tree 29babf569314c9ad823b15b44033aa8f3d43fc04
parent 8874bef159af77ab9e746fc3c80b2219b3652045
author Nigel Tao <nigeltao@golang.org> 1476936953 +1100
committer Nigel Tao <nigeltao@golang.org> 1477172362 +0000

vector: remove a shift from the inner loop.

PSHUFB already lets us pick certain bytes out of an XMM register.
There's no need to shift by 8 bits (1 byte) beforehand.

The code generator is simpler. There's also a small win on the
benchmarks, especially for FixedAccumulateOpOverSIMD.

name                              old time/op  new time/op  delta
FixedAccumulateOpOverSIMD16-8      183ns ± 0%   174ns ± 0%  -4.92%    (p=0.000 n=8+8)
FixedAccumulateOpSrcSIMD16-8      87.0ns ± 1%  86.3ns ± 0%  -0.77%   (p=0.000 n=10+9)
FixedAccumulateMaskSIMD16-8       80.4ns ± 1%  81.2ns ± 1%  +1.01%  (p=0.000 n=10+10)
FloatingAccumulateOpOverSIMD16-8   250ns ± 1%   244ns ± 0%  -2.39%   (p=0.000 n=10+8)
FloatingAccumulateOpSrcSIMD16-8    176ns ± 1%   176ns ± 0%    ~      (p=0.142 n=10+8)
FloatingAccumulateMaskSIMD16-8     167ns ± 0%   167ns ± 0%    ~      (p=0.137 n=8+10)
FixedAccumulateOpOverSIMD64-8     2.73µs ± 1%  2.58µs ± 0%  -5.36%   (p=0.000 n=10+7)
FixedAccumulateOpSrcSIMD64-8      1.18µs ± 1%  1.17µs ± 0%  -0.33%   (p=0.003 n=10+9)
FixedAccumulateMaskSIMD64-8       1.09µs ± 0%  1.09µs ± 0%  -0.17%    (p=0.047 n=9+9)
FloatingAccumulateOpOverSIMD64-8  3.67µs ± 0%  3.61µs ± 1%  -1.47%   (p=0.000 n=7+10)
FloatingAccumulateOpSrcSIMD64-8   2.60µs ± 0%  2.61µs ± 0%  +0.19%    (p=0.003 n=8+8)
FloatingAccumulateMaskSIMD64-8    2.47µs ± 0%  2.46µs ± 0%    ~      (p=0.162 n=10+9)
GlyphAlpha16Over-8                2.99µs ± 0%  2.98µs ± 1%  -0.50%   (p=0.021 n=9+10)
GlyphAlpha16Src-8                 2.89µs ± 1%  2.89µs ± 0%    ~     (p=0.381 n=10+10)
GlyphAlpha32Over-8                4.53µs ± 0%  4.50µs ± 0%  -0.83%  (p=0.000 n=10+10)
GlyphAlpha32Src-8                 4.14µs ± 0%  4.13µs ± 0%  -0.21%   (p=0.026 n=9+10)
GlyphAlpha64Over-8                8.97µs ± 1%  8.80µs ± 0%  -1.85%   (p=0.000 n=10+9)
GlyphAlpha64Src-8                 7.42µs ± 1%  7.39µs ± 0%  -0.45%  (p=0.011 n=10+10)
GlyphAlpha128Over-8               21.8µs ± 0%  21.2µs ± 0%  -2.91%    (p=0.000 n=9+9)
GlyphAlpha128Src-8                15.6µs ± 0%  15.6µs ± 0%    ~      (p=0.982 n=10+7)
GlyphAlpha256Over-8               66.3µs ± 1%  63.7µs ± 0%  -3.84%   (p=0.000 n=10+9)
GlyphAlpha256Src-8                41.2µs ± 1%  41.2µs ± 1%    ~     (p=1.000 n=10+10)
GlyphRGBA16Over-8                 4.75µs ± 0%  4.75µs ± 1%    ~      (p=0.735 n=9+10)
GlyphRGBA16Src-8                  4.20µs ± 0%  4.20µs ± 0%    ~       (p=0.503 n=8+8)
GlyphRGBA32Over-8                 11.4µs ± 0%  11.4µs ± 0%    ~       (p=0.119 n=9+9)
GlyphRGBA32Src-8                  9.34µs ± 1%  9.32µs ± 0%    ~       (p=0.062 n=9+8)
GlyphRGBA64Over-8                 36.0µs ± 0%  36.1µs ± 0%    ~       (p=0.209 n=8+9)
GlyphRGBA64Src-8                  27.9µs ± 1%  27.8µs ± 0%    ~     (p=0.796 n=10+10)
GlyphRGBA128Over-8                 131µs ± 0%   131µs ± 0%    ~       (p=0.931 n=9+9)
GlyphRGBA128Src-8                 97.9µs ± 0%  97.7µs ± 1%    ~      (p=0.053 n=9+10)
GlyphRGBA256Over-8                 503µs ± 0%   503µs ± 1%    ~      (p=0.274 n=8+10)
GlyphRGBA256Src-8                  370µs ± 0%   369µs ± 0%    ~      (p=0.497 n=9+10)

Change-Id: I56651e70b258792b83ea2a74904756243c88bef4
Reviewed-on: https://go-review.googlesource.com/31537
Reviewed-by: David Crawshaw <crawshaw@golang.org>