text: //===- llvm37/ADT/DepthFirstIterator.h - Depth First iterator -----*- C++ -*-===//
  //
  //                     The LLVM37 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 generic depth
  // first graph iterator.  This file exposes the following functions/types:
  //
  // df_begin/df_end/df_iterator
  //   * Normal depth-first iteration - visit a node and then all of its children.
  //
  // idf_begin/idf_end/idf_iterator
  //   * Depth-first iteration on the 'inverse' graph.
  //
  // df_ext_begin/df_ext_end/df_ext_iterator
  //   * Normal depth-first iteration - visit a node and then all of its children.
  //     This iterator stores the 'visited' set in an external set, which allows
  //     it to be more efficient, and allows external clients to use the set for
  //     other purposes.
  //
  // idf_ext_begin/idf_ext_end/idf_ext_iterator
  //   * Depth-first iteration on the 'inverse' graph.
  //     This iterator stores the 'visited' set in an external set, which allows
  //     it to be more efficient, and allows external clients to use the set for
  //     other purposes.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM37_ADT_DEPTHFIRSTITERATOR_H
  #define LLVM37_ADT_DEPTHFIRSTITERATOR_H
  
  #include "llvm37/ADT/GraphTraits.h"
  #include "llvm37/ADT/PointerIntPair.h"
  #include "llvm37/ADT/SmallPtrSet.h"
  #include "llvm37/ADT/iterator_range.h"
  #include <set>
  #include <vector>
  
  namespace llvm37 {
  
  // df_iterator_storage - A private class which is used to figure out where to
  // store the visited set.
  template<class SetType, bool External>   // Non-external set
  class df_iterator_storage {
  public:
    SetType Visited;
  };
  
  template<class SetType>
  class df_iterator_storage<SetType, true> {
  public:
    df_iterator_storage(SetType &VSet) : Visited(VSet) {}
    df_iterator_storage(const df_iterator_storage &S) : Visited(S.Visited) {}
    SetType &Visited;
  };
  
  
  // Generic Depth First Iterator
  template<class GraphT,
  class SetType = llvm37::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>,
           bool ExtStorage = false, class GT = GraphTraits<GraphT> >
  class df_iterator : public std::iterator<std::forward_iterator_tag,
                                           typename GT::NodeType, ptrdiff_t>,
                      public df_iterator_storage<SetType, ExtStorage> {
    typedef std::iterator<std::forward_iterator_tag,
                          typename GT::NodeType, ptrdiff_t> super;
  
    typedef typename GT::NodeType          NodeType;
    typedef typename GT::ChildIteratorType ChildItTy;
    typedef PointerIntPair<NodeType*, 1>   PointerIntTy;
  
    // VisitStack - Used to maintain the ordering.  Top = current block
    // First element is node pointer, second is the 'next child' to visit
    // if the int in PointerIntTy is 0, the 'next child' to visit is invalid
    std::vector<std::pair<PointerIntTy, ChildItTy> > VisitStack;
  private:
    inline df_iterator(NodeType *Node) {
      this->Visited.insert(Node);
      VisitStack.push_back(std::make_pair(PointerIntTy(Node, 0), 
                                          GT::child_begin(Node)));
    }
    inline df_iterator() { 
      // End is when stack is empty 
    }
    inline df_iterator(NodeType *Node, SetType &S)
      : df_iterator_storage<SetType, ExtStorage>(S) {
      if (!S.count(Node)) {
        VisitStack.push_back(std::make_pair(PointerIntTy(Node, 0), 
                                            GT::child_begin(Node)));
        this->Visited.insert(Node);
      }
    }
    inline df_iterator(SetType &S)
      : df_iterator_storage<SetType, ExtStorage>(S) {
      // End is when stack is empty
    }
  
    inline void toNext() {
      do {
        std::pair<PointerIntTy, ChildItTy> &Top = VisitStack.back();
        NodeType *Node = Top.first.getPointer();
        ChildItTy &It  = Top.second;
        if (!Top.first.getInt()) {
          // now retrieve the real begin of the children before we dive in
          It = GT::child_begin(Node);
          Top.first.setInt(1);
        }
  
        while (It != GT::child_end(Node)) {
          NodeType *Next = *It++;
          // Has our next sibling been visited?
          if (Next && this->Visited.insert(Next).second) {
            // No, do it now.
            VisitStack.push_back(std::make_pair(PointerIntTy(Next, 0), 
                                                GT::child_begin(Next)));
            return;
          }
        }
  
        // Oops, ran out of successors... go up a level on the stack.
        VisitStack.pop_back();
      } while (!VisitStack.empty());
    }
  
  public:
    typedef typename super::pointer pointer;
  
    // Provide static begin and end methods as our public "constructors"
    static df_iterator begin(const GraphT &G) {
      return df_iterator(GT::getEntryNode(G));
    }
    static df_iterator end(const GraphT &G) { return df_iterator(); }
  
    // Static begin and end methods as our public ctors for external iterators
    static df_iterator begin(const GraphT &G, SetType &S) {
      return df_iterator(GT::getEntryNode(G), S);
    }
    static df_iterator end(const GraphT &G, SetType &S) { return df_iterator(S); }
  
    bool operator==(const df_iterator &x) const {
      return VisitStack == x.VisitStack;
    }
    bool operator!=(const df_iterator &x) const { return !(*this == x); }
  
    pointer operator*() const { return VisitStack.back().first.getPointer(); }
  
    // This is a nonstandard operator-> that dereferences the pointer an extra
    // time... so that you can actually call methods ON the Node, because
    // the contained type is a pointer.  This allows BBIt->getTerminator() f.e.
    //
    NodeType *operator->() const { return **this; }
  
    df_iterator &operator++() { // Preincrement
      toNext();
      return *this;
    }
  
    /// \brief Skips all children of the current node and traverses to next node
    ///
    /// Note: This function takes care of incrementing the iterator. If you
    /// always increment and call this function, you risk walking off the end.
    df_iterator &skipChildren() {
      VisitStack.pop_back();
      if (!VisitStack.empty())
        toNext();
      return *this;
    }
  
    df_iterator operator++(int) { // Postincrement
      df_iterator tmp = *this;
      ++*this;
      return tmp;
    }
  
    // nodeVisited - return true if this iterator has already visited the
    // specified node.  This is public, and will probably be used to iterate over
    // nodes that a depth first iteration did not find: ie unreachable nodes.
    //
    bool nodeVisited(NodeType *Node) const {
      return this->Visited.count(Node) != 0;
    }
  
    /// getPathLength - Return the length of the path from the entry node to the
    /// current node, counting both nodes.
    unsigned getPathLength() const { return VisitStack.size(); }
  
    /// getPath - Return the n'th node in the path from the entry node to the
    /// current node.
    NodeType *getPath(unsigned n) const {
      return VisitStack[n].first.getPointer();
    }
  };
  
  
  // Provide global constructors that automatically figure out correct types...
  //
  template <class T>
  df_iterator<T> df_begin(const T& G) {
    return df_iterator<T>::begin(G);
  }
  
  template <class T>
  df_iterator<T> df_end(const T& G) {
    return df_iterator<T>::end(G);
  }
  
  // Provide an accessor method to use them in range-based patterns.
  template <class T>
  iterator_range<df_iterator<T>> depth_first(const T& G) {
    return make_range(df_begin(G), df_end(G));
  }
  
  // Provide global definitions of external depth first iterators...
  template <class T, class SetTy = std::set<typename GraphTraits<T>::NodeType*> >
  struct df_ext_iterator : public df_iterator<T, SetTy, true> {
    df_ext_iterator(const df_iterator<T, SetTy, true> &V)
      : df_iterator<T, SetTy, true>(V) {}
  };
  
  template <class T, class SetTy>
  df_ext_iterator<T, SetTy> df_ext_begin(const T& G, SetTy &S) {
    return df_ext_iterator<T, SetTy>::begin(G, S);
  }
  
  template <class T, class SetTy>
  df_ext_iterator<T, SetTy> df_ext_end(const T& G, SetTy &S) {
    return df_ext_iterator<T, SetTy>::end(G, S);
  }
  
  template <class T, class SetTy>
  iterator_range<df_ext_iterator<T, SetTy>> depth_first_ext(const T& G,
                                                            SetTy &S) {
    return make_range(df_ext_begin(G, S), df_ext_end(G, S));
  }
  
  
  // Provide global definitions of inverse depth first iterators...
  template <class T,
    class SetTy = llvm37::SmallPtrSet<typename GraphTraits<T>::NodeType*, 8>,
            bool External = false>
  struct idf_iterator : public df_iterator<Inverse<T>, SetTy, External> {
    idf_iterator(const df_iterator<Inverse<T>, SetTy, External> &V)
      : df_iterator<Inverse<T>, SetTy, External>(V) {}
  };
  
  template <class T>
  idf_iterator<T> idf_begin(const T& G) {
    return idf_iterator<T>::begin(Inverse<T>(G));
  }
  
  template <class T>
  idf_iterator<T> idf_end(const T& G){
    return idf_iterator<T>::end(Inverse<T>(G));
  }
  
  // Provide an accessor method to use them in range-based patterns.
  template <class T>
  iterator_range<idf_iterator<T>> inverse_depth_first(const T& G) {
    return make_range(idf_begin(G), idf_end(G));
  }
  
  // Provide global definitions of external inverse depth first iterators...
  template <class T, class SetTy = std::set<typename GraphTraits<T>::NodeType*> >
  struct idf_ext_iterator : public idf_iterator<T, SetTy, true> {
    idf_ext_iterator(const idf_iterator<T, SetTy, true> &V)
      : idf_iterator<T, SetTy, true>(V) {}
    idf_ext_iterator(const df_iterator<Inverse<T>, SetTy, true> &V)
      : idf_iterator<T, SetTy, true>(V) {}
  };
  
  template <class T, class SetTy>
  idf_ext_iterator<T, SetTy> idf_ext_begin(const T& G, SetTy &S) {
    return idf_ext_iterator<T, SetTy>::begin(Inverse<T>(G), S);
  }
  
  template <class T, class SetTy>
  idf_ext_iterator<T, SetTy> idf_ext_end(const T& G, SetTy &S) {
    return idf_ext_iterator<T, SetTy>::end(Inverse<T>(G), S);
  }
  
  template <class T, class SetTy>
  iterator_range<idf_ext_iterator<T, SetTy>> inverse_depth_first_ext(const T& G,
                                                                     SetTy &S) {
    return make_range(idf_ext_begin(G, S), idf_ext_end(G, S));
  }
  
  } // End llvm37 namespace
  
  #endif
  