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Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/invoke.texi | 109 |
1 files changed, 59 insertions, 50 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 614fdd5..cef6fac 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -6759,56 +6759,65 @@ optimization. Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. @item -fira-algorithm=@var{algorithm} -Use specified coloring algorithm for the integrated register -allocator. The @var{algorithm} argument should be @code{priority} or -@code{CB}. The first algorithm specifies Chow's priority coloring, -the second one specifies Chaitin-Briggs coloring. The second -algorithm can be unimplemented for some architectures. If it is -implemented, it is the default because Chaitin-Briggs coloring as a -rule generates a better code. +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 @code{all}, @code{mixed}, or -@code{one}. The first value means using all loops as register -allocation regions, the second value which is enabled by default when -compiling with optimization for speed (@option{-O}, @option{-O2}, -@dots{}) means using all loops except for loops with small register -pressure as the regions, and third one which is enabled by default for -@option{-Os} or @option{-O0} means using all function as a single -region. The first value can give best result for machines with small -size and irregular register set, the third one results in faster and -generates decent code and the smallest size code, and the second value -usually give the best results in most cases and for most -architectures. +@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-loop-pressure @opindex fira-loop-pressure -Use IRA to evaluate register pressure in loops for decision to move -loop invariants. Usage of this option usually results in generation -of faster and smaller code on machines with big register files (>= 32 -registers) but it can slow compiler down. +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 -Switch off sharing stack slots used for saving call used hard -registers living through a call. Each hard register will get a -separate stack slot and as a result function stack frame will be -bigger. +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 -Switch off sharing stack slots allocated for pseudo-registers. Each -pseudo-register that did not get a hard register will get a separate -stack slot and as a result function stack frame will be bigger. +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 -Set up how verbose dump file for the integrated register allocator -will be. Default value is 5. If the value is greater or equal to 10, -the dump file will be stderr as if the value were @var{n} minus 10. +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 -fdelayed-branch @opindex fdelayed-branch @@ -9103,28 +9112,28 @@ function will not be done and optimizations depending on it will be disabled. The default maximum SCC size is 10000. @item ira-max-loops-num -IRA uses a regional register allocation by default. If a function -contains loops more than number given by the parameter, only at most -given number of the most frequently executed loops will form regions -for the regional register allocation. The default value of the +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 of compression conflict -table, the table can be still big for huge functions. If the conflict -table for a function could be more than size in MB given by the -parameter, the conflict table is not built and faster, simpler, and -lower quality register allocation algorithm will be used. The -algorithm do not use pseudo-register conflicts. The default value of -the parameter is 2000. +@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 decision to move loop invariants (see @option{-O3}). The number -of available registers reserved for some other purposes is described -by this parameter. The default value of the parameter is 2 which is -minimal number of registers needed for execution of typical -instruction. This value is the best found from numerous experiments. +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 |