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SubjectRe: kernel + gcc 4.1 = several problems
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On Wed, 2007-01-03 at 12:44 +0000, Alan wrote:
> > > fixed. At that point an i686 kernel would contain i686 instructions and
> > > actually run on all i686 processors ending all the i586 pain for most
> > > users and distributions.
> > Could you explain why CMOV is pointless now? Are there any benchmarks
> > proving that?
>
> Take a look at the recent ffmpeg bits on the mplayer list for one example
> I have to hand - P4 cmov is pretty slow. The crypto folks find the same
> things.

cmov is effectively the same cost as a compare and jump, in both cases
the cpu needs to do a prediction, and on a mispredict, restart.

the reason cmov can make sense is because it's smaller code...

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