option{-E} is used for preprocessing. Debug dumps can be enabled with a @option{-fdump-rtl} switch or some @option{-d} option @var{letters}. Here are the possible letters for use in @var{pass} and @var{letters}, and their meanings: @table @gcctabopt @item -fdump-rtl-alignments @opindex fdump-rtl-alignments Dump after branch alignments have been computed. @item -fdump-rtl-asmcons @opindex fdump-rtl-asmcons Dump after fixing rtl statements that have unsatisfied in/out constraints. @item -fdump-rtl-auto_inc_dec @opindex fdump-rtl-auto_inc_dec Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions. @item -fdump-rtl-barriers @opindex fdump-rtl-barriers Dump after cleaning up the barrier instructions. @item -fdump-rtl-bbpart @opindex fdump-rtl-bbpart Dump after partitioning hot and cold basic blocks. @item -fdump-rtl-bbro @opindex fdump-rtl-bbro Dump after block reordering. @item -fdump-rtl-btl1 @itemx -fdump-rtl-btl2 @opindex fdump-rtl-btl2 @opindex fdump-rtl-btl2 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping after the two branch target load optimization passes. @item -fdump-rtl-bypass @opindex fdump-rtl-bypass Dump after jump bypassing and control flow optimizations. @item -fdump-rtl-combine @opindex fdump-rtl-combine Dump after the RTL instruction combination pass. @item -fdump-rtl-compgotos @opindex fdump-rtl-compgotos Dump after duplicating the computed gotos. @item -fdump-rtl-ce1 @itemx -fdump-rtl-ce2 @itemx -fdump-rtl-ce3 @opindex fdump-rtl-ce1 @opindex fdump-rtl-ce2 @opindex fdump-rtl-ce3 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and @option{-fdump-rtl-ce3} enable dumping after the three if conversion passes. @item -fdump-rtl-cprop_hardreg @opindex fdump-rtl-cprop_hardreg Dump after hard register copy propagation. @item -fdump-rtl-csa @opindex fdump-rtl-csa Dump after combining stack adjustments. @item -fdump-rtl-cse1 @itemx -fdump-rtl-cse2 @opindex fdump-rtl-cse1 @opindex fdump-rtl-cse2 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after the two common subexpression elimination passes. @item -fdump-rtl-dce @opindex fdump-rtl-dce Dump after the standalone dead code elimination passes. @item -fdump-rtl-dbr @opindex fdump-rtl-dbr Dump after delayed branch scheduling. @item -fdump-rtl-dce1 @itemx -fdump-rtl-dce2 @opindex fdump-rtl-dce1 @opindex fdump-rtl-dce2 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after the two dead store elimination passes. @item -fdump-rtl-eh @opindex fdump-rtl-eh Dump after finalization of EH handling code. @item -fdump-rtl-eh_ranges @opindex fdump-rtl-eh_ranges Dump after conversion of EH handling range regions. @item -fdump-rtl-expand @opindex fdump-rtl-expand Dump after RTL generation. @item -fdump-rtl-fwprop1 @itemx -fdump-rtl-fwprop2 @opindex fdump-rtl-fwprop1 @opindex fdump-rtl-fwprop2 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable dumping after the two forward propagation passes. @item -fdump-rtl-gcse1 @itemx -fdump-rtl-gcse2 @opindex fdump-rtl-gcse1 @opindex fdump-rtl-gcse2 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping after global common subexpression elimination. @item -fdump-rtl-init-regs @opindex fdump-rtl-init-regs Dump after the initialization of the registers. @item -fdump-rtl-initvals @opindex fdump-rtl-initvals Dump after the computation of the initial value sets. @item -fdump-rtl-into_cfglayout @opindex fdump-rtl-into_cfglayout Dump after converting to cfglayout mode. @item -fdump-rtl-ira @opindex fdump-rtl-ira Dump after iterated register allocation. @item -fdump-rtl-jump @opindex fdump-rtl-jump Dump after the second jump optimization. @item -fdump-rtl-loop2 @opindex fdump-rtl-loop2 @option{-fdump-rtl-loop2} enables dumping after the rtl loop optimization passes. @item -fdump-rtl-mach @opindex fdump-rtl-mach Dump after performing the machine dependent reorganization pass, if that pass exists. @item -fdump-rtl-mode_sw @opindex fdump-rtl-mode_sw Dump after removing redundant mode switches. @item -fdump-rtl-rnreg @opindex fdump-rtl-rnreg Dump after register renumbering. @item -fdump-rtl-outof_cfglayout @opindex fdump-rtl-outof_cfglayout Dump after converting from cfglayout mode. @item -fdump-rtl-peephole2 @opindex fdump-rtl-peephole2 Dump after the peephole pass. @item -fdump-rtl-postreload @opindex fdump-rtl-postreload Dump after post-reload optimizations. @item -fdump-rtl-pro_and_epilogue @opindex fdump-rtl-pro_and_epilogue Dump after generating the function prologues and epilogues. @item -fdump-rtl-sched1 @itemx -fdump-rtl-sched2 @opindex fdump-rtl-sched1 @opindex fdump-rtl-sched2 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping after the basic block scheduling passes. @item -fdump-rtl-ree @opindex fdump-rtl-ree Dump after sign/zero extension elimination. @item -fdump-rtl-seqabstr @opindex fdump-rtl-seqabstr Dump after common sequence discovery. @item -fdump-rtl-shorten @opindex fdump-rtl-shorten Dump after shortening branches. @item -fdump-rtl-sibling @opindex fdump-rtl-sibling Dump after sibling call optimizations. @item -fdump-rtl-split1 @itemx -fdump-rtl-split2 @itemx -fdump-rtl-split3 @itemx -fdump-rtl-split4 @itemx -fdump-rtl-split5 @opindex fdump-rtl-split1 @opindex fdump-rtl-split2 @opindex fdump-rtl-split3 @opindex fdump-rtl-split4 @opindex fdump-rtl-split5 @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2}, @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and @option{-fdump-rtl-split5} enable dumping after five rounds of instruction splitting. @item -fdump-rtl-sms @opindex fdump-rtl-sms Dump after modulo scheduling. This pass is only run on some architectures. @item -fdump-rtl-stack @opindex fdump-rtl-stack Dump after conversion from GCC's ``flat register file'' registers to the x87's stack-like registers. This pass is only run on x86 variants. @item -fdump-rtl-subreg1 @itemx -fdump-rtl-subreg2 @opindex fdump-rtl-subreg1 @opindex fdump-rtl-subreg2 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after the two subreg expansion passes. @item -fdump-rtl-unshare @opindex fdump-rtl-unshare Dump after all rtl has been unshared. @item -fdump-rtl-vartrack @opindex fdump-rtl-vartrack Dump after variable tracking. @item -fdump-rtl-vregs @opindex fdump-rtl-vregs Dump after converting virtual registers to hard registers. @item -fdump-rtl-web @opindex fdump-rtl-web Dump after live range splitting. @item -fdump-rtl-regclass @itemx -fdump-rtl-subregs_of_mode_init @itemx -fdump-rtl-subregs_of_mode_finish @itemx -fdump-rtl-dfinit @itemx -fdump-rtl-dfinish @opindex fdump-rtl-regclass @opindex fdump-rtl-subregs_of_mode_init @opindex fdump-rtl-subregs_of_mode_finish @opindex fdump-rtl-dfinit @opindex fdump-rtl-dfinish These dumps are defined but always produce empty files. @item -da @itemx -fdump-rtl-all @opindex da @opindex fdump-rtl-all Produce all the dumps listed above. @item -dA @opindex dA Annotate the assembler output with miscellaneous debugging information. @item -dD @opindex dD Dump all macro definitions, at the end of preprocessing, in addition to normal output. @item -dH @opindex dH Produce a core dump whenever an error occurs. @item -dp @opindex dp Annotate the assembler output with a comment indicating which pattern and alternative is used. The length of each instruction is also printed. @item -dP @opindex dP Dump the RTL in the assembler output as a comment before each instruction. Also turns on @option{-dp} annotation. @item -dx @opindex dx Just generate RTL for a function instead of compiling it. Usually used with @option{-fdump-rtl-expand}. @end table @item -fdump-noaddr @opindex fdump-noaddr When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different text / bss / data / heap / stack / dso start locations. @item -freport-bug @opindex freport-bug Collect and dump debug information into temporary file if ICE in C/C++ compiler occured. @item -fdump-unnumbered @opindex fdump-unnumbered When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without @option{-g}. @item -fdump-unnumbered-links @opindex fdump-unnumbered-links When doing debugging dumps (see @option{-d} option above), suppress instruction numbers for the links to the previous and next instructions in a sequence. @item -fdump-translation-unit @r{(C++ only)} @itemx -fdump-translation-unit-@var{options} @r{(C++ only)} @opindex fdump-translation-unit Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending @file{.tu} to the source file name, and the file is created in the same directory as the output file. If the @samp{-@var{options}} form is used, @var{options} controls the details of the dump as described for the @option{-fdump-tree} options. @item -fdump-class-hierarchy @r{(C++ only)} @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} @opindex fdump-class-hierarchy Dump a representation of each class's hierarchy and virtual function table layout to a file. The file name is made by appending @file{.class} to the source file name, and the file is created in the same directory as the output file. If the @samp{-@var{options}} form is used, @var{options} controls the details of the dump as described for the @option{-fdump-tree} options. @item -fdump-ipa-@var{switch} @opindex fdump-ipa Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. The following dumps are possible: @table @samp @item all Enables all inter-procedural analysis dumps. @item cgraph Dumps information about call-graph optimization, unused function removal, and inlining decisions. @item inline Dump after function inlining. @end table @item -fdump-passes @opindex fdump-passes Dump the list of optimization passes that are turned on and off by the current command-line options. @item -fdump-statistics-@var{option} @opindex fdump-statistics Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in @samp{.statistics} to the source file name, and the file is created in the same directory as the output file. If the @samp{-@var{option}} form is used, @samp{-stats} causes counters to be summed over the whole compilation unit while @samp{-details} dumps every event as the passes generate them. The default with no option is to sum counters for each function compiled. @item -fdump-tree-@var{switch} @itemx -fdump-tree-@var{switch}-@var{options} @itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} @opindex fdump-tree Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch-specific suffix to the source file name, and the file is created in the same directory as the output file. In case of @option{=@var{filename}} option, the dump is output on the given file instead of the auto named dump files. If the @samp{-@var{options}} form is used, @var{options} is a list of @samp{-} separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following options are available @table @samp @item address Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment. @item asmname If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that in the dump instead of @code{DECL_NAME}. Its primary use is ease of use working backward from mangled names in the assembly file. @item slim When dumping front-end intermediate representations, inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path. When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures. When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation. @item raw Print a raw representation of the tree. By default, trees are pretty-printed into a C-like representation. @item details Enable more detailed dumps (not honored by every dump option). Also include information from the optimization passes. @item stats Enable dumping various statistics about the pass (not honored by every dump option). @item blocks Enable showing basic block boundaries (disabled in raw dumps). @item graph For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), dump a representation of the control flow graph suitable for viewing with GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot. This option currently only works for RTL dumps, and the RTL is always dumped in slim form. @item vops Enable showing virtual operands for every statement. @item lineno Enable showing line numbers for statements. @item uid Enable showing the unique ID (@code{DECL_UID}) for each variable. @item verbose Enable showing the tree dump for each statement. @item eh Enable showing the EH region number holding each statement. @item scev Enable showing scalar evolution analysis details. @item optimized Enable showing optimization information (only available in certain passes). @item missed Enable showing missed optimization information (only available in certain passes). @item note Enable other detailed optimization information (only available in certain passes). @item =@var{filename} Instead of an auto named dump file, output into the given file name. The file names @file{stdout} and @file{stderr} are treated specially and are considered already open standard streams. For example, @smallexample gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump -fdump-tree-pre=stderr file.c @end smallexample outputs vectorizer dump into @file{foo.dump}, while the PRE dump is output on to @file{stderr}. If two conflicting dump filenames are given for the same pass, then the latter option overrides the earlier one. @item all Turn on all options, except @option{raw}, @option{slim}, @option{verbose} and @option{lineno}. @item optall Turn on all optimization options, i.e., @option{optimized}, @option{missed}, and @option{note}. @end table The following tree dumps are possible: @table @samp @item original @opindex fdump-tree-original Dump before any tree based optimization, to @file{@var{file}.original}. @item optimized @opindex fdump-tree-optimized Dump after all tree based optimization, to @file{@var{file}.optimized}. @item gimple @opindex fdump-tree-gimple Dump each function before and after the gimplification pass to a file. The file name is made by appending @file{.gimple} to the source file name. @item cfg @opindex fdump-tree-cfg Dump the control flow graph of each function to a file. The file name is made by appending @file{.cfg} to the source file name. @item ch @opindex fdump-tree-ch Dump each function after copying loop headers. The file name is made by appending @file{.ch} to the source file name. @item ssa @opindex fdump-tree-ssa Dump SSA related information to a file. The file name is made by appending @file{.ssa} to the source file name. @item alias @opindex fdump-tree-alias Dump aliasing information for each function. The file name is made by appending @file{.alias} to the source file name. @item ccp @opindex fdump-tree-ccp Dump each function after CCP@. The file name is made by appending @file{.ccp} to the source file name. @item storeccp @opindex fdump-tree-storeccp Dump each function after STORE-CCP@. The file name is made by appending @file{.storeccp} to the source file name. @item pre @opindex fdump-tree-pre Dump trees after partial redundancy elimination. The file name is made by appending @file{.pre} to the source file name. @item fre @opindex fdump-tree-fre Dump trees after full redundancy elimination. The file name is made by appending @file{.fre} to the source file name. @item copyprop @opindex fdump-tree-copyprop Dump trees after copy propagation. The file name is made by appending @file{.copyprop} to the source file name. @item store_copyprop @opindex fdump-tree-store_copyprop Dump trees after store copy-propagation. The file name is made by appending @file{.store_copyprop} to the source file name. @item dce @opindex fdump-tree-dce Dump each function after dead code elimination. The file name is made by appending @file{.dce} to the source file name. @item sra @opindex fdump-tree-sra Dump each function after performing scalar replacement of aggregates. The file name is made by appending @file{.sra} to the source file name. @item sink @opindex fdump-tree-sink Dump each function after performing code sinking. The file name is made by appending @file{.sink} to the source file name. @item dom @opindex fdump-tree-dom Dump each function after applying dominator tree optimizations. The file name is made by appending @file{.dom} to the source file name. @item dse @opindex fdump-tree-dse Dump each function after applying dead store elimination. The file name is made by appending @file{.dse} to the source file name. @item phiopt @opindex fdump-tree-phiopt Dump each function after optimizing PHI nodes into straightline code. The file name is made by appending @file{.phiopt} to the source file name. @item forwprop @opindex fdump-tree-forwprop Dump each function after forward propagating single use variables. The file name is made by appending @file{.forwprop} to the source file name. @item copyrename @opindex fdump-tree-copyrename Dump each function after applying the copy rename optimization. The file name is made by appending @file{.copyrename} to the source file name. @item nrv @opindex fdump-tree-nrv Dump each function after applying the named return value optimization on generic trees. The file name is made by appending @file{.nrv} to the source file name. @item vect @opindex fdump-tree-vect Dump each function after applying vectorization of loops. The file name is made by appending @file{.vect} to the source file name. @item slp @opindex fdump-tree-slp Dump each function after applying vectorization of basic blocks. The file name is made by appending @file{.slp} to the source file name. @item vrp @opindex fdump-tree-vrp Dump each function after Value Range Propagation (VRP). The file name is made by appending @file{.vrp} to the source file name. @item all @opindex fdump-tree-all Enable all the available tree dumps with the flags provided in this option. @end table @item -fopt-info @itemx -fopt-info-@var{options} @itemx -fopt-info-@var{options}=@var{filename} @opindex fopt-info Controls optimization dumps from various optimization passes. If the @samp{-@var{options}} form is used, @var{options} is a list of @samp{-} separated options to select the dump details and optimizations. If @var{options} is not specified, it defaults to @option{optimized} for details and @option{optall} for optimization groups. If the @var{filename} is not specified, it defaults to @file{stderr}. Note that the output @var{filename} will be overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, @file{stderr} should be used instead. The options can be divided into two groups, 1) options describing the verbosity of the dump, and 2) options describing which optimizations should be included. The options from both the groups can be freely mixed as they are non-overlapping. However, in case of any conflicts, the latter options override the earlier options on the command line. Though multiple -fopt-info options are accepted, only one of them can have @option{=filename}. If other filenames are provided then all but the first one are ignored. The dump verbosity has the following options @table @samp @item optimized Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location of loops which got successfully vectorized. @item missed Print information about missed optimizations. Individual passes control which information to include in the output. For example, @smallexample gcc -O2 -ftree-vectorize -fopt-info-vec-missed @end smallexample will print information about missed optimization opportunities from vectorization passes on stderr. @item note Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc. @item all Print detailed optimization information. This includes @var{optimized}, @var{missed}, and @var{note}. @end table The second set of options describes a group of optimizations and may include one or more of the following. @table @samp @item ipa Enable dumps from all interprocedural optimizations. @item loop Enable dumps from all loop optimizations. @item inline Enable dumps from all inlining optimizations. @item vec Enable dumps from all vectorization optimizations. @item optall Enable dumps from all optimizations. This is a superset of the optimization groups listed above. @end table For example, @smallexample gcc -O3 -fopt-info-missed=missed.all @end smallexample outputs missed optimization report from all the passes into @file{missed.all}. As another example, @smallexample gcc -O3 -fopt-info-inline-optimized-missed=inline.txt @end smallexample will output information about missed optimizations as well as optimized locations from all the inlining passes into @file{inline.txt}. If the @var{filename} is provided, then the dumps from all the applicable optimizations are concatenated into the @file{filename}. Otherwise the dump is output onto @file{stderr}. If @var{options} is omitted, it defaults to @option{all-optall}, which means dump all available optimization info from all the passes. In the following example, all optimization info is output on to @file{stderr}. @smallexample gcc -O3 -fopt-info @end smallexample Note that @option{-fopt-info-vec-missed} behaves the same as @option{-fopt-info-missed-vec}. As another example, consider @smallexample gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt @end smallexample Here the two output filenames @file{vec.miss} and @file{loop.opt} are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only the @file{vec.miss} is produced which contains dumps from the vectorizer about missed opportunities. @item -frandom-seed=@var{number} @opindex frandom-seed This option provides a seed that GCC uses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the @option{-frandom-seed} option to produce reproducibly identical object files. The @var{number} should be different for every file you compile. @item -fsched-verbose=@var{n} @opindex fsched-verbose On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints. This information is written to standard error, unless @option{-fdump-rtl-sched1} or @option{-fdump-rtl-sched2} is specified, in which case it is output to the usual dump listing file, @file{.sched1} or @file{.sched2} respectively. However for @var{n} greater than nine, the output is always printed to standard error. For @var{n} greater than zero, @option{-fsched-verbose} outputs the same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. For @var{n} greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For @var{n} greater than two, it includes RTL at abort point, control-flow and regions info. And for @var{n} over four, @option{-fsched-verbose} also includes dependence info. @item -save-temps @itemx -save-temps=cwd @opindex save-temps Store the usual ``temporary'' intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling @file{foo.c} with @option{-c -save-temps} produces files @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a preprocessed @file{foo.i} output file even though the compiler now normally uses an integrated preprocessor. When used in combination with the @option{-x} command-line option, @option{-save-temps} is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using @option{-save-temps}. If you invoke GCC in parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance: @smallexample gcc -save-temps -o outdir1/foo.o indir1/foo.c& gcc -save-temps -o outdir2/foo.o indir2/foo.c& @end smallexample may result in @file{foo.i} and @file{foo.o} being written to simultaneously by both compilers. @item -save-temps=obj @opindex save-temps=obj Store the usual ``temporary'' intermediate files permanently. If the @option{-o} option is used, the temporary files are based on the object file. If the @option{-o} option is not used, the @option{-save-temps=obj} switch behaves like @option{-save-temps}. For example: @smallexample gcc -save-temps=obj -c foo.c gcc -save-temps=obj -c bar.c -o dir/xbar.o gcc -save-temps=obj foobar.c -o dir2/yfoobar @end smallexample @noindent creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i}, @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and @file{dir2/yfoobar.o}. @item -time@r{[}=@var{file}@r{]} @opindex time Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done). Without the specification of an output file, the output looks like this: @smallexample # cc1 0.12 0.01 # as 0.00 0.01 @end smallexample The first number on each line is the ``user time'', that is time spent executing the program itself. The second number is ``system time'', time spent executing operating system routines on behalf of the program. Both numbers are in seconds. With the specification of an output file, the output is appended to the named file, and it looks like this: @smallexample 0.12 0.01 cc1 @var{options} 0.00 0.01 as @var{options} @end smallexample The ``user time'' and the ``system time'' are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options. @item -fvar-tracking @opindex fvar-tracking Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports this information). It is enabled by default when compiling with optimization (@option{-Os}, @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and the debug info format supports it. @item -fvar-tracking-assignments @opindex fvar-tracking-assignments @opindex fno-var-tracking-assignments Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug information while optimizing. Use of @option{-gdwarf-4} is recommended along with it. It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. @item -fvar-tracking-assignments-toggle @opindex fvar-tracking-assignments-toggle @opindex fno-var-tracking-assignments-toggle Toggle @option{-fvar-tracking-assignments}, in the same way that @option{-gtoggle} toggles @option{-g}. @item -print-file-name=@var{library} @opindex print-file-name Print the full absolute name of the library file @var{library} that would be used when linking---and don't do anything else. With this option, GCC does not compile or link anything; it just prints the file name. @item -print-multi-directory @opindex print-multi-directory Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in @env{GCC_EXEC_PREFIX}. @item -print-multi-lib @opindex print-multi-lib Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by @samp{;}, and each switch starts with an @samp{@@} instead of the @samp{-}, without spaces between multiple switches. This is supposed to ease shell processing. @item -print-multi-os-directory @opindex print-multi-os-directory Print the path to OS libraries for the selected multilib, relative to some @file{lib} subdirectory. If OS libraries are present in the @file{lib} subdirectory and no multilibs are used, this is usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. @item -print-multiarch @opindex print-multiarch Print the path to OS libraries for the selected multiarch, relative to some @file{lib} subdirectory. @item -print-prog-name=@var{program} @opindex print-prog-name Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. @item -print-libgcc-file-name @opindex print-libgcc-file-name Same as @option{-print-file-name=libgcc.a}. This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} but you do want to link with @file{libgcc.a}. You can do: @smallexample gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` @end smallexample @item -print-search-dirs @opindex print-search-dirs Print the name of the configured installation directory and a list of program and library directories @command{gcc} searches---and don't do anything else. This is useful when @command{gcc} prints the error message @samp{installation problem, cannot exec cpp0: No such file or directory}. To resolve this you either need to put @file{cpp0} and the other compiler components where @command{gcc} expects to find them, or you can set the environment variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. Don't forget the trailing @samp{/}. @xref{Environment Variables}. @item -print-sysroot @opindex print-sysroot Print the target sysroot directory that is used during compilation. This is the target sysroot specified either at configure time or using the @option{--sysroot} option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing. @item -print-sysroot-headers-suffix @opindex print-sysroot-headers-suffix Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffix---and don't do anything else. @item -dumpmachine @opindex dumpmachine Print the compiler's target machine (for example, @samp{i686-pc-linux-gnu})---and don't do anything else. @item -dumpversion @opindex dumpversion Print the compiler version (for example, @samp{3.0})---and don't do anything else. @item -dumpspecs @opindex dumpspecs Print the compiler's built-in specs---and don't do anything else. (This is used when GCC itself is being built.) @xref{Spec Files}. @item -fno-eliminate-unused-debug-types @opindex feliminate-unused-debug-types @opindex fno-eliminate-unused-debug-types Normally, when producing DWARF 2 output, GCC avoids producing debug symbol output for types that are nowhere used in the source file being compiled. Sometimes it is useful to have GCC emit debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit, for example if, in the debugger, you want to cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space. @end table @node Optimize Options @section Options That Control Optimization @cindex optimize options @cindex options, optimization These options control various sorts of optimizations. Without any optimization option, the compiler's goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect from the source code. Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program. The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them. Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section. Most optimizations are only enabled if an @option{-O} level is set on the command line. Otherwise they are disabled, even if individual optimization flags are specified. Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each @option{-O} level than those listed here. You can invoke GCC with @option{-Q --help=optimizers} to find out the exact set of optimizations that are enabled at each level. @xref{Overall Options}, for examples. @table @gcctabopt @item -O @itemx -O1 @opindex O @opindex O1 Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. With @option{-O}, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. @option{-O} turns on the following optimization flags: @gccoptlist{ -fauto-inc-dec @gol -fbranch-count-reg @gol -fcombine-stack-adjustments @gol -fcompare-elim @gol -fcprop-registers @gol -fdce @gol -fdefer-pop @gol -fdelayed-branch @gol -fdse @gol -fforward-propagate @gol -fguess-branch-probability @gol -fif-conversion2 @gol -fif-conversion @gol -finline-functions-called-once @gol -fipa-pure-const @gol -fipa-profile @gol -fipa-reference @gol -fmerge-constants @gol -fmove-loop-invariants @gol -fshrink-wrap @gol -fsplit-wide-types @gol -ftree-bit-ccp @gol -ftree-ccp @gol -fssa-phiopt @gol -ftree-ch @gol -ftree-copy-prop @gol -ftree-copyrename @gol -ftree-dce @gol -ftree-dominator-opts @gol -ftree-dse @gol -ftree-forwprop @gol -ftree-fre @gol -ftree-phiprop @gol -ftree-sink @gol -ftree-slsr @gol -ftree-sra @gol -ftree-pta @gol -ftree-ter @gol -funit-at-a-time} @option{-O} also turns on @option{-fomit-frame-pointer} on machines where doing so does not interfere with debugging. @item -O2 @opindex O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to @option{-O}, this option increases both compilation time and the performance of the generated code. @option{-O2} turns on all optimization flags specified by @option{-O}. It also turns on the following optimization flags: @gccoptlist{-fthread-jumps @gol -falign-functions -falign-jumps @gol -falign-loops -falign-labels @gol -fcaller-saves @gol -fcrossjumping @gol -fcse-follow-jumps -fcse-skip-blocks @gol -fdelete-null-pointer-checks @gol -fdevirtualize -fdevirtualize-speculatively @gol -fexpensive-optimizations @gol -fgcse -fgcse-lm @gol -fhoist-adjacent-loads @gol -finline-small-functions @gol -findirect-inlining @gol -fipa-cp @gol -fipa-sra @gol -fipa-icf @gol -fisolate-erroneous-paths-dereference @gol -flra-remat @gol -foptimize-sibling-calls @gol -foptimize-strlen @gol -fpartial-inlining @gol -fpeephole2 @gol -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol -frerun-cse-after-loop @gol -fsched-interblock -fsched-spec @gol -fschedule-insns -fschedule-insns2 @gol -fstrict-aliasing -fstrict-overflow @gol -ftree-builtin-call-dce @gol -ftree-switch-conversion -ftree-tail-merge @gol -ftree-pre @gol -ftree-vrp @gol -fuse-caller-save} Please note the warning under @option{-fgcse} about invoking @option{-O2} on programs that use computed gotos. @item -O3 @opindex O3 Optimize yet more. @option{-O3} turns on all optimizations specified by @option{-O2} and also turns on the @option{-finline-functions}, @option{-funswitch-loops}, @option{-fpredictive-commoning}, @option{-fgcse-after-reload}, @option{-ftree-loop-vectorize}, @option{-ftree-loop-distribute-patterns}, @option{-ftree-slp-vectorize}, @option{-fvect-cost-model}, @option{-ftree-partial-pre} and @option{-fipa-cp-clone} options. @item -O0 @opindex O0 Reduce compilation time and make debugging produce the expected results. This is the default. @item -Os @opindex Os Optimize for size. @option{-Os} enables all @option{-O2} optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size. @option{-Os} disables the following optimization flags: @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol -fprefetch-loop-arrays} @item -Ofast @opindex Ofast Disregard strict standards compliance. @option{-Ofast} enables all @option{-O3} optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on @option{-ffast-math} and the Fortran-specific @option{-fno-protect-parens} and @option{-fstack-arrays}. @item -Og @opindex Og Optimize debugging experience. @option{-Og} enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience. If you use multiple @option{-O} options, with or without level numbers, the last such option is the one that is effective. @end table Options of the form @option{-f@var{flag}} specify machine-independent flags. Most flags have both positive and negative forms; the negative form of @option{-ffoo} is @option{-fno-foo}. In the table below, only one of the forms is listed---the one you typically use. You can figure out the other form by either removing @samp{no-} or adding it. The following options control specific optimizations. They are either activated by @option{-O} options or are related to ones that are. You can use the following flags in the rare cases when ``fine-tuning'' of optimizations to be performed is desired. @table @gcctabopt @item -fno-defer-pop @opindex fno-defer-pop Always pop the arguments to each function call as soon as that function returns. For machines that must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fforward-propagate @opindex fforward-propagate Perform a forward propagation pass on RTL@. The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and the second is scheduled after loop unrolling. This option is enabled by default at optimization levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -ffp-contract=@var{style} @opindex ffp-contract @option{-ffp-contract=off} disables floating-point expression contraction. @option{-ffp-contract=fast} enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. @option{-ffp-contract=on} enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to @option{-ffp-contract=off}. The default is @option{-ffp-contract=fast}. @item -fomit-frame-pointer @opindex fomit-frame-pointer Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. @strong{It also makes debugging impossible on some machines.} On some machines, such as the VAX, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro @code{FRAME_POINTER_REQUIRED} controls whether a target machine supports this flag. @xref{Registers,,Register Usage, gccint, GNU Compiler Collection (GCC) Internals}. Starting with GCC version 4.6, the default setting (when not optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets has been changed to @option{-fomit-frame-pointer}. The default can be reverted to @option{-fno-omit-frame-pointer} by configuring GCC with the @option{--enable-frame-pointer} configure option. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -foptimize-sibling-calls @opindex foptimize-sibling-calls Optimize sibling and tail recursive calls. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -foptimize-strlen @opindex foptimize-strlen Optimize various standard C string functions (e.g. @code{strlen}, @code{strchr} or @code{strcpy}) and their @code{_FORTIFY_SOURCE} counterparts into faster alternatives. Enabled at levels @option{-O2}, @option{-O3}. @item -fno-inline @opindex fno-inline Do not expand any functions inline apart from those marked with the @code{always_inline} attribute. This is the default when not optimizing. Single functions can be exempted from inlining by marking them with the @code{noinline} attribute. @item -finline-small-functions @opindex finline-small-functions Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline. Enabled at level @option{-O2}. @item -findirect-inlining @opindex findirect-inlining Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the @option{-finline-functions} or @option{-finline-small-functions} options. Enabled at level @option{-O2}. @item -finline-functions @opindex finline-functions Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way. If all calls to a given function are integrated, and the function is declared @code{static}, then the function is normally not output as assembler code in its own right. Enabled at level @option{-O3}. @item -finline-functions-called-once @opindex finline-functions-called-once Consider all @code{static} functions called once for inlining into their caller even if they are not marked @code{inline}. If a call to a given function is integrated, then the function is not output as assembler code in its own right. Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}. @item -fearly-inlining @opindex fearly-inlining Inline functions marked by @code{always_inline} and functions whose body seems smaller than the function call overhead early before doing @option{-fprofile-generate} instrumentation and real inlining pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions. Enabled by default. @item -fipa-sra @opindex fipa-sra Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value. Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. @item -finline-limit=@var{n} @opindex finline-limit By default, GCC limits the size of functions that can be inlined. This flag allows coarse control of this limit. @var{n} is the size of functions that can be inlined in number of pseudo instructions. Inlining is actually controlled by a number of parameters, which may be specified individually by using @option{--param @var{name}=@var{value}}. The @option{-finline-limit=@var{n}} option sets some of these parameters as follows: @table @gcctabopt @item max-inline-insns-single is set to @var{n}/2. @item max-inline-insns-auto is set to @var{n}/2. @end table See below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters. @emph{Note:} there may be no value to @option{-finline-limit} that results in default behavior. @emph{Note:} pseudo instruction represents, in this particular context, an abstract measurement of function's size. In no way does it represent a count of assembly instructions and as such its exact meaning might change from one release to an another. @item -fno-keep-inline-dllexport @opindex -fno-keep-inline-dllexport This is a more fine-grained version of @option{-fkeep-inline-functions}, which applies only to functions that are declared using the @code{dllexport} attribute or declspec (@xref{Function Attributes,,Declaring Attributes of Functions}.) @item -fkeep-inline-functions @opindex fkeep-inline-functions In C, emit @code{static} functions that are declared @code{inline} into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the @code{extern inline} extension in GNU C90@. In C++, emit any and all inline functions into the object file. @item -fkeep-static-consts @opindex fkeep-static-consts Emit variables declared @code{static const} when optimization isn't turned on, even if the variables aren't referenced. GCC enables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the @option{-fno-keep-static-consts} option. @item -fmerge-constants @opindex fmerge-constants Attempt to merge identical constants (string constants and floating-point constants) across compilation units. This option is the default for optimized compilation if the assembler and linker support it. Use @option{-fno-merge-constants} to inhibit this behavior. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fmerge-all-constants @opindex fmerge-all-constants Attempt to merge identical constants and identical variables. This option implies @option{-fmerge-constants}. In addition to @option{-fmerge-constants} this considers e.g.@: even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or C++ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in non-conforming behavior. @item -fmodulo-sched @opindex fmodulo-sched Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations. @item -fmodulo-sched-allow-regmoves @opindex fmodulo-sched-allow-regmoves Perform more aggressive SMS-based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges are deleted, which triggers the generation of reg-moves based on the life-range analysis. This option is effective only with @option{-fmodulo-sched} enabled. @item -fno-branch-count-reg @opindex fno-branch-count-reg Do not use ``decrement and branch'' instructions on a count register, but instead generate a sequence of instructions that decrement a register, compare it against zero, then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390. Enabled by default at @option{-O1} and higher. The default is @option{-fbranch-count-reg}. @item -fno-function-cse @opindex fno-function-cse Do not put function addresses in registers; make each instruction that calls a constant function contain the function's address explicitly. This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used. The default is @option{-ffunction-cse} @item -fno-zero-initialized-in-bss @opindex fno-zero-initialized-in-bss If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS@. This can save space in the resulting code. This option turns off this behavior because some programs explicitly rely on variables going to the data section---e.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that. The default is @option{-fzero-initialized-in-bss}. @item -fthread-jumps @opindex fthread-jumps Perform optimizations that check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fsplit-wide-types @opindex fsplit-wide-types When using a type that occupies multiple registers, such as @code{long long} on a 32-bit system, split the registers apart and allocate them independently. This normally generates better code for those types, but may make debugging more difficult. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fcse-follow-jumps @opindex fcse-follow-jumps In common subexpression elimination (CSE), scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an @code{if} statement with an @code{else} clause, CSE follows the jump when the condition tested is false. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fcse-skip-blocks @opindex fcse-skip-blocks This is similar to @option{-fcse-follow-jumps}, but causes CSE to follow jumps that conditionally skip over blocks. When CSE encounters a simple @code{if} statement with no else clause, @option{-fcse-skip-blocks} causes CSE to follow the jump around the body of the @code{if}. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -frerun-cse-after-loop @opindex frerun-cse-after-loop Re-run common subexpression elimination after loop optimizations are performed. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fgcse @opindex fgcse Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. @emph{Note:} When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding @option{-fno-gcse} to the command line. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fgcse-lm @opindex fgcse-lm When @option{-fgcse-lm} is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. Enabled by default when @option{-fgcse} is enabled. @item -fgcse-sm @opindex fgcse-sm When @option{-fgcse-sm} is enabled, a store motion pass is run after global common subexpression elimination. This pass attempts to move stores out of loops. When used in conjunction with @option{-fgcse-lm}, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop. Not enabled at any optimization level. @item -fgcse-las @opindex fgcse-las When @option{-fgcse-las} is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full redundancies). Not enabled at any optimization level. @item -fgcse-after-reload @opindex fgcse-after-reload When @option{-fgcse-after-reload} is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to clean up redundant spilling. @item -faggressive-loop-optimizations @opindex faggressive-loop-optimizations This option tells the loop optimizer to use language constraints to derive bounds for the number of iterations of a loop. This assumes that loop code does not invoke undefined behavior by for example causing signed integer overflows or out-of-bound array accesses. The bounds for the number of iterations of a loop are used to guide loop unrolling and peeling and loop exit test optimizations. This option is enabled by default. @item -funsafe-loop-optimizations @opindex funsafe-loop-optimizations This option tells the loop optimizer to assume that loop indices do not overflow, and that loops with nontrivial exit condition are not infinite. This enables a wider range of loop optimizations even if the loop optimizer itself cannot prove that these assumptions are valid. If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you if it finds this kind of loop. @item -fcrossjumping @opindex fcrossjumping Perform cross-jumping transformation. This transformation unifies equivalent code and saves code size. The resulting code may or may not perform better than without cross-jumping. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fauto-inc-dec @opindex fauto-inc-dec Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at @option{-O} and higher on architectures that support this. @item -fdce @opindex fdce Perform dead code elimination (DCE) on RTL@. Enabled by default at @option{-O} and higher. @item -fdse @opindex fdse Perform dead store elimination (DSE) on RTL@. Enabled by default at @option{-O} and higher. @item -fif-conversion @opindex fif-conversion Attempt to transform conditional jumps into branch-less equivalents. This includes use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by @code{if-conversion2}. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fif-conversion2 @opindex fif-conversion2 Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fdeclone-ctor-dtor @opindex fdeclone-ctor-dtor The C++ ABI requires multiple entry points for constructors and destructors: one for a base subobject, one for a complete object, and one for a virtual destructor that calls operator delete afterwards. For a hierarchy with virtual bases, the base and complete variants are clones, which means two copies of the function. With this option, the base and complete variants are changed to be thunks that call a common implementation. Enabled by @option{-Os}. @item -fdelete-null-pointer-checks @opindex fdelete-null-pointer-checks Assume that programs cannot safely dereference null pointers, and that no code or data element resides there. This enables simple constant folding optimizations at all optimization levels. In addition, other optimization passes in GCC use this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that if a pointer is checked after it has already been dereferenced, it cannot be null. Note however that in some environments this assumption is not true. Use @option{-fno-delete-null-pointer-checks} to disable this optimization for programs that depend on that behavior. Some targets, especially embedded ones, disable this option at all levels. Otherwise it is enabled at all levels: @option{-O0}, @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information are enabled independently at different optimization levels. @item -fdevirtualize @opindex fdevirtualize Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining (@code{-findirect-inlining}) and interprocedural constant propagation (@option{-fipa-cp}). Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fdevirtualize-speculatively @opindex fdevirtualize-speculatively Attempt to convert calls to virtual functions to speculative direct calls. Based on the analysis of the type inheritance graph, determine for a given call the set of likely targets. If the set is small, preferably of size 1, change the call into an conditional deciding on direct and indirect call. The speculative calls enable more optimizations, such as inlining. When they seem useless after further optimization, they are converted back into original form. @item -fexpensive-optimizations @opindex fexpensive-optimizations Perform a number of minor optimizations that are relatively expensive. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -free @opindex free Attempt to remove redundant extension instructions. This is especially helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit registers after writing to their lower 32-bit half. Enabled for Alpha, AArch64 and x86 at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -flive-range-shrinkage @opindex flive-range-shrinkage Attempt to decrease register pressure through register live range shrinkage. This is helpful for fast processors with small or moderate size register sets. @item -fira-algorithm=@var{algorithm} Use the specified coloring algorithm for the integrated register allocator. The @var{algorithm} argument can be @samp{priority}, which specifies Chow's priority coloring, or @samp{CB}, which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code. @item -fira-region=@var{region} Use specified regions for the integrated register allocator. The @var{region} argument should be one of the following: @table @samp @item all Use all loops as register allocation regions. This can give the best results for machines with a small and/or irregular register set. @item mixed Use all loops except for loops with small register pressure as the regions. This value usually gives the best results in most cases and for most architectures, and is enabled by default when compiling with optimization for speed (@option{-O}, @option{-O2}, @dots{}). @item one Use all functions as a single region. This typically results in the smallest code size, and is enabled by default for @option{-Os} or @option{-O0}. @end table @item -fira-hoist-pressure @opindex fira-hoist-pressure Use IRA to evaluate register pressure in the code hoisting pass for decisions to hoist expressions. This option usually results in smaller code, but it can slow the compiler down. This option is enabled at level @option{-Os} for all targets. @item -fira-loop-pressure @opindex fira-loop-pressure Use IRA to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register files (>= 32 registers), but it can slow the compiler down. This option is enabled at level @option{-O3} for some targets. @item -fno-ira-share-save-slots @opindex fno-ira-share-save-slots Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are larger. @item -fno-ira-share-spill-slots @opindex fno-ira-share-spill-slots Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are larger. @item -fira-verbose=@var{n} @opindex fira-verbose Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value @var{n} is greater or equal to 10, the dump output is sent to stderr using the same format as @var{n} minus 10. @item -flra-remat @opindex fcaller-saves Enable CFG-sensitive rematerialization in LRA. Instead of loading values of spilled pseudos, LRA tries to rematerialize (recalculate) values if it is profitable. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fdelayed-branch @opindex fdelayed-branch If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fschedule-insns @opindex fschedule-insns If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required. Enabled at levels @option{-O2}, @option{-O3}. @item -fschedule-insns2 @opindex fschedule-insns2 Similar to @option{-fschedule-insns}, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fno-sched-interblock @opindex fno-sched-interblock Don't schedule instructions across basic blocks. This is normally enabled by default when scheduling before register allocation, i.e.@: with @option{-fschedule-insns} or at @option{-O2} or higher. @item -fno-sched-spec @opindex fno-sched-spec Don't allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e.@: with @option{-fschedule-insns} or at @option{-O2} or higher. @item -fsched-pressure @opindex fsched-pressure Enable register pressure sensitive insn scheduling before register allocation. This only makes sense when scheduling before register allocation is enabled, i.e.@: with @option{-fschedule-insns} or at @option{-O2} or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and subsequent spills in register allocation. @item -fsched-spec-load @opindex fsched-spec-load Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e.@: with @option{-fschedule-insns} or at @option{-O2} or higher. @item -fsched-spec-load-dangerous @opindex fsched-spec-load-dangerous Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e.@: with @option{-fschedule-insns} or at @option{-O2} or higher. @item -fsched-stalled-insns @itemx -fsched-stalled-insns=@var{n} @opindex fsched-stalled-insns Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list during the second scheduling pass. @option{-fno-sched-stalled-insns} means that no insns are moved prematurely, @option{-fsched-stalled-insns=0} means there is no limit on how many queued insns can be moved prematurely. @option{-fsched-stalled-insns} without a value is equivalent to @option{-fsched-stalled-insns=1}. @item -fsched-stalled-insns-dep @itemx -fsched-stalled-insns-dep=@var{n} @opindex fsched-stalled-insns-dep Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal from the queue of stalled insns. This has an effect only during the second scheduling pass, and only if @option{-fsched-stalled-insns} is used. @option{-fno-sched-stalled-insns-dep} is equivalent to @option{-fsched-stalled-insns-dep=0}. @option{-fsched-stalled-insns-dep} without a value is equivalent to @option{-fsched-stalled-insns-dep=1}. @item -fsched2-use-superblocks @opindex fsched2-use-superblocks When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This option is experimental, as not all machine descriptions used by GCC model the CPU closely enough to avoid unreliable results from the algorithm. This only makes sense when scheduling after register allocation, i.e.@: with @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-group-heuristic @opindex fsched-group-heuristic Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-critical-path-heuristic @opindex fsched-critical-path-heuristic Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-spec-insn-heuristic @opindex fsched-spec-insn-heuristic Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-rank-heuristic @opindex fsched-rank-heuristic Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-last-insn-heuristic @opindex fsched-last-insn-heuristic Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -fsched-dep-count-heuristic @opindex fsched-dep-count-heuristic Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or at @option{-O2} or higher. @item -freschedule-modulo-scheduled-loops @opindex freschedule-modulo-scheduled-loops Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option to control that behavior. @item -fselective-scheduling @opindex fselective-scheduling Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass. @item -fselective-scheduling2 @opindex fselective-scheduling2 Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass. @item -fsel-sched-pipelining @opindex fsel-sched-pipelining Enable software pipelining of innermost loops during selective scheduling. This option has no effect unless one of @option{-fselective-scheduling} or @option{-fselective-scheduling2} is turned on. @item -fsel-sched-pipelining-outer-loops @opindex fsel-sched-pipelining-outer-loops When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect unless @option{-fsel-sched-pipelining} is turned on. @item -fsemantic-interposition @opindex fsemantic-interposition Some object formats, like ELF, allow interposing of symbols by dynamic linker. This means that for symbols exported from the DSO compiler can not perform inter-procedural propagation, inlining and other optimizations in anticipation that the function or variable in question may change. While this feature is useful, for example, to rewrite memory allocation functions by a debugging implementation, it is expensive in the terms of code quality. With @option{-fno-semantic-inteposition} compiler assumest that if interposition happens for functions the overwritting function will have precisely same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag has no effect for functions explicitly declared inline, where interposition changing semantic is never allowed and for symbols explicitly declared weak. @item -fshrink-wrap @opindex fshrink-wrap Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at @option{-O} and higher. @item -fcaller-saves @opindex fcaller-saves Enable allocation of values to registers that are clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code. This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fcombine-stack-adjustments @opindex fcombine-stack-adjustments Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them. Enabled by default at @option{-O1} and higher. @item -fuse-caller-save Use caller save registers for allocation if those registers are not used by any called function. In that case it is not necessary to save and restore them around calls. This is only possible if called functions are part of same compilation unit as current function and they are compiled before it. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fconserve-stack @opindex fconserve-stack Attempt to minimize stack usage. The compiler attempts to use less stack space, even if that makes the program slower. This option implies setting the @option{large-stack-frame} parameter to 100 and the @option{large-stack-frame-growth} parameter to 400. @item -ftree-reassoc @opindex ftree-reassoc Perform reassociation on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-pre @opindex ftree-pre Perform partial redundancy elimination (PRE) on trees. This flag is enabled by default at @option{-O2} and @option{-O3}. @item -ftree-partial-pre @opindex ftree-partial-pre Make partial redundancy elimination (PRE) more aggressive. This flag is enabled by default at @option{-O3}. @item -ftree-forwprop @opindex ftree-forwprop Perform forward propagation on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-fre @opindex ftree-fre Perform full redundancy elimination (FRE) on trees. The difference between FRE and PRE is that FRE only considers expressions that are computed on all paths leading to the redundant computation. This analysis is faster than PRE, though it exposes fewer redundancies. This flag is enabled by default at @option{-O} and higher. @item -ftree-phiprop @opindex ftree-phiprop Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at @option{-O} and higher. @item -fhoist-adjacent-loads @opindex hoist-adjacent-loads Speculatively hoist loads from both branches of an if-then-else if the loads are from adjacent locations in the same structure and the target architecture has a conditional move instruction. This flag is enabled by default at @option{-O2} and higher. @item -ftree-copy-prop @opindex ftree-copy-prop Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at @option{-O} and higher. @item -fipa-pure-const @opindex fipa-pure-const Discover which functions are pure or constant. Enabled by default at @option{-O} and higher. @item -fipa-reference @opindex fipa-reference Discover which static variables do not escape the compilation unit. Enabled by default at @option{-O} and higher. @item -fipa-pta @opindex fipa-pta Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. It is not enabled by default at any optimization level. @item -fipa-profile @opindex fipa-profile Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as @code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at @option{-O} and higher. @item -fipa-cp @opindex fipa-cp Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. @item -fipa-cp-clone @opindex fipa-cp-clone Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation performs function cloning when externally visible function can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see @option{--param ipcp-unit-growth=@var{value}}). This flag is enabled by default at @option{-O3}. @item -fipa-icf @opindex fipa-icf Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a different name. The optimization works more effectively with link time optimization enabled. Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF works on different levels and thus the optimizations are not same - there are equivalences that are found only by GCC and equivalences found only by Gold. This flag is enabled by default at @option{-O2} and @option{-Os}. @item -fisolate-erroneous-paths-dereference Detect paths which trigger erroneous or undefined behaviour due to dereferencing a NULL pointer. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behaviour into a trap. @item -fisolate-erroneous-paths-attribute Detect paths which trigger erroneous or undefined behaviour due a NULL value being used in a way which is forbidden by a @code{returns_nonnull} or @code{nonnull} attribute. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behaviour into a trap. This is not currently enabled, but may be enabled by @code{-O2} in the future. @item -ftree-sink @opindex ftree-sink Perform forward store motion on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-bit-ccp @opindex ftree-bit-ccp Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled. @item -ftree-ccp @opindex ftree-ccp Perform sparse conditional constant propagation (CCP) on trees. This pass only operates on local scalar variables and is enabled by default at @option{-O} and higher. @item -fssa-phiopt @opindex fssa-phiopt Perform pattern matching on SSA PHI nodes to optimize conditional code. This pass is enabled by default at @option{-O} and higher. @item -ftree-switch-conversion Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at @option{-O2} and higher. @item -ftree-tail-merge Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at @option{-O2} and higher. The compilation time in this pass can be limited using @option{max-tail-merge-comparisons} parameter and @option{max-tail-merge-iterations} parameter. @item -ftree-dce @opindex ftree-dce Perform dead code elimination (DCE) on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-builtin-call-dce @opindex ftree-builtin-call-dce Perform conditional dead code elimination (DCE) for calls to built-in functions that may set @code{errno} but are otherwise side-effect free. This flag is enabled by default at @option{-O2} and higher if @option{-Os} is not also specified. @item -ftree-dominator-opts @opindex ftree-dominator-opts Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at @option{-O} and higher. @item -ftree-dse @opindex ftree-dse Perform dead store elimination (DSE) on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled by default at @option{-O} and higher. @item -ftree-ch @opindex ftree-ch Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at @option{-O} and higher. It is not enabled for @option{-Os}, since it usually increases code size. @item -ftree-loop-optimize @opindex ftree-loop-optimize Perform loop optimizations on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-loop-linear @opindex ftree-loop-linear Perform loop interchange transformations on tree. Same as @option{-floop-interchange}. To use this code transformation, GCC has to be configured with @option{--with-ppl} and @option{--with-cloog} to enable the Graphite loop transformation infrastructure. @item -floop-interchange @opindex floop-interchange Perform loop interchange transformations on loops. Interchanging two nested loops switches the inner and outer loops. For example, given a loop like: @smallexample DO J = 1, M DO I = 1, N A(J, I) = A(J, I) * C ENDDO ENDDO @end smallexample loop interchange transforms the loop as if it were written: @smallexample DO I = 1, N DO J = 1, M A(J, I) = A(J, I) * C ENDDO ENDDO @end smallexample which can be beneficial when @code{N} is larger than the caches, because in Fortran, the elements of an array are stored in memory contiguously by column, and the original loop iterates over rows, potentially creating at each access a cache miss. This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with @option{--with-ppl} and @option{--with-cloog} to enable the Graphite loop transformation infrastructure. @item -floop-strip-mine @opindex floop-strip-mine Perform loop strip mining transformations on loops. Strip mining splits a loop into two nested loops. The outer loop has strides equal to the strip size and the inner loop has strides of the original loop within a strip. The strip length can be changed using the @option{loop-block-tile-size} parameter. For example, given a loop like: @smallexample DO I = 1, N A(I) = A(I) + C ENDDO @end smallexample loop strip mining transforms the loop as if it were written: @smallexample DO II = 1, N, 51 DO I = II, min (II + 50, N) A(I) = A(I) + C ENDDO ENDDO @end smallexample This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with @option{--with-ppl} and @option{--with-cloog} to enable the Graphite loop transformation infrastructure. @item -floop-block @opindex floop-block Perform loop blocking transformations on loops. Blocking strip mines each loop in the loop nest such that the memory accesses of the element loops fit inside caches. The strip length can be changed using the @option{loop-block-tile-size} parameter. For example, given a loop like: @smallexample DO I = 1, N DO J = 1, M A(J, I) = B(I) + C(J) ENDDO ENDDO @end smallexample loop blocking transforms the loop as if it were written: @smallexample DO II = 1, N, 51 DO JJ = 1, M, 51 DO I = II, min (II + 50, N) DO J = JJ, min (JJ + 50, M) A(J, I) = B(I) + C(J) ENDDO ENDDO ENDDO ENDDO @end smallexample which can be beneficial when @code{M} is larger than the caches, because the innermost loop iterates over a smaller amount of data which can be kept in the caches. This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with @option{--with-ppl} and @option{--with-cloog} to enable the Graphite loop transformation infrastructure. @item -fgraphite-identity @opindex fgraphite-identity Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using @option{-fgraphite-identity} we can check the costs or benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations are also performed by the code generator CLooG, like index splitting and dead code elimination in loops. @item -floop-nest-optimize @opindex floop-nest-optimize Enable the ISL based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms. It calculates a loop structure optimized for data-locality and parallelism. This option is experimental. @item -floop-parallelize-all @opindex floop-parallelize-all Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops. @item -fcheck-data-deps @opindex fcheck-data-deps Compare the results of several data dependence analyzers. This option is used for debugging the data dependence analyzers. @item -ftree-loop-if-convert Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled. @item -ftree-loop-if-convert-stores Attempt to also if-convert conditional jumps containing memory writes. This transformation can be unsafe for multi-threaded programs as it transforms conditional memory writes into unconditional memory writes. For example, @smallexample for (i = 0; i < N; i++) if (cond) A[i] = expr; @end smallexample is transformed to @smallexample for (i = 0; i < N; i++) A[i] = cond ? expr : A[i]; @end smallexample potentially producing data races. @item -ftree-loop-distribution Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop @smallexample DO I = 1, N A(I) = B(I) + C D(I) = E(I) * F ENDDO @end smallexample is transformed to @smallexample DO I = 1, N A(I) = B(I) + C ENDDO DO I = 1, N D(I) = E(I) * F ENDDO @end smallexample @item -ftree-loop-distribute-patterns Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at @option{-O3}. This pass distributes the initialization loops and generates a call to memset zero. For example, the loop @smallexample DO I = 1, N A(I) = 0 B(I) = A(I) + I ENDDO @end smallexample is transformed to @smallexample DO I = 1, N A(I) = 0 ENDDO DO I = 1, N B(I) = A(I) + I ENDDO @end smallexample and the initialization loop is transformed into a call to memset zero. @item -ftree-loop-im @opindex ftree-loop-im Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTL level (function calls, operations that expand to nontrivial sequences of insns). With @option{-funswitch-loops} it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion. @item -ftree-loop-ivcanon @opindex ftree-loop-ivcanon Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling. @item -fivopts @opindex fivopts Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. @item -ftree-parallelize-loops=n @opindex ftree-parallelize-loops Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g.@: by memory bandwidth. This option implies @option{-pthread}, and thus is only supported on targets that have support for @option{-pthread}. @item -ftree-pta @opindex ftree-pta Perform function-local points-to analysis on trees. This flag is enabled by default at @option{-O} and higher. @item -ftree-sra @opindex ftree-sra Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at @option{-O} and higher. @item -ftree-copyrename @opindex ftree-copyrename Perform copy renaming on trees. This pass attempts to rename compiler temporaries to other variables at copy locations, usually resulting in variable names which more closely resemble the original variables. This flag is enabled by default at @option{-O} and higher. @item -ftree-coalesce-inlined-vars @opindex ftree-coalesce-inlined-vars Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to combine small user-defined variables too, but only if they were inlined from other functions. It is a more limited form of @option{-ftree-coalesce-vars}. This may harm debug information of such inlined variables, but it will keep variables of the inlined-into function apart from each other, such that they are more likely to contain the expected values in a debugging session. This was the default in GCC versions older than 4.7. @item -ftree-coalesce-vars @opindex ftree-coalesce-vars Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to combine small user-defined variables too, instead of just compiler temporaries. This may severely limit the ability to debug an optimized program compiled with @option{-fno-var-tracking-assignments}. In the negated form, this flag prevents SSA coalescing of user variables, including inlined ones. This option is enabled by default. @item -ftree-ter @opindex ftree-ter Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation. This is enabled by default at @option{-O} and higher. @item -ftree-slsr @opindex ftree-slsr Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is enabled by default at @option{-O} and higher. @item -ftree-vectorize @opindex ftree-vectorize Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize} and @option{-ftree-slp-vectorize} if not explicitly specified. @item -ftree-loop-vectorize @opindex ftree-loop-vectorize Perform loop vectorization on trees. This flag is enabled by default at @option{-O3} and when @option{-ftree-vectorize} is enabled. @item -ftree-slp-vectorize @opindex ftree-slp-vectorize Perform basic block vectorization on trees. This flag is enabled by default at @option{-O3} and when @option{-ftree-vectorize} is enabled. @item -fvect-cost-model=@var{model} @opindex fvect-cost-model Alter the cost model used for vectorization. The @var{model} argument should be one of @code{unlimited}, @code{dynamic} or @code{cheap}. With the @code{unlimited} model the vectorized code-path is assumed to be profitable while with the @code{dynamic} model a runtime check will guard the vectorized code-path to enable it only for iteration counts that will likely execute faster than when executing the original scalar loop. The @code{cheap} model will disable vectorization of loops where doing so would be cost prohibitive for example due to required runtime checks for data dependence or alignment but otherwise is equal to the @code{dynamic} model. The default cost model depends on other optimization flags and is either @code{dynamic} or @code{cheap}. @item -fsimd-cost-model=@var{model} @opindex fsimd-cost-model Alter the cost model used for vectorization of loops marked with the OpenMP or Cilk Plus simd directive. The @var{model} argument should be one of @code{unlimited}, @code{dynamic}, @code{cheap}. All values of @var{model} have the same meaning as described in @option{-fvect-cost-model} and by default a cost model defined with @option{-fvect-cost-model} is used. @item -ftree-vrp @opindex ftree-vrp Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at @option{-O2} and higher. Null pointer check elimination is only done if @option{-fdelete-null-pointer-checks} is enabled. @item -ftracer @opindex ftracer Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. @item -funroll-loops @opindex funroll-loops Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. @option{-funroll-loops} implies @option{-frerun-cse-after-loop}. This option makes code larger, and may or may not make it run faster. @item -funroll-all-loops @opindex funroll-all-loops Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. @option{-funroll-all-loops} implies the same options as @option{-funroll-loops}, @item -fsplit-ivs-in-unroller @opindex fsplit-ivs-in-unroller Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving efficiency of the scheduling passes. A combination of @option{-fweb} and CSE is often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSE pass. This optimization is enabled by default. @item -fvariable-expansion-in-unroller @opindex fvariable-expansion-in-unroller With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code. @item -fpartial-inlining @opindex fpartial-inlining Inline parts of functions. This option has any effect only when inlining itself is turned on by the @option{-finline-functions} or @option{-finline-small-functions} options. Enabled at level @option{-O2}. @item -fpredictive-commoning @opindex fpredictive-commoning Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops. This option is enabled at level @option{-O3}. @item -fprefetch-loop-arrays @opindex fprefetch-loop-arrays If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. Disabled at level @option{-Os}. @item -fno-peephole @itemx -fno-peephole2 @opindex fno-peephole @opindex fno-peephole2 Disable any machine-specific peephole optimizations. The difference between @option{-fno-peephole} and @option{-fno-peephole2} is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. @option{-fpeephole} is enabled by default. @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fno-guess-branch-probability @opindex fno-guess-branch-probability Do not guess branch probabilities using heuristics. GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback (@option{-fprofile-arcs}). These heuristics are based on the control flow graph. If some branch probabilities are specified by @samp{__builtin_expect}, then the heuristics are used to guess branch probabilities for the rest of the control flow graph, taking the @samp{__builtin_expect} info into account. The interactions between the heuristics and @samp{__builtin_expect} can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of @samp{__builtin_expect} are easier to understand. The default is @option{-fguess-branch-probability} at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -freorder-blocks @opindex freorder-blocks Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. Enabled at levels @option{-O2}, @option{-O3}. @item -freorder-blocks-and-partition @opindex freorder-blocks-and-partition In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and .o files, to improve paging and cache locality performance. This optimization is automatically turned off in the presence of exception handling, for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections. Enabled for x86 at levels @option{-O2}, @option{-O3}. @item -freorder-functions @opindex freorder-functions Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections @code{.text.hot} for most frequently executed functions and @code{.text.unlikely} for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. Also profile feedback must be available to make this option effective. See @option{-fprofile-arcs} for details. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fstrict-aliasing @opindex fstrict-aliasing Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an @code{unsigned int} can alias an @code{int}, but not a @code{void*} or a @code{double}. A character type may alias any other type. @anchor{Type-punning}Pay special attention to code like this: @smallexample union a_union @{ int i; double d; @}; int f() @{ union a_union t; t.d = 3.0; return t.i; @} @end smallexample The practice of reading from a different union member than the one most recently written to (called ``type-punning'') is common. Even with @option{-fstrict-aliasing}, type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. @xref{Structures unions enumerations and bit-fields implementation}. However, this code might not: @smallexample int f() @{ union a_union t; int* ip; t.d = 3.0; ip = &t.i; return *ip; @} @end smallexample Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.: @smallexample int f() @{ double d = 3.0; return ((union a_union *) &d)->i; @} @end smallexample The @option{-fstrict-aliasing} option is enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fstrict-overflow @opindex fstrict-overflow Allow the compiler to assume strict signed overflow rules, depending on the language being compiled. For C (and C++) this means that overflow when doing arithmetic with signed numbers is undefined, which means that the compiler may assume that it does not happen. This permits various optimizations. For example, the compiler assumes that an expression like @code{i + 10 > i} is always true for signed @code{i}. This assumption is only valid if signed overflow is undefined, as the expression is false if @code{i + 10} overflows when using twos complement arithmetic. When this option is in effect any attempt to determine whether an operation on signed numbers overflows must be written carefully to not actually involve overflow. This option also allows the compiler to assume strict pointer semantics: given a pointer to an object, if adding an offset to that pointer does not produce a pointer to the same object, the addition is undefined. This permits the compiler to conclude that @code{p + u > p} is always true for a pointer @code{p} and unsigned integer @code{u}. This assumption is only valid because pointer wraparound is undefined, as the expression is false if @code{p + u} overflows using twos complement arithmetic. See also the @option{-fwrapv} option. Using @option{-fwrapv} means that integer signed overflow is fully defined: it wraps. When @option{-fwrapv} is used, there is no difference between @option{-fstrict-overflow} and @option{-fno-strict-overflow} for integers. With @option{-fwrapv} certain types of overflow are permitted. For example, if the compiler gets an overflow when doing arithmetic on constants, the overflowed value can still be used with @option{-fwrapv}, but not otherwise. The @option{-fstrict-overflow} option is enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -falign-functions @itemx -falign-functions=@var{n} @opindex falign-functions Align the start of functions to the next power-of-two greater than @var{n}, skipping up to @var{n} bytes. For instance, @option{-falign-functions=32} aligns functions to the next 32-byte boundary, but @option{-falign-functions=24} aligns to the next 32-byte boundary only if this can be done by skipping 23 bytes or less. @option{-fno-align-functions} and @option{-falign-functions=1} are equivalent and mean that functions are not aligned. Some assemblers only support this flag when @var{n} is a power of two; in that case, it is rounded up. If @var{n} is not specified or is zero, use a machine-dependent default. Enabled at levels @option{-O2}, @option{-O3}. @item -falign-labels @itemx -falign-labels=@var{n} @opindex falign-labels Align all branch targets to a power-of-two boundary, skipping up to @var{n} bytes like @option{-falign-functions}. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code. @option{-fno-align-labels} and @option{-falign-labels=1} are equivalent and mean that labels are not aligned. If @option{-falign-loops} or @option{-falign-jumps} are applicable and are greater than this value, then their values are used instead. If @var{n} is not specified or is zero, use a machine-dependent default which is very likely to be @samp{1}, meaning no alignment. Enabled at levels @option{-O2}, @option{-O3}. @item -falign-loops @itemx -falign-loops=@var{n} @opindex falign-loops Align loops to a power-of-two boundary, skipping up to @var{n} bytes like @option{-falign-functions}. If the loops are executed many times, this makes up for any execution of the dummy operations. @option{-fno-align-loops} and @option{-falign-loops=1} are equivalent and mean that loops are not aligned. If @var{n} is not specified or is zero, use a machine-dependent default. Enabled at levels @option{-O2}, @option{-O3}. @item -falign-jumps @itemx -falign-jumps=@var{n} @opindex falign-jumps Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to @var{n} bytes like @option{-falign-functions}. In this case, no dummy operations need be executed. @option{-fno-align-jumps} and @option{-falign-jumps=1} are equivalent and mean that loops are not aligned. If @var{n} is not specified or is zero, use a machine-dependent default. Enabled at levels @option{-O2}, @option{-O3}. @item -funit-at-a-time @opindex funit-at-a-time This option is left for compatibility reasons. @option{-funit-at-a-time} has no effect, while @option{-fno-unit-at-a-time} implies @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. Enabled by default. @item -fno-toplevel-reorder @opindex fno-toplevel-reorder Do not reorder top-level functions, variables, and @code{asm} statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables are not removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes when possible. Enabled at level @option{-O0}. When disabled explicitly, it also implies @option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some targets. @item -fweb @opindex fweb Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables no longer stay in a ``home register''. Enabled by default with @option{-funroll-loops}. @item -fwhole-program @opindex fwhole-program Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of @code{main} and those merged by attribute @code{externally_visible} become static functions and in effect are optimized more aggressively by interprocedural optimizers. This option should not be used in combination with @code{-flto}. Instead relying on a linker plugin should provide safer and more precise information. @item -flto[=@var{n}] @opindex flto This option runs the standard link-time optimizer. When invoked with source code, it generates GIMPLE (one of GCC's internal representations) and writes it to special ELF sections in the object file. When the object files are linked together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit. To use the link-time optimizer, @option{-flto} and optimization options should be specified at compile time and during the final link. For example: @smallexample gcc -c -O2 -flto foo.c gcc -c -O2 -flto bar.c gcc -o myprog -flto -O2 foo.o bar.o @end smallexample The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside @file{foo.o} and @file{bar.o}. The final invocation reads the GIMPLE bytecode from @file{foo.o} and @file{bar.o}, merges the two files into a single internal image, and compiles the result as usual. Since both @file{foo.o} and @file{bar.o} are merged into a single image, this causes all the interprocedural analyses and optimizations in GCC to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in @file{bar.o} into functions in @file{foo.o} and vice-versa. Another (simpler) way to enable link-time optimization is: @smallexample gcc -o myprog -flto -O2 foo.c bar.c @end smallexample The above generates bytecode for @file{foo.c} and @file{bar.c}, merges them together into a single GIMPLE representation and optimizes them as usual to produce @file{myprog}. The only important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link-step. GCC then automatically performs link-time optimization if any of the objects involved were compiled with the @option{-flto}. You generally should specify the optimization options to be used for link-time optimization though GCC will try to be clever at guessing an optimization level to use from the options used at compile-time if you fail to specify one at link-time. You can always override the automatic decision to do link-time optimization at link-time by passing @option{-fno-lto} to the link command. To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see @option{-fuse-linker-plugin}) passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, @option{-fwhole-program} should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions. When @option{-fuse-linker-plugin} is not enabled then, when a file is compiled with @option{-flto}, the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code (see @option{-ffat-lto-objects}. This means that object files with LTO information can be linked as normal object files; if @option{-fno-lto} is passed to the linker, no interprocedural optimizations are applied. Note that when @option{-fno-fat-lto-objects} is enabled the compile-stage is faster but you cannot perform a regular, non-LTO link on them. Additionally, the optimization flags used to compile individual files are not necessarily related to those used at link time. For instance, @smallexample gcc -c -O0 -ffat-lto-objects -flto foo.c gcc -c -O0 -ffat-lto-objects -flto bar.c gcc -o myprog -O3 foo.o bar.o @end smallexample This produces individual object files with unoptimized assembler code, but the resulting binary @file{myprog} is optimized at @option{-O3}. If, instead, the final binary is generated with @option{-fno-lto}, then @file{myprog} is not optimized. When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing. There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link stage. Generally options specified at link-time override those specified at compile-time. If you do not specify an optimization level option @option{-O} at link-time then GCC will compute one based on the optimization levels used when compiling the object files. The highest optimization level will win here. Currently, the following options and their setting are take from the first object file that explicitely specified it: @option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon}, @option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm} and all the @option{-m} target flags. Certain ABI changing flags are required to match in all compilation-units and trying to override this at link-time with a conflicting value is ignored. This includes options such as @option{-freg-struct-return} and @option{-fpcc-struct-return}. Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow}, @option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing} are passed through to the link stage and merged conservatively for conflicting translation units. Specifically @option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take precedence and for example @option{-ffp-contract=off} takes precedence over @option{-ffp-contract=fast}. You can override them at linke-time. It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time. If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages: @smallexample gcc -c -flto foo.c g++ -c -flto bar.cc gfortran -c -flto baz.f90 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran @end smallexample Notice that the final link is done with @command{g++} to get the C++ runtime libraries and @option{-lgfortran} is added to get the Fortran runtime libraries. In general, when mixing languages in LTO mode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation. If object files containing GIMPLE bytecode are stored in a library archive, say @file{libfoo.a}, it is possible to extract and use them in an LTO link if you are using a linker with plugin support. To create static libraries suitable for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar} and @code{ranlib}; to show the symbols of object files with GIMPLE bytecode, use @command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib} and @command{nm} have been compiled with plugin support. At link time, use the the flag @option{-fuse-linker-plugin} to ensure that the library participates in the LTO optimization process: @smallexample gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo @end smallexample With the linker plugin enabled, the linker extracts the needed GIMPLE files from @file{libfoo.a} and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized. If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside @file{libfoo.a} are extracted and linked as usual, but they do not participate in the LTO optimization process. In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with @option{-flto} @code{-ffat-lto-objects}. Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine @option{-flto} and @option{-fwhole-program} to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of @option{-fwhole-program} is not needed when linker plugin is active (see @option{-fuse-linker-plugin}). The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC will not work with an older or newer version of GCC. Link-time optimization does not work well with generation of debugging information. Combining @option{-flto} with @option{-g} is currently experimental and expected to produce unexpected results. If you specify the optional @var{n}, the optimization and code generation done at link time is executed in parallel using @var{n} parallel jobs by utilizing an installed @command{make} program. The environment variable @env{MAKE} may be used to override the program used. The default value for @var{n} is 1. You can also specify @option{-flto=jobserver} to use GNU make's job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCC is already executing in parallel. You must prepend a @samp{+} to the command recipe in the parent Makefile for this to work. This option likely only works if @env{MAKE} is GNU make. @item -flto-partition=@var{alg} @opindex flto-partition Specify the partitioning algorithm used by the link-time optimizer. The value is either @code{1to1} to specify a partitioning mirroring the original source files or @code{balanced} to specify partitioning into equally sized chunks (whenever possible) or @code{max} to create new partition for every symbol where possible. Specifying @code{none} as an algorithm disables partitioning and streaming completely. The default value is @code{balanced}. While @code{1to1} can be used as an workaround for various code ordering issues, the @code{max} partitioning is intended for internal testing only. The value @code{one} specifies that exactly one partition should be used while the value @code{none} bypasses partitioning and executes the link-time optimization step directly from the WPA phase. @item -flto-odr-type-merging @opindex flto-odr-type-merging Enable streaming of mangled types names of C++ types and their unification at linktime. This increases size of LTO object files, but enable diagnostics about One Definition Rule violations. @item -flto-compression-level=@var{n} This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode (@option{-flto}). Valid values are 0 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is not given, a default balanced compression setting is used. @item -flto-report Prints a report with internal details on the workings of the link-time optimizer. The contents of this report vary from version to version. It is meant to be useful to GCC developers when processing object files in LTO mode (via @option{-flto}). Disabled by default. @item -flto-report-wpa Like @option{-flto-report}, but only print for the WPA phase of Link Time Optimization. @item -fuse-linker-plugin Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNU ld 2.21 or newer. This option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to @code{-fwhole-program}. See @option{-flto} for a description of the effect of this flag and how to use it. This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold). @item -ffat-lto-objects @opindex ffat-lto-objects Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking. This option is effective only when compiling with @option{-flto} and is ignored at link time. @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker plugin support for basic functionality. Additionally, @command{nm}, @command{ar} and @command{ranlib} need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCC provides the @command{gcc-ar}, @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them. The default is @option{-fno-fat-lto-objects} on targets with linker plugin support. @item -fcompare-elim @opindex fcompare-elim After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation. This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fuse-ld=bfd @opindex fuse-ld=bfd Use the @command{bfd} linker instead of the default linker. @item -fuse-ld=gold @opindex fuse-ld=gold Use the @command{gold} linker instead of the default linker. @item -fcprop-registers @opindex fcprop-registers After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. @item -fprofile-correction @opindex fprofile-correction Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected. @item -fprofile-dir=@var{path} @opindex fprofile-dir Set the directory to search for the profile data files in to @var{path}. This option affects only the profile data generated by @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} and used by @option{-fprofile-use} and @option{-fbranch-probabilities} and its related options. Both absolute and relative paths can be used. By default, GCC uses the current directory as @var{path}, thus the profile data file appears in the same directory as the object file. @item -fprofile-generate @itemx -fprofile-generate=@var{path} @opindex fprofile-generate Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use @option{-fprofile-generate} both when compiling and when linking your program. The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}. If @var{path} is specified, GCC looks at the @var{path} to find the profile feedback data files. See @option{-fprofile-dir}. @item -fprofile-use @itemx -fprofile-use=@var{path} @opindex fprofile-use Enable profile feedback directed optimizations, and optimizations generally profitable only with profile feedback available. The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}, @code{-ftree-vectorize}, @code{ftree-loop-distribute-patterns} By default, GCC emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using @option{-Wcoverage-mismatch}. Note this may result in poorly optimized code. If @var{path} is specified, GCC looks at the @var{path} to find the profile feedback data files. See @option{-fprofile-dir}. @item -fauto-profile @itemx -fauto-profile=@var{path} @opindex fauto-profile Enable sampling based feedback directed optimizations, and optimizations generally profitable only with profile feedback available. The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}, @code{-ftree-vectorize}, @code{-finline-functions}, @code{-fipa-cp}, @code{-fipa-cp-clone}, @code{-fpredictive-commoning}, @code{-funswitch-loops}, @code{-fgcse-after-reload}, @code{-ftree-loop-distribute-patterns}, If @var{path} is specified, GCC looks at the @var{path} to find the profile feedback data files. In order to collect AutoFDO profile, you need to have: 1. A linux system with linux perf support 2. (optional) An Intel processor with last branch record (LBR) support. This is to guarantee accurate instruction level profile, which is important for AutoFDO performance. To collect the profile, first use linux perf to collect raw profile (see @uref{https://perf.wiki.kernel.org/}). E.g. @code{perf record -e br_inst_retired:near_taken -b -o perf.data -- your_program} Then use create_gcov tool, which takes raw profile and unstripped binary to generate AutoFDO profile that can be used by GCC. (see @uref{https://github.com/google/autofdo}). E.g. @code{create_gcov --binary=your_program.unstripped --profile=perf.data --gcov=profile.afdo} @end table The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled. @table @gcctabopt @item -ffloat-store @opindex ffloat-store Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory. @cindex floating-point precision This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a @code{double} is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use @option{-ffloat-store} for such programs, after modifying them to store all pertinent intermediate computations into variables. @item -fexcess-precision=@var{style} @opindex fexcess-precision This option allows further control over excess precision on machines where floating-point registers have more precision than the IEEE @code{float} and @code{double} types and the processor does not support operations rounding to those types. By default, @option{-fexcess-precision=fast} is in effect; this means that operations are carried out in the precision of the registers and that it is unpredictable when rounding to the types specified in the source code takes place. When compiling C, if @option{-fexcess-precision=standard} is specified then excess precision follows the rules specified in ISO C99; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas @option{-ffloat-store} only affects assignments). This option is enabled by default for C if a strict conformance option such as @option{-std=c99} is used. @opindex mfpmath @option{-fexcess-precision=standard} is not implemented for languages other than C, and has no effect if @option{-funsafe-math-optimizations} or @option{-ffast-math} is specified. On the x86, it also has no effect if @option{-mfpmath=sse} or @option{-mfpmath=sse+387} is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable. @item -ffast-math @opindex ffast-math Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @option{-ffinite-math-only}, @option{-fno-rounding-math}, @option{-fno-signaling-nans} and @option{-fcx-limited-range}. This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. This option is not turned on by any @option{-O} option besides @option{-Ofast} since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. @item -fno-math-errno @opindex fno-math-errno Do not set @code{errno} after calling math functions that are executed with a single instruction, e.g., @code{sqrt}. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. This option is not turned on by any @option{-O} option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is @option{-fmath-errno}. On Darwin systems, the math library never sets @code{errno}. There is therefore no reason for the compiler to consider the possibility that it might, and @option{-fno-math-errno} is the default. @item -funsafe-math-optimizations @opindex funsafe-math-optimizations Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link-time, it may include libraries or startup files that change the default FPU control word or other similar optimizations. This option is not turned on by any @option{-O} option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, @option{-fassociative-math} and @option{-freciprocal-math}. The default is @option{-fno-unsafe-math-optimizations}. @item -fassociative-math @opindex fassociative-math Allow re-association of operands in series of floating-point operations. This violates the ISO C and C++ language standard by possibly changing computation result. NOTE: re-ordering may change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like @code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both @option{-fno-signed-zeros} and @option{-fno-trapping-math} be in effect. Moreover, it doesn't make much sense with @option{-frounding-math}. For Fortran the option is automatically enabled when both @option{-fno-signed-zeros} and @option{-fno-trapping-math} are in effect. The default is @option{-fno-associative-math}. @item -freciprocal-math @opindex freciprocal-math Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example @code{x / y} can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value. The default is @option{-fno-reciprocal-math}. @item -ffinite-math-only @opindex ffinite-math-only Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs. This option is not turned on by any @option{-O} option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. The default is @option{-fno-finite-math-only}. @item -fno-signed-zeros @opindex fno-signed-zeros Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEE arithmetic specifies the behavior of distinct +0.0 and @minus{}0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). This option implies that the sign of a zero result isn't significant. The default is @option{-fsigned-zeros}. @item -fno-trapping-math @opindex fno-trapping-math Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option requires that @option{-fno-signaling-nans} be in effect. Setting this option may allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. This option should never be turned on by any @option{-O} option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. The default is @option{-ftrapping-math}. @item -frounding-math @opindex frounding-math Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes. The default is @option{-fno-rounding-math}. This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode. Future versions of GCC may provide finer control of this setting using C99's @code{FENV_ACCESS} pragma. This command-line option will be used to specify the default state for @code{FENV_ACCESS}. @item -fsignaling-nans @opindex fsignaling-nans Compile code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies @option{-ftrapping-math}. This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to be defined. The default is @option{-fno-signaling-nans}. This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. @item -fsingle-precision-constant @opindex fsingle-precision-constant Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants. @item -fcx-limited-range @opindex fcx-limited-range When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or division is @code{NaN + I*NaN}, with an attempt to rescue the situation in that case. The default is @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}. This option controls the default setting of the ISO C99 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to all languages. @item -fcx-fortran-rules @opindex fcx-fortran-rules Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or division is @code{NaN + I*NaN}, with an attempt to rescue the situation in that case. The default is @option{-fno-cx-fortran-rules}. @end table The following options control optimizations that may improve performance, but are not enabled by any @option{-O} options. This section includes experimental options that may produce broken code. @table @gcctabopt @item -fbranch-probabilities @opindex fbranch-probabilities After running a program compiled with @option{-fprofile-arcs} (@pxref{Debugging Options,, Options for Debugging Your Program or @command{gcc}}), you can compile it a second time using @option{-fbranch-probabilities}, to improve optimizations based on the number of times each branch was taken. When a program compiled with @option{-fprofile-arcs} exits, it saves arc execution counts to a file called @file{@var{sourcename}.gcda} for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations. With @option{-fbranch-probabilities}, GCC puts a @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. These can be used to improve optimization. Currently, they are only used in one place: in @file{reorg.c}, instead of guessing which path a branch is most likely to take, the @samp{REG_BR_PROB} values are used to exactly determine which path is taken more often. @item -fprofile-values @opindex fprofile-values If combined with @option{-fprofile-arcs}, it adds code so that some data about values of expressions in the program is gathered. With @option{-fbranch-probabilities}, it reads back the data gathered from profiling values of expressions for usage in optimizations. Enabled with @option{-fprofile-generate} and @option{-fprofile-use}. @item -fprofile-reorder-functions @opindex fprofile-reorder-functions Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. Enabled with @option{-fprofile-use}. @item -fvpt @opindex fvpt If combined with @option{-fprofile-arcs}, this option instructs the compiler to add code to gather information about values of expressions. With @option{-fbranch-probabilities}, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator. @item -frename-registers @opindex frename-registers Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables no longer stay in a ``home register''. Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}. @item -fschedule-fusion @opindex fschedule-fusion Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -ftracer @opindex ftracer Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job. Enabled with @option{-fprofile-use}. @item -funroll-loops @opindex funroll-loops Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. @option{-funroll-loops} implies @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. It also turns on complete loop peeling (i.e.@: complete removal of loops with a small constant number of iterations). This option makes code larger, and may or may not make it run faster. Enabled with @option{-fprofile-use}. @item -funroll-all-loops @opindex funroll-all-loops Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. @option{-funroll-all-loops} implies the same options as @option{-funroll-loops}. @item -fpeel-loops @opindex fpeel-loops Peels loops for which there is enough information that they do not roll much (from profile feedback). It also turns on complete loop peeling (i.e.@: complete removal of loops with small constant number of iterations). Enabled with @option{-fprofile-use}. @item -fmove-loop-invariants @opindex fmove-loop-invariants Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level @option{-O1} @item -funswitch-loops @opindex funswitch-loops Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition). @item -ffunction-sections @itemx -fdata-sections @opindex ffunction-sections @opindex fdata-sections Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the section's name in the output file. Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELF object format and SPARC processors running Solaris 2 have linkers with such optimizations. AIX may have these optimizations in the future. Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. You cannot use @code{gprof} on all systems if you specify this option, and you may have problems with debugging if you specify both this option and @option{-g}. @item -fbranch-target-load-optimize @opindex fbranch-target-load-optimize Perform branch target register load optimization before prologue / epilogue threading. The use of target registers can typically be exposed only during reload, thus hoisting loads out of loops and doing inter-block scheduling needs a separate optimization pass. @item -fbranch-target-load-optimize2 @opindex fbranch-target-load-optimize2 Perform branch target register load optimization after prologue / epilogue threading. @item -fbtr-bb-exclusive @opindex fbtr-bb-exclusive When performing branch target register load optimization, don't reuse branch target registers within any basic block. @item -fstack-protector @opindex fstack-protector Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call @code{alloca}, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits. @item -fstack-protector-all @opindex fstack-protector-all Like @option{-fstack-protector} except that all functions are protected. @item -fstack-protector-strong @opindex fstack-protector-strong Like @option{-fstack-protector} but includes additional functions to be protected --- those that have local array definitions, or have references to local frame addresses. @item -fsection-anchors @opindex fsection-anchors Try to reduce the number of symbolic address calculations by using shared ``anchor'' symbols to address nearby objects. This transformation can help to reduce the number of GOT entries and GOT accesses on some targets. For example, the implementation of the following function @code{foo}: @smallexample static int a, b, c; int foo (void) @{ return a + b + c; @} @end smallexample @noindent usually calculates the addresses of all three variables, but if you compile it with @option{-fsection-anchors}, it accesses the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isn't valid C): @smallexample int foo (void) @{ register int *xr = &x; return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; @} @end smallexample Not all targets support this option. @item --param @var{name}=@var{value} @opindex param In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the @option{--param} option. The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases. In each case, the @var{value} is an integer. The allowable choices for @var{name} are: @table @gcctabopt @item predictable-branch-outcome When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable. The default is 10. @item max-crossjump-edges The maximum number of incoming edges to consider for cross-jumping. The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in the number of edges incoming to each block. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size. @item min-crossjump-insns The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched. The default value is 5. @item max-grow-copy-bb-insns The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. The default value is 8. @item max-goto-duplication-insns The maximum number of instructions to duplicate to a block that jumps to a computed goto. To avoid @math{O(N^2)} behavior in a number of passes, GCC factors computed gotos early in the compilation process, and unfactors them as late as possible. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored. The default value is 8. @item max-delay-slot-insn-search The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time. @item max-delay-slot-live-search When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph. @item max-gcse-memory The approximate maximum amount of memory that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done. @item max-gcse-insertion-ratio If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream. The default value is 20. @item max-pending-list-length The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources. @item max-modulo-backtrack-attempts The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. @item max-inline-insns-single Several parameters control the tree inliner used in GCC@. This number sets the maximum number of instructions (counted in GCC's internal representation) in a single function that the tree inliner considers for inlining. This only affects functions declared inline and methods implemented in a class declaration (C++). The default value is 400. @item max-inline-insns-auto When you use @option{-finline-functions} (included in @option{-O3}), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a different (more restrictive) limit compared to functions declared inline can be applied. The default value is 40. @item inline-min-speedup When estimated performance improvement of caller + callee runtime exceeds this threshold (in precent), the function can be inlined regardless the limit on @option{--param max-inline-insns-single} and @option{--param max-inline-insns-auto}. @item large-function-insns The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by @option{--param large-function-growth}. This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end. The default value is 2700. @item large-function-growth Specifies maximal growth of large function caused by inlining in percents. The default value is 100 which limits large function growth to 2.0 times the original size. @item large-unit-insns The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by @option{--param inline-unit-growth}. For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times. If B is small relative to A, the growth of unit is 300\% and yet such inlining is very sane. For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to @option{--param large-unit-insns} before applying @option{--param inline-unit-growth}. The default is 10000. @item inline-unit-growth Specifies maximal overall growth of the compilation unit caused by inlining. The default value is 30 which limits unit growth to 1.3 times the original size. Cold functions (either marked cold via an attribute or by profile feedback) are not accounted into the unit size. @item ipcp-unit-growth Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. The default value is 10 which limits unit growth to 1.1 times the original size. @item large-stack-frame The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. The default value is 256 bytes. @item large-stack-frame-growth Specifies maximal growth of large stack frames caused by inlining in percents. The default value is 1000 which limits large stack frame growth to 11 times the original size. @item max-inline-insns-recursive @itemx max-inline-insns-recursive-auto Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. For functions declared inline, @option{--param max-inline-insns-recursive} is taken into account. For functions not declared inline, recursive inlining happens only when @option{-finline-functions} (included in @option{-O3}) is enabled and @option{--param max-inline-insns-recursive-auto} is used. The default value is 450. @item max-inline-recursive-depth @itemx max-inline-recursive-depth-auto Specifies the maximum recursion depth used for recursive inlining. For functions declared inline, @option{--param max-inline-recursive-depth} is taken into account. For functions not declared inline, recursive inlining happens only when @option{-finline-functions} (included in @option{-O3}) is enabled and @option{--param max-inline-recursive-depth-auto} is used. The default value is 8. @item min-inline-recursive-probability Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers. When profile feedback is available (see @option{-fprofile-generate}) the actual recursion depth can be guessed from probability that function recurses via a given call expression. This parameter limits inlining only to call expressions whose probability exceeds the given threshold (in percents). The default value is 10. @item early-inlining-insns Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. The default value is 10. @item max-early-inliner-iterations @itemx max-early-inliner-iterations Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining. @item comdat-sharing-probability @itemx comdat-sharing-probability Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units. The default value is 20. @item profile-func-internal-id @itemx profile-func-internal-id A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler will use id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc. The default value is 0. @item min-vect-loop-bound The minimum number of iterations under which loops are not vectorized when @option{-ftree-vectorize} is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization. The default value is 0. @item gcse-cost-distance-ratio Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than @option{gcse-unrestricted-cost}. Specifying 0 disables hoisting of simple expressions. The default value is 10. @item gcse-unrestricted-cost Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel. This is currently supported only in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. The default value is 3. @item max-hoist-depth The depth of search in the dominator tree for expressions to hoist. This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may slow down compilation of huge functions. The default value is 30. @item max-tail-merge-comparisons The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. The default value is 10. @item max-tail-merge-iterations The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. The default value is 2. @item max-unrolled-insns The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. @item max-average-unrolled-insns The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled. @item max-unroll-times The maximum number of unrollings of a single loop. @item max-peeled-insns The maximum number of instructions that a loop may have to be peeled. If a loop is peeled, this parameter also determines how many times the loop code is peeled. @item max-peel-times The maximum number of peelings of a single loop. @item max-peel-branches The maximum number of branches on the hot path through the peeled sequence. @item max-completely-peeled-insns The maximum number of insns of a completely peeled loop. @item max-completely-peel-times The maximum number of iterations of a loop to be suitable for complete peeling. @item max-completely-peel-loop-nest-depth The maximum depth of a loop nest suitable for complete peeling. @item max-unswitch-insns The maximum number of insns of an unswitched loop. @item max-unswitch-level The maximum number of branches unswitched in a single loop. @item lim-expensive The minimum cost of an expensive expression in the loop invariant motion. @item iv-consider-all-candidates-bound Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations. If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity. @item iv-max-considered-uses The induction variable optimizations give up on loops that contain more induction variable uses. @item iv-always-prune-cand-set-bound If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one. @item scev-max-expr-size Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer. @item scev-max-expr-complexity Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer. @item omega-max-vars The maximum number of variables in an Omega constraint system. The default value is 128. @item omega-max-geqs The maximum number of inequalities in an Omega constraint system. The default value is 256. @item omega-max-eqs The maximum number of equalities in an Omega constraint system. The default value is 128. @item omega-max-wild-cards The maximum number of wildcard variables that the Omega solver is able to insert. The default value is 18. @item omega-hash-table-size The size of the hash table in the Omega solver. The default value is 550. @item omega-max-keys The maximal number of keys used by the Omega solver. The default value is 500. @item omega-eliminate-redundant-constraints When set to 1, use expensive methods to eliminate all redundant constraints. The default value is 0. @item vect-max-version-for-alignment-checks The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer. @item vect-max-version-for-alias-checks The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer. @item vect-max-peeling-for-alignment The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means 'no limit'. @item max-iterations-to-track The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate. @item hot-bb-count-ws-permille A basic block profile count is considered hot if it contributes to the given permillage (i.e. 0...1000) of the entire profiled execution. @item hot-bb-frequency-fraction Select fraction of the entry block frequency of executions of basic block in function given basic block needs to have to be considered hot. @item max-predicted-iterations The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10. This means that the loop without bounds appears artificially cold relative to the other one. @item builtin-expect-probability Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input. The default probability of 90 is obtained empirically. @item align-threshold Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block. @item align-loop-iterations A loop expected to iterate at least the selected number of iterations is aligned. @item tracer-dynamic-coverage @itemx tracer-dynamic-coverage-feedback This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion. The @option{tracer-dynamic-coverage-feedback} is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value. @item tracer-max-code-growth Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth. @item tracer-min-branch-ratio Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent). @item tracer-min-branch-ratio @itemx tracer-min-branch-ratio-feedback Stop forward growth if the best edge has probability lower than this threshold. Similarly to @option{tracer-dynamic-coverage} two values are present, one for compilation for profile feedback and one for compilation without. The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective. @item max-cse-path-length The maximum number of basic blocks on path that CSE considers. The default is 10. @item max-cse-insns The maximum number of instructions CSE processes before flushing. The default is 1000. @item ggc-min-expand GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand between collections. Tuning this may improve compilation speed; it has no effect on code generation. The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If GCC is not able to calculate RAM on a particular platform, the lower bound of 30% is used. Setting this parameter and @option{ggc-min-heapsize} to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging. @item ggc-min-heapsize Minimum size of the garbage collector's heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, tuning this may improve compilation speed, and has no effect on code generation. The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes). If GCC is not able to calculate RAM on a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and @option{ggc-min-expand} to zero causes a full collection to occur at every opportunity. @item max-reload-search-insns The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. The default value is 100. @item max-cselib-memory-locations The maximum number of memory locations cselib should take into account. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. The default value is 500. @item reorder-blocks-duplicate @itemx reorder-blocks-duplicate-feedback Used by the basic block reordering pass to decide whether to use unconditional branch or duplicate the code on its destination. Code is duplicated when its estimated size is smaller than this value multiplied by the estimated size of unconditional jump in the hot spots of the program. The @option{reorder-block-duplicate-feedback} is used only when profile feedback is available. It may be set to higher values than @option{reorder-block-duplicate} since information about the hot spots is more accurate. @item max-sched-ready-insns The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass. Increasing values mean more thorough searches, making the compilation time increase with probably little benefit. The default value is 100. @item max-sched-region-blocks The maximum number of blocks in a region to be considered for interblock scheduling. The default value is 10. @item max-pipeline-region-blocks The maximum number of blocks in a region to be considered for pipelining in the selective scheduler. The default value is 15. @item max-sched-region-insns The maximum number of insns in a region to be considered for interblock scheduling. The default value is 100. @item max-pipeline-region-insns The maximum number of insns in a region to be considered for pipelining in the selective scheduler. The default value is 200. @item min-spec-prob The minimum probability (in percents) of reaching a source block for interblock speculative scheduling. The default value is 40. @item max-sched-extend-regions-iters The maximum number of iterations through CFG to extend regions. A value of 0 (the default) disables region extensions. @item max-sched-insn-conflict-delay The maximum conflict delay for an insn to be considered for speculative motion. The default value is 3. @item sched-spec-prob-cutoff The minimal probability of speculation success (in percents), so that speculative insns are scheduled. The default value is 40. @item sched-spec-state-edge-prob-cutoff The minimum probability an edge must have for the scheduler to save its state across it. The default value is 10. @item sched-mem-true-dep-cost Minimal distance (in CPU cycles) between store and load targeting same memory locations. The default value is 1. @item selsched-max-lookahead The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions. The default value is 50. @item selsched-max-sched-times The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined. The default value is 2. @item selsched-max-insns-to-rename The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler. The default value is 2. @item sms-min-sc The minimum value of stage count that swing modulo scheduler generates. The default value is 2. @item max-last-value-rtl The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register. The default is 10000. @item max-combine-insns The maximum number of instructions the RTL combiner tries to combine. The default value is 2 at @option{-Og} and 4 otherwise. @item integer-share-limit Small integer constants can use a shared data structure, reducing the compiler's memory usage and increasing its speed. This sets the maximum value of a shared integer constant. The default value is 256. @item ssp-buffer-size The minimum size of buffers (i.e.@: arrays) that receive stack smashing protection when @option{-fstack-protection} is used. @item min-size-for-stack-sharing The minimum size of variables taking part in stack slot sharing when not optimizing. The default value is 32. @item max-jump-thread-duplication-stmts Maximum number of statements allowed in a block that needs to be duplicated when threading jumps. @item max-fields-for-field-sensitive Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis. The default is zero for @option{-O0} and @option{-O1}, and 100 for @option{-Os}, @option{-O2}, and @option{-O3}. @item prefetch-latency Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to less streams being prefetched (see @option{simultaneous-prefetches}). @item simultaneous-prefetches Maximum number of prefetches that can run at the same time. @item l1-cache-line-size The size of cache line in L1 cache, in bytes. @item l1-cache-size The size of L1 cache, in kilobytes. @item l2-cache-size The size of L2 cache, in kilobytes. @item min-insn-to-prefetch-ratio The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop. @item prefetch-min-insn-to-mem-ratio The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop. @item use-canonical-types Whether the compiler should use the ``canonical'' type system. By default, this should always be 1, which uses a more efficient internal mechanism for comparing types in C++ and Objective-C++. However, if bugs in the canonical type system are causing compilation failures, set this value to 0 to disable canonical types. @item switch-conversion-max-branch-ratio Switch initialization conversion refuses to create arrays that are bigger than @option{switch-conversion-max-branch-ratio} times the number of branches in the switch. @item max-partial-antic-length Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization (@option{-ftree-pre}) when optimizing at @option{-O3} and above. For some sorts of source code the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets that are computed, which prevents the runaway behavior. Setting a value of 0 for this parameter allows an unlimited set length. @item sccvn-max-scc-size Maximum size of a strongly connected component (SCC) during SCCVN processing. If this limit is hit, SCCVN processing for the whole function is not done and optimizations depending on it are disabled. The default maximum SCC size is 10000. @item sccvn-max-alias-queries-per-access Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores. If this limit is hit the search is aborted and the load or store is not considered redundant. The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry. The default maxmimum number of queries is 1000. @item ira-max-loops-num IRA uses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently-executed loops form regions for regional register allocation. The default value of the parameter is 100. @item ira-max-conflict-table-size Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions. If the conflict table for a function could be more than the size in MB given by this parameter, the register allocator instead uses a faster, simpler, and lower-quality algorithm that does not require building a pseudo-register conflict table. The default value of the parameter is 2000. @item ira-loop-reserved-regs IRA can be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see @option{-O3}). The number of available registers reserved for some other purposes is given by this parameter. The default value of the parameter is 2, which is the minimal number of registers needed by typical instructions. This value is the best found from numerous experiments. @item loop-invariant-max-bbs-in-loop Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops. Loops with more basic blocks than this parameter won't have loop invariant motion optimization performed on them. The default value of the parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above. @item loop-max-datarefs-for-datadeps Building data dapendencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis. These large loops are no handled by the optimizations using loop data dependencies. The default value is 1000. @item max-vartrack-size Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function. If this limit is exceeded with variable tracking at assignments enabled, analysis for that function is retried without it, after removing all debug insns from the function. If the limit is exceeded even without debug insns, var tracking analysis is completely disabled for the function. Setting the parameter to zero makes it unlimited. @item max-vartrack-expr-depth Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions. This trades compilation time for more complete debug information. If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the compiler to find more complex debug expressions, but compile time and memory use may grow. The default is 12. @item min-nondebug-insn-uid Use uids starting at this parameter for nondebug insns. The range below the parameter is reserved exclusively for debug insns created by @option{-fvar-tracking-assignments}, but debug insns may get (non-overlapping) uids above it if the reserved range is exhausted. @item ipa-sra-ptr-growth-factor IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to @option{ipa-sra-ptr-growth-factor} times the size of the original pointer parameter. @item sra-max-scalarization-size-Ospeed @item sra-max-scalarization-size-Osize The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables. These parameters control the maximum size, in storage units, of aggregate which will be considered for replacement when compiling for speed (@option{sra-max-scalarization-size-Ospeed}) or size (@option{sra-max-scalarization-size-Osize}) respectively. @item tm-max-aggregate-size When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to save/restore code sequence pairs. This option only applies when using @option{-fgnu-tm}. @item graphite-max-nb-scop-params To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. The default value is 10 parameters. A variable whose value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP. @item graphite-max-bbs-per-function To avoid exponential effects in the detection of SCoPs, the size of the functions analyzed by Graphite is bounded. The default value is 100 basic blocks. @item loop-block-tile-size Loop blocking or strip mining transforms, enabled with @option{-floop-block} or @option{-floop-strip-mine}, strip mine each loop in the loop nest by a given number of iterations. The strip length can be changed using the @option{loop-block-tile-size} parameter. The default value is 51 iterations. @item ipa-cp-value-list-size IPA-CP attempts to track all possible values and types passed to a function's parameter in order to propagate them and perform devirtualization. @option{ipa-cp-value-list-size} is the maximum number of values and types it stores per one formal parameter of a function. @item ipa-cp-eval-threshold IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed @option{ipa-cp-eval-threshold}. @item ipa-max-agg-items IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. @option{ipa-max-agg-items} controls the maximum number of such values per one parameter. @item ipa-cp-loop-hint-bonus When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of @option{ipa-cp-loop-hint-bonus} to the profitability score of the candidate. @item ipa-cp-array-index-hint-bonus When IPA-CP determines that a cloning candidate would make the index of an array access known, it adds a bonus of @option{ipa-cp-array-index-hint-bonus} to the profitability score of the candidate. @item ipa-max-aa-steps During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters. In order not spend too much time analyzing huge functions, it will give up and consider all memory clobbered after examining @option{ipa-max-aa-steps} statements modifying memory. @item lto-partitions Specify desired number of partitions produced during WHOPR compilation. The number of partitions should exceed the number of CPUs used for compilation. The default value is 32. @item lto-minpartition Size of minimal partition for WHOPR (in estimated instructions). This prevents expenses of splitting very small programs into too many partitions. @item cxx-max-namespaces-for-diagnostic-help The maximum number of namespaces to consult for suggestions when C++ name lookup fails for an identifier. The default is 1000. @item sink-frequency-threshold The maximum relative execution frequency (in percents) of the target block relative to a statement's original block to allow statement sinking of a statement. Larger numbers result in more aggressive statement sinking. The default value is 75. A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink. @item max-stores-to-sink The maximum number of conditional stores paires that can be sunk. Set to 0 if either vectorization (@option{-ftree-vectorize}) or if-conversion (@option{-ftree-loop-if-convert}) is disabled. The default is 2. @item allow-store-data-races Allow optimizers to introduce new data races on stores. Set to 1 to allow, otherwise to 0. This option is enabled by default at optimization level @option{-Ofast}. @item case-values-threshold The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. If the value is 0, use the default for the machine. The default is 0. @item tree-reassoc-width Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value. @item sched-pressure-algorithm Choose between the two available implementations of @option{-fsched-pressure}. Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler. It relies more heavily on having a regular register file and accurate register pressure classes. See @file{haifa-sched.c} in the GCC sources for more details. The default choice depends on the target. @item max-slsr-cand-scan Set the maximum number of existing candidates that will be considered when seeking a basis for a new straight-line strength reduction candidate. @item asan-globals Enable buffer overflow detection for global objects. This kind of protection is enabled by default if you are using @option{-fsanitize=address} option. To disable global objects protection use @option{--param asan-globals=0}. @item asan-stack Enable buffer overflow detection for stack objects. This kind of protection is enabled by default when using@option{-fsanitize=address}. To disable stack protection use @option{--param asan-stack=0} option. @item asan-instrument-reads Enable buffer overflow detection for memory reads. This kind of protection is enabled by default when using @option{-fsanitize=address}. To disable memory reads protection use @option{--param asan-instrument-reads=0}. @item asan-instrument-writes Enable buffer overflow detection for memory writes. This kind of protection is enabled by default when using @option{-fsanitize=address}. To disable memory writes protection use @option{--param asan-instrument-writes=0} option. @item asan-memintrin Enable detection for built-in functions. This kind of protection is enabled by default when using @option{-fsanitize=address}. To disable built-in functions protection use @option{--param asan-memintrin=0}. @item asan-use-after-return Enable detection of use-after-return. This kind of protection is enabled by default when using @option{-fsanitize=address} option. To disable use-after-return detection use @option{--param asan-use-after-return=0}. @item asan-instrumentation-with-call-threshold If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks. E.g. to disable inline code use @option{--param asan-instrumentation-with-call-threshold=0}. @item chkp-max-ctor-size Static constructors generated by Pointer Bounds Checker may become very large and significantly increase compile time at optimization level @option{-O1} and higher. This parameter is a maximum nubmer of statements in a single generated constructor. Default value is 5000. @end table @end table @node Preprocessor Options @section Options Controlling the Preprocessor @cindex preprocessor options @cindex options, preprocessor These options control the C preprocessor, which is run on each C source file before actual compilation. If you use the @option{-E} option, nothing is done except preprocessing. Some of these options make sense only together with @option{-E} because they cause the preprocessor output to be unsuitable for actual compilation. @table @gcctabopt @item -Wp,@var{option} @opindex Wp You can use @option{-Wp,@var{option}} to bypass the compiler driver and pass @var{option} directly through to the preprocessor. If @var{option} contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and @option{-Wp} forcibly bypasses this phase. The preprocessor's direct interface is undocumented and subject to change, so whenever possible you should avoid using @option{-Wp} and let the driver handle the options instead. @item -Xpreprocessor @var{option} @opindex Xpreprocessor Pass @var{option} as an option to the preprocessor. You can use this to supply system-specific preprocessor options that GCC does not recognize. If you want to pass an option that takes an argument, you must use @option{-Xpreprocessor} twice, once for the option and once for the argument. @item -no-integrated-cpp @opindex no-integrated-cpp Perform preprocessing as a separate pass before compilation. By default, GCC performs preprocessing as an integrated part of input tokenization and parsing. If this option is provided, the appropriate language front end (@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, and Objective-C, respectively) is instead invoked twice, once for preprocessing only and once for actual compilation of the preprocessed input. This option may be useful in conjunction with the @option{-B} or @option{-wrapper} options to specify an alternate preprocessor or perform additional processing of the program source between normal preprocessing and compilation. @end table @include cppopts.texi @node Assembler Options @section Passing Options to the Assembler @c prevent bad page break with this line You can pass options to the assembler. @table @gcctabopt @item -Wa,@var{option} @opindex Wa Pass @var{option} as an option to the assembler. If @var{option} contains commas, it is split into multiple options at the commas. @item -Xassembler @var{option} @opindex Xassembler Pass @var{option} as an option to the assembler. You can use this to supply system-specific assembler options that GCC does not recognize. If you want to pass an option that takes an argument, you must use @option{-Xassembler} twice, once for the option and once for the argument. @end table @node Link Options @section Options for Linking @cindex link options @cindex options, linking These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step. @table @gcctabopt @cindex file names @item @var{object-file-name} A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker. @item -c @itemx -S @itemx -E @opindex c @opindex S @opindex E If any of these options is used, then the linker is not run, and object file names should not be used as arguments. @xref{Overall Options}. @cindex Libraries @item -l@var{library} @itemx -l @var{library} @opindex l Search the library named @var{library} when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.) It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers to functions in @samp{z}, those functions may not be loaded. The linker searches a standard list of directories for the library, which is actually a file named @file{lib@var{library}.a}. The linker then uses this file as if it had been specified precisely by name. The directories searched include several standard system directories plus any that you specify with @option{-L}. Normally the files found this way are library files---archive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an @option{-l} option and specifying a file name is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} and searches several directories. @item -lobjc @opindex lobjc You need this special case of the @option{-l} option in order to link an Objective-C or Objective-C++ program. @item -nostartfiles @opindex nostartfiles Do not use the standard system startup files when linking. The standard system libraries are used normally, unless @option{-nostdlib} or @option{-nodefaultlibs} is used. @item -nodefaultlibs @opindex nodefaultlibs Do not use the standard system libraries when linking. Only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as @code{-static-libgcc} or @code{-shared-libgcc}, are ignored. The standard startup files are used normally, unless @option{-nostartfiles} is used. The compiler may generate calls to @code{memcmp}, @code{memset}, @code{memcpy} and @code{memmove}. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. @item -nostdlib @opindex nostdlib Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as @code{-static-libgcc} or @code{-shared-libgcc}, are ignored. The compiler may generate calls to @code{memcmp}, @code{memset}, @code{memcpy} and @code{memmove}. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified. @cindex @option{-lgcc}, use with @option{-nostdlib} @cindex @option{-nostdlib} and unresolved references @cindex unresolved references and @option{-nostdlib} @cindex @option{-lgcc}, use with @option{-nodefaultlibs} @cindex @option{-nodefaultlibs} and unresolved references @cindex unresolved references and @option{-nodefaultlibs} One of the standard libraries bypassed by @option{-nostdlib} and @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs for some languages. (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler Collection (GCC) Internals}, for more discussion of @file{libgcc.a}.) In most cases, you need @file{libgcc.a} even when you want to avoid other standard libraries. In other words, when you specify @option{-nostdlib} or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. This ensures that you have no unresolved references to internal GCC library subroutines. (An example of such an internal subroutine is @samp{__main}, used to ensure C++ constructors are called; @pxref{Collect2,,@code{collect2}, gccint, GNU Compiler Collection (GCC) Internals}.) @item -pie @opindex pie Produce a position independent executable on targets that support it. For predictable results, you must also specify the same set of options used for compilation (@option{-fpie}, @option{-fPIE}, or model suboptions) when you specify this linker option. @item -rdynamic @opindex rdynamic Pass the flag @option{-export-dynamic} to the ELF linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of @code{dlopen} or to allow obtaining backtraces from within a program. @item -s @opindex s Remove all symbol table and relocation information from the executable. @item -static @opindex static On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect. @item -shared @opindex shared Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options used for compilation (@option{-fpic}, @option{-fPIC}, or model suboptions) when you specify this linker option.@footnote{On some systems, @samp{gcc -shared} needs to build supplementary stub code for constructors to work. On multi-libbed systems, @samp{gcc -shared} must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous.} @item -shared-libgcc @itemx -static-libgcc @opindex shared-libgcc @opindex static-libgcc On systems that provide @file{libgcc} as a shared library, these options force the use of either the shared or static version, respectively. If no shared version of @file{libgcc} was built when the compiler was configured, these options have no effect. There are several situations in which an application should use the shared @file{libgcc} instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared @file{libgcc}. Therefore, the G++ and GCJ drivers automatically add @option{-shared-libgcc} whenever you build a shared library or a main executable, because C++ and Java programs typically use exceptions, so this is the right thing to do. If, instead, you use the GCC driver to create shared libraries, you may find that they are not always linked with the shared @file{libgcc}. If GCC finds, at its configuration time, that you have a non-GNU linker or a GNU linker that does not support option @option{--eh-frame-hdr}, it links the shared version of @file{libgcc} into shared libraries by default. Otherwise, it takes advantage of the linker and optimizes away the linking with the shared version of @file{libgcc}, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time. However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or GCJ driver, as appropriate for the languages used in the program, or using the option @option{-shared-libgcc}, such that it is linked with the shared @file{libgcc}. @item -static-libasan @opindex static-libasan When the @option{-fsanitize=address} option is used to link a program, the GCC driver automatically links against @option{libasan}. If @file{libasan} is available as a shared library, and the @option{-static} option is not used, then this links against the shared version of @file{libasan}. The @option{-static-libasan} option directs the GCC driver to link @file{libasan} statically, without necessarily linking other libraries statically. @item -static-libtsan @opindex static-libtsan When the @option{-fsanitize=thread} option is used to link a program, the GCC driver automatically links against @option{libtsan}. If @file{libtsan} is available as a shared library, and the @option{-static} option is not used, then this links against the shared version of @file{libtsan}. The @option{-static-libtsan} option directs the GCC driver to link @file{libtsan} statically, without necessarily linking other libraries statically. @item -static-liblsan @opindex static-liblsan When the @option{-fsanitize=leak} option is used to link a program, the GCC driver automatically links against @option{liblsan}. If @file{liblsan} is available as a shared library, and the @option{-static} option is not used, then this links against the shared version of @file{liblsan}. The @option{-static-liblsan} option directs the GCC driver to link @file{liblsan} statically, without necessarily linking other libraries statically. @item -static-libubsan @opindex static-libubsan When the @option{-fsanitize=undefined} option is used to link a program, the GCC driver automatically links against @option{libubsan}. If @file{libubsan} is available as a shared library, and the @option{-static} option is not used, then this links against the shared version of @file{libubsan}. The @option{-static-libubsan} option directs the GCC driver to link @file{libubsan} statically, without necessarily linking other libraries statically. @item -static-libstdc++ @opindex static-libstdc++ When the @command{g++} program is used to link a C++ program, it normally automatically links against @option{libstdc++}. If @file{libstdc++} is available as a shared library, and the @option{-static} option is not used, then this links against the shared version of @file{libstdc++}. That is normally fine. However, it is sometimes useful to freeze the version of @file{libstdc++} used by the program without going all the way to a fully static link. The @option{-static-libstdc++} option directs the @command{g++} driver to link @file{libstdc++} statically, without necessarily linking other libraries statically. @item -symbolic @opindex symbolic Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option @option{-Xlinker -z -Xlinker defs}). Only a few systems support this option. @item -T @var{script} @opindex T @cindex linker script Use @var{script} as the linker script. This option is supported by most systems using the GNU linker. On some targets, such as bare-board targets without an operating system, the @option{-T} option may be required when linking to avoid references to undefined symbols. @item -Xlinker @var{option} @opindex Xlinker Pass @var{option} as an option to the linker. You can use this to supply system-specific linker options that GCC does not recognize. If you want to pass an option that takes a separate argument, you must use @option{-Xlinker} twice, once for the option and once for the argument. For example, to pass @option{-assert definitions}, you must write @option{-Xlinker -assert -Xlinker definitions}. It does not work to write @option{-Xlinker "-assert definitions"}, because this passes the entire string as a single argument, which is not what the linker expects. When using the GNU linker, it is usually more convenient to pass arguments to linker options using the @option{@var{option}=@var{value}} syntax than as separate arguments. For example, you can specify @option{-Xlinker -Map=output.map} rather than @option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support this syntax for command-line options. @item -Wl,@var{option} @opindex Wl Pass @var{option} as an option to the linker. If @var{option} contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the linker. When using the GNU linker, you can also get the same effect with @option{-Wl,-Map=output.map}. @item -u @var{symbol} @opindex u Pretend the symbol @var{symbol} is undefined, to force linking of library modules to define it. You can use @option{-u} multiple times with different symbols to force loading of additional library modules. @item -z @var{keyword} @opindex z @option{-z} is passed directly on to the linker along with the keyword @var{keyword}. See the section in the documentation of your linker for permitted values and their meanings. @end table @node Directory Options @section Options for Directory Search @cindex directory options @cindex options, directory search @cindex search path These options specify directories to search for header files, for libraries and for parts of the compiler: @table @gcctabopt @item -I@var{dir} @opindex I Add the directory @var{dir} to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use @option{-isystem} for that). If you use more than one @option{-I} option, the directories are scanned in left-to-right order; the standard system directories come after. If a standard system include directory, or a directory specified with @option{-isystem}, is also specified with @option{-I}, the @option{-I} option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCC's procedure to fix buggy system headers and the ordering for the @code{include_next} directive are not inadvertently changed. If you really need to change the search order for system directories, use the @option{-nostdinc} and/or @option{-isystem} options. @item -iplugindir=@var{dir} @opindex iplugindir= Set the directory to search for plugins that are passed by @option{-fplugin=@var{name}} instead of @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant to be used by the user, but only passed by the driver. @item -iquote@var{dir} @opindex iquote Add the directory @var{dir} to the head of the list of directories to be searched for header files only for the case of @samp{#include "@var{file}"}; they are not searched for @samp{#include <@var{file}>}, otherwise just like @option{-I}. @item -L@var{dir} @opindex L Add directory @var{dir} to the list of directories to be searched for @option{-l}. @item -B@var{prefix} @opindex B This option specifies where to find the executables, libraries, include files, and data files of the compiler itself. The compiler driver program runs one or more of the subprograms @command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries @var{prefix} as a prefix for each program it tries to run, both with and without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). For each subprogram to be run, the compiler driver first tries the @option{-B} prefix, if any. If that name is not found, or if @option{-B} is not specified, the driver tries two standard prefixes, @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your @env{PATH} environment variable. The compiler checks to see if the path provided by the @option{-B} refers to a directory, and if necessary it adds a directory separator character at the end of the path. @option{-B} prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into @option{-L} options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into @option{-isystem} options for the preprocessor. In this case, the compiler appends @samp{include} to the prefix. The runtime support file @file{libgcc.a} can also be searched for using the @option{-B} prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means. Another way to specify a prefix much like the @option{-B} prefix is to use the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment Variables}. As a special kludge, if the path provided by @option{-B} is @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to 9, then it is replaced by @file{[dir/]include}. This is to help with boot-strapping the compiler. @item -specs=@var{file} @opindex specs Process @var{file} after the compiler reads in the standard @file{specs} file, in order to override the defaults which the @command{gcc} driver program uses when determining what switches to pass to @command{cc1}, @command{cc1plus}, @command{as}, @command{ld}, etc. More than one @option{-specs=@var{file}} can be specified on the command line, and they are processed in order, from left to right. @item --sysroot=@var{dir} @opindex sysroot Use @var{dir} as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in @file{/usr/include} and libraries in @file{/usr/lib}, it instead searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. If you use both this option and the @option{-isysroot} option, then the @option{--sysroot} option applies to libraries, but the @option{-isysroot} option applies to header files. The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of @option{--sysroot} still works, but the library aspect does not. @item --no-sysroot-suffix @opindex no-sysroot-suffix For some targets, a suffix is added to the root directory specified with @option{--sysroot}, depending on the other options used, so that headers may for example be found in @file{@var{dir}/@var{suffix}/usr/include} instead of @file{@var{dir}/usr/include}. This option disables the addition of such a suffix. @item -I- @opindex I- This option has been deprecated. Please use @option{-iquote} instead for @option{-I} directories before the @option{-I-} and remove the @option{-I-}. Any directories you specify with @option{-I} options before the @option{-I-} option are searched only for the case of @samp{#include "@var{file}"}; they are not searched for @samp{#include <@var{file}>}. If additional directories are specified with @option{-I} options after the @option{-I-}, these directories are searched for all @samp{#include} directives. (Ordinarily @emph{all} @option{-I} directories are used this way.) In addition, the @option{-I-} option inhibits the use of the current directory (where the current input file came from) as the first search directory for @samp{#include "@var{file}"}. There is no way to override this effect of @option{-I-}. With @option{-I.} you can specify searching the directory that is current when the compiler is invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory. @option{-I-} does not inhibit the use of the standard system directories for header files. Thus, @option{-I-} and @option{-nostdinc} are independent. @end table @c man end @node Spec Files @section Specifying subprocesses and the switches to pass to them @cindex Spec Files @command{gcc} is a driver program. It performs its job by invoking a sequence of other programs to do the work of compiling, assembling and linking. GCC interprets its command-line parameters and uses these to deduce which programs it should invoke, and which command-line options it ought to place on their command lines. This behavior is controlled by @dfn{spec strings}. In most cases there is one spec string for each program that GCC can invoke, but a few programs have multiple spec strings to control their behavior. The spec strings built into GCC can be overridden by using the @option{-specs=} command-line switch to specify a spec file. @dfn{Spec files} are plaintext files that are used to construct spec strings. They consist of a sequence of directives separated by blank lines. The type of directive is determined by the first non-whitespace character on the line, which can be one of the following: @table @code @item %@var{command} Issues a @var{command} to the spec file processor. The commands that can appear here are: @table @code @item %include <@var{file}> @cindex @code{%include} Search for @var{file} and insert its text at the current point in the specs file. @item %include_noerr <@var{file}> @cindex @code{%include_noerr} Just like @samp{%include}, but do not generate an error message if the include file cannot be found. @item %rename @var{old_name} @var{new_name} @cindex @code{%rename} Rename the spec string @var{old_name} to @var{new_name}. @end table @item *[@var{spec_name}]: This tells the compiler to create, override or delete the named spec string. All lines after this directive up to the next directive or blank line are considered to be the text for the spec string. If this results in an empty string then the spec is deleted. (Or, if the spec did not exist, then nothing happens.) Otherwise, if the spec does not currently exist a new spec is created. If the spec does exist then its contents are overridden by the text of this directive, unless the first character of that text is the @samp{+} character, in which case the text is appended to the spec. @item [@var{suffix}]: Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive and up to the next directive or blank line are considered to make up the spec string for the indicated suffix. When the compiler encounters an input file with the named suffix, it processes the spec string in order to work out how to compile that file. For example: @smallexample .ZZ: z-compile -input %i @end smallexample This says that any input file whose name ends in @samp{.ZZ} should be passed to the program @samp{z-compile}, which should be invoked with the command-line switch @option{-input} and with the result of performing the @samp{%i} substitution. (See below.) As an alternative to providing a spec string, the text following a suffix directive can be one of the following: @table @code @item @@@var{language} This says that the suffix is an alias for a known @var{language}. This is similar to using the @option{-x} command-line switch to GCC to specify a language explicitly. For example: @smallexample .ZZ: @@c++ @end smallexample Says that .ZZ files are, in fact, C++ source files. @item #@var{name} This causes an error messages saying: @smallexample @var{name} compiler not installed on this system. @end smallexample @end table GCC already has an extensive list of suffixes built into it. This directive adds an entry to the end of the list of suffixes, but since the list is searched from the end backwards, it is effectively possible to override earlier entries using this technique. @end table GCC has the following spec strings built into it. Spec files can override these strings or create their own. Note that individual targets can also add their own spec strings to this list. @smallexample asm Options to pass to the assembler asm_final Options to pass to the assembler post-processor cpp Options to pass to the C preprocessor cc1 Options to pass to the C compiler cc1plus Options to pass to the C++ compiler endfile Object files to include at the end of the link link Options to pass to the linker lib Libraries to include on the command line to the linker libgcc Decides which GCC support library to pass to the linker linker Sets the name of the linker predefines Defines to be passed to the C preprocessor signed_char Defines to pass to CPP to say whether @code{char} is signed by default startfile Object files to include at the start of the link @end smallexample Here is a small example of a spec file: @smallexample %rename lib old_lib *lib: --start-group -lgcc -lc -leval1 --end-group %(old_lib) @end smallexample This example renames the spec called @samp{lib} to @samp{old_lib} and then overrides the previous definition of @samp{lib} with a new one. The new definition adds in some extra command-line options before including the text of the old definition. @dfn{Spec strings} are a list of command-line options to be passed to their corresponding program. In addition, the spec strings can contain @samp{%}-prefixed sequences to substitute variable text or to conditionally insert text into the command line. Using these constructs it is possible to generate quite complex command lines. Here is a table of all defined @samp{%}-sequences for spec strings. Note that spaces are not generated automatically around the results of expanding these sequences. Therefore you can concatenate them together or combine them with constant text in a single argument. @table @code @item %% Substitute one @samp{%} into the program name or argument. @item %i Substitute the name of the input file being processed. @item %b Substitute the basename of the input file being processed. This is the substring up to (and not including) the last period and not including the directory. @item %B This is the same as @samp{%b}, but include the file suffix (text after the last period). @item %d Marks the argument containing or following the @samp{%d} as a temporary file name, so that that file is deleted if GCC exits successfully. Unlike @samp{%g}, this contributes no text to the argument. @item %g@var{suffix} Substitute a file name that has suffix @var{suffix} and is chosen once per compilation, and mark the argument in the same way as @samp{%d}. To reduce exposure to denial-of-service attacks, the file name is now chosen in a way that is hard to predict even when previously chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} was simply substituted with a file name chosen once per compilation, without regard to any appended suffix (which was therefore treated just like ordinary text), making such attacks more likely to succeed. @item %u@var{suffix} Like @samp{%g}, but generates a new temporary file name each time it appears instead of once per compilation. @item %U@var{suffix} Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a new one if there is no such last file name. In the absence of any @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} involves the generation of two distinct file names, one for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was simply substituted with a file name chosen for the previous @samp{%u}, without regard to any appended suffix. @item %j@var{suffix} Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is writable, and if @option{-save-temps} is not used; otherwise, substitute the name of a temporary file, just like @samp{%u}. This temporary file is not meant for communication between processes, but rather as a junk disposal mechanism. @item %|@var{suffix} @itemx %m@var{suffix} Like @samp{%g}, except if @option{-pipe} is in effect. In that case @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at all. These are the two most common ways to instruct a program that it should read from standard input or write to standard output. If you need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} construct: see for example @file{f/lang-specs.h}. @item %.@var{SUFFIX} Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args when it is subsequently output with @samp{%*}. @var{SUFFIX} is terminated by the next space or %. @item %w Marks the argument containing or following the @samp{%w} as the designated output file of this compilation. This puts the argument into the sequence of arguments that @samp{%o} substitutes. @item %o Substitutes the names of all the output files, with spaces automatically placed around them. You should write spaces around the @samp{%o} as well or the results are undefined. @samp{%o} is for use in the specs for running the linker. Input files whose names have no recognized suffix are not compiled at all, but they are included among the output files, so they are linked. @item %O Substitutes the suffix for object files. Note that this is handled specially when it immediately follows @samp{%g, %u, or %U}, because of the need for those to form complete file names. The handling is such that @samp{%O} is treated exactly as if it had already been substituted, except that @samp{%g, %u, and %U} do not currently support additional @var{suffix} characters following @samp{%O} as they do following, for example, @samp{.o}. @item %p Substitutes the standard macro predefinitions for the current target machine. Use this when running @code{cpp}. @item %P Like @samp{%p}, but puts @samp{__} before and after the name of each predefined macro, except for macros that start with @samp{__} or with @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO C@. @item %I Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) and @option{-imultilib} as necessary. @item %s Current argument is the name of a library or startup file of some sort. Search for that file in a standard list of directories and substitute the full name found. The current working directory is included in the list of directories scanned. @item %T Current argument is the name of a linker script. Search for that file in the current list of directories to scan for libraries. If the file is located insert a @option{--script} option into the command line followed by the full path name found. If the file is not found then generate an error message. Note: the current working directory is not searched. @item %e@var{str} Print @var{str} as an error message. @var{str} is terminated by a newline. Use this when inconsistent options are detected. @item %(@var{name}) Substitute the contents of spec string @var{name} at this point. @item %x@{@var{option}@} Accumulate an option for @samp{%X}. @item %X Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} spec string. @item %Y Output the accumulated assembler options specified by @option{-Wa}. @item %Z Output the accumulated preprocessor options specified by @option{-Wp}. @item %a Process the @code{asm} spec. This is used to compute the switches to be passed to the assembler. @item %A Process the @code{asm_final} spec. This is a spec string for passing switches to an assembler post-processor, if such a program is needed. @item %l Process the @code{link} spec. This is the spec for computing the command line passed to the linker. Typically it makes use of the @samp{%L %G %S %D and %E} sequences. @item %D Dump out a @option{-L} option for each directory that GCC believes might contain startup files. If the target supports multilibs then the current multilib directory is prepended to each of these paths. @item %L Process the @code{lib} spec. This is a spec string for deciding which libraries are included on the command line to the linker. @item %G Process the @code{libgcc} spec. This is a spec string for deciding which GCC support library is included on the command line to the linker. @item %S Process the @code{startfile} spec. This is a spec for deciding which object files are the first ones passed to the linker. Typically this might be a file named @file{crt0.o}. @item %E Process the @code{endfile} spec. This is a spec string that specifies the last object files that are passed to the linker. @item %C Process the @code{cpp} spec. This is used to construct the arguments to be passed to the C preprocessor. @item %1 Process the @code{cc1} spec. This is used to construct the options to be passed to the actual C compiler (@samp{cc1}). @item %2 Process the @code{cc1plus} spec. This is used to construct the options to be passed to the actual C++ compiler (@samp{cc1plus}). @item %* Substitute the variable part of a matched option. See below. Note that each comma in the substituted string is replaced by a single space. @item %<@code{S} Remove all occurrences of @code{-S} from the command line. Note---this command is position dependent. @samp{%} commands in the spec string before this one see @code{-S}, @samp{%} commands in the spec string after this one do not. @item %:@var{function}(@var{args}) Call the named function @var{function}, passing it @var{args}. @var{args} is first processed as a nested spec string, then split into an argument vector in the usual fashion. The function returns a string which is processed as if it had appeared literally as part of the current spec. The following built-in spec functions are provided: @table @code @item @code{getenv} The @code{getenv} spec function takes two arguments: an environment variable name and a string. If the environment variable is not defined, a fatal error is issued. Otherwise, the return value is the value of the environment variable concatenated with the string. For example, if @env{TOPDIR} is defined as @file{/path/to/top}, then: @smallexample %:getenv(TOPDIR /include) @end smallexample expands to @file{/path/to/top/include}. @item @code{if-exists} The @code{if-exists} spec function takes one argument, an absolute pathname to a file. If the file exists, @code{if-exists} returns the pathname. Here is a small example of its usage: @smallexample *startfile: crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s @end smallexample @item @code{if-exists-else} The @code{if-exists-else} spec function is similar to the @code{if-exists} spec function, except that it takes two arguments. The first argument is an absolute pathname to a file. If the file exists, @code{if-exists-else} returns the pathname. If it does not exist, it returns the second argument. This way, @code{if-exists-else} can be used to select one file or another, based on the existence of the first. Here is a small example of its usage: @smallexample *startfile: crt0%O%s %:if-exists(crti%O%s) \ %:if-exists-else(crtbeginT%O%s crtbegin%O%s) @end smallexample @item @code{replace-outfile} The @code{replace-outfile} spec function takes two arguments. It looks for the first argument in the outfiles array and replaces it with the second argument. Here is a small example of its usage: @smallexample %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} @end smallexample @item @code{remove-outfile} The @code{remove-outfile} spec function takes one argument. It looks for the first argument in the outfiles array and removes it. Here is a small example its usage: @smallexample %:remove-outfile(-lm) @end smallexample @item @code{pass-through-libs} The @code{pass-through-libs} spec function takes any number of arguments. It finds any @option{-l} options and any non-options ending in @file{.a} (which it assumes are the names of linker input library archive files) and returns a result containing all the found arguments each prepended by @option{-plugin-opt=-pass-through=} and joined by spaces. This list is intended to be passed to the LTO linker plugin. @smallexample %:pass-through-libs(%G %L %G) @end smallexample @item @code{print-asm-header} The @code{print-asm-header} function takes no arguments and simply prints a banner like: @smallexample Assembler options ================= Use "-Wa,OPTION" to pass "OPTION" to the assembler. @end smallexample It is used to separate compiler options from assembler options in the @option{--target-help} output. @end table @item %@{@code{S}@} Substitutes the @code{-S} switch, if that switch is given to GCC@. If that switch is not specified, this substitutes nothing. Note that the leading dash is omitted when specifying this option, and it is automatically inserted if the substitution is performed. Thus the spec string @samp{%@{foo@}} matches the command-line option @option{-foo} and outputs the command-line option @option{-foo}. @item %W@{@code{S}@} Like %@{@code{S}@} but mark last argument supplied within as a file to be deleted on failure. @item %@{@code{S}*@} Substitutes all the switches specified to GCC whose names start with @code{-S}, but which also take an argument. This is used for switches like @option{-o}, @option{-D}, @option{-I}, etc. GCC considers @option{-o foo} as being one switch whose name starts with @samp{o}. %@{o*@} substitutes this text, including the space. Thus two arguments are generated. @item %@{@code{S}*&@code{T}*@} Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options (the order of @code{S} and @code{T} in the spec is not significant). There can be any number of ampersand-separated variables; for each the wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. @item %@{@code{S}:@code{X}@} Substitutes @code{X}, if the @option{-S} switch is given to GCC@. @item %@{!@code{S}:@code{X}@} Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. @item %@{@code{S}*:@code{X}@} Substitutes @code{X} if one or more switches whose names start with @code{-S} are specified to GCC@. Normally @code{X} is substituted only once, no matter how many such switches appeared. However, if @code{%*} appears somewhere in @code{X}, then @code{X} is substituted once for each matching switch, with the @code{%*} replaced by the part of that switch matching the @code{*}. If @code{%*} appears as the last part of a spec sequence then a space will be added after the end of the last substitution. If there is more text in the sequence however then a space will not be generated. This allows the @code{%*} substitution to be used as part of a larger string. For example, a spec string like this: @smallexample %@{mcu=*:--script=%*/memory.ld@} @end smallexample when matching an option like @code{-mcu=newchip} will produce: @smallexample --script=newchip/memory.ld @end smallexample @item %@{.@code{S}:@code{X}@} Substitutes @code{X}, if processing a file with suffix @code{S}. @item %@{!.@code{S}:@code{X}@} Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. @item %@{,@code{S}:@code{X}@} Substitutes @code{X}, if processing a file for language @code{S}. @item %@{!,@code{S}:@code{X}@} Substitutes @code{X}, if not processing a file for language @code{S}. @item %@{@code{S}|@code{P}:@code{X}@} Substitutes @code{X} if either @code{-S} or @code{-P} is given to GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and @code{*} sequences as well, although they have a stronger binding than the @samp{|}. If @code{%*} appears in @code{X}, all of the alternatives must be starred, and only the first matching alternative is substituted. For example, a spec string like this: @smallexample %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} @end smallexample @noindent outputs the following command-line options from the following input command-line options: @smallexample fred.c -foo -baz jim.d -bar -boggle -d fred.c -foo -baz -boggle -d jim.d -bar -baz -boggle @end smallexample @item %@{S:X; T:Y; :D@} If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can be as many clauses as you need. This may be combined with @code{.}, @code{,}, @code{!}, @code{|}, and @code{*} as needed. @end table The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar construct may contain other nested @samp{%} constructs or spaces, or even newlines. They are processed as usual, as described above. Trailing white space in @code{X} is ignored. White space may also appear anywhere on the left side of the colon in these constructs, except between @code{.} or @code{*} and the corresponding word. The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are handled specifically in these constructs. If another value of @option{-O} or the negated form of a @option{-f}, @option{-m}, or @option{-W} switch is found later in the command line, the earlier switch value is ignored, except with @{@code{S}*@} where @code{S} is just one letter, which passes all matching options. The character @samp{|} at the beginning of the predicate text is used to indicate that a command should be piped to the following command, but only if @option{-pipe} is specified. It is built into GCC which switches take arguments and which do not. (You might think it would be useful to generalize this to allow each compiler's spec to say which switches take arguments. But this cannot be done in a consistent fashion. GCC cannot even decide which input files have been specified without knowing which switches take arguments, and it must know which input files to compile in order to tell which compilers to run). GCC also knows implicitly that arguments starting in @option{-l} are to be treated as compiler output files, and passed to the linker in their proper position among the other output files. @c man begin OPTIONS @node Target Options @section Specifying Target Machine and Compiler Version @cindex target options @cindex cross compiling @cindex specifying machine version @cindex specifying compiler version and target machine @cindex compiler version, specifying @cindex target machine, specifying The usual way to run GCC is to run the executable called @command{gcc}, or @command{@var{machine}-gcc} when cross-compiling, or @command{@var{machine}-gcc-@var{version}} to run a version other than the one that was installed last. @node Submodel Options @section Hardware Models and Configurations @cindex submodel options @cindex specifying hardware config @cindex hardware models and configurations, specifying @cindex machine dependent options Each target machine types can have its own special options, starting with @samp{-m}, to choose among various hardware models or configurations---for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified. Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform. @c This list is ordered alphanumerically by subsection name. @c It should be the same order and spelling as these options are listed @c in Machine Dependent Options @menu * AArch64 Options:: * Adapteva Epiphany Options:: * ARC Options:: * ARM Options:: * AVR Options:: * Blackfin Options:: * C6X Options:: * CRIS Options:: * CR16 Options:: * Darwin Options:: * DEC Alpha Options:: * FR30 Options:: * FRV Options:: * GNU/Linux Options:: * H8/300 Options:: * HPPA Options:: * i386 and x86-64 Options:: * i386 and x86-64 Windows Options:: * IA-64 Options:: * LM32 Options:: * M32C Options:: * M32R/D Options:: * M680x0 Options:: * MCore Options:: * MeP Options:: * MicroBlaze Options:: * MIPS Options:: * MMIX Options:: * MN10300 Options:: * Moxie Options:: * MSP430 Options:: * NDS32 Options:: * Nios II Options:: * PDP-11 Options:: * picoChip Options:: * PowerPC Options:: * RL78 Options:: * RS/6000 and PowerPC Options:: * RX Options:: * S/390 and zSeries Options:: * Score Options:: * SH Options:: * Solaris 2 Options:: * SPARC Options:: * SPU Options:: * System V Options:: * TILE-Gx Options:: * TILEPro Options:: * V850 Options:: * VAX Options:: * VMS Options:: * VxWorks Options:: * x86-64 Options:: * Xstormy16 Options:: * Xtensa Options:: * zSeries Options:: @end menu @node AArch64 Options @subsection AArch64 Options @cindex AArch64 Options These options are defined for AArch64 implementations: @table @gcctabopt @item -mabi=@var{name} @opindex mabi Generate code for the specified data model. Permissible values are @samp{ilp32} for SysV-like data model where int, long int and pointer are 32-bit, and @samp{lp64} for SysV-like data model where int is 32-bit, but long int and pointer are 64-bit. The default depends on the specific target configuration. Note that the LP64 and ILP32 ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries. @item -mbig-endian @opindex mbig-endian Generate big-endian code. This is the default when GCC is configured for an @samp{aarch64_be-*-*} target. @item -mgeneral-regs-only @opindex mgeneral-regs-only Generate code which uses only the general registers. @item -mlittle-endian @opindex mlittle-endian Generate little-endian code. This is the default when GCC is configured for an @samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. @item -mcmodel=tiny @opindex mcmodel=tiny Generate code for the tiny code model. The program and its statically defined symbols must be within 1GB of each other. Pointers are 64 bits. Programs can be statically or dynamically linked. This model is not fully implemented and mostly treated as @samp{small}. @item -mcmodel=small @opindex mcmodel=small Generate code for the small code model. The program and its statically defined symbols must be within 4GB of each other. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model. @item -mcmodel=large @opindex mcmodel=large Generate code for the large code model. This makes no assumptions about addresses and sizes of sections. Pointers are 64 bits. Programs can be statically linked only. @item -mstrict-align @opindex mstrict-align Do not assume that unaligned memory references will be handled by the system. @item -momit-leaf-frame-pointer @itemx -mno-omit-leaf-frame-pointer @opindex momit-leaf-frame-pointer @opindex mno-omit-leaf-frame-pointer Omit or keep the frame pointer in leaf functions. The former behaviour is the default. @item -mtls-dialect=desc @opindex mtls-dialect=desc Use TLS descriptors as the thread-local storage mechanism for dynamic accesses of TLS variables. This is the default. @item -mtls-dialect=traditional @opindex mtls-dialect=traditional Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS variables. @item -mfix-cortex-a53-835769 @itemx -mno-fix-cortex-a53-835769 @opindex -mfix-cortex-a53-835769 @opindex -mno-fix-cortex-a53-835769 Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. This will involve inserting a NOP instruction between memory instructions and 64-bit integer multiply-accumulate instructions. @item -march=@var{name} @opindex march Specify the name of the target architecture, optionally suffixed by one or more feature modifiers. This option has the form @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the only permissible value for @var{arch} is @samp{armv8-a}. The permissible values for @var{feature} are documented in the sub-section below. Where conflicting feature modifiers are specified, the right-most feature is used. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Where @option{-march} is specified without either of @option{-mtune} or @option{-mcpu} also being specified, the code will be tuned to perform well across a range of target processors implementing the target architecture. @item -mtune=@var{name} @opindex mtune Specify the name of the target processor for which GCC should tune the performance of the code. Permissible values for this option are: @samp{generic}, @samp{cortex-a53}, @samp{cortex-a57}, @samp{thunderx}. Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. The only permissible value is @samp{cortex-a57.cortex-a53}. Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=} are specified, the code will be tuned to perform well across a range of target processors. This option cannot be suffixed by feature modifiers. @item -mcpu=@var{name} @opindex mcpu Specify the name of the target processor, optionally suffixed by one or more feature modifiers. This option has the form @option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the permissible values for @var{cpu} are the same as those available for @option{-mtune}. The permissible values for @var{feature} are documented in the sub-section below. Where conflicting feature modifiers are specified, the right-most feature is used. GCC uses this name to determine what kind of instructions it can emit when generating assembly code (as if by @option{-march}) and to determine the target processor for which to tune for performance (as if by @option{-mtune}). Where this option is used in conjunction with @option{-march} or @option{-mtune}, those options take precedence over the appropriate part of this option. @end table @subsubsection @option{-march} and @option{-mcpu} feature modifiers @cindex @option{-march} feature modifiers @cindex @option{-mcpu} feature modifiers Feature modifiers used with @option{-march} and @option{-mcpu} can be one the following: @table @samp @item crc Enable CRC extension. @item crypto Enable Crypto extension. This implies Advanced SIMD is enabled. @item fp Enable floating-point instructions. @item simd Enable Advanced SIMD instructions. This implies floating-point instructions are enabled. This is the default for all current possible values for options @option{-march} and @option{-mcpu=}. @end table @node Adapteva Epiphany Options @subsection Adapteva Epiphany Options These @samp{-m} options are defined for Adapteva Epiphany: @table @gcctabopt @item -mhalf-reg-file @opindex mhalf-reg-file Don't allocate any register in the range @code{r32}@dots{}@code{r63}. That allows code to run on hardware variants that lack these registers. @item -mprefer-short-insn-regs @opindex mprefer-short-insn-regs Preferrentially allocate registers that allow short instruction generation. This can result in increased instruction count, so this may either reduce or increase overall code size. @item -mbranch-cost=@var{num} @opindex mbranch-cost Set the cost of branches to roughly @var{num} ``simple'' instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. @item -mcmove @opindex mcmove Enable the generation of conditional moves. @item -mnops=@var{num} @opindex mnops Emit @var{num} NOPs before every other generated instruction. @item -mno-soft-cmpsf @opindex mno-soft-cmpsf For single-precision floating-point comparisons, emit an @code{fsub} instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, software comparisons. @item -mstack-offset=@var{num} @opindex mstack-offset Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} can be used by leaf functions without stack allocation. Values other than @samp{8} or @samp{16} are untested and unlikely to work. Note also that this option changes the ABI; compiling a program with a different stack offset than the libraries have been compiled with generally does not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different stack offset to build working programs, it is recommended to configure the toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. @item -mno-round-nearest @opindex mno-round-nearest Make the scheduler assume that the rounding mode has been set to truncating. The default is @option{-mround-nearest}. @item -mlong-calls @opindex mlong-calls If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the @code{b} / @code{bl} instructions, and therefore load the function address into a register before performing a (otherwise direct) call. This is the default. @item -mshort-calls @opindex short-calls If not otherwise specified by an attribute, assume all direct calls are in the range of the @code{b} / @code{bl} instructions, so use these instructions for direct calls. The default is @option{-mlong-calls}. @item -msmall16 @opindex msmall16 Assume addresses can be loaded as 16-bit unsigned values. This does not apply to function addresses for which @option{-mlong-calls} semantics are in effect. @item -mfp-mode=@var{mode} @opindex mfp-mode Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches. @var{mode} can be set to one the following values: @table @samp @item caller Any mode at function entry is valid, and retained or restored when the function returns, and when it calls other functions. This mode is useful for compiling libraries or other compilation units you might want to incorporate into different programs with different prevailing FPU modes, and the convenience of being able to use a single object file outweighs the size and speed overhead for any extra mode switching that might be needed, compared with what would be needed with a more specific choice of prevailing FPU mode. @item truncate This is the mode used for floating-point calculations with truncating (i.e.@: round towards zero) rounding mode. That includes conversion from floating point to integer. @item round-nearest This is the mode used for floating-point calculations with round-to-nearest-or-even rounding mode. @item int This is the mode used to perform integer calculations in the FPU, e.g.@: integer multiply, or integer multiply-and-accumulate. @end table The default is @option{-mfp-mode=caller} @item -mnosplit-lohi @itemx -mno-postinc @itemx -mno-postmodify @opindex mnosplit-lohi @opindex mno-postinc @opindex mno-postmodify Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are @option{msplit-lohi}, @option{-mpost-inc}, and @option{-mpost-modify}. @item -mnovect-double @opindex mno-vect-double Change the preferred SIMD mode to SImode. The default is @option{-mvect-double}, which uses DImode as preferred SIMD mode. @item -max-vect-align=@var{num} @opindex max-vect-align The maximum alignment for SIMD vector mode types. @var{num} may be 4 or 8. The default is 8. Note that this is an ABI change, even though many library function interfaces are unaffected if they don't use SIMD vector modes in places that affect size and/or alignment of relevant types. @item -msplit-vecmove-early @opindex msplit-vecmove-early Split vector moves into single word moves before reload. In theory this can give better register allocation, but so far the reverse seems to be generally the case. @item -m1reg-@var{reg} @opindex m1reg- Specify a register to hold the constant @minus{}1, which makes loading small negative constants and certain bitmasks faster. Allowable values for @var{reg} are @samp{r43} and @samp{r63}, which specify use of that register as a fixed register, and @samp{none}, which means that no register is used for this purpose. The default is @option{-m1reg-none}. @end table @node ARC Options @subsection ARC Options @cindex ARC options The following options control the architecture variant for which code is being compiled: @c architecture variants @table @gcctabopt @item -mbarrel-shifter @opindex mbarrel-shifter Generate instructions supported by barrel shifter. This is the default unless @samp{-mcpu=ARC601} is in effect. @item -mcpu=@var{cpu} @opindex mcpu Set architecture type, register usage, and instruction scheduling parameters for @var{cpu}. There are also shortcut alias options available for backward compatibility and convenience. Supported values for @var{cpu} are @table @samp @opindex mA6 @opindex mARC600 @item ARC600 Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}. @item ARC601 @opindex mARC601 Compile for ARC601. Alias: @option{-mARC601}. @item ARC700 @opindex mA7 @opindex mARC700 Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}. This is the default when configured with @samp{--with-cpu=arc700}@. @end table @item -mdpfp @opindex mdpfp @itemx -mdpfp-compact @opindex mdpfp-compact FPX: Generate Double Precision FPX instructions, tuned for the compact implementation. @item -mdpfp-fast @opindex mdpfp-fast FPX: Generate Double Precision FPX instructions, tuned for the fast implementation. @item -mno-dpfp-lrsr @opindex mno-dpfp-lrsr Disable LR and SR instructions from using FPX extension aux registers. @item -mea @opindex mea Generate Extended arithmetic instructions. Currently only @code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are supported. This is always enabled for @samp{-mcpu=ARC700}. @item -mno-mpy @opindex mno-mpy Do not generate mpy instructions for ARC700. @item -mmul32x16 @opindex mmul32x16 Generate 32x16 bit multiply and mac instructions. @item -mmul64 @opindex mmul64 Generate mul64 and mulu64 instructions. Only valid for @samp{-mcpu=ARC600}. @item -mnorm @opindex mnorm Generate norm instruction. This is the default if @samp{-mcpu=ARC700} is in effect. @item -mspfp @opindex mspfp @itemx -mspfp-compact @opindex mspfp-compact FPX: Generate Single Precision FPX instructions, tuned for the compact implementation. @item -mspfp-fast @opindex mspfp-fast FPX: Generate Single Precision FPX instructions, tuned for the fast implementation. @item -msimd @opindex msimd Enable generation of ARC SIMD instructions via target-specific builtins. Only valid for @samp{-mcpu=ARC700}. @item -msoft-float @opindex msoft-float This option ignored; it is provided for compatibility purposes only. Software floating point code is emitted by default, and this default can overridden by FPX options; @samp{mspfp}, @samp{mspfp-compact}, or @samp{mspfp-fast} for single precision, and @samp{mdpfp}, @samp{mdpfp-compact}, or @samp{mdpfp-fast} for double precision. @item -mswap @opindex mswap Generate swap instructions. @end table The following options are passed through to the assembler, and also define preprocessor macro symbols. @c Flags used by the assembler, but for which we define preprocessor @c macro symbols as well. @table @gcctabopt @item -mdsp-packa @opindex mdsp-packa Passed down to the assembler to enable the DSP Pack A extensions. Also sets the preprocessor symbol @code{__Xdsp_packa}. @item -mdvbf @opindex mdvbf Passed down to the assembler to enable the dual viterbi butterfly extension. Also sets the preprocessor symbol @code{__Xdvbf}. @c ARC700 4.10 extension instruction @item -mlock @opindex mlock Passed down to the assembler to enable the Locked Load/Store Conditional extension. Also sets the preprocessor symbol @code{__Xlock}. @item -mmac-d16 @opindex mmac-d16 Passed down to the assembler. Also sets the preprocessor symbol @code{__Xxmac_d16}. @item -mmac-24 @opindex mmac-24 Passed down to the assembler. Also sets the preprocessor symbol @code{__Xxmac_24}. @c ARC700 4.10 extension instruction @item -mrtsc @opindex mrtsc Passed down to the assembler to enable the 64-bit Time-Stamp Counter extension instruction. Also sets the preprocessor symbol @code{__Xrtsc}. @c ARC700 4.10 extension instruction @item -mswape @opindex mswape Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol @code{__Xswape}. @item -mtelephony @opindex mtelephony Passed down to the assembler to enable dual and single operand instructions for telephony. Also sets the preprocessor symbol @code{__Xtelephony}. @item -mxy @opindex mxy Passed down to the assembler to enable the XY Memory extension. Also sets the preprocessor symbol @code{__Xxy}. @end table The following options control how the assembly code is annotated: @c Assembly annotation options @table @gcctabopt @item -misize @opindex misize Annotate assembler instructions with estimated addresses. @item -mannotate-align @opindex mannotate-align Explain what alignment considerations lead to the decision to make an instruction short or long. @end table The following options are passed through to the linker: @c options passed through to the linker @table @gcctabopt @item -marclinux @opindex marclinux Passed through to the linker, to specify use of the @code{arclinux} emulation. This option is enabled by default in tool chains built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets when profiling is not requested. @item -marclinux_prof @opindex marclinux_prof Passed through to the linker, to specify use of the @code{arclinux_prof} emulation. This option is enabled by default in tool chains built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets when profiling is requested. @end table The following options control the semantics of generated code: @c semantically relevant code generation options @table @gcctabopt @item -mepilogue-cfi @opindex mepilogue-cfi Enable generation of call frame information for epilogues. @item -mno-epilogue-cfi @opindex mno-epilogue-cfi Disable generation of call frame information for epilogues. @item -mlong-calls @opindex mlong-calls Generate call insns as register indirect calls, thus providing access to the full 32-bit address range. @item -mmedium-calls @opindex mmedium-calls Don't use less than 25 bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, to allow use of the 25-bit range, rather than the 21-bit range with conditional branch-and-link. This is the default for tool chains built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets. @item -mno-sdata @opindex mno-sdata Do not generate sdata references. This is the default for tool chains built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets. @item -mucb-mcount @opindex mucb-mcount Instrument with mcount calls as used in UCB code. I.e. do the counting in the callee, not the caller. By default ARC instrumentation counts in the caller. @item -mvolatile-cache @opindex mvolatile-cache Use ordinarily cached memory accesses for volatile references. This is the default. @item -mno-volatile-cache @opindex mno-volatile-cache Enable cache bypass for volatile references. @end table The following options fine tune code generation: @c code generation tuning options @table @gcctabopt @item -malign-call @opindex malign-call Do alignment optimizations for call instructions. @item -mauto-modify-reg @opindex mauto-modify-reg Enable the use of pre/post modify with register displacement. @item -mbbit-peephole @opindex mbbit-peephole Enable bbit peephole2. @item -mno-brcc @opindex mno-brcc This option disables a target-specific pass in @file{arc_reorg} to generate @code{BRcc} instructions. It has no effect on @code{BRcc} generation driven by the combiner pass. @item -mcase-vector-pcrel @opindex mcase-vector-pcrel Use pc-relative switch case tables - this enables case table shortening. This is the default for @option{-Os}. @item -mcompact-casesi @opindex mcompact-casesi Enable compact casesi pattern. This is the default for @option{-Os}. @item -mno-cond-exec @opindex mno-cond-exec Disable ARCompact specific pass to generate conditional execution instructions. Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find more conditional execution generating opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using @option{-mmedium-calls} instead. @item -mearly-cbranchsi @opindex mearly-cbranchsi Enable pre-reload use of the cbranchsi pattern. @item -mexpand-adddi @opindex mexpand-adddi Expand @code{adddi3} and @code{subdi3} at rtl generation time into @code{add.f}, @code{adc} etc. @item -mindexed-loads @opindex mindexed-loads Enable the use of indexed loads. This can be problematic because some optimizers will then assume the that indexed stores exist, which is not the case. @item -mlra @opindex mlra Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. @samp{-mno-lra}). @item -mlra-priority-none @opindex mlra-priority-none Don't indicate any priority for target registers. @item -mlra-priority-compact @opindex mlra-priority-compact Indicate target register priority for r0..r3 / r12..r15. @item -mlra-priority-noncompact @opindex mlra-priority-noncompact Reduce target regsiter priority for r0..r3 / r12..r15. @item -mno-millicode @opindex mno-millicode When optimizing for size (using @option{-Os}), prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this is referred to as a @emph{millicode} call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn off millicode call generation. @item -mmixed-code @opindex mmixed-code Tweak register allocation to help 16-bit instruction generation. This generally has the effect of decreasing the average instruction size while increasing the instruction count. @item -mq-class @opindex mq-class Enable 'q' instruction alternatives. This is the default for @option{-Os}. @item -mRcq @opindex mRcq Enable Rcq constraint handling - most short code generation depends on this. This is the default. @item -mRcw @opindex mRcw Enable Rcw constraint handling - ccfsm condexec mostly depends on this. This is the default. @item -msize-level=@var{level} @opindex msize-level Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for @var{level} are: @table @samp @item 0 No size optimization. This level is deprecated and treated like @samp{1}. @item 1 Short instructions are used opportunistically. @item 2 In addition, alignment of loops and of code after barriers are dropped. @item 3 In addition, optional data alignment is dropped, and the option @option{Os} is enabled. @end table This defaults to @samp{3} when @option{-Os} is in effect. Otherwise, the behavior when this is not set is equivalent to level @samp{1}. @item -mtune=@var{cpu} @opindex mtune Set instruction scheduling parameters for @var{cpu}, overriding any implied by @option{-mcpu=}. Supported values for @var{cpu} are @table @samp @item ARC600 Tune for ARC600 cpu. @item ARC601 Tune for ARC601 cpu. @item ARC700 Tune for ARC700 cpu with standard multiplier block. @item ARC700-xmac Tune for ARC700 cpu with XMAC block. @item ARC725D Tune for ARC725D cpu. @item ARC750D Tune for ARC750D cpu. @end table @item -mmultcost=@var{num} @opindex mmultcost Cost to assume for a multiply instruction, with @samp{4} being equal to a normal instruction. @item -munalign-prob-threshold=@var{probability} @opindex munalign-prob-threshold Set probability threshold for unaligning branches. When tuning for @samp{ARC700} and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless profiling indicates that the probability for the branch to be taken is below @var{probability}. @xref{Cross-profiling}. The default is (REG_BR_PROB_BASE/2), i.e.@: 5000. @end table The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release: @c Deprecated options @table @gcctabopt @item -margonaut @opindex margonaut Obsolete FPX. @item -mbig-endian @opindex mbig-endian @itemx -EB @opindex EB Compile code for big endian targets. Use of these options is now deprecated. Users wanting big-endian code, should use the @w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets when building the tool chain, for which big-endian is the default. @item -mlittle-endian @opindex mlittle-endian @itemx -EL @opindex EL Compile code for little endian targets. Use of these options is now deprecated. Users wanting little-endian code should use the @w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets when building the tool chain, for which little-endian is the default. @item -mbarrel_shifter @opindex mbarrel_shifter Replaced by @samp{-mbarrel-shifter} @item -mdpfp_compact @opindex mdpfp_compact Replaced by @samp{-mdpfp-compact} @item -mdpfp_fast @opindex mdpfp_fast Replaced by @samp{-mdpfp-fast} @item -mdsp_packa @opindex mdsp_packa Replaced by @samp{-mdsp-packa} @item -mEA @opindex mEA Replaced by @samp{-mea} @item -mmac_24 @opindex mmac_24 Replaced by @samp{-mmac-24} @item -mmac_d16 @opindex mmac_d16 Replaced by @samp{-mmac-d16} @item -mspfp_compact @opindex mspfp_compact Replaced by @samp{-mspfp-compact} @item -mspfp_fast @opindex mspfp_fast Replaced by @samp{-mspfp-fast} @item -mtune=@var{cpu} @opindex mtune Values @samp{arc600}, @samp{arc601}, @samp{arc700} and @samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600}, @samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively @item -multcost=@var{num} @opindex multcost Replaced by @samp{-mmultcost}. @end table @node ARM Options @subsection ARM Options @cindex ARM options These @samp{-m} options are defined for Advanced RISC Machines (ARM) architectures: @table @gcctabopt @item -mabi=@var{name} @opindex mabi Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. @item -mapcs-frame @opindex mapcs-frame Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying @option{-fomit-frame-pointer} with this option causes the stack frames not to be generated for leaf functions. The default is @option{-mno-apcs-frame}. @item -mapcs @opindex mapcs This is a synonym for @option{-mapcs-frame}. @ignore @c not currently implemented @item -mapcs-stack-check @opindex mapcs-stack-check Generate code to check the amount of stack space available upon entry to every function (that actually uses some stack space). If there is insufficient space available then either the function @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} is called, depending upon the amount of stack space required. The runtime system is required to provide these functions. The default is @option{-mno-apcs-stack-check}, since this produces smaller code. @c not currently implemented @item -mapcs-float @opindex mapcs-float Pass floating-point arguments using the floating-point registers. This is one of the variants of the APCS@. This option is recommended if the target hardware has a floating-point unit or if a lot of floating-point arithmetic is going to be performed by the code. The default is @option{-mno-apcs-float}, since the size of integer-only code is slightly increased if @option{-mapcs-float} is used. @c not currently implemented @item -mapcs-reentrant @opindex mapcs-reentrant Generate reentrant, position-independent code. The default is @option{-mno-apcs-reentrant}. @end ignore @item -mthumb-interwork @opindex mthumb-interwork Generate code that supports calling between the ARM and Thumb instruction sets. Without this option, on pre-v5 architectures, the two instruction sets cannot be reliably used inside one program. The default is @option{-mno-thumb-interwork}, since slightly larger code is generated when @option{-mthumb-interwork} is specified. In AAPCS configurations this option is meaningless. @item -mno-sched-prolog @opindex mno-sched-prolog Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the function's body. This means that all functions start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an executable piece of code. The default is @option{-msched-prolog}. @item -mfloat-abi=@var{name} @opindex mfloat-abi Specifies which floating-point ABI to use. Permissible values are: @samp{soft}, @samp{softfp} and @samp{hard}. Specifying @samp{soft} causes GCC to generate output containing library calls for floating-point operations. @samp{softfp} allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. @samp{hard} allows generation of floating-point instructions and uses FPU-specific calling conventions. The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries. @item -mlittle-endian @opindex mlittle-endian Generate code for a processor running in little-endian mode. This is the default for all standard configurations. @item -mbig-endian @opindex mbig-endian Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor. @item -march=@var{name} @opindex march This specifies the name of the target ARM architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te}, @samp{armv6}, @samp{armv6j}, @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m}, @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7e-m}, @samp{armv7ve}, @samp{armv8-a}, @samp{armv8-a+crc}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}. @option{-march=armv7ve} is the armv7-a architecture with virtualization extensions. @option{-march=armv8-a+crc} enables code generation for the ARMv8-A architecture together with the optional CRC32 extensions. @option{-march=native} causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. @item -mtune=@var{name} @opindex mtune This option specifies the name of the target ARM processor for which GCC should tune the performance of the code. For some ARM implementations better performance can be obtained by using this option. Permissible names are: @samp{arm2}, @samp{arm250}, @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, @samp{arm720}, @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s}, @samp{arm710t}, @samp{arm720t}, @samp{arm740t}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, @samp{strongarm1110}, @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s}, @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a53}, @samp{cortex-a57}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-m7}, @samp{cortex-m4}, @samp{cortex-m3}, @samp{cortex-m1}, @samp{cortex-m0}, @samp{cortex-m0plus}, @samp{cortex-m1.small-multiply}, @samp{cortex-m0.small-multiply}, @samp{cortex-m0plus.small-multiply}, @samp{marvell-pj4}, @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, @samp{fa526}, @samp{fa626}, @samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}. Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible names are: @samp{cortex-a15.cortex-a7}, @samp{cortex-a57.cortex-a53}. @option{-mtune=generic-@var{arch}} specifies that GCC should tune the performance for a blend of processors within architecture @var{arch}. The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC versions as CPU models come and go. @option{-mtune=native} causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. @item -mcpu=@var{name} @opindex mcpu This specifies the name of the target ARM processor. GCC uses this name to derive the name of the target ARM architecture (as if specified by @option{-march}) and the ARM processor type for which to tune for performance (as if specified by @option{-mtune}). Where this option is used in conjunction with @option{-march} or @option{-mtune}, those options take precedence over the appropriate part of this option. Permissible names for this option are the same as those for @option{-mtune}. @option{-mcpu=generic-@var{arch}} is also permissible, and is equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. See @option{-mtune} for more information. @option{-mcpu=native} causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. @item -mfpu=@var{name} @opindex mfpu This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, @samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, @samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, @samp{fpv5-d16}, @samp{fpv5-sp-d16}, @samp{fp-armv8}, @samp{neon-fp-armv8}, and @samp{crypto-neon-fp-armv8}. If @option{-msoft-float} is specified this specifies the format of floating-point values. If the selected floating-point hardware includes the NEON extension (e.g. @option{-mfpu}=@samp{neon}), note that floating-point operations are not generated by GCC's auto-vectorization pass unless @option{-funsafe-math-optimizations} is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of NEON instructions may lead to a loss of precision. @item -mfp16-format=@var{name} @opindex mfp16-format Specify the format of the @code{__fp16} half-precision floating-point type. Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; the default is @samp{none}, in which case the @code{__fp16} type is not defined. @xref{Half-Precision}, for more information. @item -mstructure-size-boundary=@var{n} @opindex mstructure-size-boundary The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different toolchains. For the COFF targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying ABI supports it. Specifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions. @item -mabort-on-noreturn @opindex mabort-on-noreturn Generate a call to the function @code{abort} at the end of a @code{noreturn} function. It is executed if the function tries to return. @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 64-megabyte addressing range of the offset-based version of subroutine call instruction. Even if this switch is enabled, not all function calls are turned into long calls. The heuristic is that static functions, functions that have the @samp{short-call} attribute, functions that are inside the scope of a @samp{#pragma no_long_calls} directive, and functions whose definitions have already been compiled within the current compilation unit are not turned into long calls. The exceptions to this rule are that weak function definitions, functions with the @samp{long-call} attribute or the @samp{section} attribute, and functions that are within the scope of a @samp{#pragma long_calls} directive are always turned into long calls. This feature is not enabled by default. Specifying @option{-mno-long-calls} restores the default behavior, as does placing the function calls within the scope of a @samp{#pragma long_calls_off} directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. @item -msingle-pic-base @opindex msingle-pic-base Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. @item -mpic-register=@var{reg} @opindex mpic-register Specify the register to be used for PIC addressing. For standard PIC base case, the default will be any suitable register determined by compiler. For single PIC base case, the default is @samp{R9} if target is EABI based or stack-checking is enabled, otherwise the default is @samp{R10}. @item -mpic-data-is-text-relative @opindex mpic-data-is-text-relative Assume that each data segments are relative to text segment at load time. Therefore, it permits addressing data using PC-relative operations. This option is on by default for targets other than VxWorks RTP. @item -mpoke-function-name @opindex mpoke-function-name Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this: @smallexample t0 .ascii "arm_poke_function_name", 0 .align t1 .word 0xff000000 + (t1 - t0) arm_poke_function_name mov ip, sp stmfd sp!, @{fp, ip, lr, pc@} sub fp, ip, #4 @end smallexample When performing a stack backtrace, code can inspect the value of @code{pc} stored at @code{fp + 0}. If the trace function then looks at location @code{pc - 12} and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length @code{((pc[-3]) & 0xff000000)}. @item -mthumb @itemx -marm @opindex marm @opindex mthumb Select between generating code that executes in ARM and Thumb states. The default for most configurations is to generate code that executes in ARM state, but the default can be changed by configuring GCC with the @option{--with-mode=}@var{state} configure option. @item -mtpcs-frame @opindex mtpcs-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is @option{-mno-tpcs-frame}. @item -mtpcs-leaf-frame @opindex mtpcs-leaf-frame Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. @item -mcallee-super-interworking @opindex mcallee-super-interworking Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. This option is not valid in AAPCS configurations because interworking is enabled by default. @item -mcaller-super-interworking @opindex mcaller-super-interworking Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in AAPCS configurations because interworking is enabled by default. @item -mtp=@var{name} @opindex mtp Specify the access model for the thread local storage pointer. The valid models are @option{soft}, which generates calls to @code{__aeabi_read_tp}, @option{cp15}, which fetches the thread pointer from @code{cp15} directly (supported in the arm6k architecture), and @option{auto}, which uses the best available method for the selected processor. The default setting is @option{auto}. @item -mtls-dialect=@var{dialect} @opindex mtls-dialect Specify the dialect to use for accessing thread local storage. Two @var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The @samp{gnu} dialect selects the original GNU scheme for supporting local and global dynamic TLS models. The @samp{gnu2} dialect selects the GNU descriptor scheme, which provides better performance for shared libraries. The GNU descriptor scheme is compatible with the original scheme, but does require new assembler, linker and library support. Initial and local exec TLS models are unaffected by this option and always use the original scheme. @item -mword-relocations @opindex mword-relocations Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} is specified. @item -mfix-cortex-m3-ldrd @opindex mfix-cortex-m3-ldrd Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This option is enabled by default when @option{-mcpu=cortex-m3} is specified. @item -munaligned-access @itemx -mno-unaligned-access @opindex munaligned-access @opindex mno-unaligned-access Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is disabled for all pre-ARMv6 and all ARMv6-M architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures will be accessed a byte at a time. The ARM attribute @code{Tag_CPU_unaligned_access} will be set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} will also be defined. @item -mneon-for-64bits @opindex mneon-for-64bits Enables using Neon to handle scalar 64-bits operations. This is disabled by default since the cost of moving data from core registers to Neon is high. @item -mslow-flash-data @opindex mslow-flash-data Assume loading data from flash is slower than fetching instruction. Therefore literal load is minimized for better performance. This option is only supported when compiling for ARMv7 M-profile and off by default. @item -masm-syntax-unified @opindex masm-syntax-unified Assume inline assembler is using unified asm syntax. The default is currently off which implies divided syntax. Currently this option is available only for Thumb1 and has no effect on ARM state and Thumb2. However, this may change in future releases of GCC. Divided syntax should be considered deprecated. @item -mrestrict-it @opindex mrestrict-it Restricts generation of IT blocks to conform to the rules of ARMv8. IT blocks can only contain a single 16-bit instruction from a select set of instructions. This option is on by default for ARMv8 Thumb mode. @end table @node AVR Options @subsection AVR Options @cindex AVR Options These options are defined for AVR implementations: @table @gcctabopt @item -mmcu=@var{mcu} @opindex mmcu Specify Atmel AVR instruction set architectures (ISA) or MCU type. The default for this option is@tie{}@code{avr2}. GCC supports the following AVR devices and ISAs: @include avr-mmcu.texi @item -maccumulate-args @opindex maccumulate-args Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments are pushed before calling a function and popped afterwards. Popping the arguments after the function call can be expensive on AVR so that accumulating the stack space might lead to smaller executables because arguments need not to be removed from the stack after such a function call. This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions. @item -mbranch-cost=@var{cost} @opindex mbranch-cost Set the branch costs for conditional branch instructions to @var{cost}. Reasonable values for @var{cost} are small, non-negative integers. The default branch cost is 0. @item -mcall-prologues @opindex mcall-prologues Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller. @item -mint8 @opindex mint8 Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a @code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, and @code{long long} is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size. @item -mno-interrupts @opindex mno-interrupts Generated code is not compatible with hardware interrupts. Code size is smaller. @item -mrelax @opindex mrelax Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter @code{RCALL} resp.@: @code{RJMP} instruction if applicable. Setting @code{-mrelax} just adds the @code{--relax} option to the linker command line when the linker is called. Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code. Relaxing must be turned on if linker stubs are needed, see the section on @code{EIND} and linker stubs below. @item -msp8 @opindex msp8 Treat the stack pointer register as an 8-bit register, i.e.@: assume the high byte of the stack pointer is zero. In general, you don't need to set this option by hand. This option is used internally by the compiler to select and build multilibs for architectures @code{avr2} and @code{avr25}. These architectures mix devices with and without @code{SPH}. For any setting other than @code{-mmcu=avr2} or @code{-mmcu=avr25} the compiler driver will add or remove this option from the compiler proper's command line, because the compiler then knows if the device or architecture has an 8-bit stack pointer and thus no @code{SPH} register or not. @item -mstrict-X @opindex mstrict-X Use address register @code{X} in a way proposed by the hardware. This means that @code{X} is only used in indirect, post-increment or pre-decrement addressing. Without this option, the @code{X} register may be used in the same way as @code{Y} or @code{Z} which then is emulated by additional instructions. For example, loading a value with @code{X+const} addressing with a small non-negative @code{const < 64} to a register @var{Rn} is performed as @example adiw r26, const ; X += const ld @var{Rn}, X ; @var{Rn} = *X sbiw r26, const ; X -= const @end example @item -mtiny-stack @opindex mtiny-stack Only change the lower 8@tie{}bits of the stack pointer. @item -Waddr-space-convert @opindex Waddr-space-convert Warn about conversions between address spaces in the case where the resulting address space is not contained in the incoming address space. @end table @subsubsection @code{EIND} and Devices with more than 128 Ki Bytes of Flash @cindex @code{EIND} Pointers in the implementation are 16@tie{}bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64@tie{}Ki words. In order to facilitate indirect jump on devices with more than 128@tie{}Ki bytes of program memory space, there is a special function register called @code{EIND} that serves as most significant part of the target address when @code{EICALL} or @code{EIJMP} instructions are used. Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations: @itemize @bullet @item The compiler never sets @code{EIND}. @item The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP} instructions or might read @code{EIND} directly in order to emulate an indirect call/jump by means of a @code{RET} instruction. @item The compiler assumes that @code{EIND} never changes during the startup code or during the application. In particular, @code{EIND} is not saved/restored in function or interrupt service routine prologue/epilogue. @item For indirect calls to functions and computed goto, the linker generates @emph{stubs}. Stubs are jump pads sometimes also called @emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. The stub contains a direct jump to the desired address. @item Linker relaxation must be turned on so that the linker will generate the stubs correctly an all situaltion. See the compiler option @code{-mrelax} and the linler option @code{--relax}. There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message. @item The default linker script is arranged for code with @code{EIND = 0}. If code is supposed to work for a setup with @code{EIND != 0}, a custom linker script has to be used in order to place the sections whose name start with @code{.trampolines} into the segment where @code{EIND} points to. @item The startup code from libgcc never sets @code{EIND}. Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on @code{EIND}, see the @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}. @item It is legitimate for user-specific startup code to set up @code{EIND} early, for example by means of initialization code located in section @code{.init3}. Such code runs prior to general startup code that initializes RAM and calls constructors, but after the bit of startup code from AVR-LibC that sets @code{EIND} to the segment where the vector table is located. @example #include static void __attribute__((section(".init3"),naked,used,no_instrument_function)) init3_set_eind (void) @{ __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" "out %i0,r24" :: "n" (&EIND) : "r24","memory"); @} @end example @noindent The @code{__trampolines_start} symbol is defined in the linker script. @item Stubs are generated automatically by the linker if the following two conditions are met: @itemize @minus @item The address of a label is taken by means of the @code{gs} modifier (short for @emph{generate stubs}) like so: @example LDI r24, lo8(gs(@var{func})) LDI r25, hi8(gs(@var{func})) @end example @item The final location of that label is in a code segment @emph{outside} the segment where the stubs are located. @end itemize @item The compiler emits such @code{gs} modifiers for code labels in the following situations: @itemize @minus @item Taking address of a function or code label. @item Computed goto. @item If prologue-save function is used, see @option{-mcall-prologues} command-line option. @item Switch/case dispatch tables. If you do not want such dispatch tables you can specify the @option{-fno-jump-tables} command-line option. @item C and C++ constructors/destructors called during startup/shutdown. @item If the tools hit a @code{gs()} modifier explained above. @end itemize @item Jumping to non-symbolic addresses like so is @emph{not} supported: @example int main (void) @{ /* Call function at word address 0x2 */ return ((int(*)(void)) 0x2)(); @} @end example Instead, a stub has to be set up, i.e.@: the function has to be called through a symbol (@code{func_4} in the example): @example int main (void) @{ extern int func_4 (void); /* Call function at byte address 0x4 */ return func_4(); @} @end example and the application be linked with @code{-Wl,--defsym,func_4=0x4}. Alternatively, @code{func_4} can be defined in the linker script. @end itemize @subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers @cindex @code{RAMPD} @cindex @code{RAMPX} @cindex @code{RAMPY} @cindex @code{RAMPZ} Some AVR devices support memories larger than the 64@tie{}KiB range that can be accessed with 16-bit pointers. To access memory locations outside this 64@tie{}KiB range, the contentent of a @code{RAMP} register is used as high part of the address: The @code{X}, @code{Y}, @code{Z} address register is concatenated with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function register, respectively, to get a wide address. Similarly, @code{RAMPD} is used together with direct addressing. @itemize @item The startup code initializes the @code{RAMP} special function registers with zero. @item If a @ref{AVR Named Address Spaces,named address space} other than generic or @code{__flash} is used, then @code{RAMPZ} is set as needed before the operation. @item If the device supports RAM larger than 64@tie{}KiB and the compiler needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} is reset to zero after the operation. @item If the device comes with a specific @code{RAMP} register, the ISR prologue/epilogue saves/restores that SFR and initializes it with zero in case the ISR code might (implicitly) use it. @item RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets. If you use inline assembler to read from locations outside the 16-bit address range and change one of the @code{RAMP} registers, you must reset it to zero after the access. @end itemize @subsubsection AVR Built-in Macros GCC defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the @code{-mmcu=} command-line option. For even more AVR-specific built-in macros see @ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. @table @code @item __AVR_ARCH__ Build-in macro that resolves to a decimal number that identifies the architecture and depends on the @code{-mmcu=@var{mcu}} option. Possible values are: @code{2}, @code{25}, @code{3}, @code{31}, @code{35}, @code{4}, @code{5}, @code{51}, @code{6}, @code{102}, @code{104}, @code{105}, @code{106}, @code{107} for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31}, @code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6}, @code{avrxmega2}, @code{avrxmega4}, @code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively. If @var{mcu} specifies a device, this built-in macro is set accordingly. For example, with @code{-mmcu=atmega8} the macro will be defined to @code{4}. @item __AVR_@var{Device}__ Setting @code{-mmcu=@var{device}} defines this built-in macro which reflects the device's name. For example, @code{-mmcu=atmega8} defines the built-in macro @code{__AVR_ATmega8__}, @code{-mmcu=attiny261a} defines @code{__AVR_ATtiny261A__}, etc. The built-in macros' names follow the scheme @code{__AVR_@var{Device}__} where @var{Device} is the device name as from the AVR user manual. The difference between @var{Device} in the built-in macro and @var{device} in @code{-mmcu=@var{device}} is that the latter is always lowercase. If @var{device} is not a device but only a core architecture like @code{avr51}, this macro will not be defined. @item __AVR_DEVICE_NAME__ Setting @code{-mmcu=@var{device}} defines this built-in macro to the device's name. For example, with @code{-mmcu=atmega8} the macro will be defined to @code{atmega8}. If @var{device} is not a device but only a core architecture like @code{avr51}, this macro will not be defined. @item __AVR_XMEGA__ The device / architecture belongs to the XMEGA family of devices. @item __AVR_HAVE_ELPM__ The device has the the @code{ELPM} instruction. @item __AVR_HAVE_ELPMX__ The device has the @code{ELPM R@var{n},Z} and @code{ELPM R@var{n},Z+} instructions. @item __AVR_HAVE_MOVW__ The device has the @code{MOVW} instruction to perform 16-bit register-register moves. @item __AVR_HAVE_LPMX__ The device has the @code{LPM R@var{n},Z} and @code{LPM R@var{n},Z+} instructions. @item __AVR_HAVE_MUL__ The device has a hardware multiplier. @item __AVR_HAVE_JMP_CALL__ The device has the @code{JMP} and @code{CALL} instructions. This is the case for devices with at least 16@tie{}KiB of program memory. @item __AVR_HAVE_EIJMP_EICALL__ @itemx __AVR_3_BYTE_PC__ The device has the @code{EIJMP} and @code{EICALL} instructions. This is the case for devices with more than 128@tie{}KiB of program memory. This also means that the program counter (PC) is 3@tie{}bytes wide. @item __AVR_2_BYTE_PC__ The program counter (PC) is 2@tie{}bytes wide. This is the case for devices with up to 128@tie{}KiB of program memory. @item __AVR_HAVE_8BIT_SP__ @itemx __AVR_HAVE_16BIT_SP__ The stack pointer (SP) register is treated as 8-bit respectively 16-bit register by the compiler. The definition of these macros is affected by @code{-mtiny-stack}. @item __AVR_HAVE_SPH__ @itemx __AVR_SP8__ The device has the SPH (high part of stack pointer) special function register or has an 8-bit stack pointer, respectively. The definition of these macros is affected by @code{-mmcu=} and in the cases of @code{-mmcu=avr2} and @code{-mmcu=avr25} also by @code{-msp8}. @item __AVR_HAVE_RAMPD__ @itemx __AVR_HAVE_RAMPX__ @itemx __AVR_HAVE_RAMPY__ @itemx __AVR_HAVE_RAMPZ__ The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function register, respectively. @item __NO_INTERRUPTS__ This macro reflects the @code{-mno-interrupts} command line option. @item __AVR_ERRATA_SKIP__ @itemx __AVR_ERRATA_SKIP_JMP_CALL__ Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions because of a hardware erratum. Skip instructions are @code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also set. @item __AVR_ISA_RMW__ The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). @item __AVR_SFR_OFFSET__=@var{offset} Instructions that can address I/O special function registers directly like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different address as if addressed by an instruction to access RAM like @code{LD} or @code{STS}. This offset depends on the device architecture and has to be subtracted from the RAM address in order to get the respective I/O@tie{}address. @item __WITH_AVRLIBC__ The compiler is configured to be used together with AVR-Libc. See the @code{--with-avrlibc} configure option. @end table @node Blackfin Options @subsection Blackfin Options @cindex Blackfin Options @table @gcctabopt @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @opindex mcpu= Specifies the name of the target Blackfin processor. Currently, @var{cpu} can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, @samp{bf561}, @samp{bf592}. The optional @var{sirevision} specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. If @var{sirevision} is @samp{any}, all workarounds for the targeted processor are enabled. The @code{__SILICON_REVISION__} macro is defined to two hexadecimal digits representing the major and minor numbers in the silicon revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} is not defined. If @var{sirevision} is @samp{any}, the @code{__SILICON_REVISION__} is defined to be @code{0xffff}. If this optional @var{sirevision} is not used, GCC assumes the latest known silicon revision of the targeted Blackfin processor. GCC defines a preprocessor macro for the specified @var{cpu}. For the @samp{bfin-elf} toolchain, this option causes the hardware BSP provided by libgloss to be linked in if @option{-msim} is not given. Without this option, @samp{bf532} is used as the processor by default. Note that support for @samp{bf561} is incomplete. For @samp{bf561}, only the preprocessor macro is defined. @item -msim @opindex msim Specifies that the program will be run on the simulator. This causes the simulator BSP provided by libgloss to be linked in. This option has effect only for @samp{bfin-elf} toolchain. Certain other options, such as @option{-mid-shared-library} and @option{-mfdpic}, imply @option{-msim}. @item -momit-leaf-frame-pointer @opindex momit-leaf-frame-pointer Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option @option{-fomit-frame-pointer} removes the frame pointer for all functions, which might make debugging harder. @item -mspecld-anomaly @opindex mspecld-anomaly When enabled, the compiler ensures that the generated code does not contain speculative loads after jump instructions. If this option is used, @code{__WORKAROUND_SPECULATIVE_LOADS} is defined. @item -mno-specld-anomaly @opindex mno-specld-anomaly Don't generate extra code to prevent speculative loads from occurring. @item -mcsync-anomaly @opindex mcsync-anomaly When enabled, the compiler ensures that the generated code does not contain CSYNC or SSYNC instructions too soon after conditional branches. If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. @item -mno-csync-anomaly @opindex mno-csync-anomaly Don't generate extra code to prevent CSYNC or SSYNC instructions from occurring too soon after a conditional branch. @item -mlow-64k @opindex mlow-64k When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory. @item -mno-low-64k @opindex mno-low-64k Assume that the program is arbitrarily large. This is the default. @item -mstack-check-l1 @opindex mstack-check-l1 Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel. @item -mid-shared-library @opindex mid-shared-library Generate code that supports shared libraries via the library ID method. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies @option{-fPIC}. With a @samp{bfin-elf} target, this option implies @option{-msim}. @item -mno-id-shared-library @opindex mno-id-shared-library Generate code that doesn't assume ID-based shared libraries are being used. This is the default. @item -mleaf-id-shared-library @opindex mleaf-id-shared-library Generate code that supports shared libraries via the library ID method, but assumes that this library or executable won't link against any other ID shared libraries. That allows the compiler to use faster code for jumps and calls. @item -mno-leaf-id-shared-library @opindex mno-leaf-id-shared-library Do not assume that the code being compiled won't link against any ID shared libraries. Slower code is generated for jump and call insns. @item -mshared-library-id=n @opindex mshared-library-id Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library but is no more space- or time-efficient than omitting this option. @item -msep-data @opindex msep-data Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against the text section. @item -mno-sep-data @opindex mno-sep-data Generate code that assumes that the data segment follows the text segment. This is the default. @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 24-bit addressing range of the offset-based version of subroutine call instruction. This feature is not enabled by default. Specifying @option{-mno-long-calls} restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers. @item -mfast-fp @opindex mfast-fp Link with the fast floating-point library. This library relaxes some of the IEEE floating-point standard's rules for checking inputs against Not-a-Number (NAN), in the interest of performance. @item -minline-plt @opindex minline-plt Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without @option{-mfdpic}. @item -mmulticore @opindex mmulticore Build a standalone application for multicore Blackfin processors. This option causes proper start files and link scripts supporting multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. This option can be used with @option{-mcorea} or @option{-mcoreb}, which selects the one-application-per-core programming model. Without @option{-mcorea} or @option{-mcoreb}, the single-application/dual-core programming model is used. In this model, the main function of Core B should be named as @code{coreb_main}. If this option is not used, the single-core application programming model is used. @item -mcorea @opindex mcorea Build a standalone application for Core A of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core A, and the macro @code{__BFIN_COREA} is defined. This option can only be used in conjunction with @option{-mmulticore}. @item -mcoreb @opindex mcoreb Build a standalone application for Core B of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core B, and the macro @code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} should be used instead of @code{main}. This option can only be used in conjunction with @option{-mmulticore}. @item -msdram @opindex msdram Build a standalone application for SDRAM. Proper start files and link scripts are used to put the application into SDRAM, and the macro @code{__BFIN_SDRAM} is defined. The loader should initialize SDRAM before loading the application. @item -micplb @opindex micplb Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications the default is off. @end table @node C6X Options @subsection C6X Options @cindex C6X Options @table @gcctabopt @item -march=@var{name} @opindex march This specifies the name of the target architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: @samp{c62x}, @samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. @item -mbig-endian @opindex mbig-endian Generate code for a big-endian target. @item -mlittle-endian @opindex mlittle-endian Generate code for a little-endian target. This is the default. @item -msim @opindex msim Choose startup files and linker script suitable for the simulator. @item -msdata=default @opindex msdata=default Put small global and static data in the @samp{.neardata} section, which is pointed to by register @code{B14}. Put small uninitialized global and static data in the @samp{.bss} section, which is adjacent to the @samp{.neardata} section. Put small read-only data into the @samp{.rodata} section. The corresponding sections used for large pieces of data are @samp{.fardata}, @samp{.far} and @samp{.const}. @item -msdata=all @opindex msdata=all Put all data, not just small objects, into the sections reserved for small data, and use addressing relative to the @code{B14} register to access them. @item -msdata=none @opindex msdata=none Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the @samp{.fardata} section, and all uninitialized data in the @samp{.far} section. Put all constant data into the @samp{.const} section. @end table @node CRIS Options @subsection CRIS Options @cindex CRIS Options These options are defined specifically for the CRIS ports. @table @gcctabopt @item -march=@var{architecture-type} @itemx -mcpu=@var{architecture-type} @opindex march @opindex mcpu Generate code for the specified architecture. The choices for @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. Default is @samp{v0} except for cris-axis-linux-gnu, where the default is @samp{v10}. @item -mtune=@var{architecture-type} @opindex mtune Tune to @var{architecture-type} everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for @var{architecture-type} are the same as for @option{-march=@var{architecture-type}}. @item -mmax-stack-frame=@var{n} @opindex mmax-stack-frame Warn when the stack frame of a function exceeds @var{n} bytes. @item -metrax4 @itemx -metrax100 @opindex metrax4 @opindex metrax100 The options @option{-metrax4} and @option{-metrax100} are synonyms for @option{-march=v3} and @option{-march=v8} respectively. @item -mmul-bug-workaround @itemx -mno-mul-bug-workaround @opindex mmul-bug-workaround @opindex mno-mul-bug-workaround Work around a bug in the @code{muls} and @code{mulu} instructions for CPU models where it applies. This option is active by default. @item -mpdebug @opindex mpdebug Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect of turning off the @samp{#NO_APP} formatted-code indicator to the assembler at the beginning of the assembly file. @item -mcc-init @opindex mcc-init Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes. @item -mno-side-effects @opindex mno-side-effects Do not emit instructions with side effects in addressing modes other than post-increment. @item -mstack-align @itemx -mno-stack-align @itemx -mdata-align @itemx -mno-data-align @itemx -mconst-align @itemx -mno-const-align @opindex mstack-align @opindex mno-stack-align @opindex mdata-align @opindex mno-data-align @opindex mconst-align @opindex mno-const-align These options (@samp{no-} options) arrange (eliminate arrangements) for the stack frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPU model. The default is to arrange for 32-bit alignment. ABI details such as structure layout are not affected by these options. @item -m32-bit @itemx -m16-bit @itemx -m8-bit @opindex m32-bit @opindex m16-bit @opindex m8-bit Similar to the stack- data- and const-align options above, these options arrange for stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit alignment. @item -mno-prologue-epilogue @itemx -mprologue-epilogue @opindex mno-prologue-epilogue @opindex mprologue-epilogue With @option{-mno-prologue-epilogue}, the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variables needs to be allocated. @item -mno-gotplt @itemx -mgotplt @opindex mno-gotplt @opindex mgotplt With @option{-fpic} and @option{-fPIC}, don't generate (do generate) instruction sequences that load addresses for functions from the PLT part of the GOT rather than (traditional on other architectures) calls to the PLT@. The default is @option{-mgotplt}. @item -melf @opindex melf Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets. @item -mlinux @opindex mlinux Legacy no-op option only recognized with the cris-axis-linux-gnu target. @item -sim @opindex sim This option, recognized for the cris-axis-elf, arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively. @item -sim2 @opindex sim2 Like @option{-sim}, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000. @end table @node CR16 Options @subsection CR16 Options @cindex CR16 Options These options are defined specifically for the CR16 ports. @table @gcctabopt @item -mmac @opindex mmac Enable the use of multiply-accumulate instructions. Disabled by default. @item -mcr16cplus @itemx -mcr16c @opindex mcr16cplus @opindex mcr16c Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is default. @item -msim @opindex msim Links the library libsim.a which is in compatible with simulator. Applicable to ELF compiler only. @item -mint32 @opindex mint32 Choose integer type as 32-bit wide. @item -mbit-ops @opindex mbit-ops Generates @code{sbit}/@code{cbit} instructions for bit manipulations. @item -mdata-model=@var{model} @opindex mdata-model Choose a data model. The choices for @var{model} are @samp{near}, @samp{far} or @samp{medium}. @samp{medium} is default. However, @samp{far} is not valid with @option{-mcr16c}, as the CR16C architecture does not support the far data model. @end table @node Darwin Options @subsection Darwin Options @cindex Darwin options These options are defined for all architectures running the Darwin operating system. FSF GCC on Darwin does not create ``fat'' object files; it creates an object file for the single architecture that GCC was built to target. Apple's GCC on Darwin does create ``fat'' files if multiple @option{-arch} options are used; it does so by running the compiler or linker multiple times and joining the results together with @file{lipo}. The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or @samp{i686}) is determined by the flags that specify the ISA that GCC is targeting, like @option{-mcpu} or @option{-march}. The @option{-force_cpusubtype_ALL} option can be used to override this. The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, @file{as}, only permits instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64-bit instructions in a @samp{ppc750} object file. The linker for shared libraries, @file{/usr/bin/libtool}, fails and prints an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a @samp{ppc970} object file in a @samp{ppc7400} library). The linker for executables, @command{ld}, quietly gives the executable the most restrictive subtype of any of its input files. @table @gcctabopt @item -F@var{dir} @opindex F Add the framework directory @var{dir} to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by @option{-I} options and are scanned in a left-to-right order. A framework directory is a directory with frameworks in it. A framework is a directory with a @file{Headers} and/or @file{PrivateHeaders} directory contained directly in it that ends in @file{.framework}. The name of a framework is the name of this directory excluding the @file{.framework}. Headers associated with the framework are found in one of those two directories, with @file{Headers} being searched first. A subframework is a framework directory that is in a framework's @file{Frameworks} directory. Includes of subframework headers can only appear in a header of a framework that contains the subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework; a warning is issued if this is violated. Currently a subframework cannot have subframeworks; in the future, the mechanism may be extended to support this. The standard frameworks can be found in @file{/System/Library/Frameworks} and @file{/Library/Frameworks}. An example include looks like @code{#include }, where @file{Framework} denotes the name of the framework and @file{header.h} is found in the @file{PrivateHeaders} or @file{Headers} directory. @item -iframework@var{dir} @opindex iframework Like @option{-F} except the directory is a treated as a system directory. The main difference between this @option{-iframework} and @option{-F} is that with @option{-iframework} the compiler does not warn about constructs contained within header files found via @var{dir}. This option is valid only for the C family of languages. @item -gused @opindex gused Emit debugging information for symbols that are used. For stabs debugging format, this enables @option{-feliminate-unused-debug-symbols}. This is by default ON@. @item -gfull @opindex gfull Emit debugging information for all symbols and types. @item -mmacosx-version-min=@var{version} The earliest version of MacOS X that this executable will run on is @var{version}. Typical values of @var{version} include @code{10.1}, @code{10.2}, and @code{10.3.9}. If the compiler was built to use the system's headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible. @item -mkernel @opindex mkernel Enable kernel development mode. The @option{-mkernel} option sets @option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit}, @option{-fno-exceptions}, @option{-fno-non-call-exceptions}, @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where applicable. This mode also sets @option{-mno-altivec}, @option{-msoft-float}, @option{-fno-builtin} and @option{-mlong-branch} for PowerPC targets. @item -mone-byte-bool @opindex mone-byte-bool Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}. By default @samp{sizeof(bool)} is @samp{4} when compiling for Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this option has no effect on x86. @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model. @item -mfix-and-continue @itemx -ffix-and-continue @itemx -findirect-data @opindex mfix-and-continue @opindex ffix-and-continue @opindex findirect-data Generate code suitable for fast turnaround development, such as to allow GDB to dynamically load @code{.o} files into already-running programs. @option{-findirect-data} and @option{-ffix-and-continue} are provided for backwards compatibility. @item -all_load @opindex all_load Loads all members of static archive libraries. See man ld(1) for more information. @item -arch_errors_fatal @opindex arch_errors_fatal Cause the errors having to do with files that have the wrong architecture to be fatal. @item -bind_at_load @opindex bind_at_load Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched. @item -bundle @opindex bundle Produce a Mach-o bundle format file. See man ld(1) for more information. @item -bundle_loader @var{executable} @opindex bundle_loader This option specifies the @var{executable} that will load the build output file being linked. See man ld(1) for more information. @item -dynamiclib @opindex dynamiclib When passed this option, GCC produces a dynamic library instead of an executable when linking, using the Darwin @file{libtool} command. @item -force_cpusubtype_ALL @opindex force_cpusubtype_ALL This causes GCC's output file to have the @var{ALL} subtype, instead of one controlled by the @option{-mcpu} or @option{-march} option. @item -allowable_client @var{client_name} @itemx -client_name @itemx -compatibility_version @itemx -current_version @itemx -dead_strip @itemx -dependency-file @itemx -dylib_file @itemx -dylinker_install_name @itemx -dynamic @itemx -exported_symbols_list @itemx -filelist @need 800 @itemx -flat_namespace @itemx -force_flat_namespace @itemx -headerpad_max_install_names @itemx -image_base @itemx -init @itemx -install_name @itemx -keep_private_externs @itemx -multi_module @itemx -multiply_defined @itemx -multiply_defined_unused @need 800 @itemx -noall_load @itemx -no_dead_strip_inits_and_terms @itemx -nofixprebinding @itemx -nomultidefs @itemx -noprebind @itemx -noseglinkedit @itemx -pagezero_size @itemx -prebind @itemx -prebind_all_twolevel_modules @itemx -private_bundle @need 800 @itemx -read_only_relocs @itemx -sectalign @itemx -sectobjectsymbols @itemx -whyload @itemx -seg1addr @itemx -sectcreate @itemx -sectobjectsymbols @itemx -sectorder @itemx -segaddr @itemx -segs_read_only_addr @need 800 @itemx -segs_read_write_addr @itemx -seg_addr_table @itemx -seg_addr_table_filename @itemx -seglinkedit @itemx -segprot @itemx -segs_read_only_addr @itemx -segs_read_write_addr @itemx -single_module @itemx -static @itemx -sub_library @need 800 @itemx -sub_umbrella @itemx -twolevel_namespace @itemx -umbrella @itemx -undefined @itemx -unexported_symbols_list @itemx -weak_reference_mismatches @itemx -whatsloaded @opindex allowable_client @opindex client_name @opindex compatibility_version @opindex current_version @opindex dead_strip @opindex dependency-file @opindex dylib_file @opindex dylinker_install_name @opindex dynamic @opindex exported_symbols_list @opindex filelist @opindex flat_namespace @opindex force_flat_namespace @opindex headerpad_max_install_names @opindex image_base @opindex init @opindex install_name @opindex keep_private_externs @opindex multi_module @opindex multiply_defined @opindex multiply_defined_unused @opindex noall_load @opindex no_dead_strip_inits_and_terms @opindex nofixprebinding @opindex nomultidefs @opindex noprebind @opindex noseglinkedit @opindex pagezero_size @opindex prebind @opindex prebind_all_twolevel_modules @opindex private_bundle @opindex read_only_relocs @opindex sectalign @opindex sectobjectsymbols @opindex whyload @opindex seg1addr @opindex sectcreate @opindex sectobjectsymbols @opindex sectorder @opindex segaddr @opindex segs_read_only_addr @opindex segs_read_write_addr @opindex seg_addr_table @opindex seg_addr_table_filename @opindex seglinkedit @opindex segprot @opindex segs_read_only_addr @opindex segs_read_write_addr @opindex single_module @opindex static @opindex sub_library @opindex sub_umbrella @opindex twolevel_namespace @opindex umbrella @opindex undefined @opindex unexported_symbols_list @opindex weak_reference_mismatches @opindex whatsloaded These options are passed to the Darwin linker. The Darwin linker man page describes them in detail. @end table @node DEC Alpha Options @subsection DEC Alpha Options These @samp{-m} options are defined for the DEC Alpha implementations: @table @gcctabopt @item -mno-soft-float @itemx -msoft-float @opindex mno-soft-float @opindex msoft-float Use (do not use) the hardware floating-point instructions for floating-point operations. When @option{-msoft-float} is specified, functions in @file{libgcc.a} are used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them. Note that Alpha implementations without floating-point operations are required to have floating-point registers. @item -mfp-reg @itemx -mno-fp-regs @opindex mfp-reg @opindex mno-fp-regs Generate code that uses (does not use) the floating-point register set. @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point register set is not used, floating-point operands are passed in integer registers as if they were integers and floating-point results are passed in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with @option{-mno-fp-regs} must also be compiled with that option. A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers. @item -mieee @opindex mieee The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating-point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE-compliant code @emph{except} that the @var{inexact-flag} is not maintained (see below). If this option is turned on, the preprocessor macro @code{_IEEE_FP} is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option @option{-ieee_with_no_inexact}. @item -mieee-with-inexact @opindex mieee-with-inexact This is like @option{-mieee} except the generated code also maintains the IEEE @var{inexact-flag}. Turning on this option causes the generated code to implement fully-compliant IEEE math. In addition to @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the @var{inexact-flag}, you should normally not specify this option. Other Alpha compilers call this option @option{-ieee_with_inexact}. @item -mfp-trap-mode=@var{trap-mode} @opindex mfp-trap-mode This option controls what floating-point related traps are enabled. Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. The trap mode can be set to one of four values: @table @samp @item n This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap). @item u In addition to the traps enabled by @samp{n}, underflow traps are enabled as well. @item su Like @samp{u}, but the instructions are marked to be safe for software completion (see Alpha architecture manual for details). @item sui Like @samp{su}, but inexact traps are enabled as well. @end table @item -mfp-rounding-mode=@var{rounding-mode} @opindex mfp-rounding-mode Selects the IEEE rounding mode. Other Alpha compilers call this option @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one of: @table @samp @item n Normal IEEE rounding mode. Floating-point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie. @item m Round towards minus infinity. @item c Chopped rounding mode. Floating-point numbers are rounded towards zero. @item d Dynamic rounding mode. A field in the floating-point control register (@var{fpcr}, see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes this register for rounding towards plus infinity. Thus, unless your program modifies the @var{fpcr}, @samp{d} corresponds to round towards plus infinity. @end table @item -mtrap-precision=@var{trap-precision} @opindex mtrap-precision In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. GCC can generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an application, different levels of precisions can be selected: @table @samp @item p Program precision. This option is the default and means a trap handler can only identify which program caused a floating-point exception. @item f Function precision. The trap handler can determine the function that caused a floating-point exception. @item i Instruction precision. The trap handler can determine the exact instruction that caused a floating-point exception. @end table Other Alpha compilers provide the equivalent options called @option{-scope_safe} and @option{-resumption_safe}. @item -mieee-conformant @opindex mieee-conformant This option marks the generated code as IEEE conformant. You must not use this option unless you also specify @option{-mtrap-precision=i} and either @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect is to emit the line @samp{.eflag 48} in the function prologue of the generated assembly file. @item -mbuild-constants @opindex mbuild-constants Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it outputs the constant as a literal and generates code to load it from the data segment at run time. Use this option to require GCC to construct @emph{all} integer constants using code, even if it takes more instructions (the maximum is six). You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment. @item -mbwx @itemx -mno-bwx @itemx -mcix @itemx -mno-cix @itemx -mfix @itemx -mno-fix @itemx -mmax @itemx -mno-max @opindex mbwx @opindex mno-bwx @opindex mcix @opindex mno-cix @opindex mfix @opindex mno-fix @opindex mmax @opindex mno-max Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets. The default is to use the instruction sets supported by the CPU type specified via @option{-mcpu=} option or that of the CPU on which GCC was built if none is specified. @item -mfloat-vax @itemx -mfloat-ieee @opindex mfloat-vax @opindex mfloat-ieee Generate code that uses (does not use) VAX F and G floating-point arithmetic instead of IEEE single and double precision. @item -mexplicit-relocs @itemx -mno-explicit-relocs @opindex mexplicit-relocs @opindex mno-explicit-relocs Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. GNU binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCC detects the capabilities of the assembler when it is built and sets the default accordingly. @item -msmall-data @itemx -mlarge-data @opindex msmall-data @opindex mlarge-data When @option{-mexplicit-relocs} is in effect, static data is accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} (the @code{.sdata} and @code{.sbss} sections) and are accessed via 16-bit relocations off of the @code{$gp} register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction. The default is @option{-mlarge-data}. With this option the data area is limited to just below 2GB@. Programs that require more than 2GB of data must use @code{malloc} or @code{mmap} to allocate the data in the heap instead of in the program's data segment. When generating code for shared libraries, @option{-fpic} implies @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. @item -msmall-text @itemx -mlarge-text @opindex msmall-text @opindex mlarge-text When @option{-msmall-text} is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When @option{-msmall-data} is used, the compiler can assume that all local symbols share the same @code{$gp} value, and thus reduce the number of instructions required for a function call from 4 to 1. The default is @option{-mlarge-text}. @item -mcpu=@var{cpu_type} @opindex mcpu Set the instruction set and instruction scheduling parameters for machine type @var{cpu_type}. You can specify either the @samp{EV} style name or the corresponding chip number. GCC supports scheduling parameters for the EV4, EV5 and EV6 family of processors and chooses the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCC defaults to the processor on which the compiler was built. Supported values for @var{cpu_type} are @table @samp @item ev4 @itemx ev45 @itemx 21064 Schedules as an EV4 and has no instruction set extensions. @item ev5 @itemx 21164 Schedules as an EV5 and has no instruction set extensions. @item ev56 @itemx 21164a Schedules as an EV5 and supports the BWX extension. @item pca56 @itemx 21164pc @itemx 21164PC Schedules as an EV5 and supports the BWX and MAX extensions. @item ev6 @itemx 21264 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. @item ev67 @itemx 21264a Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. @end table Native toolchains also support the value @samp{native}, which selects the best architecture option for the host processor. @option{-mcpu=native} has no effect if GCC does not recognize the processor. @item -mtune=@var{cpu_type} @opindex mtune Set only the instruction scheduling parameters for machine type @var{cpu_type}. The instruction set is not changed. Native toolchains also support the value @samp{native}, which selects the best architecture option for the host processor. @option{-mtune=native} has no effect if GCC does not recognize the processor. @item -mmemory-latency=@var{time} @opindex mmemory-latency Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine. Valid options for @var{time} are @table @samp @item @var{number} A decimal number representing clock cycles. @item L1 @itemx L2 @itemx L3 @itemx main The compiler contains estimates of the number of clock cycles for ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main memory. Note that L3 is only valid for EV5. @end table @end table @node FR30 Options @subsection FR30 Options @cindex FR30 Options These options are defined specifically for the FR30 port. @table @gcctabopt @item -msmall-model @opindex msmall-model Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses fit into a 20-bit range. @item -mno-lsim @opindex mno-lsim Assume that runtime support has been provided and so there is no need to include the simulator library (@file{libsim.a}) on the linker command line. @end table @node FRV Options @subsection FRV Options @cindex FRV Options @table @gcctabopt @item -mgpr-32 @opindex mgpr-32 Only use the first 32 general-purpose registers. @item -mgpr-64 @opindex mgpr-64 Use all 64 general-purpose registers. @item -mfpr-32 @opindex mfpr-32 Use only the first 32 floating-point registers. @item -mfpr-64 @opindex mfpr-64 Use all 64 floating-point registers. @item -mhard-float @opindex mhard-float Use hardware instructions for floating-point operations. @item -msoft-float @opindex msoft-float Use library routines for floating-point operations. @item -malloc-cc @opindex malloc-cc Dynamically allocate condition code registers. @item -mfixed-cc @opindex mfixed-cc Do not try to dynamically allocate condition code registers, only use @code{icc0} and @code{fcc0}. @item -mdword @opindex mdword Change ABI to use double word insns. @item -mno-dword @opindex mno-dword Do not use double word instructions. @item -mdouble @opindex mdouble Use floating-point double instructions. @item -mno-double @opindex mno-double Do not use floating-point double instructions. @item -mmedia @opindex mmedia Use media instructions. @item -mno-media @opindex mno-media Do not use media instructions. @item -mmuladd @opindex mmuladd Use multiply and add/subtract instructions. @item -mno-muladd @opindex mno-muladd Do not use multiply and add/subtract instructions. @item -mfdpic @opindex mfdpic Select the FDPIC ABI, which uses function descriptors to represent pointers to functions. Without any PIC/PIE-related options, it implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it assumes GOT entries and small data are within a 12-bit range from the GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets are computed with 32 bits. With a @samp{bfin-elf} target, this option implies @option{-msim}. @item -minline-plt @opindex minline-plt Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without @option{-mfdpic}. It's enabled by default if optimizing for speed and compiling for shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an optimization option such as @option{-O3} or above is present in the command line. @item -mTLS @opindex mTLS Assume a large TLS segment when generating thread-local code. @item -mtls @opindex mtls Do not assume a large TLS segment when generating thread-local code. @item -mgprel-ro @opindex mgprel-ro Enable the use of @code{GPREL} relocations in the FDPIC ABI for data that is known to be in read-only sections. It's enabled by default, except for @option{-fpic} or @option{-fpie}: even though it may help make the global offset table smaller, it trades 1 instruction for 4. With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a GOT entry for the referenced symbol, so it's more likely to be a win. If it is not, @option{-mno-gprel-ro} can be used to disable it. @item -multilib-library-pic @opindex multilib-library-pic Link with the (library, not FD) pic libraries. It's implied by @option{-mlibrary-pic}, as well as by @option{-fPIC} and @option{-fpic} without @option{-mfdpic}. You should never have to use it explicitly. @item -mlinked-fp @opindex mlinked-fp Follow the EABI requirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with @option{-mno-linked-fp}. @item -mlong-calls @opindex mlong-calls Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32-bit address space. @item -malign-labels @opindex malign-labels Try to align labels to an 8-byte boundary by inserting NOPs into the previous packet. This option only has an effect when VLIW packing is enabled. It doesn't create new packets; it merely adds NOPs to existing ones. @item -mlibrary-pic @opindex mlibrary-pic Generate position-independent EABI code. @item -macc-4 @opindex macc-4 Use only the first four media accumulator registers. @item -macc-8 @opindex macc-8 Use all eight media accumulator registers. @item -mpack @opindex mpack Pack VLIW instructions. @item -mno-pack @opindex mno-pack Do not pack VLIW instructions. @item -mno-eflags @opindex mno-eflags Do not mark ABI switches in e_flags. @item -mcond-move @opindex mcond-move Enable the use of conditional-move instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-cond-move @opindex mno-cond-move Disable the use of conditional-move instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mscc @opindex mscc Enable the use of conditional set instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-scc @opindex mno-scc Disable the use of conditional set instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mcond-exec @opindex mcond-exec Enable the use of conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-cond-exec @opindex mno-cond-exec Disable the use of conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mvliw-branch @opindex mvliw-branch Run a pass to pack branches into VLIW instructions (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-vliw-branch @opindex mno-vliw-branch Do not run a pass to pack branches into VLIW instructions. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mmulti-cond-exec @opindex mmulti-cond-exec Enable optimization of @code{&&} and @code{||} in conditional execution (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-multi-cond-exec @opindex mno-multi-cond-exec Disable optimization of @code{&&} and @code{||} in conditional execution. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mnested-cond-exec @opindex mnested-cond-exec Enable nested conditional execution optimizations (default). This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -mno-nested-cond-exec @opindex mno-nested-cond-exec Disable nested conditional execution optimizations. This switch is mainly for debugging the compiler and will likely be removed in a future version. @item -moptimize-membar @opindex moptimize-membar This switch removes redundant @code{membar} instructions from the compiler-generated code. It is enabled by default. @item -mno-optimize-membar @opindex mno-optimize-membar This switch disables the automatic removal of redundant @code{membar} instructions from the generated code. @item -mtomcat-stats @opindex mtomcat-stats Cause gas to print out tomcat statistics. @item -mcpu=@var{cpu} @opindex mcpu Select the processor type for which to generate code. Possible values are @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. @end table @node GNU/Linux Options @subsection GNU/Linux Options These @samp{-m} options are defined for GNU/Linux targets: @table @gcctabopt @item -mglibc @opindex mglibc Use the GNU C library. This is the default except on @samp{*-*-linux-*uclibc*} and @samp{*-*-linux-*android*} targets. @item -muclibc @opindex muclibc Use uClibc C library. This is the default on @samp{*-*-linux-*uclibc*} targets. @item -mbionic @opindex mbionic Use Bionic C library. This is the default on @samp{*-*-linux-*android*} targets. @item -mandroid @opindex mandroid Compile code compatible with Android platform. This is the default on @samp{*-*-linux-*android*} targets. When compiling, this option enables @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, this option makes the GCC driver pass Android-specific options to the linker. Finally, this option causes the preprocessor macro @code{__ANDROID__} to be defined. @item -tno-android-cc @opindex tno-android-cc Disable compilation effects of @option{-mandroid}, i.e., do not enable @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and @option{-fno-rtti} by default. @item -tno-android-ld @opindex tno-android-ld Disable linking effects of @option{-mandroid}, i.e., pass standard Linux linking options to the linker. @end table @node H8/300 Options @subsection H8/300 Options These @samp{-m} options are defined for the H8/300 implementations: @table @gcctabopt @item -mrelax @opindex mrelax Shorten some address references at link time, when possible; uses the linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, ld, Using ld}, for a fuller description. @item -mh @opindex mh Generate code for the H8/300H@. @item -ms @opindex ms Generate code for the H8S@. @item -mn @opindex mn Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with @option{-mh} or @option{-ms}. @item -ms2600 @opindex ms2600 Generate code for the H8S/2600. This switch must be used with @option{-ms}. @item -mexr @opindex mexr Extended registers are stored on stack before execution of function with monitor attribute. Default option is @option{-mexr}. This option is valid only for H8S targets. @item -mno-exr @opindex mno-exr Extended registers are not stored on stack before execution of function with monitor attribute. Default option is @option{-mno-exr}. This option is valid only for H8S targets. @item -mint32 @opindex mint32 Make @code{int} data 32 bits by default. @item -malign-300 @opindex malign-300 On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4-byte boundaries. @option{-malign-300} causes them to be aligned on 2-byte boundaries. This option has no effect on the H8/300. @end table @node HPPA Options @subsection HPPA Options @cindex HPPA Options These @samp{-m} options are defined for the HPPA family of computers: @table @gcctabopt @item -march=@var{architecture-type} @opindex march Generate code for the specified architecture. The choices for @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA 1.1, and @samp{2.0} for PA 2.0 processors. Refer to @file{/usr/lib/sched.models} on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around. @item -mpa-risc-1-0 @itemx -mpa-risc-1-1 @itemx -mpa-risc-2-0 @opindex mpa-risc-1-0 @opindex mpa-risc-1-1 @opindex mpa-risc-2-0 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. @item -mjump-in-delay @opindex mjump-in-delay This option is ignored and provided for compatibility purposes only. @item -mdisable-fpregs @opindex mdisable-fpregs Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point registers. If you use this option and attempt to perform floating-point operations, the compiler aborts. @item -mdisable-indexing @opindex mdisable-indexing Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIG generated code under MACH@. @item -mno-space-regs @opindex mno-space-regs Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes. Such code is suitable for level 0 PA systems and kernels. @item -mfast-indirect-calls @opindex mfast-indirect-calls Generate code that assumes calls never cross space boundaries. This allows GCC to emit code that performs faster indirect calls. This option does not work in the presence of shared libraries or nested functions. @item -mfixed-range=@var{register-range} @opindex mfixed-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. @item -mlong-load-store @opindex mlong-load-store Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the @samp{+k} option to the HP compilers. @item -mportable-runtime @opindex mportable-runtime Use the portable calling conventions proposed by HP for ELF systems. @item -mgas @opindex mgas Enable the use of assembler directives only GAS understands. @item -mschedule=@var{cpu-type} @opindex mschedule Schedule code according to the constraints for the machine type @var{cpu-type}. The choices for @var{cpu-type} are @samp{700} @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer to @file{/usr/lib/sched.models} on an HP-UX system to determine the proper scheduling option for your machine. The default scheduling is @samp{8000}. @item -mlinker-opt @opindex mlinker-opt Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when linking some programs. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all HPPA targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. @option{-msoft-float} changes the calling convention in the output file; therefore, it is only useful if you compile @emph{all} of a program with this option. In particular, you need to compile @file{libgcc.a}, the library that comes with GCC, with @option{-msoft-float} in order for this to work. @item -msio @opindex msio Generate the predefine, @code{_SIO}, for server IO@. The default is @option{-mwsio}. This generates the predefines, @code{__hp9000s700}, @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These options are available under HP-UX and HI-UX@. @item -mgnu-ld @opindex mgnu-ld Use options specific to GNU @command{ld}. This passes @option{-shared} to @command{ld} when building a shared library. It is the default when GCC is configured, explicitly or implicitly, with the GNU linker. This option does not affect which @command{ld} is called; it only changes what parameters are passed to that @command{ld}. The @command{ld} that is called is determined by the @option{--with-ld} configure option, GCC's program search path, and finally by the user's @env{PATH}. The linker used by GCC can be printed using @samp{which `gcc -print-prog-name=ld`}. This option is only available on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. @item -mhp-ld @opindex mhp-ld Use options specific to HP @command{ld}. This passes @option{-b} to @command{ld} when building a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all links. It is the default when GCC is configured, explicitly or implicitly, with the HP linker. This option does not affect which @command{ld} is called; it only changes what parameters are passed to that @command{ld}. The @command{ld} that is called is determined by the @option{--with-ld} configure option, GCC's program search path, and finally by the user's @env{PATH}. The linker used by GCC can be printed using @samp{which `gcc -print-prog-name=ld`}. This option is only available on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. @item -mlong-calls @opindex mno-long-calls Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the PA 2.0 and PA 1.X architectures. Sibcalls are always limited at 240,000 bytes. Distances are measured from the beginning of functions when using the @option{-ffunction-sections} option, or when using the @option{-mgas} and @option{-mno-portable-runtime} options together under HP-UX with the SOM linker. It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the application. The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit ELF systems in pic code and it is quite long. @item -munix=@var{unix-std} @opindex march Generate compiler predefines and select a startfile for the specified UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX 11.11 and later. The default values are @samp{93} for HP-UX 10.00, @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 and later. @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. It is @emph{important} to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, @emph{extreme} care is needed in using this option. Library code that is intended to operate with more than one UNIX standard must test, set and restore the variable @var{__xpg4_extended_mask} as appropriate. Most GNU software doesn't provide this capability. @item -nolibdld @opindex nolibdld Suppress the generation of link options to search libdld.sl when the @option{-static} option is specified on HP-UX 10 and later. @item -static @opindex static The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isn't an archive version of libdld.sl. Thus, when the @option{-static} option is specified, special link options are needed to resolve this dependency. On HP-UX 10 and later, the GCC driver adds the necessary options to link with libdld.sl when the @option{-static} option is specified. This causes the resulting binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries by default in any case. The @option{-nolibdld} option can be used to prevent the GCC driver from adding these link options. @item -threads @opindex threads Add support for multithreading with the @dfn{dce thread} library under HP-UX@. This option sets flags for both the preprocessor and linker. @end table @node i386 and x86-64 Options @subsection Intel 386 and AMD x86-64 Options @cindex i386 Options @cindex x86-64 Options @cindex Intel 386 Options @cindex AMD x86-64 Options These @samp{-m} options are defined for the i386 and x86-64 family of computers: @table @gcctabopt @item -march=@var{cpu-type} @opindex march Generate instructions for the machine type @var{cpu-type}. In contrast to @option{-mtune=@var{cpu-type}}, which merely tunes the generated code for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC to generate code that may not run at all on processors other than the one indicated. Specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}. The choices for @var{cpu-type} are: @table @samp @item native This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using @option{-march=native} enables all instruction subsets supported by the local machine (hence the result might not run on different machines). Using @option{-mtune=native} produces code optimized for the local machine under the constraints of the selected instruction set. @item i386 Original Intel i386 CPU@. @item i486 Intel i486 CPU@. (No scheduling is implemented for this chip.) @item i586 @itemx pentium Intel Pentium CPU with no MMX support. @item pentium-mmx Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. @item pentiumpro Intel Pentium Pro CPU@. @item i686 When used with @option{-march}, the Pentium Pro instruction set is used, so the code runs on all i686 family chips. When used with @option{-mtune}, it has the same meaning as @samp{generic}. @item pentium2 Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set support. @item pentium3 @itemx pentium3m Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction set support. @item pentium-m Intel Pentium M; low-power version of Intel Pentium III CPU with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks. @item pentium4 @itemx pentium4m Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support. @item prescott Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction set support. @item nocona Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, SSE2 and SSE3 instruction set support. @item core2 Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. @item nehalem Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support. @item westmere Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support. @item sandybridge Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support. @item ivybridge Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction set support. @item haswell Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction set support. @item broadwell Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX and PREFETCHW instruction set support. @item bonnell Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support. @item silvermont Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support. @item k6 AMD K6 CPU with MMX instruction set support. @item k6-2 @itemx k6-3 Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. @item athlon @itemx athlon-tbird AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions support. @item athlon-4 @itemx athlon-xp @itemx athlon-mp Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE instruction set support. @item k8 @itemx opteron @itemx athlon64 @itemx athlon-fx Processors based on the AMD K8 core with x86-64 instruction set support, including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit instruction set extensions.) @item k8-sse3 @itemx opteron-sse3 @itemx athlon64-sse3 Improved versions of AMD K8 cores with SSE3 instruction set support. @item amdfam10 @itemx barcelona CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.) @item bdver1 CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) @item bdver2 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) @item bdver3 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions. @item bdver4 AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions. @item btver1 CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit instruction set extensions.) @item btver2 CPUs based on AMD Family 16h cores with x86-64 instruction set support. This includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. @item winchip-c6 IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction set support. @item winchip2 IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: instruction set support. @item c3 VIA C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is implemented for this chip.) @item c3-2 VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.) @item geode AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. @end table @item -mtune=@var{cpu-type} @opindex mtune Tune to @var{cpu-type} everything applicable about the generated code, except for the ABI and the set of available instructions. While picking a specific @var{cpu-type} schedules things appropriately for that particular chip, the compiler does not generate any code that cannot run on the default machine type unless you use a @option{-march=@var{cpu-type}} option. For example, if GCC is configured for i686-pc-linux-gnu then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 but still runs on i686 machines. The choices for @var{cpu-type} are the same as for @option{-march}. In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}: @table @samp @item generic Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. If you know the CPU on which your code will run, then you should use the corresponding @option{-mtune} or @option{-march} option instead of @option{-mtune=generic}. But, if you do not know exactly what CPU users of your application will have, then you should use this option. As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the processors that are most common at the time that version of GCC is released. There is no @option{-march=generic} option because @option{-march} indicates the instruction set the compiler can use, and there is no generic instruction set applicable to all processors. In contrast, @option{-mtune} indicates the processor (or, in this case, collection of processors) for which the code is optimized. @item intel Produce code optimized for the most current Intel processors, which are Haswell and Silvermont for this version of GCC. If you know the CPU on which your code will run, then you should use the corresponding @option{-mtune} or @option{-march} option instead of @option{-mtune=intel}. But, if you want your application performs better on both Haswell and Silvermont, then you should use this option. As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the most current Intel processors at the time that version of GCC is released. There is no @option{-march=intel} option because @option{-march} indicates the instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, @option{-mtune} indicates the processor (or, in this case, collection of processors) for which the code is optimized. @end table @item -mcpu=@var{cpu-type} @opindex mcpu A deprecated synonym for @option{-mtune}. @item -mfpmath=@var{unit} @opindex mfpmath Generate floating-point arithmetic for selected unit @var{unit}. The choices for @var{unit} are: @table @samp @item 387 Use the standard 387 floating-point coprocessor present on the majority of chips and emulated otherwise. Code compiled with this option runs almost everywhere. The temporary results are computed in 80-bit precision instead of the precision specified by the type, resulting in slightly different results compared to most of other chips. See @option{-ffloat-store} for more detailed description. This is the default choice for i386 compiler. @item sse Use scalar floating-point instructions present in the SSE instruction set. This instruction set is supported by Pentium III and newer chips, and in the AMD line by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE instruction set supports only single-precision arithmetic, thus the double and extended-precision arithmetic are still done using 387. A later version, present only in Pentium 4 and AMD x86-64 chips, supports double-precision arithmetic too. For the i386 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} or @option{-msse2} switches to enable SSE extensions and make this option effective. For the x86-64 compiler, these extensions are enabled by default. The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80 bits. This is the default choice for the x86-64 compiler. @item sse,387 @itemx sse+387 @itemx both Attempt to utilize both instruction sets at once. This effectively doubles the amount of available registers, and on chips with separate execution units for 387 and SSE the execution resources too. Use this option with care, as it is still experimental, because the GCC register allocator does not model separate functional units well, resulting in unstable performance. @end table @item -masm=@var{dialect} @opindex masm=@var{dialect} Output assembly instructions using selected @var{dialect}. Supported choices are @samp{intel} or @samp{att} (the default). Darwin does not support @samp{intel}. @item -mieee-fp @itemx -mno-ieee-fp @opindex mieee-fp @opindex mno-ieee-fp Control whether or not the compiler uses IEEE floating-point comparisons. These correctly handle the case where the result of a comparison is unordered. @item -msoft-float @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not part of GCC@. Normally the facilities of the machine's usual C compiler are used, but this can't be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if @option{-msoft-float} is used. @item -mno-fp-ret-in-387 @opindex mno-fp-ret-in-387 Do not use the FPU registers for return values of functions. The usual calling convention has functions return values of types @code{float} and @code{double} in an FPU register, even if there is no FPU@. The idea is that the operating system should emulate an FPU@. The option @option{-mno-fp-ret-in-387} causes such values to be returned in ordinary CPU registers instead. @item -mno-fancy-math-387 @opindex mno-fancy-math-387 Some 387 emulators do not support the @code{sin}, @code{cos} and @code{sqrt} instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD, OpenBSD and NetBSD@. This option is overridden when @option{-march} indicates that the target CPU always has an FPU and so the instruction does not need emulation. These instructions are not generated unless you also use the @option{-funsafe-math-optimizations} switch. @item -malign-double @itemx -mno-align-double @opindex malign-double @opindex mno-align-double Control whether GCC aligns @code{double}, @code{long double}, and @code{long long} variables on a two-word boundary or a one-word boundary. Aligning @code{double} variables on a two-word boundary produces code that runs somewhat faster on a Pentium at the expense of more memory. On x86-64, @option{-malign-double} is enabled by default. @strong{Warning:} if you use the @option{-malign-double} switch, structures containing the above types are aligned differently than the published application binary interface specifications for the 386 and are not binary compatible with structures in code compiled without that switch. @item -m96bit-long-double @itemx -m128bit-long-double @opindex m96bit-long-double @opindex m128bit-long-double These switches control the size of @code{long double} type. The i386 application binary interface specifies the size to be 96 bits, so @option{-m96bit-long-double} is the default in 32-bit mode. Modern architectures (Pentium and newer) prefer @code{long double} to be aligned to an 8- or 16-byte boundary. In arrays or structures conforming to the ABI, this is not possible. So specifying @option{-m128bit-long-double} aligns @code{long double} to a 16-byte boundary by padding the @code{long double} with an additional 32-bit zero. In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as its ABI specifies that @code{long double} is aligned on 16-byte boundary. Notice that neither of these options enable any extra precision over the x87 standard of 80 bits for a @code{long double}. @strong{Warning:} if you override the default value for your target ABI, this changes the size of structures and arrays containing @code{long double} variables, as well as modifying the function calling convention for functions taking @code{long double}. Hence they are not binary-compatible with code compiled without that switch. @item -mlong-double-64 @itemx -mlong-double-80 @itemx -mlong-double-128 @opindex mlong-double-64 @opindex mlong-double-80 @opindex mlong-double-128 These switches control the size of @code{long double} type. A size of 64 bits makes the @code{long double} type equivalent to the @code{double} type. This is the default for 32-bit Bionic C library. A size of 128 bits makes the @code{long double} type equivalent to the @code{__float128} type. This is the default for 64-bit Bionic C library. @strong{Warning:} if you override the default value for your target ABI, this changes the size of structures and arrays containing @code{long double} variables, as well as modifying the function calling convention for functions taking @code{long double}. Hence they are not binary-compatible with code compiled without that switch. @item -mlarge-data-threshold=@var{threshold} @opindex mlarge-data-threshold When @option{-mcmodel=medium} is specified, data objects larger than @var{threshold} are placed in the large data section. This value must be the same across all objects linked into the binary, and defaults to 65535. @item -mrtd @opindex mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the @code{ret @var{num}} instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. You can specify that an individual function is called with this calling sequence with the function attribute @samp{stdcall}. You can also override the @option{-mrtd} option by using the function attribute @samp{cdecl}. @xref{Function Attributes}. @strong{Warning:} this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including @code{printf}); otherwise incorrect code is generated for calls to those functions. In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) @item -mregparm=@var{num} @opindex mregparm Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute @samp{regparm}. @xref{Function Attributes}. @strong{Warning:} if you use this switch, and @var{num} is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. @item -msseregparm @opindex msseregparm Use SSE register passing conventions for float and double arguments and return values. You can control this behavior for a specific function by using the function attribute @samp{sseregparm}. @xref{Function Attributes}. @strong{Warning:} if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules. @item -mvect8-ret-in-mem @opindex mvect8-ret-in-mem Return 8-byte vectors in memory instead of MMX registers. This is the default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun Studio compilers until version 12. Later compiler versions (starting with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which is the default on Solaris@tie{}10 and later. @emph{Only} use this option if you need to remain compatible with existing code produced by those previous compiler versions or older versions of GCC@. @item -mpc32 @itemx -mpc64 @itemx -mpc80 @opindex mpc32 @opindex mpc64 @opindex mpc80 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} is specified, the significands of results of floating-point operations are rounded to 24 bits (single precision); @option{-mpc64} rounds the significands of results of floating-point operations to 53 bits (double precision) and @option{-mpc80} rounds the significands of results of floating-point operations to 64 bits (extended double precision), which is the default. When this option is used, floating-point operations in higher precisions are not available to the programmer without setting the FPU control word explicitly. Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended-precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called ``catastrophic cancellation'', when this option is used to set the precision to less than extended precision. @item -mstackrealign @opindex mstackrealign Realign the stack at entry. On the Intel x86, the @option{-mstackrealign} option generates an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy codes that keep 4-byte stack alignment with modern codes that keep 16-byte stack alignment for SSE compatibility. See also the attribute @code{force_align_arg_pointer}, applicable to individual functions. @item -mpreferred-stack-boundary=@var{num} @opindex mpreferred-stack-boundary Attempt to keep the stack boundary aligned to a 2 raised to @var{num} byte boundary. If @option{-mpreferred-stack-boundary} is not specified, the default is 4 (16 bytes or 128 bits). @strong{Warning:} When generating code for the x86-64 architecture with SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be used to keep the stack boundary aligned to 8 byte boundary. Since x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option will lead to wrong code when functions compiled with 16 byte stack alignment (such as functions from a standard library) are called with misaligned stack. In this case, SSE instructions may lead to misaligned memory access traps. In addition, variable arguments will be handled incorrectly for 16 byte aligned objects (including x87 long double and __int128), leading to wrong results. You must build all modules with @option{-mpreferred-stack-boundary=3}, including any libraries. This includes the system libraries and startup modules. @item -mincoming-stack-boundary=@var{num} @opindex mincoming-stack-boundary Assume the incoming stack is aligned to a 2 raised to @var{num} byte boundary. If @option{-mincoming-stack-boundary} is not specified, the one specified by @option{-mpreferred-stack-boundary} is used. On Pentium and Pentium Pro, @code{double} and @code{long double} values should be aligned to an 8-byte boundary (see @option{-malign-double}) or suffer significant run time performance penalties. On Pentium III, the Streaming SIMD Extension (SSE) data type @code{__m128} may not work properly if it is not 16-byte aligned. To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary most likely misaligns the stack. It is recommended that libraries that use callbacks always use the default setting. This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to @option{-mpreferred-stack-boundary=2}. @item -mmmx @itemx -mno-mmx @itemx -msse @itemx -mno-sse @itemx -msse2 @itemx -mno-sse2 @itemx -msse3 @itemx -mno-sse3 @itemx -mssse3 @itemx -mno-ssse3 @itemx -msse4.1 @need 800 @itemx -mno-sse4.1 @itemx -msse4.2 @itemx -mno-sse4.2 @itemx -msse4 @itemx -mno-sse4 @itemx -mavx @itemx -mno-avx @itemx -mavx2 @itemx -mno-avx2 @itemx -mavx512f @itemx -mno-avx512f @need 800 @itemx -mavx512pf @itemx -mno-avx512pf @itemx -mavx512er @itemx -mno-avx512er @itemx -mavx512cd @itemx -mno-avx512cd @itemx -msha @itemx -mno-sha @itemx -maes @itemx -mno-aes @itemx -mpclmul @itemx -mno-pclmul @itemx -mclfushopt @itemx -mno-clflsuhopt @need 800 @itemx -mfsgsbase @itemx -mno-fsgsbase @itemx -mrdrnd @itemx -mno-rdrnd @itemx -mf16c @itemx -mno-f16c @itemx -mfma @itemx -mno-fma @itemx -mprefetchwt1 @itemx -mno-prefetchwt1 @itemx -msse4a @itemx -mno-sse4a @itemx -mfma4 @itemx -mno-fma4 @need 800 @itemx -mxop @itemx -mno-xop @itemx -mlwp @itemx -mno-lwp @itemx -m3dnow @itemx -mno-3dnow @itemx -mpopcnt @itemx -mno-popcnt @itemx -mabm @itemx -mno-abm @itemx -mbmi @itemx -mbmi2 @itemx -mno-bmi @itemx -mno-bmi2 @itemx -mlzcnt @itemx -mno-lzcnt @itemx -mfxsr @itemx -mxsave @itemx -mxsaveopt @itemx -mrtm @itemx -mtbm @itemx -mno-tbm @itemx -mxsavec @itemx -mno-xsavec @itemx -mxsaves @itemx -mno-xsaves @itemx -mmpx @itemx -mno-mpx @opindex mmmx @opindex mno-mmx @opindex msse @opindex mno-sse @opindex m3dnow @opindex mno-3dnow These switches enable or disable the use of instructions in the MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD, SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, FXSR, XSAVE, XSAVEOPT, LZCNT, RTM, MPX or 3DNow!@: extended instruction sets. These extensions are also available as built-in functions: see @ref{X86 Built-in Functions}, for details of the functions enabled and disabled by these switches. To generate SSE/SSE2 instructions automatically from floating-point code (as opposed to 387 instructions), see @option{-mfpmath=sse}. GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when needed. These options enable GCC to use these extended instructions in generated code, even without @option{-mfpmath=sse}. Applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options. @item -mdump-tune-features @opindex mdump-tune-features This option instructs GCC to dump the names of the x86 performance tuning features and default settings. The names can be used in @option{-mtune-ctrl=@var{feature-list}}. @item -mtune-ctrl=@var{feature-list} @opindex mtune-ctrl=@var{feature-list} This option is used to do fine grain control of x86 code generation features. @var{feature-list} is a comma separated list of @var{feature} names. See also @option{-mdump-tune-features}. When specified, the @var{feature} will be turned on if it is not preceded with @code{^}, otherwise, it will be turned off. @option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC developers. Using it may lead to code paths not covered by testing and can potentially result in compiler ICEs or runtime errors. @item -mno-default @opindex mno-default This option instructs GCC to turn off all tunable features. See also @option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}. @item -mcld @opindex mcld This option instructs GCC to emit a @code{cld} instruction in the prologue of functions that use string instructions. String instructions depend on the DF flag to select between autoincrement or autodecrement mode. While the ABI specifies the DF flag to be cleared on function entry, some operating systems violate this specification by not clearing the DF flag in their exception dispatchers. The exception handler can be invoked with the DF flag set, which leads to wrong direction mode when string instructions are used. This option can be enabled by default on 32-bit x86 targets by configuring GCC with the @option{--enable-cld} configure option. Generation of @code{cld} instructions can be suppressed with the @option{-mno-cld} compiler option in this case. @item -mvzeroupper @opindex mvzeroupper This option instructs GCC to emit a @code{vzeroupper} instruction before a transfer of control flow out of the function to minimize the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} intrinsics. @item -mprefer-avx128 @opindex mprefer-avx128 This option instructs GCC to use 128-bit AVX instructions instead of 256-bit AVX instructions in the auto-vectorizer. @item -mcx16 @opindex mcx16 This option enables GCC to generate @code{CMPXCHG16B} instructions. @code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword (or oword) data types. This is useful for high-resolution counters that can be updated by multiple processors (or cores). This instruction is generated as part of atomic built-in functions: see @ref{__sync Builtins} or @ref{__atomic Builtins} for details. @item -msahf @opindex msahf This option enables generation of @code{SAHF} instructions in 64-bit code. Early Intel Pentium 4 CPUs with Intel 64 support, prior to the introduction of Pentium 4 G1 step in December 2005, lacked the @code{LAHF} and @code{SAHF} instructions which were supported by AMD64. These are load and store instructions, respectively, for certain status flags. In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, @code{drem}, and @code{remainder} built-in functions; see @ref{Other Builtins} for details. @item -mmovbe @opindex mmovbe This option enables use of the @code{movbe} instruction to implement @code{__builtin_bswap32} and @code{__builtin_bswap64}. @item -mcrc32 @opindex mcrc32 This option enables built-in functions @code{__builtin_ia32_crc32qi}, @code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and @code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. @item -mrecip @opindex mrecip This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions (and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) with an additional Newton-Raphson step to increase precision instead of @code{DIVSS} and @code{SQRTSS} (and their vectorized variants) for single-precision floating-point arguments. These instructions are generated only when @option{-funsafe-math-optimizations} is enabled together with @option{-finite-math-only} and @option{-fno-trapping-math}. Note that while the throughput of the sequence is higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} (or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option combination), and doesn't need @option{-mrecip}. Also note that GCC emits the above sequence with additional Newton-Raphson step for vectorized single-float division and vectorized @code{sqrtf(@var{x})} already with @option{-ffast-math} (or the above option combination), and doesn't need @option{-mrecip}. @item -mrecip=@var{opt} @opindex mrecip=opt This option controls which reciprocal estimate instructions may be used. @var{opt} is a comma-separated list of options, which may be preceded by a @samp{!} to invert the option: @table @samp @item all Enable all estimate instructions. @item default Enable the default instructions, equivalent to @option{-mrecip}. @item none Disable all estimate instructions, equivalent to @option{-mno-recip}. @item div Enable the approximation for scalar division. @item vec-div Enable the approximation for vectorized division. @item sqrt Enable the approximation for scalar square root. @item vec-sqrt Enable the approximation for vectorized square root. @end table So, for example, @option{-mrecip=all,!sqrt} enables all of the reciprocal approximations, except for square root. @item -mveclibabi=@var{type} @opindex mveclibabi Specifies the ABI type to use for vectorizing intrinsics using an external library. Supported values for @var{type} are @samp{svml} for the Intel short vector math library and @samp{acml} for the AMD math core library. To use this option, both @option{-ftree-vectorize} and @option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML ABI-compatible library must be specified at link time. GCC currently emits calls to @code{vmldExp2}, @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2}, @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104}, @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, @code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type when @option{-mveclibabi=acml} is used. @item -mabi=@var{name} @opindex mabi Generate code for the specified calling convention. Permissible values are @samp{sysv} for the ABI used on GNU/Linux and other systems, and @samp{ms} for the Microsoft ABI. The default is to use the Microsoft ABI when targeting Microsoft Windows and the SysV ABI on all other systems. You can control this behavior for a specific function by using the function attribute @samp{ms_abi}/@samp{sysv_abi}. @xref{Function Attributes}. @item -mtls-dialect=@var{type} @opindex mtls-dialect Generate code to access thread-local storage using the @samp{gnu} or @samp{gnu2} conventions. @samp{gnu} is the conservative default; @samp{gnu2} is more efficient, but it may add compile- and run-time requirements that cannot be satisfied on all systems. @item -mpush-args @itemx -mno-push-args @opindex mpush-args @opindex mno-push-args Use PUSH operations to store outgoing parameters. This method is shorter and usually equally fast as method using SUB/MOV operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies. @item -maccumulate-outgoing-args @opindex maccumulate-outgoing-args If enabled, the maximum amount of space required for outgoing arguments is computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when the preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies @option{-mno-push-args}. @item -mthreads @opindex mthreads Support thread-safe exception handling on MinGW. Programs that rely on thread-safe exception handling must compile and link all code with the @option{-mthreads} option. When compiling, @option{-mthreads} defines @code{-D_MT}; when linking, it links in a special thread helper library @option{-lmingwthrd} which cleans up per-thread exception-handling data. @item -mno-align-stringops @opindex mno-align-stringops Do not align the destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but GCC doesn't know about it. @item -minline-all-stringops @opindex minline-all-stringops By default GCC inlines string operations only when the destination is known to be aligned to least a 4-byte boundary. This enables more inlining and increases code size, but may improve performance of code that depends on fast @code{memcpy}, @code{strlen}, and @code{memset} for short lengths. @item -minline-stringops-dynamically @opindex minline-stringops-dynamically For string operations of unknown size, use run-time checks with inline code for small blocks and a library call for large blocks. @item -mstringop-strategy=@var{alg} @opindex mstringop-strategy=@var{alg} Override the internal decision heuristic for the particular algorithm to use for inlining string operations. The allowed values for @var{alg} are: @table @samp @item rep_byte @itemx rep_4byte @itemx rep_8byte Expand using i386 @code{rep} prefix of the specified size. @item byte_loop @itemx loop @itemx unrolled_loop Expand into an inline loop. @item libcall Always use a library call. @end table @item -mmemcpy-strategy=@var{strategy} @opindex mmemcpy-strategy=@var{strategy} Override the internal decision heuristic to decide if @code{__builtin_memcpy} should be inlined and what inline algorithm to use when the expected size of the copy operation is known. @var{strategy} is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets. @var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies the max byte size with which inline algorithm @var{alg} is allowed. For the last triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets in the list must be specified in increasing order. The minimal byte size for @var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the preceding range. @item -mmemset-strategy=@var{strategy} @opindex mmemset-strategy=@var{strategy} The option is similar to @option{-mmemcpy-strategy=} except that it is to control @code{__builtin_memset} expansion. @item -momit-leaf-frame-pointer @opindex momit-leaf-frame-pointer Don't keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up, and restore frame pointers and makes an extra register available in leaf functions. The option @option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, which might make debugging harder. @item -mtls-direct-seg-refs @itemx -mno-tls-direct-seg-refs @opindex mtls-direct-seg-refs Controls whether TLS variables may be accessed with offsets from the TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), or whether the thread base pointer must be added. Whether or not this is valid depends on the operating system, and whether it maps the segment to cover the entire TLS area. For systems that use the GNU C Library, the default is on. @item -msse2avx @itemx -mno-sse2avx @opindex msse2avx Specify that the assembler should encode SSE instructions with VEX prefix. The option @option{-mavx} turns this on by default. @item -mfentry @itemx -mno-fentry @opindex mfentry If profiling is active (@option{-pg}), put the profiling counter call before the prologue. Note: On x86 architectures the attribute @code{ms_hook_prologue} isn't possible at the moment for @option{-mfentry} and @option{-pg}. @item -mrecord-mcount @itemx -mno-record-mcount @opindex mrecord-mcount If profiling is active (@option{-pg}), generate a __mcount_loc section that contains pointers to each profiling call. This is useful for automatically patching and out calls. @item -mnop-mcount @itemx -mno-nop-mcount @opindex mnop-mcount If profiling is active (@option{-pg}), generate the calls to the profiling functions as nops. This is useful when they should be patched in later dynamically. This is likely only useful together with @option{-mrecord-mcount}. @item -m8bit-idiv @itemx -mno-8bit-idiv @opindex 8bit-idiv On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than 32-bit/64-bit integer divide. This option generates a run-time check. If both dividend and divisor are within range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide. @item -mavx256-split-unaligned-load @itemx -mavx256-split-unaligned-store @opindex avx256-split-unaligned-load @opindex avx256-split-unaligned-store Split 32-byte AVX unaligned load and store. @item -mstack-protector-guard=@var{guard} @opindex mstack-protector-guard=@var{guard} Generate stack protection code using canary at @var{guard}. Supported locations are @samp{global} for global canary or @samp{tls} for per-thread canary in the TLS block (the default). This option has effect only when @option{-fstack-protector} or @option{-fstack-protector-all} is specified. @end table These @samp{-m} switches are supported in addition to the above on x86-64 processors in 64-bit environments. @table @gcctabopt @item -m32 @itemx -m64 @itemx -mx32 @itemx -m16 @opindex m32 @opindex m64 @opindex mx32 @opindex m16 Generate code for a 16-bit, 32-bit or 64-bit environment. The @option{-m32} option sets @code{int}, @code{long}, and pointer types to 32 bits, and generates code that runs on any i386 system. The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer types to 64 bits, and generates code for the x86-64 architecture. For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} and @option{-mdynamic-no-pic} options. The @option{-mx32} option sets @code{int}, @code{long}, and pointer types to 32 bits, and generates code for the x86-64 architecture. The @option{-m16} option is the same as @option{-m32}, except for that it outputs the @code{.code16gcc} assembly directive at the beginning of the assembly output so that the binary can run in 16-bit mode. @item -mno-red-zone @opindex mno-red-zone Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated by the x86-64 ABI; it is a 128-byte area beyond the location of the stack pointer that is not modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag @option{-mno-red-zone} disables this red zone. @item -mcmodel=small @opindex mcmodel=small Generate code for the small code model: the program and its symbols must be linked in the lower 2 GB of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model. @item -mcmodel=kernel @opindex mcmodel=kernel Generate code for the kernel code model. The kernel runs in the negative 2 GB of the address space. This model has to be used for Linux kernel code. @item -mcmodel=medium @opindex mcmodel=medium Generate code for the medium model: the program is linked in the lower 2 GB of the address space. Small symbols are also placed there. Symbols with sizes larger than @option{-mlarge-data-threshold} are put into large data or BSS sections and can be located above 2GB. Programs can be statically or dynamically linked. @item -mcmodel=large @opindex mcmodel=large Generate code for the large model. This model makes no assumptions about addresses and sizes of sections. @item -maddress-mode=long @opindex maddress-mode=long Generate code for long address mode. This is only supported for 64-bit and x32 environments. It is the default address mode for 64-bit environments. @item -maddress-mode=short @opindex maddress-mode=short Generate code for short address mode. This is only supported for 32-bit and x32 environments. It is the default address mode for 32-bit and x32 environments. @end table @node i386 and x86-64 Windows Options @subsection i386 and x86-64 Windows Options @cindex i386 and x86-64 Windows Options These additional options are available for Microsoft Windows targets: @table @gcctabopt @item -mconsole @opindex mconsole This option specifies that a console application is to be generated, by instructing the linker to set the PE header subsystem type required for console applications. This option is available for Cygwin and MinGW targets and is enabled by default on those targets. @item -mdll @opindex mdll This option is available for Cygwin and MinGW targets. It specifies that a DLL---a dynamic link library---is to be generated, enabling the selection of the required runtime startup object and entry point. @item -mnop-fun-dllimport @opindex mnop-fun-dllimport This option is available for Cygwin and MinGW targets. It specifies that the @code{dllimport} attribute should be ignored. @item -mthread @opindex mthread This option is available for MinGW targets. It specifies that MinGW-specific thread support is to be used. @item -municode @opindex municode This option is available for MinGW-w64 targets. It causes the @code{UNICODE} preprocessor macro to be predefined, and chooses Unicode-capable runtime startup code. @item -mwin32 @opindex mwin32 This option is available for Cygwin and MinGW targets. It specifies that the typical Microsoft Windows predefined macros are to be set in the pre-processor, but does not influence the choice of runtime library/startup code. @item -mwindows @opindex mwindows This option is available for Cygwin and MinGW targets. It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately. @item -fno-set-stack-executable @opindex fno-set-stack-executable This option is available for MinGW targets. It specifies that the executable flag for the stack used by nested functions isn't set. This is necessary for binaries running in kernel mode of Microsoft Windows, as there the User32 API, which is used to set executable privileges, isn't available. @item -fwritable-relocated-rdata @opindex fno-writable-relocated-rdata This option is available for MinGW and Cygwin targets. It specifies that relocated-data in read-only section is put into .data section. This is a necessary for older runtimes not supporting modification of .rdata sections for pseudo-relocation. @item -mpe-aligned-commons @opindex mpe-aligned-commons This option is available for Cygwin and MinGW targets. It specifies that the GNU extension to the PE file format that permits the correct alignment of COMMON variables should be used when generating code. It is enabled by default if GCC detects that the target assembler found during configuration supports the feature. @end table See also under @ref{i386 and x86-64 Options} for standard options. @node IA-64 Options @subsection IA-64 Options @cindex IA-64 Options These are the @samp{-m} options defined for the Intel IA-64 architecture. @table @gcctabopt @item -mbig-endian @opindex mbig-endian Generate code for a big-endian target. This is the default for HP-UX@. @item -mlittle-endian @opindex mlittle-endian Generate code for a little-endian target. This is the default for AIX5 and GNU/Linux. @item -mgnu-as @itemx -mno-gnu-as @opindex mgnu-as @opindex mno-gnu-as Generate (or don't) code for the GNU assembler. This is the default. @c Also, this is the default if the configure option @option{--with-gnu-as} @c is used. @item -mgnu-ld @itemx -mno-gnu-ld @opindex mgnu-ld @opindex mno-gnu-ld Generate (or don't) code for the GNU linker. This is the default. @c Also, this is the default if the configure option @option{--with-gnu-ld} @c is used. @item -mno-pic @opindex mno-pic Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI@. @item -mvolatile-asm-stop @itemx -mno-volatile-asm-stop @opindex mvolatile-asm-stop @opindex mno-volatile-asm-stop Generate (or don't) a stop bit immediately before and after volatile asm statements. @item -mregister-names @itemx -mno-register-names @opindex mregister-names @opindex mno-register-names Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for the stacked registers. This may make assembler output more readable. @item -mno-sdata @itemx -msdata @opindex mno-sdata @opindex msdata Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs. @item -mconstant-gp @opindex mconstant-gp Generate code that uses a single constant global pointer value. This is useful when compiling kernel code. @item -mauto-pic @opindex mauto-pic Generate code that is self-relocatable. This implies @option{-mconstant-gp}. This is useful when compiling firmware code. @item -minline-float-divide-min-latency @opindex minline-float-divide-min-latency Generate code for inline divides of floating-point values using the minimum latency algorithm. @item -minline-float-divide-max-throughput @opindex minline-float-divide-max-throughput Generate code for inline divides of floating-point values using the maximum throughput algorithm. @item -mno-inline-float-divide @opindex mno-inline-float-divide Do not generate inline code for divides of floating-point values. @item -minline-int-divide-min-latency @opindex minline-int-divide-min-latency Generate code for inline divides of integer values using the minimum latency algorithm. @item -minline-int-divide-max-throughput @opindex minline-int-divide-max-throughput Generate code for inline divides of integer values using the maximum throughput algorithm. @item -mno-inline-int-divide @opindex mno-inline-int-divide Do not generate inline code for divides of integer values. @item -minline-sqrt-min-latency @opindex minline-sqrt-min-latency Generate code for inline square roots using the minimum latency algorithm. @item -minline-sqrt-max-throughput @opindex minline-sqrt-max-throughput Generate code for inline square roots using the maximum throughput algorithm. @item -mno-inline-sqrt @opindex mno-inline-sqrt Do not generate inline code for @code{sqrt}. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Do (don't) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions. @item -mno-dwarf2-asm @itemx -mdwarf2-asm @opindex mno-dwarf2-asm @opindex mdwarf2-asm Don't (or do) generate assembler code for the DWARF 2 line number debugging info. This may be useful when not using the GNU assembler. @item -mearly-stop-bits @itemx -mno-early-stop-bits @opindex mearly-stop-bits @opindex mno-early-stop-bits Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so. @item -mfixed-range=@var{register-range} @opindex mfixed-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. @item -mtls-size=@var{tls-size} @opindex mtls-size Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 64. @item -mtune=@var{cpu-type} @opindex mtune Tune the instruction scheduling for a particular CPU, Valid values are @samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, and @samp{mckinley}. @item -milp32 @itemx -mlp64 @opindex milp32 @opindex mlp64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. These are HP-UX specific flags. @item -mno-sched-br-data-spec @itemx -msched-br-data-spec @opindex mno-sched-br-data-spec @opindex msched-br-data-spec (Dis/En)able data speculative scheduling before reload. This results in generation of @code{ld.a} instructions and the corresponding check instructions (@code{ld.c} / @code{chk.a}). The default is 'disable'. @item -msched-ar-data-spec @itemx -mno-sched-ar-data-spec @opindex msched-ar-data-spec @opindex mno-sched-ar-data-spec (En/Dis)able data speculative scheduling after reload. This results in generation of @code{ld.a} instructions and the corresponding check instructions (@code{ld.c} / @code{chk.a}). The default is 'enable'. @item -mno-sched-control-spec @itemx -msched-control-spec @opindex mno-sched-control-spec @opindex msched-control-spec (Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e.@: before reload). This results in generation of the @code{ld.s} instructions and the corresponding check instructions @code{chk.s}. The default is 'disable'. @item -msched-br-in-data-spec @itemx -mno-sched-br-in-data-spec @opindex msched-br-in-data-spec @opindex mno-sched-br-in-data-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with @option{-msched-br-data-spec} enabled. The default is 'enable'. @item -msched-ar-in-data-spec @itemx -mno-sched-ar-in-data-spec @opindex msched-ar-in-data-spec @opindex mno-sched-ar-in-data-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with @option{-msched-ar-data-spec} enabled. The default is 'enable'. @item -msched-in-control-spec @itemx -mno-sched-in-control-spec @opindex msched-in-control-spec @opindex mno-sched-in-control-spec (En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with @option{-msched-control-spec} enabled. The default is 'enable'. @item -mno-sched-prefer-non-data-spec-insns @itemx -msched-prefer-non-data-spec-insns @opindex mno-sched-prefer-non-data-spec-insns @opindex msched-prefer-non-data-spec-insns If enabled, data-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the data speculation much more conservative. The default is 'disable'. @item -mno-sched-prefer-non-control-spec-insns @itemx -msched-prefer-non-control-spec-insns @opindex mno-sched-prefer-non-control-spec-insns @opindex msched-prefer-non-control-spec-insns If enabled, control-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the control speculation much more conservative. The default is 'disable'. @item -mno-sched-count-spec-in-critical-path @itemx -msched-count-spec-in-critical-path @opindex mno-sched-count-spec-in-critical-path @opindex msched-count-spec-in-critical-path If enabled, speculative dependencies are considered during computation of the instructions priorities. This makes the use of the speculation a bit more conservative. The default is 'disable'. @item -msched-spec-ldc @opindex msched-spec-ldc Use a simple data speculation check. This option is on by default. @item -msched-control-spec-ldc @opindex msched-spec-ldc Use a simple check for control speculation. This option is on by default. @item -msched-stop-bits-after-every-cycle @opindex msched-stop-bits-after-every-cycle Place a stop bit after every cycle when scheduling. This option is on by default. @item -msched-fp-mem-deps-zero-cost @opindex msched-fp-mem-deps-zero-cost Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default. @item -msel-sched-dont-check-control-spec @opindex msel-sched-dont-check-control-spec Generate checks for control speculation in selective scheduling. This flag is disabled by default. @item -msched-max-memory-insns=@var{max-insns} @opindex msched-max-memory-insns Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent cache bank conflicts. The default value is 1. @item -msched-max-memory-insns-hard-limit @opindex msched-max-memory-insns-hard-limit Makes the limit specified by @option{msched-max-memory-insns} a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit is ``soft'', meaning that non-memory operations are preferred when the limit is reached, but memory operations may still be scheduled. @end table @node LM32 Options @subsection LM32 Options @cindex LM32 options These @option{-m} options are defined for the LatticeMico32 architecture: @table @gcctabopt @item -mbarrel-shift-enabled @opindex mbarrel-shift-enabled Enable barrel-shift instructions. @item -mdivide-enabled @opindex mdivide-enabled Enable divide and modulus instructions. @item -mmultiply-enabled @opindex multiply-enabled Enable multiply instructions. @item -msign-extend-enabled @opindex msign-extend-enabled Enable sign extend instructions. @item -muser-enabled @opindex muser-enabled Enable user-defined instructions. @end table @node M32C Options @subsection M32C Options @cindex M32C options @table @gcctabopt @item -mcpu=@var{name} @opindex mcpu= Select the CPU for which code is generated. @var{name} may be one of @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for the M32C/80 series. @item -msim @opindex msim Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O@. You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed. @item -memregs=@var{number} @opindex memregs= Specifies the number of memory-based pseudo-registers GCC uses during code generation. These pseudo-registers are used like real registers, so there is a tradeoff between GCC's ability to fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this option. Because of that, you must not use this option with GCC's default runtime libraries. @end table @node M32R/D Options @subsection M32R/D Options @cindex M32R/D options These @option{-m} options are defined for Renesas M32R/D architectures: @table @gcctabopt @item -m32r2 @opindex m32r2 Generate code for the M32R/2@. @item -m32rx @opindex m32rx Generate code for the M32R/X@. @item -m32r @opindex m32r Generate code for the M32R@. This is the default. @item -mmodel=small @opindex mmodel=small Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the @code{ld24} instruction), and assume all subroutines are reachable with the @code{bl} instruction. This is the default. The addressability of a particular object can be set with the @code{model} attribute. @item -mmodel=medium @opindex mmodel=medium Assume objects may be anywhere in the 32-bit address space (the compiler generates @code{seth/add3} instructions to load their addresses), and assume all subroutines are reachable with the @code{bl} instruction. @item -mmodel=large @opindex mmodel=large Assume objects may be anywhere in the 32-bit address space (the compiler generates @code{seth/add3} instructions to load their addresses), and assume subroutines may not be reachable with the @code{bl} instruction (the compiler generates the much slower @code{seth/add3/jl} instruction sequence). @item -msdata=none @opindex msdata=none Disable use of the small data area. Variables are put into one of @samp{.data}, @samp{.bss}, or @samp{.rodata} (unless the @code{section} attribute has been specified). This is the default. The small data area consists of sections @samp{.sdata} and @samp{.sbss}. Objects may be explicitly put in the small data area with the @code{section} attribute using one of these sections. @item -msdata=sdata @opindex msdata=sdata Put small global and static data in the small data area, but do not generate special code to reference them. @item -msdata=use @opindex msdata=use Put small global and static data in the small data area, and generate special instructions to reference them. @item -G @var{num} @opindex G @cindex smaller data references Put global and static objects less than or equal to @var{num} bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of @var{num} is 8. The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} for this option to have any effect. All modules should be compiled with the same @option{-G @var{num}} value. Compiling with different values of @var{num} may or may not work; if it doesn't the linker gives an error message---incorrect code is not generated. @item -mdebug @opindex mdebug Makes the M32R-specific code in the compiler display some statistics that might help in debugging programs. @item -malign-loops @opindex malign-loops Align all loops to a 32-byte boundary. @item -mno-align-loops @opindex mno-align-loops Do not enforce a 32-byte alignment for loops. This is the default. @item -missue-rate=@var{number} @opindex missue-rate=@var{number} Issue @var{number} instructions per cycle. @var{number} can only be 1 or 2. @item -mbranch-cost=@var{number} @opindex mbranch-cost=@var{number} @var{number} can only be 1 or 2. If it is 1 then branches are preferred over conditional code, if it is 2, then the opposite applies. @item -mflush-trap=@var{number} @opindex mflush-trap=@var{number} Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive. @item -mno-flush-trap @opindex mno-flush-trap Specifies that the cache cannot be flushed by using a trap. @item -mflush-func=@var{name} @opindex mflush-func=@var{name} Specifies the name of the operating system function to call to flush the cache. The default is @emph{_flush_cache}, but a function call is only used if a trap is not available. @item -mno-flush-func @opindex mno-flush-func Indicates that there is no OS function for flushing the cache. @end table @node M680x0 Options @subsection M680x0 Options @cindex M680x0 options These are the @samp{-m} options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below. @table @gcctabopt @item -march=@var{arch} @opindex march Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of @var{arch} for M680x0 architectures are: @samp{68000}, @samp{68010}, @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire architectures are selected according to Freescale's ISA classification and the permissible values are: @samp{isaa}, @samp{isaaplus}, @samp{isab} and @samp{isac}. GCC defines a macro @samp{__mcf@var{arch}__} whenever it is generating code for a ColdFire target. The @var{arch} in this macro is one of the @option{-march} arguments given above. When used together, @option{-march} and @option{-mtune} select code that runs on a family of similar processors but that is optimized for a particular microarchitecture. @item -mcpu=@var{cpu} @opindex mcpu Generate code for a specific M680x0 or ColdFire processor. The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table below, which also classifies the CPUs into families: @multitable @columnfractions 0.20 0.80 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments} @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} @item @samp{5206e} @tab @samp{5206e} @item @samp{5208} @tab @samp{5207} @samp{5208} @item @samp{5211a} @tab @samp{5210a} @samp{5211a} @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} @item @samp{5216} @tab @samp{5214} @samp{5216} @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} @item @samp{5225} @tab @samp{5224} @samp{5225} @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} @item @samp{5249} @tab @samp{5249} @item @samp{5250} @tab @samp{5250} @item @samp{5271} @tab @samp{5270} @samp{5271} @item @samp{5272} @tab @samp{5272} @item @samp{5275} @tab @samp{5274} @samp{5275} @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} @item @samp{5307} @tab @samp{5307} @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} @item @samp{5407} @tab @samp{5407} @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} @end multitable @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if @var{arch} is compatible with @var{cpu}. Other combinations of @option{-mcpu} and @option{-march} are rejected. GCC defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}}, where the value of @var{family} is given by the table above. @item -mtune=@var{tune} @opindex mtune Tune the code for a particular microarchitecture within the constraints set by @option{-march} and @option{-mcpu}. The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. The ColdFire microarchitectures are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. You can also use @option{-mtune=68020-40} for code that needs to run relatively well on 68020, 68030 and 68040 targets. @option{-mtune=68020-60} is similar but includes 68060 targets as well. These two options select the same tuning decisions as @option{-m68020-40} and @option{-m68020-60} respectively. GCC defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__} when tuning for 680x0 architecture @var{arch}. It also defines @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} option is used. If GCC is tuning for a range of architectures, as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, it defines the macros for every architecture in the range. GCC also defines the macro @samp{__m@var{uarch}__} when tuning for ColdFire microarchitecture @var{uarch}, where @var{uarch} is one of the arguments given above. @item -m68000 @itemx -mc68000 @opindex m68000 @opindex mc68000 Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. It is equivalent to @option{-march=68000}. Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. @item -m68010 @opindex m68010 Generate output for a 68010. This is the default when the compiler is configured for 68010-based systems. It is equivalent to @option{-march=68010}. @item -m68020 @itemx -mc68020 @opindex m68020 @opindex mc68020 Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. It is equivalent to @option{-march=68020}. @item -m68030 @opindex m68030 Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. It is equivalent to @option{-march=68030}. @item -m68040 @opindex m68040 Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. It is equivalent to @option{-march=68040}. This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions. @item -m68060 @opindex m68060 Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. It is equivalent to @option{-march=68060}. This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions. @item -mcpu32 @opindex mcpu32 Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to @option{-march=cpu32}. Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360. @item -m5200 @opindex m5200 Generate output for a 520X ColdFire CPU@. This is the default when the compiler is configured for 520X-based systems. It is equivalent to @option{-mcpu=5206}, and is now deprecated in favor of that option. Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5206. @item -m5206e @opindex m5206e Generate output for a 5206e ColdFire CPU@. The option is now deprecated in favor of the equivalent @option{-mcpu=5206e}. @item -m528x @opindex m528x Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent @option{-mcpu=528x}. @item -m5307 @opindex m5307 Generate output for a ColdFire 5307 CPU@. The option is now deprecated in favor of the equivalent @option{-mcpu=5307}. @item -m5407 @opindex m5407 Generate output for a ColdFire 5407 CPU@. The option is now deprecated in favor of the equivalent @option{-mcpu=5407}. @item -mcfv4e @opindex mcfv4e Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to @option{-mcpu=547x}, and is now deprecated in favor of that option. @item -m68020-40 @opindex m68020-40 Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040. The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. @item -m68020-60 @opindex m68020-60 Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060. The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. @item -mhard-float @itemx -m68881 @opindex mhard-float @opindex m68881 Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an FPU@. It defines the macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__} on ColdFire targets. @item -msoft-float @opindex msoft-float Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no FPU. @item -mdiv @itemx -mno-div @opindex mdiv @opindex mno-div Generate (do not generate) ColdFire hardware divide and remainder instructions. If @option{-march} is used without @option{-mcpu}, the default is ``on'' for ColdFire architectures and ``off'' for M680x0 architectures. Otherwise, the default is taken from the target CPU (either the default CPU, or the one specified by @option{-mcpu}). For example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for @option{-mcpu=5206e}. GCC defines the macro @samp{__mcfhwdiv__} when this option is enabled. @item -mshort @opindex mshort Consider type @code{int} to be 16 bits wide, like @code{short int}. Additionally, parameters passed on the stack are also aligned to a 16-bit boundary even on targets whose API mandates promotion to 32-bit. @item -mno-short @opindex mno-short Do not consider type @code{int} to be 16 bits wide. This is the default. @item -mnobitfield @itemx -mno-bitfield @opindex mnobitfield @opindex mno-bitfield Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} and @option{-m5200} options imply @w{@option{-mnobitfield}}. @item -mbitfield @opindex mbitfield Do use the bit-field instructions. The @option{-m68020} option implies @option{-mbitfield}. This is the default if you use a configuration designed for a 68020. @item -mrtd @opindex mrtd Use a different function-calling convention, in which functions that take a fixed number of arguments return with the @code{rtd} instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there. This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler. Also, you must provide function prototypes for all functions that take variable numbers of arguments (including @code{printf}); otherwise incorrect code is generated for calls to those functions. In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.) The @code{rtd} instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. @item -mno-rtd @opindex mno-rtd Do not use the calling conventions selected by @option{-mrtd}. This is the default. @item -malign-int @itemx -mno-align-int @opindex malign-int @opindex mno-align-int Control whether GCC aligns @code{int}, @code{long}, @code{long long}, @code{float}, @code{double}, and @code{long double} variables on a 32-bit boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). Aligning variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory. @strong{Warning:} if you use the @option{-malign-int} switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k. @item -mpcrel @opindex mpcrel Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies @option{-fpic}, allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is not presently supported with @option{-mpcrel}, though this could be supported for 68020 and higher processors. @item -mno-strict-align @itemx -mstrict-align @opindex mno-strict-align @opindex mstrict-align Do not (do) assume that unaligned memory references are handled by the system. @item -msep-data Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute-in-place in an environment without virtual memory management. This option implies @option{-fPIC}. @item -mno-sep-data Generate code that assumes that the data segment follows the text segment. This is the default. @item -mid-shared-library Generate code that supports shared libraries via the library ID method. This allows for execute-in-place and shared libraries in an environment without virtual memory management. This option implies @option{-fPIC}. @item -mno-id-shared-library Generate code that doesn't assume ID-based shared libraries are being used. This is the default. @item -mshared-library-id=n Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library, but is no more space- or time-efficient than omitting this option. @item -mxgot @itemx -mno-xgot @opindex mxgot @opindex mno-xgot When generating position-independent code for ColdFire, generate code that works if the GOT has more than 8192 entries. This code is larger and slower than code generated without this option. On M680x0 processors, this option is not needed; @option{-fPIC} suffices. GCC normally uses a single instruction to load values from the GOT@. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: @cindex relocation truncated to fit (ColdFire) @smallexample relocation truncated to fit: R_68K_GOT16O foobar @end smallexample If this happens, you should recompile your code with @option{-mxgot}. It should then work with very large GOTs. However, code generated with @option{-mxgot} is less efficient, since it takes 4 instructions to fetch the value of a global symbol. Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort GOT entries. If you have such a linker, you should only need to use @option{-mxgot} when compiling a single object file that accesses more than 8192 GOT entries. Very few do. These options have no effect unless GCC is generating position-independent code. @end table @node MCore Options @subsection MCore Options @cindex MCore options These are the @samp{-m} options defined for the Motorola M*Core processors. @table @gcctabopt @item -mhardlit @itemx -mno-hardlit @opindex mhardlit @opindex mno-hardlit Inline constants into the code stream if it can be done in two instructions or less. @item -mdiv @itemx -mno-div @opindex mdiv @opindex mno-div Use the divide instruction. (Enabled by default). @item -mrelax-immediate @itemx -mno-relax-immediate @opindex mrelax-immediate @opindex mno-relax-immediate Allow arbitrary-sized immediates in bit operations. @item -mwide-bitfields @itemx -mno-wide-bitfields @opindex mwide-bitfields @opindex mno-wide-bitfields Always treat bit-fields as @code{int}-sized. @item -m4byte-functions @itemx -mno-4byte-functions @opindex m4byte-functions @opindex mno-4byte-functions Force all functions to be aligned to a 4-byte boundary. @item -mcallgraph-data @itemx -mno-callgraph-data @opindex mcallgraph-data @opindex mno-callgraph-data Emit callgraph information. @item -mslow-bytes @itemx -mno-slow-bytes @opindex mslow-bytes @opindex mno-slow-bytes Prefer word access when reading byte quantities. @item -mlittle-endian @itemx -mbig-endian @opindex mlittle-endian @opindex mbig-endian Generate code for a little-endian target. @item -m210 @itemx -m340 @opindex m210 @opindex m340 Generate code for the 210 processor. @item -mno-lsim @opindex mno-lsim Assume that runtime support has been provided and so omit the simulator library (@file{libsim.a)} from the linker command line. @item -mstack-increment=@var{size} @opindex mstack-increment Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000. @end table @node MeP Options @subsection MeP Options @cindex MeP options @table @gcctabopt @item -mabsdiff @opindex mabsdiff Enables the @code{abs} instruction, which is the absolute difference between two registers. @item -mall-opts @opindex mall-opts Enables all the optional instructions---average, multiply, divide, bit operations, leading zero, absolute difference, min/max, clip, and saturation. @item -maverage @opindex maverage Enables the @code{ave} instruction, which computes the average of two registers. @item -mbased=@var{n} @opindex mbased= Variables of size @var{n} bytes or smaller are placed in the @code{.based} section by default. Based variables use the @code{$tp} register as a base register, and there is a 128-byte limit to the @code{.based} section. @item -mbitops @opindex mbitops Enables the bit operation instructions---bit test (@code{btstm}), set (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and test-and-set (@code{tas}). @item -mc=@var{name} @opindex mc= Selects which section constant data is placed in. @var{name} may be @code{tiny}, @code{near}, or @code{far}. @item -mclip @opindex mclip Enables the @code{clip} instruction. Note that @code{-mclip} is not useful unless you also provide @code{-mminmax}. @item -mconfig=@var{name} @opindex mconfig= Selects one of the built-in core configurations. Each MeP chip has one or more modules in it; each module has a core CPU and a variety of coprocessors, optional instructions, and peripherals. The @code{MeP-Integrator} tool, not part of GCC, provides these configurations through this option; using this option is the same as using all the corresponding command-line options. The default configuration is @code{default}. @item -mcop @opindex mcop Enables the coprocessor instructions. By default, this is a 32-bit coprocessor. Note that the coprocessor is normally enabled via the @code{-mconfig=} option. @item -mcop32 @opindex mcop32 Enables the 32-bit coprocessor's instructions. @item -mcop64 @opindex mcop64 Enables the 64-bit coprocessor's instructions. @item -mivc2 @opindex mivc2 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. @item -mdc @opindex mdc Causes constant variables to be placed in the @code{.near} section. @item -mdiv @opindex mdiv Enables the @code{div} and @code{divu} instructions. @item -meb @opindex meb Generate big-endian code. @item -mel @opindex mel Generate little-endian code. @item -mio-volatile @opindex mio-volatile Tells the compiler that any variable marked with the @code{io} attribute is to be considered volatile. @item -ml @opindex ml Causes variables to be assigned to the @code{.far} section by default. @item -mleadz @opindex mleadz Enables the @code{leadz} (leading zero) instruction. @item -mm @opindex mm Causes variables to be assigned to the @code{.near} section by default. @item -mminmax @opindex mminmax Enables the @code{min} and @code{max} instructions. @item -mmult @opindex mmult Enables the multiplication and multiply-accumulate instructions. @item -mno-opts @opindex mno-opts Disables all the optional instructions enabled by @code{-mall-opts}. @item -mrepeat @opindex mrepeat Enables the @code{repeat} and @code{erepeat} instructions, used for low-overhead looping. @item -ms @opindex ms Causes all variables to default to the @code{.tiny} section. Note that there is a 65536-byte limit to this section. Accesses to these variables use the @code{%gp} base register. @item -msatur @opindex msatur Enables the saturation instructions. Note that the compiler does not currently generate these itself, but this option is included for compatibility with other tools, like @code{as}. @item -msdram @opindex msdram Link the SDRAM-based runtime instead of the default ROM-based runtime. @item -msim @opindex msim Link the simulator run-time libraries. @item -msimnovec @opindex msimnovec Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and tables. @item -mtf @opindex mtf Causes all functions to default to the @code{.far} section. Without this option, functions default to the @code{.near} section. @item -mtiny=@var{n} @opindex mtiny= Variables that are @var{n} bytes or smaller are allocated to the @code{.tiny} section. These variables use the @code{$gp} base register. The default for this option is 4, but note that there's a 65536-byte limit to the @code{.tiny} section. @end table @node MicroBlaze Options @subsection MicroBlaze Options @cindex MicroBlaze Options @table @gcctabopt @item -msoft-float @opindex msoft-float Use software emulation for floating point (default). @item -mhard-float @opindex mhard-float Use hardware floating-point instructions. @item -mmemcpy @opindex mmemcpy Do not optimize block moves, use @code{memcpy}. @item -mno-clearbss @opindex mno-clearbss This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. @item -mcpu=@var{cpu-type} @opindex mcpu= Use features of, and schedule code for, the given CPU. Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, where @var{X} is a major version, @var{YY} is the minor version, and @var{Z} is compatibility code. Example values are @samp{v3.00.a}, @samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}. @item -mxl-soft-mul @opindex mxl-soft-mul Use software multiply emulation (default). @item -mxl-soft-div @opindex mxl-soft-div Use software emulation for divides (default). @item -mxl-barrel-shift @opindex mxl-barrel-shift Use the hardware barrel shifter. @item -mxl-pattern-compare @opindex mxl-pattern-compare Use pattern compare instructions. @item -msmall-divides @opindex msmall-divides Use table lookup optimization for small signed integer divisions. @item -mxl-stack-check @opindex mxl-stack-check This option is deprecated. Use @option{-fstack-check} instead. @item -mxl-gp-opt @opindex mxl-gp-opt Use GP-relative @code{.sdata}/@code{.sbss} sections. @item -mxl-multiply-high @opindex mxl-multiply-high Use multiply high instructions for high part of 32x32 multiply. @item -mxl-float-convert @opindex mxl-float-convert Use hardware floating-point conversion instructions. @item -mxl-float-sqrt @opindex mxl-float-sqrt Use hardware floating-point square root instruction. @item -mbig-endian @opindex mbig-endian Generate code for a big-endian target. @item -mlittle-endian @opindex mlittle-endian Generate code for a little-endian target. @item -mxl-reorder @opindex mxl-reorder Use reorder instructions (swap and byte reversed load/store). @item -mxl-mode-@var{app-model} Select application model @var{app-model}. Valid models are @table @samp @item executable normal executable (default), uses startup code @file{crt0.o}. @item xmdstub for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug agent called xmdstub. This uses startup file @file{crt1.o} and sets the start address of the program to 0x800. @item bootstrap for applications that are loaded using a bootloader. This model uses startup file @file{crt2.o} which does not contain a processor reset vector handler. This is suitable for transferring control on a processor reset to the bootloader rather than the application. @item novectors for applications that do not require any of the MicroBlaze vectors. This option may be useful for applications running within a monitoring application. This model uses @file{crt3.o} as a startup file. @end table Option @option{-xl-mode-@var{app-model}} is a deprecated alias for @option{-mxl-mode-@var{app-model}}. @end table @node MIPS Options @subsection MIPS Options @cindex MIPS options @table @gcctabopt @item -EB @opindex EB Generate big-endian code. @item -EL @opindex EL Generate little-endian code. This is the default for @samp{mips*el-*-*} configurations. @item -march=@var{arch} @opindex march Generate code that runs on @var{arch}, which can be the name of a generic MIPS ISA, or the name of a particular processor. The ISA names are: @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, @samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3} and @samp{mips64r5}. The processor names are: @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, @samp{5kc}, @samp{5kf}, @samp{20kc}, @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, @samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, @samp{m4k}, @samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec}, @samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3}, @samp{orion}, @samp{p5600}, @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, @samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000}, @samp{rm7000}, @samp{rm9000}, @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, @samp{sb1}, @samp{sr71000}, @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, @samp{vr5000}, @samp{vr5400}, @samp{vr5500}, @samp{xlr} and @samp{xlp}. The special value @samp{from-abi} selects the most compatible architecture for the selected ABI (that is, @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. The native Linux/GNU toolchain also supports the value @samp{native}, which selects the best architecture option for the host processor. @option{-march=native} has no effect if GCC does not recognize the processor. In processor names, a final @samp{000} can be abbreviated as @samp{k} (for example, @option{-march=r2k}). Prefixes are optional, and @samp{vr} may be written @samp{r}. Names of the form @samp{@var{n}f2_1} refer to processors with FPUs clocked at half the rate of the core, names of the form @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same rate as the core, and names of the form @samp{@var{n}f3_2} refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, @samp{@var{n}f} is accepted as a synonym for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are accepted as synonyms for @samp{@var{n}f1_1}. GCC defines two macros based on the value of this option. The first is @samp{_MIPS_ARCH}, which gives the name of target architecture, as a string. The second has the form @samp{_MIPS_ARCH_@var{foo}}, where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@. For example, @option{-march=r2000} sets @samp{_MIPS_ARCH} to @samp{"r2000"} and defines the macro @samp{_MIPS_ARCH_R2000}. Note that the @samp{_MIPS_ARCH} macro uses the processor names given above. In other words, it has the full prefix and does not abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, the macro names the resolved architecture (either @samp{"mips1"} or @samp{"mips3"}). It names the default architecture when no @option{-march} option is given. @item -mtune=@var{arch} @opindex mtune Optimize for @var{arch}. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of @var{arch} values is the same as for @option{-march}. When this option is not used, GCC optimizes for the processor specified by @option{-march}. By using @option{-march} and @option{-mtune} together, it is possible to generate code that runs on a family of processors, but optimize the code for one particular member of that family. @option{-mtune} defines the macros @samp{_MIPS_TUNE} and @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the @option{-march} ones described above. @item -mips1 @opindex mips1 Equivalent to @option{-march=mips1}. @item -mips2 @opindex mips2 Equivalent to @option{-march=mips2}. @item -mips3 @opindex mips3 Equivalent to @option{-march=mips3}. @item -mips4 @opindex mips4 Equivalent to @option{-march=mips4}. @item -mips32 @opindex mips32 Equivalent to @option{-march=mips32}. @item -mips32r3 @opindex mips32r3 Equivalent to @option{-march=mips32r3}. @item -mips32r5 @opindex mips32r5 Equivalent to @option{-march=mips32r5}. @item -mips64 @opindex mips64 Equivalent to @option{-march=mips64}. @item -mips64r2 @opindex mips64r2 Equivalent to @option{-march=mips64r2}. @item -mips64r3 @opindex mips64r3 Equivalent to @option{-march=mips64r3}. @item -mips64r5 @opindex mips64r5 Equivalent to @option{-march=mips64r5}. @item -mips16 @itemx -mno-mips16 @opindex mips16 @opindex mno-mips16 Generate (do not generate) MIPS16 code. If GCC is targeting a MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. MIPS16 code generation can also be controlled on a per-function basis by means of @code{mips16} and @code{nomips16} attributes. @xref{Function Attributes}, for more information. @item -mflip-mips16 @opindex mflip-mips16 Generate MIPS16 code on alternating functions. This option is provided for regression testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code. @item -minterlink-compressed @item -mno-interlink-compressed @opindex minterlink-compressed @opindex mno-interlink-compressed Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-compatible with MIPS16 and microMIPS code, and vice versa. For example, code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code; it must either use a call or an indirect jump. @option{-minterlink-compressed} therefore disables direct jumps unless GCC knows that the target of the jump is not compressed. @item -minterlink-mips16 @itemx -mno-interlink-mips16 @opindex minterlink-mips16 @opindex mno-interlink-mips16 Aliases of @option{-minterlink-compressed} and @option{-mno-interlink-compressed}. These options predate the microMIPS ASE and are retained for backwards compatibility. @item -mabi=32 @itemx -mabi=o64 @itemx -mabi=n32 @itemx -mabi=64 @itemx -mabi=eabi @opindex mabi=32 @opindex mabi=o64 @opindex mabi=n32 @opindex mabi=64 @opindex mabi=eabi Generate code for the given ABI@. Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use @option{-mgp32} to get 32-bit code instead. For information about the O64 ABI, see @uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}. GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather than 32 bits wide. You can select this combination with @option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} and @code{mfhc1} instructions and is therefore only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors. The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, scalar floating-point values are returned in @samp{$f0} only, not a @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are saved. Two additional variants of the o32 ABI are supported to enable a transition from 32-bit to 64-bit registers. These are FPXX (@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}). The FPXX extension mandates that all code must execute correctly when run using 32-bit or 64-bit registers. The code can be interlinked with either FP32 or FP64, but not both. The FP64A extension is similar to the FP64 extension but forbids the use of odd-numbered single-precision registers. This can be used in conjunction with the @code{FRE} mode of FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to interlink and run in the same process without changing FPU modes. @item -mabicalls @itemx -mno-abicalls @opindex mabicalls @opindex mno-abicalls Generate (do not generate) code that is suitable for SVR4-style dynamic objects. @option{-mabicalls} is the default for SVR4-based systems. @item -mshared @itemx -mno-shared Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects @option{-mabicalls}. All @option{-mabicalls} code has traditionally been position-independent, regardless of options like @option{-fPIC} and @option{-fpic}. However, as an extension, the GNU toolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally-defined functions. This mode is selected by @option{-mno-shared}. @option{-mno-shared} depends on binutils 2.16 or higher and generates objects that can only be linked by the GNU linker. However, the option does not affect the ABI of the final executable; it only affects the ABI of relocatable objects. Using @option{-mno-shared} generally makes executables both smaller and quicker. @option{-mshared} is the default. @item -mplt @itemx -mno-plt @opindex mplt @opindex mno-plt Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects @option{-mno-shared -mabicalls}. For the n64 ABI, this option has no effect without @option{-msym32}. You can make @option{-mplt} the default by configuring GCC with @option{--with-mips-plt}. The default is @option{-mno-plt} otherwise. @item -mxgot @itemx -mno-xgot @opindex mxgot @opindex mno-xgot Lift (do not lift) the usual restrictions on the size of the global offset table. GCC normally uses a single instruction to load values from the GOT@. While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as: @cindex relocation truncated to fit (MIPS) @smallexample relocation truncated to fit: R_MIPS_GOT16 foobar @end smallexample If this happens, you should recompile your code with @option{-mxgot}. This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value of a global symbol. Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use @option{-mxgot} when a single object file accesses more than 64k's worth of GOT entries. Very few do. These options have no effect unless GCC is generating position independent code. @item -mgp32 @opindex mgp32 Assume that general-purpose registers are 32 bits wide. @item -mgp64 @opindex mgp64 Assume that general-purpose registers are 64 bits wide. @item -mfp32 @opindex mfp32 Assume that floating-point registers are 32 bits wide. @item -mfp64 @opindex mfp64 Assume that floating-point registers are 64 bits wide. @item -mfpxx @opindex mfpxx Do not assume the width of floating-point registers. @item -mhard-float @opindex mhard-float Use floating-point coprocessor instructions. @item -msoft-float @opindex msoft-float Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead. @item -mno-float @opindex mno-float Equivalent to @option{-msoft-float}, but additionally asserts that the program being compiled does not perform any floating-point operations. This option is presently supported only by some bare-metal MIPS configurations, where it may select a special set of libraries that lack all floating-point support (including, for example, the floating-point @code{printf} formats). If code compiled with @code{-mno-float} accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure. @item -msingle-float @opindex msingle-float Assume that the floating-point coprocessor only supports single-precision operations. @item -mdouble-float @opindex mdouble-float Assume that the floating-point coprocessor supports double-precision operations. This is the default. @item -modd-spreg @itemx -mno-odd-spreg @opindex modd-spreg @opindex mno-odd-spreg Enable the use of odd-numbered single-precision floating-point registers for the o32 ABI. This is the default for processors that are known to support these registers. When using the o32 FPXX ABI, @code{-mno-odd-spreg} is set by default. @item -mabs=2008 @itemx -mabs=legacy @opindex mabs=2008 @opindex mabs=legacy These options control the treatment of the special not-a-number (NaN) IEEE 754 floating-point data with the @code{abs.@i{fmt}} and @code{neg.@i{fmt}} machine instructions. By default or when the @option{-mabs=legacy} is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the @option{-ffinite-math-only} option has also been specified. The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN. These instructions are therefore always used for the respective operations. @item -mnan=2008 @itemx -mnan=legacy @opindex mnan=2008 @opindex mnan=legacy These options control the encoding of the special not-a-number (NaN) IEEE 754 floating-point data. The @option{-mnan=legacy} option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signalling NaNs (sNaNs) are denoted by the first bit of their trailing significand field being 1. The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit of their trailing significand field being 0. The default is @option{-mnan=legacy} unless GCC has been configured with @option{--with-nan=2008}. @item -mllsc @itemx -mno-llsc @opindex mllsc @opindex mno-llsc Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to implement atomic memory built-in functions. When neither option is specified, GCC uses the instructions if the target architecture supports them. @option{-mllsc} is useful if the runtime environment can emulate the instructions and @option{-mno-llsc} can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring GCC with @option{--with-llsc} and @option{--without-llsc} respectively. @option{--with-llsc} is the default for some configurations; see the installation documentation for details. @item -mdsp @itemx -mno-dsp @opindex mdsp @opindex mno-dsp Use (do not use) revision 1 of the MIPS DSP ASE@. @xref{MIPS DSP Built-in Functions}. This option defines the preprocessor macro @samp{__mips_dsp}. It also defines @samp{__mips_dsp_rev} to 1. @item -mdspr2 @itemx -mno-dspr2 @opindex mdspr2 @opindex mno-dspr2 Use (do not use) revision 2 of the MIPS DSP ASE@. @xref{MIPS DSP Built-in Functions}. This option defines the preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}. It also defines @samp{__mips_dsp_rev} to 2. @item -msmartmips @itemx -mno-smartmips @opindex msmartmips @opindex mno-smartmips Use (do not use) the MIPS SmartMIPS ASE. @item -mpaired-single @itemx -mno-paired-single @opindex mpaired-single @opindex mno-paired-single Use (do not use) paired-single floating-point instructions. @xref{MIPS Paired-Single Support}. This option requires hardware floating-point support to be enabled. @item -mdmx @itemx -mno-mdmx @opindex mdmx @opindex mno-mdmx Use (do not use) MIPS Digital Media Extension instructions. This option can only be used when generating 64-bit code and requires hardware floating-point support to be enabled. @item -mips3d @itemx -mno-mips3d @opindex mips3d @opindex mno-mips3d Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. The option @option{-mips3d} implies @option{-mpaired-single}. @item -mmicromips @itemx -mno-micromips @opindex mmicromips @opindex mno-mmicromips Generate (do not generate) microMIPS code. MicroMIPS code generation can also be controlled on a per-function basis by means of @code{micromips} and @code{nomicromips} attributes. @xref{Function Attributes}, for more information. @item -mmt @itemx -mno-mt @opindex mmt @opindex mno-mt Use (do not use) MT Multithreading instructions. @item -mmcu @itemx -mno-mcu @opindex mmcu @opindex mno-mcu Use (do not use) the MIPS MCU ASE instructions. @item -meva @itemx -mno-eva @opindex meva @opindex mno-eva Use (do not use) the MIPS Enhanced Virtual Addressing instructions. @item -mvirt @itemx -mno-virt @opindex mvirt @opindex mno-virt Use (do not use) the MIPS Virtualization Application Specific instructions. @item -mxpa @itemx -mno-xpa @opindex mxpa @opindex mno-xpa Use (do not use) the MIPS eXtended Physical Address (XPA) instructions. @item -mlong64 @opindex mlong64 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for an explanation of the default and the way that the pointer size is determined. @item -mlong32 @opindex mlong32 Force @code{long}, @code{int}, and pointer types to be 32 bits wide. The default size of @code{int}s, @code{long}s and pointers depends on the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI uses 64-bit @code{long}s, as does the 64-bit EABI; the others use 32-bit @code{long}s. Pointers are the same size as @code{long}s, or the same size as integer registers, whichever is smaller. @item -msym32 @itemx -mno-sym32 @opindex msym32 @opindex mno-sym32 Assume (do not assume) that all symbols have 32-bit values, regardless of the selected ABI@. This option is useful in combination with @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC to generate shorter and faster references to symbolic addresses. @item -G @var{num} @opindex G Put definitions of externally-visible data in a small data section if that data is no bigger than @var{num} bytes. GCC can then generate more efficient accesses to the data; see @option{-mgpopt} for details. The default @option{-G} option depends on the configuration. @item -mlocal-sdata @itemx -mno-local-sdata @opindex mlocal-sdata @opindex mno-local-sdata Extend (do not extend) the @option{-G} behavior to local data too, such as to static variables in C@. @option{-mlocal-sdata} is the default for all configurations. If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with @option{-mno-local-sdata}. You might also want to build large libraries with @option{-mno-local-sdata}, so that the libraries leave more room for the main program. @item -mextern-sdata @itemx -mno-extern-sdata @opindex mextern-sdata @opindex mno-extern-sdata Assume (do not assume) that externally-defined data is in a small data section if the size of that data is within the @option{-G} limit. @option{-mextern-sdata} is the default for all configurations. If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} that is no bigger than @var{num} bytes, you must make sure that @var{Var} is placed in a small data section. If @var{Var} is defined by another module, you must either compile that module with a high-enough @option{-G} setting or attach a @code{section} attribute to @var{Var}'s definition. If @var{Var} is common, you must link the application with a high-enough @option{-G} setting. The easiest way of satisfying these restrictions is to compile and link every module with the same @option{-G} option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported @option{-G} setting and additionally using @option{-mno-extern-sdata} to stop the library from making assumptions about externally-defined data. @item -mgpopt @itemx -mno-gpopt @opindex mgpopt @opindex mno-gpopt Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see @option{-G}, @option{-mlocal-sdata} and @option{-mextern-sdata}. @option{-mgpopt} is the default for all configurations. @option{-mno-gpopt} is useful for cases where the @code{$gp} register might not hold the value of @code{_gp}. For example, if the code is part of a library that might be used in a boot monitor, programs that call boot monitor routines pass an unknown value in @code{$gp}. (In such situations, the boot monitor itself is usually compiled with @option{-G0}.) @option{-mno-gpopt} implies @option{-mno-local-sdata} and @option{-mno-extern-sdata}. @item -membedded-data @itemx -mno-embedded-data @opindex membedded-data @opindex mno-embedded-data Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems. @item -muninit-const-in-rodata @itemx -mno-uninit-const-in-rodata @opindex muninit-const-in-rodata @opindex mno-uninit-const-in-rodata Put uninitialized @code{const} variables in the read-only data section. This option is only meaningful in conjunction with @option{-membedded-data}. @item -mcode-readable=@var{setting} @opindex mcode-readable Specify whether GCC may generate code that reads from executable sections. There are three possible settings: @table @gcctabopt @item -mcode-readable=yes Instructions may freely access executable sections. This is the default setting. @item -mcode-readable=pcrel MIPS16 PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful on 4KSc and 4KSd processors when the code TLBs have the Read Inhibit bit set. It is also useful on processors that can be configured to have a dual instruction/data SRAM interface and that, like the M4K, automatically redirect PC-relative loads to the instruction RAM. @item -mcode-readable=no Instructions must not access executable sections. This option can be useful on targets that are configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do not automatically redirect PC-relative loads to the instruction RAM. @end table @item -msplit-addresses @itemx -mno-split-addresses @opindex msplit-addresses @opindex mno-split-addresses Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler relocation operators. This option has been superseded by @option{-mexplicit-relocs} but is retained for backwards compatibility. @item -mexplicit-relocs @itemx -mno-explicit-relocs @opindex mexplicit-relocs @opindex mno-explicit-relocs Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by @option{-mno-explicit-relocs}, is to use assembler macros instead. @option{-mexplicit-relocs} is the default if GCC was configured to use an assembler that supports relocation operators. @item -mcheck-zero-division @itemx -mno-check-zero-division @opindex mcheck-zero-division @opindex mno-check-zero-division Trap (do not trap) on integer division by zero. The default is @option{-mcheck-zero-division}. @item -mdivide-traps @itemx -mdivide-breaks @opindex mdivide-traps @opindex mdivide-breaks MIPS systems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on MIPS II and later. Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to allow conditional traps on architectures that support them and @option{-mdivide-breaks} to force the use of breaks. The default is usually @option{-mdivide-traps}, but this can be overridden at configure time using @option{--with-divide=breaks}. Divide-by-zero checks can be completely disabled using @option{-mno-check-zero-division}. @item -mmemcpy @itemx -mno-memcpy @opindex mmemcpy @opindex mno-memcpy Force (do not force) the use of @code{memcpy()} for non-trivial block moves. The default is @option{-mno-memcpy}, which allows GCC to inline most constant-sized copies. @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Disable (do not disable) use of the @code{jal} instruction. Calling functions using @code{jal} is more efficient but requires the caller and callee to be in the same 256 megabyte segment. This option has no effect on abicalls code. The default is @option{-mno-long-calls}. @item -mmad @itemx -mno-mad @opindex mmad @opindex mno-mad Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} instructions, as provided by the R4650 ISA@. @item -mimadd @itemx -mno-imadd @opindex mimadd @opindex mno-imadd Enable (disable) use of the @code{madd} and @code{msub} integer instructions. The default is @option{-mimadd} on architectures that support @code{madd} and @code{msub} except for the 74k architecture where it was found to generate slower code. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is @option{-mfused-madd}. On the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions. @item -nocpp @opindex nocpp Tell the MIPS assembler to not run its preprocessor over user assembler files (with a @samp{.s} suffix) when assembling them. @item -mfix-24k @item -mno-fix-24k @opindex mfix-24k @opindex mno-fix-24k Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by GCC@. @item -mfix-r4000 @itemx -mno-fix-r4000 @opindex mfix-r4000 @opindex mno-fix-r4000 Work around certain R4000 CPU errata: @itemize @minus @item A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. @item A double-word or a variable shift may give an incorrect result if executed while an integer multiplication is in progress. @item An integer division may give an incorrect result if started in a delay slot of a taken branch or a jump. @end itemize @item -mfix-r4400 @itemx -mno-fix-r4400 @opindex mfix-r4400 @opindex mno-fix-r4400 Work around certain R4400 CPU errata: @itemize @minus @item A double-word or a variable shift may give an incorrect result if executed immediately after starting an integer division. @end itemize @item -mfix-r10000 @itemx -mno-fix-r10000 @opindex mfix-r10000 @opindex mno-fix-r10000 Work around certain R10000 errata: @itemize @minus @item @code{ll}/@code{sc} sequences may not behave atomically on revisions prior to 3.0. They may deadlock on revisions 2.6 and earlier. @end itemize This option can only be used if the target architecture supports branch-likely instructions. @option{-mfix-r10000} is the default when @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default otherwise. @item -mfix-rm7000 @itemx -mno-fix-rm7000 @opindex mfix-rm7000 Work around the RM7000 @code{dmult}/@code{dmultu} errata. The workarounds are implemented by the assembler rather than by GCC@. @item -mfix-vr4120 @itemx -mno-fix-vr4120 @opindex mfix-vr4120 Work around certain VR4120 errata: @itemize @minus @item @code{dmultu} does not always produce the correct result. @item @code{div} and @code{ddiv} do not always produce the correct result if one of the operands is negative. @end itemize The workarounds for the division errata rely on special functions in @file{libgcc.a}. At present, these functions are only provided by the @code{mips64vr*-elf} configurations. Other VR4120 errata require a NOP to be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCC itself. @item -mfix-vr4130 @opindex mfix-vr4130 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The workarounds are implemented by the assembler rather than by GCC, although GCC avoids using @code{mflo} and @code{mfhi} if the VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} instructions are available instead. @item -mfix-sb1 @itemx -mno-fix-sb1 @opindex mfix-sb1 Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 ``F1'' and ``F2'' floating-point errata.) @item -mr10k-cache-barrier=@var{setting} @opindex mr10k-cache-barrier Specify whether GCC should insert cache barriers to avoid the side-effects of speculation on R10K processors. In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the ``taken'' branch. It later aborts these instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects. This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a DMA operation writes to the same area of memory before the ``dirty'' line is flushed, the cached data overwrites the DMA-ed data. See the R10K processor manual for a full description, including other potential problems. One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} controls GCC's implementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects: @enumerate @item the memory occupied by the current function's stack frame; @item the memory occupied by an incoming stack argument; @item the memory occupied by an object with a link-time-constant address. @end enumerate It is the kernel's responsibility to ensure that speculative accesses to these regions are indeed safe. If the input program contains a function declaration such as: @smallexample void foo (void); @end smallexample then the implementation of @code{foo} must allow @code{j foo} and @code{jal foo} to be executed speculatively. GCC honors this restriction for functions it compiles itself. It expects non-GCC functions (such as hand-written assembly code) to do the same. The option has three forms: @table @gcctabopt @item -mr10k-cache-barrier=load-store Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted. @item -mr10k-cache-barrier=store Insert a cache barrier before a store that might be speculatively executed and that might have side effects even if aborted. @item -mr10k-cache-barrier=none Disable the insertion of cache barriers. This is the default setting. @end table @item -mflush-func=@var{func} @itemx -mno-flush-func @opindex mflush-func Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common @code{_flush_func()}, that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCC was configured for, but commonly is either @samp{_flush_func} or @samp{__cpu_flush}. @item mbranch-cost=@var{num} @opindex mbranch-cost Set the cost of branches to roughly @var{num} ``simple'' instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly selects the default, which is based on the @option{-mtune} setting. @item -mbranch-likely @itemx -mno-branch-likely @opindex mbranch-likely @opindex mno-branch-likely Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the MIPS32 and MIPS64 architectures and processors that implement those architectures; for those, Branch Likely instructions are not be generated by default because the MIPS32 and MIPS64 architectures specifically deprecate their use. @item -mfp-exceptions @itemx -mno-fp-exceptions @opindex mfp-exceptions Specifies whether FP exceptions are enabled. This affects how FP instructions are scheduled for some processors. The default is that FP exceptions are enabled. For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we can use both FP pipes. Otherwise, we can only use one FP pipe. @item -mvr4130-align @itemx -mno-vr4130-align @opindex mvr4130-align The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8-byte aligned. When this option is enabled, GCC aligns pairs of instructions that it thinks should execute in parallel. This option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level @option{-O3}. @item -msynci @itemx -mno-synci @opindex msynci Enable (disable) generation of @code{synci} instructions on architectures that support it. The @code{synci} instructions (if enabled) are generated when @code{__builtin___clear_cache()} is compiled. This option defaults to @code{-mno-synci}, but the default can be overridden by configuring with @code{--with-synci}. When compiling code for single processor systems, it is generally safe to use @code{synci}. However, on many multi-core (SMP) systems, it does not invalidate the instruction caches on all cores and may lead to undefined behavior. @item -mrelax-pic-calls @itemx -mno-relax-pic-calls @opindex mrelax-pic-calls Try to turn PIC calls that are normally dispatched via register @code{$25} into direct calls. This is only possible if the linker can resolve the destination at link-time and if the destination is within range for a direct call. @option{-mrelax-pic-calls} is the default if GCC was configured to use an assembler and a linker that support the @code{.reloc} assembly directive and @code{-mexplicit-relocs} is in effect. With @code{-mno-explicit-relocs}, this optimization can be performed by the assembler and the linker alone without help from the compiler. @item -mmcount-ra-address @itemx -mno-mcount-ra-address @opindex mmcount-ra-address @opindex mno-mcount-ra-address Emit (do not emit) code that allows @code{_mcount} to modify the calling function's return address. When enabled, this option extends the usual @code{_mcount} interface with a new @var{ra-address} parameter, which has type @code{intptr_t *} and is passed in register @code{$12}. @code{_mcount} can then modify the return address by doing both of the following: @itemize @item Returning the new address in register @code{$31}. @item Storing the new address in @code{*@var{ra-address}}, if @var{ra-address} is nonnull. @end itemize The default is @option{-mno-mcount-ra-address}. @end table @node MMIX Options @subsection MMIX Options @cindex MMIX Options These options are defined for the MMIX: @table @gcctabopt @item -mlibfuncs @itemx -mno-libfuncs @opindex mlibfuncs @opindex mno-libfuncs Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size. @item -mepsilon @itemx -mno-epsilon @opindex mepsilon @opindex mno-epsilon Generate floating-point comparison instructions that compare with respect to the @code{rE} epsilon register. @item -mabi=mmixware @itemx -mabi=gnu @opindex mabi=mmixware @opindex mabi=gnu Generate code that passes function parameters and return values that (in the called function) are seen as registers @code{$0} and up, as opposed to the GNU ABI which uses global registers @code{$231} and up. @item -mzero-extend @itemx -mno-zero-extend @opindex mzero-extend @opindex mno-zero-extend When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones. @item -mknuthdiv @itemx -mno-knuthdiv @opindex mknuthdiv @opindex mno-knuthdiv Make the result of a division yielding a remainder have the same sign as the divisor. With the default, @option{-mno-knuthdiv}, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used. @item -mtoplevel-symbols @itemx -mno-toplevel-symbols @opindex mtoplevel-symbols @opindex mno-toplevel-symbols Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly code can be used with the @code{PREFIX} assembly directive. @item -melf @opindex melf Generate an executable in the ELF format, rather than the default @samp{mmo} format used by the @command{mmix} simulator. @item -mbranch-predict @itemx -mno-branch-predict @opindex mbranch-predict @opindex mno-branch-predict Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch. @item -mbase-addresses @itemx -mno-base-addresses @opindex mbase-addresses @opindex mno-base-addresses Generate (do not generate) code that uses @emph{base addresses}. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require @option{-mno-base-addresses}. @item -msingle-exit @itemx -mno-single-exit @opindex msingle-exit @opindex mno-single-exit Force (do not force) generated code to have a single exit point in each function. @end table @node MN10300 Options @subsection MN10300 Options @cindex MN10300 options These @option{-m} options are defined for Matsushita MN10300 architectures: @table @gcctabopt @item -mmult-bug @opindex mmult-bug Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default. @item -mno-mult-bug @opindex mno-mult-bug Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors. @item -mam33 @opindex mam33 Generate code using features specific to the AM33 processor. @item -mno-am33 @opindex mno-am33 Do not generate code using features specific to the AM33 processor. This is the default. @item -mam33-2 @opindex mam33-2 Generate code using features specific to the AM33/2.0 processor. @item -mam34 @opindex mam34 Generate code using features specific to the AM34 processor. @item -mtune=@var{cpu-type} @opindex mtune Use the timing characteristics of the indicated CPU type when scheduling instructions. This does not change the targeted processor type. The CPU type must be one of @samp{mn10300}, @samp{am33}, @samp{am33-2} or @samp{am34}. @item -mreturn-pointer-on-d0 @opindex mreturn-pointer-on-d0 When generating a function that returns a pointer, return the pointer in both @code{a0} and @code{d0}. Otherwise, the pointer is returned only in @code{a0}, and attempts to call such functions without a prototype result in errors. Note that this option is on by default; use @option{-mno-return-pointer-on-d0} to disable it. @item -mno-crt0 @opindex mno-crt0 Do not link in the C run-time initialization object file. @item -mrelax @opindex mrelax Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step. This option makes symbolic debugging impossible. @item -mliw @opindex mliw Allow the compiler to generate @emph{Long Instruction Word} instructions if the target is the @samp{AM33} or later. This is the default. This option defines the preprocessor macro @samp{__LIW__}. @item -mnoliw @opindex mnoliw Do not allow the compiler to generate @emph{Long Instruction Word} instructions. This option defines the preprocessor macro @samp{__NO_LIW__}. @item -msetlb @opindex msetlb Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} instructions if the target is the @samp{AM33} or later. This is the default. This option defines the preprocessor macro @samp{__SETLB__}. @item -mnosetlb @opindex mnosetlb Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} instructions. This option defines the preprocessor macro @samp{__NO_SETLB__}. @end table @node Moxie Options @subsection Moxie Options @cindex Moxie Options @table @gcctabopt @item -meb @opindex meb Generate big-endian code. This is the default for @samp{moxie-*-*} configurations. @item -mel @opindex mel Generate little-endian code. @item -mno-crt0 @opindex mno-crt0 Do not link in the C run-time initialization object file. @end table @node MSP430 Options @subsection MSP430 Options @cindex MSP430 Options These options are defined for the MSP430: @table @gcctabopt @item -masm-hex @opindex masm-hex Force assembly output to always use hex constants. Normally such constants are signed decimals, but this option is available for testsuite and/or aesthetic purposes. @item -mmcu= @opindex mmcu= Select the MCU to target. This is used to create a C preprocessor symbol based upon the MCU name, converted to upper case and pre- and post- fixed with @code{__}. This in turn will be used by the @code{msp430.h} header file to select an MCU specific supplimentary header file. The option also sets the ISA to use. If the MCU name is one that is known to only support the 430 ISA then that is selected, otherwise the 430X ISA is selected. A generic MCU name of @code{msp430} can also be used to select the 430 ISA. Similarly the generic @code{msp430x} MCU name will select the 430X ISA. In addition an MCU specific linker script will be added to the linker command line. The script's name is the name of the MCU with @code{.ld} appended. Thus specifying @option{-mmcu=xxx} on the gcc command line will define the C preprocessor symbol @code{__XXX__} and cause the linker to search for a script called @file{xxx.ld}. This option is also passed on to the assembler. @item -mcpu= @opindex -mcpu= Specifies the ISA to use. Accepted values are @code{msp430}, @code{msp430x} and @code{msp430xv2}. This option is deprecated. The @option{-mmcu=} option should be used to select the ISA. @item -msim @opindex msim Link to the simulator runtime libraries and linker script. Overrides any scripts that would be selected by the @option{-mmcu=} option. @item -mlarge @opindex mlarge Use large-model addressing (20-bit pointers, 32-bit @code{size_t}). @item -msmall @opindex msmall Use small-model addressing (16-bit pointers, 16-bit @code{size_t}). @item -mrelax @opindex mrelax This option is passed to the assembler and linker, and allows the linker to perform certain optimizations that cannot be done until the final link. @item mhwmult= @opindex mhwmult= Describes the type of hardware multiply supported by the target. Accepted values are @code{none} for no hardware multiply, @code{16bit} for the original 16-bit-only multiply supported by early MCUs. @code{32bit} for the 16/32-bit multiply supported by later MCUs and @code{f5series} for the 16/32-bit multiply supported by F5-series MCUs. A value of @code{auto} can also be given. This tells GCC to deduce the hardware multiply support based upon the MCU name provided by the @option{-mmcu} option. If no @option{-mmcu} option is specified then @code{32bit} hardware multiply support is assumed. @code{auto} is the default setting. Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at @code{-O3} or higher however the hardware multiplier is invoked inline. This makes for bigger, but faster code. The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as in normal code. @item -minrt @opindex minrt Enable the use of a minimum runtime environment - no static initializers or constructors. This is intended for memory-constrained devices. The compiler will include special symbols in some objects that tell the linker and runtime which code fragments are required. @end table @node NDS32 Options @subsection NDS32 Options @cindex NDS32 Options These options are defined for NDS32 implementations: @table @gcctabopt @item -mbig-endian @opindex mbig-endian Generate code in big-endian mode. @item -mlittle-endian @opindex mlittle-endian Generate code in little-endian mode. @item -mreduced-regs @opindex mreduced-regs Use reduced-set registers for register allocation. @item -mfull-regs @opindex mfull-regs Use full-set registers for register allocation. @item -mcmov @opindex mcmov Generate conditional move instructions. @item -mno-cmov @opindex mno-cmov Do not generate conditional move instructions. @item -mperf-ext @opindex mperf-ext Generate performance extension instructions. @item -mno-perf-ext @opindex mno-perf-ext Do not generate performance extension instructions. @item -mv3push @opindex mv3push Generate v3 push25/pop25 instructions. @item -mno-v3push @opindex mno-v3push Do not generate v3 push25/pop25 instructions. @item -m16-bit @opindex m16-bit Generate 16-bit instructions. @item -mno-16-bit @opindex mno-16-bit Do not generate 16-bit instructions. @item -mgp-direct @opindex mgp-direct Generate GP base instructions directly. @item -mno-gp-direct @opindex mno-gp-direct Do no generate GP base instructions directly. @item -misr-vector-size=@var{num} @opindex misr-vector-size Specify the size of each interrupt vector, which must be 4 or 16. @item -mcache-block-size=@var{num} @opindex mcache-block-size Specify the size of each cache block, which must be a power of 2 between 4 and 512. @item -march=@var{arch} @opindex march Specify the name of the target architecture. @item -mforce-fp-as-gp @opindex mforce-fp-as-gp Prevent $fp being allocated during register allocation so that compiler is able to force performing fp-as-gp optimization. @item -mforbid-fp-as-gp @opindex mforbid-fp-as-gp Forbid using $fp to access static and global variables. This option strictly forbids fp-as-gp optimization regardless of @option{-mforce-fp-as-gp}. @item -mex9 @opindex mex9 Use special directives to guide linker doing ex9 optimization. @item -mctor-dtor @opindex mctor-dtor Enable constructor/destructor feature. @item -mrelax @opindex mrelax Guide linker to relax instructions. @end table @node Nios II Options @subsection Nios II Options @cindex Nios II options @cindex Altera Nios II options These are the options defined for the Altera Nios II processor. @table @gcctabopt @item -G @var{num} @opindex G @cindex smaller data references Put global and static objects less than or equal to @var{num} bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of @var{num} is 8. @item -mgpopt @itemx -mno-gpopt @opindex mgpopt @opindex mno-gpopt Generate (do not generate) GP-relative accesses for objects in the small data or BSS sections. The default is @option{-mgpopt} except when @option{-fpic} or @option{-fPIC} is specified to generate position-independent code. Note that the Nios II ABI does not permit GP-relative accesses from shared libraries. You may need to specify @option{-mno-gpopt} explicitly when building programs that include large amounts of small data, including large GOT data sections. In this case, the 16-bit offset for GP-relative addressing may not be large enough to allow access to the entire small data section. @item -mel @itemx -meb @opindex mel @opindex meb Generate little-endian (default) or big-endian (experimental) code, respectively. @item -mbypass-cache @itemx -mno-bypass-cache @opindex mno-bypass-cache @opindex mbypass-cache Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache. @item -mno-cache-volatile @itemx -mcache-volatile @opindex mcache-volatile @opindex mno-cache-volatile Volatile memory access bypass the cache using the I/O variants of the load and store instructions. The default is not to bypass the cache. @item -mno-fast-sw-div @itemx -mfast-sw-div @opindex mno-fast-sw-div @opindex mfast-sw-div Do not use table-based fast divide for small numbers. The default is to use the fast divide at @option{-O3} and above. @item -mno-hw-mul @itemx -mhw-mul @itemx -mno-hw-mulx @itemx -mhw-mulx @itemx -mno-hw-div @itemx -mhw-div @opindex mno-hw-mul @opindex mhw-mul @opindex mno-hw-mulx @opindex mhw-mulx @opindex mno-hw-div @opindex mhw-div Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of instructions by the compiler. The default is to emit @code{mul} and not emit @code{div} and @code{mulx}. @item -mcustom-@var{insn}=@var{N} @itemx -mno-custom-@var{insn} @opindex mcustom-@var{insn} @opindex mno-custom-@var{insn} Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a custom instruction with encoding @var{N} when generating code that uses @var{insn}. For example, @code{-mcustom-fadds=253} generates custom instruction 253 for single-precision floating-point add operations instead of the default behavior of using a library call. The following values of @var{insn} are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the C operators or the equivalent GCC built-in functions (@pxref{Other Builtins}). Single-precision floating point: @table @asis @item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls} Binary arithmetic operations. @item @samp{fnegs} Unary negation. @item @samp{fabss} Unary absolute value. @item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes} Comparison operations. @item @samp{fmins}, @samp{fmaxs} Floating-point minimum and maximum. These instructions are only generated if @option{-ffinite-math-only} is specified. @item @samp{fsqrts} Unary square root operation. @item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs} Floating-point trigonometric and exponential functions. These instructions are only generated if @option{-funsafe-math-optimizations} is also specified. @end table Double-precision floating point: @table @asis @item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld} Binary arithmetic operations. @item @samp{fnegd} Unary negation. @item @samp{fabsd} Unary absolute value. @item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned} Comparison operations. @item @samp{fmind}, @samp{fmaxd} Double-precision minimum and maximum. These instructions are only generated if @option{-ffinite-math-only} is specified. @item @samp{fsqrtd} Unary square root operation. @item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd} Double-precision trigonometric and exponential functions. These instructions are only generated if @option{-funsafe-math-optimizations} is also specified. @end table Conversions: @table @asis @item @samp{fextsd} Conversion from single precision to double precision. @item @samp{ftruncds} Conversion from double precision to single precision. @item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu} Conversion from floating point to signed or unsigned integer types, with truncation towards zero. @item @samp{round} Conversion from single-precision floating point to signed integer, rounding to the nearest integer and ties away from zero. This corresponds to the @code{__builtin_lroundf} function when @option{-fno-math-errno} is used. @item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud} Conversion from signed or unsigned integer types to floating-point types. @end table In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect the first operand in the 64-bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the least significant half in source register @var{src1} and the most significant half in @var{src2}. A custom instruction that returns a double-precision result returns the most significant 32 bits in the destination register and the other half in 32-bit register Y. GCC automatically generates the necessary code sequences to write register X and/or read register Y when double-precision floating-point instructions are used. @table @asis @item @samp{fwrx} Write @var{src1} into the least significant half of X and @var{src2} into the most significant half of X. @item @samp{fwry} Write @var{src1} into Y. @item @samp{frdxhi}, @samp{frdxlo} Read the most or least (respectively) significant half of X and store it in @var{dest}. @item @samp{frdy} Read the value of Y and store it into @var{dest}. @end table Note that you can gain more local control over generation of Nios II custom instructions by using the @code{target("custom-@var{insn}=@var{N}")} and @code{target("no-custom-@var{insn}")} function attributes (@pxref{Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}). @item -mcustom-fpu-cfg=@var{name} @opindex mcustom-fpu-cfg This option enables a predefined, named set of custom instruction encodings (see @option{-mcustom-@var{insn}} above). Currently, the following sets are defined: @option{-mcustom-fpu-cfg=60-1} is equivalent to: @gccoptlist{-mcustom-fmuls=252 @gol -mcustom-fadds=253 @gol -mcustom-fsubs=254 @gol -fsingle-precision-constant} @option{-mcustom-fpu-cfg=60-2} is equivalent to: @gccoptlist{-mcustom-fmuls=252 @gol -mcustom-fadds=253 @gol -mcustom-fsubs=254 @gol -mcustom-fdivs=255 @gol -fsingle-precision-constant} @option{-mcustom-fpu-cfg=72-3} is equivalent to: @gccoptlist{-mcustom-floatus=243 @gol -mcustom-fixsi=244 @gol -mcustom-floatis=245 @gol -mcustom-fcmpgts=246 @gol -mcustom-fcmples=249 @gol -mcustom-fcmpeqs=250 @gol -mcustom-fcmpnes=251 @gol -mcustom-fmuls=252 @gol -mcustom-fadds=253 @gol -mcustom-fsubs=254 @gol -mcustom-fdivs=255 @gol -fsingle-precision-constant} Custom instruction assignments given by individual @option{-mcustom-@var{insn}=} options override those given by @option{-mcustom-fpu-cfg=}, regardless of the order of the options on the command line. Note that you can gain more local control over selection of a FPU configuration by using the @code{target("custom-fpu-cfg=@var{name}")} function attribute (@pxref{Function Attributes}) or pragma (@pxref{Function Specific Option Pragmas}). @end table These additional @samp{-m} options are available for the Altera Nios II ELF (bare-metal) target: @table @gcctabopt @item -mhal @opindex mhal Link with HAL BSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with @option{-msys-crt0=} to specify the location of the alternate startup code provided by the HAL BSP. @item -msmallc @opindex msmallc Link with a limited version of the C library, @option{-lsmallc}, rather than Newlib. @item -msys-crt0=@var{startfile} @opindex msys-crt0 @var{startfile} is the file name of the startfile (crt0) to use when linking. This option is only useful in conjunction with @option{-mhal}. @item -msys-lib=@var{systemlib} @opindex msys-lib @var{systemlib} is the library name of the library that provides low-level system calls required by the C library, e.g. @code{read} and @code{write}. This option is typically used to link with a library provided by a HAL BSP. @end table @node PDP-11 Options @subsection PDP-11 Options @cindex PDP-11 Options These options are defined for the PDP-11: @table @gcctabopt @item -mfpu @opindex mfpu Use hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.) @item -msoft-float @opindex msoft-float Do not use hardware floating point. @item -mac0 @opindex mac0 Return floating-point results in ac0 (fr0 in Unix assembler syntax). @item -mno-ac0 @opindex mno-ac0 Return floating-point results in memory. This is the default. @item -m40 @opindex m40 Generate code for a PDP-11/40. @item -m45 @opindex m45 Generate code for a PDP-11/45. This is the default. @item -m10 @opindex m10 Generate code for a PDP-11/10. @item -mbcopy-builtin @opindex mbcopy-builtin Use inline @code{movmemhi} patterns for copying memory. This is the default. @item -mbcopy @opindex mbcopy Do not use inline @code{movmemhi} patterns for copying memory. @item -mint16 @itemx -mno-int32 @opindex mint16 @opindex mno-int32 Use 16-bit @code{int}. This is the default. @item -mint32 @itemx -mno-int16 @opindex mint32 @opindex mno-int16 Use 32-bit @code{int}. @item -mfloat64 @itemx -mno-float32 @opindex mfloat64 @opindex mno-float32 Use 64-bit @code{float}. This is the default. @item -mfloat32 @itemx -mno-float64 @opindex mfloat32 @opindex mno-float64 Use 32-bit @code{float}. @item -mabshi @opindex mabshi Use @code{abshi2} pattern. This is the default. @item -mno-abshi @opindex mno-abshi Do not use @code{abshi2} pattern. @item -mbranch-expensive @opindex mbranch-expensive Pretend that branches are expensive. This is for experimenting with code generation only. @item -mbranch-cheap @opindex mbranch-cheap Do not pretend that branches are expensive. This is the default. @item -munix-asm @opindex munix-asm Use Unix assembler syntax. This is the default when configured for @samp{pdp11-*-bsd}. @item -mdec-asm @opindex mdec-asm Use DEC assembler syntax. This is the default when configured for any PDP-11 target other than @samp{pdp11-*-bsd}. @end table @node picoChip Options @subsection picoChip Options @cindex picoChip options These @samp{-m} options are defined for picoChip implementations: @table @gcctabopt @item -mae=@var{ae_type} @opindex mcpu Set the instruction set, register set, and instruction scheduling parameters for array element type @var{ae_type}. Supported values for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. @option{-mae=ANY} selects a completely generic AE type. Code generated with this option runs on any of the other AE types. The code is not as efficient as it would be if compiled for a specific AE type, and some types of operation (e.g., multiplication) do not work properly on all types of AE. @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type for compiled code, and is the default. @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this option may suffer from poor performance of byte (char) manipulation, since the DSP AE does not provide hardware support for byte load/stores. @item -msymbol-as-address Enable the compiler to directly use a symbol name as an address in a load/store instruction, without first loading it into a register. Typically, the use of this option generates larger programs, which run faster than when the option isn't used. However, the results vary from program to program, so it is left as a user option, rather than being permanently enabled. @item -mno-inefficient-warnings Disables warnings about the generation of inefficient code. These warnings can be generated, for example, when compiling code that performs byte-level memory operations on the MAC AE type. The MAC AE has no hardware support for byte-level memory operations, so all byte load/stores must be synthesized from word load/store operations. This is inefficient and a warning is generated to indicate that you should rewrite the code to avoid byte operations, or to target an AE type that has the necessary hardware support. This option disables these warnings. @end table @node PowerPC Options @subsection PowerPC Options @cindex PowerPC options These are listed under @xref{RS/6000 and PowerPC Options}. @node RL78 Options @subsection RL78 Options @cindex RL78 Options @table @gcctabopt @item -msim @opindex msim Links in additional target libraries to support operation within a simulator. @item -mmul=none @itemx -mmul=g13 @itemx -mmul=rl78 @opindex mmul Specifies the type of hardware multiplication support to be used. The default is @code{none}, which uses software multiplication functions. The @code{g13} option is for the hardware multiply/divide peripheral only on the RL78/G13 targets. The @code{rl78} option is for the standard hardware multiplication defined in the RL78 software manual. @item -m64bit-doubles @itemx -m32bit-doubles @opindex m64bit-doubles @opindex m32bit-doubles Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) or 32 bits (@option{-m32bit-doubles}) in size. The default is @option{-m32bit-doubles}. @end table @node RS/6000 and PowerPC Options @subsection IBM RS/6000 and PowerPC Options @cindex RS/6000 and PowerPC Options @cindex IBM RS/6000 and PowerPC Options These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: @table @gcctabopt @item -mpowerpc-gpopt @itemx -mno-powerpc-gpopt @itemx -mpowerpc-gfxopt @itemx -mno-powerpc-gfxopt @need 800 @itemx -mpowerpc64 @itemx -mno-powerpc64 @itemx -mmfcrf @itemx -mno-mfcrf @itemx -mpopcntb @itemx -mno-popcntb @itemx -mpopcntd @itemx -mno-popcntd @itemx -mfprnd @itemx -mno-fprnd @need 800 @itemx -mcmpb @itemx -mno-cmpb @itemx -mmfpgpr @itemx -mno-mfpgpr @itemx -mhard-dfp @itemx -mno-hard-dfp @opindex mpowerpc-gpopt @opindex mno-powerpc-gpopt @opindex mpowerpc-gfxopt @opindex mno-powerpc-gfxopt @opindex mpowerpc64 @opindex mno-powerpc64 @opindex mmfcrf @opindex mno-mfcrf @opindex mpopcntb @opindex mno-popcntb @opindex mpopcntd @opindex mno-popcntd @opindex mfprnd @opindex mno-fprnd @opindex mcmpb @opindex mno-cmpb @opindex mmfpgpr @opindex mno-mfpgpr @opindex mhard-dfp @opindex mno-hard-dfp You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC@. Specifying the @option{-mcpu=@var{cpu_type}} overrides the specification of these options. We recommend you use the @option{-mcpu=@var{cpu_type}} option rather than the options listed above. Specifying @option{-mpowerpc-gpopt} allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying @option{-mpowerpc-gfxopt} allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select. The @option{-mmfcrf} option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The @option{-mpopcntb} option allows GCC to generate the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture. The @option{-mpopcntd} option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The @option{-mfprnd} option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture. The @option{-mcmpb} option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture. The @option{-mmfpgpr} option allows GCC to generate the FP move to/from general-purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture. The @option{-mhard-dfp} option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors. The @option{-mpowerpc64} option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to @option{-mno-powerpc64}. @item -mcpu=@var{cpu_type} @opindex mcpu Set architecture type, register usage, and instruction scheduling parameters for machine type @var{cpu_type}. Supported values for @var{cpu_type} are @samp{401}, @samp{403}, @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, @samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, @samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, @samp{powerpc}, @samp{powerpc64}, and @samp{rs64}. @option{-mcpu=powerpc}, and @option{-mcpu=powerpc64} specify pure 32-bit PowerPC and 64-bit PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes. The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others. The @option{-mcpu} options automatically enable or disable the following options: @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol -mpopcntb -mpopcntd -mpowerpc64 @gol -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx @gol -mcrypto -mdirect-move -mpower8-fusion -mpower8-vector @gol -mquad-memory -mquad-memory-atomic} The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the actual hardware's capabilities. If you wish to set an individual option to a particular value, you may specify it after the @option{-mcpu} option, like @option{-mcpu=970 -mno-altivec}. On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are not enabled or disabled by the @option{-mcpu} option at present because AIX does not have full support for these options. You may still enable or disable them individually if you're sure it'll work in your environment. @item -mtune=@var{cpu_type} @opindex mtune Set the instruction scheduling parameters for machine type @var{cpu_type}, but do not set the architecture type or register usage, as @option{-mcpu=@var{cpu_type}} does. The same values for @var{cpu_type} are used for @option{-mtune} as for @option{-mcpu}. If both are specified, the code generated uses the architecture and registers set by @option{-mcpu}, but the scheduling parameters set by @option{-mtune}. @item -mcmodel=small @opindex mcmodel=small Generate PowerPC64 code for the small model: The TOC is limited to 64k. @item -mcmodel=medium @opindex mcmodel=medium Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of 4G in size. @item -mcmodel=large @opindex mcmodel=large Generate PowerPC64 code for the large model: The TOC may be up to 4G in size. Other data and code is only limited by the 64-bit address space. @item -maltivec @itemx -mno-altivec @opindex maltivec @opindex mno-altivec Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI enhancements. When @option{-maltivec} is used, rather than @option{-maltivec=le} or @option{-maltivec=be}, the element order for Altivec intrinsics such as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert} will match array element order corresponding to the endianness of the target. That is, element zero identifies the leftmost element in a vector register when targeting a big-endian platform, and identifies the rightmost element in a vector register when targeting a little-endian platform. @item -maltivec=be @opindex maltivec=be Generate Altivec instructions using big-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a big-endian platform. The element order is used to interpret element numbers in Altivec intrinsics such as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}. By default, these will match array element order corresponding to the endianness for the target. @item -maltivec=le @opindex maltivec=le Generate Altivec instructions using little-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a little-endian platform. This option is currently ignored when targeting a big-endian platform. The element order is used to interpret element numbers in Altivec intrinsics such as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}. By default, these will match array element order corresponding to the endianness for the target. @item -mvrsave @itemx -mno-vrsave @opindex mvrsave @opindex mno-vrsave Generate VRSAVE instructions when generating AltiVec code. @item -mgen-cell-microcode @opindex mgen-cell-microcode Generate Cell microcode instructions. @item -mwarn-cell-microcode @opindex mwarn-cell-microcode Warn when a Cell microcode instruction is emitted. An example of a Cell microcode instruction is a variable shift. @item -msecure-plt @opindex msecure-plt Generate code that allows @command{ld} and @command{ld.so} to build executables and shared libraries with non-executable @code{.plt} and @code{.got} sections. This is a PowerPC 32-bit SYSV ABI option. @item -mbss-plt @opindex mbss-plt Generate code that uses a BSS @code{.plt} section that @command{ld.so} fills in, and requires @code{.plt} and @code{.got} sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option. @item -misel @itemx -mno-isel @opindex misel @opindex mno-isel This switch enables or disables the generation of ISEL instructions. @item -misel=@var{yes/no} This switch has been deprecated. Use @option{-misel} and @option{-mno-isel} instead. @item -mspe @itemx -mno-spe @opindex mspe @opindex mno-spe This switch enables or disables the generation of SPE simd instructions. @item -mpaired @itemx -mno-paired @opindex mpaired @opindex mno-paired This switch enables or disables the generation of PAIRED simd instructions. @item -mspe=@var{yes/no} This option has been deprecated. Use @option{-mspe} and @option{-mno-spe} instead. @item -mvsx @itemx -mno-vsx @opindex mvsx @opindex mno-vsx Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set. @item -mcrypto @itemx -mno-crypto @opindex mcrypto @opindex mno-crypto Enable the use (disable) of the built-in functions that allow direct access to the cryptographic instructions that were added in version 2.07 of the PowerPC ISA. @item -mdirect-move @itemx -mno-direct-move @opindex mdirect-move @opindex mno-direct-move Generate code that uses (does not use) the instructions to move data between the general purpose registers and the vector/scalar (VSX) registers that were added in version 2.07 of the PowerPC ISA. @item -mpower8-fusion @itemx -mno-power8-fusion @opindex mpower8-fusion @opindex mno-power8-fusion Generate code that keeps (does not keeps) some integer operations adjacent so that the instructions can be fused together on power8 and later processors. @item -mpower8-vector @itemx -mno-power8-vector @opindex mpower8-vector @opindex mno-power8-vector Generate code that uses (does not use) the vector and scalar instructions that were added in version 2.07 of the PowerPC ISA. Also enable the use of built-in functions that allow more direct access to the vector instructions. @item -mquad-memory @itemx -mno-quad-memory @opindex mquad-memory @opindex mno-quad-memory Generate code that uses (does not use) the non-atomic quad word memory instructions. The @option{-mquad-memory} option requires use of 64-bit mode. @item -mquad-memory-atomic @itemx -mno-quad-memory-atomic @opindex mquad-memory-atomic @opindex mno-quad-memory-atomic Generate code that uses (does not use) the atomic quad word memory instructions. The @option{-mquad-memory-atomic} option requires use of 64-bit mode. @item -mfloat-gprs=@var{yes/single/double/no} @itemx -mfloat-gprs @opindex mfloat-gprs This switch enables or disables the generation of floating-point operations on the general-purpose registers for architectures that support it. The argument @var{yes} or @var{single} enables the use of single-precision floating-point operations. The argument @var{double} enables the use of single and double-precision floating-point operations. The argument @var{no} disables floating-point operations on the general-purpose registers. This option is currently only available on the MPC854x. @item -m32 @itemx -m64 @opindex m32 @opindex m64 Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for @option{-mpowerpc64}. @item -mfull-toc @itemx -mno-fp-in-toc @itemx -mno-sum-in-toc @itemx -mminimal-toc @opindex mfull-toc @opindex mno-fp-in-toc @opindex mno-sum-in-toc @opindex mminimal-toc Modify generation of the TOC (Table Of Contents), which is created for every executable file. The @option{-mfull-toc} option is selected by default. In that case, GCC allocates at least one TOC entry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC@. However, only 16,384 entries are available in the TOC@. If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. @option{-mno-fp-in-toc} prevents GCC from putting floating-point constants in the TOC and @option{-mno-sum-in-toc} forces GCC to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC@. You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space. If you still run out of space in the TOC even when you specify both of these options, specify @option{-mminimal-toc} instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently-executed code. @item -maix64 @itemx -maix32 @opindex maix64 @opindex maix32 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit @code{long} type, and the infrastructure needed to support them. Specifying @option{-maix64} implies @option{-mpowerpc64}, while @option{-maix32} disables the 64-bit ABI and implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. @item -mxl-compat @itemx -mno-xl-compat @opindex mxl-compat @opindex mno-xl-compat Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI@. Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use XL symbol names for long double support routines. The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization. @item -mpe @opindex mpe Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file must be overridden with the @option{-specs=} option to specify the appropriate directory location. The Parallel Environment does not support threads, so the @option{-mpe} option and the @option{-pthread} option are incompatible. @item -malign-natural @itemx -malign-power @opindex malign-natural @opindex malign-power On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option @option{-malign-natural} overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option @option{-malign-power} instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI@. On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} is not supported. @item -msoft-float @itemx -mhard-float @opindex msoft-float @opindex mhard-float Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the @option{-msoft-float} option, and pass the option to GCC when linking. @item -msingle-float @itemx -mdouble-float @opindex msingle-float @opindex mdouble-float Generate code for single- or double-precision floating-point operations. @option{-mdouble-float} implies @option{-msingle-float}. @item -msimple-fpu @opindex msimple-fpu Do not generate @code{sqrt} and @code{div} instructions for hardware floating-point unit. @item -mfpu=@var{name} @opindex mfpu Specify type of floating-point unit. Valid values for @var{name} are @samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}), @samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}), @samp{sp_full} (equivalent to @option{-msingle-float}), and @samp{dp_full} (equivalent to @option{-mdouble-float}). @item -mxilinx-fpu @opindex mxilinx-fpu Perform optimizations for the floating-point unit on Xilinx PPC 405/440. @item -mmultiple @itemx -mno-multiple @opindex mmultiple @opindex mno-multiple Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode. @item -mstring @itemx -mno-string @opindex mstring @opindex mno-string Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use @option{-mstring} on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode. @item -mupdate @itemx -mno-update @opindex mupdate @opindex mno-update Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use @option{-mno-update}, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data. @item -mavoid-indexed-addresses @itemx -mno-avoid-indexed-addresses @opindex mavoid-indexed-addresses @opindex mno-avoid-indexed-addresses Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent @option{-mfused-madd} option is now mapped to the machine-independent @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is mapped to @option{-ffp-contract=off}. @item -mmulhw @itemx -mno-mulhw @opindex mmulhw @opindex mno-mulhw Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors. @item -mdlmzb @itemx -mno-dlmzb @opindex mdlmzb @opindex mno-dlmzb Generate code that uses (does not use) the string-search @samp{dlmzb} instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors. @item -mno-bit-align @itemx -mbit-align @opindex mno-bit-align @opindex mbit-align On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field. For example, by default a structure containing nothing but 8 @code{unsigned} bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, the structure is aligned to a 1-byte boundary and is 1 byte in size. @item -mno-strict-align @itemx -mstrict-align @opindex mno-strict-align @opindex mstrict-align On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system. @item -mrelocatable @itemx -mno-relocatable @opindex mrelocatable @opindex mno-relocatable Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of @code{.got2} and 4-byte locations listed in the @code{.fixup} section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}. @option{-mrelocatable} code aligns the stack to an 8-byte boundary. @item -mrelocatable-lib @itemx -mno-relocatable-lib @opindex mrelocatable-lib @opindex mno-relocatable-lib Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a @code{.fixup} section to allow static executables to be relocated at run time, but @option{-mrelocatable-lib} does not use the smaller stack alignment of @option{-mrelocatable}. Objects compiled with @option{-mrelocatable-lib} may be linked with objects compiled with any combination of the @option{-mrelocatable} options. @item -mno-toc @itemx -mtoc @opindex mno-toc @opindex mtoc On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program. @item -mlittle @itemx -mlittle-endian @opindex mlittle @opindex mlittle-endian On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The @option{-mlittle-endian} option is the same as @option{-mlittle}. @item -mbig @itemx -mbig-endian @opindex mbig @opindex mbig-endian On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The @option{-mbig-endian} option is the same as @option{-mbig}. @item -mdynamic-no-pic @opindex mdynamic-no-pic On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries. @item -msingle-pic-base @opindex msingle-pic-base Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins. @item -mprioritize-restricted-insns=@var{priority} @opindex mprioritize-restricted-insns This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, or @samp{2} to assign no, highest, or second-highest (respectively) priority to dispatch-slot restricted instructions. @item -msched-costly-dep=@var{dependence_type} @opindex msched-costly-dep This option controls which dependences are considered costly by the target during instruction scheduling. The argument @var{dependence_type} takes one of the following values: @table @asis @item @samp{no} No dependence is costly. @item @samp{all} All dependences are costly. @item @samp{true_store_to_load} A true dependence from store to load is costly. @item @samp{store_to_load} Any dependence from store to load is costly. @item @var{number} Any dependence for which the latency is greater than or equal to @var{number} is costly. @end table @item -minsert-sched-nops=@var{scheme} @opindex minsert-sched-nops This option controls which NOP insertion scheme is used during the second scheduling pass. The argument @var{scheme} takes one of the following values: @table @asis @item @samp{no} Don't insert NOPs. @item @samp{pad} Pad with NOPs any dispatch group that has vacant issue slots, according to the scheduler's grouping. @item @samp{regroup_exact} Insert NOPs to force costly dependent insns into separate groups. Insert exactly as many NOPs as needed to force an insn to a new group, according to the estimated processor grouping. @item @var{number} Insert NOPs to force costly dependent insns into separate groups. Insert @var{number} NOPs to force an insn to a new group. @end table @item -mcall-sysv @opindex mcall-sysv On System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using @samp{powerpc-*-eabiaix}. @item -mcall-sysv-eabi @itemx -mcall-eabi @opindex mcall-sysv-eabi @opindex mcall-eabi Specify both @option{-mcall-sysv} and @option{-meabi} options. @item -mcall-sysv-noeabi @opindex mcall-sysv-noeabi Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. @item -mcall-aixdesc @opindex m On System V.4 and embedded PowerPC systems compile code for the AIX operating system. @item -mcall-linux @opindex mcall-linux On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system. @item -mcall-freebsd @opindex mcall-freebsd On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system. @item -mcall-netbsd @opindex mcall-netbsd On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system. @item -mcall-openbsd @opindex mcall-netbsd On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system. @item -maix-struct-return @opindex maix-struct-return Return all structures in memory (as specified by the AIX ABI)@. @item -msvr4-struct-return @opindex msvr4-struct-return Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI)@. @item -mabi=@var{abi-type} @opindex mabi Extend the current ABI with a particular extension, or remove such extension. Valid values are @var{altivec}, @var{no-altivec}, @var{spe}, @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}, @var{elfv1}, @var{elfv2}@. @item -mabi=spe @opindex mabi=spe Extend the current ABI with SPE ABI extensions. This does not change the default ABI, instead it adds the SPE ABI extensions to the current ABI@. @item -mabi=no-spe @opindex mabi=no-spe Disable Book-E SPE ABI extensions for the current ABI@. @item -mabi=ibmlongdouble @opindex mabi=ibmlongdouble Change the current ABI to use IBM extended-precision long double. This is a PowerPC 32-bit SYSV ABI option. @item -mabi=ieeelongdouble @opindex mabi=ieeelongdouble Change the current ABI to use IEEE extended-precision long double. This is a PowerPC 32-bit Linux ABI option. @item -mabi=elfv1 @opindex mabi=elfv1 Change the current ABI to use the ELFv1 ABI. This is the default ABI for big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways. @item -mabi=elfv2 @opindex mabi=elfv2 Change the current ABI to use the ELFv2 ABI. This is the default ABI for little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways. @item -mprototype @itemx -mno-prototype @opindex mprototype @opindex mno-prototype On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non-prototyped call to set or clear bit 6 of the condition code register (@var{CR}) to indicate whether floating-point values are passed in the floating-point registers in case the function takes variable arguments. With @option{-mprototype}, only calls to prototyped variable argument functions set or clear the bit. @item -msim @opindex msim On embedded PowerPC systems, assume that the startup module is called @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and @file{libc.a}. This is the default for @samp{powerpc-*-eabisim} configurations. @item -mmvme @opindex mmvme On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libmvme.a} and @file{libc.a}. @item -mads @opindex mads On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libads.a} and @file{libc.a}. @item -myellowknife @opindex myellowknife On embedded PowerPC systems, assume that the startup module is called @file{crt0.o} and the standard C libraries are @file{libyk.a} and @file{libc.a}. @item -mvxworks @opindex mvxworks On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system. @item -memb @opindex memb On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags header to indicate that @samp{eabi} extended relocations are used. @item -meabi @itemx -mno-eabi @opindex meabi @opindex mno-eabi On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (EABI), which is a set of modifications to the System V.4 specifications. Selecting @option{-meabi} means that the stack is aligned to an 8-byte boundary, a function @code{__eabi} is called from @code{main} to set up the EABI environment, and the @option{-msdata} option can use both @code{r2} and @code{r13} to point to two separate small data areas. Selecting @option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, no EABI initialization function is called from @code{main}, and the @option{-msdata} option only uses @code{r13} to point to a single small data area. The @option{-meabi} option is on by default if you configured GCC using one of the @samp{powerpc*-*-eabi*} options. @item -msdata=eabi @opindex msdata=eabi On System V.4 and embedded PowerPC systems, put small initialized @code{const} global and static data in the @samp{.sdata2} section, which is pointed to by register @code{r2}. Put small initialized non-@code{const} global and static data in the @samp{.sdata} section, which is pointed to by register @code{r13}. Put small uninitialized global and static data in the @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. The @option{-msdata=eabi} option is incompatible with the @option{-mrelocatable} option. The @option{-msdata=eabi} option also sets the @option{-memb} option. @item -msdata=sysv @opindex msdata=sysv On System V.4 and embedded PowerPC systems, put small global and static data in the @samp{.sdata} section, which is pointed to by register @code{r13}. Put small uninitialized global and static data in the @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. The @option{-msdata=sysv} option is incompatible with the @option{-mrelocatable} option. @item -msdata=default @itemx -msdata @opindex msdata=default @opindex msdata On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, compile code the same as @option{-msdata=eabi}, otherwise compile code the same as @option{-msdata=sysv}. @item -msdata=data @opindex msdata=data On System V.4 and embedded PowerPC systems, put small global data in the @samp{.sdata} section. Put small uninitialized global data in the @samp{.sbss} section. Do not use register @code{r13} to address small data however. This is the default behavior unless other @option{-msdata} options are used. @item -msdata=none @itemx -mno-sdata @opindex msdata=none @opindex mno-sdata On embedded PowerPC systems, put all initialized global and static data in the @samp{.data} section, and all uninitialized data in the @samp{.bss} section. @item -mblock-move-inline-limit=@var{num} @opindex mblock-move-inline-limit Inline all block moves (such as calls to @code{memcpy} or structure copies) less than or equal to @var{num} bytes. The minimum value for @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets. The default value is target-specific. @item -G @var{num} @opindex G @cindex smaller data references (PowerPC) @cindex .sdata/.sdata2 references (PowerPC) On embedded PowerPC systems, put global and static items less than or equal to @var{num} bytes into the small data or BSS sections instead of the normal data or BSS section. By default, @var{num} is 8. The @option{-G @var{num}} switch is also passed to the linker. All modules should be compiled with the same @option{-G @var{num}} value. @item -mregnames @itemx -mno-regnames @opindex mregnames @opindex mno-regnames On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms. @item -mlongcall @itemx -mno-longcall @opindex mlongcall @opindex mno-longcall By default assume that all calls are far away so that a longer and more expensive calling sequence is required. This is required for calls farther than 32 megabytes (33,554,432 bytes) from the current location. A short call is generated if the compiler knows the call cannot be that far away. This setting can be overridden by the @code{shortcall} function attribute, or by @code{#pragma longcall(0)}. Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well. On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr callee, L42}, plus a @dfn{branch island} (glue code). The two target addresses represent the callee and the branch island. The Darwin/PPC linker prefers the first address and generates a @code{bl callee} if the PPC @code{bl} instruction reaches the callee directly; otherwise, the linker generates @code{bl L42} to call the branch island. The branch island is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it. On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it. In the future, GCC may ignore all longcall specifications when the linker is known to generate glue. @item -mtls-markers @itemx -mno-tls-markers @opindex mtls-markers @opindex mno-tls-markers Mark (do not mark) calls to @code{__tls_get_addr} with a relocation specifying the function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn allows GCC to better schedule the sequence. @item -pthread @opindex pthread Adds support for multithreading with the @dfn{pthreads} library. This option sets flags for both the preprocessor and linker. @item -mrecip @itemx -mno-recip @opindex mrecip This option enables use of the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or square root and divide for floating-point arguments. You should use the @option{-ffast-math} option when using @option{-mrecip} (or at least @option{-funsafe-math-optimizations}, @option{-finite-math-only}, @option{-freciprocal-math} and @option{-fno-trapping-math}). Note that while the throughput of the sequence is generally higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square roots. @item -mrecip=@var{opt} @opindex mrecip=opt This option controls which reciprocal estimate instructions may be used. @var{opt} is a comma-separated list of options, which may be preceded by a @code{!} to invert the option: @code{all}: enable all estimate instructions, @code{default}: enable the default instructions, equivalent to @option{-mrecip}, @code{none}: disable all estimate instructions, equivalent to @option{-mno-recip}; @code{div}: enable the reciprocal approximation instructions for both single and double precision; @code{divf}: enable the single-precision reciprocal approximation instructions; @code{divd}: enable the double-precision reciprocal approximation instructions; @code{rsqrt}: enable the reciprocal square root approximation instructions for both single and double precision; @code{rsqrtf}: enable the single-precision reciprocal square root approximation instructions; @code{rsqrtd}: enable the double-precision reciprocal square root approximation instructions; So, for example, @option{-mrecip=all,!rsqrtd} enables all of the reciprocal estimate instructions, except for the @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions which handle the double-precision reciprocal square root calculations. @item -mrecip-precision @itemx -mno-recip-precision @opindex mrecip-precision Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or @option{-mcpu=power8} automatically selects @option{-mrecip-precision}. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate that converges after three steps. @item -mveclibabi=@var{type} @opindex mveclibabi Specifies the ABI type to use for vectorizing intrinsics using an external library. The only type supported at present is @code{mass}, which specifies to use IBM's Mathematical Acceleration Subsystem (MASS) libraries for vectorizing intrinsics using external libraries. GCC currently emits calls to @code{acosd2}, @code{acosf4}, @code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, @code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, @code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, @code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, @code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, @code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, @code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, @code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, @code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, @code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, @code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, @code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, @code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code for power7. Both @option{-ftree-vectorize} and @option{-funsafe-math-optimizations} must also be enabled. The MASS libraries must be specified at link time. @item -mfriz @itemx -mno-friz @opindex mfriz Generate (do not generate) the @code{friz} instruction when the @option{-funsafe-math-optimizations} option is used to optimize rounding of floating-point values to 64-bit integer and back to floating point. The @code{friz} instruction does not return the same value if the floating-point number is too large to fit in an integer. @item -mpointers-to-nested-functions @itemx -mno-pointers-to-nested-functions @opindex mpointers-to-nested-functions Generate (do not generate) code to load up the static chain register (@var{r11}) when calling through a pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving the function address, TOC value to be loaded in register @var{r2}, and static chain value to be loaded in register @var{r11}. The @option{-mpointers-to-nested-functions} is on by default. You cannot call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use the @option{-mno-pointers-to-nested-functions}. @item -msave-toc-indirect @itemx -mno-save-toc-indirect @opindex msave-toc-indirect Generate (do not generate) code to save the TOC value in the reserved stack location in the function prologue if the function calls through a pointer on AIX and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is saved just before the call through the pointer. The @option{-mno-save-toc-indirect} option is the default. @item -mcompat-align-parm @itemx -mno-compat-align-parm @opindex mcompat-align-parm Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for compatibility with older versions of GCC. Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC. The @option{-mno-compat-align-parm} option is the default. @end table @node RX Options @subsection RX Options @cindex RX Options These command-line options are defined for RX targets: @table @gcctabopt @item -m64bit-doubles @itemx -m32bit-doubles @opindex m64bit-doubles @opindex m32bit-doubles Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) or 32 bits (@option{-m32bit-doubles}) in size. The default is @option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only works on 32-bit values, which is why the default is @option{-m32bit-doubles}. @item -fpu @itemx -nofpu @opindex fpu @opindex nofpu Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX floating-point hardware. The default is enabled for the @var{RX600} series and disabled for the @var{RX200} series. Floating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the @option{-m64bit-doubles} option is used. @emph{Note} If the @option{-fpu} option is enabled then @option{-funsafe-math-optimizations} is also enabled automatically. This is because the RX FPU instructions are themselves unsafe. @item -mcpu=@var{name} @opindex -mcpu Selects the type of RX CPU to be targeted. Currently three types are supported, the generic @var{RX600} and @var{RX200} series hardware and the specific @var{RX610} CPU. The default is @var{RX600}. The only difference between @var{RX600} and @var{RX610} is that the @var{RX610} does not support the @code{MVTIPL} instruction. The @var{RX200} series does not have a hardware floating-point unit and so @option{-nofpu} is enabled by default when this type is selected. @item -mbig-endian-data @itemx -mlittle-endian-data @opindex mbig-endian-data @opindex mlittle-endian-data Store data (but not code) in the big-endian format. The default is @option{-mlittle-endian-data}, i.e.@: to store data in the little-endian format. @item -msmall-data-limit=@var{N} @opindex msmall-data-limit Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the RX's registers (usually @code{r13}) is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held in this register. Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable. The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (@option{-O2} etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the @option{-mpid} option for a description of how the actual register to hold the small data area pointer is chosen. @item -msim @itemx -mno-sim @opindex msim @opindex mno-sim Use the simulator runtime. The default is to use the libgloss board-specific runtime. @item -mas100-syntax @itemx -mno-as100-syntax @opindex mas100-syntax @opindex mno-as100-syntax When generating assembler output use a syntax that is compatible with Renesas's AS100 assembler. This syntax can also be handled by the GAS assembler, but it has some restrictions so it is not generated by default. @item -mmax-constant-size=@var{N} @opindex mmax-constant-size Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX instruction. Although the RX instruction set does allow constants of up to 4 bytes in length to be used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. Constants that are too big are instead placed into a constant pool and referenced via register indirection. The value @var{N} can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed. @item -mrelax @opindex mrelax Enable linker relaxation. Linker relaxation is a process whereby the linker attempts to reduce the size of a program by finding shorter versions of various instructions. Disabled by default. @item -mint-register=@var{N} @opindex mint-register Specify the number of registers to reserve for fast interrupt handler functions. The value @var{N} can be between 0 and 4. A value of 1 means that register @code{r13} is reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves @code{r13} and @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. A value of 0, the default, does not reserve any registers. @item -msave-acc-in-interrupts @opindex msave-acc-in-interrupts Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster. @item -mpid @itemx -mno-pid @opindex mpid @opindex mno-pid Enables the generation of position independent data. When enabled any access to constant data is done via an offset from a base address held in a register. This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be modified is not affected by this option. Note, using this feature reserves a register, usually @code{r13}, for the constant data base address. This can result in slower and/or larger code, especially in complicated functions. The actual register chosen to hold the constant data base address depends upon whether the @option{-msmall-data-limit} and/or the @option{-mint-register} command-line options are enabled. Starting with register @code{r13} and proceeding downwards, registers are allocated first to satisfy the requirements of @option{-mint-register}, then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it is possible for the small data area register to be @code{r8} if both @option{-mint-register=4} and @option{-mpid} are specified on the command line. By default this feature is not enabled. The default can be restored via the @option{-mno-pid} command-line option. @item -mno-warn-multiple-fast-interrupts @itemx -mwarn-multiple-fast-interrupts @opindex mno-warn-multiple-fast-interrupts @opindex mwarn-multiple-fast-interrupts Prevents GCC from issuing a warning message if it finds more than one fast interrupt handler when it is compiling a file. The default is to issue a warning for each extra fast interrupt handler found, as the RX only supports one such interrupt. @end table @emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} has special significance to the RX port when used with the @code{interrupt} function attribute. This attribute indicates a function intended to process fast interrupts. GCC ensures that it only uses the registers @code{r10}, @code{r11}, @code{r12} and/or @code{r13} and only provided that the normal use of the corresponding registers have been restricted via the @option{-ffixed-@var{reg}} or @option{-mint-register} command-line options. @node S/390 and zSeries Options @subsection S/390 and zSeries Options @cindex S/390 and zSeries Options These are the @samp{-m} options defined for the S/390 and zSeries architecture. @table @gcctabopt @item -mhard-float @itemx -msoft-float @opindex mhard-float @opindex msoft-float Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When @option{-msoft-float} is specified, functions in @file{libgcc.a} are used to perform floating-point operations. When @option{-mhard-float} is specified, the compiler generates IEEE floating-point instructions. This is the default. @item -mhard-dfp @itemx -mno-hard-dfp @opindex mhard-dfp @opindex mno-hard-dfp Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point operations. When @option{-mno-hard-dfp} is specified, functions in @file{libgcc.a} are used to perform decimal-floating-point operations. When @option{-mhard-dfp} is specified, the compiler generates decimal-floating-point hardware instructions. This is the default for @option{-march=z9-ec} or higher. @item -mlong-double-64 @itemx -mlong-double-128 @opindex mlong-double-64 @opindex mlong-double-128 These switches control the size of @code{long double} type. A size of 64 bits makes the @code{long double} type equivalent to the @code{double} type. This is the default. @item -mbackchain @itemx -mno-backchain @opindex mbackchain @opindex mno-backchain Store (do not store) the address of the caller's frame as backchain pointer into the callee's stack frame. A backchain may be needed to allow debugging using tools that do not understand DWARF 2 call frame information. When @option{-mno-packed-stack} is in effect, the backchain pointer is stored at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, the backchain is placed into the topmost word of the 96/160 byte register save area. In general, code compiled with @option{-mbackchain} is call-compatible with code compiled with @option{-mmo-backchain}; however, use of the backchain for debugging purposes usually requires that the whole binary is built with @option{-mbackchain}. Note that the combination of @option{-mbackchain}, @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order to build a linux kernel use @option{-msoft-float}. The default is to not maintain the backchain. @item -mpacked-stack @itemx -mno-packed-stack @opindex mpacked-stack @opindex mno-packed-stack Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is specified, the compiler uses the all fields of the 96/160 byte register save area only for their default purpose; unused fields still take up stack space. When @option{-mpacked-stack} is specified, register save slots are densely packed at the top of the register save area; unused space is reused for other purposes, allowing for more efficient use of the available stack space. However, when @option{-mbackchain} is also in effect, the topmost word of the save area is always used to store the backchain, and the return address register is always saved two words below the backchain. As long as the stack frame backchain is not used, code generated with @option{-mpacked-stack} is call-compatible with code generated with @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with @option{-mpacked-stack}. Also, note that the combination of @option{-mbackchain}, @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order to build a linux kernel use @option{-msoft-float}. The default is to not use the packed stack layout. @item -msmall-exec @itemx -mno-small-exec @opindex msmall-exec @opindex mno-small-exec Generate (or do not generate) code using the @code{bras} instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the @code{basr} instruction instead, which does not have this limitation. @item -m64 @itemx -m31 @opindex m64 @opindex m31 When @option{-m31} is specified, generate code compliant to the GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in particular to generate 64-bit instructions. For the @samp{s390} targets, the default is @option{-m31}, while the @samp{s390x} targets default to @option{-m64}. @item -mzarch @itemx -mesa @opindex mzarch @opindex mesa When @option{-mzarch} is specified, generate code using the instructions available on z/Architecture. When @option{-mesa} is specified, generate code using the instructions available on ESA/390. Note that @option{-mesa} is not possible with @option{-m64}. When generating code compliant to the GNU/Linux for S/390 ABI, the default is @option{-mesa}. When generating code compliant to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. @item -mmvcle @itemx -mno-mvcle @opindex mmvcle @opindex mno-mvcle Generate (or do not generate) code using the @code{mvcle} instruction to perform block moves. When @option{-mno-mvcle} is specified, use a @code{mvc} loop instead. This is the default unless optimizing for size. @item -mdebug @itemx -mno-debug @opindex mdebug @opindex mno-debug Print (or do not print) additional debug information when compiling. The default is to not print debug information. @item -march=@var{cpu-type} @opindex march Generate code that runs on @var{cpu-type}, which is the name of a system representing a certain processor type. Possible values for @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990}, @samp{z9-109}, @samp{z9-ec} and @samp{z10}. When generating code using the instructions available on z/Architecture, the default is @option{-march=z900}. Otherwise, the default is @option{-march=g5}. @item -mtune=@var{cpu-type} @opindex mtune Tune to @var{cpu-type} everything applicable about the generated code, except for the ABI and the set of available instructions. The list of @var{cpu-type} values is the same as for @option{-march}. The default is the value used for @option{-march}. @item -mtpf-trace @itemx -mno-tpf-trace @opindex mtpf-trace @opindex mno-tpf-trace Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating system. This option is off by default, even when compiling for the TPF OS@. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. @item -mwarn-framesize=@var{framesize} @opindex mwarn-framesize Emit a warning if the current function exceeds the given frame size. Because this is a compile-time check it doesn't need to be a real problem when the program runs. It is intended to identify functions that most probably cause a stack overflow. It is useful to be used in an environment with limited stack size e.g.@: the linux kernel. @item -mwarn-dynamicstack @opindex mwarn-dynamicstack Emit a warning if the function calls @code{alloca} or uses dynamically-sized arrays. This is generally a bad idea with a limited stack size. @item -mstack-guard=@var{stack-guard} @itemx -mstack-size=@var{stack-size} @opindex mstack-guard @opindex mstack-size If these options are provided the S/390 back end emits additional instructions in the function prologue that trigger a trap if the stack size is @var{stack-guard} bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). If the @var{stack-guard} option is omitted the smallest power of 2 larger than the frame size of the compiled function is chosen. These options are intended to be used to help debugging stack overflow problems. The additionally emitted code causes only little overhead and hence can also be used in production-like systems without greater performance degradation. The given values have to be exact powers of 2 and @var{stack-size} has to be greater than @var{stack-guard} without exceeding 64k. In order to be efficient the extra code makes the assumption that the stack starts at an address aligned to the value given by @var{stack-size}. The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. @item -mhotpatch[=@var{halfwords}] @itemx -mno-hotpatch @opindex mhotpatch If the hotpatch option is enabled, a ``hot-patching'' function prologue is generated for all functions in the compilation unit. The funtion label is prepended with the given number of two-byte Nop instructions (@var{halfwords}, maximum 1000000) or 12 Nop instructions if no argument is present. Functions with a hot-patching prologue are never inlined automatically, and a hot-patching prologue is never generated for functions that are explicitly inline. This option can be overridden for individual functions with the @code{hotpatch} attribute. @end table @node Score Options @subsection Score Options @cindex Score Options These options are defined for Score implementations: @table @gcctabopt @item -meb @opindex meb Compile code for big-endian mode. This is the default. @item -mel @opindex mel Compile code for little-endian mode. @item -mnhwloop @opindex mnhwloop Disable generation of @code{bcnz} instructions. @item -muls @opindex muls Enable generation of unaligned load and store instructions. @item -mmac @opindex mmac Enable the use of multiply-accumulate instructions. Disabled by default. @item -mscore5 @opindex mscore5 Specify the SCORE5 as the target architecture. @item -mscore5u @opindex mscore5u Specify the SCORE5U of the target architecture. @item -mscore7 @opindex mscore7 Specify the SCORE7 as the target architecture. This is the default. @item -mscore7d @opindex mscore7d Specify the SCORE7D as the target architecture. @end table @node SH Options @subsection SH Options These @samp{-m} options are defined for the SH implementations: @table @gcctabopt @item -m1 @opindex m1 Generate code for the SH1. @item -m2 @opindex m2 Generate code for the SH2. @item -m2e Generate code for the SH2e. @item -m2a-nofpu @opindex m2a-nofpu Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point unit is not used. @item -m2a-single-only @opindex m2a-single-only Generate code for the SH2a-FPU, in such a way that no double-precision floating-point operations are used. @item -m2a-single @opindex m2a-single Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by default. @item -m2a @opindex m2a Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by default. @item -m3 @opindex m3 Generate code for the SH3. @item -m3e @opindex m3e Generate code for the SH3e. @item -m4-nofpu @opindex m4-nofpu Generate code for the SH4 without a floating-point unit. @item -m4-single-only @opindex m4-single-only Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic. @item -m4-single @opindex m4-single Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default. @item -m4 @opindex m4 Generate code for the SH4. @item -m4-100 @opindex m4-100 Generate code for SH4-100. @item -m4-100-nofpu @opindex m4-100-nofpu Generate code for SH4-100 in such a way that the floating-point unit is not used. @item -m4-100-single @opindex m4-100-single Generate code for SH4-100 assuming the floating-point unit is in single-precision mode by default. @item -m4-100-single-only @opindex m4-100-single-only Generate code for SH4-100 in such a way that no double-precision floating-point operations are used. @item -m4-200 @opindex m4-200 Generate code for SH4-200. @item -m4-200-nofpu @opindex m4-200-nofpu Generate code for SH4-200 without in such a way that the floating-point unit is not used. @item -m4-200-single @opindex m4-200-single Generate code for SH4-200 assuming the floating-point unit is in single-precision mode by default. @item -m4-200-single-only @opindex m4-200-single-only Generate code for SH4-200 in such a way that no double-precision floating-point operations are used. @item -m4-300 @opindex m4-300 Generate code for SH4-300. @item -m4-300-nofpu @opindex m4-300-nofpu Generate code for SH4-300 without in such a way that the floating-point unit is not used. @item -m4-300-single @opindex m4-300-single Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. @item -m4-300-single-only @opindex m4-300-single-only Generate code for SH4-300 in such a way that no double-precision floating-point operations are used. @item -m4-340 @opindex m4-340 Generate code for SH4-340 (no MMU, no FPU). @item -m4-500 @opindex m4-500 Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the assembler. @item -m4a-nofpu @opindex m4a-nofpu Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not used. @item -m4a-single-only @opindex m4a-single-only Generate code for the SH4a, in such a way that no double-precision floating-point operations are used. @item -m4a-single @opindex m4a-single Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default. @item -m4a @opindex m4a Generate code for the SH4a. @item -m4al @opindex m4al Same as @option{-m4a-nofpu}, except that it implicitly passes @option{-dsp} to the assembler. GCC doesn't generate any DSP instructions at the moment. @item -m5-32media @opindex m5-32media Generate 32-bit code for SHmedia. @item -m5-32media-nofpu @opindex m5-32media-nofpu Generate 32-bit code for SHmedia in such a way that the floating-point unit is not used. @item -m5-64media @opindex m5-64media Generate 64-bit code for SHmedia. @item -m5-64media-nofpu @opindex m5-64media-nofpu Generate 64-bit code for SHmedia in such a way that the floating-point unit is not used. @item -m5-compact @opindex m5-compact Generate code for SHcompact. @item -m5-compact-nofpu @opindex m5-compact-nofpu Generate code for SHcompact in such a way that the floating-point unit is not used. @item -mb @opindex mb Compile code for the processor in big-endian mode. @item -ml @opindex ml Compile code for the processor in little-endian mode. @item -mdalign @opindex mdalign Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library do not work unless you recompile it first with @option{-mdalign}. @item -mrelax @opindex mrelax Shorten some address references at link time, when possible; uses the linker option @option{-relax}. @item -mbigtable @opindex mbigtable Use 32-bit offsets in @code{switch} tables. The default is to use 16-bit offsets. @item -mbitops @opindex mbitops Enable the use of bit manipulation instructions on SH2A. @item -mfmovd @opindex mfmovd Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for alignment constraints. @item -mrenesas @opindex mrenesas Comply with the calling conventions defined by Renesas. @item -mno-renesas @opindex mno-renesas Comply with the calling conventions defined for GCC before the Renesas conventions were available. This option is the default for all targets of the SH toolchain. @item -mnomacsave @opindex mnomacsave Mark the @code{MAC} register as call-clobbered, even if @option{-mrenesas} is given. @item -mieee @itemx -mno-ieee @opindex mieee @opindex mno-ieee Control the IEEE compliance of floating-point comparisons, which affects the handling of cases where the result of a comparison is unordered. By default @option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is enabled @option{-mno-ieee} is implicitly set, which results in faster floating-point greater-equal and less-equal comparisons. The implcit settings can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. @item -minline-ic_invalidate @opindex minline-ic_invalidate Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if @option{-musermode} is in effect and the selected code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi} instruction. If the selected code generation option does not allow the use of the @code{icbi} instruction, and @option{-musermode} is not in effect, the inlined code manipulates the instruction cache address array directly with an associative write. This not only requires privileged mode at run time, but it also fails if the cache line had been mapped via the TLB and has become unmapped. @item -misize @opindex misize Dump instruction size and location in the assembly code. @item -mpadstruct @opindex mpadstruct This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the SH ABI@. @item -matomic-model=@var{model} @opindex matomic-model=@var{model} Sets the model of atomic operations and additional parameters as a comma separated list. For details on the atomic built-in functions see @ref{__atomic Builtins}. The following models and parameters are supported: @table @samp @item none Disable compiler generated atomic sequences and emit library calls for atomic operations. This is the default if the target is not @code{sh*-*-linux*}. @item soft-gusa Generate GNU/Linux compatible gUSA software atomic sequences for the atomic built-in functions. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for SH3* and SH4* single-core systems. This option is enabled by default when the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A, this option will also partially utilize the hardware atomic instructions @code{movli.l} and @code{movco.l} to create more efficient code, unless @samp{strict} is specified. @item soft-tcb Generate software atomic sequences that use a variable in the thread control block. This is a variation of the gUSA sequences which can also be used on SH1* and SH2* targets. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for single-core systems. When using this model, the @samp{gbr-offset=} parameter has to be specified as well. @item soft-imask Generate software atomic sequences that temporarily disable interrupts by setting @code{SR.IMASK = 1111}. This model works only when the program runs in privileged mode and is only suitable for single-core systems. Additional support from the interrupt/exception handling code of the system is not required. This model is enabled by default when the target is @code{sh*-*-linux*} and SH1* or SH2*. @item hard-llcs Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l} instructions only. This is only available on SH4A and is suitable for multi-core systems. Since the hardware instructions support only 32 bit atomic variables access to 8 or 16 bit variables is emulated with 32 bit accesses. Code compiled with this option will also be compatible with other software atomic model interrupt/exception handling systems if executed on an SH4A system. Additional support from the interrupt/exception handling code of the system is not required for this model. @item gbr-offset= This parameter specifies the offset in bytes of the variable in the thread control block structure that should be used by the generated atomic sequences when the @samp{soft-tcb} model has been selected. For other models this parameter is ignored. The specified value must be an integer multiple of four and in the range 0-1020. @item strict This parameter prevents mixed usage of multiple atomic models, even though they would be compatible, and will make the compiler generate atomic sequences of the specified model only. @end table @item -mtas @opindex mtas Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. Notice that depending on the particular hardware and software configuration this can degrade overall performance due to the operand cache line flushes that are implied by the @code{tas.b} instruction. On multi-core SH4A processors the @code{tas.b} instruction must be used with caution since it can result in data corruption for certain cache configurations. @item -mprefergot @opindex mprefergot When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table. @item -musermode @itemx -mno-usermode @opindex musermode @opindex mno-usermode Don't allow (allow) the compiler generating privileged mode code. Specifying @option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the inlined code would not work in user mode. @option{-musermode} is the default when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2* @option{-musermode} has no effect, since there is no user mode. @item -multcost=@var{number} @opindex multcost=@var{number} Set the cost to assume for a multiply insn. @item -mdiv=@var{strategy} @opindex mdiv=@var{strategy} Set the division strategy to be used for integer division operations. For SHmedia @var{strategy} can be one of: @table @samp @item fp Performs the operation in floating point. This has a very high latency, but needs only a few instructions, so it might be a good choice if your code has enough easily-exploitable ILP to allow the compiler to schedule the floating-point instructions together with other instructions. Division by zero causes a floating-point exception. @item inv Uses integer operations to calculate the inverse of the divisor, and then multiplies the dividend with the inverse. This strategy allows CSE and hoisting of the inverse calculation. Division by zero calculates an unspecified result, but does not trap. @item inv:minlat A variant of @samp{inv} where, if no CSE or hoisting opportunities have been found, or if the entire operation has been hoisted to the same place, the last stages of the inverse calculation are intertwined with the final multiply to reduce the overall latency, at the expense of using a few more instructions, and thus offering fewer scheduling opportunities with other code. @item call Calls a library function that usually implements the @samp{inv:minlat} strategy. This gives high code density for @code{m5-*media-nofpu} compilations. @item call2 Uses a different entry point of the same library function, where it assumes that a pointer to a lookup table has already been set up, which exposes the pointer load to CSE and code hoisting optimizations. @item inv:call @itemx inv:call2 @itemx inv:fp Use the @samp{inv} algorithm for initial code generation, but if the code stays unoptimized, revert to the @samp{call}, @samp{call2}, or @samp{fp} strategies, respectively. Note that the potentially-trapping side effect of division by zero is carried by a separate instruction, so it is possible that all the integer instructions are hoisted out, but the marker for the side effect stays where it is. A recombination to floating-point operations or a call is not possible in that case. @item inv20u @itemx inv20l Variants of the @samp{inv:minlat} strategy. In the case that the inverse calculation is not separated from the multiply, they speed up division where the dividend fits into 20 bits (plus sign where applicable) by inserting a test to skip a number of operations in this case; this test slows down the case of larger dividends. @samp{inv20u} assumes the case of a such a small dividend to be unlikely, and @samp{inv20l} assumes it to be likely. @end table For targets other than SHmedia @var{strategy} can be one of: @table @samp @item call-div1 Calls a library function that uses the single-step division instruction @code{div1} to perform the operation. Division by zero calculates an unspecified result and does not trap. This is the default except for SH4, SH2A and SHcompact. @item call-fp Calls a library function that performs the operation in double precision floating point. Division by zero causes a floating-point exception. This is the default for SHcompact with FPU. Specifying this for targets that do not have a double precision FPU will default to @code{call-div1}. @item call-table Calls a library function that uses a lookup table for small divisors and the @code{div1} instruction with case distinction for larger divisors. Division by zero calculates an unspecified result and does not trap. This is the default for SH4. Specifying this for targets that do not have dynamic shift instructions will default to @code{call-div1}. @end table When a division strategy has not been specified the default strategy will be selected based on the current target. For SH2A the default strategy is to use the @code{divs} and @code{divu} instructions instead of library function calls. @item -maccumulate-outgoing-args @opindex maccumulate-outgoing-args Reserve space once for outgoing arguments in the function prologue rather than around each call. Generally beneficial for performance and size. Also needed for unwinding to avoid changing the stack frame around conditional code. @item -mdivsi3_libfunc=@var{name} @opindex mdivsi3_libfunc=@var{name} Set the name of the library function used for 32-bit signed division to @var{name}. This only affects the name used in the @samp{call} and @samp{inv:call} division strategies, and the compiler still expects the same sets of input/output/clobbered registers as if this option were not present. @item -mfixed-range=@var{register-range} @opindex mfixed-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. @item -mindexed-addressing @opindex mindexed-addressing Enable the use of the indexed addressing mode for SHmedia32/SHcompact. This is only safe if the hardware and/or OS implement 32-bit wrap-around semantics for the indexed addressing mode. The architecture allows the implementation of processors with 64-bit MMU, which the OS could use to get 32-bit addressing, but since no current hardware implementation supports this or any other way to make the indexed addressing mode safe to use in the 32-bit ABI, the default is @option{-mno-indexed-addressing}. @item -mgettrcost=@var{number} @opindex mgettrcost=@var{number} Set the cost assumed for the @code{gettr} instruction to @var{number}. The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise. @item -mpt-fixed @opindex mpt-fixed Assume @code{pt*} instructions won't trap. This generally generates better-scheduled code, but is unsafe on current hardware. The current architecture definition says that @code{ptabs} and @code{ptrel} trap when the target anded with 3 is 3. This has the unintentional effect of making it unsafe to schedule these instructions before a branch, or hoist them out of a loop. For example, @code{__do_global_ctors}, a part of @file{libgcc} that runs constructors at program startup, calls functions in a list which is delimited by @minus{}1. With the @option{-mpt-fixed} option, the @code{ptabs} is done before testing against @minus{}1. That means that all the constructors run a bit more quickly, but when the loop comes to the end of the list, the program crashes because @code{ptabs} loads @minus{}1 into a target register. Since this option is unsafe for any hardware implementing the current architecture specification, the default is @option{-mno-pt-fixed}. Unless specified explicitly with @option{-mgettrcost}, @option{-mno-pt-fixed} also implies @option{-mgettrcost=100}; this deters register allocation from using target registers for storing ordinary integers. @item -minvalid-symbols @opindex minvalid-symbols Assume symbols might be invalid. Ordinary function symbols generated by the compiler are always valid to load with @code{movi}/@code{shori}/@code{ptabs} or @code{movi}/@code{shori}/@code{ptrel}, but with assembler and/or linker tricks it is possible to generate symbols that cause @code{ptabs} or @code{ptrel} to trap. This option is only meaningful when @option{-mno-pt-fixed} is in effect. It prevents cross-basic-block CSE, hoisting and most scheduling of symbol loads. The default is @option{-mno-invalid-symbols}. @item -mbranch-cost=@var{num} @opindex mbranch-cost=@var{num} Assume @var{num} to be the cost for a branch instruction. Higher numbers make the compiler try to generate more branch-free code if possible. If not specified the value is selected depending on the processor type that is being compiled for. @item -mzdcbranch @itemx -mno-zdcbranch @opindex mzdcbranch @opindex mno-zdcbranch Assume (do not assume) that zero displacement conditional branch instructions @code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the compiler will try to prefer zero displacement branch code sequences. This is enabled by default when generating code for SH4 and SH4A. It can be explicitly disabled by specifying @option{-mno-zdcbranch}. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent @option{-mfused-madd} option is now mapped to the machine-independent @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is mapped to @option{-ffp-contract=off}. @item -mfsca @itemx -mno-fsca @opindex mfsca @opindex mno-fsca Allow or disallow the compiler to emit the @code{fsca} instruction for sine and cosine approximations. The option @code{-mfsca} must be used in combination with @code{-funsafe-math-optimizations}. It is enabled by default when generating code for SH4A. Using @code{-mno-fsca} disables sine and cosine approximations even if @code{-funsafe-math-optimizations} is in effect. @item -mfsrra @itemx -mno-fsrra @opindex mfsrra @opindex mno-fsrra Allow or disallow the compiler to emit the @code{fsrra} instruction for reciprocal square root approximations. The option @code{-mfsrra} must be used in combination with @code{-funsafe-math-optimizations} and @code{-ffinite-math-only}. It is enabled by default when generating code for SH4A. Using @code{-mno-fsrra} disables reciprocal square root approximations even if @code{-funsafe-math-optimizations} and @code{-ffinite-math-only} are in effect. @item -mpretend-cmove @opindex mpretend-cmove Prefer zero-displacement conditional branches for conditional move instruction patterns. This can result in faster code on the SH4 processor. @end table @node Solaris 2 Options @subsection Solaris 2 Options @cindex Solaris 2 options These @samp{-m} options are supported on Solaris 2: @table @gcctabopt @item -mclear-hwcap @opindex mclear-hwcap @option{-mclear-hwcap} tells the compiler to remove the hardware capabilities generated by the Solaris assembler. This is only necessary when object files use ISA extensions not supported by the current machine, but check at runtime whether or not to use them. @item -mimpure-text @opindex mimpure-text @option{-mimpure-text}, used in addition to @option{-shared}, tells the compiler to not pass @option{-z text} to the linker when linking a shared object. Using this option, you can link position-dependent code into a shared object. @option{-mimpure-text} suppresses the ``relocations remain against allocatable but non-writable sections'' linker error message. However, the necessary relocations trigger copy-on-write, and the shared object is not actually shared across processes. Instead of using @option{-mimpure-text}, you should compile all source code with @option{-fpic} or @option{-fPIC}. @end table These switches are supported in addition to the above on Solaris 2: @table @gcctabopt @item -pthreads @opindex pthreads Add support for multithreading using the POSIX threads library. This option sets flags for both the preprocessor and linker. This option does not affect the thread safety of object code produced by the compiler or that of libraries supplied with it. @item -pthread @opindex pthread This is a synonym for @option{-pthreads}. @end table @node SPARC Options @subsection SPARC Options @cindex SPARC options These @samp{-m} options are supported on the SPARC: @table @gcctabopt @item -mno-app-regs @itemx -mapp-regs @opindex mno-app-regs @opindex mapp-regs Specify @option{-mapp-regs} to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the global register 1, each global register 2 through 4 is then treated as an allocable register that is clobbered by function calls. This is the default. To be fully SVR4 ABI-compliant at the cost of some performance loss, specify @option{-mno-app-regs}. You should compile libraries and system software with this option. @item -mflat @itemx -mno-flat @opindex mflat @opindex mno-flat With @option{-mflat}, the compiler does not generate save/restore instructions and uses a ``flat'' or single register window model. This model is compatible with the regular register window model. The local registers and the input registers (0--5) are still treated as ``call-saved'' registers and are saved on the stack as needed. With @option{-mno-flat} (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode. @item -mfpu @itemx -mhard-float @opindex mfpu @opindex mhard-float Generate output containing floating-point instructions. This is the default. @item -mno-fpu @itemx -msoft-float @opindex mno-fpu @opindex msoft-float Generate output containing library calls for floating point. @strong{Warning:} the requisite libraries are not available for all SPARC targets. Normally the facilities of the machine's usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets @samp{sparc-*-aout} and @samp{sparclite-*-*} do provide software floating-point support. @option{-msoft-float} changes the calling convention in the output file; therefore, it is only useful if you compile @emph{all} of a program with this option. In particular, you need to compile @file{libgcc.a}, the library that comes with GCC, with @option{-msoft-float} in order for this to work. @item -mhard-quad-float @opindex mhard-quad-float Generate output containing quad-word (long double) floating-point instructions. @item -msoft-quad-float @opindex msoft-quad-float Generate output containing library calls for quad-word (long double) floating-point instructions. The functions called are those specified in the SPARC ABI@. This is the default. As of this writing, there are no SPARC implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the @option{-msoft-quad-float} option is the default. @item -mno-unaligned-doubles @itemx -munaligned-doubles @opindex mno-unaligned-doubles @opindex munaligned-doubles Assume that doubles have 8-byte alignment. This is the default. With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating-point code. @item -muser-mode @itemx -mno-user-mode @opindex muser-mode @opindex mno-user-mode Do not generate code that can only run in supervisor mode. This is relevant only for the @code{casa} instruction emitted for the LEON3 processor. The default is @option{-mno-user-mode}. @item -mno-faster-structs @itemx -mfaster-structs @opindex mno-faster-structs @opindex mfaster-structs With @option{-mfaster-structs}, the compiler assumes that structures should have 8-byte alignment. This enables the use of pairs of @code{ldd} and @code{std} instructions for copies in structure assignment, in place of twice as many @code{ld} and @code{st} pairs. However, the use of this changed alignment directly violates the SPARC ABI@. Thus, it's intended only for use on targets where the developer acknowledges that their resulting code is not directly in line with the rules of the ABI@. @item -mcpu=@var{cpu_type} @opindex mcpu Set the instruction set, register set, and instruction scheduling parameters for machine type @var{cpu_type}. Supported values for @var{cpu_type} are @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{sparclite}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3} and @samp{niagara4}. Native Solaris and GNU/Linux toolchains also support the value @samp{native}, which selects the best architecture option for the host processor. @option{-mcpu=native} has no effect if GCC does not recognize the processor. Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are @samp{v7}, @samp{v8}, @samp{sparclite}, @samp{sparclet}, @samp{v9}. Here is a list of each supported architecture and their supported implementations. @table @asis @item v7 cypress, leon3v7 @item v8 supersparc, hypersparc, leon, leon3 @item sparclite f930, f934, sparclite86x @item sparclet tsc701 @item v9 ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4 @end table By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler additionally optimizes it for the Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc. With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC-V8 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series. With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of the SPARC architecture. This adds the integer multiply, integer divide step and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. With @option{-mcpu=f930}, the compiler additionally optimizes it for the Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu MB86934 chip, which is the more recent SPARClite with FPU@. With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of the SPARC architecture. This adds the integer multiply, multiply/accumulate, integer divide step and scan (@code{ffs}) instructions which exist in SPARClet but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally optimizes it for the TEMIC SPARClet chip. With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code registers and conditional move instructions. With @option{-mcpu=ultrasparc}, the compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi chips. With @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With @option{-mcpu=niagara}, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler additionally optimizes it for Sun UltraSPARC T2 chips. With @option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler additionally optimizes it for Sun UltraSPARC T4 chips. @item -mtune=@var{cpu_type} @opindex mtune Set the instruction scheduling parameters for machine type @var{cpu_type}, but do not set the instruction set or register set that the option @option{-mcpu=@var{cpu_type}} does. The same values for @option{-mcpu=@var{cpu_type}} can be used for @option{-mtune=@var{cpu_type}}, but the only useful values are those that select a particular CPU implementation. Those are @samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3} and @samp{niagara4}. With native Solaris and GNU/Linux toolchains, @samp{native} can also be used. @item -mv8plus @itemx -mno-v8plus @opindex mv8plus @opindex mno-v8plus With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The difference from the V8 ABI is that the global and out registers are considered 64 bits wide. This is enabled by default on Solaris in 32-bit mode for all SPARC-V9 processors. @item -mvis @itemx -mno-vis @opindex mvis @opindex mno-vis With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC Visual Instruction Set extensions. The default is @option{-mno-vis}. @item -mvis2 @itemx -mno-vis2 @opindex mvis2 @opindex mno-vis2 With @option{-mvis2}, GCC generates code that takes advantage of version 2.0 of the UltraSPARC Visual Instruction Set extensions. The default is @option{-mvis2} when targeting a cpu that supports such instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} also sets @option{-mvis}. @item -mvis3 @itemx -mno-vis3 @opindex mvis3 @opindex mno-vis3 With @option{-mvis3}, GCC generates code that takes advantage of version 3.0 of the UltraSPARC Visual Instruction Set extensions. The default is @option{-mvis3} when targeting a cpu that supports such instructions, such as niagara-3 and later. Setting @option{-mvis3} also sets @option{-mvis2} and @option{-mvis}. @item -mcbcond @itemx -mno-cbcond @opindex mcbcond @opindex mno-cbcond With @option{-mcbcond}, GCC generates code that takes advantage of compare-and-branch instructions, as defined in the Sparc Architecture 2011. The default is @option{-mcbcond} when targeting a cpu that supports such instructions, such as niagara-4 and later. @item -mpopc @itemx -mno-popc @opindex mpopc @opindex mno-popc With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC population count instruction. The default is @option{-mpopc} when targeting a cpu that supports such instructions, such as Niagara-2 and later. @item -mfmaf @itemx -mno-fmaf @opindex mfmaf @opindex mno-fmaf With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-point extensions. The default is @option{-mfmaf} when targeting a cpu that supports such instructions, such as Niagara-3 and later. @item -mfix-at697f @opindex mfix-at697f Enable the documented workaround for the single erratum of the Atmel AT697F processor (which corresponds to erratum #13 of the AT697E processor). @item -mfix-ut699 @opindex mfix-ut699 Enable the documented workarounds for the floating-point errata and the data cache nullify errata of the UT699 processor. @end table These @samp{-m} options are supported in addition to the above on SPARC-V9 processors in 64-bit environments: @table @gcctabopt @item -m32 @itemx -m64 @opindex m32 @opindex m64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. @item -mcmodel=@var{which} @opindex mcmodel Set the code model to one of @table @samp @item medlow The Medium/Low code model: 64-bit addresses, programs must be linked in the low 32 bits of memory. Programs can be statically or dynamically linked. @item medmid The Medium/Middle code model: 64-bit addresses, programs must be linked in the low 44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. @item medany The Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment. @item embmedany The Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments must be less than 2GB in size, both starting anywhere in memory (determined at link time). The global register %g4 points to the base of the data segment. Programs are statically linked and PIC is not supported. @end table @item -mmemory-model=@var{mem-model} @opindex mmemory-model Set the memory model in force on the processor to one of @table @samp @item default The default memory model for the processor and operating system. @item rmo Relaxed Memory Order @item pso Partial Store Order @item tso Total Store Order @item sc Sequential Consistency @end table These memory models are formally defined in Appendix D of the Sparc V9 architecture manual, as set in the processor's @code{PSTATE.MM} field. @item -mstack-bias @itemx -mno-stack-bias @opindex mstack-bias @opindex mno-stack-bias With @option{-mstack-bias}, GCC assumes that the stack pointer, and frame pointer if present, are offset by @minus{}2047 which must be added back when making stack frame references. This is the default in 64-bit mode. Otherwise, assume no such offset is present. @end table @node SPU Options @subsection SPU Options @cindex SPU options These @samp{-m} options are supported on the SPU: @table @gcctabopt @item -mwarn-reloc @itemx -merror-reloc @opindex mwarn-reloc @opindex merror-reloc The loader for SPU does not handle dynamic relocations. By default, GCC gives an error when it generates code that requires a dynamic relocation. @option{-mno-error-reloc} disables the error, @option{-mwarn-reloc} generates a warning instead. @item -msafe-dma @itemx -munsafe-dma @opindex msafe-dma @opindex munsafe-dma Instructions that initiate or test completion of DMA must not be reordered with respect to loads and stores of the memory that is being accessed. With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect memory accesses, but that can lead to inefficient code in places where the memory is known to not change. Rather than mark the memory as volatile, you can use @option{-msafe-dma} to tell the compiler to treat the DMA instructions as potentially affecting all memory. @item -mbranch-hints @opindex mbranch-hints By default, GCC generates a branch hint instruction to avoid pipeline stalls for always-taken or probably-taken branches. A hint is not generated closer than 8 instructions away from its branch. There is little reason to disable them, except for debugging purposes, or to make an object a little bit smaller. @item -msmall-mem @itemx -mlarge-mem @opindex msmall-mem @opindex mlarge-mem By default, GCC generates code assuming that addresses are never larger than 18 bits. With @option{-mlarge-mem} code is generated that assumes a full 32-bit address. @item -mstdmain @opindex mstdmain By default, GCC links against startup code that assumes the SPU-style main function interface (which has an unconventional parameter list). With @option{-mstdmain}, GCC links your program against startup code that assumes a C99-style interface to @code{main}, including a local copy of @code{argv} strings. @item -mfixed-range=@var{register-range} @opindex mfixed-range Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma. @item -mea32 @itemx -mea64 @opindex mea32 @opindex mea64 Compile code assuming that pointers to the PPU address space accessed via the @code{__ea} named address space qualifier are either 32 or 64 bits wide. The default is 32 bits. As this is an ABI-changing option, all object code in an executable must be compiled with the same setting. @item -maddress-space-conversion @itemx -mno-address-space-conversion @opindex maddress-space-conversion @opindex mno-address-space-conversion Allow/disallow treating the @code{__ea} address space as superset of the generic address space. This enables explicit type casts between @code{__ea} and generic pointer as well as implicit conversions of generic pointers to @code{__ea} pointers. The default is to allow address space pointer conversions. @item -mcache-size=@var{cache-size} @opindex mcache-size This option controls the version of libgcc that the compiler links to an executable and selects a software-managed cache for accessing variables in the @code{__ea} address space with a particular cache size. Possible options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64} and @samp{128}. The default cache size is 64KB. @item -matomic-updates @itemx -mno-atomic-updates @opindex matomic-updates @opindex mno-atomic-updates This option controls the version of libgcc that the compiler links to an executable and selects whether atomic updates to the software-managed cache of PPU-side variables are used. If you use atomic updates, changes to a PPU variable from SPU code using the @code{__ea} named address space qualifier do not interfere with changes to other PPU variables residing in the same cache line from PPU code. If you do not use atomic updates, such interference may occur; however, writing back cache lines is more efficient. The default behavior is to use atomic updates. @item -mdual-nops @itemx -mdual-nops=@var{n} @opindex mdual-nops By default, GCC inserts nops to increase dual issue when it expects it to increase performance. @var{n} can be a value from 0 to 10. A smaller @var{n} inserts fewer nops. 10 is the default, 0 is the same as @option{-mno-dual-nops}. Disabled with @option{-Os}. @item -mhint-max-nops=@var{n} @opindex mhint-max-nops Maximum number of nops to insert for a branch hint. A branch hint must be at least 8 instructions away from the branch it is affecting. GCC inserts up to @var{n} nops to enforce this, otherwise it does not generate the branch hint. @item -mhint-max-distance=@var{n} @opindex mhint-max-distance The encoding of the branch hint instruction limits the hint to be within 256 instructions of the branch it is affecting. By default, GCC makes sure it is within 125. @item -msafe-hints @opindex msafe-hints Work around a hardware bug that causes the SPU to stall indefinitely. By default, GCC inserts the @code{hbrp} instruction to make sure this stall won't happen. @end table @node System V Options @subsection Options for System V These additional options are available on System V Release 4 for compatibility with other compilers on those systems: @table @gcctabopt @item -G @opindex G Create a shared object. It is recommended that @option{-symbolic} or @option{-shared} be used instead. @item -Qy @opindex Qy Identify the versions of each tool used by the compiler, in a @code{.ident} assembler directive in the output. @item -Qn @opindex Qn Refrain from adding @code{.ident} directives to the output file (this is the default). @item -YP,@var{dirs} @opindex YP Search the directories @var{dirs}, and no others, for libraries specified with @option{-l}. @item -Ym,@var{dir} @opindex Ym Look in the directory @var{dir} to find the M4 preprocessor. The assembler uses this option. @c This is supposed to go with a -Yd for predefined M4 macro files, but @c the generic assembler that comes with Solaris takes just -Ym. @end table @node TILE-Gx Options @subsection TILE-Gx Options @cindex TILE-Gx options These @samp{-m} options are supported on the TILE-Gx: @table @gcctabopt @item -mcmodel=small @opindex mcmodel=small Generate code for the small model. The distance for direct calls is limited to 500M in either direction. PC-relative addresses are 32 bits. Absolute addresses support the full address range. @item -mcmodel=large @opindex mcmodel=large Generate code for the large model. There is no limitation on call distance, pc-relative addresses, or absolute addresses. @item -mcpu=@var{name} @opindex mcpu Selects the type of CPU to be targeted. Currently the only supported type is @samp{tilegx}. @item -m32 @itemx -m64 @opindex m32 @opindex m64 Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long, and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. @item -mbig-endian @itemx -mlittle-endian @opindex mbig-endian @opindex mlittle-endian Generate code in big/little endian mode, respectively. @end table @node TILEPro Options @subsection TILEPro Options @cindex TILEPro options These @samp{-m} options are supported on the TILEPro: @table @gcctabopt @item -mcpu=@var{name} @opindex mcpu Selects the type of CPU to be targeted. Currently the only supported type is @samp{tilepro}. @item -m32 @opindex m32 Generate code for a 32-bit environment, which sets int, long, and pointer to 32 bits. This is the only supported behavior so the flag is essentially ignored. @end table @node V850 Options @subsection V850 Options @cindex V850 Options These @samp{-m} options are defined for V850 implementations: @table @gcctabopt @item -mlong-calls @itemx -mno-long-calls @opindex mlong-calls @opindex mno-long-calls Treat all calls as being far away (near). If calls are assumed to be far away, the compiler always loads the function's address into a register, and calls indirect through the pointer. @item -mno-ep @itemx -mep @opindex mno-ep @opindex mep Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the @code{ep} register, and use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} option is on by default if you optimize. @item -mno-prolog-function @itemx -mprolog-function @opindex mno-prolog-function @opindex mprolog-function Do not use (do use) external functions to save and restore registers at the prologue and epilogue of a function. The external functions are slower, but use less code space if more than one function saves the same number of registers. The @option{-mprolog-function} option is on by default if you optimize. @item -mspace @opindex mspace Try to make the code as small as possible. At present, this just turns on the @option{-mep} and @option{-mprolog-function} options. @item -mtda=@var{n} @opindex mtda Put static or global variables whose size is @var{n} bytes or less into the tiny data area that register @code{ep} points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte references). @item -msda=@var{n} @opindex msda Put static or global variables whose size is @var{n} bytes or less into the small data area that register @code{gp} points to. The small data area can hold up to 64 kilobytes. @item -mzda=@var{n} @opindex mzda Put static or global variables whose size is @var{n} bytes or less into the first 32 kilobytes of memory. @item -mv850 @opindex mv850 Specify that the target processor is the V850. @item -mv850e3v5 @opindex mv850e3v5 Specify that the target processor is the V850E3V5. The preprocessor constant @samp{__v850e3v5__} is defined if this option is used. @item -mv850e2v4 @opindex mv850e2v4 Specify that the target processor is the V850E3V5. This is an alias for the @option{-mv850e3v5} option. @item -mv850e2v3 @opindex mv850e2v3 Specify that the target processor is the V850E2V3. The preprocessor constant @samp{__v850e2v3__} is defined if this option is used. @item -mv850e2 @opindex mv850e2 Specify that the target processor is the V850E2. The preprocessor constant @samp{__v850e2__} is defined if this option is used. @item -mv850e1 @opindex mv850e1 Specify that the target processor is the V850E1. The preprocessor constants @samp{__v850e1__} and @samp{__v850e__} are defined if this option is used. @item -mv850es @opindex mv850es Specify that the target processor is the V850ES. This is an alias for the @option{-mv850e1} option. @item -mv850e @opindex mv850e Specify that the target processor is the V850E@. The preprocessor constant @samp{__v850e__} is defined if this option is used. If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5} are defined then a default target processor is chosen and the relevant @samp{__v850*__} preprocessor constant is defined. The preprocessor constants @samp{__v850} and @samp{__v851__} are always defined, regardless of which processor variant is the target. @item -mdisable-callt @itemx -mno-disable-callt @opindex mdisable-callt @opindex mno-disable-callt This option suppresses generation of the @code{CALLT} instruction for the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 architecture. This option is enabled by default when the RH850 ABI is in use (see @option{-mrh850-abi}), and disabled by default when the GCC ABI is in use. If @code{CALLT} instructions are being generated then the C preprocessor symbol @code{__V850_CALLT__} will be defined. @item -mrelax @itemx -mno-relax @opindex mrelax @opindex mno-relax Pass on (or do not pass on) the @option{-mrelax} command line option to the assembler. @item -mlong-jumps @itemx -mno-long-jumps @opindex mlong-jumps @opindex mno-long-jumps Disable (or re-enable) the generation of PC-relative jump instructions. @item -msoft-float @itemx -mhard-float @opindex msoft-float @opindex mhard-float Disable (or re-enable) the generation of hardware floating point instructions. This option is only significant when the target architecture is @samp{V850E2V3} or higher. If hardware floating point instructions are being generated then the C preprocessor symbol @code{__FPU_OK__} will be defined, otherwise the symbol @code{__NO_FPU__} will be defined. @item -mloop @opindex mloop Enables the use of the e3v5 LOOP instruction. The use of this instruction is not enabled by default when the e3v5 architecture is selected because its use is still experimental. @item -mrh850-abi @itemx -mghs @opindex mrh850-abi @opindex mghs Enables support for the RH850 version of the V850 ABI. This is the default. With this version of the ABI the following rules apply: @itemize @item Integer sized structures and unions are returned via a memory pointer rather than a register. @item Large structures and unions (more than 8 bytes in size) are passed by value. @item Functions are aligned to 16-bit boundaries. @item The @option{-m8byte-align} command line option is supported. @item The @option{-mdisable-callt} command line option is enabled by default. The @option{-mno-disable-callt} command line option is not supported. @end itemize When this version of the ABI is enabled the C preprocessor symbol @code{__V850_RH850_ABI__} is defined. @item -mgcc-abi @opindex mgcc-abi Enables support for the old GCC version of the V850 ABI. With this version of the ABI the following rules apply: @itemize @item Integer sized structures and unions are returned in register @code{r10}. @item Large structures and unions (more than 8 bytes in size) are passed by reference. @item Functions are aligned to 32-bit boundaries, unless optimizing for size. @item The @option{-m8byte-align} command line option is not supported. @item The @option{-mdisable-callt} command line option is supported but not enabled by default. @end itemize When this version of the ABI is enabled the C preprocessor symbol @code{__V850_GCC_ABI__} is defined. @item -m8byte-align @itemx -mno-8byte-align @opindex m8byte-align @opindex mno-8byte-align Enables support for @code{doubles} and @code{long long} types to be aligned on 8-byte boundaries. The default is to restrict the alignment of all objects to at most 4-bytes. When @option{-m8byte-align} is in effect the C preprocessor symbol @code{__V850_8BYTE_ALIGN__} will be defined. @item -mbig-switch @opindex mbig-switch Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table. @item -mapp-regs @opindex mapp-regs This option causes r2 and r5 to be used in the code generated by the compiler. This setting is the default. @item -mno-app-regs @opindex mno-app-regs This option causes r2 and r5 to be treated as fixed registers. @end table @node VAX Options @subsection VAX Options @cindex VAX options These @samp{-m} options are defined for the VAX: @table @gcctabopt @item -munix @opindex munix Do not output certain jump instructions (@code{aobleq} and so on) that the Unix assembler for the VAX cannot handle across long ranges. @item -mgnu @opindex mgnu Do output those jump instructions, on the assumption that the GNU assembler is being used. @item -mg @opindex mg Output code for G-format floating-point numbers instead of D-format. @end table @node VMS Options @subsection VMS Options These @samp{-m} options are defined for the VMS implementations: @table @gcctabopt @item -mvms-return-codes @opindex mvms-return-codes Return VMS condition codes from @code{main}. The default is to return POSIX-style condition (e.g.@ error) codes. @item -mdebug-main=@var{prefix} @opindex mdebug-main=@var{prefix} Flag the first routine whose name starts with @var{prefix} as the main routine for the debugger. @item -mmalloc64 @opindex mmalloc64 Default to 64-bit memory allocation routines. @item -mpointer-size=@var{size} @opindex -mpointer-size=@var{size} Set the default size of pointers. Possible options for @var{size} are @samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. The later option disables @code{pragma pointer_size}. @end table @node VxWorks Options @subsection VxWorks Options @cindex VxWorks Options The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target. @table @gcctabopt @item -mrtp @opindex mrtp GCC can generate code for both VxWorks kernels and real time processes (RTPs). This option switches from the former to the latter. It also defines the preprocessor macro @code{__RTP__}. @item -non-static @opindex non-static Link an RTP executable against shared libraries rather than static libraries. The options @option{-static} and @option{-shared} can also be used for RTPs (@pxref{Link Options}); @option{-static} is the default. @item -Bstatic @itemx -Bdynamic @opindex Bstatic @opindex Bdynamic These options are passed down to the linker. They are defined for compatibility with Diab. @item -Xbind-lazy @opindex Xbind-lazy Enable lazy binding of function calls. This option is equivalent to @option{-Wl,-z,now} and is defined for compatibility with Diab. @item -Xbind-now @opindex Xbind-now Disable lazy binding of function calls. This option is the default and is defined for compatibility with Diab. @end table @node x86-64 Options @subsection x86-64 Options @cindex x86-64 options These are listed under @xref{i386 and x86-64 Options}. @node Xstormy16 Options @subsection Xstormy16 Options @cindex Xstormy16 Options These options are defined for Xstormy16: @table @gcctabopt @item -msim @opindex msim Choose startup files and linker script suitable for the simulator. @end table @node Xtensa Options @subsection Xtensa Options @cindex Xtensa Options These options are supported for Xtensa targets: @table @gcctabopt @item -mconst16 @itemx -mno-const16 @opindex mconst16 @opindex mno-const16 Enable or disable use of @code{CONST16} instructions for loading constant values. The @code{CONST16} instruction is currently not a standard option from Tensilica. When enabled, @code{CONST16} instructions are always used in place of the standard @code{L32R} instructions. The use of @code{CONST16} is enabled by default only if the @code{L32R} instruction is not available. @item -mfused-madd @itemx -mno-fused-madd @opindex mfused-madd @opindex mno-fused-madd Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases where strict IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with @emph{more} bits of precision than specified by the IEEE standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compiler's ability to combine multiply and add/subtract operations. @item -mserialize-volatile @itemx -mno-serialize-volatile @opindex mserialize-volatile @opindex mno-serialize-volatile When this option is enabled, GCC inserts @code{MEMW} instructions before @code{volatile} memory references to guarantee sequential consistency. The default is @option{-mserialize-volatile}. Use @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. @item -mforce-no-pic @opindex mforce-no-pic For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code. @item -mtext-section-literals @itemx -mno-text-section-literals @opindex mtext-section-literals @opindex mno-text-section-literals Control the treatment of literal pools. The default is @option{-mno-text-section-literals}, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With @option{-mtext-section-literals}, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files. @item -mtarget-align @itemx -mno-target-align @opindex mtarget-align @opindex mno-target-align When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening is performed. The default is @option{-mtarget-align}. These options do not affect the treatment of auto-aligned instructions like @code{LOOP}, which the assembler always aligns, either by widening density instructions or by inserting NOP instructions. @item -mlongcalls @itemx -mno-longcalls @opindex mlongcalls @opindex mno-longcalls When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct @code{CALL} instruction into an @code{L32R} followed by a @code{CALLX} instruction. The default is @option{-mno-longcalls}. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by GCC still shows direct call instructions---look at the disassembled object code to see the actual instructions. Note that the assembler uses an indirect call for every cross-file call, not just those that really are out of range. @end table @node zSeries Options @subsection zSeries Options @cindex zSeries options These are listed under @xref{S/390 and zSeries Options}. @node Code Gen Options @section Options for Code Generation Conventions @cindex code generation conventions @cindex options, code generation @cindex run-time options These machine-independent options control the interface conventions used in code generation. Most of them have both positive and negative forms; the negative form of @option{-ffoo} is @option{-fno-foo}. In the table below, only one of the forms is listed---the one that is not the default. You can figure out the other form by either removing @samp{no-} or adding it. @table @gcctabopt @item -fbounds-check @opindex fbounds-check For front ends that support it, generate additional code to check that indices used to access arrays are within the declared range. This is currently only supported by the Java and Fortran front ends, where this option defaults to true and false respectively. @item -fstack-reuse=@var{reuse-level} @opindex fstack_reuse This option controls stack space reuse for user declared local/auto variables and compiler generated temporaries. @var{reuse_level} can be @samp{all}, @samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all local variables and temporaries, @samp{named_vars} enables the reuse only for user defined local variables with names, and @samp{none} disables stack reuse completely. The default value is @samp{all}. The option is needed when the program extends the lifetime of a scoped local variable or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a variable ends, and if the variable lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. Legacy code extending local lifetime will likely to break with the stack reuse optimization. For example, @smallexample int *p; @{ int local1; p = &local1; local1 = 10; .... @} @{ int local2; local2 = 20; ... @} if (*p == 10) // out of scope use of local1 @{ @} @end smallexample Another example: @smallexample struct A @{ A(int k) : i(k), j(k) @{ @} int i; int j; @}; A *ap; void foo(const A& ar) @{ ap = &ar; @} void bar() @{ foo(A(10)); // temp object's lifetime ends when foo returns @{ A a(20); .... @} ap->i+= 10; // ap references out of scope temp whose space // is reused with a. What is the value of ap->i? @} @end smallexample The lifetime of a compiler generated temporary is well defined by the C++ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older compilers in which temporaries' stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization. @item -ftrapv @opindex ftrapv This option generates traps for signed overflow on addition, subtraction, multiplication operations. @item -fwrapv @opindex fwrapv This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. This option is enabled by default for the Java front end, as required by the Java language specification. @item -fexceptions @opindex fexceptions Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC generates frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, GCC enables it by default for languages like C++ that normally require exception handling, and disables it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in C++. You may also wish to disable this option if you are compiling older C++ programs that don't use exception handling. @item -fnon-call-exceptions @opindex fnon-call-exceptions Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows @emph{trapping} instructions to throw exceptions, i.e.@: memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as @code{SIGALRM}. @item -fdelete-dead-exceptions @opindex fdelete-dead-exceptions Consider that instructions that may throw exceptions but don't otherwise contribute to the execution of the program can be optimized away. This option is enabled by default for the Ada front end, as permitted by the Ada language specification. Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. @item -funwind-tables @opindex funwind-tables Similar to @option{-fexceptions}, except that it just generates any needed static data, but does not affect the generated code in any other way. You normally do not need to enable this option; instead, a language processor that needs this handling enables it on your behalf. @item -fasynchronous-unwind-tables @opindex fasynchronous-unwind-tables Generate unwind table in DWARF 2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector). @item -fno-gnu-unique @opindex fno-gnu-unique On systems with recent GNU assembler and C library, the C++ compiler uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions of template static data members and static local variables in inline functions are unique even in the presence of @code{RTLD_LOCAL}; this is necessary to avoid problems with a library used by two different @code{RTLD_LOCAL} plugins depending on a definition in one of them and therefore disagreeing with the other one about the binding of the symbol. But this causes @code{dlclose} to be ignored for affected DSOs; if your program relies on reinitialization of a DSO via @code{dlclose} and @code{dlopen}, you can use @option{-fno-gnu-unique}. @item -fpcc-struct-return @opindex fpcc-struct-return Return ``short'' @code{struct} and @code{union} values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc). The precise convention for returning structures in memory depends on the target configuration macros. Short structures and unions are those whose size and alignment match that of some integer type. @strong{Warning:} code compiled with the @option{-fpcc-struct-return} switch is not binary compatible with code compiled with the @option{-freg-struct-return} switch. Use it to conform to a non-default application binary interface. @item -freg-struct-return @opindex freg-struct-return Return @code{struct} and @code{union} values in registers when possible. This is more efficient for small structures than @option{-fpcc-struct-return}. If you specify neither @option{-fpcc-struct-return} nor @option{-freg-struct-return}, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to @option{-fpcc-struct-return}, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative. @strong{Warning:} code compiled with the @option{-freg-struct-return} switch is not binary compatible with code compiled with the @option{-fpcc-struct-return} switch. Use it to conform to a non-default application binary interface. @item -fshort-enums @opindex fshort-enums Allocate to an @code{enum} type only as many bytes as it needs for the declared range of possible values. Specifically, the @code{enum} type is equivalent to the smallest integer type that has enough room. @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. @item -fshort-double @opindex fshort-double Use the same size for @code{double} as for @code{float}. @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. @item -fshort-wchar @opindex fshort-wchar Override the underlying type for @samp{wchar_t} to be @samp{short unsigned int} instead of the default for the target. This option is useful for building programs to run under WINE@. @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. @item -fno-common @opindex fno-common In C code, controls the placement of uninitialized global variables. Unix C compilers have traditionally permitted multiple definitions of such variables in different compilation units by placing the variables in a common block. This is the behavior specified by @option{-fcommon}, and is the default for GCC on most targets. On the other hand, this behavior is not required by ISO C, and on some targets may carry a speed or code size penalty on variable references. The @option{-fno-common} option specifies that the compiler should place uninitialized global variables in the data section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without @code{extern}) in two different compilations, you get a multiple-definition error when you link them. In this case, you must compile with @option{-fcommon} instead. Compiling with @option{-fno-common} is useful on targets for which it provides better performance, or if you wish to verify that the program will work on other systems that always treat uninitialized variable declarations this way. @item -fno-ident @opindex fno-ident Ignore the @samp{#ident} directive. @item -finhibit-size-directive @opindex finhibit-size-directive Don't output a @code{.size} assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling @file{crtstuff.c}; you should not need to use it for anything else. @item -fverbose-asm @opindex fverbose-asm Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself). @option{-fno-verbose-asm}, the default, causes the extra information to be omitted and is useful when comparing two assembler files. @item -frecord-gcc-switches @opindex frecord-gcc-switches This switch causes the command line used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact format of the recording is target and binary file format dependent, but it usually takes the form of a section containing ASCII text. This switch is related to the @option{-fverbose-asm} switch, but that switch only records information in the assembler output file as comments, so it never reaches the object file. See also @option{-grecord-gcc-switches} for another way of storing compiler options into the object file. @item -fpic @opindex fpic @cindex global offset table @cindex PIC Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (GOT)@. The dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of GCC; it is part of the operating system). If the GOT size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that @option{-fpic} does not work; in that case, recompile with @option{-fPIC} instead. (These maximums are 8k on the SPARC and 32k on the m68k and RS/6000. The 386 has no such limit.) Position-independent code requires special support, and therefore works only on certain machines. For the 386, GCC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent. When this flag is set, the macros @code{__pic__} and @code{__PIC__} are defined to 1. @item -fPIC @opindex fPIC If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, PowerPC and SPARC@. Position-independent code requires special support, and therefore works only on certain machines. When this flag is set, the macros @code{__pic__} and @code{__PIC__} are defined to 2. @item -fpie @itemx -fPIE @opindex fpie @opindex fPIE These options are similar to @option{-fpic} and @option{-fPIC}, but generated position independent code can be only linked into executables. Usually these options are used when @option{-pie} GCC option is used during linking. @option{-fpie} and @option{-fPIE} both define the macros @code{__pie__} and @code{__PIE__}. The macros have the value 1 for @option{-fpie} and 2 for @option{-fPIE}. @item -fno-jump-tables @opindex fno-jump-tables Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with @option{-fpic} or @option{-fPIC} for building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a GOT and this option is not needed. @item -ffixed-@var{reg} @opindex ffixed Treat the register named @var{reg} as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role). @var{reg} must be the name of a register. The register names accepted are machine-specific and are defined in the @code{REGISTER_NAMES} macro in the machine description macro file. This flag does not have a negative form, because it specifies a three-way choice. @item -fcall-used-@var{reg} @opindex fcall-used Treat the register named @var{reg} as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way do not save and restore the register @var{reg}. It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. This flag does not have a negative form, because it specifies a three-way choice. @item -fcall-saved-@var{reg} @opindex fcall-saved Treat the register named @var{reg} as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way save and restore the register @var{reg} if they use it. It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machine's execution model produces disastrous results. A different sort of disaster results from the use of this flag for a register in which function values may be returned. This flag does not have a negative form, because it specifies a three-way choice. @item -fpack-struct[=@var{n}] @opindex fpack-struct Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location. @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface. @item -finstrument-functions @opindex finstrument-functions Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are called with the address of the current function and its call site. (On some platforms, @code{__builtin_return_address} does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.) @smallexample void __cyg_profile_func_enter (void *this_fn, void *call_site); void __cyg_profile_func_exit (void *this_fn, void *call_site); @end smallexample The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table. This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use @samp{extern inline} in your C code, an addressable version of such functions must be provided. (This is normally the case anyway, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.) A function may be given the attribute @code{no_instrument_function}, in which case this instrumentation is not done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory). @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @opindex finstrument-functions-exclude-file-list Set the list of functions that are excluded from instrumentation (see the description of @code{-finstrument-functions}). If the file that contains a function definition matches with one of @var{file}, then that function is not instrumented. The match is done on substrings: if the @var{file} parameter is a substring of the file name, it is considered to be a match. For example: @smallexample -finstrument-functions-exclude-file-list=/bits/stl,include/sys @end smallexample @noindent excludes any inline function defined in files whose pathnames contain @code{/bits/stl} or @code{include/sys}. If, for some reason, you want to include letter @code{','} in one of @var{sym}, write @code{'\,'}. For example, @code{-finstrument-functions-exclude-file-list='\,\,tmp'} (note the single quote surrounding the option). @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @opindex finstrument-functions-exclude-function-list This is similar to @code{-finstrument-functions-exclude-file-list}, but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its user-visible name, such as @code{vector blah(const vector &)}, not the internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The match is done on substrings: if the @var{sym} parameter is a substring of the function name, it is considered to be a match. For C99 and C++ extended identifiers, the function name must be given in UTF-8, not using universal character names. @item -fstack-check @opindex fstack-check Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but you only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack. Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended. You can additionally specify a string parameter: @code{no} means no checking, @code{generic} means force the use of old-style checking, @code{specific} means use the best checking method and is equivalent to bare @option{-fstack-check}. Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks: @enumerate @item Modified allocation strategy for large objects: they are always allocated dynamically if their size exceeds a fixed threshold. @item Fixed limit on the size of the static frame of functions: when it is topped by a particular function, stack checking is not reliable and a warning is issued by the compiler. @item Inefficiency: because of both the modified allocation strategy and the generic implementation, code performance is hampered. @end enumerate Note that old-style stack checking is also the fallback method for @code{specific} if no target support has been added in the compiler. @item -fstack-limit-register=@var{reg} @itemx -fstack-limit-symbol=@var{sym} @itemx -fno-stack-limit @opindex fstack-limit-register @opindex fstack-limit-symbol @opindex fno-stack-limit Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If a larger stack is required, a signal is raised at run time. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions. For instance, if the stack starts at absolute address @samp{0x80000000} and grows downwards, you can use the flags @option{-fstack-limit-symbol=__stack_limit} and @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit of 128KB@. Note that this may only work with the GNU linker. @item -fsplit-stack @opindex fsplit-stack Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the i386 and x86_64 back ends running GNU/Linux. When code compiled with @option{-fsplit-stack} calls code compiled without @option{-fsplit-stack}, there may not be much stack space available for the latter code to run. If compiling all code, including library code, with @option{-fsplit-stack} is not an option, then the linker can fix up these calls so that the code compiled without @option{-fsplit-stack} always has a large stack. Support for this is implemented in the gold linker in GNU binutils release 2.21 and later. @item -fleading-underscore @opindex fleading-underscore This option and its counterpart, @option{-fno-leading-underscore}, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code. @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch. @item -ftls-model=@var{model} @opindex ftls-model Alter the thread-local storage model to be used (@pxref{Thread-Local}). The @var{model} argument should be one of @code{global-dynamic}, @code{local-dynamic}, @code{initial-exec} or @code{local-exec}. Note that the choice is subject to optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if @option{-fpic} is not given on the command line. The default without @option{-fpic} is @code{initial-exec}; with @option{-fpic} the default is @code{global-dynamic}. @item -fvisibility=@var{default|internal|hidden|protected} @opindex fvisibility Set the default ELF image symbol visibility to the specified option---all symbols are marked with this unless overridden within the code. Using this feature can very substantially improve linking and load times of shared object libraries, produce more optimized code, provide near-perfect API export and prevent symbol clashes. It is @strong{strongly} recommended that you use this in any shared objects you distribute. Despite the nomenclature, @code{default} always means public; i.e., available to be linked against from outside the shared object. @code{protected} and @code{internal} are pretty useless in real-world usage so the only other commonly used option is @code{hidden}. The default if @option{-fvisibility} isn't specified is @code{default}, i.e., make every symbol public---this causes the same behavior as previous versions of GCC@. A good explanation of the benefits offered by ensuring ELF symbols have the correct visibility is given by ``How To Write Shared Libraries'' by Ulrich Drepper (which can be found at @w{@uref{http://people.redhat.com/~drepper/}})---however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark things public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} and @code{__attribute__ ((visibility("default")))} instead of @code{__declspec(dllexport)} you get almost identical semantics with identical syntax. This is a great boon to those working with cross-platform projects. For those adding visibility support to existing code, you may find @samp{#pragma GCC visibility} of use. This works by you enclosing the declarations you wish to set visibility for with (for example) @samp{#pragma GCC visibility push(hidden)} and @samp{#pragma GCC visibility pop}. Bear in mind that symbol visibility should be viewed @strong{as part of the API interface contract} and thus all new code should always specify visibility when it is not the default; i.e., declarations only for use within the local DSO should @strong{always} be marked explicitly as hidden as so to avoid PLT indirection overheads---making this abundantly clear also aids readability and self-documentation of the code. Note that due to ISO C++ specification requirements, @code{operator new} and @code{operator delete} must always be of default visibility. Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the default. You may need to explicitly say @samp{#pragma GCC visibility push(default)} before including any such headers. @samp{extern} declarations are not affected by @option{-fvisibility}, so a lot of code can be recompiled with @option{-fvisibility=hidden} with no modifications. However, this means that calls to @code{extern} functions with no explicit visibility use the PLT, so it is more effective to use @code{__attribute ((visibility))} and/or @code{#pragma GCC visibility} to tell the compiler which @code{extern} declarations should be treated as hidden. Note that @option{-fvisibility} does affect C++ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default visibility so that the @samp{type_info} nodes are unified between the DSOs. An overview of these techniques, their benefits and how to use them is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}. @item -fstrict-volatile-bitfields @opindex fstrict-volatile-bitfields This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of the field's type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag you can declare all peripheral bit-fields as @code{unsigned short} (assuming short is 16 bits on these targets) to force GCC to use 16-bit accesses instead of, perhaps, a more efficient 32-bit access. If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that accesses bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated. In some cases, such as when the @code{packed} attribute is applied to a structure field, it may not be possible to access the field with a single read or write that is correctly aligned for the target machine. In this case GCC falls back to generating multiple accesses rather than code that will fault or truncate the result at run time. Note: Due to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the field's type as bit-field members. The default value of this option is determined by the application binary interface for the target processor. @item -fsync-libcalls @opindex fsync-libcalls This option controls whether any out-of-line instance of the @code{__sync} family of functions may be used to implement the C++11 @code{__atomic} family of functions. The default value of this option is enabled, thus the only useful form of the option is @option{-fno-sync-libcalls}. This option is used in the implementation of the @file{libatomic} runtime library. @end table @c man end @node Environment Variables @section Environment Variables Affecting GCC @cindex environment variables @c man begin ENVIRONMENT This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment. Note that you can also specify places to search using options such as @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC@. @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, GNU Compiler Collection (GCC) Internals}. @table @env @item LANG @itemx LC_CTYPE @c @itemx LC_COLLATE @itemx LC_MESSAGES @c @itemx LC_MONETARY @c @itemx LC_NUMERIC @c @itemx LC_TIME @itemx LC_ALL @findex LANG @findex LC_CTYPE @c @findex LC_COLLATE @findex LC_MESSAGES @c @findex LC_MONETARY @c @findex LC_NUMERIC @c @findex LC_TIME @findex LC_ALL @cindex locale These environment variables control the way that GCC uses localization information which allows GCC to work with different national conventions. GCC inspects the locale categories @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is @samp{en_GB.UTF-8} for English in the United Kingdom encoded in UTF-8. The @env{LC_CTYPE} environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that are otherwise interpreted as a string end or escape. The @env{LC_MESSAGES} environment variable specifies the language to use in diagnostic messages. If the @env{LC_ALL} environment variable is set, it overrides the value of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} and @env{LC_MESSAGES} default to the value of the @env{LANG} environment variable. If none of these variables are set, GCC defaults to traditional C English behavior. @item TMPDIR @findex TMPDIR If @env{TMPDIR} is set, it specifies the directory to use for temporary files. GCC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper. @item GCC_COMPARE_DEBUG @findex GCC_COMPARE_DEBUG Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing @option{-fcompare-debug} to the compiler driver. See the documentation of this option for more details. @item GCC_EXEC_PREFIX @findex GCC_EXEC_PREFIX If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish. If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out an appropriate prefix to use based on the pathname it is invoked with. If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram. The default value of @env{GCC_EXEC_PREFIX} is @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to the installed compiler. In many cases @var{prefix} is the value of @code{prefix} when you ran the @file{configure} script. Other prefixes specified with @option{-B} take precedence over this prefix. This prefix is also used for finding files such as @file{crt0.o} that are used for linking. In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with @samp{/usr/local/lib/gcc} (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with @option{-Bfoo/}, GCC searches @file{foo/bar} just before it searches the standard directory @file{/usr/local/lib/bar}. If a standard directory begins with the configured @var{prefix} then the value of @var{prefix} is replaced by @env{GCC_EXEC_PREFIX} when looking for header files. @item COMPILER_PATH @findex COMPILER_PATH The value of @env{COMPILER_PATH} is a colon-separated list of directories, much like @env{PATH}. GCC tries the directories thus specified when searching for subprograms, if it can't find the subprograms using @env{GCC_EXEC_PREFIX}. @item LIBRARY_PATH @findex LIBRARY_PATH The value of @env{LIBRARY_PATH} is a colon-separated list of directories, much like @env{PATH}. When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking using GCC also uses these directories when searching for ordinary libraries for the @option{-l} option (but directories specified with @option{-L} come first). @item LANG @findex LANG @cindex locale definition This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and C++. When the compiler is configured to allow multibyte characters, the following values for @env{LANG} are recognized: @table @samp @item C-JIS Recognize JIS characters. @item C-SJIS Recognize SJIS characters. @item C-EUCJP Recognize EUCJP characters. @end table If @env{LANG} is not defined, or if it has some other value, then the compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to recognize and translate multibyte characters. @end table @noindent Some additional environment variables affect the behavior of the preprocessor. @include cppenv.texi @c man end @node Precompiled Headers @section Using Precompiled Headers @cindex precompiled headers @cindex speed of compilation Often large projects have many header files that are included in every source file. The time the compiler takes to process these header files over and over again can account for nearly all of the time required to build the project. To make builds faster, GCC allows you to @dfn{precompile} a header file. To create a precompiled header file, simply compile it as you would any other file, if necessary using the @option{-x} option to make the driver treat it as a C or C++ header file. You may want to use a tool like @command{make} to keep the precompiled header up-to-date when the headers it contains change. A precompiled header file is searched for when @code{#include} is seen in the compilation. As it searches for the included file (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the compiler looks for a precompiled header in each directory just before it looks for the include file in that directory. The name searched for is the name specified in the @code{#include} with @samp{.gch} appended. If the precompiled header file can't be used, it is ignored. For instance, if you have @code{#include "all.h"}, and you have @file{all.h.gch} in the same directory as @file{all.h}, then the precompiled header file is used if possible, and the original header is used otherwise. Alternatively, you might decide to put the precompiled header file in a directory and use @option{-I} to ensure that directory is searched before (or instead of) the directory containing the original header. Then, if you want to check that the precompiled header file is always used, you can put a file of the same name as the original header in this directory containing an @code{#error} command. This also works with @option{-include}. So yet another way to use precompiled headers, good for projects not designed with precompiled header files in mind, is to simply take most of the header files used by a project, include them from another header file, precompile that header file, and @option{-include} the precompiled header. If the header files have guards against multiple inclusion, they are skipped because they've already been included (in the precompiled header). If you need to precompile the same header file for different languages, targets, or compiler options, you can instead make a @emph{directory} named like @file{all.h.gch}, and put each precompiled header in the directory, perhaps using @option{-o}. It doesn't matter what you call the files in the directory; every precompiled header in the directory is considered. The first precompiled header encountered in the directory that is valid for this compilation is used; they're searched in no particular order. There are many other possibilities, limited only by your imagination, good sense, and the constraints of your build system. A precompiled header file can be used only when these conditions apply: @itemize @item Only one precompiled header can be used in a particular compilation. @item A precompiled header can't be used once the first C token is seen. You can have preprocessor directives before a precompiled header; you cannot include a precompiled header from inside another header. @item The precompiled header file must be produced for the same language as the current compilation. You can't use a C precompiled header for a C++ compilation. @item The precompiled header file must have been produced by the same compiler binary as the current compilation is using. @item Any macros defined before the precompiled header is included must either be defined in the same way as when the precompiled header was generated, or must not affect the precompiled header, which usually means that they don't appear in the precompiled header at all. The @option{-D} option is one way to define a macro before a precompiled header is included; using a @code{#define} can also do it. There are also some options that define macros implicitly, like @option{-O} and @option{-Wdeprecated}; the same rule applies to macros defined this way. @item If debugging information is output when using the precompiled header, using @option{-g} or similar, the same kind of debugging information must have been output when building the precompiled header. However, a precompiled header built using @option{-g} can be used in a compilation when no debugging information is being output. @item The same @option{-m} options must generally be used when building and using the precompiled header. @xref{Submodel Options}, for any cases where this rule is relaxed. @item Each of the following options must be the same when building and using the precompiled header: @gccoptlist{-fexceptions} @item Some other command-line options starting with @option{-f}, @option{-p}, or @option{-O} must be defined in the same way as when the precompiled header was generated. At present, it's not clear which options are safe to change and which are not; the safest choice is to use exactly the same options when generating and using the precompiled header. The following are known to be safe: @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol -fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol -pedantic-errors} @end itemize For all of these except the last, the compiler automatically ignores the precompiled header if the conditions aren't met. If you find an option combination that doesn't work and doesn't cause the precompiled header to be ignored, please consider filing a bug report, see @ref{Bugs}. If you do use differing options when generating and using the precompiled header, the actual behavior is a mixture of the behavior for the options. For instance, if you use @option{-g} to generate the precompiled header but not when using it, you may or may not get debugging information for routines in the precompiled header.