Re: [FFmpeg-devel] [PATCH v2 3/3] avfilter/vf_colordetect: add x86 SIMD implementation

[James Almer <jamrial@gmail.com>]

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On 7/16/2025 6:49 PM, Niklas Haas wrote:
> On Wed, 16 Jul 2025 17:25:12 -0300 James Almer <jamrial@gmail.com> wrote:
>> On 7/16/2025 1:24 PM, Niklas Haas wrote:
>>> +cglobal detect_alpha%1_%3, 6, 7, 6, color, color_stride, alpha, alpha_stride, width, height, x
>>> +    pxor m0, m0
>>> +    add colorq, widthq
>>> +    add alphaq, widthq
>>> +    neg widthq
>>> +%ifidn %3, limited
>>> +%if ARCH_X86_64
>>> +    movq xm3, r6mp ; p
>>> +    movq xm4, r7mp ; q
>>> +    movq xm5, r8mp ; k
>>
>> They are int arguments, so no point using movq.
> 
> This is to avoid an error:
> 
> src/libavfilter/x86/vf_colordetect.asm:145: error: invalid combination of opcode and operands
> src/libavfilter/x86/vf_colordetect.asm:75: ... from macro `detect_alpha_fn' defined here
> src//libavutil/x86/x86inc.asm:1518: ... from macro `movd' defined here
> src//libavutil/x86/x86inc.asm:1501: ... from macro `RUN_AVX_INSTR' defined here

That's probably because of the mp suffix. If you use m, it works (as in, 
"movd xm3, r6m").

In any case, you can just combine these into a single vpbroadcast%2 that 
reads from memory:

%ifidn %3, limited
     vpbroadcast%2 m3, r6m
     vpbroadcast%2 m4, r7m
     vpbroadcast%2 m5, r8m
%endif

> 
>>
>>> +%else
>>> +    movd xm3, r6mp ; p
>>> +    movd xm4, r7mp ; q
>>> +    movd xm5, r8mp ; k
>>> +%endif
>>> +    vpbroadcast%2 m3, xm3
>>> +    vpbroadcast%2 m4, xm4
>>> +    vpbroadcast%2 m5, xm5
>>> +%endif
>>> +.lineloop:
>>> +    mov xq, widthq
>>> +    .loop:
>>> +    %ifidn %3, full
>>> +        movu m1, [colorq + xq]
>>> +        movu m2, [alphaq + xq]
>>> +        pmaxu%1 m1, m2
>>> +    %else
>>> +        pmovzx%1%2 m1, [colorq + xq]
>>> +        pmovzx%1%2 m2, [alphaq + xq]
>>> +        pmull%2 m1, m3
>>> +        pmull%2 m2, m4
>>
>> pmulld is painfully slow, so try to instead use pmaddwd. It should be
>> doable because the input are words.
> 
> Will give it a try tomorrow.
> 
>>
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