llvm/llvm/include/llvm/ADT/GraphTraits.h

//===- 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/STLExtras.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 { … };

namespace detail {
has_number_t;
} // namespace detail

/// Indicate whether a GraphTraits<NodeT>::getNumber() is supported.
GraphHasNodeNumbers;

// 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 { … };

// Provide a partial specialization of GraphTraits so that the inverse of an
// inverse falls back to the original graph.
GraphTraits<Inverse<Inverse<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) { … }
template <class GraphType>
iterator_range<typename GraphTraits<Inverse<GraphType>>::nodes_iterator>
inverse_nodes(const GraphType &G) { … }

template <class GraphType>
iterator_range<typename GraphTraits<GraphType>::ChildIteratorType>
children(const typename GraphTraits<GraphType>::NodeRef &G) { … }

template <class GraphType>
iterator_range<typename GraphTraits<Inverse<GraphType>>::ChildIteratorType>
inverse_children(const typename GraphTraits<GraphType>::NodeRef &G) { … }

template <class GraphType>
iterator_range<typename GraphTraits<GraphType>::ChildEdgeIteratorType>
children_edges(const typename GraphTraits<GraphType>::NodeRef &G) { … }

} // end namespace llvm

#endif // LLVM_ADT_GRAPHTRAITS_H