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//===- llvm/ADT/GraphTraits.h - Graph traits template -----------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

///

/// \file

/// 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_ADT_GRAPHTRAITS_H

#define LLVM_ADT_GRAPHTRAITS_H

#include "llvm/ADT/iterator_range.h"

namespace llvm {

// GraphTraits - This class should be specialized by different graph types...

// which is why the default version is empty.

//

// This template evolved from supporting `BasicBlock` to also later supporting

// more complex types (e.g. CFG and DomTree).

//

// GraphTraits can be used to create a view over a graph interpreting it

// differently without requiring a copy of the original graph. This could

// be achieved by carrying more data in NodeRef. See LoopBodyTraits for one

// example.

template<class GraphType>

struct GraphTraits {

  // Elements to provide:

  // typedef NodeRef           - Type of Node token in the graph, which should

  //                             be cheap to copy.

  // typedef ChildIteratorType - Type used to iterate over children in graph,

  //                             dereference to a NodeRef.

  // static NodeRef getEntryNode(const GraphType &)

  //    Return the entry node of the graph

  // static ChildIteratorType child_begin(NodeRef)

  // static ChildIteratorType child_end  (NodeRef)

  //    Return iterators that point to the beginning and ending of the child

  //    node list for the specified node.

  // typedef  ...iterator nodes_iterator; - dereference to a NodeRef

  // static nodes_iterator nodes_begin(GraphType *G)

  // static nodes_iterator nodes_end  (GraphType *G)

  //    nodes_iterator/begin/end - Allow iteration over all nodes in the graph

  // typedef EdgeRef           - Type of Edge token in the graph, which should

  //                             be cheap to copy.

  // typedef ChildEdgeIteratorType - Type used to iterate over children edges in

  //                             graph, dereference to a EdgeRef.

  // static ChildEdgeIteratorType child_edge_begin(NodeRef)

  // static ChildEdgeIteratorType child_edge_end(NodeRef)

  //     Return iterators that point to the beginning and ending of the

  //     edge list for the given callgraph node.

  //

  // static NodeRef edge_dest(EdgeRef)

  //     Return the destination node of an edge.

  // static unsigned       size       (GraphType *G)

  //    Return total number of nodes in the graph

  // 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. Either that or

  // your argument to XXX_begin(...) is unknown or needs to have the proper .h

  // file #include'd.

  using NodeRef = typename GraphType::UnknownGraphTypeError;

};

// 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:

//

// idf_iterator<Method*> I = idf_begin(M), E = idf_end(M);

// for (; I != E; ++I) { ... }

//

// Which is equivalent to:

// df_iterator<Inverse<Method*>> I = idf_begin(M), E = idf_end(M);

// for (; I != E; ++I) { ... }

//

template <class GraphType>

struct Inverse {

  const GraphType &Graph;

  inline Inverse(const GraphType &G) : Graph(G) {}

};

// Provide a partial specialization of GraphTraits so that the inverse of an

// inverse falls back to the original graph.

template <class T> struct GraphTraits<Inverse<Inverse<T>>> : GraphTraits<T> {};

// Provide iterator ranges for the graph traits nodes and children

template <class GraphType>

iterator_range<typename GraphTraits<GraphType>::nodes_iterator>

nodes(const GraphType &G) {

  return make_range(GraphTraits<GraphType>::nodes_begin(G),

                    GraphTraits<GraphType>::nodes_end(G));

}

template <class GraphType>

iterator_range<typename GraphTraits<Inverse<GraphType>>::nodes_iterator>

inverse_nodes(const GraphType &G) {

  return make_range(GraphTraits<Inverse<GraphType>>::nodes_begin(G),

                    GraphTraits<Inverse<GraphType>>::nodes_end(G));

}

template <class GraphType>

iterator_range<typename GraphTraits<GraphType>::ChildIteratorType>

children(const typename GraphTraits<GraphType>::NodeRef &G) {

  return make_range(GraphTraits<GraphType>::child_begin(G),

                    GraphTraits<GraphType>::child_end(G));

}

template <class GraphType>

iterator_range<typename GraphTraits<Inverse<GraphType>>::ChildIteratorType>

inverse_children(const typename GraphTraits<GraphType>::NodeRef &G) {

  return make_range(GraphTraits<Inverse<GraphType>>::child_begin(G),

                    GraphTraits<Inverse<GraphType>>::child_end(G));

}

template <class GraphType>

iterator_range<typename GraphTraits<GraphType>::ChildEdgeIteratorType>

children_edges(const typename GraphTraits<GraphType>::NodeRef &G) {

  return make_range(GraphTraits<GraphType>::child_edge_begin(G),

                    GraphTraits<GraphType>::child_edge_end(G));

}

} // end namespace llvm

#endif // LLVM_ADT_GRAPHTRAITS_H