Handle a special case xor undef, undef -> 0. Technically this should be transformed to undef. But this is such a common idiom (misuse) we are going to handle it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48792 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2229743..e24a294 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2119,6 +2119,9 @@
if (FoldedVOp.Val) return FoldedVOp;
}
+ // fold (xor undef, undef) -> 0. This is a common idiom (misuse).
+ if (N0.getOpcode() == ISD::UNDEF && N1.getOpcode() == ISD::UNDEF)
+ return DAG.getConstant(0, VT);
// fold (xor x, undef) -> undef
if (N0.getOpcode() == ISD::UNDEF)
return N0;