make memdep use the getModRefInfo method for stores instead of the
low-level alias() method, allowing it to reason more aggressively
about pointers into constant memory. PR4189
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72403 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 74c9621..3b21029 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -202,9 +202,17 @@
}
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ // If alias analysis can tell that this store is guaranteed to not modify
+ // the query pointer, ignore it. Use getModRefInfo to handle cases where
+ // the query pointer points to constant memory etc.
+ if (AA->getModRefInfo(SI, MemPtr, MemSize) == AliasAnalysis::NoModRef)
+ continue;
+
+ // Ok, this store might clobber the query pointer. Check to see if it is
+ // a must alias: in this case, we want to return this as a def.
Value *Pointer = SI->getPointerOperand();
uint64_t PointerSize = TD->getTypeStoreSize(SI->getOperand(0)->getType());
-
+
// If we found a pointer, check if it could be the same as our pointer.
AliasAnalysis::AliasResult R =
AA->alias(Pointer, PointerSize, MemPtr, MemSize);