Previously GraphWriter assumed operator*() for node_iterator always

returned a reference type.  This patch allows operator*() to return a
non-reference type while still maintaining the old behavior when it
does return a reference type.

This patch was motivated when I tried to use "df_iterator" (see
llvm/ADT/DepthFirstIterator.h) as a "node_iterator", as df_iterator
does not return a reference type and thus we would get a compilation
error when trying to take the address of a temporary.

llvm-svn: 42151

llvm/include/llvm/Support/GraphWriter.h

@@ -101,7 +101,11 @@ public:
     // Loop over the graph, printing it out...
     for (node_iterator I = GTraits::nodes_begin(G), E = GTraits::nodes_end(G);
          I != E; ++I)
-      writeNode(&*I);
+      writeNode(*I);
+  }
+  
+  void writeNode(NodeType& Node) {
+    writeNode(&Node);
   }
 
   void writeNode(NodeType *const *Node) {