[MPlayer-users] Fresh svn mplayer crashes on many ac3 streams

[Reimar Döffinger]

On Sun, May 29, 2011 at 11:10:34AM +0200, Reimar Döffinger wrote:
> On Sun, May 29, 2011 at 01:01:17AM +0400, Vladimir Mosgalin wrote:
> > Anyhow it's a bit unfair to blame it on ".0" here, I think, since this
> > issue is related to avx as well and 4.6.0 was first stable release to
> > include avx support. It's, like, not gccs fault that avx support
> > appeared in .0 version and not some other..
> 
> In the about 10 years since I've been with MPlayer I don't think
> I've ever seen a .0 gcc version that didn't miscompile some
> part of it.
> 
> > I can turn off avx or ftree-vectorize, it's np to me - though I expected
> > some serious speedups from gcc 4.6.0 and avx support, like shown in some
> > phoronix benchmarks, for example
> > http://www.phoronix.com/data/img/results/intel_avx_gcc/6.png
> > http://www.phoronix.com/data/img/results/intel_avx_gcc/7.png
> 
> If I was mean I'd ask if they actually checked the results.
> It's really easy to be fast when you generate incorrect code.
> Though the real point is that that was a pure-C program for
> compute-intensive stuff with probably a lot of embarrasingly
> parallel code.
> Which is to say, it probably has no relevance to MPlayer speed.
> Also if you care so much for speed you should probably rather
> compile with Intel's ICC compiler, for personal use
> (or something like that) it is free of cost IIRC.

You also forgot to mention that a lot (if not most) tests
lost performance when enabling the AVX-math option that
gave a speed boost in that case.
Past experience tells that for most, and all relevant,
formats (some unusual formats are simple but still not
asm-optimized, those might gain) a reduction in performance
is exactly what you'll see with MPlayer, too.