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Date: Sun, 26 Oct 2003 06:18:01 -0500 (EST)
From: Jeff Roberson <jroberson@chesapeake.net>
To: Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?= <des@des.no>
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cc: Peter Wemm <peter@wemm.org>
Subject: Re: cvs commit: src/sys/i386/i386 pmap.c
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On Sun, 26 Oct 2003, Dag-Erling [iso-8859-1] Sm=F8rgrav wrote:

> Peter Wemm <peter@wemm.org> writes:
> > Massively deep pipelines help get the MHz up, and careful optimization =
can
> > stop it affecting frame rates.  But it blows chunks if you mispredict a
> > branch in typical gcc generated code.  Or take our libc syscall stubs..
> > every single one will be mispredicted because the usual case (no errors=
)
> > has an opposite direction branch to what intel's static branch predicti=
on
> > expects.
>
> Is there any way to teach (or trick) gcc to generate a branch which
> the p4 will predict correctly?

I doubt the effect would be measurable.  We could simply rearrange the
code.  I do not know why it is arranged the way it is now but you would
expect that there is some good reason.

>
> DES
> --
> Dag-Erling Sm=F8rgrav - des@des.no
>