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" 21 #include <set> 22 #include <vector> 23 24 namespace llvm { 25 26 // The po_iterator_storage template provides access to the set of already 27 // visited nodes during the po_iterator's depth-first traversal. 28 // 29 // The default implementation simply contains a set of visited nodes, while 30 // the Extended=true version uses a reference to an external set. 31 // 32 // It is possible to prune the depth-first traversal in several ways: 33 // 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 37 // single node. 38 // 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. 42 // 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. 46 // 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. 51 52 /// Default po_iterator_storage implementation with an internal set object. 53 template<class SetType, bool External> 54 class po_iterator_storage { 55 SetType Visited; 56 public: 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); 61 } 62 63 // Called after all children of BB have been visited. 64 template<typename NodeType> 65 void finishPostorder(NodeType *BB) {} 66 }; 67 68 /// Specialization of po_iterator_storage that references an external set. 69 template<class SetType> 70 class po_iterator_storage<SetType, true> { 71 SetType &Visited; 72 public: 73 po_iterator_storage(SetType &VSet) : Visited(VSet) {} 74 po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {} 75 76 // Return true if edge destination should be visited, called with From = 0 for 77 // the root node. 78 // Graph edges can be pruned by specializing this function. 79 template<class NodeType> 80 bool insertEdge(NodeType *From, NodeType *To) { return Visited.insert(To); } 81 82 // Called after all children of BB have been visited. 83 template<class NodeType> 84 void finishPostorder(NodeType *BB) {} 85 }; 86 87 template<class GraphT, 88 class SetType = llvm::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>, 89 bool ExtStorage = false, 90 class GT = GraphTraits<GraphT> > 91 class po_iterator : public std::iterator<std::forward_iterator_tag, 92 typename GT::NodeType, ptrdiff_t>, 93 public po_iterator_storage<SetType, ExtStorage> { 94 typedef std::iterator<std::forward_iterator_tag, 95 typename GT::NodeType, ptrdiff_t> super; 96 typedef typename GT::NodeType NodeType; 97 typedef typename GT::ChildIteratorType ChildItTy; 98 99 // VisitStack - Used to maintain the ordering. Top = current block 100 // First element is basic block pointer, second is the 'next child' to visit 101 std::vector<std::pair<NodeType *, ChildItTy> > VisitStack; 102 103 void traverseChild() { 104 while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) { 105 NodeType *BB = *VisitStack.back().second++; 106 if (this->insertEdge(VisitStack.back().first, BB)) { 107 // If the block is not visited... 108 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB))); 109 } 110 } 111 } 112 113 inline po_iterator(NodeType *BB) { 114 this->insertEdge((NodeType*)nullptr, BB); 115 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB))); 116 traverseChild(); 117 } 118 inline po_iterator() {} // End is when stack is empty. 119 120 inline po_iterator(NodeType *BB, SetType &S) : 121 po_iterator_storage<SetType, ExtStorage>(S) { 122 if (this->insertEdge((NodeType*)nullptr, BB)) { 123 VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB))); 124 traverseChild(); 125 } 126 } 127 128 inline po_iterator(SetType &S) : 129 po_iterator_storage<SetType, ExtStorage>(S) { 130 } // End is when stack is empty. 131 public: 132 typedef typename super::pointer pointer; 133 typedef po_iterator<GraphT, SetType, ExtStorage, GT> _Self; 134 135 // Provide static "constructors"... 136 static inline _Self begin(GraphT G) { return _Self(GT::getEntryNode(G)); } 137 static inline _Self end (GraphT G) { return _Self(); } 138 139 static inline _Self begin(GraphT G, SetType &S) { 140 return _Self(GT::getEntryNode(G), S); 141 } 142 static inline _Self end (GraphT G, SetType &S) { return _Self(S); } 143 144 inline bool operator==(const _Self& x) const { 145 return VisitStack == x.VisitStack; 146 } 147 inline bool operator!=(const _Self& x) const { return !operator==(x); } 148 149 inline pointer operator*() const { 150 return VisitStack.back().first; 151 } 152 153 // 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. 156 // 157 inline NodeType *operator->() const { return operator*(); } 158 159 inline _Self& operator++() { // Preincrement 160 this->finishPostorder(VisitStack.back().first); 161 VisitStack.pop_back(); 162 if (!VisitStack.empty()) 163 traverseChild(); 164 return *this; 165 } 166 167 inline _Self operator++(int) { // Postincrement 168 _Self tmp = *this; ++*this; return tmp; 169 } 170 }; 171 172 // Provide global constructors that automatically figure out correct types... 173 // 174 template <class T> 175 po_iterator<T> po_begin(T G) { return po_iterator<T>::begin(G); } 176 template <class T> 177 po_iterator<T> po_end (T G) { return po_iterator<T>::end(G); } 178 179 // Provide global definitions of external postorder iterators... 180 template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> > 181 struct po_ext_iterator : public po_iterator<T, SetType, true> { 182 po_ext_iterator(const po_iterator<T, SetType, true> &V) : 183 po_iterator<T, SetType, true>(V) {} 184 }; 185 186 template<class T, class SetType> 187 po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) { 188 return po_ext_iterator<T, SetType>::begin(G, S); 189 } 190 191 template<class T, class SetType> 192 po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) { 193 return po_ext_iterator<T, SetType>::end(G, S); 194 } 195 196 // Provide global definitions of inverse post order iterators... 197 template <class T, 198 class SetType = std::set<typename GraphTraits<T>::NodeType*>, 199 bool External = false> 200 struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External > { 201 ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) : 202 po_iterator<Inverse<T>, SetType, External> (V) {} 203 }; 204 205 template <class T> 206 ipo_iterator<T> ipo_begin(T G, bool Reverse = false) { 207 return ipo_iterator<T>::begin(G, Reverse); 208 } 209 210 template <class T> 211 ipo_iterator<T> ipo_end(T G){ 212 return ipo_iterator<T>::end(G); 213 } 214 215 // Provide global definitions of external inverse postorder iterators... 216 template <class T, 217 class SetType = std::set<typename GraphTraits<T>::NodeType*> > 218 struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> { 219 ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) : 220 ipo_iterator<T, SetType, true>(V) {} 221 ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) : 222 ipo_iterator<T, SetType, true>(V) {} 223 }; 224 225 template <class T, class SetType> 226 ipo_ext_iterator<T, SetType> ipo_ext_begin(T G, SetType &S) { 227 return ipo_ext_iterator<T, SetType>::begin(G, S); 228 } 229 230 template <class T, class SetType> 231 ipo_ext_iterator<T, SetType> ipo_ext_end(T G, SetType &S) { 232 return ipo_ext_iterator<T, SetType>::end(G, S); 233 } 234 235 //===--------------------------------------------------------------------===// 236 // Reverse Post Order CFG iterator code 237 //===--------------------------------------------------------------------===// 238 // 239 // This is used to visit basic blocks in a method in reverse post order. This 240 // class is awkward to use because I don't know a good incremental algorithm to 241 // computer RPO from a graph. Because of this, the construction of the 242 // ReversePostOrderTraversal object is expensive (it must walk the entire graph 243 // with a postorder iterator to build the data structures). The moral of this 244 // story is: Don't create more ReversePostOrderTraversal classes than necessary. 245 // 246 // This class should be used like this: 247 // { 248 // ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create 249 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) { 250 // ... 251 // } 252 // for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) { 253 // ... 254 // } 255 // } 256 // 257 258 template<class GraphT, class GT = GraphTraits<GraphT> > 259 class ReversePostOrderTraversal { 260 typedef typename GT::NodeType NodeType; 261 std::vector<NodeType*> Blocks; // Block list in normal PO order 262 inline void Initialize(NodeType *BB) { 263 std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks)); 264 } 265 public: 266 typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator; 267 268 inline ReversePostOrderTraversal(GraphT G) { 269 Initialize(GT::getEntryNode(G)); 270 } 271 272 // Because we want a reverse post order, use reverse iterators from the vector 273 inline rpo_iterator begin() { return Blocks.rbegin(); } 274 inline rpo_iterator end() { return Blocks.rend(); } 275 }; 276 277 } // End llvm namespace 278 279 #endif 280
