Re: [gentoo-portage-dev] src_profile() request for comments

[Jason Stubbs]

On Wednesday 28 September 2005 23:42, Bastian Balthazar Bux wrote:
> 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 ?

       -fno-guess-branch-probability
           Do not guess branch probabilities using a randomized model.

           Sometimes GCC will opt to use a randomized model to guess branch
           probabilities, when none are available from either profiling feed-
           back (-fprofile-arcs) or __builtin_expect.  This means that differ-
           ent runs of the compiler on the same program may produce different
           object code.

           In a hard real-time system, people don't want different runs of the
           compiler to produce code that has different behavior; minimizing
           non-determinism is of paramount import.  This switch allows users
           to reduce non-determinism, possibly at the expense of inferior
           optimization.

           The default is -fguess-branch-probability at levels -O, -O2, -O3,
           -Os.

Any "test data" that could be used to automatically profile is essentially 
just a randomized model. So it would seem gcc has it inbuilt already.

--
Jason Stubbs
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