lavc/aarch64: Provide optimized implementation of vsse8 for arm64.

Provide optimized implementation of vsse8 for arm64.

Performance comparison tests are shown below.
- vsse_1_c: 141.5
- vsse_1_neon: 32.5

Benchmarks and tests are run with checkasm tool on AWS Graviton 3.

Signed-off-by: Grzegorz Bernacki <gjb@semihalf.com>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/aarch64/me_cmp_init_aarch64.c

@@ -71,6 +71,9 @@ int nsse8_neon(int multiplier, const uint8_t *s, const uint8_t *s2,
 int nsse8_neon_wrapper(MpegEncContext *c, const uint8_t *s1, const uint8_t *s2,
                        ptrdiff_t stride, int h);
 
+int vsse8_neon(MpegEncContext *c, const uint8_t *s1, const uint8_t *s2,
+               ptrdiff_t stride, int h);
+
 av_cold void ff_me_cmp_init_aarch64(MECmpContext *c, AVCodecContext *avctx)
 {
     int cpu_flags = av_get_cpu_flags();
@@ -96,6 +99,8 @@ av_cold void ff_me_cmp_init_aarch64(MECmpContext *c, AVCodecContext *avctx)
         c->vsad[5] = vsad_intra8_neon;
 
         c->vsse[0] = vsse16_neon;
+        c->vsse[1] = vsse8_neon;
+
         c->vsse[4] = vsse_intra16_neon;
 
         c->nsse[0] = nsse16_neon_wrapper;

libavcodec/aarch64/me_cmp_neon.S

@@ -838,6 +838,76 @@ function vsad16_neon, export=1
         ret
 endfunc
 
+function vsse8_neon, export=1
+        // x0           unused
+        // x1           uint8_t *pix1
+        // x2           uint8_t *pix2
+        // x3           ptrdiff_t stride
+        // w4           int h
+
+        ld1             {v0.8b}, [x1], x3              // Load pix1[0], first iteration
+        ld1             {v1.8b}, [x2], x3              // Load pix2[0], first iteration
+
+        sub             w4, w4, #1                      // we need to make h-1 iterations
+        movi            v16.4s, #0
+        movi            v17.4s, #0
+
+        cmp             w4, #3                          // check if we can make 3 iterations at once
+        usubl           v31.8h, v0.8b, v1.8b            // Signed difference of pix1[0] - pix2[0], first iteration
+        b.lt            2f
+
+
+1:
+        // x = abs(pix1[0] - pix2[0] - pix1[0 + stride] + pix2[0 + stride])
+        // res = (x) * (x)
+        ld1             {v0.8b}, [x1], x3              // Load pix1[0 + stride], first iteration
+        ld1             {v1.8b}, [x2], x3              // Load pix2[0 + stride], first iteration
+        ld1             {v2.8b}, [x1], x3              // Load pix1[0 + stride], second iteration
+        ld1             {v3.8b}, [x2], x3              // Load pix2[0 + stride], second iteration
+        usubl           v29.8h, v0.8b, v1.8b
+        usubl2          v28.8h, v0.16b, v1.16b
+        ld1             {v4.8b}, [x1], x3              // Load pix1[0 + stride], third iteration
+        ld1             {v5.8b}, [x2], x3              // Load pix1[0 + stride], third iteration
+        sabd            v31.8h, v31.8h, v29.8h
+        usubl           v27.8h, v2.8b, v3.8b
+        usubl           v25.8h, v4.8b, v5.8b
+        sabd            v29.8h, v29.8h, v27.8h
+        sabd            v27.8h, v27.8h, v25.8h
+        umlal           v16.4s, v31.4h, v31.4h
+        umlal2          v17.4s, v31.8h, v31.8h
+        mov             v31.16b, v25.16b
+        umlal           v16.4s, v29.4h, v29.4h
+        umlal2          v17.4s, v29.8h, v29.8h
+        sub             w4, w4, #3
+        umlal           v16.4s, v27.4h, v27.4h
+        umlal2          v17.4s, v27.8h, v27.8h
+        cmp             w4, #3
+
+        b.ge            1b
+
+        cbz             w4, 3f
+
+// iterate by once
+2:
+        ld1             {v0.8b}, [x1], x3
+        ld1             {v1.8b}, [x2], x3
+        subs            w4, w4, #1
+        usubl           v29.8h, v0.8b, v1.8b
+        sabd            v31.8h, v31.8h, v29.8h
+        umlal           v16.4s, v31.4h, v31.4h
+        umlal2          v17.4s, v31.8h, v31.8h
+        mov             v31.16b, v29.16b
+        b.ne            2b
+
+3:
+        add             v16.4s, v16.4s, v17.4s
+        uaddlv          d17, v16.4s
+        fmov            w0, s17
+
+        ret
+endfunc
+
+
 function vsse16_neon, export=1
         // x0           unused
         // x1           uint8_t *pix1