Teach memdep to use pointsToConstantMemory to determine that loads
from constant memory don't alias any stores.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117636 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 5940105..c72cd1e 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -161,8 +161,9 @@
}
/// getPointerDependencyFrom - Return the instruction on which a memory
-/// location depends. If isLoad is true, this routine ignore may-aliases with
-/// read-only operations.
+/// location depends. If isLoad is true, this routine ignores may-aliases with
+/// read-only operations. If isLoad is false, this routine ignores may-aliases
+/// with reads from read-only locations.
MemDepResult MemoryDependenceAnalysis::
getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
BasicBlock::iterator ScanIt, BasicBlock *BB) {
@@ -225,17 +226,21 @@
Value *Pointer = LI->getPointerOperand();
uint64_t PointerSize = AA->getTypeStoreSize(LI->getType());
MDNode *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
+ AliasAnalysis::Location LoadLoc(Pointer, PointerSize, TBAATag);
// If we found a pointer, check if it could be the same as our pointer.
- AliasAnalysis::AliasResult R =
- AA->alias(AliasAnalysis::Location(Pointer, PointerSize, TBAATag),
- MemLoc);
+ AliasAnalysis::AliasResult R = AA->alias(LoadLoc, MemLoc);
if (R == AliasAnalysis::NoAlias)
continue;
// May-alias loads don't depend on each other without a dependence.
if (isLoad && R == AliasAnalysis::MayAlias)
continue;
+
+ // Stores don't alias loads from read-only memory.
+ if (!isLoad && AA->pointsToConstantMemory(LoadLoc))
+ continue;
+
// Stores depend on may and must aliased loads, loads depend on must-alias
// loads.
return MemDepResult::getDef(Inst);