[MPlayer-dev-eng] Re: [SURVEY] change default CPU target when compiled with runtime CPU detection

[Rich Felker]

On Tue, Nov 15, 2005 at 02:09:33PM +0800, Zuxy wrote:
> 2005/11/15, Rich Felker <dalias at aerifal.cx>:
> > On Tue, Nov 15, 2005 at 05:57:32AM +0200, Jan Knutar wrote:
> > > On Monday 14 November 2005 18:21, Matthias Wieser wrote:
> > >
> > >
> > > Although, the Athlon is made for running unoptimized code and wont do too
> > > badly on  P4 optimized code :-)
> >
> > P4-optimized code is not "unoptimized", it's "anti-optimized". i.e.
> > stupid things which should be slow are done because they're the only
> > way to make it perform well on the P4. :)
> >
> 
> Well I'd say that's a rumor. It's true that P4s are more sensitive to
> instruction selection, and imply stricter rules for compilers to do
> that. However, it's still far from so called 'anti-optimized', since
> these rules have minimal negative impact on earlier CPUs, i.e. they
> usually don't care. Besides, instruction selection is only a small

False. Just look at bitshift optimizations for an example. foo<<3 may
be slower than ((foo+foo)+(foo+foo))+((foo+foo)+(foo+foo)) on a P4,
the latter is obviously stupid on any sane cpu!

Making P4 the default is absolutely not acceptable. P4 is shit.

Rich