[FFmpeg-devel] [PATCH v7] libavfilter/x86/vf_convolution: add sobel filter optimization and unit test with intel AVX512 VNNI

[James Almer]

On 11/14/2022 10:30 AM, Wang, Bin wrote:
>> By using xmm# you're not taking into account any x86inc SWAPing, so this is
>> using xmm0 and xmm1 where the single scalar float input arguments reside (at
>> least on unix64), instead of xm0 and xm1 (xmm16 and xmm17) where the
>> broadcasted scalars were stored.
>> This, again, only worked by chance on unix64 because you're using scalar fmadd,
>> and shouldn't work at all on win64.
>>
>> Also, all these as is are being encoded as VEX, not EVEX, but it should be fine
>> leaving them untouched instead of using xm#, since they will be shorter (five
>> bytes instead of six for some) by using the lower, non callee-saved regs.
> 
> Thanks for the help. I'm not familiar with WIN64 asm. So what I need to do is change the WIN64 swap from:
> SWAP xmm0, xmm2
> SWAP xmm1, xmm3
> To:
> VBROADCASTSS m0, xmm2
> VBROADCASTSS m1, xmm3
> 
> Is that correct?

Yes, that will ultimately broadcast the two scalars in xmm2 and xmm3 to 
zmm16 and zmm17.
After that what you need to do is either change the fmaddss instruction 
to use xm0 and xm1 macros instead of xmm0 and xmm1 (so xmm16 and xmm17 
with EVEX encoding is used), or much like the broadcast above use xmm2 
and xmm3 explicitly on win64, so it remains VEX encoded.