192b675f17
On amd64 ReverseBytes16 is lowered to a rotate instruction. However arm64 doesn't
have 16-bit rotate instruction, but has a REV16W instruction which can be used
for ReverseBytes16. This CL adds a rule to turn the patterns like (x<<8) | (x>>8)
(the type of x is uint16, and "|" can also be "^" or "+") to a REV16W instruction.
Code:
func reverseBytes16(i uint16) uint16 { return bits.ReverseBytes16(i) }
Before:
0x0004 00004 (test.go:6) MOVHU "".i(FP), R0
0x0008 00008 ($GOROOT/src/math/bits/bits.go:262) UBFX $8, R0, $8, R1
0x000c 00012 ($GOROOT/src/math/bits/bits.go:262) ORR R0<<8, R1, R0
0x0010 00016 (test.go:6) MOVH R0, "".~r1+8(FP)
0x0014 00020 (test.go:6) RET (R30)
After:
0x0000 00000 (test.go:6) MOVHU "".i(FP), R0
0x0004 00004 (test.go:6) REV16W R0, R0
0x0008 00008 (test.go:6) MOVH R0, "".~r1+8(FP)
0x000c 00012 (test.go:6) RET (R30)
Benchmarks:
name old time/op new time/op delta
ReverseBytes-224 1.000000ns +- 0% 1.000000ns +- 0% ~ (all equal)
ReverseBytes16-224 1.500000ns +- 0% 1.000000ns +- 0% -33.33% (p=0.000 n=9+10)
ReverseBytes32-224 1.000000ns +- 0% 1.000000ns +- 0% ~ (all equal)
ReverseBytes64-224 1.000000ns +- 0% 1.000000ns +- 0% ~ (all equal)
Change-Id: I87cd41b2d8e549bf39c601f185d5775bd42d739c
Reviewed-on: https://go-review.googlesource.com/c/157757
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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| AUTHORS | ||
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