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cmd/compile: use math/bits functions where possible

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Use the math/bits functions to calculate the number of leading/
trailing zeros, bit length and the population count.

The math/bits package is built as part of the bootstrap process
so we do not need to provide an alternative implementation for
Go versions prior to 1.9.

Passes toolstash-check -all.

Change-Id: I393b4cc1c8accd0ca7cb3599d3926fa6319b574f
Reviewed-on: https://go-review.googlesource.com/113336
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Michael Munday 2018-05-16 11:21:18 +01:00
parent cc09212f59
commit 5654114d04
4 changed files with 14 additions and 70 deletions
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24
src/cmd/compile/internal/ssa/bits_bootstrap.go
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@ -1,24 +0,0 @@
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build !go1.9
package ssa
const deBruijn64 = 0x03f79d71b4ca8b09
var deBruijn64tab = [64]byte{
0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
}
// TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
func TrailingZeros64(x uint64) int {
if x == 0 {
return 64
}
return int(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)])
}

13
src/cmd/compile/internal/ssa/bits_go19.go
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@ -1,13 +0,0 @@
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build go1.9
package ssa
import "math/bits"
func TrailingZeros64(x uint64) int {
return bits.TrailingZeros64(x)
}

11
src/cmd/compile/internal/ssa/debug.go
View File

@ -8,6 +8,7 @@ import (
"cmd/internal/obj"
"encoding/hex"
"fmt"
"math/bits"
"sort"
"strings"
)
@ -92,7 +93,7 @@ func (state *stateAtPC) reset(live []liveSlot) {
if mask == 0 {
break
}
reg := uint8(TrailingZeros64(mask))
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
registers[reg] = append(registers[reg], live.slot)
@ -116,7 +117,7 @@ func (s *debugState) LocString(loc VarLoc) string {
if mask == 0 {
break
}
reg := uint8(TrailingZeros64(mask))
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
storage = append(storage, s.registers[reg].String())
@ -613,7 +614,7 @@ func (state *debugState) mergePredecessors(b *Block, blockLocs []*BlockDebug) ([
if mask == 0 {
break
}
reg := uint8(TrailingZeros64(mask))
reg := uint8(bits.TrailingZeros64(mask))
mask &^= 1 << reg
state.currentState.registers[reg] = append(state.currentState.registers[reg], predSlot.slot)
@ -643,7 +644,7 @@ func (state *debugState) processValue(v *Value, vSlots []SlotID, vReg *Register)
if clobbers == 0 {
break
}
reg := uint8(TrailingZeros64(clobbers))
reg := uint8(bits.TrailingZeros64(clobbers))
clobbers &^= 1 << reg
for _, slot := range locs.registers[reg] {
@ -812,7 +813,7 @@ func firstReg(set RegisterSet) uint8 {
// produce locations with no storage.
return 0
}
return uint8(TrailingZeros64(uint64(set)))
return uint8(bits.TrailingZeros64(uint64(set)))
}
// buildLocationLists builds location lists for all the user variables in

36
src/cmd/compile/internal/ssa/rewrite.go
View File

@ -11,6 +11,7 @@ import (
"fmt"
"io"
"math"
"math/bits"
"os"
"path/filepath"
)
@ -322,17 +323,16 @@ func isSameSym(sym interface{}, name string) bool {
// nlz returns the number of leading zeros.
func nlz(x int64) int64 {
// log2(0) == 1, so nlz(0) == 64
return 63 - log2(x)
return int64(bits.LeadingZeros64(uint64(x)))
}
// ntz returns the number of trailing zeros.
func ntz(x int64) int64 {
return 64 - nlz(^x&(x-1))
return int64(bits.TrailingZeros64(uint64(x)))
}
func oneBit(x int64) bool {
return nlz(x)+ntz(x) == 63
return bits.OnesCount64(uint64(x)) == 1
}
// nlo returns the number of leading ones.
@ -347,34 +347,14 @@ func nto(x int64) int64 {
// log2 returns logarithm in base 2 of uint64(n), with log2(0) = -1.
// Rounds down.
func log2(n int64) (l int64) {
l = -1
x := uint64(n)
for ; x >= 0x8000; x >>= 16 {
l += 16
}
if x >= 0x80 {
x >>= 8
l += 8
}
if x >= 0x8 {
x >>= 4
l += 4
}
if x >= 0x2 {
x >>= 2
l += 2
}
if x >= 0x1 {
l++
}
return
func log2(n int64) int64 {
return int64(bits.Len64(uint64(n))) - 1
}
// log2uint32 returns logarithm in base 2 of uint32(n), with log2(0) = -1.
// Rounds down.
func log2uint32(n int64) (l int64) {
return log2(int64(uint32(n)))
func log2uint32(n int64) int64 {
return int64(bits.Len32(uint32(n))) - 1
}
// isPowerOfTwo reports whether n is a power of 2.