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diff --git a/build/docs/pgo.rst b/build/docs/pgo.rst new file mode 100644 index 000000000..51d03c625 --- /dev/null +++ b/build/docs/pgo.rst @@ -0,0 +1,40 @@ +.. _pgo: + +=========================== +Profile Guided Optimization +=========================== + +:abbr:`PGO (Profile Guided Optimization)` is the process of adding +probes to a compiled binary, running said binary, then using the +run-time information to *recompile* the binary to (hopefully) make it +faster. + +How PGO Builds Work +=================== + +The supported interface for invoking a PGO build is to evaluate the +*build* target of client.mk with *MOZ_PGO* defined. e.g.:: + + $ make -f client.mk MOZ_PGO=1 + +This is equivalent to:: + + $ make -f client.mk profiledbuild + +Which is roughly equivalent to: + +#. Perform a build with *MOZ_PROFILE_GENERATE=1* and *MOZ_PGO_INSTRUMENTED=1* +#. Package with *MOZ_PGO_INSTRUMENTED=1* +#. Performing a run of the instrumented binaries +#. $ make maybe_clobber_profiledbuild +#. Perform a build with *MOZ_PROFILE_USE=1* + +Differences between toolchains +============================== + +There are some implementation differences depending on the compiler +toolchain being used. + +The *maybe_clobber_profiledbuild* step gets its name because of a +difference. On Windows, this step merely moves some *.pgc* files around. +Using GCC or Clang, it is equivalent to a *make clean*. |