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MemCpyOpt: replace an AA query with MSSA query (NFC) #108535

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Merged
merged 4 commits into from
Sep 24, 2024
Merged

MemCpyOpt: replace an AA query with MSSA query (NFC) #108535

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5ca5b93
MemCpyOpt: replace an AA query with MSSA query
artagnon Sep 13, 2024
c865654
MemCpyOpt: fix bug
artagnon Sep 14, 2024
3300903
MemCpyOpt: address review
artagnon Sep 23, 2024
db57832
MemCpyOpt: add test
artagnon Sep 23, 2024
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25 changes: 12 additions & 13 deletions llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -647,19 +647,18 @@ bool MemCpyOptPass::processStoreOfLoad(StoreInst *SI, LoadInst *LI,
(EnableMemCpyOptWithoutLibcalls ||
(TLI->has(LibFunc_memcpy) && TLI->has(LibFunc_memmove)))) {
MemoryLocation LoadLoc = MemoryLocation::get(LI);

// We use alias analysis to check if an instruction may store to
// the memory we load from in between the load and the store. If
// such an instruction is found, we try to promote there instead
// of at the store position.
// TODO: Can use MSSA for this.
Instruction *P = SI;
for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
if (isModSet(AA->getModRefInfo(&I, LoadLoc))) {
P = &I;
break;
}
}
MemoryUseOrDef *LoadAccess = MSSA->getMemoryAccess(LI),
*StoreAccess = MSSA->getMemoryAccess(SI);

// We use MSSA to check if an instruction may store to the memory we load
// from in between the load and the store. If such an instruction is found,
// we try to promote there instead of at the store position.
BatchAAResults BAA(*AA);
auto *Clobber =
cast<MemoryUseOrDef>(MSSA->getWalker()->getClobberingMemoryAccess(
StoreAccess->getDefiningAccess(), LoadLoc, BAA));
Instruction *P =
MSSA->dominates(LoadAccess, Clobber) ? Clobber->getMemoryInst() : SI;

// If we found an instruction that may write to the loaded memory,
// we can try to promote at this position instead of the store
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