[C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.

llvm-svn: 206142
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
index 1483fdd..aceb2b4 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
@@ -124,9 +124,9 @@
 
     static void addCustomGraphFeatures(SelectionDAG *G,
                                        GraphWriter<SelectionDAG*> &GW) {
-      GW.emitSimpleNode(0, "plaintext=circle", "GraphRoot");
+      GW.emitSimpleNode(nullptr, "plaintext=circle", "GraphRoot");
       if (G->getRoot().getNode())
-        GW.emitEdge(0, -1, G->getRoot().getNode(), G->getRoot().getResNo(),
+        GW.emitEdge(nullptr, -1, G->getRoot().getNode(), G->getRoot().getResNo(),
                     "color=blue,style=dashed");
     }
   };
@@ -289,10 +289,10 @@
 void ScheduleDAGSDNodes::getCustomGraphFeatures(GraphWriter<ScheduleDAG*> &GW) const {
   if (DAG) {
     // Draw a special "GraphRoot" node to indicate the root of the graph.
-    GW.emitSimpleNode(0, "plaintext=circle", "GraphRoot");
+    GW.emitSimpleNode(nullptr, "plaintext=circle", "GraphRoot");
     const SDNode *N = DAG->getRoot().getNode();
     if (N && N->getNodeId() != -1)
-      GW.emitEdge(0, -1, &SUnits[N->getNodeId()], -1,
+      GW.emitEdge(nullptr, -1, &SUnits[N->getNodeId()], -1,
                   "color=blue,style=dashed");
   }
 }