Re: [PR] avcodec/x86/pngdsp.asm: replace MMX with SSE2 (PR #24157)

On Sat, 15 Aug 2026, 03:03 zuxy via ffmpeg-devel, <[email protected]>
wrote:

> PR #24157 opened by zuxy
> URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24157
> Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24157.patch
>
> No more use of mm registers and emms. Performance identical except when
> bpp=8 (very rare in practice), for which the SSE2 version is ~2x faster.
>
> Signed-off-by: Zuxy Meng <[email protected]>
>
>
>
>
> >From 5be8d9bab560a2d7a4d40904ca10c1dfec3b8195 Mon Sep 17 00:00:00 2001
> From: Zuxy Meng <[email protected]>
> Date: Wed, 12 Aug 2026 00:18:34 -0700
> Subject: [PATCH] avcodec/x86/pngdsp.asm: replace MMX with SSE2
>
> No more use of mm registers and emms. Performance identical except when
> bpp=8 (very rare in practice), for which the SSE2 version is ~2x faster.
>
> Signed-off-by: Zuxy Meng <[email protected]>
> ---
>  libavcodec/x86/pngdsp.asm | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/libavcodec/x86/pngdsp.asm b/libavcodec/x86/pngdsp.asm
> index e0a3b602de..59f16569a7 100644
> --- a/libavcodec/x86/pngdsp.asm
> +++ b/libavcodec/x86/pngdsp.asm
> @@ -76,8 +76,8 @@ cglobal add_bytes_l2, 4, 6, 2, dst, src1, src2, wa, w, i
>      jl .loop_s
>      RET
>
> -INIT_MMX ssse3
> -cglobal png_add_paeth_prediction, 5, 7, 0, dst, src, top, w, bpp, end,
> cntr
> +INIT_XMM ssse3
> +cglobal png_add_paeth_prediction, 5, 7, 8, dst, src, top, w, bpp, end,
> cntr
>  %if ARCH_X86_64
>      movsxd            bppq, bppd
>      movsxd              wq, wd
> @@ -89,8 +89,10 @@ cglobal png_add_paeth_prediction, 5, 7, 0, dst, src,
> top, w, bpp, end, cntr
>      pxor                m7, m7
>
>      PUSH              dstq
> -    lea              cntrq, [bppq-1]
> -    shr              cntrq, 2 + mmsize/16
> +    xor              cntrd, cntrd
> +    cmp               bppd, 6
> +    jne .bpp_loop
> +    inc              cntrd
>  .bpp_loop:
>      lea               dstq, [dstq+cntrq*(mmsize/2)]
>      movh                m0, [dstq]
> @@ -138,5 +140,4 @@ cglobal png_add_paeth_prediction, 5, 7, 0, dst, src,
> top, w, bpp, end, cntr
>      dec              cntrq
>      jge .bpp_loop
>      POP               dstq
> -    emms
>      RET
> --
> 2.52.0
>

Lgtm

>
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