lavc/aarch64: Add neon implementation for sse8

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>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/aarch64/me_cmp_init_aarch64.c

@@ -34,6 +34,8 @@ 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);
 
@@ -49,6 +51,7 @@ av_cold void ff_me_cmp_init_aarch64(MECmpContext *c, AVCodecContext *avctx)
 
         c->sad[0] = ff_pix_abs16_neon;
         c->sse[0] = sse16_neon;
+        c->sse[1] = sse8_neon;
         c->sse[2] = sse4_neon;
     }
 }

libavcodec/aarch64/me_cmp_neon.S

@@ -420,6 +420,70 @@ function sse16_neon, export=1
         ret
 endfunc
 
+function sse8_neon, export=1
+        // x0 - unused
+        // x1 - pix1
+        // x2 - pix2
+        // x3 - stride
+        // w4 - h
+
+        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, first iteration
+        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
+
+        fmov            w0, s17
+        ret
+
+endfunc
+
 function sse4_neon, export=1
         // x0 - unused
         // x1 - pix1