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

[Alexander Strange]

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.

Hmm, I think PTLSim actually supports SSE and not MMX, but I don't remember the details at all.