1 //===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_ADT_POSTORDERITERATOR_H
17 #define LLVM_ADT_POSTORDERITERATOR_H
19 #include "llvm/ADT/GraphTraits.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/iterator_range.h"
27 // The po_iterator_storage template provides access to the set of already
28 // visited nodes during the po_iterator's depth-first traversal.
30 // The default implementation simply contains a set of visited nodes, while
31 // the Extended=true version uses a reference to an external set.
33 // It is possible to prune the depth-first traversal in several ways:
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
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.
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.
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.
53 /// Default po_iterator_storage implementation with an internal set object.
54 template<class SetType, bool External>
55 class po_iterator_storage {
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;
64 // Called after all children of BB have been visited.
65 template<typename NodeType>
66 void finishPostorder(NodeType *BB) {}
69 /// Specialization of po_iterator_storage that references an external set.
70 template<class SetType>
71 class po_iterator_storage<SetType, true> {
74 po_iterator_storage(SetType &VSet) : Visited(VSet) {}
75 po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
77 // Return true if edge destination should be visited, called with From = 0 for
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;
84 // Called after all children of BB have been visited.
85 template<class NodeType>
86 void finishPostorder(NodeType *BB) {}
89 template<class GraphT,
90 class SetType = llvm::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>,
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;
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;
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)));
115 po_iterator(NodeType *BB) {
116 this->insertEdge((NodeType*)nullptr, BB);
117 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
120 po_iterator() {} // End is when stack is empty.
122 po_iterator(NodeType *BB, SetType &S)
123 : po_iterator_storage<SetType, ExtStorage>(S) {
124 if (this->insertEdge((NodeType*)nullptr, BB)) {
125 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
130 po_iterator(SetType &S)
131 : po_iterator_storage<SetType, ExtStorage>(S) {
132 } // End is when stack is empty.
134 typedef typename super::pointer pointer;
136 // Provide static "constructors"...
137 static po_iterator begin(GraphT G) {
138 return po_iterator(GT::getEntryNode(G));
140 static po_iterator end(GraphT G) { return po_iterator(); }
142 static po_iterator begin(GraphT G, SetType &S) {
143 return po_iterator(GT::getEntryNode(G), S);
145 static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
147 bool operator==(const po_iterator &x) const {
148 return VisitStack == x.VisitStack;
150 bool operator!=(const po_iterator &x) const { return !(*this == x); }
152 pointer operator*() const { return VisitStack.back().first; }
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.
158 NodeType *operator->() const { return **this; }
160 po_iterator &operator++() { // Preincrement
161 this->finishPostorder(VisitStack.back().first);
162 VisitStack.pop_back();
163 if (!VisitStack.empty())
168 po_iterator operator++(int) { // Postincrement
169 po_iterator tmp = *this;
175 // Provide global constructors that automatically figure out correct types...
178 po_iterator<T> po_begin(const T &G) { return po_iterator<T>::begin(G); }
180 po_iterator<T> po_end (const T &G) { return po_iterator<T>::end(G); }
182 template <class T> iterator_range<po_iterator<T>> post_order(const T &G) {
183 return make_range(po_begin(G), po_end(G));
186 // Provide global definitions of external postorder iterators...
187 template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> >
188 struct po_ext_iterator : public po_iterator<T, SetType, true> {
189 po_ext_iterator(const po_iterator<T, SetType, true> &V) :
190 po_iterator<T, SetType, true>(V) {}
193 template<class T, class SetType>
194 po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) {
195 return po_ext_iterator<T, SetType>::begin(G, S);
198 template<class T, class SetType>
199 po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) {
200 return po_ext_iterator<T, SetType>::end(G, S);
203 template <class T, class SetType>
204 iterator_range<po_ext_iterator<T, SetType>> post_order_ext(const T &G, SetType &S) {
205 return make_range(po_ext_begin(G, S), po_ext_end(G, S));
208 // Provide global definitions of inverse post order iterators...
210 class SetType = std::set<typename GraphTraits<T>::NodeType*>,
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) {}
218 ipo_iterator<T> ipo_begin(const T &G, bool Reverse = false) {
219 return ipo_iterator<T>::begin(G, Reverse);
223 ipo_iterator<T> ipo_end(const T &G){
224 return ipo_iterator<T>::end(G);
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));
232 // Provide global definitions of external inverse postorder iterators...
234 class SetType = std::set<typename GraphTraits<T>::NodeType*> >
235 struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
236 ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
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) {}
242 template <class T, class SetType>
243 ipo_ext_iterator<T, SetType> ipo_ext_begin(const T &G, SetType &S) {
244 return ipo_ext_iterator<T, SetType>::begin(G, S);
247 template <class T, class SetType>
248 ipo_ext_iterator<T, SetType> ipo_ext_end(const T &G, SetType &S) {
249 return ipo_ext_iterator<T, SetType>::end(G, S);
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));
258 //===--------------------------------------------------------------------===//
259 // Reverse Post Order CFG iterator code
260 //===--------------------------------------------------------------------===//
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.
269 // This class should be used like this:
271 // ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
272 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
275 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
281 template<class GraphT, class GT = GraphTraits<GraphT> >
282 class ReversePostOrderTraversal {
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));
289 typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;
291 ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
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(); }
298 } // End llvm namespace