include/llvm/ADT/GraphTraits.h

   1 //===- llvm/ADT/GraphTraits.h - Graph traits template -----------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the little GraphTraits<X> template class that should be
  10 // specialized by classes that want to be iteratable by generic graph iterators.
  11 //
  12 // This file also defines the marker class Inverse that is used to iterate over
  13 // graphs in a graph defined, inverse ordering...
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_ADT_GRAPHTRAITS_H
  18 #define LLVM_ADT_GRAPHTRAITS_H
  19
  20 #include "llvm/ADT/iterator_range.h"
  21
  22 namespace llvm {
  23
  24 // GraphTraits - This class should be specialized by different graph types...
  25 // which is why the default version is empty.
  26 //
  27 // This template evolved from supporting `BasicBlock` to also later supporting
  28 // more complex types (e.g. CFG and DomTree).
  29 //
  30 // GraphTraits can be used to create a view over a graph interpreting it
  31 // differently without requiring a copy of the original graph. This could
  32 // be achieved by carrying more data in NodeRef. See LoopBodyTraits for one
  33 // example.
  34 template<class GraphType>
  35 struct GraphTraits {
  36   // Elements to provide:
  37
  38   // typedef NodeRef           - Type of Node token in the graph, which should
  39   //                             be cheap to copy.
  40   // typedef ChildIteratorType - Type used to iterate over children in graph,
  41   //                             dereference to a NodeRef.
  42
  43   // static NodeRef getEntryNode(const GraphType &)
  44   //    Return the entry node of the graph
  45
  46   // static ChildIteratorType child_begin(NodeRef)
  47   // static ChildIteratorType child_end  (NodeRef)
  48   //    Return iterators that point to the beginning and ending of the child
  49   //    node list for the specified node.
  50
  51   // typedef  ...iterator nodes_iterator; - dereference to a NodeRef
  52   // static nodes_iterator nodes_begin(GraphType *G)
  53   // static nodes_iterator nodes_end  (GraphType *G)
  54   //    nodes_iterator/begin/end - Allow iteration over all nodes in the graph
  55
  56   // typedef EdgeRef           - Type of Edge token in the graph, which should
  57   //                             be cheap to copy.
  58   // typedef ChildEdgeIteratorType - Type used to iterate over children edges in
  59   //                             graph, dereference to a EdgeRef.
  60
  61   // static ChildEdgeIteratorType child_edge_begin(NodeRef)
  62   // static ChildEdgeIteratorType child_edge_end(NodeRef)
  63   //     Return iterators that point to the beginning and ending of the
  64   //     edge list for the given callgraph node.
  65   //
  66   // static NodeRef edge_dest(EdgeRef)
  67   //     Return the destination node of an edge.
  68
  69   // static unsigned       size       (GraphType *G)
  70   //    Return total number of nodes in the graph
  71
  72   // If anyone tries to use this class without having an appropriate
  73   // specialization, make an error.  If you get this error, it's because you
  74   // need to include the appropriate specialization of GraphTraits<> for your
  75   // graph, or you need to define it for a new graph type. Either that or
  76   // your argument to XXX_begin(...) is unknown or needs to have the proper .h
  77   // file #include'd.
  78   using NodeRef = typename GraphType::UnknownGraphTypeError;
  79 };
  80
  81 // Inverse - This class is used as a little marker class to tell the graph
  82 // iterator to iterate over the graph in a graph defined "Inverse" ordering.
  83 // Not all graphs define an inverse ordering, and if they do, it depends on
  84 // the graph exactly what that is.  Here's an example of usage with the
  85 // df_iterator:
  86 //
  87 // idf_iterator<Method*> I = idf_begin(M), E = idf_end(M);
  88 // for (; I != E; ++I) { ... }
  89 //
  90 // Which is equivalent to:
  91 // df_iterator<Inverse<Method*>> I = idf_begin(M), E = idf_end(M);
  92 // for (; I != E; ++I) { ... }
  93 //
  94 template <class GraphType>
  95 struct Inverse {
  96   const GraphType &Graph;
  97
  98   inline Inverse(const GraphType &G) : Graph(G) {}
  99 };
 100
 101 // Provide a partial specialization of GraphTraits so that the inverse of an
 102 // inverse falls back to the original graph.
 103 template <class T> struct GraphTraits<Inverse<Inverse<T>>> : GraphTraits<T> {};
 104
 105 // Provide iterator ranges for the graph traits nodes and children
 106 template <class GraphType>
 107 iterator_range<typename GraphTraits<GraphType>::nodes_iterator>
 108 nodes(const GraphType &G) {
 109   return make_range(GraphTraits<GraphType>::nodes_begin(G),
 110                     GraphTraits<GraphType>::nodes_end(G));
 111 }
 112 template <class GraphType>
 113 iterator_range<typename GraphTraits<Inverse<GraphType>>::nodes_iterator>
 114 inverse_nodes(const GraphType &G) {
 115   return make_range(GraphTraits<Inverse<GraphType>>::nodes_begin(G),
 116                     GraphTraits<Inverse<GraphType>>::nodes_end(G));
 117 }
 118
 119 template <class GraphType>
 120 iterator_range<typename GraphTraits<GraphType>::ChildIteratorType>
 121 children(const typename GraphTraits<GraphType>::NodeRef &G) {
 122   return make_range(GraphTraits<GraphType>::child_begin(G),
 123                     GraphTraits<GraphType>::child_end(G));
 124 }
 125
 126 template <class GraphType>
 127 iterator_range<typename GraphTraits<Inverse<GraphType>>::ChildIteratorType>
 128 inverse_children(const typename GraphTraits<GraphType>::NodeRef &G) {
 129   return make_range(GraphTraits<Inverse<GraphType>>::child_begin(G),
 130                     GraphTraits<Inverse<GraphType>>::child_end(G));
 131 }
 132
 133 template <class GraphType>
 134 iterator_range<typename GraphTraits<GraphType>::ChildEdgeIteratorType>
 135 children_edges(const typename GraphTraits<GraphType>::NodeRef &G) {
 136   return make_range(GraphTraits<GraphType>::child_edge_begin(G),
 137                     GraphTraits<GraphType>::child_edge_end(G));
 138 }
 139
 140 } // end namespace llvm
 141
 142 #endif // LLVM_ADT_GRAPHTRAITS_H