Re: [FFmpeg-devel] [PATCH 1/5] lavc/aarch64: Add neon implementation for sse16

["Martin Storsjö" <martin@martin.st>]

On Tue, 16 Aug 2022, Hubert Mazur wrote:

> Provide neon implementation for sse16 function.
>
> Performance comparison tests are shown below.
> - sse_0_c: 268.2
> - sse_0_neon: 43.5
>
> 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         | 76 ++++++++++++++++++++++++
> 2 files changed, 80 insertions(+)
>
> diff --git a/libavcodec/aarch64/me_cmp_init_aarch64.c b/libavcodec/aarch64/me_cmp_init_aarch64.c
> index 79c739914f..7780009d41 100644
> --- a/libavcodec/aarch64/me_cmp_init_aarch64.c
> +++ b/libavcodec/aarch64/me_cmp_init_aarch64.c
> @@ -30,6 +30,9 @@ int ff_pix_abs16_xy2_neon(MpegEncContext *s, const uint8_t *blk1, const uint8_t
> int ff_pix_abs16_x2_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
>                       ptrdiff_t stride, int h);
> 
> +int sse16_neon(MpegEncContext *v, const uint8_t *pix1, const uint8_t *pix2,
> +                      ptrdiff_t stride, int h);
> +

The second line of the function delcaration is incorrectly indented (it 
should be aligned with the opening parenthesis). I fixed this for the 
preexisting cases and the new patches, that I pushed.

> diff --git a/libavcodec/aarch64/me_cmp_neon.S b/libavcodec/aarch64/me_cmp_neon.S
> index cda7ce0408..825ce45d13 100644
> --- a/libavcodec/aarch64/me_cmp_neon.S
> +++ b/libavcodec/aarch64/me_cmp_neon.S
> @@ -270,3 +270,79 @@ function ff_pix_abs16_x2_neon, export=1
>
>         ret
> endfunc
> +
> +function sse16_neon, export=1
> +        // x0 - unused
> +        // x1 - pix1
> +        // x2 - pix2
> +        // x3 - stride
> +        // w4 - h
> +
> +        cmp             w4, #4
> +        movi            d18, #0

The d18 register was essentially unused

> +3:
> +        uaddlv          d16, v17.4s                     // add up accumulator vector
> +        add             d18, d18, d16
> +
> +        fmov            w0, s18

Here, the d18 register could be left out entirely.

// Martin

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