[SelectionDAG] Use DAG.getNOT to further simplify some code. NFC

Followup to D109483

Author: topperc

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -3240,8 +3240,7 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     assert(TLI.isOperationLegalOrCustom(ISD::ADD, VT) &&
            TLI.isOperationLegalOrCustom(ISD::XOR, VT) &&
            "Don't know how to expand this subtraction!");
-    Tmp1 = DAG.getNode(ISD::XOR, dl, VT, Node->getOperand(1),
-                       DAG.getAllOnesConstant(dl, VT));
+    Tmp1 = DAG.getNOT(dl, Node->getOperand(1), VT);
     Tmp1 = DAG.getNode(ISD::ADD, dl, VT, Tmp1, DAG.getConstant(1, dl, VT));
     Results.push_back(DAG.getNode(ISD::ADD, dl, VT, Node->getOperand(0), Tmp1));
     break;

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp

@@ -958,8 +958,7 @@ SDValue VectorLegalizer::ExpandSELECT(SDNode *Node) {
   Op1 = DAG.getNode(ISD::BITCAST, DL, MaskTy, Op1);
   Op2 = DAG.getNode(ISD::BITCAST, DL, MaskTy, Op2);
 
-  SDValue AllOnes = DAG.getAllOnesConstant(DL, MaskTy);
-  SDValue NotMask = DAG.getNode(ISD::XOR, DL, MaskTy, Mask, AllOnes);
+  SDValue NotMask = DAG.getNOT(DL, Mask, MaskTy);
 
   Op1 = DAG.getNode(ISD::AND, DL, MaskTy, Op1, Mask);
   Op2 = DAG.getNode(ISD::AND, DL, MaskTy, Op2, NotMask);
@@ -1204,8 +1203,7 @@ SDValue VectorLegalizer::ExpandVSELECT(SDNode *Node) {
   Op1 = DAG.getNode(ISD::BITCAST, DL, VT, Op1);
   Op2 = DAG.getNode(ISD::BITCAST, DL, VT, Op2);
 
-  SDValue AllOnes = DAG.getAllOnesConstant(DL, VT);
-  SDValue NotMask = DAG.getNode(ISD::XOR, DL, VT, Mask, AllOnes);
+  SDValue NotMask = DAG.getNOT(DL, Mask, VT);
 
   Op1 = DAG.getNode(ISD::AND, DL, VT, Op1, Mask);
   Op2 = DAG.getNode(ISD::AND, DL, VT, Op2, NotMask);