The Tor Browser: build/docs/pgo.rst@97036ab72558

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

     1 .. _pgo:

     3 ===========================

     4 Profile Guided Optimization

     5 ===========================

     7 :abbr:`PGO (Profile Guided Optimization)` is the process of adding

     8 probes to a compiled binary, running said binary, then using the

     9 run-time information to *recompile* the binary to (hopefully) make it

    10 faster.

    12 How PGO Builds Work

    13 ===================

    15 The supported interface for invoking a PGO build is to evaluate the

    16 *build* target of client.mk with *MOZ_PGO* defined. e.g.::

    18     $ make -f client.mk MOZ_PGO=1

    20 This is equivalent to::

    22     $ make -f client.mk profiledbuild

    24 Which is roughly equivalent to:

    26 #. Perform a build with *MOZ_PROFILE_GENERATE=1* and *MOZ_PGO_INSTRUMENTED=1*

    27 #. Package with *MOZ_PGO_INSTRUMENTED=1*

    28 #. Performing a run of the instrumented binaries

    29 #. $ make maybe_clobber_profiledbuild

    30 #. Perform a build with *MOZ_PROFILE_USE=1*

    32 Differences between toolchains

    33 ==============================

    35 There are some implementation differences depending on the compiler

    36 toolchain being used.

    38 The *maybe_clobber_profiledbuild* step gets its name because of a

    39 difference. On Windows, this step merely moves some *.pgc* files around.

    40 Using GCC or Clang, it is equivalent to a *make clean*.

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