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swscale/aarch64: use multiply accumulate and shift-right narrow 

This patch rewrites the innermost loop of ff_yuv2planeX_8_neon to avoid zips and
horizontal adds by using fused multiply adds. The patch also uses ld1r to load
one element and replicate it across all lanes of the vector. The patch also
improves the clipping code by removing the shift right instructions and
performing the shift with the shift-right narrow instructions.

I see 8% difference on an m6g instance with neoverse-n1 CPUs:
$ ffmpeg -nostats -f lavfi -i testsrc2=4k:d=2 -vf bench=start,scale=1024x1024,bench=stop -f null -
before: t:0.014015 avg:0.014096 max:0.015018 min:0.013971
after:  t:0.012985 avg:0.013013 max:0.013996 min:0.012818

Tested with `make check` on aarch64-linux.

Signed-off-by: Sebastian Pop <spop@amazon.com>
Reviewed-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Sebastian Pop 2019-12-09 14:25:01 +00:00 committed by Michael Niedermayer
parent ebbc976ae6
commit c3a17ffff6
1 changed files with 12 additions and 20 deletions
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32
libswscale/aarch64/output.S
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@ -38,29 +38,21 @@ function ff_yuv2planeX_8_neon, export=1
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
ldr w11, [x10], #4 // read 2x16-bit coeffs (X, Y) at (filter[j], filter[j+1])
zip1 v16.8H, v5.8H, v6.8H // A,I,B,J,C,K,D,L
zip2 v17.8H, v5.8H, v6.8H // E,M,F,N,F,O,H,P
dup v7.4S, w11 // X,Y,X,Y,X,Y,X,Y
smull v18.4S, v16.4H, v7.4H // A.X I.Y B.X J.Y
smull v20.4S, v17.4H, v7.4H // E.X M.Y F.X N.Y
smull2 v19.4S, v16.8H, v7.8H // C.X K.Y D.X L.Y
smull2 v21.4S, v17.8H, v7.8H // G.X O.Y H.X P.Y
addp v16.4S, v18.4S, v19.4S // A.X+I.Y B.X+J.Y C.X+K.Y D.X+L.Y
addp v17.4S, v20.4S, v21.4S // E.X+M.Y F.X+N.Y F.X+O.Y H.X+P.Y
add v3.4S, v3.4S, v16.4S // update val accumulator for part 1
add v4.4S, v4.4S, v17.4S // update val accumulator for part 2
ld1r {v7.8H}, [x10], #2 // read 1x16-bit coeff X at filter[j ] and duplicate across lanes
ld1r {v8.8H}, [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, v8.4H // val0 += {I,J,K,L} * Y
smlal2 v4.4S, v6.8H, v8.8H // val1 += {M,N,O,P} * Y
subs w8, w8, #2 // tmpfilterSize -= 2
b.gt 3b // loop until filterSize consumed
sshr v3.4S, v3.4S, #19 // val>>19 (part 1)
sshr v4.4S, v4.4S, #19 // val>>19 (part 2)
sqxtun v3.4H, v3.4S // clip16(val>>19) (part 1)
sqxtun v4.4H, v4.4S // clip16(val>>19) (part 2)
mov v3.D[1], v4.D[0] // merge part 1 and part 2
uqxtn v3.8B, v3.8H // clip8(val>>19)
st1 {v3.1D}, [x3], #8 // write to destination
add x7, x7, #8 // i += 8
sqshrun v3.4h, v3.4s, #16 // clip16(val0>>16)
sqshrun2 v3.8h, v4.4s, #16 // clip16(val1>>16)
uqshrn v3.8b, v3.8h, #3 // clip8(val>>19)
st1 {v3.8b}, [x3], #8 // write to destination
subs w4, w4, #8 // dstW -= 8
add x7, x7, #8 // i += 8
b.gt 2b // loop until width consumed
ret
endfunc