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//===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file builds on the ADT/GraphTraits.h file to build a generic graph
// post order iterator.  This should work over any graph type that has a
// GraphTraits specialization.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_POSTORDERITERATOR_H
#define LLVM_ADT_POSTORDERITERATOR_H

#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator"
#include <stack>
#include <set>
#include <vector>

namespace llvm {

template<class SetType, bool External>   // Non-external set 
class po_iterator_storage { 
public: 
  SetType Visited; 
}; 

template<class SetType> 
class po_iterator_storage<SetType, true> { 
public: 
  po_iterator_storage(SetType &VSet) : Visited(VSet) {} 
  po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {} 
  SetType &Visited; 
}; 

template<class GraphT, 
        class SetType = std::set<typename GraphTraits<GraphT>::NodeType*>, 
        bool ExtStorage = false, 
        class GT = GraphTraits<GraphT> > 
class po_iterator : public forward_iterator<typename GT::NodeType, ptrdiff_t>, 
                    public po_iterator_storage<SetType, ExtStorage> { 
  typedef forward_iterator<typename GT::NodeType, ptrdiff_t> super;
  typedef typename GT::NodeType          NodeType;
  typedef typename GT::ChildIteratorType ChildItTy;
  
  // VisitStack - Used to maintain the ordering.  Top = current block
  // First element is basic block pointer, second is the 'next child' to visit
  std::stack<std::pair<NodeType *, ChildItTy> > VisitStack;

  void traverseChild() {
    while (VisitStack.top().second != GT::child_end(VisitStack.top().first)) {
      NodeType *BB = *VisitStack.top().second++;
      if (!this->Visited.count(BB)) {  // If the block is not visited...
        this->Visited.insert(BB);
        VisitStack.push(std::make_pair(BB, GT::child_begin(BB)));
      }
    }
  }

  inline po_iterator(NodeType *BB) {
    this->Visited.insert(BB);
    VisitStack.push(std::make_pair(BB, GT::child_begin(BB)));
    traverseChild();
  }
  inline po_iterator() {} // End is when stack is empty. 
     
  inline po_iterator(NodeType *BB, SetType &S) : 
    po_iterator_storage<SetType, ExtStorage>(&S) { 
    if(!S.count(BB)) { 
      this->Visited.insert(BB); 
      VisitStack.push(std::make_pair(BB, GT::child_begin(BB))); 
      traverseChild(); 
    } 
  } 
 
  inline po_iterator(SetType &S) : 
      po_iterator_storage<SetType, ExtStorage>(&S) {
  } // End is when stack is empty. 
public:
  typedef typename super::pointer pointer;
  typedef po_iterator<GraphT, SetType, ExtStorage, GT> _Self; 

  // Provide static "constructors"...
  static inline _Self begin(GraphT G) { return _Self(GT::getEntryNode(G)); }
  static inline _Self end  (GraphT G) { return _Self(); }

  static inline _Self begin(GraphT G, SetType &S) { 
    return _Self(GT::getEntryNode(G), S); 
  } 
  static inline _Self end  (GraphT G, SetType &S) { return _Self(S); } 
  
  inline bool operator==(const _Self& x) const {
    return VisitStack == x.VisitStack;
  }
  inline bool operator!=(const _Self& x) const { return !operator==(x); }

  inline pointer operator*() const {
    return VisitStack.top().first;
  }

  // This is a nonstandard operator-> that dereferences the pointer an extra
  // time... so that you can actually call methods ON the BasicBlock, because
  // the contained type is a pointer.  This allows BBIt->getTerminator() f.e.
  //
  inline NodeType *operator->() const { return operator*(); }

  inline _Self& operator++() {   // Preincrement
    VisitStack.pop();
    if (!VisitStack.empty())
      traverseChild();
    return *this;
  }

  inline _Self operator++(int) { // Postincrement
    _Self tmp = *this; ++*this; return tmp;
  }
};

// Provide global constructors that automatically figure out correct types...
//
template <class T>
po_iterator<T> po_begin(T G) { return po_iterator<T>::begin(G); }
template <class T>
po_iterator<T> po_end  (T G) { return po_iterator<T>::end(G); }

// Provide global definitions of external postorder iterators... 
template<class T, class SetType=std::set<typename GraphTraits<T>::NodeType*> > 
struct po_ext_iterator : public po_iterator<T, SetType, true> { 
  po_ext_iterator(const po_iterator<T, SetType, true> &V) :  
  po_iterator<T, SetType, true>(V) {} 
}; 
 
template<class T, class SetType> 
po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) { 
  return po_ext_iterator<T, SetType>::begin(G, S); 
} 

template<class T, class SetType> 
po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) { 
  return po_ext_iterator<T, SetType>::end(G, S); 
} 

// Provide global definitions of inverse post order iterators...
template <class T, 
          class SetType = std::set<typename GraphTraits<T>::NodeType*>,  
          bool External = false> 
struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External > { 
  ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) : 
     po_iterator<Inverse<T>, SetType, External> (V) {} 
};

template <class T>
ipo_iterator<T> ipo_begin(T G, bool Reverse = false) {
  return ipo_iterator<T>::begin(G, Reverse);
}

template <class T>
ipo_iterator<T> ipo_end(T G){
  return ipo_iterator<T>::end(G);
}

//Provide global definitions of external inverse postorder iterators... 
template <class T, class SetType = std::set<typename GraphTraits<T>::NodeType*> > 
struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> { 
  ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) : 
    ipo_iterator<T, SetType, true>(&V) {} 
  ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) : 
    ipo_iterator<T, SetType, true>(&V) {} 
}; 

template <class T, class SetType> 
ipo_ext_iterator<T, SetType> ipo_ext_begin(T G, SetType &S) { 
  return ipo_ext_iterator<T, SetType>::begin(G, S); 
} 

template <class T, class SetType> 
ipo_ext_iterator<T, SetType> ipo_ext_end(T G, SetType &S) { 
  return ipo_ext_iterator<T, SetType>::end(G, S); 
} 

//===--------------------------------------------------------------------===//
// Reverse Post Order CFG iterator code
//===--------------------------------------------------------------------===//
//
// This is used to visit basic blocks in a method in reverse post order.  This
// class is awkward to use because I don't know a good incremental algorithm to
// computer RPO from a graph.  Because of this, the construction of the
// ReversePostOrderTraversal object is expensive (it must walk the entire graph
// with a postorder iterator to build the data structures).  The moral of this
// story is: Don't create more ReversePostOrderTraversal classes than necessary.
//
// This class should be used like this:
// {
//   ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
//   for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
//      ...
//   }
//   for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
//      ...
//   }
// }
//

template<class GraphT, class GT = GraphTraits<GraphT> >
class ReversePostOrderTraversal {
  typedef typename GT::NodeType NodeType;
  std::vector<NodeType*> Blocks;       // Block list in normal PO order
  inline void Initialize(NodeType *BB) {
    copy(po_begin(BB), po_end(BB), back_inserter(Blocks));
  }
public:
  typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;

  inline ReversePostOrderTraversal(GraphT G) {
    Initialize(GT::getEntryNode(G));
  }

  // Because we want a reverse post order, use reverse iterators from the vector
  inline rpo_iterator begin() { return Blocks.rbegin(); }
  inline rpo_iterator end()   { return Blocks.rend(); }
};

} // End llvm namespace

#endif