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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*.