diff options
Diffstat (limited to 'gcc/doc/invoke.texi')
| -rw-r--r-- | gcc/doc/invoke.texi | 66 |
1 files changed, 46 insertions, 20 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 31d4f10..e0e59f6 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -365,9 +365,11 @@ Objective-C and Objective-C++ Dialects}. @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 +@gccoptlist{-faggressive-loop-optimizations @gol +-falign-functions[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @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 @@ -9240,19 +9242,36 @@ The @option{-fstrict-aliasing} option is enabled at levels @item -falign-functions @itemx -falign-functions=@var{n} +@itemx -falign-functions=@var{n}:@var{m} +@itemx -falign-functions=@var{n}:@var{m}:@var{n2} +@itemx -falign-functions=@var{n}:@var{m}:@var{n2}:@var{m2} @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. +@var{n}, skipping up to @var{m}-1 bytes. This ensures that at least +the first @var{m} bytes of the function can be fetched by the CPU +without crossing an @var{n}-byte alignment boundary. -@option{-fno-align-functions} and @option{-falign-functions=1} are -equivalent and mean that functions are not aligned. +If @var{m} is not specified, it defaults to @var{n}. + +Examples: @option{-falign-functions=32} aligns functions to the next +32-byte boundary, @option{-falign-functions=24} aligns to the next +32-byte boundary only if this can be done by skipping 23 bytes or less, +@option{-falign-functions=32:7} aligns to the next +32-byte boundary only if this can be done by skipping 6 bytes or less. + +The second pair of @var{n2}:@var{m2} values allows you to specify +a secondary alignment: @option{-falign-functions=64:7:32:3} aligns to +the next 64-byte boundary if this can be done by skipping 6 bytes or less, +otherwise aligns to the next 32-byte boundary if this can be done +by skipping 2 bytes or less. +If @var{m2} is not specified, it defaults to @var{n2}. Some assemblers only support this flag when @var{n} is a power of two; in that case, it is rounded up. +@option{-fno-align-functions} and @option{-falign-functions=1} are +equivalent and mean that functions are not aligned. + If @var{n} is not specified or is zero, use a machine-dependent default. The maximum allowed @var{n} option value is 65536. @@ -9266,12 +9285,13 @@ skip more bytes than the size of the function. @item -falign-labels @itemx -falign-labels=@var{n} +@itemx -falign-labels=@var{n}:@var{m} +@itemx -falign-labels=@var{n}:@var{m}:@var{n2} +@itemx -falign-labels=@var{n}:@var{m}:@var{n2}:@var{m2} @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. +Align all branch targets to a power-of-two boundary. +Parameters of this option are analogous to the @option{-falign-functions} option. @option{-fno-align-labels} and @option{-falign-labels=1} are equivalent and mean that labels are not aligned. @@ -9286,12 +9306,15 @@ Enabled at levels @option{-O2}, @option{-O3}. @item -falign-loops @itemx -falign-loops=@var{n} +@itemx -falign-loops=@var{n}:@var{m} +@itemx -falign-loops=@var{n}:@var{m}:@var{n2} +@itemx -falign-loops=@var{n}:@var{m}:@var{n2}:@var{m2} @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. +Align loops to a power-of-two boundary. If the loops are executed +many times, this makes up for any execution of the dummy padding +instructions. +Parameters of this option are analogous to the @option{-falign-functions} option. @option{-fno-align-loops} and @option{-falign-loops=1} are equivalent and mean that loops are not aligned. The maximum allowed @var{n} option value is 65536. @@ -9302,12 +9325,15 @@ Enabled at levels @option{-O2}, @option{-O3}. @item -falign-jumps @itemx -falign-jumps=@var{n} +@itemx -falign-jumps=@var{n}:@var{m} +@itemx -falign-jumps=@var{n}:@var{m}:@var{n2} +@itemx -falign-jumps=@var{n}:@var{m}:@var{n2}:@var{m2} @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. +where the targets can only be reached by jumping. In this case, +no dummy operations need be executed. +Parameters of this option are analogous to the @option{-falign-functions} option. @option{-fno-align-jumps} and @option{-falign-jumps=1} are equivalent and mean that loops are not aligned. |