[FFmpeg-devel] libavcodec/exr : add x86 SIMD for predictor

[Henrik Gramner]

On Fri, Sep 22, 2017 at 11:12 PM, Martin Vignali
<martin.vignali at gmail.com> wrote:
> +static void predictor_scalar(uint8_t *src, ptrdiff_t size)
> +{
> +    uint8_t *t    = src + 1;
> +    uint8_t *stop = src + size;
> +
> +    while (t < stop) {
> +        int d = (int) t[-1] + (int) t[0] - 128;
> +        t[0] = d;
> +        ++t;
> +    }
> +}

Can be simplified quite a bit:

static void predictor_scalar(uint8_t *src, ptrdiff_t size)
{
    for (size_t i = 1; i < size; i++)
        src[i] += src[i-1] - 128;
}

> +SECTION_RODATA 32
> +
> +neg_128: times 16 db -128
> +shuffle_15: times 16 db 15

Drop the 32-byte alignment from the section directive, we don't need it here.

db -128 is weird since it's identical to +128. I would rename those as such:

pb_128: times 16 db 128
pb_15:  times 16 db 15

> +INIT_XMM ssse3
> +cglobal predictor, 2,3,5, src, size, tmp
> +
> +    mov                tmpb, [srcq]
> +    xor                tmpb, -128
> +    mov              [srcq], tmpb
> +
> +;offset src by size
> +    add                srcq, sizeq
> +    neg               sizeq                ; size = offset for src
> +
> +;init mm
> +    mova                 m0, [neg_128]     ; m0 = const for xor high byte
> +    mova                 m1, [shuffle_15]  ; m1 = shuffle mask
> +    pxor                 m2, m2            ; m2 = prev_buffer
> +
> +
> +.loop:
> +    mova                 m3, [srcq + sizeq]
> +    pxor                 m3, m0
> +
> +    ;compute prefix sum
> +    mova             m4, m3
> +    pslldq               m4, 1
> +
> +    paddb                m4, m3
> +    mova                 m3, m4
> +    pslldq               m3, 2
> +
> +    paddb                m3, m4
> +    mova                 m4, m3
> +    pslldq               m4, 4
> +
> +    paddb                m4, m3
> +    mova                 m3, m4
> +    pslldq               m3, 8
> +
> +    paddb                m4, m2
> +    paddb                m4, m3
> +
> +    mova     [srcq + sizeq], m4
> +
> +    ;broadcast high byte for next iter
> +    pshufb m4, m1
> +    mova m2, m4
> +
> +    add     sizeq, mmsize
> +    jl .loop
> +    RET

%macro PREDICTOR 0
cglobal predictor, 2,3,5, src, size, tmp
%if mmsize == 32
    vbroadcasti128   m0, [pb_128]
%else
    mova            xm0, [pb_128]
%endif
    mova            xm1, [pb_15]
    mova            xm2, xm0
    add            srcq, sizeq
    neg           sizeq
.loop:
    pxor             m3, m0, [srcq + sizeq]
    pslldq           m4, m3, 1
    paddb            m3, m4
    pslldq           m4, m3, 2
    paddb            m3, m4
    pslldq           m4, m3, 4
    paddb            m3, m4
    pslldq           m4, m3, 8
%if mmsize == 32
    paddb            m3, m4
    paddb           xm2, xm3
    vextracti128    xm4, m3, 1
    mova [srcq + sizeq], xm2
    pshufb          xm2, xm1
    paddb           xm2, xm4
    mova [srcq + sizeq + 16], xm2
%else
    paddb            m2, m3
    paddb            m2, m4
    mova [srcq + sizeq], m2
%endif
    pshufb          xm2, xm1
    add           sizeq, mmsize
    jl .loop
    RET
%endmacro

INIT_XMM ssse3
PREDICTOR

INIT_XMM avx
PREDICTOR

%if HAVE_AVX2_EXTERNAL
INIT_YMM avx2
PREDICTOR
%endif

predictor_c: 15351.5
predictor_ssse3: 1206.5
predictor_avx: 1207.5
predictor_avx2: 880.0

On SKL-X. Only tested in checkasm.

AVX is same speed as SSSE3 since modern Intel CPU:s eliminate reg-reg
moves in the register renaming stage, but somewhat older CPU:s such as
Sandy Bridge, which is still quite popular, does not so it should help
there.

On Fri, Sep 22, 2017 at 11:12 PM, Martin Vignali
<martin.vignali at gmail.com> wrote:
> Hello,
>
> in attach a patch
> with a port to asm of the predictor part of this patch :
>
> https://github.com/openexr/openexr/pull/229/commits/4198128397c033d4f69e5cc0833195da500c31cf
>
> Tested on OSX, pass fate test for me
> Check asm also pass for me
>
> Results with reorder simd disable :
> SSSE3 : 94.5s
> 1036758 decicycles in predictor,  130751 runs,    321 skips
>
> Scalar : 114s
> 4255109 decicycles in predictor,  130276 runs,    796 skips
>
> using reorder and predictor simd : 82.6s
>
>
> Check asm benchmark :
> ./tests/checkasm/checkasm --test=exrdsp --bench
>
> predictor_c: 10635.1
> predictor_ssse3: 1634.6
>
>
> Comments welcome
>
>
> Martin
>
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