>From man gcc:

-fprofile-generate
    Enable options usually used for instrumenting application to produce
    profile useful for later recompilation with profile
    feedback based optimization.  You must use "-fprofile-generate" both
    when compiling and when linking your program.

    The following options are enabled: "-fprofile-arcs",
    "-fprofile-values", "-fvpt".

-fprofile-use
    Enable profile feedback directed optimizations, and optimizations
    generally profitable only with profile feedback available.

    The following options are enabled: "-fbranch-probabilities",
    "-fvpt", "-funroll-loops", "-fpeel-loops", "-ftracer".


Starting saying that this staff have never been tried by me, make sense
to add a specific optional function src_profile() to manage the eventual
profiling?

With this option the flow of an emerge should be something like this:

 --------------
|  pkg_setup   |...src.....
 --------------           .
       .                  .
      bin          --------------
       .          |  src_unpack  |
       .           --------------
       .                  .
       .           --------------
       .          | src_compile  |........................
       .           --------------           .            .
       .                  .                 .            .
       .                  .           --------------     .
       .                  .          |   src_test   |.....
       .                  .           --------------     .
       .                  .                 .            .
       .                  .                 .     ################
       .                  .                 .     # src_profile  #
       .                  .                 .     ################
       .           --------------           .            .
       .          | src_install  |........................
       .           --------------
       .                  .
 --------------           .
| pkg_preinst  |...........
 --------------
       .
 --------------
| pkg_postinst |
 --------------


with src_profile() responsible to do basically two things:
- run the builded app with some fake data
- rebuild the source using the gathered profile info.

The first step within some ebuilds could be done by src_test, the second
is basically a reduced src_compile.

any thoughts ?

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