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From: Ian Lance Taylor <iant@google.com>
To: Scott Meyers <NeverRead@aristeia.com>
Cc: gcc-help@gcc.gnu.org
Subject: Re: __builtin_expect vs. PGO
References: <jcrthc$3b8$1@dough.gmane.org>
Date: Wed, 21 Dec 2011 16:56:00 -0000
In-Reply-To: <jcrthc$3b8$1@dough.gmane.org> (Scott Meyers's message of "Tue,	20 Dec 2011 22:15:06 -0800")
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Scott Meyers <NeverRead@aristeia.com> writes:

> What has more weight during codegen in a compilation with
> -fprofile-use when the code uses __builtin_expect to favor one branch
> while the PGO data says the other branch is more likely?

I believe the probabilities will be combined in that case.  The
weighting of __builtin_expect is such that it will most likely be the
predicted case, unless the profiling data says that the unexpected path
is always taken.

Ian