From 4e2b0dda8cbab104635d59ef5a68e4342250094b Mon Sep 17 00:00:00 2001 From: erifan01 Date: Thu, 3 Jan 2019 09:25:06 +0000 Subject: cmd/compile: eliminate unnecessary type conversions in TrailingZeros(16|8) for arm64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This CL eliminates unnecessary type conversion operations: OpZeroExt16to64 and OpZeroExt8to64. If the input argrument is a nonzero value, then ORconst operation can also be eliminated. Benchmarks: name old time/op new time/op delta TrailingZeros-8 2.75ns ± 0% 2.75ns ± 0% ~ (all equal) TrailingZeros8-8 3.49ns ± 1% 2.93ns ± 0% -16.00% (p=0.000 n=10+10) TrailingZeros16-8 3.49ns ± 1% 2.93ns ± 0% -16.05% (p=0.000 n=9+10) TrailingZeros32-8 2.67ns ± 1% 2.68ns ± 1% ~ (p=0.468 n=10+10) TrailingZeros64-8 2.67ns ± 1% 2.65ns ± 0% -0.62% (p=0.022 n=10+9) code: func f16(x uint) { z = bits.TrailingZeros16(uint16(x)) } Before: "".f16 STEXT size=48 args=0x8 locals=0x0 leaf 0x0000 00000 (test.go:7) TEXT "".f16(SB), LEAF|NOFRAME|ABIInternal, $0-8 0x0000 00000 (test.go:7) FUNCDATA ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) FUNCDATA $3, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) PCDATA $2, ZR 0x0000 00000 (test.go:7) PCDATA ZR, ZR 0x0000 00000 (test.go:7) MOVD "".x(FP), R0 0x0004 00004 (test.go:7) MOVHU R0, R0 0x0008 00008 (test.go:7) ORR $65536, R0, R0 0x000c 00012 (test.go:7) RBIT R0, R0 0x0010 00016 (test.go:7) CLZ R0, R0 0x0014 00020 (test.go:7) MOVD R0, "".z(SB) 0x0020 00032 (test.go:7) RET (R30) This line of code is unnecessary: 0x0004 00004 (test.go:7) MOVHU R0, R0 After: "".f16 STEXT size=32 args=0x8 locals=0x0 leaf 0x0000 00000 (test.go:7) TEXT "".f16(SB), LEAF|NOFRAME|ABIInternal, $0-8 0x0000 00000 (test.go:7) FUNCDATA ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) FUNCDATA $3, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB) 0x0000 00000 (test.go:7) PCDATA $2, ZR 0x0000 00000 (test.go:7) PCDATA ZR, ZR 0x0000 00000 (test.go:7) MOVD "".x(FP), R0 0x0004 00004 (test.go:7) ORR $65536, R0, R0 0x0008 00008 (test.go:7) RBITW R0, R0 0x000c 00012 (test.go:7) CLZW R0, R0 0x0010 00016 (test.go:7) MOVD R0, "".z(SB) 0x001c 00028 (test.go:7) RET (R30) The situation of TrailingZeros8 is similar to TrailingZeros16. Change-Id: I473bdca06be8460a0be87abbae6fe640017e4c9d Reviewed-on: https://go-review.googlesource.com/c/go/+/156999 Reviewed-by: Cherry Zhang Run-TryBot: Cherry Zhang TryBot-Result: Gobot Gobot --- test/codegen/mathbits.go | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'test/codegen/mathbits.go') diff --git a/test/codegen/mathbits.go b/test/codegen/mathbits.go index 09939bb6be..c77b66c3f7 100644 --- a/test/codegen/mathbits.go +++ b/test/codegen/mathbits.go @@ -242,6 +242,7 @@ func RotateLeftVariable32(n uint32, m int) uint32 { func TrailingZeros(n uint) int { // amd64:"BSFQ","MOVL\t\\$64","CMOVQEQ" + // arm64:"RBIT","CLZ" // s390x:"FLOGR" // ppc64:"ANDN","POPCNTD" // ppc64le:"ANDN","POPCNTD" @@ -250,6 +251,7 @@ func TrailingZeros(n uint) int { func TrailingZeros64(n uint64) int { // amd64:"BSFQ","MOVL\t\\$64","CMOVQEQ" + // arm64:"RBIT","CLZ" // s390x:"FLOGR" // ppc64:"ANDN","POPCNTD" // ppc64le:"ANDN","POPCNTD" @@ -258,6 +260,7 @@ func TrailingZeros64(n uint64) int { func TrailingZeros32(n uint32) int { // amd64:"BTSQ\\t\\$32","BSFQ" + // arm64:"RBITW","CLZW" // s390x:"FLOGR","MOVWZ" // ppc64:"ANDN","POPCNTW" // ppc64le:"ANDN","POPCNTW" @@ -266,6 +269,7 @@ func TrailingZeros32(n uint32) int { func TrailingZeros16(n uint16) int { // amd64:"BSFL","BTSL\\t\\$16" + // arm64:"ORR\t\\$65536","RBITW","CLZW",-"MOVHU\tR",-"RBIT\t",-"CLZ\t" // s390x:"FLOGR","OR\t\\$65536" // ppc64:"POPCNTD","OR\\t\\$65536" // ppc64le:"POPCNTD","OR\\t\\$65536" @@ -274,6 +278,7 @@ func TrailingZeros16(n uint16) int { func TrailingZeros8(n uint8) int { // amd64:"BSFL","BTSL\\t\\$8" + // arm64:"ORR\t\\$256","RBITW","CLZW",-"MOVBU\tR",-"RBIT\t",-"CLZ\t" // s390x:"FLOGR","OR\t\\$256" return bits.TrailingZeros8(n) } @@ -314,6 +319,7 @@ func IterateBits16(n uint16) int { i := 0 for n != 0 { // amd64:"BSFL",-"BTSL" + // arm64:"RBITW","CLZW",-"ORR" i += bits.TrailingZeros16(n) n &= n - 1 } @@ -324,6 +330,7 @@ func IterateBits8(n uint8) int { i := 0 for n != 0 { // amd64:"BSFL",-"BTSL" + // arm64:"RBITW","CLZW",-"ORR" i += bits.TrailingZeros8(n) n &= n - 1 } -- cgit v1.3