[FFmpeg-devel] [PATCH v3 2/3] swscale/aarch64: vscale optimization

["Swinney, Jonathan" <jswinney@amazon.com>]

Use scalar times vector multiply accumlate instructions instead of
vector times vector to remove the need for replicating load instructions
which are slightly slower.

On AWS c7g (Graviton 3, Neoverse V1) instances:
yuv2yuvX_8_0_512_accurate_neon:  1144.8  987.4
yuv2yuvX_16_0_512_accurate_neon: 2080.5 1869.4

Signed-off-by: Jonathan Swinney <jswinney@amazon.com>
---
 libswscale/aarch64/output.S | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/libswscale/aarch64/output.S b/libswscale/aarch64/output.S
index af71de6050..991750cf31 100644
--- a/libswscale/aarch64/output.S
+++ b/libswscale/aarch64/output.S
@@ -34,16 +34,15 @@ function ff_yuv2planeX_8_neon, export=1
         mov                 x9, x2                          // srcp    = src
         mov                 x10, x0                         // filterp = filter
 3:      ldp                 x11, x12, [x9], #16             // get 2 pointers: src[j] and src[j+1]
+        ldr                 s7, [x10], #4                   // read 2x16-bit coeff X and Y at filter[j] and filter[j+1]
         add                 x11, x11, x7, lsl #1            // &src[j  ][i]
         add                 x12, x12, x7, lsl #1            // &src[j+1][i]
         ld1                 {v5.8H}, [x11]                  // read 8x16-bit @ src[j  ][i + {0..7}]: A,B,C,D,E,F,G,H
         ld1                 {v6.8H}, [x12]                  // read 8x16-bit @ src[j+1][i + {0..7}]: I,J,K,L,M,N,O,P
-        ld1r                {v7.8H}, [x10], #2              // read 1x16-bit coeff X at filter[j  ] and duplicate across lanes
-        ld1r                {v16.8H}, [x10], #2             // read 1x16-bit coeff Y at filter[j+1] and duplicate across lanes
-        smlal               v3.4S, v5.4H, v7.4H             // val0 += {A,B,C,D} * X
-        smlal2              v4.4S, v5.8H, v7.8H             // val1 += {E,F,G,H} * X
-        smlal               v3.4S, v6.4H, v16.4H            // val0 += {I,J,K,L} * Y
-        smlal2              v4.4S, v6.8H, v16.8H            // val1 += {M,N,O,P} * Y
+        smlal               v3.4S, v5.4H, v7.H[0]           // val0 += {A,B,C,D} * X
+        smlal2              v4.4S, v5.8H, v7.H[0]           // val1 += {E,F,G,H} * X
+        smlal               v3.4S, v6.4H, v7.H[1]           // val0 += {I,J,K,L} * Y
+        smlal2              v4.4S, v6.8H, v7.H[1]           // val1 += {M,N,O,P} * Y
         subs                w8, w8, #2                      // tmpfilterSize -= 2
         b.gt                3b                              // loop until filterSize consumed
 
-- 
2.37.1

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