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[SCEV] Don't perform implication checks with many predicates #158652

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Sep 16, 2025
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[SCEV] Don't perform implication checks with many predicates #158652

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9 changes: 7 additions & 2 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15176,15 +15176,20 @@ void SCEVUnionPredicate::add(const SCEVPredicate *N, ScalarEvolution &SE) {
return;
}

// Implication checks are quadratic in the number of predicates. Stop doing
// them if there are many predicates, as they should be too expensive to use
// anyway at that point.
bool CheckImplies = Preds.size() < 16;

// Only add predicate if it is not already implied by this union predicate.
if (implies(N, SE))
if (CheckImplies && implies(N, SE))
return;

// Build a new vector containing the current predicates, except the ones that
// are implied by the new predicate N.
SmallVector<const SCEVPredicate *> PrunedPreds;
for (auto *P : Preds) {
if (N->implies(P, SE))
if (CheckImplies && N->implies(P, SE))
continue;
PrunedPreds.push_back(P);
}
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