| .. _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*. |
