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[dev.simd] cmd/compile: mark SIMD types non-fat

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This CL fixes the merge locals error.
The culprit is that liveness analysis wrongly mark SIMD structs fat,
hence making `StoreReg` of SIMD vectors not a varkill effect, making the
liveness range of SIMD vectors not closed correctly, further making
mergelocals merged 2 concurrently-live SIMD vectors.

Is looks like mergelocals will treat the live range as one instruction
if it's not closed: [st, st+1). Should we make it [st, +inf) instead? So
that we won't have similar errors in the future.

Also, I feel we really need to examine every "case types.TSTRUCT" or "if
t.Kind() == types.TSTRUCT" in the codebase correctly for SIMD types...

Change-Id: I2f4f4f36a890bd317d582cfa73a8f6a789382d91
Reviewed-on: https://go-review.googlesource.com/c/go/+/687775
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Junyang Shao 2025-07-12 08:13:04 +00:00
parent b69622b83e
commit 3f789721d6
2 changed files with 3 additions and 8 deletions
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3
src/cmd/compile/internal/liveness/plive.go
View file

@ -1534,6 +1534,9 @@ func isfat(t *types.Type) bool {
} }
return true return true
case types.TSTRUCT: case types.TSTRUCT:
if t.IsSIMD() {
return false
}
// Struct with 1 field, check if field is fat // Struct with 1 field, check if field is fat
if t.NumFields() == 1 { if t.NumFields() == 1 {
return isfat(t.Field(0).Type) return isfat(t.Field(0).Type)

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

@ -850,13 +850,6 @@ func (f *Func) NewLocal(pos src.XPos, typ *types.Type) *ir.Name {
// items larger than what CanSSA would allow (approximateky, we disallow things // items larger than what CanSSA would allow (approximateky, we disallow things
// marked as open defer slots so as to avoid complicating liveness // marked as open defer slots so as to avoid complicating liveness
// analysis. // analysis.
//
// TODO: make SIMD variables mergible.
//
// Right now this check excludes SIMD vars because sometimes two live SIMD
// vectors will be put into the same partition by mergelocals, we need to figure
// out why because these vectors are big and should be merged when possible.
// Details in CL 687375.
func IsMergeCandidate(n *ir.Name) bool { func IsMergeCandidate(n *ir.Name) bool {
if base.Debug.MergeLocals == 0 || if base.Debug.MergeLocals == 0 ||
base.Flag.N != 0 || base.Flag.N != 0 ||
@ -864,7 +857,6 @@ func IsMergeCandidate(n *ir.Name) bool {
n.Type().Size() <= int64(3*types.PtrSize) || n.Type().Size() <= int64(3*types.PtrSize) ||
n.Addrtaken() || n.Addrtaken() ||
n.NonMergeable() || n.NonMergeable() ||
n.Type().IsSIMD() ||
n.OpenDeferSlot() { n.OpenDeferSlot() {
return false return false
} }