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[SimplifyCFG] Only consider provenance capture in store speculation #138548

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May 22, 2025
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[SimplifyCFG] Only consider provenance capture in store speculation #138548

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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3057,7 +3057,9 @@ static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
Value *Obj = getUnderlyingObject(StorePtr);
bool ExplicitlyDereferenceableOnly;
if (isWritableObject(Obj, ExplicitlyDereferenceableOnly) &&
!PointerMayBeCaptured(Obj, /*ReturnCaptures=*/false) &&
capturesNothing(
PointerMayBeCaptured(Obj, /*ReturnCaptures=*/false,
CaptureComponents::Provenance)) &&
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Similar pattern in LICM:

llvm-project/llvm/lib/Transforms/Scalar/LICM.cpp

Lines 2188 to 2200 in 6a99d81

// We know we can hoist the load, but don't have a guaranteed store.
// Check whether the location is writable and thread-local. If it is, then we
// can insert stores along paths which originally didn't have them without
// violating the memory model.
if (StoreSafety == StoreSafetyUnknown) {
Value *Object = getUnderlyingObject(SomePtr);
bool ExplicitlyDereferenceableOnly;
if (isWritableObject(Object, ExplicitlyDereferenceableOnly) &&
(!ExplicitlyDereferenceableOnly ||
isDereferenceablePointer(SomePtr, AccessTy, MDL)) &&
isThreadLocalObject(Object, CurLoop, DT, TTI))
StoreSafety = StoreSafe;
}

llvm-project/llvm/lib/Transforms/Scalar/LICM.cpp

Lines 1925 to 1954 in 6a99d81

bool isNotCapturedBeforeOrInLoop(const Value *V, const Loop *L,
DominatorTree *DT) {
// We can perform the captured-before check against any instruction in the
// loop header, as the loop header is reachable from any instruction inside
// the loop.
// TODO: ReturnCaptures=true shouldn't be necessary here.
return !PointerMayBeCapturedBefore(V, /* ReturnCaptures */ true,
L->getHeader()->getTerminator(), DT);
}
/// Return true if we can prove that a caller cannot inspect the object if an
/// unwind occurs inside the loop.
bool isNotVisibleOnUnwindInLoop(const Value *Object, const Loop *L,
DominatorTree *DT) {
bool RequiresNoCaptureBeforeUnwind;
if (!isNotVisibleOnUnwind(Object, RequiresNoCaptureBeforeUnwind))
return false;
return !RequiresNoCaptureBeforeUnwind ||
isNotCapturedBeforeOrInLoop(Object, L, DT);
}
bool isThreadLocalObject(const Value *Object, const Loop *L, DominatorTree *DT,
TargetTransformInfo *TTI) {
// The object must be function-local to start with, and then not captured
// before/in the loop.
return (isIdentifiedFunctionLocal(Object) &&
isNotCapturedBeforeOrInLoop(Object, L, DT)) ||
(TTI->isSingleThreaded() || SingleThread);
}

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Updated in #141731.

(!ExplicitlyDereferenceableOnly ||
isDereferenceablePointer(StorePtr, StoreTy,
LI->getDataLayout()))) {
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7 changes: 2 additions & 5 deletions llvm/test/Transforms/SimplifyCFG/speculate-store.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -203,11 +203,8 @@ define i32 @load_before_store_escape_addr_only(i64 %i, i32 %b) {
; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds [2 x i32], ptr [[A]], i64 0, i64 [[I:%.*]]
; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[TMP0]], [[B:%.*]]
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: store i32 [[B]], ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[SPEC_STORE_SELECT:%.*]] = select i1 [[CMP]], i32 [[B]], i32 [[TMP0]]
; CHECK-NEXT: store i32 [[SPEC_STORE_SELECT]], ptr [[ARRAYIDX]], align 4
; CHECK-NEXT: [[TMP1:%.*]] = load i32, ptr [[A]], align 4
; CHECK-NEXT: [[ARRAYIDX2:%.*]] = getelementptr inbounds [2 x i32], ptr [[A]], i64 0, i64 1
; CHECK-NEXT: [[TMP2:%.*]] = load i32, ptr [[ARRAYIDX2]], align 4
Expand Down