diff options
Diffstat (limited to 'gcc/doc/invoke.texi')
| -rw-r--r-- | gcc/doc/invoke.texi | 59 |
1 files changed, 14 insertions, 45 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 6122f79..5114f70 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -5129,14 +5129,10 @@ 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. Optimization levels @option{-O} and above, in -particular, enable @emph{unit-at-a-time} mode, which allows the -compiler to consider information gained from later functions in -the file when compiling a function. Compiling multiple files at -once to a single output file in @emph{unit-at-a-time} mode allows -the compiler to use information gained from all of the files when -compiling each of them. +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. @@ -5342,7 +5338,7 @@ 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 if @option{-funit-at-a-time} is enabled. +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}. @item -fearly-inlining @opindex fearly-inlining @@ -6316,39 +6312,11 @@ Enabled at levels @option{-O2}, @option{-O3}. @item -funit-at-a-time @opindex funit-at-a-time -Parse the whole compilation unit before starting to produce code. -This allows some extra optimizations to take place but consumes -more memory (in general). There are some compatibility issues -with @emph{unit-at-a-time} mode: -@itemize @bullet -@item -enabling @emph{unit-at-a-time} mode may change the order -in which functions, variables, and top-level @code{asm} statements -are emitted, and will likely break code relying on some particular -ordering. The majority of such top-level @code{asm} statements, -though, can be replaced by @code{section} attributes. The -@option{fno-toplevel-reorder} option may be used to keep the ordering -used in the input file, at the cost of some optimizations. - -@item -@emph{unit-at-a-time} mode removes unreferenced static variables -and functions. This may result in undefined references -when an @code{asm} statement refers directly to variables or functions -that are otherwise unused. In that case either the variable/function -shall be listed as an operand of the @code{asm} statement operand or, -in the case of top-level @code{asm} statements the attribute @code{used} -shall be used on the declaration. - -@item -Static functions now can use non-standard passing conventions that -may break @code{asm} statements calling functions directly. Again, -attribute @code{used} will prevent this behavior. -@end itemize - -As a temporary workaround, @option{-fno-unit-at-a-time} can be used, -but this scheme may not be supported by future releases of GCC@. +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 at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. +Enabled by default. @item -fno-toplevel-reorder @opindex fno-toplevel-reorder @@ -6359,6 +6327,10 @@ will not be removed. This option is intended to support existing code which relies on a particular ordering. For new code, it is better to use attributes. +Enabled at level @option{-O0}. When disabled explicitly, it also imply +@option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some +targets. + @item -fweb @opindex fweb Constructs webs as commonly used for register allocation purposes and assign @@ -6944,12 +6916,10 @@ 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 backend. -This parameter is ignored when @option{-funit-at-a-time} is not used. The default value is 2700. @item large-function-growth Specifies maximal growth of large function caused by inlining in percents. -This parameter is ignored when @option{-funit-at-a-time} is not used. The default value is 100 which limits large function growth to 2.0 times the original size. @@ -6966,7 +6936,6 @@ 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. -This parameter is ignored when @option{-funit-at-a-time} is not used. The default value is 30 which limits unit growth to 1.3 times the original size. @@ -15616,7 +15585,7 @@ 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 -funit-at-a-time} +@gccoptlist{-fexceptions} @item Some other command-line options starting with @option{-f}, |