[FFmpeg-devel] [PATCH] Improve handling of cmov usage enablement

Reimar Döffinger Reimar.Doeffinger
Sat Nov 1 14:05:15 CET 2008

On Sat, Nov 01, 2008 at 01:52:02PM +0100, Dominik 'Rathann' Mierzejewski wrote:
> The attached patch enables CMOV by default on x86_64 arch, because
> all x86_64 CPUs have it. It doesn't enable fast_cmov, because x86_64
> includes some NetBurst-architecture CPUs from Intel, which are known
> to have a slow implementation of CMOV.
> The second part of the patch disables fast_cmov for the "i686" cpu
> target, because that target might include NetBurst-arch CPUs.
> OK to apply?

Given the statements by Intel I saw, my opinion is that we should go
with "enable fast_cmov unless we are really sure it is slow" - unless it
is some really predictable condition (in which case cmov probably is a
bad idea for all CPUs) cmov is likely to be faster on all CPUs except
netburst, including future CPUs.
Or in other words: Netburst is the special case, and our configure
should treat it as such, and personally my opinion is: you bought a
crappy CPU when everybody could have told you it is stupid (and going by
my experience a lot of people have told and been ignored), now live with
it, not our problem unless it is no effort for us. Complain to Intel if

Reimar D?ffinger

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