[Bug gcov/profile/24487] [3.4/4.0/4.1 Regression] Basic block frequencies inaccurate

["hubicka at ucw dot cz" <gcc-bugzilla@gcc.gnu.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