cmd/5c, cmd/5g, cmd/5l: turn MOVB, MOVH into plain moves, optimize short arithmetic.
Pseudo-instructions MOVBS and MOVHS are used to clarify
the semantics of short integers vs. registers:
* 8-bit and 16-bit values in registers are assumed to always
be zero-extended or sign-extended depending on their type.
* MOVB is truncation or move of an already extended value
between registers.
* MOVBU enforces zero-extension at the destination (register).
* MOVBS enforces sign-extension at the destination (register).
And similarly for MOVH/MOVS/MOVHU.
The linker is adapted to assemble MOVB and MOVH to an ordinary
mov. Also a peephole pass in 5g that aims at eliminating
redundant zero/sign extensions is improved.
encoding/binary:
benchmark old ns/op new ns/op delta
BenchmarkReadSlice1000Int32s 220387 217185 -1.45%
BenchmarkReadStruct 12839 12910 +0.55%
BenchmarkReadInts 5692 5534 -2.78%
BenchmarkWriteInts 6137 6016 -1.97%
BenchmarkPutUvarint32 257 241 -6.23%
BenchmarkPutUvarint64 812 754 -7.14%
benchmark old MB/s new MB/s speedup
BenchmarkReadSlice1000Int32s 18.15 18.42 1.01x
BenchmarkReadStruct 5.45 5.42 0.99x
BenchmarkReadInts 5.27 5.42 1.03x
BenchmarkWriteInts 4.89 4.99 1.02x
BenchmarkPutUvarint32 15.56 16.57 1.06x
BenchmarkPutUvarint64 9.85 10.60 1.08x
crypto/des:
benchmark old ns/op new ns/op delta
BenchmarkEncrypt 7002 5169 -26.18%
BenchmarkDecrypt 7015 5195 -25.94%
benchmark old MB/s new MB/s speedup
BenchmarkEncrypt 1.14 1.55 1.36x
BenchmarkDecrypt 1.14 1.54 1.35x
strconv:
benchmark old ns/op new ns/op delta
BenchmarkAtof64Decimal 457 385 -15.75%
BenchmarkAtof64Float 574 479 -16.55%
BenchmarkAtof64FloatExp 1035 906 -12.46%
BenchmarkAtof64Big 1793 1457 -18.74%
BenchmarkAtof64RandomBits 2267 2066 -8.87%
BenchmarkAtof64RandomFloats 1416 1194 -15.68%
BenchmarkAtof32Decimal 451 379 -15.96%
BenchmarkAtof32Float 547 435 -20.48%
BenchmarkAtof32FloatExp 1095 986 -9.95%
BenchmarkAtof32Random 1154 1006 -12.82%
BenchmarkAtoi 1415 1380 -2.47%
BenchmarkAtoiNeg 1414 1401 -0.92%
BenchmarkAtoi64 1744 1671 -4.19%
BenchmarkAtoi64Neg 1737 1662 -4.32%
Fixes #1837.
R=rsc, dave, bradfitz
CC=golang-dev
https://golang.org/cl/
12424043