[FFmpeg-devel] [PATCH] Fix configure to disable MMX for Pentium Pro

[Reimar Döffinger]

On Thu, Aug 26, 2010 at 05:13:37PM -0400, Alexander Strange wrote:
> 
> On Aug 26, 2010, at 5:07 PM, Reimar D?ffinger wrote:
> 
> > On Thu, Aug 26, 2010 at 10:38:53PM +0200, Michael Niedermayer wrote:
> >> On Thu, Aug 26, 2010 at 10:22:57PM +0200, Reimar D?ffinger wrote:
> >>> On Thu, Aug 26, 2010 at 09:53:44PM +0200, Michael Niedermayer wrote:
> >>>> On Thu, Aug 26, 2010 at 08:52:24PM +0200, Reimar D?ffinger wrote:
> >>>>> On Thu, Aug 26, 2010 at 01:37:06PM -0400, Alex Converse wrote:
> >>>>>>> We should revert r24946:  Disable MMX for i686 and pentiumpro
> >>>>>> 
> >>>>>> If something should be reverted it is dropping runtime detection for MMX
> >>>>> 
> >>>>> At the very least I think it would be nice to be able to have SSE,
> >>>>> does someone know out of their head why we have
> >>>>> sse_deps="mmx"
> >>>>> ? I always thought that at least in principle you could have and
> >>>>> use SSE without MMX and that also would avoid the emms issue...
> >>>> 
> >>>> there is no cpu that supports SSE without MMX and if the features no
> >>>> longer match the cpu then alot of assumtations of what is faster and
> >>>> what cpus code will run on become wrong
> >>>> its btw silly to disable mmx on a mmx cpu unless its for debuging or other
> >>>> uncommon things
> >>> 
> >>> How about "emms causes all kinds of issues, I'd like a build without
> >>> those issues but still ok speed?"
> >> 
> >> wrong assumtion thus following theorems are flawed
> > 
> > How about, "while nearly impossible, I can imagine MMX being deprecated
> > while SSE being kept similarly to 3dnow, as well as I can imagine
> > global optimization might actually cause real issues with our too-late
> > emms and thus I'd like to be able to do some tests of SSE-without-MMX
> > just in case if I don't miss an obvious problem".
> 
> I think we'll have to deal with such global optimizations by turning them off.
> 
> Also note that several sse* functions mix MMX freely (like the xvid idct), and I don't think they have mmx listed as an explicit dependency.

Yes, assuming I actually find the time, I would like to look into these and possibly add
an explicit HAVE_MMX/cpu flags check, unless others say such changes would never ever be
accepted :-)