[FFmpeg-devel] [PATCH] Add check for Athlon64 and similar AMD processors with slow SSE2.

[Måns Rullgård]

Justin Ruggles <justin.ruggles at gmail.com> writes:

> ---
> This was ported from x264 so we need permission to relicense from
> Loren, Jason, or whoever added this particular check in x264.

I doubt there's much copyright on checking a single bit, but it's
always nice to ask first.

> Once this is added, I can go through libavcodec/x86 and test various
> SSE2 functions on my Athlon64 to check if they're faster with other
> versions.  We also have a couple functions now that are hackishly
> handled by disabling SSE2 for all AMD processors by checking the
> 3DNow flag.  Those are the ones I'll test first.
>
>  libavutil/x86/cpu.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
>
> diff --git a/libavutil/x86/cpu.c b/libavutil/x86/cpu.c
> index 4b6cb0d..7e847c1 100644
> --- a/libavutil/x86/cpu.c
> +++ b/libavutil/x86/cpu.c
> @@ -109,6 +109,13 @@ int ff_get_cpu_flags_x86(void)
>              rval |= AV_CPU_FLAG_MMX;
>          if (ext_caps & (1<<22))
>              rval |= AV_CPU_FLAG_MMX2;
> +
> +        /* Allow for selectively disabling SSE2 functions on AMD processors
> +           with SSE2 support but not SSE4a.  This includes Athlon64,
> +           some Opteron, and some Sempron processors.  MMX, SSE, or 3DNow! are
> +           faster than SSE2 often enough to utilize this special-case flag. */
> +        if (rval & AV_CPU_FLAG_SSE2 && !(ecx & 0x00000040))
> +            rval |= AV_CPU_FLAG_SSE2SLOW;
>      }
>  
>      if (!strncmp(vendor.c, "GenuineIntel", 12) &&

Why does this code only affect AMD processors?  I guess it has
something to do with those magic bit checks before it...

-- 
M?ns Rullg?rd
mans at mansr.com