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cmd/compile: clarify division bounds check optimization

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The name of the function should mention division.
Eliminate double negatives from the comment describing it.

Change-Id: Icef1a5139b3a91b86acb930af97938f5160f7342
Reviewed-on: https://go-review.googlesource.com/c/go/+/217001
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
This commit is contained in:
Josh Bleecher Snyder 2020-01-23 22:18:30 -08:00
parent e932f0addc
commit 1b47fde55c
4 changed files with 9 additions and 7 deletions
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2
src/cmd/compile/internal/amd64/ssa.go
View file

@ -257,7 +257,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
// CPU faults upon signed overflow, which occurs when the most // CPU faults upon signed overflow, which occurs when the most
// negative int is divided by -1. Handle divide by -1 as a special case. // negative int is divided by -1. Handle divide by -1 as a special case.
if ssa.NeedsFixUp(v) { if ssa.DivisionNeedsFixUp(v) {
var c *obj.Prog var c *obj.Prog
switch v.Op { switch v.Op {
case ssa.OpAMD64DIVQ: case ssa.OpAMD64DIVQ:

8
src/cmd/compile/internal/ssa/prove.go
View file

@ -1243,9 +1243,11 @@ func simplifyBlock(sdom SparseTree, ft *factsTable, b *Block) {
divdLim, divdLimok := ft.limits[divd.ID] divdLim, divdLimok := ft.limits[divd.ID]
if (divrLimok && (divrLim.max < -1 || divrLim.min > -1)) || if (divrLimok && (divrLim.max < -1 || divrLim.min > -1)) ||
(divdLimok && divdLim.min > mostNegativeDividend[v.Op]) { (divdLimok && divdLim.min > mostNegativeDividend[v.Op]) {
v.AuxInt = 1 // see NeedsFixUp in genericOps - v.AuxInt = 0 means we have not proved // See DivisionNeedsFixUp in rewrite.go.
// that the divisor is not -1 and the dividend is not the most negative, // v.AuxInt = 1 means we have proved both that the divisor is not -1
// so we need to add fix-up code. // and that the dividend is not the most negative integer,
// so we do not need to add fix-up code.
v.AuxInt = 1
if b.Func.pass.debug > 0 { if b.Func.pass.debug > 0 {
b.Func.Warnl(v.Pos, "Proved %v does not need fix-up", v.Op) b.Func.Warnl(v.Pos, "Proved %v does not need fix-up", v.Op)
} }

4
src/cmd/compile/internal/ssa/rewrite.go
View file

@ -480,8 +480,8 @@ func extend32Fto64F(f float32) float64 {
return math.Float64frombits(r) return math.Float64frombits(r)
} }
// NeedsFixUp reports whether the division needs fix-up code. // DivisionNeedsFixUp reports whether the division needs fix-up code.
func NeedsFixUp(v *Value) bool { func DivisionNeedsFixUp(v *Value) bool {
return v.AuxInt == 0 return v.AuxInt == 0
} }

2
src/cmd/compile/internal/x86/ssa.go
View file

@ -199,7 +199,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
if v.Op == ssa.Op386DIVL || v.Op == ssa.Op386DIVW || if v.Op == ssa.Op386DIVL || v.Op == ssa.Op386DIVW ||
v.Op == ssa.Op386MODL || v.Op == ssa.Op386MODW { v.Op == ssa.Op386MODL || v.Op == ssa.Op386MODW {
if ssa.NeedsFixUp(v) { if ssa.DivisionNeedsFixUp(v) {
var c *obj.Prog var c *obj.Prog
switch v.Op { switch v.Op {
case ssa.Op386DIVL, ssa.Op386MODL: case ssa.Op386DIVL, ssa.Op386MODL: