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cmd/compile: repair bisection behavior for float-to-unsigned conversion

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My stab at a bisect-reproducer failed, but I verified that
it fixed the problem described in the issue.

Updates #75834

Change-Id: I9e0dfacd2bbd22cbc557e144920ee3417a48088c
Reviewed-on: https://go-review.googlesource.com/c/go/+/710997
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
David Chase 2025-10-10 17:08:20 -04:00
parent e8a53538b4
commit 48bb7a6114
1 changed files with 16 additions and 2 deletions
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18
src/cmd/compile/internal/ssagen/ssa.go
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@ -2865,7 +2865,19 @@ func (s *state) conv(n ir.Node, v *ssa.Value, ft, tt *types.Type) *ssa.Value {
}
if ft.IsFloat() || tt.IsFloat() {
conv, ok := fpConvOpToSSA[twoTypes{s.concreteEtype(ft), s.concreteEtype(tt)}]
cft, ctt := s.concreteEtype(ft), s.concreteEtype(tt)
conv, ok := fpConvOpToSSA[twoTypes{cft, ctt}]
// there's a change to a conversion-op table, this restores the old behavior if ConvertHash is false.
// use salted hash to distinguish unsigned convert at a Pos from signed convert at a Pos
if ctt == types.TUINT32 && ft.IsFloat() && !base.ConvertHash.MatchPosWithInfo(n.Pos(), "U", nil) {
// revert to old behavior
conv.op1 = ssa.OpCvt64Fto64
if cft == types.TFLOAT32 {
conv.op1 = ssa.OpCvt32Fto64
}
conv.op2 = ssa.OpTrunc64to32
}
if s.config.RegSize == 4 && Arch.LinkArch.Family != sys.MIPS && !s.softFloat {
if conv1, ok1 := fpConvOpToSSA32[twoTypes{s.concreteEtype(ft), s.concreteEtype(tt)}]; ok1 {
conv = conv1
@ -5862,6 +5874,7 @@ func (s *state) floatToUint(cvttab *f2uCvtTab, n ir.Node, x *ssa.Value, ft, tt *
// cutoff:=1<<(intY_Size-1)
// if x < floatX(cutoff) {
// result = uintY(x) // bThen
// // gated by ConvertHash, clamp negative inputs to zero
// if x < 0 { // unlikely
// result = 0 // bZero
// }
@ -5879,7 +5892,8 @@ func (s *state) floatToUint(cvttab *f2uCvtTab, n ir.Node, x *ssa.Value, ft, tt *
b.Likely = ssa.BranchLikely
var bThen, bZero *ssa.Block
newConversion := base.ConvertHash.MatchPos(n.Pos(), nil)
// use salted hash to distinguish unsigned convert at a Pos from signed convert at a Pos
newConversion := base.ConvertHash.MatchPosWithInfo(n.Pos(), "U", nil)
if newConversion {
bZero = s.f.NewBlock(ssa.BlockPlain)
bThen = s.f.NewBlock(ssa.BlockIf)