1 files changed, 11 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index e1cf417..0f72e4b 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -1392,7 +1392,7 @@ MachineConstantPool::~MachineConstantPool() {
 }
 
 /// Test whether the given two constants can be allocated the same constant pool
-/// entry.
+/// entry referenced by \param A.
 static bool CanShareConstantPoolEntry(const Constant *A, const Constant *B,
                                       const DataLayout &DL) {
   // Handle the trivial case quickly.
@@ -1412,6 +1412,8 @@ static bool CanShareConstantPoolEntry(const Constant *A, const Constant *B,
   if (StoreSize != DL.getTypeStoreSize(B->getType()) || StoreSize > 128)
     return false;
 
+  bool ContainsUndefOrPoisonA = A->containsUndefOrPoisonElement();
+
   Type *IntTy = IntegerType::get(A->getContext(), StoreSize*8);
 
   // Try constant folding a bitcast of both instructions to an integer.  If we
@@ -1431,7 +1433,14 @@ static bool CanShareConstantPoolEntry(const Constant *A, const Constant *B,
     B = ConstantFoldCastOperand(Instruction::BitCast, const_cast<Constant *>(B),
                                 IntTy, DL);
 
-  return A == B;
+  if (A != B)
+    return false;
+
+  // Constants only safely match if A doesn't contain undef/poison.
+  // As we'll be reusing A, it doesn't matter if B contain undef/poison.
+  // TODO: Handle cases where A and B have the same undef/poison elements.
+  // TODO: Merge A and B with mismatching undef/poison elements.
+  return !ContainsUndefOrPoisonA;
 }
 
 /// Create a new entry in the constant pool or return an existing one.