DAG: Fix getNode dropping flags if there's a glue output

The AMDGPU non-strict fdiv lowering needs to introduce an FP mode
switch in some cases, and has custom nodes to provide chain/glue for
the intermediate FP operations. We need to propagate nofpexcept here,
but getNode was dropping the flags.

Adding nofpexcept in the AMDGPU custom lowering is left to a future
patch.

Also fix a second case where flags were dropped, but in this case it
seems it just didn't handle this number of operands.

Test will be included in future AMDGPU patch.

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -7444,6 +7444,7 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     createOperands(N, Ops);
   }
 
+  N->setFlags(Flags);
   InsertNode(N);
   SDValue V(N, 0);
   NewSDValueDbgMsg(V, "Creating new node: ", this);
@@ -7525,13 +7526,14 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, SDVTList VTList,
       return SDValue(E, 0);
 
     N = newSDNode<SDNode>(Opcode, DL.getIROrder(), DL.getDebugLoc(), VTList);
-    N->setFlags(Flags);
     createOperands(N, Ops);
     CSEMap.InsertNode(N, IP);
   } else {
     N = newSDNode<SDNode>(Opcode, DL.getIROrder(), DL.getDebugLoc(), VTList);
     createOperands(N, Ops);
   }
+
+  N->setFlags(Flags);
   InsertNode(N);
   SDValue V(N, 0);
   NewSDValueDbgMsg(V, "Creating new node: ", this);