DataStructure.cpp

//===- DataStructure.cpp - Implement the core data structure analysis -----===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This file implements the core data structure functionality.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/DSGraph.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/iOther.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Assembly/Writer.h"
#include "Support/CommandLine.h"
#include "Support/Debug.h"
#include "Support/STLExtras.h"
#include "Support/Statistic.h"
#include "Support/Timer.h"
#include <algorithm>
using namespace llvm;

namespace {
  Statistic<> NumFolds          ("dsa", "Number of nodes completely folded");
  Statistic<> NumCallNodesMerged("dsa", "Number of call nodes merged");
  Statistic<> NumNodeAllocated  ("dsa", "Number of nodes allocated");
  Statistic<> NumDNE            ("dsa", "Number of nodes removed by reachability");
  Statistic<> NumTrivialDNE     ("dsa", "Number of nodes trivially removed");
  Statistic<> NumTrivialGlobalDNE("dsa", "Number of globals trivially removed");
};

#if 1
#define TIME_REGION(VARNAME, DESC) \
   NamedRegionTimer VARNAME(DESC)
#else
#define TIME_REGION(VARNAME, DESC)
#endif

using namespace DS;

DSNode *DSNodeHandle::HandleForwarding() const {
  assert(N->isForwarding() && "Can only be invoked if forwarding!");

  // Handle node forwarding here!
  DSNode *Next = N->ForwardNH.getNode();  // Cause recursive shrinkage
  Offset += N->ForwardNH.getOffset();

  if (--N->NumReferrers == 0) {
    // Removing the last referrer to the node, sever the forwarding link
    N->stopForwarding();
  }

  N = Next;
  N->NumReferrers++;
  if (N->Size <= Offset) {
    assert(N->Size <= 1 && "Forwarded to shrunk but not collapsed node?");
    Offset = 0;
  }
  return N;
}

//===----------------------------------------------------------------------===//
// DSNode Implementation
//===----------------------------------------------------------------------===//

DSNode::DSNode(const Type *T, DSGraph *G)
  : NumReferrers(0), Size(0), ParentGraph(G), Ty(Type::VoidTy), NodeType(0) {
  // Add the type entry if it is specified...
  if (T) mergeTypeInfo(T, 0);
  if (G) G->addNode(this);
  ++NumNodeAllocated;
}

// DSNode copy constructor... do not copy over the referrers list!
DSNode::DSNode(const DSNode &N, DSGraph *G, bool NullLinks)
  : NumReferrers(0), Size(N.Size), ParentGraph(G),
    Ty(N.Ty), Globals(N.Globals), NodeType(N.NodeType) {
  if (!NullLinks)
    Links = N.Links;
  else
    Links.resize(N.Links.size()); // Create the appropriate number of null links
  G->addNode(this);
  ++NumNodeAllocated;
}

/// getTargetData - Get the target data object used to construct this node.
///
const TargetData &DSNode::getTargetData() const {
  return ParentGraph->getTargetData();
}

void DSNode::assertOK() const {
  assert((Ty != Type::VoidTy ||
          Ty == Type::VoidTy && (Size == 0 ||
                                 (NodeType & DSNode::Array))) &&
         "Node not OK!");

  assert(ParentGraph && "Node has no parent?");
  const DSScalarMap &SM = ParentGraph->getScalarMap();
  for (unsigned i = 0, e = Globals.size(); i != e; ++i) {
    assert(SM.count(Globals[i]));
    assert(SM.find(Globals[i])->second.getNode() == this);
  }
}

/// forwardNode - Mark this node as being obsolete, and all references to it
/// should be forwarded to the specified node and offset.
///
void DSNode::forwardNode(DSNode *To, unsigned Offset) {
  assert(this != To && "Cannot forward a node to itself!");
  assert(ForwardNH.isNull() && "Already forwarding from this node!");
  if (To->Size <= 1) Offset = 0;
  assert((Offset < To->Size || (Offset == To->Size && Offset == 0)) &&
         "Forwarded offset is wrong!");
  ForwardNH.setNode(To);
  ForwardNH.setOffset(Offset);
  NodeType = DEAD;
  Size = 0;
  Ty = Type::VoidTy;

  // Remove this node from the parent graph's Nodes list.
  ParentGraph->unlinkNode(this);  
  ParentGraph = 0;
}

// addGlobal - Add an entry for a global value to the Globals list.  This also
// marks the node with the 'G' flag if it does not already have it.
//
void DSNode::addGlobal(GlobalValue *GV) {
  // Keep the list sorted.
  std::vector<GlobalValue*>::iterator I =
    std::lower_bound(Globals.begin(), Globals.end(), GV);

  if (I == Globals.end() || *I != GV) {
    //assert(GV->getType()->getElementType() == Ty);
    Globals.insert(I, GV);
    NodeType |= GlobalNode;
  }
}

/// foldNodeCompletely - If we determine that this node has some funny
/// behavior happening to it that we cannot represent, we fold it down to a
/// single, completely pessimistic, node.  This node is represented as a
/// single byte with a single TypeEntry of "void".
///
void DSNode::foldNodeCompletely() {
  if (isNodeCompletelyFolded()) return;  // If this node is already folded...

  ++NumFolds;

  // If this node has a size that is <= 1, we don't need to create a forwarding
  // node.
  if (getSize() <= 1) {
    NodeType |= DSNode::Array;
    Ty = Type::VoidTy;
    Size = 1;
    assert(Links.size() <= 1 && "Size is 1, but has more links?");
    Links.resize(1);
  } else {
    // Create the node we are going to forward to.  This is required because
    // some referrers may have an offset that is > 0.  By forcing them to
    // forward, the forwarder has the opportunity to correct the offset.
    DSNode *DestNode = new DSNode(0, ParentGraph);
    DestNode->NodeType = NodeType|DSNode::Array;
    DestNode->Ty = Type::VoidTy;
    DestNode->Size = 1;
    DestNode->Globals.swap(Globals);
    
    // Start forwarding to the destination node...
    forwardNode(DestNode, 0);
    
    if (!Links.empty()) {
      DestNode->Links.reserve(1);
      
      DSNodeHandle NH(DestNode);
      DestNode->Links.push_back(Links[0]);
      
      // If we have links, merge all of our outgoing links together...
      for (unsigned i = Links.size()-1; i != 0; --i)
        NH.getNode()->Links[0].mergeWith(Links[i]);
      Links.clear();
    } else {
      DestNode->Links.resize(1);
    }
  }
}

/// isNodeCompletelyFolded - Return true if this node has been completely
/// folded down to something that can never be expanded, effectively losing
/// all of the field sensitivity that may be present in the node.
///
bool DSNode::isNodeCompletelyFolded() const {
  return getSize() == 1 && Ty == Type::VoidTy && isArray();
}

namespace {
  /// TypeElementWalker Class - Used for implementation of physical subtyping...
  ///
  class TypeElementWalker {
    struct StackState {
      const Type *Ty;
      unsigned Offset;
      unsigned Idx;
      StackState(const Type *T, unsigned Off = 0)
        : Ty(T), Offset(Off), Idx(0) {}
    };

    std::vector<StackState> Stack;
    const TargetData &TD;
  public:
    TypeElementWalker(const Type *T, const TargetData &td) : TD(td) {
      Stack.push_back(T);
      StepToLeaf();
    }

    bool isDone() const { return Stack.empty(); }
    const Type *getCurrentType()   const { return Stack.back().Ty;     }
    unsigned    getCurrentOffset() const { return Stack.back().Offset; }

    void StepToNextType() {
      PopStackAndAdvance();
      StepToLeaf();
    }

  private:
    /// PopStackAndAdvance - Pop the current element off of the stack and
    /// advance the underlying element to the next contained member.
    void PopStackAndAdvance() {
      assert(!Stack.empty() && "Cannot pop an empty stack!");
      Stack.pop_back();
      while (!Stack.empty()) {
        StackState &SS = Stack.back();
        if (const StructType *ST = dyn_cast<StructType>(SS.Ty)) {
          ++SS.Idx;
          if (SS.Idx != ST->getNumElements()) {
            const StructLayout *SL = TD.getStructLayout(ST);
            SS.Offset += SL->MemberOffsets[SS.Idx]-SL->MemberOffsets[SS.Idx-1];
            return;
          }
          Stack.pop_back();  // At the end of the structure
        } else {
          const ArrayType *AT = cast<ArrayType>(SS.Ty);
          ++SS.Idx;
          if (SS.Idx != AT->getNumElements()) {
            SS.Offset += TD.getTypeSize(AT->getElementType());
            return;
          }
          Stack.pop_back();  // At the end of the array
        }
      }
    }

    /// StepToLeaf - Used by physical subtyping to move to the first leaf node
    /// on the type stack.
    void StepToLeaf() {
      if (Stack.empty()) return;
      while (!Stack.empty() && !Stack.back().Ty->isFirstClassType()) {
        StackState &SS = Stack.back();
        if (const StructType *ST = dyn_cast<StructType>(SS.Ty)) {
          if (ST->getNumElements() == 0) {
            assert(SS.Idx == 0);
            PopStackAndAdvance();
          } else {
            // Step into the structure...
            assert(SS.Idx < ST->getNumElements());
            const StructLayout *SL = TD.getStructLayout(ST);
            Stack.push_back(StackState(ST->getElementType(SS.Idx),
                                       SS.Offset+SL->MemberOffsets[SS.Idx]));
          }
        } else {
          const ArrayType *AT = cast<ArrayType>(SS.Ty);
          if (AT->getNumElements() == 0) {
            assert(SS.Idx == 0);
            PopStackAndAdvance();
          } else {
            // Step into the array...
            assert(SS.Idx < AT->getNumElements());
            Stack.push_back(StackState(AT->getElementType(),
                                       SS.Offset+SS.Idx*
                                       TD.getTypeSize(AT->getElementType())));
          }
        }
      }
    }
  };
} // end anonymous namespace

/// ElementTypesAreCompatible - Check to see if the specified types are
/// "physically" compatible.  If so, return true, else return false.  We only
/// have to check the fields in T1: T2 may be larger than T1.  If AllowLargerT1
/// is true, then we also allow a larger T1.
///
static bool ElementTypesAreCompatible(const Type *T1, const Type *T2,
                                      bool AllowLargerT1, const TargetData &TD){
  TypeElementWalker T1W(T1, TD), T2W(T2, TD);
  
  while (!T1W.isDone() && !T2W.isDone()) {
    if (T1W.getCurrentOffset() != T2W.getCurrentOffset())
      return false;

    const Type *T1 = T1W.getCurrentType();
    const Type *T2 = T2W.getCurrentType();
    if (T1 != T2 && !T1->isLosslesslyConvertibleTo(T2))
      return false;
    
    T1W.StepToNextType();
    T2W.StepToNextType();
  }
  
  return AllowLargerT1 || T1W.isDone();
}


/// mergeTypeInfo - This method merges the specified type into the current node
/// at the specified offset.  This may update the current node's type record if
/// this gives more information to the node, it may do nothing to the node if
/// this information is already known, or it may merge the node completely (and
/// return true) if the information is incompatible with what is already known.
///
/// This method returns true if the node is completely folded, otherwise false.
///
bool DSNode::mergeTypeInfo(const Type *NewTy, unsigned Offset,
                           bool FoldIfIncompatible) {
  const TargetData &TD = getTargetData();
  // Check to make sure the Size member is up-to-date.  Size can be one of the
  // following:
  //  Size = 0, Ty = Void: Nothing is known about this node.
  //  Size = 0, Ty = FnTy: FunctionPtr doesn't have a size, so we use zero
  //  Size = 1, Ty = Void, Array = 1: The node is collapsed
  //  Otherwise, sizeof(Ty) = Size
  //
  assert(((Size == 0 && Ty == Type::VoidTy && !isArray()) ||
          (Size == 0 && !Ty->isSized() && !isArray()) ||
          (Size == 1 && Ty == Type::VoidTy && isArray()) ||
          (Size == 0 && !Ty->isSized() && !isArray()) ||
          (TD.getTypeSize(Ty) == Size)) &&
         "Size member of DSNode doesn't match the type structure!");
  assert(NewTy != Type::VoidTy && "Cannot merge void type into DSNode!");

  if (Offset == 0 && NewTy == Ty)
    return false;  // This should be a common case, handle it efficiently

  // Return true immediately if the node is completely folded.
  if (isNodeCompletelyFolded()) return true;

  // If this is an array type, eliminate the outside arrays because they won't
  // be used anyway.  This greatly reduces the size of large static arrays used
  // as global variables, for example.
  //
  bool WillBeArray = false;
  while (const ArrayType *AT = dyn_cast<ArrayType>(NewTy)) {
    // FIXME: we might want to keep small arrays, but must be careful about
    // things like: [2 x [10000 x int*]]
    NewTy = AT->getElementType();
    WillBeArray = true;
  }

  // Figure out how big the new type we're merging in is...
  unsigned NewTySize = NewTy->isSized() ? TD.getTypeSize(NewTy) : 0;

  // Otherwise check to see if we can fold this type into the current node.  If
  // we can't, we fold the node completely, if we can, we potentially update our
  // internal state.
  //
  if (Ty == Type::VoidTy) {
    // If this is the first type that this node has seen, just accept it without
    // question....
    assert(Offset == 0 && !isArray() &&
           "Cannot have an offset into a void node!");
    Ty = NewTy;
    NodeType &= ~Array;
    if (WillBeArray) NodeType |= Array;
    Size = NewTySize;

    // Calculate the number of outgoing links from this node.
    Links.resize((Size+DS::PointerSize-1) >> DS::PointerShift);
    return false;
  }

  // Handle node expansion case here...
  if (Offset+NewTySize > Size) {
    // It is illegal to grow this node if we have treated it as an array of
    // objects...
    if (isArray()) {
      if (FoldIfIncompatible) foldNodeCompletely();
      return true;
    }

    if (Offset) {  // We could handle this case, but we don't for now...
      std::cerr << "UNIMP: Trying to merge a growth type into "
                << "offset != 0: Collapsing!\n";
      if (FoldIfIncompatible) foldNodeCompletely();
      return true;
    }

    // Okay, the situation is nice and simple, we are trying to merge a type in
    // at offset 0 that is bigger than our current type.  Implement this by
    // switching to the new type and then merge in the smaller one, which should
    // hit the other code path here.  If the other code path decides it's not
    // ok, it will collapse the node as appropriate.
    //
    const Type *OldTy = Ty;
    Ty = NewTy;
    NodeType &= ~Array;
    if (WillBeArray) NodeType |= Array;
    Size = NewTySize;

    // Must grow links to be the appropriate size...
    Links.resize((Size+DS::PointerSize-1) >> DS::PointerShift);

    // Merge in the old type now... which is guaranteed to be smaller than the
    // "current" type.
    return mergeTypeInfo(OldTy, 0);
  }

  assert(Offset <= Size &&
         "Cannot merge something into a part of our type that doesn't exist!");

  // Find the section of Ty that NewTy overlaps with... first we find the
  // type that starts at offset Offset.
  //
  unsigned O = 0;
  const Type *SubType = Ty;
  while (O < Offset) {
    assert(Offset-O < TD.getTypeSize(SubType) && "Offset out of range!");

    switch (SubType->getPrimitiveID()) {
    case Type::StructTyID: {
      const StructType *STy = cast<StructType>(SubType);
      const StructLayout &SL = *TD.getStructLayout(STy);

      unsigned i = 0, e = SL.MemberOffsets.size();
      for (; i+1 < e && SL.MemberOffsets[i+1] <= Offset-O; ++i)
        /* empty */;

      // The offset we are looking for must be in the i'th element...
      SubType = STy->getElementType(i);
      O += SL.MemberOffsets[i];
      break;
    }
    case Type::ArrayTyID: {
      SubType = cast<ArrayType>(SubType)->getElementType();
      unsigned ElSize = TD.getTypeSize(SubType);
      unsigned Remainder = (Offset-O) % ElSize;
      O = Offset-Remainder;
      break;
    }
    default:
      if (FoldIfIncompatible) foldNodeCompletely();
      return true;
    }
  }

  assert(O == Offset && "Could not achieve the correct offset!");

  // If we found our type exactly, early exit
  if (SubType == NewTy) return false;

  // Differing function types don't require us to merge.  They are not values anyway.
  if (isa<FunctionType>(SubType) &&
      isa<FunctionType>(NewTy)) return false;

  unsigned SubTypeSize = SubType->isSized() ? TD.getTypeSize(SubType) : 0;

  // Ok, we are getting desperate now.  Check for physical subtyping, where we
  // just require each element in the node to be compatible.
  if (NewTySize <= SubTypeSize && NewTySize && NewTySize < 256 &&
      SubTypeSize && SubTypeSize < 256 && 
      ElementTypesAreCompatible(NewTy, SubType, !isArray(), TD))
    return false;

  // Okay, so we found the leader type at the offset requested.  Search the list
  // of types that starts at this offset.  If SubType is currently an array or
  // structure, the type desired may actually be the first element of the
  // composite type...
  //
  unsigned PadSize = SubTypeSize; // Size, including pad memory which is ignored
  while (SubType != NewTy) {
    const Type *NextSubType = 0;
    unsigned NextSubTypeSize = 0;
    unsigned NextPadSize = 0;
    switch (SubType->getPrimitiveID()) {
    case Type::StructTyID: {
      const StructType *STy = cast<StructType>(SubType);
      const StructLayout &SL = *TD.getStructLayout(STy);
      if (SL.MemberOffsets.size() > 1)
        NextPadSize = SL.MemberOffsets[1];
      else
        NextPadSize = SubTypeSize;
      NextSubType = STy->getElementType(0);
      NextSubTypeSize = TD.getTypeSize(NextSubType);
      break;
    }
    case Type::ArrayTyID:
      NextSubType = cast<ArrayType>(SubType)->getElementType();
      NextSubTypeSize = TD.getTypeSize(NextSubType);
      NextPadSize = NextSubTypeSize;
      break;
    default: ;
      // fall out 
    }

    if (NextSubType == 0)
      break;   // In the default case, break out of the loop

    if (NextPadSize < NewTySize)
      break;   // Don't allow shrinking to a smaller type than NewTySize
    SubType = NextSubType;
    SubTypeSize = NextSubTypeSize;
    PadSize = NextPadSize;
  }

  // If we found the type exactly, return it...
  if (SubType == NewTy)
    return false;

  // Check to see if we have a compatible, but different type...
  if (NewTySize == SubTypeSize) {
    // Check to see if this type is obviously convertible... int -> uint f.e.
    if (NewTy->isLosslesslyConvertibleTo(SubType))
      return false;

    // Check to see if we have a pointer & integer mismatch going on here,
    // loading a pointer as a long, for example.
    //
    if (SubType->isInteger() && isa<PointerType>(NewTy) ||
        NewTy->isInteger() && isa<PointerType>(SubType))
      return false;
  } else if (NewTySize > SubTypeSize && NewTySize <= PadSize) {
    // We are accessing the field, plus some structure padding.  Ignore the
    // structure padding.
    return false;
  }

  Module *M = 0;
  if (getParentGraph()->getReturnNodes().size())
    M = getParentGraph()->getReturnNodes().begin()->first->getParent();
  DEBUG(std::cerr << "MergeTypeInfo Folding OrigTy: ";
        WriteTypeSymbolic(std::cerr, Ty, M) << "\n due to:";
        WriteTypeSymbolic(std::cerr, NewTy, M) << " @ " << Offset << "!\n"
                  << "SubType: ";
        WriteTypeSymbolic(std::cerr, SubType, M) << "\n\n");

  if (FoldIfIncompatible) foldNodeCompletely();
  return true;
}



// addEdgeTo - Add an edge from the current node to the specified node.  This
// can cause merging of nodes in the graph.
//
void DSNode::addEdgeTo(unsigned Offset, const DSNodeHandle &NH) {
  if (NH.isNull()) return;       // Nothing to do

  DSNodeHandle &ExistingEdge = getLink(Offset);
  if (!ExistingEdge.isNull()) {
    // Merge the two nodes...
    ExistingEdge.mergeWith(NH);
  } else {                             // No merging to perform...
    setLink(Offset, NH);               // Just force a link in there...
  }
}


// MergeSortedVectors - Efficiently merge a vector into another vector where
// duplicates are not allowed and both are sorted.  This assumes that 'T's are
// efficiently copyable and have sane comparison semantics.
//
static void MergeSortedVectors(std::vector<GlobalValue*> &Dest,
                               const std::vector<GlobalValue*> &Src) {
  // By far, the most common cases will be the simple ones.  In these cases,
  // avoid having to allocate a temporary vector...
  //
  if (Src.empty()) {             // Nothing to merge in...
    return;
  } else if (Dest.empty()) {     // Just copy the result in...
    Dest = Src;
  } else if (Src.size() == 1) {  // Insert a single element...
    const GlobalValue *V = Src[0];
    std::vector<GlobalValue*>::iterator I =
      std::lower_bound(Dest.begin(), Dest.end(), V);
    if (I == Dest.end() || *I != Src[0])  // If not already contained...
      Dest.insert(I, Src[0]);
  } else if (Dest.size() == 1) {
    GlobalValue *Tmp = Dest[0];           // Save value in temporary...
    Dest = Src;                           // Copy over list...
    std::vector<GlobalValue*>::iterator I =
      std::lower_bound(Dest.begin(), Dest.end(), Tmp);
    if (I == Dest.end() || *I != Tmp)     // If not already contained...
      Dest.insert(I, Tmp);

  } else {
    // Make a copy to the side of Dest...
    std::vector<GlobalValue*> Old(Dest);
    
    // Make space for all of the type entries now...
    Dest.resize(Dest.size()+Src.size());
    
    // Merge the two sorted ranges together... into Dest.
    std::merge(Old.begin(), Old.end(), Src.begin(), Src.end(), Dest.begin());
    
    // Now erase any duplicate entries that may have accumulated into the 
    // vectors (because they were in both of the input sets)
    Dest.erase(std::unique(Dest.begin(), Dest.end()), Dest.end());
  }
}

void DSNode::mergeGlobals(const std::vector<GlobalValue*> &RHS) {
  MergeSortedVectors(Globals, RHS);
}

// MergeNodes - Helper function for DSNode::mergeWith().
// This function does the hard work of merging two nodes, CurNodeH
// and NH after filtering out trivial cases and making sure that
// CurNodeH.offset >= NH.offset.
// 
// ***WARNING***
// Since merging may cause either node to go away, we must always
// use the node-handles to refer to the nodes.  These node handles are
// automatically updated during merging, so will always provide access
// to the correct node after a merge.
//
void DSNode::MergeNodes(DSNodeHandle& CurNodeH, DSNodeHandle& NH) {
  assert(CurNodeH.getOffset() >= NH.getOffset() &&
         "This should have been enforced in the caller.");

  // Now we know that Offset >= NH.Offset, so convert it so our "Offset" (with
  // respect to NH.Offset) is now zero.  NOffset is the distance from the base
  // of our object that N starts from.
  //
  unsigned NOffset = CurNodeH.getOffset()-NH.getOffset();
  unsigned NSize = NH.getNode()->getSize();

  // If the two nodes are of different size, and the smaller node has the array
  // bit set, collapse!
  if (NSize != CurNodeH.getNode()->getSize()) {
    if (NSize < CurNodeH.getNode()->getSize()) {
      if (NH.getNode()->isArray())
        NH.getNode()->foldNodeCompletely();
    } else if (CurNodeH.getNode()->isArray()) {
      NH.getNode()->foldNodeCompletely();
    }
  }

  // Merge the type entries of the two nodes together...    
  if (NH.getNode()->Ty != Type::VoidTy)
    CurNodeH.getNode()->mergeTypeInfo(NH.getNode()->Ty, NOffset);
  assert(!CurNodeH.getNode()->isDeadNode());

  // If we are merging a node with a completely folded node, then both nodes are
  // now completely folded.
  //
  if (CurNodeH.getNode()->isNodeCompletelyFolded()) {
    if (!NH.getNode()->isNodeCompletelyFolded()) {
      NH.getNode()->foldNodeCompletely();
      assert(NH.getNode() && NH.getOffset() == 0 &&
             "folding did not make offset 0?");
      NOffset = NH.getOffset();
      NSize = NH.getNode()->getSize();
      assert(NOffset == 0 && NSize == 1);
    }
  } else if (NH.getNode()->isNodeCompletelyFolded()) {
    CurNodeH.getNode()->foldNodeCompletely();
    assert(CurNodeH.getNode() && CurNodeH.getOffset() == 0 &&
           "folding did not make offset 0?");
    NOffset = NH.getOffset();
    NSize = NH.getNode()->getSize();
    assert(NOffset == 0 && NSize == 1);
  }

  DSNode *N = NH.getNode();
  if (CurNodeH.getNode() == N || N == 0) return;
  assert(!CurNodeH.getNode()->isDeadNode());

  // Merge the NodeType information.
  CurNodeH.getNode()->NodeType |= N->NodeType;

  // Start forwarding to the new node!
  N->forwardNode(CurNodeH.getNode(), NOffset);
  assert(!CurNodeH.getNode()->isDeadNode());

  // Make all of the outgoing links of N now be outgoing links of CurNodeH.
  //
  for (unsigned i = 0; i < N->getNumLinks(); ++i) {
    DSNodeHandle &Link = N->getLink(i << DS::PointerShift);
    if (Link.getNode()) {
      // Compute the offset into the current node at which to
      // merge this link.  In the common case, this is a linear
      // relation to the offset in the original node (with
      // wrapping), but if the current node gets collapsed due to
      // recursive merging, we must make sure to merge in all remaining
      // links at offset zero.
      unsigned MergeOffset = 0;
      DSNode *CN = CurNodeH.getNode();
      if (CN->Size != 1)
        MergeOffset = ((i << DS::PointerShift)+NOffset) % CN->getSize();
      CN->addEdgeTo(MergeOffset, Link);
    }
  }

  // Now that there are no outgoing edges, all of the Links are dead.
  N->Links.clear();

  // Merge the globals list...
  if (!N->Globals.empty()) {
    CurNodeH.getNode()->mergeGlobals(N->Globals);

    // Delete the globals from the old node...
    std::vector<GlobalValue*>().swap(N->Globals);
  }
}


// mergeWith - Merge this node and the specified node, moving all links to and
// from the argument node into the current node, deleting the node argument.
// Offset indicates what offset the specified node is to be merged into the
// current node.
//
// The specified node may be a null pointer (in which case, we update it to
// point to this node).
//
void DSNode::mergeWith(const DSNodeHandle &NH, unsigned Offset) {
  DSNode *N = NH.getNode();
  if (N == this && NH.getOffset() == Offset)
    return;  // Noop

  // If the RHS is a null node, make it point to this node!
  if (N == 0) {
    NH.mergeWith(DSNodeHandle(this, Offset));
    return;
  }

  assert(!N->isDeadNode() && !isDeadNode());
  assert(!hasNoReferrers() && "Should not try to fold a useless node!");

  if (N == this) {
    // We cannot merge two pieces of the same node together, collapse the node
    // completely.
    DEBUG(std::cerr << "Attempting to merge two chunks of"
                    << " the same node together!\n");
    foldNodeCompletely();
    return;
  }

  // If both nodes are not at offset 0, make sure that we are merging the node
  // at an later offset into the node with the zero offset.
  //
  if (Offset < NH.getOffset()) {
    N->mergeWith(DSNodeHandle(this, Offset), NH.getOffset());
    return;
  } else if (Offset == NH.getOffset() && getSize() < N->getSize()) {
    // If the offsets are the same, merge the smaller node into the bigger node
    N->mergeWith(DSNodeHandle(this, Offset), NH.getOffset());
    return;
  }

  // Ok, now we can merge the two nodes.  Use a static helper that works with
  // two node handles, since "this" may get merged away at intermediate steps.
  DSNodeHandle CurNodeH(this, Offset);
  DSNodeHandle NHCopy(NH);
  DSNode::MergeNodes(CurNodeH, NHCopy);
}


//===----------------------------------------------------------------------===//
// ReachabilityCloner Implementation
//===----------------------------------------------------------------------===//

DSNodeHandle ReachabilityCloner::getClonedNH(const DSNodeHandle &SrcNH) {
  if (SrcNH.isNull()) return DSNodeHandle();
  const DSNode *SN = SrcNH.getNode();

  DSNodeHandle &NH = NodeMap[SN];
  if (!NH.isNull())    // Node already mapped?
    return DSNodeHandle(NH.getNode(), NH.getOffset()+SrcNH.getOffset());

  DSNode *DN = new DSNode(*SN, &Dest, true /* Null out all links */);
  DN->maskNodeTypes(BitsToKeep);
  NH = DN;
  
  // Next, recursively clone all outgoing links as necessary.  Note that
  // adding these links can cause the node to collapse itself at any time, and
  // the current node may be merged with arbitrary other nodes.  For this
  // reason, we must always go through NH.
  DN = 0;
  for (unsigned i = 0, e = SN->getNumLinks(); i != e; ++i) {
    const DSNodeHandle &SrcEdge = SN->getLink(i << DS::PointerShift);
    if (!SrcEdge.isNull()) {
      const DSNodeHandle &DestEdge = getClonedNH(SrcEdge);
      // Compute the offset into the current node at which to
      // merge this link.  In the common case, this is a linear
      // relation to the offset in the original node (with
      // wrapping), but if the current node gets collapsed due to
      // recursive merging, we must make sure to merge in all remaining
      // links at offset zero.
      unsigned MergeOffset = 0;
      DSNode *CN = NH.getNode();
      if (CN->getSize() != 1)
        MergeOffset = ((i << DS::PointerShift)+NH.getOffset()
                       - SrcNH.getOffset()) %CN->getSize();
      CN->addEdgeTo(MergeOffset, DestEdge);
    }
  }
  
  // If this node contains any globals, make sure they end up in the scalar
  // map with the correct offset.
  for (DSNode::global_iterator I = SN->global_begin(), E = SN->global_end();
       I != E; ++I) {
    GlobalValue *GV = *I;
    const DSNodeHandle &SrcGNH = Src.getNodeForValue(GV);
    DSNodeHandle &DestGNH = NodeMap[SrcGNH.getNode()];
    assert(DestGNH.getNode() == NH.getNode() &&"Global mapping inconsistent");
    Dest.getNodeForValue(GV).mergeWith(DSNodeHandle(DestGNH.getNode(),
                                       DestGNH.getOffset()+SrcGNH.getOffset()));
    
    if (CloneFlags & DSGraph::UpdateInlinedGlobals)
      Dest.getInlinedGlobals().insert(GV);
  }

  return DSNodeHandle(NH.getNode(), NH.getOffset()+SrcNH.getOffset());
}

void ReachabilityCloner::merge(const DSNodeHandle &NH,
                               const DSNodeHandle &SrcNH) {
  if (SrcNH.isNull()) return;  // Noop
  if (NH.isNull()) {
    // If there is no destination node, just clone the source and assign the
    // destination node to be it.
    NH.mergeWith(getClonedNH(SrcNH));
    return;
  }

  // Okay, at this point, we know that we have both a destination and a source
  // node that need to be merged.  Check to see if the source node has already
  // been cloned.
  const DSNode *SN = SrcNH.getNode();
  DSNodeHandle &SCNH = NodeMap[SN];  // SourceClonedNodeHandle
  if (!SCNH.isNull()) {   // Node already cloned?
    NH.mergeWith(DSNodeHandle(SCNH.getNode(),
                              SCNH.getOffset()+SrcNH.getOffset()));

    return;  // Nothing to do!
  }

  // Okay, so the source node has not already been cloned.  Instead of creating
  // a new DSNode, only to merge it into the one we already have, try to perform
  // the merge in-place.  The only case we cannot handle here is when the offset
  // into the existing node is less than the offset into the virtual node we are
  // merging in.  In this case, we have to extend the existing node, which
  // requires an allocation anyway.
  DSNode *DN = NH.getNode();   // Make sure the Offset is up-to-date
  if (NH.getOffset() >= SrcNH.getOffset()) {
    if (!DN->isNodeCompletelyFolded()) {
      // Make sure the destination node is folded if the source node is folded.
      if (SN->isNodeCompletelyFolded()) {
        DN->foldNodeCompletely();
        DN = NH.getNode();
      } else if (SN->getSize() != DN->getSize()) {
        // If the two nodes are of different size, and the smaller node has the
        // array bit set, collapse!
        if (SN->getSize() < DN->getSize()) {
          if (SN->isArray()) {
            DN->foldNodeCompletely();
            DN = NH.getNode();
          }
        } else if (DN->isArray()) {
          DN->foldNodeCompletely();
          DN = NH.getNode();
        }
      }
    
      // Merge the type entries of the two nodes together...    
      if (SN->getType() != Type::VoidTy && !DN->isNodeCompletelyFolded()) {
        DN->mergeTypeInfo(SN->getType(), NH.getOffset()-SrcNH.getOffset());
        DN = NH.getNode();
      }
    }

    assert(!DN->isDeadNode());
    
    // Merge the NodeType information.
    DN->mergeNodeFlags(SN->getNodeFlags() & BitsToKeep);

    // Before we start merging outgoing links and updating the scalar map, make
    // sure it is known that this is the representative node for the src node.
    SCNH = DSNodeHandle(DN, NH.getOffset()-SrcNH.getOffset());

    // If the source node contains any globals, make sure they end up in the
    // scalar map with the correct offset.
    if (SN->global_begin() != SN->global_end()) {
      // Update the globals in the destination node itself.
      DN->mergeGlobals(SN->getGlobals());

      // Update the scalar map for the graph we are merging the source node
      // into.
      for (DSNode::global_iterator I = SN->global_begin(), E = SN->global_end();
           I != E; ++I) {
        GlobalValue *GV = *I;
        const DSNodeHandle &SrcGNH = Src.getNodeForValue(GV);
        DSNodeHandle &DestGNH = NodeMap[SrcGNH.getNode()];
        assert(DestGNH.getNode()==NH.getNode() &&"Global mapping inconsistent");
        Dest.getNodeForValue(GV).mergeWith(DSNodeHandle(DestGNH.getNode(),
                                      DestGNH.getOffset()+SrcGNH.getOffset()));
        
        if (CloneFlags & DSGraph::UpdateInlinedGlobals)
          Dest.getInlinedGlobals().insert(GV);
      }
    }
  } else {
    // We cannot handle this case without allocating a temporary node.  Fall
    // back on being simple.
    DSNode *NewDN = new DSNode(*SN, &Dest, true /* Null out all links */);
    NewDN->maskNodeTypes(BitsToKeep);

    unsigned NHOffset = NH.getOffset();
    NH.mergeWith(DSNodeHandle(NewDN, SrcNH.getOffset()));

    assert(NH.getNode() &&
           (NH.getOffset() > NHOffset ||
            (NH.getOffset() == 0 && NH.getNode()->isNodeCompletelyFolded())) &&
           "Merging did not adjust the offset!");

    // Before we start merging outgoing links and updating the scalar map, make
    // sure it is known that this is the representative node for the src node.
    SCNH = DSNodeHandle(NH.getNode(), NH.getOffset()-SrcNH.getOffset());

    // If the source node contained any globals, make sure to create entries 
    // in the scalar map for them!
    for (DSNode::global_iterator I = SN->global_begin(), E = SN->global_end();
         I != E; ++I) {
      GlobalValue *GV = *I;
      const DSNodeHandle &SrcGNH = Src.getNodeForValue(GV);
      DSNodeHandle &DestGNH = NodeMap[SrcGNH.getNode()];
      assert(DestGNH.getNode()==NH.getNode() &&"Global mapping inconsistent");
      assert(SrcGNH.getNode() == SN && "Global mapping inconsistent");
      Dest.getNodeForValue(GV).mergeWith(DSNodeHandle(DestGNH.getNode(),
                                    DestGNH.getOffset()+SrcGNH.getOffset()));
      
      if (CloneFlags & DSGraph::UpdateInlinedGlobals)
        Dest.getInlinedGlobals().insert(GV);
    }
  }


  // Next, recursively merge all outgoing links as necessary.  Note that
  // adding these links can cause the destination node to collapse itself at
  // any time, and the current node may be merged with arbitrary other nodes.
  // For this reason, we must always go through NH.
  DN = 0;
  for (unsigned i = 0, e = SN->getNumLinks(); i != e; ++i) {
    const DSNodeHandle &SrcEdge = SN->getLink(i << DS::PointerShift);
    if (!SrcEdge.isNull()) {
      // Compute the offset into the current node at which to
      // merge this link.  In the common case, this is a linear
      // relation to the offset in the original node (with
      // wrapping), but if the current node gets collapsed due to
      // recursive merging, we must make sure to merge in all remaining
      // links at offset zero.
      unsigned MergeOffset = 0;
      DSNode *CN = SCNH.getNode();
      if (CN->getSize() != 1)
        MergeOffset = ((i << DS::PointerShift)+SCNH.getOffset()) %CN->getSize();
      
      DSNodeHandle &Link = CN->getLink(MergeOffset);
      if (!Link.isNull()) {
        // Perform the recursive merging.  Make sure to create a temporary NH,
        // because the Link can disappear in the process of recursive merging.
        DSNodeHandle Tmp = Link;
        merge(Tmp, SrcEdge);
      } else {
        merge(Link, SrcEdge);
      }
    }
  }
}

/// mergeCallSite - Merge the nodes reachable from the specified src call
/// site into the nodes reachable from DestCS.
void ReachabilityCloner::mergeCallSite(const DSCallSite &DestCS,
                                       const DSCallSite &SrcCS) {
  merge(DestCS.getRetVal(), SrcCS.getRetVal());
  unsigned MinArgs = DestCS.getNumPtrArgs();
  if (SrcCS.getNumPtrArgs() < MinArgs) MinArgs = SrcCS.getNumPtrArgs();
  
  for (unsigned a = 0; a != MinArgs; ++a)
    merge(DestCS.getPtrArg(a), SrcCS.getPtrArg(a));
}


//===----------------------------------------------------------------------===//
// DSCallSite Implementation
//===----------------------------------------------------------------------===//