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 24namespace 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. 53template<class SetType, bool External> 54class po_iterator_storage { 55 SetType Visited; 56public: 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. 69template<class SetType> 70class po_iterator_storage<SetType, true> { 71 SetType &Visited; 72public: 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 87template<class GraphT, 88 class SetType = llvm::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>, 89 bool ExtStorage = false, 90 class GT = GraphTraits<GraphT> > 91class 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*)0, 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*)0, 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. 131public: 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// 174template <class T> 175po_iterator<T> po_begin(T G) { return po_iterator<T>::begin(G); } 176template <class T> 177po_iterator<T> po_end (T G) { return po_iterator<T>::end(G); } 178 179// Provide global definitions of external postorder iterators... 180template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> > 181struct 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 186template<class T, class SetType> 187po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) { 188 return po_ext_iterator<T, SetType>::begin(G, S); 189} 190 191template<class T, class SetType> 192po_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... 197template <class T, 198 class SetType = std::set<typename GraphTraits<T>::NodeType*>, 199 bool External = false> 200struct 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 205template <class T> 206ipo_iterator<T> ipo_begin(T G, bool Reverse = false) { 207 return ipo_iterator<T>::begin(G, Reverse); 208} 209 210template <class T> 211ipo_iterator<T> ipo_end(T G){ 212 return ipo_iterator<T>::end(G); 213} 214 215// Provide global definitions of external inverse postorder iterators... 216template <class T, 217 class SetType = std::set<typename GraphTraits<T>::NodeType*> > 218struct 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 225template <class T, class SetType> 226ipo_ext_iterator<T, SetType> ipo_ext_begin(T G, SetType &S) { 227 return ipo_ext_iterator<T, SetType>::begin(G, S); 228} 229 230template <class T, class SetType> 231ipo_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 258template<class GraphT, class GT = GraphTraits<GraphT> > 259class 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 copy(po_begin(BB), po_end(BB), back_inserter(Blocks)); 264 } 265public: 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