enhance jump threading to preserve TBAA information when PRE'ing loads,
fixing rdar://11039258, an issue that came up when inspecting clang's
bootstrapped codegen.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152635 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 4ef5298..429b61b 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -857,6 +857,9 @@
if (BBIt != LoadBB->begin())
return false;
+ // If all of the loads and stores that feed the value have the same TBAA tag,
+ // then we can propagate it onto any newly inserted loads.
+ MDNode *TBAATag = LI->getMetadata(LLVMContext::MD_tbaa);
SmallPtrSet<BasicBlock*, 8> PredsScanned;
typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
@@ -875,11 +878,16 @@
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
- Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
+ MDNode *ThisTBAATag = 0;
+ Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
+ 0, &ThisTBAATag);
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;
}
+
+ // If tbaa tags disagree or are not present, forget about them.
+ if (TBAATag != ThisTBAATag) TBAATag = 0;
// If so, this load is partially redundant. Remember this info so that we
// can create a PHI node.
@@ -939,6 +947,9 @@
LI->getAlignment(),
UnavailablePred->getTerminator());
NewVal->setDebugLoc(LI->getDebugLoc());
+ if (TBAATag)
+ NewVal->setMetadata(LLVMContext::MD_tbaa, TBAATag);
+
AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
}