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[Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block frequencies inaccurate
- From: "hubicka at ucw dot cz" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 28 Oct 2005 21:29:19 -0000
- Subject: [Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block frequencies inaccurate
- References: <bug-24487-327@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #4 from hubicka at ucw dot cz 2005-10-28 21:29 -------
Subject: Re: [Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block
frequencies inaccurate
>
>
> ------- Comment #3 from dje at gcc dot gnu dot org 2005-10-28 17:30 -------
> The misprediction causes (or at least contributes to) compute_alignments in
> final.c not aligning the critical loop in longest_match. The recent changes to
> bb-reorder.c moved the start of the loop from an ideal alignment to the worst
> alignment, causing a 8-10% performance drop due to instruction fetch problems.
> Without the explicit alignment directives omitted because of misprediction, the
> alignment of the loop is random.
I see, Athlon is less sensitive to alignment that might explain it. I
will try to fix my SPEC testing setup on PPC after SVN revamp and
benchmark it there too...
Honza
>
>
> --
>
> dje at gcc dot gnu dot org changed:
>
> What |Removed |Added
> ----------------------------------------------------------------------------
> CC| |dberlin at gcc dot gnu dot
> | |org
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24487
>
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24487