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Date: Tue, 23 Apr 2002 02:39:00 -0000
From: Jan Hubicka <jh@suse.cz>
To: Michel LESPINASSE <walken@zoy.org>
Cc: Richard Henderson <rth@redhat.com>, gcc list <gcc@gcc.gnu.org>
Subject: Re: GCC performance regression - its memset !
Message-ID: <20020423092540.GC27274@atrey.karlin.mff.cuni.cz>
References: <20020421005718.GA16378@zoy.org> <20020422213222.GA21429@zoy.org> <20020422165953.A32536@redhat.com> <20020423001045.GA26276@zoy.org>
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> On Mon, Apr 22, 2002 at 04:59:53PM -0700, Richard Henderson wrote:
> > See whether or not disabling glibc's inline expansion of 
> > memset affects 2.95 vs 3.x with -D__NO_STRING_INLINES.
> 
> I can get gcc 2.95 to be as slow as 3.1 snapshot by using both
> -fno-builtin and -D__NO_STRING_INLINES
> 
> but, I cant get gcc 3.1 to do the inlining for me
> 
> If I dont use -fno-builtin -D__NO_STRING_INLINES, and just compile with -O3,
> gcc 2.95 generates this:
> 
>         movl $table+2,%edi
>         cld
>         movl $31,%ecx
>         rep
>         stosl
>         stosw
> 
> while 3.1 snapshot generates this:
> 
>         movl    $table+2, (%esp)
>         movl    $0, 4(%esp)
>         movl    $126, 8(%esp)
>         call    memset
I guess the inlining threshold is too low or the default memset implementation
too lame.
I was tunning it for Athlon, so the mileage may warry from CPU to CPU.
I will investigate the misscompilation first and check this second.

Honza
> 
> Hope this helps,
> 
> -- 
> Michel "Walken" LESPINASSE
> Is this the best that god can do ? Then I'm not impressed.