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DepthFirstIterator.h
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1 //===- llvm/ADT/DepthFirstIterator.h - Depth First iterator -----*- 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 builds on the ADT/GraphTraits.h file to build generic depth
10 // first graph iterator. This file exposes the following functions/types:
11 //
12 // df_begin/df_end/df_iterator
13 // * Normal depth-first iteration - visit a node and then all of its children.
14 //
15 // idf_begin/idf_end/idf_iterator
16 // * Depth-first iteration on the 'inverse' graph.
17 //
18 // df_ext_begin/df_ext_end/df_ext_iterator
19 // * Normal depth-first iteration - visit a node and then all of its children.
20 // This iterator stores the 'visited' set in an external set, which allows
21 // it to be more efficient, and allows external clients to use the set for
22 // other purposes.
23 //
24 // idf_ext_begin/idf_ext_end/idf_ext_iterator
25 // * Depth-first iteration on the 'inverse' graph.
26 // This iterator stores the 'visited' set in an external set, which allows
27 // it to be more efficient, and allows external clients to use the set for
28 // other purposes.
29 //
30 //===----------------------------------------------------------------------===//
31 
32 #ifndef LLVM_ADT_DEPTHFIRSTITERATOR_H
33 #define LLVM_ADT_DEPTHFIRSTITERATOR_H
34 
35 #include "llvm/ADT/GraphTraits.h"
36 #include "llvm/ADT/None.h"
37 #include "llvm/ADT/Optional.h"
38 #include "llvm/ADT/SmallPtrSet.h"
40 #include <iterator>
41 #include <set>
42 #include <utility>
43 #include <vector>
44 
45 namespace llvm {
46 
47 // df_iterator_storage - A private class which is used to figure out where to
48 // store the visited set.
49 template<class SetType, bool External> // Non-external set
51 public:
52  SetType Visited;
53 };
54 
55 template<class SetType>
56 class df_iterator_storage<SetType, true> {
57 public:
58  df_iterator_storage(SetType &VSet) : Visited(VSet) {}
60 
61  SetType &Visited;
62 };
63 
64 // The visited stated for the iteration is a simple set augmented with
65 // one more method, completed, which is invoked when all children of a
66 // node have been processed. It is intended to distinguish of back and
67 // cross edges in the spanning tree but is not used in the common case.
68 template <typename NodeRef, unsigned SmallSize=8>
69 struct df_iterator_default_set : public SmallPtrSet<NodeRef, SmallSize> {
71  using iterator = typename BaseSet::iterator;
72 
73  std::pair<iterator,bool> insert(NodeRef N) { return BaseSet::insert(N); }
74  template <typename IterT>
75  void insert(IterT Begin, IterT End) { BaseSet::insert(Begin,End); }
76 
77  void completed(NodeRef) {}
78 };
79 
80 // Generic Depth First Iterator
81 template <class GraphT,
82  class SetType =
84  bool ExtStorage = false, class GT = GraphTraits<GraphT>>
86  : public std::iterator<std::forward_iterator_tag, typename GT::NodeRef>,
87  public df_iterator_storage<SetType, ExtStorage> {
88  using super = std::iterator<std::forward_iterator_tag, typename GT::NodeRef>;
89  using NodeRef = typename GT::NodeRef;
90  using ChildItTy = typename GT::ChildIteratorType;
91 
92  // First element is node reference, second is the 'next child' to visit.
93  // The second child is initialized lazily to pick up graph changes during the
94  // DFS.
95  using StackElement = std::pair<NodeRef, Optional<ChildItTy>>;
96 
97  // VisitStack - Used to maintain the ordering. Top = current block
98  std::vector<StackElement> VisitStack;
99 
100 private:
101  inline df_iterator(NodeRef Node) {
102  this->Visited.insert(Node);
103  VisitStack.push_back(StackElement(Node, None));
104  }
105 
106  inline df_iterator() = default; // End is when stack is empty
107 
108  inline df_iterator(NodeRef Node, SetType &S)
110  if (this->Visited.insert(Node).second)
111  VisitStack.push_back(StackElement(Node, None));
112  }
113 
114  inline df_iterator(SetType &S)
116  // End is when stack is empty
117  }
118 
119  inline void toNext() {
120  do {
121  NodeRef Node = VisitStack.back().first;
122  Optional<ChildItTy> &Opt = VisitStack.back().second;
123 
124  if (!Opt)
125  Opt.emplace(GT::child_begin(Node));
126 
127  // Notice that we directly mutate *Opt here, so that
128  // VisitStack.back().second actually gets updated as the iterator
129  // increases.
130  while (*Opt != GT::child_end(Node)) {
131  NodeRef Next = *(*Opt)++;
132  // Has our next sibling been visited?
133  if (this->Visited.insert(Next).second) {
134  // No, do it now.
135  VisitStack.push_back(StackElement(Next, None));
136  return;
137  }
138  }
139  this->Visited.completed(Node);
140 
141  // Oops, ran out of successors... go up a level on the stack.
142  VisitStack.pop_back();
143  } while (!VisitStack.empty());
144  }
145 
146 public:
147  using pointer = typename super::pointer;
148 
149  // Provide static begin and end methods as our public "constructors"
150  static df_iterator begin(const GraphT &G) {
151  return df_iterator(GT::getEntryNode(G));
152  }
153  static df_iterator end(const GraphT &G) { return df_iterator(); }
154 
155  // Static begin and end methods as our public ctors for external iterators
156  static df_iterator begin(const GraphT &G, SetType &S) {
157  return df_iterator(GT::getEntryNode(G), S);
158  }
159  static df_iterator end(const GraphT &G, SetType &S) { return df_iterator(S); }
160 
161  bool operator==(const df_iterator &x) const {
162  return VisitStack == x.VisitStack;
163  }
164  bool operator!=(const df_iterator &x) const { return !(*this == x); }
165 
166  const NodeRef &operator*() const { return VisitStack.back().first; }
167 
168  // This is a nonstandard operator-> that dereferences the pointer an extra
169  // time... so that you can actually call methods ON the Node, because
170  // the contained type is a pointer. This allows BBIt->getTerminator() f.e.
171  //
172  NodeRef operator->() const { return **this; }
173 
174  df_iterator &operator++() { // Preincrement
175  toNext();
176  return *this;
177  }
178 
179  /// Skips all children of the current node and traverses to next node
180  ///
181  /// Note: This function takes care of incrementing the iterator. If you
182  /// always increment and call this function, you risk walking off the end.
184  VisitStack.pop_back();
185  if (!VisitStack.empty())
186  toNext();
187  return *this;
188  }
189 
190  df_iterator operator++(int) { // Postincrement
191  df_iterator tmp = *this;
192  ++*this;
193  return tmp;
194  }
195 
196  // nodeVisited - return true if this iterator has already visited the
197  // specified node. This is public, and will probably be used to iterate over
198  // nodes that a depth first iteration did not find: ie unreachable nodes.
199  //
200  bool nodeVisited(NodeRef Node) const {
201  return this->Visited.count(Node) != 0;
202  }
203 
204  /// getPathLength - Return the length of the path from the entry node to the
205  /// current node, counting both nodes.
206  unsigned getPathLength() const { return VisitStack.size(); }
207 
208  /// getPath - Return the n'th node in the path from the entry node to the
209  /// current node.
210  NodeRef getPath(unsigned n) const { return VisitStack[n].first; }
211 };
212 
213 // Provide global constructors that automatically figure out correct types...
214 //
215 template <class T>
217  return df_iterator<T>::begin(G);
218 }
219 
220 template <class T>
222  return df_iterator<T>::end(G);
223 }
224 
225 // Provide an accessor method to use them in range-based patterns.
226 template <class T>
228  return make_range(df_begin(G), df_end(G));
229 }
230 
231 // Provide global definitions of external depth first iterators...
232 template <class T, class SetTy = std::set<typename GraphTraits<T>::NodeRef>>
233 struct df_ext_iterator : public df_iterator<T, SetTy, true> {
235  : df_iterator<T, SetTy, true>(V) {}
236 };
237 
238 template <class T, class SetTy>
241 }
242 
243 template <class T, class SetTy>
245  return df_ext_iterator<T, SetTy>::end(G, S);
246 }
247 
248 template <class T, class SetTy>
250  SetTy &S) {
251  return make_range(df_ext_begin(G, S), df_ext_end(G, S));
252 }
253 
254 // Provide global definitions of inverse depth first iterators...
255 template <class T,
256  class SetTy =
258  bool External = false>
259 struct idf_iterator : public df_iterator<Inverse<T>, SetTy, External> {
260  idf_iterator(const df_iterator<Inverse<T>, SetTy, External> &V)
261  : df_iterator<Inverse<T>, SetTy, External>(V) {}
262 };
263 
264 template <class T>
267 }
268 
269 template <class T>
271  return idf_iterator<T>::end(Inverse<T>(G));
272 }
273 
274 // Provide an accessor method to use them in range-based patterns.
275 template <class T>
277  return make_range(idf_begin(G), idf_end(G));
278 }
279 
280 // Provide global definitions of external inverse depth first iterators...
281 template <class T, class SetTy = std::set<typename GraphTraits<T>::NodeRef>>
282 struct idf_ext_iterator : public idf_iterator<T, SetTy, true> {
284  : idf_iterator<T, SetTy, true>(V) {}
285  idf_ext_iterator(const df_iterator<Inverse<T>, SetTy, true> &V)
286  : idf_iterator<T, SetTy, true>(V) {}
287 };
288 
289 template <class T, class SetTy>
292 }
293 
294 template <class T, class SetTy>
297 }
298 
299 template <class T, class SetTy>
301  SetTy &S) {
302  return make_range(idf_ext_begin(G, S), idf_ext_end(G, S));
303 }
304 
305 } // end namespace llvm
306 
307 #endif // LLVM_ADT_DEPTHFIRSTITERATOR_H
NodeRef operator->() const
bool operator==(const df_iterator &x) const
This class represents lattice values for constants.
Definition: AllocatorList.h:23
const NodeRef & operator*() const
This provides a very simple, boring adaptor for a begin and end iterator into a range type...
void emplace(ArgTypes &&... Args)
Create a new object by constructing it in place with the given arguments.
Definition: Optional.h:136
void insert(IterT Begin, IterT End)
iterator_range< idf_ext_iterator< T, SetTy > > inverse_depth_first_ext(const T &G, SetTy &S)
block Block Frequency true
bool operator!=(const df_iterator &x) const
df_iterator & skipChildren()
Skips all children of the current node and traverses to next node.
NodeRef getPath(unsigned n) const
getPath - Return the n&#39;th node in the path from the entry node to the current node.
static df_iterator end(const GraphT &G)
unsigned getPathLength() const
getPathLength - Return the length of the path from the entry node to the current node, counting both nodes.
idf_iterator(const df_iterator< Inverse< T >, SetTy, External > &V)
#define T
idf_iterator< T > idf_begin(const T &G)
idf_iterator< T > idf_end(const T &G)
SmallPtrSet< typename GraphTraits< std::conditional< IsConst, const BlockT, BlockT >::type * >::NodeRef, 8 > BaseSet
df_ext_iterator< T, SetTy > df_ext_end(const T &G, SetTy &S)
df_iterator< T > df_end(const T &G)
idf_ext_iterator< T, SetTy > idf_ext_end(const T &G, SetTy &S)
iterator_range< df_ext_iterator< T, SetTy > > depth_first_ext(const T &G, SetTy &S)
df_ext_iterator< T, SetTy > df_ext_begin(const T &G, SetTy &S)
idf_ext_iterator(const idf_iterator< T, SetTy, true > &V)
static df_iterator begin(const GraphT &G)
idf_ext_iterator< T, SetTy > idf_ext_begin(const T &G, SetTy &S)
static df_iterator end(const GraphT &G, SetType &S)
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
df_ext_iterator(const df_iterator< T, SetTy, true > &V)
iterator_range< idf_iterator< T > > inverse_depth_first(const T &G)
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
df_iterator operator++(int)
const DataFlowGraph & G
Definition: RDFGraph.cpp:210
df_iterator_storage(const df_iterator_storage &S)
std::pair< iterator, bool > insert(NodeRef N)
df_iterator< T > df_begin(const T &G)
bool nodeVisited(NodeRef Node) const
A range adaptor for a pair of iterators.
#define N
iterator_range< df_iterator< T > > depth_first(const T &G)
df_iterator & operator++()
idf_ext_iterator(const df_iterator< Inverse< T >, SetTy, true > &V)
static df_iterator begin(const GraphT &G, SetType &S)