diff options
Diffstat (limited to 'gcc/doc/invoke.texi')
| -rw-r--r-- | gcc/doc/invoke.texi | 67 |
1 files changed, 51 insertions, 16 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 67155ee..020442a 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -593,7 +593,7 @@ Objective-C and Objective-C++ Dialects}. -finline-functions -finline-functions-called-once -finline-limit=@var{n} -finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone -fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const --fipa-reference -fipa-reference-addressable +-fipa-reference -fipa-reference-addressable -fipa-reorder-for-locality -fipa-stack-alignment -fipa-icf -fira-algorithm=@var{algorithm} -flate-combine-instructions -flifetime-dse -flive-patching=@var{level} -fira-region=@var{region} -fira-hoist-pressure @@ -2199,6 +2199,7 @@ those that have already been displayed. If @option{--help} is also specified anywhere on the command line then this takes precedence over any @option{--help=} option. +@opindex Q 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 @@ -12746,6 +12747,7 @@ complexity than at @option{-O}. -fipa-pure-const -fipa-reference -fipa-reference-addressable +-fivopts -fmerge-constants -fmove-loop-invariants -fmove-loop-stores @@ -12854,6 +12856,13 @@ by @option{-O2} and also turns on the following optimization flags: Reduce compilation time and make debugging produce the expected results. This is the default. +At @option{-O0}, GCC completely disables most optimization passes; +they are not run even if you explicitly enable them on the command +line, or are listed by @option{-Q --help=optimizers} as being enabled by +default. Many optimizations performed by GCC depend on code analysis +or canonicalization passes that are enabled by @option{-O}, and it would +not be useful to run individual optimization passes in isolation. + @opindex Os @item -Os Optimize for size. @option{-Os} enables all @option{-O2} optimizations @@ -13871,6 +13880,21 @@ Enabled by default at @option{-O1} and higher. Discover read-only, write-only and non-addressable static variables. Enabled by default at @option{-O1} and higher. +@opindex fipa-reorder-for-locality +@item -fipa-reorder-for-locality +Group call chains close together in the binary layout to improve code +locality and minimize jump distances between frequently called functions. +Unlike @option{-freorder-functions} this pass considers the call +chains between functions and groups them together, rather than grouping all +hot/normal/cold/never-executed functions into separate sections. +Unlike @option{-fprofile-reorder-functions} it aims to improve code locality +throughout the runtime of the program rather than focusing on program startup. +This option is incompatible with an explicit +@option{-flto-partition=} option since it enforces a custom partitioning +scheme. +If using this option it is recommended to also use profile feedback, but this +option is not enabled by default otherwise. + @opindex fipa-stack-alignment @item -fipa-stack-alignment Reduce stack alignment on call sites if possible. @@ -14291,6 +14315,7 @@ Enabled by default at @option{-O1} and higher. @item -fivopts Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees. +Enabled by default at @option{-O1} and higher. @opindex ftree-parallelize-loops @item -ftree-parallelize-loops=n @@ -14606,11 +14631,13 @@ Enabled for x86 at levels @option{-O2}, @option{-O3}, @option{-Os}. @opindex freorder-functions @item -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. +improve code locality. Unlike @option{-fipa-reorder-for-locality} this option +prioritises grouping all functions within a category +(hot/normal/cold/never-executed) together. +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. This option isn't effective unless you either provide profile feedback (see @option{-fprofile-arcs} for details) or manually annotate functions with @@ -14622,12 +14649,14 @@ Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -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. +optimizations based on the type of expressions. In particular, accessing +an object of one type via an expression of a different type is not allowed, +unless the types are @dfn{compatible types}, differ only in signedness or +qualifiers, or the expression has a character type. Accessing scalar +objects via a corresponding vector type is also allowed. + +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 @@ -15635,7 +15664,8 @@ Enabled by @option{-fprofile-generate}, @option{-fprofile-use}, and @item -fprofile-reorder-functions Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions -in ascending order. +in ascending order, aiming to optimize program startup through more +efficient loading of text segments. Enabled with @option{-fprofile-use}. @@ -21284,8 +21314,13 @@ Toggle @option{-fvar-tracking-assignments}, in the same way that @opindex Q @item -Q -Makes the compiler print out each function name as it is compiled, and -print some statistics about each pass when it finishes. +When used on the command line prior to @option{--help=}, @option{-Q} +acts as a modifier to the help output. @xref{Overall Options}, +for details about @option{--help=}. + +Otherwise, this option makes the compiler print out each function name +as it is compiled, and print some statistics about each pass when it +finishes. @opindex ftime-report @item -ftime-report @@ -34872,7 +34907,7 @@ Intel Lakemont MCU, based on Intel Pentium CPU. Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. @item pentiumpro -Intel Pentium Pro CPU@. +Intel Pentium Pro CPU with no MMX support. @item i686 When used with @option{-march}, the Pentium Pro |