path: root/lib/Rewrite/DeltaTree.cpp

//===--- DeltaTree.cpp - B-Tree for Rewrite Delta tracking ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the DeltaTree and related classes.
//
//===----------------------------------------------------------------------===//

#include "clang/Rewrite/DeltaTree.h"
#include "llvm/Support/Casting.h"
#include <cstring>
using namespace clang;
using llvm::cast;
using llvm::dyn_cast;

namespace {
  struct SourceDelta;
  class DeltaTreeNode;
  class DeltaTreeInteriorNode;
}

/// The DeltaTree class is a multiway search tree (BTree) structure with some
/// fancy features.  B-Trees are are generally more memory and cache efficient
/// than binary trees, because they store multiple keys/values in each node.
///
/// DeltaTree implements a key/value mapping from FileIndex to Delta, allowing
/// fast lookup by FileIndex.  However, an added (important) bonus is that it
/// can also efficiently tell us the full accumulated delta for a specific
/// file offset as well, without traversing the whole tree.
///
/// The nodes of the tree are made up of instances of two classes:
/// DeltaTreeNode and DeltaTreeInteriorNode.  The later subclasses the
/// former and adds children pointers.  Each node knows the full delta of all
/// entries (recursively) contained inside of it, which allows us to get the
/// full delta implied by a whole subtree in constant time.
  
namespace {
  /// SourceDelta - As code in the original input buffer is added and deleted,
  /// SourceDelta records are used to keep track of how the input SourceLocation
  /// object is mapped into the output buffer.
  struct SourceDelta {
    unsigned FileLoc;
    int Delta;
    
    static SourceDelta get(unsigned Loc, int D) {
      SourceDelta Delta;
      Delta.FileLoc = Loc;
      Delta.Delta = D;
      return Delta;
    }
  };
} // end anonymous namespace

namespace {
  /// DeltaTreeNode - The common part of all nodes.
  ///
  class DeltaTreeNode {
    friend class DeltaTreeInteriorNode;
    
    /// WidthFactor - This controls the number of K/V slots held in the BTree:
    /// how wide it is.  Each level of the BTree is guaranteed to have at least
    /// WidthFactor-1 K/V pairs (unless the whole tree is less full than that)
    /// and may have at most 2*WidthFactor-1 K/V pairs.
    enum { WidthFactor = 8 };
    
    /// Values - This tracks the SourceDelta's currently in this node.
    ///
    SourceDelta Values[2*WidthFactor-1];
    
    /// NumValuesUsed - This tracks the number of values this node currently
    /// holds.
    unsigned char NumValuesUsed;
    
    /// IsLeaf - This is true if this is a leaf of the btree.  If false, this is
    /// an interior node, and is actually an instance of DeltaTreeInteriorNode.
    bool IsLeaf;
    
    /// FullDelta - This is the full delta of all the values in this node and
    /// all children nodes.
    int FullDelta;
  public:
    DeltaTreeNode(bool isLeaf = true)
    : NumValuesUsed(0), IsLeaf(isLeaf), FullDelta(0) {}
    
    bool isLeaf() const { return IsLeaf; }
    int getFullDelta() const { return FullDelta; }
    bool isFull() const { return NumValuesUsed == 2*WidthFactor-1; }
    
    unsigned getNumValuesUsed() const { return NumValuesUsed; }
    const SourceDelta &getValue(unsigned i) const {
      assert(i < NumValuesUsed && "Invalid value #");
      return Values[i];
    }
    SourceDelta &getValue(unsigned i) {
      assert(i < NumValuesUsed && "Invalid value #");
      return Values[i];
    }
    
    /// AddDeltaNonFull - Add a delta to this tree and/or it's children, knowing
    /// that this node is not currently full.
    void AddDeltaNonFull(unsigned FileIndex, int Delta);
    
    /// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
    /// local walk over our contained deltas.
    void RecomputeFullDeltaLocally();
    
    void Destroy();
    
    static inline bool classof(const DeltaTreeNode *) { return true; }
  };
} // end anonymous namespace

namespace {
  /// DeltaTreeInteriorNode - When isLeaf = false, a node has child pointers.
  /// This class tracks them.
  class DeltaTreeInteriorNode : public DeltaTreeNode {
    DeltaTreeNode *Children[2*WidthFactor];
    ~DeltaTreeInteriorNode() {
      for (unsigned i = 0, e = NumValuesUsed+1; i != e; ++i)
        Children[i]->Destroy();
    }
    friend class DeltaTreeNode;
  public:
    DeltaTreeInteriorNode() : DeltaTreeNode(false /*nonleaf*/) {}
    
    DeltaTreeInteriorNode(DeltaTreeNode *FirstChild)
    : DeltaTreeNode(false /*nonleaf*/) {
      FullDelta = FirstChild->FullDelta;
      Children[0] = FirstChild;
    }
    
    const DeltaTreeNode *getChild(unsigned i) const {
      assert(i < getNumValuesUsed()+1 && "Invalid child");
      return Children[i];
    }
    DeltaTreeNode *getChild(unsigned i) {
      assert(i < getNumValuesUsed()+1 && "Invalid child");
      return Children[i];
    }
    
    static inline bool classof(const DeltaTreeInteriorNode *) { return true; }
    static inline bool classof(const DeltaTreeNode *N) { return !N->isLeaf(); }
  private:
    void SplitChild(unsigned ChildNo);
  };
}


/// Destroy - A 'virtual' destructor.
void DeltaTreeNode::Destroy() {
  if (isLeaf())
    delete this;
  else
    delete cast<DeltaTreeInteriorNode>(this);
}

/// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
/// local walk over our contained deltas.
void DeltaTreeNode::RecomputeFullDeltaLocally() {
  int NewFullDelta = 0;
  for (unsigned i = 0, e = getNumValuesUsed(); i != e; ++i)
    NewFullDelta += Values[i].Delta;
  if (DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(this))
    for (unsigned i = 0, e = getNumValuesUsed()+1; i != e; ++i)
      NewFullDelta += IN->getChild(i)->getFullDelta();
  FullDelta = NewFullDelta;
}


/// AddDeltaNonFull - Add a delta to this tree and/or it's children, knowing
/// that this node is not currently full.
void DeltaTreeNode::AddDeltaNonFull(unsigned FileIndex, int Delta) {
  assert(!isFull() && "AddDeltaNonFull on a full tree?");
  
  // Maintain full delta for this node.
  FullDelta += Delta;
  
  // Find the insertion point, the first delta whose index is >= FileIndex.
  unsigned i = 0, e = getNumValuesUsed();
  while (i != e && FileIndex > getValue(i).FileLoc)
    ++i;
  
  // If we found an a record for exactly this file index, just merge this
  // value into the preexisting record and finish early.
  if (i != e && getValue(i).FileLoc == FileIndex) {
    // NOTE: Delta could drop to zero here.  This means that the next delta
    // entry is useless and could be removed.  Supporting erases is
    // significantly more complex though, so we just leave an entry with
    // Delta=0 in the tree.
    Values[i].Delta += Delta;
    return;
  }
  
  if (DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(this)) {
    // Insertion into an interior node propagates the value down to a child.
    DeltaTreeNode *Child = IN->getChild(i);
    
    // If the child tree is full, split it, pulling an element up into our
    // node.
    if (Child->isFull()) {
      IN->SplitChild(i);
      SourceDelta &MedianVal = getValue(i);
      
      // If the median value we pulled up is exactly our insert position, add
      // the delta and return.
      if (MedianVal.FileLoc == FileIndex) {
        MedianVal.Delta += Delta;
        return;
      }
      
      // If the median value pulled up is less than our current search point,
      // include those deltas and search down the RHS now.
      if (MedianVal.FileLoc < FileIndex)
        Child = IN->getChild(i+1);
    }
    
    Child->AddDeltaNonFull(FileIndex, Delta);
  } else {
    // For an insertion into a non-full leaf node, just insert the value in
    // its sorted position.  This requires moving later values over.
    if (i != e)
      memmove(&Values[i+1], &Values[i], sizeof(Values[0])*(e-i));
    Values[i] = SourceDelta::get(FileIndex, Delta);
    ++NumValuesUsed;
  }
}

/// SplitChild - At this point, we know that the current node is not full and
/// that the specified child of this node is.  Split the child in half at its
/// median, propagating one value up into us.  Child may be either an interior
/// or leaf node.
void DeltaTreeInteriorNode::SplitChild(unsigned ChildNo) {
  DeltaTreeNode *Child = getChild(ChildNo);
  assert(!isFull() && Child->isFull() && "Inconsistent constraints");
  
  // Since the child is full, it contains 2*WidthFactor-1 values.  We move
  // the first 'WidthFactor-1' values to the LHS child (which we leave in the
  // original child), propagate one value up into us, and move the last
  // 'WidthFactor-1' values into thew RHS child.
  
  // Create the new child node.
  DeltaTreeNode *NewNode;
  if (DeltaTreeInteriorNode *CIN = dyn_cast<DeltaTreeInteriorNode>(Child)) {
    // If the child is an interior node, also move over 'WidthFactor' grand
    // children into the new node.
    NewNode = new DeltaTreeInteriorNode();
    memcpy(&((DeltaTreeInteriorNode*)NewNode)->Children[0],
           &CIN->Children[WidthFactor],
           WidthFactor*sizeof(CIN->Children[0]));