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cmd/compile: special-case const comparisons against zero

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Constant comparisons against 0 are reasonably common.
Special-case and avoid allocating a new zero value each time.

Change-Id: I6c526c8ab30ef7f0fef59110133c764b7b90ba05
Reviewed-on: https://go-review.googlesource.com/20956
Reviewed-by: Alan Donovan <adonovan@google.com>
This commit is contained in:
Robert Griesemer 2016-03-21 10:52:03 -07:00
parent d3253876f2
commit 07749aef98
3 changed files with 11 additions and 10 deletions
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10
src/cmd/compile/internal/gc/mpfloat.go
View file

@ -116,11 +116,11 @@ func (a *Mpflt) Cmp(b *Mpflt) int {
return a.Val.Cmp(&b.Val) return a.Val.Cmp(&b.Val)
} }
func (b *Mpflt) CmpFloat64(c float64) int { func (a *Mpflt) CmpFloat64(c float64) int {
var a Mpflt if c == 0 {
return a.Val.Sign() // common case shortcut
a.SetFloat64(c) }
return b.Cmp(&a) return a.Val.Cmp(big.NewFloat(c))
} }
func (a *Mpflt) Float64() float64 { func (a *Mpflt) Float64() float64 {

7
src/cmd/compile/internal/gc/mpint.go
View file

@ -262,8 +262,11 @@ func (a *Mpint) Cmp(b *Mpint) int {
return a.Val.Cmp(&b.Val) return a.Val.Cmp(&b.Val)
} }
func (b *Mpint) CmpInt64(c int64) int { func (a *Mpint) CmpInt64(c int64) int {
return b.Val.Cmp(big.NewInt(c)) if c == 0 {
return a.Val.Sign() // common case shortcut
}
return a.Val.Cmp(big.NewInt(c))
} }
func (a *Mpint) Neg() { func (a *Mpint) Neg() {

4
src/cmd/compile/internal/gc/walk.go
View file

@ -10,8 +10,6 @@ import (
"strings" "strings"
) )
var mpzero Mpint
// The constant is known to runtime. // The constant is known to runtime.
const ( const (
tmpstringbufsize = 32 tmpstringbufsize = 32
@ -1229,7 +1227,7 @@ opswitch:
} }
if Isconst(n.Right, CTINT) { if Isconst(n.Right, CTINT) {
if n.Right.Val().U.(*Mpint).Cmp(&mpzero) < 0 || n.Right.Val().U.(*Mpint).Cmp(Maxintval[TINT]) > 0 { if n.Right.Val().U.(*Mpint).CmpInt64(0) < 0 || n.Right.Val().U.(*Mpint).Cmp(Maxintval[TINT]) > 0 {
Yyerror("index out of bounds") Yyerror("index out of bounds")
} }
} }