llvm/ADT/FoldingSet.h

//===-- llvm/ADT/FoldingSet.h - Uniquing Hash Set ---------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by James M. Laskey and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines a hash set that can be used to remove duplication of nodes
// in a graph.  This code was originally created by Chris Lattner for use with
// SelectionDAGCSEMap, but was isolated to provide use across the llvm code set.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_FOLDINGSET_H
#define LLVM_ADT_FOLDINGSET_H

#include "llvm/ADT/SmallVector.h"

namespace llvm {

/// This folding set used for two purposes:
///   1. Given information about a node we want to create, look up the unique
///      instance of the node in the set.  If the node already exists, return
///      it, otherwise return the bucket it should be inserted into.
///   2. Given a node that has already been created, remove it from the set.
///
/// This class is implemented as a single-link chained hash table, where the
/// "buckets" are actually the nodes themselves (the next pointer is in the
/// node).  The last node points back to the bucket to simplified node removal.
///
/// Any node that is to be included in the folding set must be a subclass of
/// FoldingSetNode.  The node class must also define a Profile method used to
/// establish the unique bits of data for the node.  The Profile method is
/// passed a FoldingSetNodeID object which is used to gather the bits.  Just
/// call one of the Add* functions defined in the FoldingSetImpl::NodeID class.
///
/// Eg.
///    class MyNode : public FoldingSetNode {
///    private:
///      std::string Name;
///      unsigned Value;
///    public:
///      MyNode(const char *N, unsigned V) : Name(N), Value(V) {}
///       ...
///      void Profile(FoldingSetNodeID &ID) {
///        ID.AddString(Name);
///        ID.AddInteger(Value);
///       }
///       ...
///     };
///
/// To define the folding set itself use the FoldingSet template;
///
/// Eg.
///    FoldingSet<MyNode> MyFoldingSet;
///
/// Four public methods are available to manipulate the folding set;
///
/// 1) If you have an existing node that you want add to the set but unsure
/// that the node might already exist then call;
///
///    MyNode *M = MyFoldingSet.GetOrInsertNode(N);
///
/// If The result is equal to the input then the node has been inserted.
/// Otherwise, the result is the node existing in the folding set, and the
/// input can be discarded (use the result instead.)
///
/// 2) If you are ready to construct a node but want to check if it already
/// exists, then call FindNodeOrInsertPos with a FoldingSetNodeID of the bits to
/// check;
///
///   FoldingSetNodeID ID;
///   ID.AddString(Name);
///   ID.AddInteger(Value);
///   void *InsertPoint;
///
///    MyNode *M = MyFoldingSet.FindNodeOrInsertPos(ID, InsertPoint);
///
/// If found then M with be non-NULL, else InsertPoint will point to where it
/// should be inserted using InsertNode.
///
/// 3) If you get a NULL result from FindNodeOrInsertPos then you can ass a new
/// node with FindNodeOrInsertPos;
///
///    InsertNode(N, InsertPoint);
///
/// 4) Finally, if you want to remove a node from the folding set call;
///
///    bool WasRemoved = RemoveNode(N);
///
/// The result indicates whether the node did exist in the folding set.


//===----------------------------------------------------------------------===//
/// FoldingSetImpl - Implements the folding set functionality.  The main
/// structure is an array of buckets.  Each bucket is indexed by the hash of
/// the nodes it contains.  The bucket itself points to the nodes contained
/// in the bucket via a singly linked list.  The last node in the list points
/// back to the bucket to facilitate node removal.
///
class FoldingSetImpl {
private:
  // Buckets - Array of bucket chains.
  void **Buckets;

  // NumBuckets - Length of the Buckets array.  Always a power of 2.
  unsigned NumBuckets;

  // NumNodes - Number of nodes in the folding set.  Growth occurs when NumNodes
  // is greater than twice teh number of buckets.
  unsigned NumNodes;

public:
  FoldingSetImpl();
  ~FoldingSetImpl();

  // Forward declaration.
  class Node;

  //===--------------------------------------------------------------------===//
  /// NodeID - This class is used to gather all the unique data bits of a
  /// node.  When all the bits are gathered this class is used to produce a
  /// hash value for the node.
  ///
  class NodeID {
    /// Bits - Vector of all the data bits that make the node unique.
    /// Use a SmallVector to avoid a heap allocation in the common case.
    SmallVector<unsigned, 32> Bits;

  public:
    NodeID() {}

    /// getRawData - Return the ith entry in the Bits data.
    ///
    unsigned getRawData(unsigned i) const {
      return Bits[i];
    }

    /// Add* - Add various data types to Bit data.
    ///
    void AddPointer(const void *Ptr);
    void AddInteger(signed I);
    void AddInteger(unsigned I);
    void AddInteger(uint64_t I);
    void AddFloat(float F);
    void AddDouble(double D);
    void AddString(const std::string &String);

    /// ComputeHash - Compute a strong hash value for this NodeID, used to
    /// lookup the node in the FoldingSetImpl.
    unsigned ComputeHash() const;

    /// operator== - Used to compare two nodes to each other.
    ///
    bool operator==(const NodeID &RHS) const;
  };

  //===--------------------------------------------------------------------===//
  /// Node - This class is used to maintain the singly linked bucket list in
  /// a folding set.
  ///
  class Node {
  private:
    // nextInBucket - next linek in the bucket list.
    void *nextInBucket;

  public:

    Node() : nextInBucket(0) {}

    // Accessors
    void *getNextInBucket() const { return nextInBucket; }
    void SetNextInBucket(void *N) { nextInBucket = N; }
  };

  /// RemoveNode - Remove a node from the folding set, returning true if one
  /// was removed or false if the node was not in the folding set.
  bool RemoveNode(Node *N);

  /// GetOrInsertNode - If there is an existing simple Node exactly
  /// equal to the specified node, return it.  Otherwise, insert 'N' and return
  /// it instead.
  Node *GetOrInsertNode(Node *N);

  /// FindNodeOrInsertPos - Look up the node specified by ID.  If it exists,
  /// return it.  If not, return the insertion token that will make insertion
  /// faster.
  Node *FindNodeOrInsertPos(const NodeID &ID, void *&InsertPos);

  /// InsertNode - Insert the specified node into the folding set, knowing that
  /// it is not already in the folding set.  InsertPos must be obtained from
  /// FindNodeOrInsertPos.
  void InsertNode(Node *N, void *InsertPos);

  private:
    /// GetNextPtr - In order to save space, each bucket is a
    /// singly-linked-list. In order to make deletion more efficient, we make
    /// the list circular, so we can delete a node without computing its hash.
    /// The problem with this is that the start of the hash buckets are not
    /// Nodes.  If NextInBucketPtr is a bucket pointer, this method returns null
    /// : use GetBucketPtr when this happens.
    Node *GetNextPtr(void *NextInBucketPtr);

    /// GetNextPtr - This is just like the previous GetNextPtr implementation,
    /// but allows a bucket array to be specified.
    Node *GetNextPtr(void *NextInBucketPtr, void **Buckets, unsigned NumBuck);

    /// GetBucketPtr - Provides a casting of a bucket pointer for isNode
    /// testing.
    void **GetBucketPtr(void *NextInBucketPtr);

    /// GetBucketFor - Hash the specified node ID and return the hash bucket for
    /// the specified ID.
    void **GetBucketFor(const NodeID &ID) const;

    /// GrowHashTable - Double the size of the hash table and rehash everything.
    ///
    void GrowHashTable();

  protected:

    /// GetNodeProfile - Instantiations of the FoldingSet template implement
    /// this function to gather data bits for teh given node.
    virtual void GetNodeProfile(NodeID &ID, Node *N) = 0;
  };

  // Convenence types to hide the implementation of the folding set.
  typedef FoldingSetImpl::Node FoldingSetNode;
  typedef FoldingSetImpl::NodeID FoldingSetNodeID;

  //===--------------------------------------------------------------------===//
  /// FoldingSet - This template class is used to instantiate a specialized
  /// implementation of the folding set to the node class T.  T must be a
  /// subclass of FoldingSetNode and implement a Profile function.
  ///
  template<class T> class FoldingSet : public FoldingSetImpl {
  private:
    /// GetNodeProfile - Each instantiatation of the FoldingSet
    virtual void GetNodeProfile(NodeID &ID, Node *N) {
      T *TN = static_cast<T *>(N);
      TN->Profile(ID);
    }

  public:
    /// RemoveNode - Remove a node from the folding set, returning true if one
    /// was removed or false if the node was not in the folding set.
    bool RemoveNode(T *N) {
      return FoldingSetImpl::RemoveNode(static_cast<FoldingSetNode *>(N));
    }

    /// GetOrInsertNode - If there is an existing simple Node exactly
    /// equal to the specified node, return it.  Otherwise, insert 'N' and
    /// return it instead.
    T *GetOrInsertNode(Node *N) {
      return static_cast<T *>(FoldingSetImpl::GetOrInsertNode(
                                             static_cast<FoldingSetNode *>(N)));
    }

    /// FindNodeOrInsertPos - Look up the node specified by ID.  If it exists,
    /// return it.  If not, return the insertion token that will make insertion
    /// faster.
    T *FindNodeOrInsertPos(const FoldingSetNodeID &ID, void *&InsertPos) {
      return static_cast<T *>(FoldingSetImpl::FindNodeOrInsertPos(ID,
                                                                  InsertPos));
    }

    /// InsertNode - Insert the specified node into the folding set, knowing
    /// that it is not already in the folding set.  InsertPos must be obtained
    /// from  FindNodeOrInsertPos.
    void InsertNode(T *N, void *InsertPos) {
      FoldingSetImpl::InsertNode(static_cast<FoldingSetNode *>(N), InsertPos);
    }
  };

}; // End of namespace llvm.


#endif