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-rw-r--r--llvm/lib/Analysis/MemoryDependenceAnalysis.cpp9
1 files changed, 9 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index ab29393..716e3e6 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -408,6 +408,10 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
// it is racy (undefined) or there is a release followed by an acquire
// between the pair of accesses under consideration.
+ // If the load is invariant, we "know" that it doesn't alias *any* write. We
+ // do want to respect mustalias results since defs are useful for value
+ // forwarding, but any mayalias write can be assumed to be noalias.
+ // Arguably, this logic should be pushed inside AliasAnalysis itself.
if (isLoad && QueryInst) {
LoadInst *LI = dyn_cast<LoadInst>(QueryInst);
if (LI && LI->getMetadata(LLVMContext::MD_invariant_load) != nullptr)
@@ -601,6 +605,8 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
if (AccessPtr == Inst || AA->isMustAlias(Inst, AccessPtr))
return MemDepResult::getDef(Inst);
+ if (isInvariantLoad)
+ continue;
// Be conservative if the accessed pointer may alias the allocation.
if (AA->alias(Inst, AccessPtr) != AliasAnalysis::NoAlias)
return MemDepResult::getClobber(Inst);
@@ -611,6 +617,9 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
continue;
}
+ if (isInvariantLoad)
+ continue;
+
// See if this instruction (e.g. a call or vaarg) mod/ref's the pointer.
AliasAnalysis::ModRefResult MR = AA->getModRefInfo(Inst, MemLoc);
// If necessary, perform additional analysis.