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cmd/compile: optimize 386's math.bits.TrailingZeros16

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This CL optimizes math.bits.TrailingZeros16 on 386 with
a pair of BSFL and ORL instrcutions.

The case TrailingZeros16-4 of the benchmark test in
math/bits shows big improvement.
name               old time/op  new time/op  delta
TrailingZeros16-4  1.55ns ± 1%  0.87ns ± 1%  -43.87%  (p=0.000 n=50+49)

Change-Id: Ia899975b0e46f45dcd20223b713ed632bc32740b
Reviewed-on: https://go-review.googlesource.com/c/go/+/189277
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Ben Shi 2019-08-07 05:20:32 +00:00
parent e1e4c499f0
commit 22355d6cd2
4 changed files with 22 additions and 1 deletions
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1
test/codegen/mathbits.go
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@ -296,6 +296,7 @@ func TrailingZeros32(n uint32) int {
func TrailingZeros16(n uint16) int {
// amd64:"BSFL","BTSL\\t\\$16"
// 386:"BSFL\t"
// arm:"ORR\t\\$65536","CLZ",-"MOVHU\tR"
// arm64:"ORR\t\\$65536","RBITW","CLZW",-"MOVHU\tR",-"RBIT\t",-"CLZ\t"
// s390x:"FLOGR","OR\t\\$65536"