LLVM  3.7.0
PostOrderIterator.h
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1 //===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file builds on the ADT/GraphTraits.h file to build a generic graph
11 // post order iterator. This should work over any graph type that has a
12 // GraphTraits specialization.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_ADT_POSTORDERITERATOR_H
17 #define LLVM_ADT_POSTORDERITERATOR_H
18 
19 #include "llvm/ADT/GraphTraits.h"
20 #include "llvm/ADT/SmallPtrSet.h"
22 #include <set>
23 #include <vector>
24 
25 namespace llvm {
26 
27 // The po_iterator_storage template provides access to the set of already
28 // visited nodes during the po_iterator's depth-first traversal.
29 //
30 // The default implementation simply contains a set of visited nodes, while
31 // the Extended=true version uses a reference to an external set.
32 //
33 // It is possible to prune the depth-first traversal in several ways:
34 //
35 // - When providing an external set that already contains some graph nodes,
36 // those nodes won't be visited again. This is useful for restarting a
37 // post-order traversal on a graph with nodes that aren't dominated by a
38 // single node.
39 //
40 // - By providing a custom SetType class, unwanted graph nodes can be excluded
41 // by having the insert() function return false. This could for example
42 // confine a CFG traversal to blocks in a specific loop.
43 //
44 // - Finally, by specializing the po_iterator_storage template itself, graph
45 // edges can be pruned by returning false in the insertEdge() function. This
46 // could be used to remove loop back-edges from the CFG seen by po_iterator.
47 //
48 // A specialized po_iterator_storage class can observe both the pre-order and
49 // the post-order. The insertEdge() function is called in a pre-order, while
50 // the finishPostorder() function is called just before the po_iterator moves
51 // on to the next node.
52 
53 /// Default po_iterator_storage implementation with an internal set object.
54 template<class SetType, bool External>
56  SetType Visited;
57 public:
58  // Return true if edge destination should be visited.
59  template<typename NodeType>
60  bool insertEdge(NodeType *From, NodeType *To) {
61  return Visited.insert(To).second;
62  }
63 
64  // Called after all children of BB have been visited.
65  template<typename NodeType>
67 };
68 
69 /// Specialization of po_iterator_storage that references an external set.
70 template<class SetType>
71 class po_iterator_storage<SetType, true> {
72  SetType &Visited;
73 public:
74  po_iterator_storage(SetType &VSet) : Visited(VSet) {}
75  po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
76 
77  // Return true if edge destination should be visited, called with From = 0 for
78  // the root node.
79  // Graph edges can be pruned by specializing this function.
80  template <class NodeType> bool insertEdge(NodeType *From, NodeType *To) {
81  return Visited.insert(To).second;
82  }
83 
84  // Called after all children of BB have been visited.
85  template<class NodeType>
87 };
88 
89 template<class GraphT,
91  bool ExtStorage = false,
92  class GT = GraphTraits<GraphT> >
93 class po_iterator : public std::iterator<std::forward_iterator_tag,
94  typename GT::NodeType, ptrdiff_t>,
95  public po_iterator_storage<SetType, ExtStorage> {
96  typedef std::iterator<std::forward_iterator_tag,
97  typename GT::NodeType, ptrdiff_t> super;
98  typedef typename GT::NodeType NodeType;
99  typedef typename GT::ChildIteratorType ChildItTy;
100 
101  // VisitStack - Used to maintain the ordering. Top = current block
102  // First element is basic block pointer, second is the 'next child' to visit
103  std::vector<std::pair<NodeType *, ChildItTy> > VisitStack;
104 
105  void traverseChild() {
106  while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
107  NodeType *BB = *VisitStack.back().second++;
108  if (this->insertEdge(VisitStack.back().first, BB)) {
109  // If the block is not visited...
110  VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
111  }
112  }
113  }
114 
115  po_iterator(NodeType *BB) {
116  this->insertEdge((NodeType*)nullptr, BB);
117  VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
118  traverseChild();
119  }
120  po_iterator() {} // End is when stack is empty.
121 
122  po_iterator(NodeType *BB, SetType &S)
124  if (this->insertEdge((NodeType*)nullptr, BB)) {
125  VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
126  traverseChild();
127  }
128  }
129 
130  po_iterator(SetType &S)
132  } // End is when stack is empty.
133 public:
134  typedef typename super::pointer pointer;
135 
136  // Provide static "constructors"...
137  static po_iterator begin(GraphT G) {
138  return po_iterator(GT::getEntryNode(G));
139  }
140  static po_iterator end(GraphT G) { return po_iterator(); }
141 
142  static po_iterator begin(GraphT G, SetType &S) {
143  return po_iterator(GT::getEntryNode(G), S);
144  }
145  static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
146 
147  bool operator==(const po_iterator &x) const {
148  return VisitStack == x.VisitStack;
149  }
150  bool operator!=(const po_iterator &x) const { return !(*this == x); }
151 
152  pointer operator*() const { return VisitStack.back().first; }
153 
154  // This is a nonstandard operator-> that dereferences the pointer an extra
155  // time... so that you can actually call methods ON the BasicBlock, because
156  // the contained type is a pointer. This allows BBIt->getTerminator() f.e.
157  //
158  NodeType *operator->() const { return **this; }
159 
160  po_iterator &operator++() { // Preincrement
161  this->finishPostorder(VisitStack.back().first);
162  VisitStack.pop_back();
163  if (!VisitStack.empty())
164  traverseChild();
165  return *this;
166  }
167 
168  po_iterator operator++(int) { // Postincrement
169  po_iterator tmp = *this;
170  ++*this;
171  return tmp;
172  }
173 };
174 
175 // Provide global constructors that automatically figure out correct types...
176 //
177 template <class T>
179 template <class T>
180 po_iterator<T> po_end (const T &G) { return po_iterator<T>::end(G); }
181 
182 template <class T> iterator_range<po_iterator<T>> post_order(const T &G) {
183  return make_range(po_begin(G), po_end(G));
184 }
185 
186 // Provide global definitions of external postorder iterators...
188 struct po_ext_iterator : public po_iterator<T, SetType, true> {
190  po_iterator<T, SetType, true>(V) {}
191 };
192 
193 template<class T, class SetType>
196 }
197 
198 template<class T, class SetType>
201 }
202 
203 template <class T, class SetType>
205  return make_range(po_ext_begin(G, S), po_ext_end(G, S));
206 }
207 
208 // Provide global definitions of inverse post order iterators...
209 template <class T,
211  bool External = false>
212 struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External > {
213  ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
214  po_iterator<Inverse<T>, SetType, External> (V) {}
215 };
216 
217 template <class T>
218 ipo_iterator<T> ipo_begin(const T &G, bool Reverse = false) {
219  return ipo_iterator<T>::begin(G, Reverse);
220 }
221 
222 template <class T>
224  return ipo_iterator<T>::end(G);
225 }
226 
227 template <class T>
228 iterator_range<ipo_iterator<T>> inverse_post_order(const T &G, bool Reverse = false) {
229  return make_range(ipo_begin(G, Reverse), ipo_end(G));
230 }
231 
232 // Provide global definitions of external inverse postorder iterators...
233 template <class T,
235 struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
237  ipo_iterator<T, SetType, true>(V) {}
238  ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
239  ipo_iterator<T, SetType, true>(V) {}
240 };
241 
242 template <class T, class SetType>
245 }
246 
247 template <class T, class SetType>
250 }
251 
252 template <class T, class SetType>
253 iterator_range<ipo_ext_iterator<T, SetType>>
254 inverse_post_order_ext(const T &G, SetType &S) {
255  return make_range(ipo_ext_begin(G, S), ipo_ext_end(G, S));
256 }
257 
258 //===--------------------------------------------------------------------===//
259 // Reverse Post Order CFG iterator code
260 //===--------------------------------------------------------------------===//
261 //
262 // This is used to visit basic blocks in a method in reverse post order. This
263 // class is awkward to use because I don't know a good incremental algorithm to
264 // computer RPO from a graph. Because of this, the construction of the
265 // ReversePostOrderTraversal object is expensive (it must walk the entire graph
266 // with a postorder iterator to build the data structures). The moral of this
267 // story is: Don't create more ReversePostOrderTraversal classes than necessary.
268 //
269 // This class should be used like this:
270 // {
271 // ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
272 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
273 // ...
274 // }
275 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
276 // ...
277 // }
278 // }
279 //
280 
281 template<class GraphT, class GT = GraphTraits<GraphT> >
283  typedef typename GT::NodeType NodeType;
284  std::vector<NodeType*> Blocks; // Block list in normal PO order
285  void Initialize(NodeType *BB) {
286  std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
287  }
288 public:
289  typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;
290 
291  ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
292 
293  // Because we want a reverse post order, use reverse iterators from the vector
294  rpo_iterator begin() { return Blocks.rbegin(); }
295  rpo_iterator end() { return Blocks.rend(); }
296 };
297 
298 } // End llvm namespace
299 
300 #endif
po_iterator & operator++()
po_ext_iterator< T, SetType > po_ext_end(T G, SetType &S)
static po_iterator end(GraphT G, SetType &S)
ipo_ext_iterator(const ipo_iterator< T, SetType, true > &V)
This provides a very simple, boring adaptor for a begin and end iterator into a range type...
static po_iterator begin(GraphT G)
ipo_ext_iterator(const po_iterator< Inverse< T >, SetType, true > &V)
po_iterator operator++(int)
po_ext_iterator(const po_iterator< T, SetType, true > &V)
bool operator!=(const po_iterator &x) const
NodeType
ISD::NodeType enum - This enum defines the target-independent operators for a SelectionDAG.
Definition: ISDOpcodes.h:39
static po_iterator begin(GraphT G, SetType &S)
bool operator==(const po_iterator &x) const
ipo_iterator< T > ipo_end(const T &G)
ipo_ext_iterator< T, SetType > ipo_ext_begin(const T &G, SetType &S)
#define G(x, y, z)
Definition: MD5.cpp:52
#define T
ipo_iterator< T > ipo_begin(const T &G, bool Reverse=false)
#define true
Definition: ConvertUTF.c:66
ipo_ext_iterator< T, SetType > ipo_ext_end(const T &G, SetType &S)
static po_iterator end(GraphT G)
po_iterator_storage(const po_iterator_storage &S)
Default po_iterator_storage implementation with an internal set object.
po_iterator< T > po_end(const T &G)
iterator_range< po_iterator< T > > post_order(const T &G)
std::vector< NodeType * >::reverse_iterator rpo_iterator
iterator_range< T > make_range(T x, T y)
Convenience function for iterating over sub-ranges.
NodeType * operator->() const
bool insertEdge(NodeType *From, NodeType *To)
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:299
iterator_range< po_ext_iterator< T, SetType > > post_order_ext(const T &G, SetType &S)
bool insertEdge(NodeType *From, NodeType *To)
A range adaptor for a pair of iterators.
iterator_range< ipo_ext_iterator< T, SetType > > inverse_post_order_ext(const T &G, SetType &S)
super::pointer pointer
po_ext_iterator< T, SetType > po_ext_begin(T G, SetType &S)
ipo_iterator(const po_iterator< Inverse< T >, SetType, External > &V)
iterator_range< ipo_iterator< T > > inverse_post_order(const T &G, bool Reverse=false)
void finishPostorder(NodeType *BB)
pointer operator*() const
po_iterator< T > po_begin(const T &G)