[DAGCombiner] Pass SDNodeFlags to getNode instead of modifying nodes. (#148744)

getNode has logic to intersect flags correctly if the new node happens
to CSE with an existing node. Setting node flags after getNode bypasses
this logic and may change the node for other uses where the flags don't
hold.

Author: topperc

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -13485,11 +13485,9 @@ SDValue DAGCombiner::visitSELECT_CC(SDNode *N) {
 
     // Fold to a simpler select_cc
     if (SCC.getOpcode() == ISD::SETCC) {
-      SDValue SelectOp =
-          DAG.getNode(ISD::SELECT_CC, DL, N2.getValueType(), SCC.getOperand(0),
-                      SCC.getOperand(1), N2, N3, SCC.getOperand(2));
-      SelectOp->setFlags(SCC->getFlags());
-      return SelectOp;
+      return DAG.getNode(ISD::SELECT_CC, DL, N2.getValueType(),
+                         SCC.getOperand(0), SCC.getOperand(1), N2, N3,
+                         SCC.getOperand(2), SCC->getFlags());
     }
   }
 
@@ -28640,9 +28638,9 @@ SDValue DAGCombiner::foldSelectOfBinops(SDNode *N) {
     SDValue N10 = N1.getOperand(0);
     SDValue N20 = N2.getOperand(0);
     SDValue NewSel = DAG.getSelect(DL, N10.getValueType(), N0, N10, N20);
-    SDValue NewBinOp = DAG.getNode(BinOpc, DL, OpVTs, NewSel, N1.getOperand(1));
-    NewBinOp->setFlags(N1->getFlags());
-    NewBinOp->intersectFlagsWith(N2->getFlags());
+    SDNodeFlags Flags = N1->getFlags() & N2->getFlags();
+    SDValue NewBinOp =
+        DAG.getNode(BinOpc, DL, OpVTs, {NewSel, N1.getOperand(1)}, Flags);
     return SDValue(NewBinOp.getNode(), N1.getResNo());
   }
 
@@ -28654,10 +28652,9 @@ SDValue DAGCombiner::foldSelectOfBinops(SDNode *N) {
     // Second op VT might be different (e.g. shift amount type)
     if (N11.getValueType() == N21.getValueType()) {
       SDValue NewSel = DAG.getSelect(DL, N11.getValueType(), N0, N11, N21);
+      SDNodeFlags Flags = N1->getFlags() & N2->getFlags();
       SDValue NewBinOp =
-          DAG.getNode(BinOpc, DL, OpVTs, N1.getOperand(0), NewSel);
-      NewBinOp->setFlags(N1->getFlags());
-      NewBinOp->intersectFlagsWith(N2->getFlags());
+          DAG.getNode(BinOpc, DL, OpVTs, {N1.getOperand(0), NewSel}, Flags);
       return SDValue(NewBinOp.getNode(), N1.getResNo());
     }
   }