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

["Wang, Bin" <bin.wang-at-intel.com@ffmpeg.org>]

> >> 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.
> >
> > So, to fix the issue, does this 2 changes looks good for you?
> > First change the WIN64 swap from:
> > SWAP xmm0, xmm2
> > SWAP xmm1, xmm3
> > To:
> > VBROADCASTSS m0, xmm2
> > VBROADCASTSS m1, xmm3
> >
> > Second change the fmaddss from:
> > fmaddss   xmm4, xmm4, xmm0, xmm1
> > To:
> > fmaddss   xmm4, xmm4, xm0, xm1
> 
> Yes.

Appreciate for your help, I commit new patch here:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20221114143551.9740-1-bin.wang@intel.com/

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