Pull iterators out of CFG.h and genericize them with GraphTraits

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@666 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/GraphTraits.h

@@ -0,0 +1,59 @@
+//===-- llvm/Support/GraphTraits.h - Graph traits template -------*- C++ -*--=//
+//
+// This file defines the little GraphTraits<X> template class that should be 
+// specialized by classes that want to be iteratable by generic graph iterators.
+//
+// This file also defines the marker class Inverse that is used to iterate over
+// graphs in a graph defined, inverse ordering...
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_GRAPH_TRAITS_H
+#define LLVM_SUPPORT_GRAPH_TRAITS_H
+
+// GraphTraits - This class should be specialized by different graph types...
+// which is why the default version is empty.
+//
+template<class GraphType>
+struct GraphTraits {
+  // Elements to provide:
+
+  // typedef NodeType          - Type of Node in the graph
+  // typedef ChildIteratorType - Type used to iterate over children in graph
+
+  // static NodeType *getEntryNode(GraphType *)
+  //    Return the entry node of the graph
+
+  // static ChildIteratorType child_begin(NodeType *)
+  // static ChildIteratorType child_end  (NodeType *)
+  //    Return iterators that point to the beginning and ending of the child 
+  //    node list for the specified node.
+  //  
+
+
+  // If anyone tries to use this class without having an appropriate
+  // specialization make an error.  If you get this error, it's because you
+  // need to include the appropriate specialization of GraphTraits<> for your
+  // graph, or you need to define it for a new graph type.
+  //
+  typedef typename GraphType::UnknownGraphTypeError NodeType;
+};
+
+
+// Inverse - This class is used as a little marker class to tell the graph
+// iterator to iterate over the graph in a graph defined "Inverse" ordering.
+// Not all graphs define an inverse ordering, and if they do, it depends on
+// the graph exactly what that is.  Here's an example of usage with the
+// df_iterator:
+//
+// df_iterator<Inverse<Method> > I = idf_begin(M), E = idf_end(M);
+// for (; I != E; ++I) { ... }
+//
+template <class GraphType>
+struct Inverse {
+  GraphType &Graph;
+
+  inline Inverse(GraphType &G) : Graph(G) {}
+};
+
+#endif