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 "llvm/ADT/iterator_range.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> 55 class po_iterator_storage { 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> 66 void finishPostorder(NodeType *BB) {} 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> 86 void finishPostorder(NodeType *BB) {} 87 }; 88 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; 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) 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))); 126 traverseChild(); 127 } 128 } 129 130 po_iterator(SetType &S) 131 : po_iterator_storage<SetType, ExtStorage>(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> 178 po_iterator<T> po_begin(const T &G) { return po_iterator<T>::begin(G); } 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... 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) {} 191 }; 192 193 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); 196 } 197 198 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); 201 } 202 203 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)); 206 } 207 208 // Provide global definitions of inverse post order iterators... 209 template <class T, 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) {} 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> 223 ipo_iterator<T> ipo_end(const T &G){ 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, 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) {} 240 }; 241 242 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); 245 } 246 247 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); 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> > 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)); 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 301