Re: [FFmpeg-devel] [PATCH 1/2] aarch64: me_cmp: Avoid redundant loads in ff_pix_abs16_y2_neon

[Hubert Mazur <hum@semihalf.com>]

LGTM, thanks!

On Wed, Sep 28, 2022 at 11:13 AM Martin Storsjö <martin@martin.st> wrote:

> This avoids one redundant load per row; pix3 from the previous
> iteration can be used as pix2 in the next one.
>
> Before:       Cortex A53    A72    A73
> pix_abs_0_2_neon:  138.0   59.7   48.0
> After:
> pix_abs_0_2_neon:  109.7   50.2   39.5
>
> Signed-off-by: Martin Storsjö <martin@martin.st>
> ---
>  libavcodec/aarch64/me_cmp_neon.S | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)
>
> diff --git a/libavcodec/aarch64/me_cmp_neon.S
> b/libavcodec/aarch64/me_cmp_neon.S
> index 11af4849f9..832a7cb22d 100644
> --- a/libavcodec/aarch64/me_cmp_neon.S
> +++ b/libavcodec/aarch64/me_cmp_neon.S
> @@ -326,9 +326,9 @@ function ff_pix_abs16_y2_neon, export=1
>          // w4           int h
>
>          // initialize buffers
> +        ld1             {v1.16b}, [x2], x3              // Load pix2
>          movi            v29.8h, #0                      // clear the
> accumulator
>          movi            v28.8h, #0                      // clear the
> accumulator
> -        add             x5, x2, x3                      // pix2 + stride
>          cmp             w4, #4
>          b.lt            2f
>
> @@ -339,29 +339,25 @@ function ff_pix_abs16_y2_neon, export=1
>          // avg2(a, b) = (((a) + (b) + 1) >> 1)
>          // abs(x) = (x < 0 ? (-x) : (x))
>
> -        ld1             {v1.16b}, [x2], x3              // Load pix2 for
> first iteration
> -        ld1             {v2.16b}, [x5], x3              // Load pix3 for
> first iteration
> +        ld1             {v2.16b}, [x2], x3              // Load pix3 for
> first iteration
>          ld1             {v0.16b}, [x1], x3              // Load pix1 for
> first iteration
>          urhadd          v30.16b, v1.16b, v2.16b         // Rounding
> halving add, first iteration
> -        ld1             {v4.16b}, [x2], x3              // Load pix2 for
> second iteration
> -        ld1             {v5.16b}, [x5], x3              // Load pix3 for
> second iteartion
> +        ld1             {v5.16b}, [x2], x3              // Load pix3 for
> second iteartion
>          uabal           v29.8h, v0.8b, v30.8b           // Absolute
> difference of lower half, first iteration
>          uabal2          v28.8h, v0.16b, v30.16b         // Absolute
> difference of upper half, first iteration
>          ld1             {v3.16b}, [x1], x3              // Load pix1 for
> second iteration
> -        urhadd          v27.16b, v4.16b, v5.16b         // Rounding
> halving add, second iteration
> -        ld1             {v7.16b}, [x2], x3              // Load pix2 for
> third iteration
> -        ld1             {v20.16b}, [x5], x3             // Load pix3 for
> third iteration
> +        urhadd          v27.16b, v2.16b, v5.16b         // Rounding
> halving add, second iteration
> +        ld1             {v20.16b}, [x2], x3             // Load pix3 for
> third iteration
>          uabal           v29.8h, v3.8b, v27.8b           // Absolute
> difference of lower half for second iteration
>          uabal2          v28.8h, v3.16b, v27.16b         // Absolute
> difference of upper half for second iteration
>          ld1             {v6.16b}, [x1], x3              // Load pix1 for
> third iteration
> -        urhadd          v26.16b, v7.16b, v20.16b        // Rounding
> halving add, third iteration
> -        ld1             {v22.16b}, [x2], x3             // Load pix2 for
> fourth iteration
> -        ld1             {v23.16b}, [x5], x3             // Load pix3 for
> fourth iteration
> +        urhadd          v26.16b, v5.16b, v20.16b        // Rounding
> halving add, third iteration
> +        ld1             {v1.16b}, [x2], x3              // Load pix3 for
> fourth iteration
>          uabal           v29.8h, v6.8b, v26.8b           // Absolute
> difference of lower half for third iteration
>          uabal2          v28.8h, v6.16b, v26.16b         // Absolute
> difference of upper half for third iteration
>          ld1             {v21.16b}, [x1], x3             // Load pix1 for
> fourth iteration
>          sub             w4, w4, #4                      // h-= 4
> -        urhadd          v25.16b, v22.16b, v23.16b       // Rounding
> halving add
> +        urhadd          v25.16b, v20.16b, v1.16b        // Rounding
> halving add
>          cmp             w4, #4
>          uabal           v29.8h, v21.8b, v25.8b          // Absolute
> difference of lower half for fourth iteration
>          uabal2          v28.8h, v21.16b, v25.16b        // Absolute
> difference of upper half for fourth iteration
> @@ -372,11 +368,11 @@ function ff_pix_abs16_y2_neon, export=1
>  // iterate by one
>  2:
>
> -        ld1             {v1.16b}, [x2], x3              // Load pix2
> -        ld1             {v2.16b}, [x5], x3              // Load pix3
> +        ld1             {v2.16b}, [x2], x3              // Load pix3
>          subs            w4, w4, #1
>          ld1             {v0.16b}, [x1], x3              // Load pix1
>          urhadd          v30.16b, v1.16b, v2.16b         // Rounding
> halving add
> +        mov             v1.16b, v2.16b                  // Shift
> pix3->pix2
>          uabal           v29.8h, v30.8b, v0.8b
>          uabal2          v28.8h, v30.16b, v0.16b
>
> --
> 2.25.1
>
>
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