Index: invoke.texi =================================================================== --- invoke.texi (revision 166652) +++ invoke.texi (working copy) @@ -399,7 +399,7 @@ Objective-C and Objective-C++ Dialects}. -funit-at-a-time -funroll-all-loops -funroll-loops @gol -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol --fwhole-program -fwhopr[=@var{n}] -fwpa -fuse-linker-plugin @gol +-fwhole-program -fwpa -fuse-linker-plugin @gol --param @var{name}=@var{value} -O -O0 -O1 -O2 -O3 -Os -Ofast} @@ -7455,6 +7455,22 @@ file. When the object files are linked bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit. +If you specify the optional @var{n} the link stage 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. See also option +@option{--param lto-partitions=@var{value}}). GCC by default split +program to fixed number of partitions. This parameter can be used +to increase the parallelism and also to reduce memory usage in the +later stage of link time optimization process. + +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 parallel. +The parent Makefile will need a @samp{+} prepended to the command recipe +for this to work. This will likely only work if @env{MAKE} is +GNU make. + To use the link-timer optimizer, @option{-flto} needs to be specified at compile time and during the final link. For example, @@ -7489,6 +7505,14 @@ The only important thing to keep in mind optimizations the @option{-flto} flag needs to be passed to both the compile and the link commands. +To make while program optimization effective, it is neccesary to make certain +level of whole program assumptions. 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 linker, the linker plugin (see +@option{-fuse-linker-plugin}) pass to the compiler information about used and +externally visible symbols. When linker plugin is not availble, +@option{-fwhole-program} should be used to get goo code quality. + Note that when a file is compiled with @option{-flto}, the generated object file will be larger than a regular object file because it will contain GIMPLE bytecodes and the usual final code. This means that @@ -7603,23 +7627,11 @@ Link time optimization does not play wel information. Combining @option{-flto} with @option{-g} is experimental. -If you specify the optional @var{n} the link stage 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. - -You can also specify @option{-fwhopr=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 parallel. -The parent Makefile will need a @samp{+} prepended to the command recipe -for this to work. This will likely only work if @env{MAKE} is -GNU make. - This option is disabled by default. @item -flto-partition=@var{alg} @opindex flto-partition -Specify partitioning algorithm used by @option{-fwhopr} mode. The value is +Specify partitioning algorithm used by link time optimizer. The value is either @code{1to1} to specify partitioning corresponding to source files or @code{balanced} to specify partitioning into, if possible, equally sized chunks. Specifying @code{none} as an algorithm disables partitioning @@ -7629,22 +7641,21 @@ The default value is @code{balanced}. @item -fwpa @opindex fwpa This is an internal option used by GCC when compiling with -@option{-fwhopr}. You should never need to use it. +@option{-flto} with partitioning enabled. You should never need to use it. -This option runs the link-time optimizer in the whole-program-analysis -(WPA) mode, which reads in summary information from all inputs and -performs a whole-program analysis based on summary information only. -It generates object files for subsequent runs of the link-time -optimizer where individual object files are optimized using both -summary information from the WPA mode and the actual function bodies. -It then drives the LTRANS phase. +This option runs the serial part of link-time optimizer performing the +inter-procedural propagation (WPA mode). Compiler reads in summary information +from all inputs and performs an analysis based on summary information only. It +generates object files for subsequent runs of the link-time optimizer where +individual object files are optimized using both summary information from the +WPA mode and the actual function bodies. It then drives the LTRANS phase. Disabled by default. @item -fltrans @opindex fltrans This is an internal option used by GCC when compiling with -@option{-fwhopr}. You should never need to use it. +@option{-flto} with partitioning enabled. You should never need to use it. This option runs the link-time optimizer in the local-transformation (LTRANS) mode, which reads in output from a previous run of the LTO in WPA mode. @@ -7655,7 +7666,7 @@ Disabled by default. @item -fltrans-output-list=@var{file} @opindex fltrans-output-list This is an internal option used by GCC when compiling with -@option{-fwhopr}. You should never need to use it. +@option{-lto}. You should never need to use it. This option specifies a file to which the names of LTRANS output files are written. This option is only meaningful in conjunction with @option{-fwpa}. @@ -7665,7 +7676,7 @@ Disabled by default. @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{-fwhopr}, @option{-flto}). Valid +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. @@ -7674,7 +7685,7 @@ given, a default balanced compression se 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{-fwhopr} or @option{-flto}). +files in LTO mode (via @option{-flto}). Disabled by default.