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[LoadStoreVectorize] Ignore interleaved invariant loads.

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The memory location an invariant load is using can never be clobbered by
any store, so it's safe to move the load ahead of the store.

Differential Revision: https://reviews.llvm.org/D46011

llvm-svn: 330725
This commit is contained in:
Benjamin Kramer
2018-04-24 15:28:47 +00:00
parent efe5afbc3d
commit f85f5da3b2
2 changed files with 41 additions and 5 deletions
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18
llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
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@@ -562,20 +562,28 @@ Vectorizer::getVectorizablePrefix(ArrayRef<Instruction *> Chain) {
if (BarrierMemoryInstr && OBB.dominates(BarrierMemoryInstr, MemInstr))
break;
if (isa<LoadInst>(MemInstr) && isa<LoadInst>(ChainInstr))
auto *MemLoad = dyn_cast<LoadInst>(MemInstr);
auto *ChainLoad = dyn_cast<LoadInst>(ChainInstr);
if (MemLoad && ChainLoad)
continue;
// We can ignore the alias if the we have a load store pair and the load
// is known to be invariant. The load cannot be clobbered by the store.
auto IsInvariantLoad = [](const LoadInst *LI) -> bool {
return LI->getMetadata(LLVMContext::MD_invariant_load);
};
// We can ignore the alias as long as the load comes before the store,
// because that means we won't be moving the load past the store to
// vectorize it (the vectorized load is inserted at the location of the
// first load in the chain).
if (isa<StoreInst>(MemInstr) && isa<LoadInst>(ChainInstr) &&
OBB.dominates(ChainInstr, MemInstr))
if (isa<StoreInst>(MemInstr) && ChainLoad &&
(IsInvariantLoad(ChainLoad) || OBB.dominates(ChainLoad, MemInstr)))
continue;
// Same case, but in reverse.
if (isa<LoadInst>(MemInstr) && isa<StoreInst>(ChainInstr) &&
OBB.dominates(MemInstr, ChainInstr))
if (MemLoad && isa<StoreInst>(ChainInstr) &&
(IsInvariantLoad(MemLoad) || OBB.dominates(MemLoad, ChainInstr)))
continue;
if (!AA.isNoAlias(MemoryLocation::get(MemInstr),