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ValueTracking: Do not look at users of constants for ephemeral values #134618

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merged 2 commits into from
Apr 9, 2025
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ValueTracking: Do not look at users of constants for ephemeral values #134618

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ValueTracking: Do not look at users of constants for ephemeral values
arsenm Apr 7, 2025
b4bde69
Change type of set and list
arsenm Apr 8, 2025
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29 changes: 16 additions & 13 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -446,9 +446,9 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
}

static bool isEphemeralValueOf(const Instruction *I, const Value *E) {
SmallVector<const Value *, 16> WorkSet(1, I);
SmallPtrSet<const Value *, 32> Visited;
SmallPtrSet<const Value *, 16> EphValues;
SmallVector<const Instruction *, 16> WorkSet(1, I);
SmallPtrSet<const Instruction *, 32> Visited;
SmallPtrSet<const Instruction *, 16> EphValues;

// The instruction defining an assumption's condition itself is always
// considered ephemeral to that assumption (even if it has other
Expand All @@ -457,23 +457,26 @@ static bool isEphemeralValueOf(const Instruction *I, const Value *E) {
return true;

while (!WorkSet.empty()) {
const Value *V = WorkSet.pop_back_val();
const Instruction *V = WorkSet.pop_back_val();
if (!Visited.insert(V).second)
continue;

// If all uses of this value are ephemeral, then so is this value.
if (llvm::all_of(V->users(), [&](const User *U) {
return EphValues.count(U);
})) {
if (all_of(V->users(), [&](const User *U) {
return EphValues.count(cast<Instruction>(U));
})) {
if (V == E)
return true;

if (V == I || (isa<Instruction>(V) &&
!cast<Instruction>(V)->mayHaveSideEffects() &&
!cast<Instruction>(V)->isTerminator())) {
EphValues.insert(V);
if (const User *U = dyn_cast<User>(V))
append_range(WorkSet, U->operands());
if (V == I || (!V->mayHaveSideEffects() && !V->isTerminator())) {
EphValues.insert(V);

if (const User *U = dyn_cast<User>(V)) {
for (const Use &U : U->operands()) {
if (const auto *I = dyn_cast<Instruction>(U.get()))
WorkSet.push_back(I);
}
}
}
}
}
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