mirror of https://github.com/golang/go.git
159b2de442
Benchmark:
name old time/op new time/op delta
Div-8 22.0ns ± 0% 22.0ns ± 0% ~ (all equal)
Div32-8 6.51ns ± 0% 3.00ns ± 0% -53.90% (p=0.000 n=10+8)
Div64-8 22.5ns ± 0% 22.5ns ± 0% ~ (all equal)
Code:
func div32(hi, lo, y uint32) (q, r uint32) {return bits.Div32(hi, lo, y)}
Before:
0x0020 00032 (test.go:24) MOVWU "".y+8(FP), R0
0x0024 00036 ($GOROOT/src/math/bits/bits.go:472) CBZW R0, 132
0x0028 00040 ($GOROOT/src/math/bits/bits.go:472) MOVWU "".hi(FP), R1
0x002c 00044 ($GOROOT/src/math/bits/bits.go:472) CMPW R1, R0
0x0030 00048 ($GOROOT/src/math/bits/bits.go:472) BLS 96
0x0034 00052 ($GOROOT/src/math/bits/bits.go:475) MOVWU "".lo+4(FP), R2
0x0038 00056 ($GOROOT/src/math/bits/bits.go:475) ORR R1<<32, R2, R1
0x003c 00060 ($GOROOT/src/math/bits/bits.go:476) CBZ R0, 140
0x0040 00064 ($GOROOT/src/math/bits/bits.go:476) UDIV R0, R1, R2
0x0044 00068 (test.go:24) MOVW R2, "".q+16(FP)
0x0048 00072 ($GOROOT/src/math/bits/bits.go:476) UREM R0, R1, R0
0x0050 00080 (test.go:24) MOVW R0, "".r+20(FP)
0x0054 00084 (test.go:24) MOVD -8(RSP), R29
0x0058 00088 (test.go:24) MOVD.P 32(RSP), R30
0x005c 00092 (test.go:24) RET (R30)
After:
0x001c 00028 (test.go:24) MOVWU "".y+8(FP), R0
0x0020 00032 (test.go:24) CBZW R0, 92
0x0024 00036 (test.go:24) MOVWU "".hi(FP), R1
0x0028 00040 (test.go:24) CMPW R0, R1
0x002c 00044 (test.go:24) BHS 84
0x0030 00048 (test.go:24) MOVWU "".lo+4(FP), R2
0x0034 00052 (test.go:24) ORR R1<<32, R2, R4
0x0038 00056 (test.go:24) UDIV R0, R4, R3
0x003c 00060 (test.go:24) MSUB R3, R4, R0, R4
0x0040 00064 (test.go:24) MOVW R3, "".q+16(FP)
0x0044 00068 (test.go:24) MOVW R4, "".r+20(FP)
0x0048 00072 (test.go:24) MOVD -8(RSP), R29
0x004c 00076 (test.go:24) MOVD.P 16(RSP), R30
0x0050 00080 (test.go:24) RET (R30)
UREM instruction in the previous assembly code will be converted to UDIV and MSUB instructions
on arm64. However the UDIV instruction in UREM is unnecessary, because it's a duplicate of the
previous UDIV. This CL adds a rule to have this extra UDIV instruction removed by CSE.
Change-Id: Ie2508784320020b2de022806d09f75a7871bb3d7
Reviewed-on: https://go-review.googlesource.com/c/159577
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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