[DAG] use !isUndef() ; NFCI

llvm-svn: 263453
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 3881415..ee58e5f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -423,7 +423,7 @@
     NewMask = APInt::getAllOnesValue(BitWidth);
   } else if (DemandedMask == 0) {
     // Not demanding any bits from Op.
-    if (Op.getOpcode() != ISD::UNDEF)
+    if (!Op.isUndef())
       return TLO.CombineTo(Op, TLO.DAG.getUNDEF(Op.getValueType()));
     return false;
   } else if (Depth == 6) {        // Limit search depth.