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.
llvm-svn: 48792
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2229743..e24a294 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/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;