Gentoo Archives: gentoo-portage-dev

From: Jason Stubbs <jstubbs@g.o>
To: gentoo-portage-dev@l.g.o
Subject: Re: [gentoo-portage-dev] src_profile() request for comments
Date: Wed, 28 Sep 2005 15:11:16
In Reply to: [gentoo-portage-dev] src_profile() request for comments by Bastian Balthazar Bux
1 On Wednesday 28 September 2005 23:42, Bastian Balthazar Bux wrote:
2 > with src_profile() responsible to do basically two things:
3 > - run the builded app with some fake data
4 > - rebuild the source using the gathered profile info.
5 >
6 > The first step within some ebuilds could be done by src_test, the second
7 > is basically a reduced src_compile.
8 >
9 > any thoughts ?
11 -fno-guess-branch-probability
12 Do not guess branch probabilities using a randomized model.
14 Sometimes GCC will opt to use a randomized model to guess branch
15 probabilities, when none are available from either profiling feed-
16 back (-fprofile-arcs) or __builtin_expect. This means that differ-
17 ent runs of the compiler on the same program may produce different
18 object code.
20 In a hard real-time system, people don't want different runs of the
21 compiler to produce code that has different behavior; minimizing
22 non-determinism is of paramount import. This switch allows users
23 to reduce non-determinism, possibly at the expense of inferior
24 optimization.
26 The default is -fguess-branch-probability at levels -O, -O2, -O3,
27 -Os.
29 Any "test data" that could be used to automatically profile is essentially
30 just a randomized model. So it would seem gcc has it inbuilt already.
32 --
33 Jason Stubbs
34 --
35 gentoo-portage-dev@g.o mailing list


Subject Author
Re: [gentoo-portage-dev] src_profile() request for comments Paul de Vrieze <pauldv@g.o>