Re: [FFmpeg-devel] [PATCH 4/5] lavc/aarch64: Add neon implementation for sse8

["Martin Storsjö" <martin@martin.st>]

On Tue, 16 Aug 2022, Hubert Mazur wrote:

> Provide optimized implementation of sse8 function for arm64.
>
> Performance comparison tests are shown below.
> - sse_1_c: 130.7
> - sse_1_neon: 29.7
>
> Benchmarks and tests run with checkasm tool on AWS Graviton 3.
>
> Signed-off-by: Hubert Mazur <hum@semihalf.com>
> ---
> libavcodec/aarch64/me_cmp_init_aarch64.c |  4 ++
> libavcodec/aarch64/me_cmp_neon.S         | 66 ++++++++++++++++++++++++
> 2 files changed, 70 insertions(+)
>
> diff --git a/libavcodec/aarch64/me_cmp_init_aarch64.c b/libavcodec/aarch64/me_cmp_init_aarch64.c
> index 1c36d3d7cb..2f51f0497e 100644
> --- a/libavcodec/aarch64/me_cmp_init_aarch64.c
> +++ b/libavcodec/aarch64/me_cmp_init_aarch64.c
> @@ -34,9 +34,12 @@ int ff_pix_abs16_y2_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *
> 
> int sse16_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
>                       ptrdiff_t stride, int h);
> +int sse8_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
> +                      ptrdiff_t stride, int h);
> int sse4_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
>                       ptrdiff_t stride, int h);

Same as the others about function declaration indentation

> diff --git a/libavcodec/aarch64/me_cmp_neon.S b/libavcodec/aarch64/me_cmp_neon.S
> index 0ec9c0465b..3f4266d4d5 100644
> --- a/libavcodec/aarch64/me_cmp_neon.S
> +++ b/libavcodec/aarch64/me_cmp_neon.S
> @@ -347,6 +347,72 @@ function sse16_neon, export=1
>         ret
> endfunc
> 
> +function sse8_neon, export=1
> +        // x0 - unused
> +        // x1 - pix1
> +        // x2 - pix2
> +        // x3 - stride
> +        // w4 - h
> +
> +        movi            d18, #0

Same as the others about d18

> +        movi            v21.4s, #0
> +        movi            v20.4s, #0
> +        cmp             w4, #4
> +        b.le            2f
> +
> +// make 4 iterations at once
> +1:
> +
> +        // res = abs(pix1[0] - pix2[0])
> +        // res * res
> +
> +        ld1             {v0.8b}, [x1], x3               // Load pix1 for first iteration
> +        ld1             {v1.8b}, [x2], x3               // Load pix2 for second iteration
> +        ld1             {v2.8b}, [x1], x3               // Load pix1 for second iteration
> +        ld1             {v3.8b}, [x2], x3               // Load pix2 for second iteration
> +        uabdl           v30.8h, v0.8b, v1.8b            // Absolute difference, first iteration
> +        ld1             {v4.8b}, [x1], x3               // Load pix1 for third iteration
> +        ld1             {v5.8b}, [x2], x3               // Load pix2 for third iteration
> +        uabdl           v29.8h, v2.8b, v3.8b            // Absolute difference, second iteration
> +        umlal           v21.4s, v30.4h, v30.4h          // Multiply lower half, first iteration
> +        ld1             {v6.8b}, [x1], x3               // Load pix1 for fourth iteration
> +        ld1             {v7.8b}, [x2], x3               // Load pix2 for fourth iteration
> +        uabdl           v28.8h, v4.8b, v5.8b            // Absolute difference, third iteration
> +        umlal           v21.4s, v29.4h, v29.4h          // Multiply lower half, second iteration
> +        umlal2          v20.4s, v30.8h, v30.8h          // Multiply upper half, second iteration

The comment was wrong here, this is about the first iteration, not the 
second one.

> +        uabdl           v27.8h, v6.8b, v7.8b            // Absolute difference, fourth iteration
> +        umlal           v21.4s, v28.4h, v28.4h          // Multiply lower half, third iteration
> +        umlal2          v20.4s, v29.8h, v29.8h          // Multiply upper half, second iteration
> +        sub             w4, w4, #4                      // h -= 4
> +        umlal2          v20.4s, v28.8h, v28.8h          // Multiply upper half, third iteration
> +        umlal           v21.4s, v27.4h, v27.4h          // Multiply lower half, fourth iteration
> +        cmp             w4, #4
> +        umlal2          v20.4s, v27.8h, v27.8h          // Multiply upper half, fourth iteration
> +        b.ge            1b
> +
> +        cbz             w4, 3f
> +
> +// iterate by one
> +2:
> +        ld1             {v0.8b}, [x1], x3               // Load pix1
> +        ld1             {v1.8b}, [x2], x3               // Load pix2
> +        subs            w4, w4, #1
> +        uabdl           v30.8h, v0.8b, v1.8b
> +        umlal           v21.4s, v30.4h, v30.4h
> +        umlal2          v20.4s, v30.8h, v30.8h
> +
> +        b.ne            2b
> +
> +3:
> +        add             v21.4s, v21.4s, v20.4s          // Add accumulator vectors together
> +        uaddlv          d17, v21.4s                     // Add up vector
> +        add             d18, d18, d17
> +

Unnecesssary d18.

// Martin

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