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.
The supported interface for invoking a PGO build is to add
MOZ_PGO=1 to configure flags and then build. e.g. in your mozconfig:
$ ./mach build
This is roughly equivalent to:
#. Perform a build with *MOZ_PROFILE_GENERATE=1* #. Performing a run of the instrumented binaries #. $ make maybe_clobber_profiledbuild #. Perform a build with *MOZ_PROFILE_USE=1*
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.