src/llvm/include/llvm/ADT/PostOrderIterator.h

   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).second;
  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> bool insertEdge(NodeType *From, NodeType *To) {
  80     return Visited.insert(To).second;
  81   }
  82
  83   // Called after all children of BB have been visited.
  84   template<class NodeType>
  85   void finishPostorder(NodeType *BB) {}
  86 };
  87
  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;
  99
 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;
 103
 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)));
 110       }
 111     }
 112   }
 113
 114   inline po_iterator(NodeType *BB) {
 115     this->insertEdge((NodeType*)nullptr, BB);
 116     VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
 117     traverseChild();
 118   }
 119   inline po_iterator() {} // End is when stack is empty.
 120
 121   inline 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)));
 125       traverseChild();
 126     }
 127   }
 128
 129   inline po_iterator(SetType &S) :
 130       po_iterator_storage<SetType, ExtStorage>(S) {
 131   } // End is when stack is empty.
 132 public:
 133   typedef typename super::pointer pointer;
 134   typedef po_iterator<GraphT, SetType, ExtStorage, GT> _Self;
 135
 136   // Provide static "constructors"...
 137   static inline _Self begin(GraphT G) { return _Self(GT::getEntryNode(G)); }
 138   static inline _Self end  (GraphT G) { return _Self(); }
 139
 140   static inline _Self begin(GraphT G, SetType &S) {
 141     return _Self(GT::getEntryNode(G), S);
 142   }
 143   static inline _Self end  (GraphT G, SetType &S) { return _Self(S); }
 144
 145   inline bool operator==(const _Self& x) const {
 146     return VisitStack == x.VisitStack;
 147   }
 148   inline bool operator!=(const _Self& x) const { return !operator==(x); }
 149
 150   inline pointer operator*() const {
 151     return VisitStack.back().first;
 152   }
 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   inline NodeType *operator->() const { return operator*(); }
 159
 160   inline _Self& operator++() {   // Preincrement
 161     this->finishPostorder(VisitStack.back().first);
 162     VisitStack.pop_back();
 163     if (!VisitStack.empty())
 164       traverseChild();
 165     return *this;
 166   }
 167
 168   inline _Self operator++(int) { // Postincrement
 169     _Self tmp = *this; ++*this; return tmp;
 170   }
 171 };
 172
 173 // Provide global constructors that automatically figure out correct types...
 174 //
 175 template <class T>
 176 po_iterator<T> po_begin(T G) { return po_iterator<T>::begin(G); }
 177 template <class T>
 178 po_iterator<T> po_end  (T G) { return po_iterator<T>::end(G); }
 179
 180 // Provide global definitions of external postorder iterators...
 181 template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> >
 182 struct po_ext_iterator : public po_iterator<T, SetType, true> {
 183   po_ext_iterator(const po_iterator<T, SetType, true> &V) :
 184   po_iterator<T, SetType, true>(V) {}
 185 };
 186
 187 template<class T, class SetType>
 188 po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) {
 189   return po_ext_iterator<T, SetType>::begin(G, S);
 190 }
 191
 192 template<class T, class SetType>
 193 po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) {
 194   return po_ext_iterator<T, SetType>::end(G, S);
 195 }
 196
 197 // Provide global definitions of inverse post order iterators...
 198 template <class T,
 199           class SetType = std::set<typename GraphTraits<T>::NodeType*>,
 200           bool External = false>
 201 struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External > {
 202   ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
 203      po_iterator<Inverse<T>, SetType, External> (V) {}
 204 };
 205
 206 template <class T>
 207 ipo_iterator<T> ipo_begin(T G, bool Reverse = false) {
 208   return ipo_iterator<T>::begin(G, Reverse);
 209 }
 210
 211 template <class T>
 212 ipo_iterator<T> ipo_end(T G){
 213   return ipo_iterator<T>::end(G);
 214 }
 215
 216 // Provide global definitions of external inverse postorder iterators...
 217 template <class T,
 218           class SetType = std::set<typename GraphTraits<T>::NodeType*> >
 219 struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
 220   ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
 221     ipo_iterator<T, SetType, true>(V) {}
 222   ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
 223     ipo_iterator<T, SetType, true>(V) {}
 224 };
 225
 226 template <class T, class SetType>
 227 ipo_ext_iterator<T, SetType> ipo_ext_begin(T G, SetType &S) {
 228   return ipo_ext_iterator<T, SetType>::begin(G, S);
 229 }
 230
 231 template <class T, class SetType>
 232 ipo_ext_iterator<T, SetType> ipo_ext_end(T G, SetType &S) {
 233   return ipo_ext_iterator<T, SetType>::end(G, S);
 234 }
 235
 236 //===--------------------------------------------------------------------===//
 237 // Reverse Post Order CFG iterator code
 238 //===--------------------------------------------------------------------===//
 239 //
 240 // This is used to visit basic blocks in a method in reverse post order.  This
 241 // class is awkward to use because I don't know a good incremental algorithm to
 242 // computer RPO from a graph.  Because of this, the construction of the
 243 // ReversePostOrderTraversal object is expensive (it must walk the entire graph
 244 // with a postorder iterator to build the data structures).  The moral of this
 245 // story is: Don't create more ReversePostOrderTraversal classes than necessary.
 246 //
 247 // This class should be used like this:
 248 // {
 249 //   ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
 250 //   for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
 251 //      ...
 252 //   }
 253 //   for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
 254 //      ...
 255 //   }
 256 // }
 257 //
 258
 259 template<class GraphT, class GT = GraphTraits<GraphT> >
 260 class ReversePostOrderTraversal {
 261   typedef typename GT::NodeType NodeType;
 262   std::vector<NodeType*> Blocks;       // Block list in normal PO order
 263   inline void Initialize(NodeType *BB) {
 264     std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
 265   }
 266 public:
 267   typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;
 268
 269   inline ReversePostOrderTraversal(GraphT G) {
 270     Initialize(GT::getEntryNode(G));
 271   }
 272
 273   // Because we want a reverse post order, use reverse iterators from the vector
 274   inline rpo_iterator begin() { return Blocks.rbegin(); }
 275   inline rpo_iterator end()   { return Blocks.rend(); }
 276 };
 277
 278 } // End llvm namespace
 279
 280 #endif