[FFmpeg-devel] [PATCH] some SIMD write-combining for h264

Alexander Strange astrange
Mon Jan 18 11:34:01 CET 2010

On Jan 17, 2010, at 8:27 PM, M?ns Rullg?rd wrote:

> Alexander Strange <astrange at ithinksw.com> writes:
>> On Sun, Jan 17, 2010 at 7:54 PM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
>>> Alexander Strange <astrange <at> ithinksw.com> writes:
>>>>>>> also what sets __MMX__ ? we have our own defines for that
>>>>>> It's a gcc builtin define, set based on ./configure --cpu=x adding
>>>>>> -march.  HAVE_MMX is for the build and not the host cpu family, and
>>>>>> this is inlined asm, so it can't use it.
>>>>> Huh?  Host... build???
>>>> Oh, that was supposed to be "target"...
>>>> Anyway, this is MMX being used like the cmov/clz inlines, so it depends on the
>>>> given --cpu and not on the build system's capabilities.
>>> Could you explain once more why this shouldn't be HAVE_MMX?
>>> If the user passes --disable-mmx to configure, he imo expects MMX to be disabled.
>>> Carl Eugen
>> HAVE_MMX isn't enough to enable it - './configure --cpu=i586' enables
>> HAVE_MMX, but i586 doesn't have it.
> Not anymore.

I think that was wrong. --cpu is the minimum required cpu, not the only expected cpu, but that turned off building dsputil mmx which is runtime-cpudetected. (even if runtime-cpudetection is disabled, actually)
Besides, './configure' also sets HAVE_MMX but targets generic x86-32 which might not have it.

>> Technically I'd say --disable-mmx should pass -mno-mmx to gcc, but
>> that seems like a complicated change to configure, so I'll check
>> HAVE_MMX to disable it as well.
> That's almost trivial to arrange.  Do we want that?

The other new architectures would have to be added as configure options (sse[234] are missing), but if you want then sure.

Applied the first patch with #if HAVE_MMX around the file and av_always_inline.
The second patch needs to be rewritten now since the decoder changed under it.

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