compress/flate: move the history buffer out of the decompressor struct.
I'm not exactly sure why there's a performance gain, but it seems like
an easy win. Maybe it's a cache line thing. Maybe it's that
unsafe.Sizeof(decompressor{}) drops to below unmappedzero, so that
checkref/checkoffset don't need to insert TESTB instructions. Maybe
it's less noise for the conservative garbage collector. Maybe it's
something else.
compress/flate benchmarks:
BenchmarkDecodeDigitsSpeed1e4 378628 349906 -7.59%
BenchmarkDecodeDigitsSpeed1e5
3481976 3204898 -7.96%
BenchmarkDecodeDigitsSpeed1e6
34419500 31750660 -7.75%
BenchmarkDecodeDigitsDefault1e4 362317 335562 -7.38%
BenchmarkDecodeDigitsDefault1e5
3290032 3107624 -5.54%
BenchmarkDecodeDigitsDefault1e6
30542540 28937480 -5.26%
BenchmarkDecodeDigitsCompress1e4 362803 335158 -7.62%
BenchmarkDecodeDigitsCompress1e5
3294512 3114526 -5.46%
BenchmarkDecodeDigitsCompress1e6
30514940 28927090 -5.20%
BenchmarkDecodeTwainSpeed1e4 412818 389521 -5.64%
BenchmarkDecodeTwainSpeed1e5
3475780 3288908 -5.38%
BenchmarkDecodeTwainSpeed1e6
33629640 31931420 -5.05%
BenchmarkDecodeTwainDefault1e4 369736 348850 -5.65%
BenchmarkDecodeTwainDefault1e5
2861050 2721383 -4.88%
BenchmarkDecodeTwainDefault1e6
27120120 25862050 -4.64%
BenchmarkDecodeTwainCompress1e4 372057 350822 -5.71%
BenchmarkDecodeTwainCompress1e5
2855109 2718664 -4.78%
BenchmarkDecodeTwainCompress1e6
26987010 26336030 -2.41%
image/png benchmarks:
BenchmarkDecodeGray
1841839 1802251 -2.15%
BenchmarkDecodeNRGBAGradient
7115318 6933280 -2.56%
BenchmarkDecodeNRGBAOpaque
6135892 6013284 -2.00%
BenchmarkDecodePaletted
1153313 1114302 -3.38%
BenchmarkDecodeRGB
5619404 5511190 -1.93%
R=rsc, r
CC=golang-dev
https://golang.org/cl/
6533048