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 .. _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*.