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"
26 // The po_iterator_storage template provides access to the set of already
27 // visited nodes during the po_iterator's depth-first traversal.
29 // The default implementation simply contains a set of visited nodes, while
30 // the Extended=true version uses a reference to an external set.
32 // It is possible to prune the depth-first traversal in several ways:
34 // - When providing an external set that already contains some graph nodes,
35 // those nodes won't be visited again. This is useful for restarting a
36 // post-order traversal on a graph with nodes that aren't dominated by a
39 // - By providing a custom SetType class, unwanted graph nodes can be excluded
40 // by having the insert() function return false. This could for example
41 // confine a CFG traversal to blocks in a specific loop.
43 // - Finally, by specializing the po_iterator_storage template itself, graph
44 // edges can be pruned by returning false in the insertEdge() function. This
45 // could be used to remove loop back-edges from the CFG seen by po_iterator.
47 // A specialized po_iterator_storage class can observe both the pre-order and
48 // the post-order. The insertEdge() function is called in a pre-order, while
49 // the finishPostorder() function is called just before the po_iterator moves
50 // on to the next node.
52 /// Default po_iterator_storage implementation with an internal set object.
53 template<class SetType, bool External>
54 class po_iterator_storage {
57 // Return true if edge destination should be visited.
58 template<typename NodeType>
59 bool insertEdge(NodeType *From, NodeType *To) {
60 return Visited.insert(To).second;
63 // Called after all children of BB have been visited.
64 template<typename NodeType>
65 void finishPostorder(NodeType *BB) {}
68 /// Specialization of po_iterator_storage that references an external set.
69 template<class SetType>
70 class po_iterator_storage<SetType, true> {
73 po_iterator_storage(SetType &VSet) : Visited(VSet) {}
74 po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
76 // Return true if edge destination should be visited, called with From = 0 for
78 // Graph edges can be pruned by specializing this function.
79 template <class NodeType> bool insertEdge(NodeType *From, NodeType *To) {
80 return Visited.insert(To).second;
83 // Called after all children of BB have been visited.
84 template<class NodeType>
85 void finishPostorder(NodeType *BB) {}
88 template<class GraphT,
89 class SetType = llvm::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>,
90 bool ExtStorage = false,
91 class GT = GraphTraits<GraphT> >
92 class po_iterator : public std::iterator<std::forward_iterator_tag,
93 typename GT::NodeType, ptrdiff_t>,
94 public po_iterator_storage<SetType, ExtStorage> {
95 typedef std::iterator<std::forward_iterator_tag,
96 typename GT::NodeType, ptrdiff_t> super;
97 typedef typename GT::NodeType NodeType;
98 typedef typename GT::ChildIteratorType ChildItTy;
100 // VisitStack - Used to maintain the ordering. Top = current block
101 // First element is basic block pointer, second is the 'next child' to visit
102 std::vector<std::pair<NodeType *, ChildItTy> > VisitStack;
104 void traverseChild() {
105 while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
106 NodeType *BB = *VisitStack.back().second++;
107 if (this->insertEdge(VisitStack.back().first, BB)) {
108 // If the block is not visited...
109 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
114 po_iterator(NodeType *BB) {
115 this->insertEdge((NodeType*)nullptr, BB);
116 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
119 po_iterator() {} // End is when stack is empty.
121 po_iterator(NodeType *BB, SetType &S)
122 : po_iterator_storage<SetType, ExtStorage>(S) {
123 if (this->insertEdge((NodeType*)nullptr, BB)) {
124 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
129 po_iterator(SetType &S)
130 : po_iterator_storage<SetType, ExtStorage>(S) {
131 } // End is when stack is empty.
133 typedef typename super::pointer pointer;
135 // Provide static "constructors"...
136 static po_iterator begin(GraphT G) {
137 return po_iterator(GT::getEntryNode(G));
139 static po_iterator end(GraphT G) { return po_iterator(); }
141 static po_iterator begin(GraphT G, SetType &S) {
142 return po_iterator(GT::getEntryNode(G), S);
144 static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
146 bool operator==(const po_iterator &x) const {
147 return VisitStack == x.VisitStack;
149 bool operator!=(const po_iterator &x) const { return !(*this == x); }
151 pointer operator*() const { return VisitStack.back().first; }
153 // This is a nonstandard operator-> that dereferences the pointer an extra
154 // time... so that you can actually call methods ON the BasicBlock, because
155 // the contained type is a pointer. This allows BBIt->getTerminator() f.e.
157 NodeType *operator->() const {
162 po_iterator &operator++() { // Preincrement
163 this->finishPostorder(VisitStack.back().first);
164 VisitStack.pop_back();
165 if (!VisitStack.empty())
170 po_iterator operator++(int) { // Postincrement
171 po_iterator tmp = *this;
177 // Provide global constructors that automatically figure out correct types...
180 po_iterator<T> po_begin(T G) { return po_iterator<T>::begin(G); }
182 po_iterator<T> po_end (T G) { return po_iterator<T>::end(G); }
184 // Provide global definitions of external postorder iterators...
185 template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> >
186 struct po_ext_iterator : public po_iterator<T, SetType, true> {
187 po_ext_iterator(const po_iterator<T, SetType, true> &V) :
188 po_iterator<T, SetType, true>(V) {}
191 template<class T, class SetType>
192 po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) {
193 return po_ext_iterator<T, SetType>::begin(G, S);
196 template<class T, class SetType>
197 po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) {
198 return po_ext_iterator<T, SetType>::end(G, S);
201 // Provide global definitions of inverse post order iterators...
203 class SetType = std::set<typename GraphTraits<T>::NodeType*>,
204 bool External = false>
205 struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External > {
206 ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
207 po_iterator<Inverse<T>, SetType, External> (V) {}
211 ipo_iterator<T> ipo_begin(T G, bool Reverse = false) {
212 return ipo_iterator<T>::begin(G, Reverse);
216 ipo_iterator<T> ipo_end(T G){
217 return ipo_iterator<T>::end(G);
220 // Provide global definitions of external inverse postorder iterators...
222 class SetType = std::set<typename GraphTraits<T>::NodeType*> >
223 struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
224 ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
225 ipo_iterator<T, SetType, true>(V) {}
226 ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
227 ipo_iterator<T, SetType, true>(V) {}
230 template <class T, class SetType>
231 ipo_ext_iterator<T, SetType> ipo_ext_begin(T G, SetType &S) {
232 return ipo_ext_iterator<T, SetType>::begin(G, S);
235 template <class T, class SetType>
236 ipo_ext_iterator<T, SetType> ipo_ext_end(T G, SetType &S) {
237 return ipo_ext_iterator<T, SetType>::end(G, S);
240 //===--------------------------------------------------------------------===//
241 // Reverse Post Order CFG iterator code
242 //===--------------------------------------------------------------------===//
244 // This is used to visit basic blocks in a method in reverse post order. This
245 // class is awkward to use because I don't know a good incremental algorithm to
246 // computer RPO from a graph. Because of this, the construction of the
247 // ReversePostOrderTraversal object is expensive (it must walk the entire graph
248 // with a postorder iterator to build the data structures). The moral of this
249 // story is: Don't create more ReversePostOrderTraversal classes than necessary.
251 // This class should be used like this:
253 // ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
254 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
257 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
263 template<class GraphT, class GT = GraphTraits<GraphT> >
264 class ReversePostOrderTraversal {
265 typedef typename GT::NodeType NodeType;
266 std::vector<NodeType*> Blocks; // Block list in normal PO order
267 void Initialize(NodeType *BB) {
268 std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
271 typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;
273 ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
275 // Because we want a reverse post order, use reverse iterators from the vector
276 rpo_iterator begin() { return Blocks.rbegin(); }
277 rpo_iterator end() { return Blocks.rend(); }
280 } // End llvm namespace