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[LoadStoreVectorizer] Batch alias analysis results to improve compile time #147555

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Merged
merged 2 commits into from
Jul 10, 2025
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[LoadStoreVectorizer] Batch alias analysis results to improve compile time #147555

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[LoadStoreVectorizer] Batch alias analysis results to improve compile…
dakersnar Jul 3, 2025
26e937c
Simplify test using loop unrolling
dakersnar Jul 8, 2025
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17 changes: 12 additions & 5 deletions llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -322,7 +322,8 @@ class Vectorizer {
template <bool IsLoadChain>
bool isSafeToMove(
Instruction *ChainElem, Instruction *ChainBegin,
const DenseMap<Instruction *, APInt /*OffsetFromLeader*/> &ChainOffsets);
const DenseMap<Instruction *, APInt /*OffsetFromLeader*/> &ChainOffsets,
BatchAAResults &BatchAA);

/// Merges the equivalence classes if they have underlying objects that differ
/// by one level of indirection (i.e., one is a getelementptr and the other is
Expand Down Expand Up @@ -543,6 +544,10 @@ std::vector<Chain> Vectorizer::splitChainByMayAliasInstrs(Chain &C) {
for (const auto &E : C)
ChainOffsets.insert({&*E.Inst, E.OffsetFromLeader});

// Across a single invocation of this function the IR is not changing, so
// using a batched Alias Analysis is safe and can reduce compile time.
BatchAAResults BatchAA(AA);

// Loads get hoisted up to the first load in the chain. Stores get sunk
// down to the last store in the chain. Our algorithm for loads is:
//
Expand All @@ -569,7 +574,7 @@ std::vector<Chain> Vectorizer::splitChainByMayAliasInstrs(Chain &C) {
NewChain.emplace_back(*ChainBegin);
for (auto ChainIt = std::next(ChainBegin); ChainIt != ChainEnd; ++ChainIt) {
if (isSafeToMove<IsLoad>(ChainIt->Inst, NewChain.front().Inst,
ChainOffsets)) {
ChainOffsets, BatchAA)) {
LLVM_DEBUG(dbgs() << "LSV: No intervening may-alias instrs; can merge "
<< *ChainIt->Inst << " into " << *ChainBegin->Inst
<< "\n");
Expand Down Expand Up @@ -999,7 +1004,8 @@ bool Vectorizer::vectorizeChain(Chain &C) {
template <bool IsLoadChain>
bool Vectorizer::isSafeToMove(
Instruction *ChainElem, Instruction *ChainBegin,
const DenseMap<Instruction *, APInt /*OffsetFromLeader*/> &ChainOffsets) {
const DenseMap<Instruction *, APInt /*OffsetFromLeader*/> &ChainOffsets,
BatchAAResults &BatchAA) {
LLVM_DEBUG(dbgs() << "LSV: isSafeToMove(" << *ChainElem << " -> "
<< *ChainBegin << ")\n");

Expand Down Expand Up @@ -1066,7 +1072,8 @@ bool Vectorizer::isSafeToMove(
LLVM_DEBUG({
// Double check that AA also sees this alias. If not, we probably
// have a bug.
ModRefInfo MR = AA.getModRefInfo(I, MemoryLocation::get(ChainElem));
ModRefInfo MR =
BatchAA.getModRefInfo(I, MemoryLocation::get(ChainElem));
assert(IsLoadChain ? isModSet(MR) : isModOrRefSet(MR));
dbgs() << "LSV: Found alias in chain: " << *I << "\n";
});
Expand All @@ -1077,7 +1084,7 @@ bool Vectorizer::isSafeToMove(
}

LLVM_DEBUG(dbgs() << "LSV: Querying AA for " << *I << "\n");
ModRefInfo MR = AA.getModRefInfo(I, MemoryLocation::get(ChainElem));
ModRefInfo MR = BatchAA.getModRefInfo(I, MemoryLocation::get(ChainElem));
if (IsLoadChain ? isModSet(MR) : isModOrRefSet(MR)) {
LLVM_DEBUG(dbgs() << "LSV: Found alias in chain:\n"
<< " Aliasing instruction:\n"
Expand Down
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