lib/Analysis/DataStructure/DataStructure.cpp

//===- DataStructure.cpp - Implement the core data structure analysis -----===//
//
// This file implements the core data structure functionality.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/DSGraph.h"
#include "llvm/Function.h"
#include "llvm/iOther.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Target/TargetData.h"
#include "Support/STLExtras.h"
#include "Support/Statistic.h"
#include "Support/Timer.h"
#include <algorithm>

namespace {
  Statistic<> NumFolds          ("dsnode", "Number of nodes completely folded");
  Statistic<> NumCallNodesMerged("dsnode", "Number of call nodes merged");
};

namespace DS {   // TODO: FIXME
  extern TargetData TD;
}
using namespace DS;

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

DSNode::DSNode(enum NodeTy NT, const Type *T)
  : Ty(Type::VoidTy), Size(0), NodeType(NT) {
  // Add the type entry if it is specified...
  if (T) mergeTypeInfo(T, 0);
}

// DSNode copy constructor... do not copy over the referrers list!
DSNode::DSNode(const DSNode &N)
  : Links(N.Links), Globals(N.Globals), Ty(N.Ty), Size(N.Size), 
    NodeType(N.NodeType) {
}

void DSNode::removeReferrer(DSNodeHandle *H) {
  // Search backwards, because we depopulate the list from the back for
  // efficiency (because it's a vector).
  std::vector<DSNodeHandle*>::reverse_iterator I =
    std::find(Referrers.rbegin(), Referrers.rend(), H);
  assert(I != Referrers.rend() && "Referrer not pointing to node!");
  Referrers.erase(I.base()-1);
}

// 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;

  ++NumFolds;

  // We are no longer typed at all...
  Ty = Type::VoidTy;
  NodeType |= Array;
  Size = 1;

  // Loop over all of our referrers, making them point to our zero bytes of
  // space.
  for (std::vector<DSNodeHandle*>::iterator I = Referrers.begin(),
         E = Referrers.end(); I != E; ++I)
    (*I)->setOffset(0);

  // If we have links, merge all of our outgoing links together...
  for (unsigned i = 1, e = Links.size(); i < e; ++i)
    Links[0].mergeWith(Links[i]);
  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();
}


/// 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) {
  // 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 && "Cannot have an offset into a void node!");
    assert(!isArray() && "This shouldn't happen!");
    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()) {
      foldNodeCompletely();
      return true;
    }

    if (Offset) {  // We could handle this case, but we don't for now...
      DEBUG(std::cerr << "UNIMP: Trying to merge a growth type into "
                      << "offset != 0: Collapsing!\n");
      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->getElementTypes()[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:
      assert(0 && "Unknown type!");
    }
  }

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

  // If we found our type exactly, early exit
  if (SubType == NewTy) 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 SubTypeSize = SubType->isSized() ? TD.getTypeSize(SubType) : 0;
  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->getElementTypes()[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 convertable... int -> uint f.e.
    if (NewTy->isLosslesslyConvertableTo(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;
  }


  DEBUG(std::cerr << "MergeTypeInfo Folding OrigTy: " << Ty
                  << "\n due to:" << NewTy << " @ " << Offset << "!\n"
                  << "SubType: " << SubType << "\n\n");

  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.getNode() == 0) return;       // Nothing to do

  DSNodeHandle &ExistingEdge = getLink(Offset);
  if (ExistingEdge.getNode()) {
    // 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());
  }
}


// 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();

  // 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()->NodeType & DSNode::DEAD) == 0);

  // 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.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.getOffset()==0 && "folding did not make offset 0?");
    NOffset = NH.getOffset();
    NSize = NH.getNode()->getSize();
    assert(NOffset == 0 && NSize == 1);
  }

  if (CurNodeH.getNode() == NH.getNode() || NH.getNode() == 0) return;
  assert((CurNodeH.getNode()->NodeType & DSNode::DEAD) == 0);

  // Remove all edges pointing at N, causing them to point to 'this' instead.
  // Make sure to adjust their offset, not just the node pointer.
  // Also, be careful to use the DSNode* rather than NH since NH is one of
  // the referrers and once NH refers to CurNodeH.getNode() this will
  // become an infinite loop.
  DSNode* N = NH.getNode();
  unsigned OldNHOffset = NH.getOffset();
  while (!N->Referrers.empty()) {
    DSNodeHandle &Ref = *N->Referrers.back();
    Ref = DSNodeHandle(CurNodeH.getNode(), NOffset+Ref.getOffset());
  }
  NH = DSNodeHandle(N, OldNHOffset);  // reset NH to point back to where it was

  assert((CurNodeH.getNode()->NodeType & DSNode::DEAD) == 0);

  // Make all of the outgoing links of *NH now be outgoing links of
  // this.  This can cause recursive merging!
  // 
  for (unsigned i = 0; i < NH.getNode()->getSize(); i += DS::PointerSize) {
    DSNodeHandle &Link = NH.getNode()->getLink(i);
    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;
      if (CurNodeH.getNode()->Size != 1)
        MergeOffset = (i+NOffset) % CurNodeH.getNode()->getSize();
      CurNodeH.getNode()->addEdgeTo(MergeOffset, Link);
    }
  }

  // Now that there are no outgoing edges, all of the Links are dead.
  NH.getNode()->Links.clear();
  NH.getNode()->Size = 0;
  NH.getNode()->Ty = Type::VoidTy;

  // Merge the node types
  CurNodeH.getNode()->NodeType |= NH.getNode()->NodeType;
  NH.getNode()->NodeType = DEAD;   // NH is now a dead node.

  // Merge the globals list...
  if (!NH.getNode()->Globals.empty()) {
    MergeSortedVectors(CurNodeH.getNode()->Globals, NH.getNode()->Globals);

    // Delete the globals from the old node...
    NH.getNode()->Globals.clear();
  }
}


// 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, nothing happens).
//
void DSNode::mergeWith(const DSNodeHandle &NH, unsigned Offset) {
  DSNode *N = NH.getNode();
  if (N == 0 || (N == this && NH.getOffset() == Offset))
    return;  // Noop

  assert((N->NodeType & DSNode::DEAD) == 0);
  assert((NodeType & DSNode::DEAD) == 0);
  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);
}

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

// Define here to avoid including iOther.h and BasicBlock.h in DSGraph.h
Function &DSCallSite::getCaller() const {
  return *Inst->getParent()->getParent();
}


//===----------------------------------------------------------------------===//
// DSGraph Implementation
//===----------------------------------------------------------------------===//

DSGraph::DSGraph(const DSGraph &G) : Func(G.Func), GlobalsGraph(0) {
  PrintAuxCalls = false;
  hash_map<const DSNode*, DSNodeHandle> NodeMap;
  RetNode = cloneInto(G, ScalarMap, NodeMap);
}

DSGraph::DSGraph(const DSGraph &G,
                 hash_map<const DSNode*, DSNodeHandle> &NodeMap)
  : Func(G.Func), GlobalsGraph(0) {
  PrintAuxCalls = false;
  RetNode = cloneInto(G, ScalarMap, NodeMap);
}

DSGraph::~DSGraph() {
  FunctionCalls.clear();
  AuxFunctionCalls.clear();
  ScalarMap.clear();
  RetNode.setNode(0);

  // Drop all intra-node references, so that assertions don't fail...
  std::for_each(Nodes.begin(), Nodes.end(),
                std::mem_fun(&DSNode::dropAllReferences));

  // Delete all of the nodes themselves...
  std::for_each(Nodes.begin(), Nodes.end(), deleter<DSNode>);
}

// dump - Allow inspection of graph in a debugger.
void DSGraph::dump() const { print(std::cerr); }


/// remapLinks - Change all of the Links in the current node according to the
/// specified mapping.
///
void DSNode::remapLinks(hash_map<const DSNode*, DSNodeHandle> &OldNodeMap) {
  for (unsigned i = 0, e = Links.size(); i != e; ++i) {
    DSNodeHandle &H = OldNodeMap[Links[i].getNode()];
    Links[i].setNode(H.getNode());
    Links[i].setOffset(Links[i].getOffset()+H.getOffset());
  }
}


// cloneInto - Clone the specified DSGraph into the current graph, returning the
// Return node of the graph.  The translated ScalarMap for the old function is
// filled into the OldValMap member.  If StripAllocas is set to true, Alloca
// markers are removed from the graph, as the graph is being cloned into a
// calling function's graph.
//
DSNodeHandle DSGraph::cloneInto(const DSGraph &G, 
                                hash_map<Value*, DSNodeHandle> &OldValMap,
                              hash_map<const DSNode*, DSNodeHandle> &OldNodeMap,
                                unsigned CloneFlags) {
  assert(OldNodeMap.empty() && "Returned OldNodeMap should be empty!");
  assert(&G != this && "Cannot clone graph into itself!");

  unsigned FN = Nodes.size();           // First new node...

  // Duplicate all of the nodes, populating the node map...
  Nodes.reserve(FN+G.Nodes.size());
  for (unsigned i = 0, e = G.Nodes.size(); i != e; ++i) {
    DSNode *Old = G.Nodes[i];
    DSNode *New = new DSNode(*Old);
    New->NodeType &= ~DSNode::DEAD;  // Clear dead flag...
    Nodes.push_back(New);
    OldNodeMap[Old] = New;
  }

#ifndef NDEBUG
  Timer::addPeakMemoryMeasurement();
#endif

  // Rewrite the links in the new nodes to point into the current graph now.
  for (unsigned i = FN, e = Nodes.size(); i != e; ++i)
    Nodes[i]->remapLinks(OldNodeMap);

  // Remove alloca markers as specified
  if (CloneFlags & (StripAllocaBit | StripModRefBits)) {
    unsigned short clearBits =   (CloneFlags & StripAllocaBit
                                  ? DSNode::AllocaNode : 0)
                               | (CloneFlags & StripModRefBits
                                  ? (DSNode::Modified | DSNode::Read) : 0);
    for (unsigned i = FN, e = Nodes.size(); i != e; ++i)
      Nodes[i]->NodeType &= ~clearBits;
  }

  // Copy the value map... and merge all of the global nodes...
  for (hash_map<Value*, DSNodeHandle>::const_iterator I = G.ScalarMap.begin(),
         E = G.ScalarMap.end(); I != E; ++I) {
    DSNodeHandle &H = OldValMap[I->first];
    DSNodeHandle &MappedNode = OldNodeMap[I->second.getNode()];
    H.setNode(MappedNode.getNode());
    H.setOffset(I->second.getOffset()+MappedNode.getOffset());

    if (isa<GlobalValue>(I->first)) {  // Is this a global?
      hash_map<Value*, DSNodeHandle>::iterator GVI = ScalarMap.find(I->first);
      if (GVI != ScalarMap.end()) {   // Is the global value in this fn already?
        GVI->second.mergeWith(H);
      } else {
        ScalarMap[I->first] = H;      // Add global pointer to this graph
      }
    }
  }

  if (!(CloneFlags & DontCloneCallNodes)) {
    // Copy the function calls list...
    unsigned FC = FunctionCalls.size();  // FirstCall
    FunctionCalls.reserve(FC+G.FunctionCalls.size());
    for (unsigned i = 0, ei = G.FunctionCalls.size(); i != ei; ++i)
      FunctionCalls.push_back(DSCallSite(G.FunctionCalls[i], OldNodeMap));
  }

  if (!(CloneFlags & DontCloneAuxCallNodes)) {
    // Copy the auxillary function calls list...
    unsigned FC = AuxFunctionCalls.size();  // FirstCall
    AuxFunctionCalls.reserve(FC+G.AuxFunctionCalls.size());
    for (unsigned i = 0, ei = G.AuxFunctionCalls.size(); i != ei; ++i)
      AuxFunctionCalls.push_back(DSCallSite(G.AuxFunctionCalls[i], OldNodeMap));
  }

  // Return the returned node pointer...
  DSNodeHandle &MappedRet = OldNodeMap[G.RetNode.getNode()];
  return DSNodeHandle(MappedRet.getNode(),
                      MappedRet.getOffset()+G.RetNode.getOffset());
}

/// mergeInGraph - The method is used for merging graphs together.  If the
/// argument graph is not *this, it makes a clone of the specified graph, then
/// merges the nodes specified in the call site with the formal arguments in the
/// graph.
///
void DSGraph::mergeInGraph(DSCallSite &CS, const DSGraph &Graph,
                           unsigned CloneFlags) {
  hash_map<Value*, DSNodeHandle> OldValMap;
  DSNodeHandle RetVal;
  hash_map<Value*, DSNodeHandle> *ScalarMap = &OldValMap;

  // If this is not a recursive call, clone the graph into this graph...
  if (&Graph != this) {
    // Clone the callee's graph into the current graph, keeping
    // track of where scalars in the old graph _used_ to point,
    // and of the new nodes matching nodes of the old graph.
    hash_map<const DSNode*, DSNodeHandle> OldNodeMap;
    
    // The clone call may invalidate any of the vectors in the data
    // structure graph.  Strip locals and don't copy the list of callers
    RetVal = cloneInto(Graph, OldValMap, OldNodeMap, CloneFlags);
    ScalarMap = &OldValMap;
  } else {
    RetVal = getRetNode();
    ScalarMap = &getScalarMap();
  }

  // Merge the return value with the return value of the context...
  RetVal.mergeWith(CS.getRetVal());

  // Resolve all of the function arguments...
  Function &F = Graph.getFunction();
  Function::aiterator AI = F.abegin();

  for (unsigned i = 0, e = CS.getNumPtrArgs(); i != e; ++i, ++AI) {
    // Advance the argument iterator to the first pointer argument...
    while (!isPointerType(AI->getType())) {
      ++AI;
#ifndef NDEBUG
      if (AI == F.aend())
        std::cerr << "Bad call to Function: " << F.getName() << "\n";
#endif
      assert(AI != F.aend() && "# Args provided is not # Args required!");
    }
    
    // Add the link from the argument scalar to the provided value
    DSNodeHandle &NH = (*ScalarMap)[AI];
    assert(NH.getNode() && "Pointer argument without scalarmap entry?");
    NH.mergeWith(CS.getPtrArg(i));
  }
}

#if 0
// cloneGlobalInto - Clone the given global node and all its target links
// (and all their llinks, recursively).
// 
DSNode *DSGraph::cloneGlobalInto(const DSNode *GNode) {
  if (GNode == 0 || GNode->getGlobals().size() == 0) return 0;

  // If a clone has already been created for GNode, return it.
  DSNodeHandle& ValMapEntry = ScalarMap[GNode->getGlobals()[0]];
  if (ValMapEntry != 0)
    return ValMapEntry;

  // Clone the node and update the ValMap.
  DSNode* NewNode = new DSNode(*GNode);
  ValMapEntry = NewNode;                // j=0 case of loop below!
  Nodes.push_back(NewNode);
  for (unsigned j = 1, N = NewNode->getGlobals().size(); j < N; ++j)
    ScalarMap[NewNode->getGlobals()[j]] = NewNode;

  // Rewrite the links in the new node to point into the current graph.
  for (unsigned j = 0, e = GNode->getNumLinks(); j != e; ++j)
    NewNode->setLink(j, cloneGlobalInto(GNode->getLink(j)));

  return NewNode;
}
#endif


// markIncompleteNodes - Mark the specified node as having contents that are not
// known with the current analysis we have performed.  Because a node makes all
// of the nodes it can reach imcomplete if the node itself is incomplete, we
// must recursively traverse the data structure graph, marking all reachable
// nodes as incomplete.
//
static void markIncompleteNode(DSNode *N) {
  // Stop recursion if no node, or if node already marked...
  if (N == 0 || (N->NodeType & DSNode::Incomplete)) return;

  // Actually mark the node
  N->NodeType |= DSNode::Incomplete;

  // Recusively process children...
  for (unsigned i = 0, e = N->getSize(); i < e; i += DS::PointerSize)
    if (DSNode *DSN = N->getLink(i).getNode())
      markIncompleteNode(DSN);
}

static void markIncomplete(DSCallSite &Call) {
  // Then the return value is certainly incomplete!
  markIncompleteNode(Call.getRetVal().getNode());

  // All objects pointed to by function arguments are incomplete!
  for (unsigned i = 0, e = Call.getNumPtrArgs(); i != e; ++i)
    markIncompleteNode(Call.getPtrArg(i).getNode());
}

// markIncompleteNodes - Traverse the graph, identifying nodes that may be
// modified by other functions that have not been resolved yet.  This marks
// nodes that are reachable through three sources of "unknownness":
//
//  Global Variables, Function Calls, and Incoming Arguments
//
// For any node that may have unknown components (because something outside the
// scope of current analysis may have modified it), the 'Incomplete' flag is
// added to the NodeType.
//
void DSGraph::markIncompleteNodes(unsigned Flags) {
  // Mark any incoming arguments as incomplete...
  if ((Flags & DSGraph::MarkFormalArgs) && Func)
    for (Function::aiterator I = Func->abegin(), E = Func->aend(); I != E; ++I)
      if (isPointerType(I->getType()) && ScalarMap.find(I) != ScalarMap.end())
        markIncompleteNode(ScalarMap[I].getNode());

  // Mark stuff passed into functions calls as being incomplete...
  if (!shouldPrintAuxCalls())
    for (unsigned i = 0, e = FunctionCalls.size(); i != e; ++i)
      markIncomplete(FunctionCalls[i]);
  else
    for (unsigned i = 0, e = AuxFunctionCalls.size(); i != e; ++i)
      markIncomplete(AuxFunctionCalls[i]);
    

  // Mark all of the nodes pointed to by global nodes as incomplete...
  for (unsigned i = 0, e = Nodes.size(); i != e; ++i)
    if (Nodes[i]->NodeType & DSNode::GlobalNode) {
      DSNode *N = Nodes[i];
      for (unsigned i = 0, e = N->getSize(); i < e; i += DS::PointerSize)
        if (DSNode *DSN = N->getLink(i).getNode())
          markIncompleteNode(DSN);
    }
}

// removeRefsToGlobal - Helper function that removes globals from the
// ScalarMap so that the referrer count will go down to zero.
static void removeRefsToGlobal(DSNode* N,
                               hash_map<Value*, DSNodeHandle> &ScalarMap) {
  while (!N->getGlobals().empty()) {
    GlobalValue *GV = N->getGlobals().back();
    N->getGlobals().pop_back();      
    ScalarMap.erase(GV);
  }
}


// isNodeDead - This method checks to see if a node is dead, and if it isn't, it
// checks to see if there are simple transformations that it can do to make it
// dead.
//
bool DSGraph::isNodeDead(DSNode *N) {
  // Is it a trivially dead shadow node?
  return N->getReferrers().empty() && (N->NodeType & ~DSNode::DEAD) == 0;
}

static inline void killIfUselessEdge(DSNodeHandle &Edge) {
  if (DSNode *N = Edge.getNode())  // Is there an edge?
    if (N->getReferrers().size() == 1)  // Does it point to a lonely node?
      if ((N->NodeType & ~DSNode::Incomplete) == 0 && // No interesting info?
          N->getType() == Type::VoidTy && !N->isNodeCompletelyFolded())
        Edge.setNode(0);  // Kill the edge!
}

static inline bool nodeContainsExternalFunction(const DSNode *N) {
  const std::vector<GlobalValue*> &Globals = N->getGlobals();
  for (unsigned i = 0, e = Globals.size(); i != e; ++i)
    if (Globals[i]->isExternal())
      return true;
  return false;
}

static void removeIdenticalCalls(std::vector<DSCallSite> &Calls,
                                 const std::string &where) {
  // Remove trivially identical function calls
  unsigned NumFns = Calls.size();
  std::sort(Calls.begin(), Calls.end());  // Sort by callee as primary key!

  // Scan the call list cleaning it up as necessary...
  DSNode *LastCalleeNode = 0;
  unsigned NumDuplicateCalls = 0;
  bool LastCalleeContainsExternalFunction = false;
  for (unsigned i = 0; i != Calls.size(); ++i) {
    DSCallSite &CS = Calls[i];

    // If the Callee is a useless edge, this must be an unreachable call site,
    // eliminate it.
    killIfUselessEdge(CS.getCallee());
    if (CS.getCallee().getNode() == 0) {
      CS.swap(Calls.back());
      Calls.pop_back();
      --i;
    } else {
      // If the return value or any arguments point to a void node with no
      // information at all in it, and the call node is the only node to point
      // to it, remove the edge to the node (killing the node).
      //
      killIfUselessEdge(CS.getRetVal());
      for (unsigned a = 0, e = CS.getNumPtrArgs(); a != e; ++a)
        killIfUselessEdge(CS.getPtrArg(a));
      
      // If this call site calls the same function as the last call site, and if
      // the function pointer contains an external function, this node will
      // never be resolved.  Merge the arguments of the call node because no
      // information will be lost.
      //
      if (CS.getCallee().getNode() == LastCalleeNode) {
        ++NumDuplicateCalls;
        if (NumDuplicateCalls == 1) {
          LastCalleeContainsExternalFunction =
            nodeContainsExternalFunction(LastCalleeNode);
        }
        
        if (LastCalleeContainsExternalFunction ||
            // This should be more than enough context sensitivity!
            // FIXME: Evaluate how many times this is tripped!
            NumDuplicateCalls > 20) {
          DSCallSite &OCS = Calls[i-1];
          OCS.mergeWith(CS);
          
          // The node will now be eliminated as a duplicate!
          if (CS.getNumPtrArgs() < OCS.getNumPtrArgs())
            CS = OCS;
          else if (CS.getNumPtrArgs() > OCS.getNumPtrArgs())
            OCS = CS;
        }
      } else {
        LastCalleeNode = CS.getCallee().getNode();
        NumDuplicateCalls = 0;
      }
    }
  }

  Calls.erase(std::unique(Calls.begin(), Calls.end()),
              Calls.end());

  // Track the number of call nodes merged away...
  NumCallNodesMerged += NumFns-Calls.size();

  DEBUG(if (NumFns != Calls.size())
          std::cerr << "Merged " << (NumFns-Calls.size())
                    << " call nodes in " << where << "\n";);
}


// removeTriviallyDeadNodes - After the graph has been constructed, this method
// removes all unreachable nodes that are created because they got merged with
// other nodes in the graph.  These nodes will all be trivially unreachable, so
// we don't have to perform any non-trivial analysis here.
//
void DSGraph::removeTriviallyDeadNodes() {
  removeIdenticalCalls(FunctionCalls, Func ? Func->getName() : "");
  removeIdenticalCalls(AuxFunctionCalls, Func ? Func->getName() : "");

  for (unsigned i = 0; i != Nodes.size(); ++i)
    if (isNodeDead(Nodes[i])) {               // This node is dead!
      delete Nodes[i];                        // Free memory...
      Nodes.erase(Nodes.begin()+i--);         // Remove from node list...
    }
}


/// markReachableNodes - This method recursively traverses the specified
/// DSNodes, marking any nodes which are reachable.  All reachable nodes it adds
/// to the set, which allows it to only traverse visited nodes once.
///
void DSNode::markReachableNodes(hash_set<DSNode*> &ReachableNodes) {
  if (this == 0) return;
  if (ReachableNodes.count(this)) return;          // Already marked reachable
  ReachableNodes.insert(this);                     // Is reachable now

  for (unsigned i = 0, e = getSize(); i < e; i += DS::PointerSize)
    getLink(i).getNode()->markReachableNodes(ReachableNodes);
}

void DSCallSite::markReachableNodes(hash_set<DSNode*> &Nodes) {
  getRetVal().getNode()->markReachableNodes(Nodes);
  getCallee().getNode()->markReachableNodes(Nodes);
  
  for (unsigned j = 0, e = getNumPtrArgs(); j != e; ++j)
    getPtrArg(j).getNode()->markReachableNodes(Nodes);
}

// CanReachAliveNodes - Simple graph walker that recursively traverses the graph
// looking for a node that is marked alive.  If an alive node is found, return
// true, otherwise return false.  If an alive node is reachable, this node is
// marked as alive...
//
static bool CanReachAliveNodes(DSNode *N, hash_set<DSNode*> &Alive,
                               hash_set<DSNode*> &Visited) {
  if (N == 0) return false;

  // If we know that this node is alive, return so!
  if (Alive.count(N)) return true;

  // Otherwise, we don't think the node is alive yet, check for infinite
  // recursion.
  if (Visited.count(N)) return false;  // Found a cycle
  Visited.insert(N);   // No recursion, insert into Visited...

  if (N->NodeType & DSNode::GlobalNode)
    return false; // Global nodes will be marked on their own

  for (unsigned i = 0, e = N->getSize(); i < e; i += DS::PointerSize)
    if (CanReachAliveNodes(N->getLink(i).getNode(), Alive, Visited)) {
      N->markReachableNodes(Alive);
      return true;
    }
  return false;
}

// CallSiteUsesAliveArgs - Return true if the specified call site can reach any
// alive nodes.
//
static bool CallSiteUsesAliveArgs(DSCallSite &CS, hash_set<DSNode*> &Alive,
                                  hash_set<DSNode*> &Visited) {
  if (CanReachAliveNodes(CS.getRetVal().getNode(), Alive, Visited) ||
      CanReachAliveNodes(CS.getCallee().getNode(), Alive, Visited))
    return true;
  for (unsigned j = 0, e = CS.getNumPtrArgs(); j != e; ++j)
    if (CanReachAliveNodes(CS.getPtrArg(j).getNode(), Alive, Visited))
      return true;
  return false;
}

// GlobalIsAlivenessRoot - Return true if the specified global node is
// intrinsically alive in the context of the current graph (ie, it is a root of
// aliveness).  For TD graphs, no globals are.  For the BU graphs all are unless
// they are trivial globals...
//
static bool GlobalIsAlivenessRoot(DSNode *N, unsigned Flags) {
  if (Flags & DSGraph::RemoveUnreachableGlobals)
    return false;                 // If we are to remove all globals, go for it.

  // Ok, we are keeping globals... hrm, we can still delete it if it has no
  // links, and no mod/ref or other info...  If it is not modified, it can't
  // have links...
  //
  if ((N->NodeType & ~(DSNode::Composition | DSNode::Array)) == 0)
    return false;
  return true;
}

// removeDeadNodes - Use a more powerful reachability analysis to eliminate
// subgraphs that are unreachable.  This often occurs because the data
// structure doesn't "escape" into it's caller, and thus should be eliminated
// from the caller's graph entirely.  This is only appropriate to use when
// inlining graphs.
//
void DSGraph::removeDeadNodes(unsigned Flags) {
  // Reduce the amount of work we have to do...
  removeTriviallyDeadNodes();

  // FIXME: Merge nontrivially identical call nodes...

  // Alive - a set that holds all nodes found to be reachable/alive.
  hash_set<DSNode*> Alive;
  std::vector<std::pair<Value*, DSNode*> > GlobalNodes;

  // Mark all nodes reachable by (non-global) scalar nodes as alive...
  for (hash_map<Value*, DSNodeHandle>::iterator I = ScalarMap.begin(),
         E = ScalarMap.end(); I != E; ++I)
    if (!isa<GlobalValue>(I->first) ||
        GlobalIsAlivenessRoot(I->second.getNode(), Flags))
      I->second.getNode()->markReachableNodes(Alive);
    else                    // Keep track of global nodes
      GlobalNodes.push_back(std::make_pair(I->first, I->second.getNode()));

  // The return value is alive as well...
  RetNode.getNode()->markReachableNodes(Alive);

  // If any global nodes points to a non-global that is "alive", the global is
  // "alive" as well...
  //
  hash_set<DSNode*> Visited;
  for (unsigned i = 0, e = GlobalNodes.size(); i != e; ++i)
    CanReachAliveNodes(GlobalNodes[i].second, Alive, Visited);

  std::vector<bool> FCallsAlive(FunctionCalls.size());
  for (unsigned i = 0, e = FunctionCalls.size(); i != e; ++i)
    if (!(Flags & DSGraph::RemoveUnreachableGlobals) ||
        CallSiteUsesAliveArgs(FunctionCalls[i], Alive, Visited)) {
      FunctionCalls[i].markReachableNodes(Alive);
      FCallsAlive[i] = true;
    }

  std::vector<bool> AuxFCallsAlive(AuxFunctionCalls.size());
  for (unsigned i = 0, e = AuxFunctionCalls.size(); i != e; ++i)
    if (CallSiteUsesAliveArgs(AuxFunctionCalls[i], Alive, Visited)) {
      AuxFunctionCalls[i].markReachableNodes(Alive);
      AuxFCallsAlive[i] = true;
    }

  // Remove all dead function calls...
  unsigned CurIdx = 0;
  for (unsigned i = 0, e = FunctionCalls.size(); i != e; ++i)
    if (FCallsAlive[i])
      FunctionCalls[CurIdx++].swap(FunctionCalls[i]);
  // Crop all the bad ones out...
  FunctionCalls.erase(FunctionCalls.begin()+CurIdx, FunctionCalls.end());

  // Remove all dead aux function calls...
  CurIdx = 0;
  for (unsigned i = 0, e = AuxFunctionCalls.size(); i != e; ++i)
    if (AuxFCallsAlive[i])
      AuxFunctionCalls[CurIdx++].swap(AuxFunctionCalls[i]);
  // Crop all the bad ones out...
  AuxFunctionCalls.erase(AuxFunctionCalls.begin()+CurIdx,
                         AuxFunctionCalls.end());


  // Remove all unreachable globals from the ScalarMap
  for (unsigned i = 0, e = GlobalNodes.size(); i != e; ++i)
    if (!Alive.count(GlobalNodes[i].second))
      ScalarMap.erase(GlobalNodes[i].first);

  // Loop over all unreachable nodes, dropping their references...
  for (unsigned i = 0; i != Nodes.size(); ++i)
    if (!Alive.count(Nodes[i])) {
      DSNode *N = Nodes[i];
      std::swap(Nodes[i--], Nodes.back());  // move node to end of vector
      Nodes.pop_back();                // Erase node from alive list.
      N->dropAllReferences();          // Drop all outgoing edges

      while (!N->getReferrers().empty())
        N->getReferrers().back()->setNode(0);
      delete N;
    }
}

#if 0
//===----------------------------------------------------------------------===//
// GlobalDSGraph Implementation
//===----------------------------------------------------------------------===//

#if 0
// Bits used in the next function
static const char ExternalTypeBits = DSNode::GlobalNode | DSNode::HeapNode;


// GlobalDSGraph::cloneNodeInto - Clone a global node and all its externally
// visible target links (and recursively their such links) into this graph.
// NodeCache maps the node being cloned to its clone in the Globals graph,
// in order to track cycles.
// GlobalsAreFinal is a flag that says whether it is safe to assume that
// an existing global node is complete.  This is important to avoid
// reinserting all globals when inserting Calls to functions.
// This is a helper function for cloneGlobals and cloneCalls.
// 
DSNode* GlobalDSGraph::cloneNodeInto(DSNode *OldNode,
                                    hash_map<const DSNode*, DSNode*> &NodeCache,
                                    bool GlobalsAreFinal) {
  if (OldNode == 0) return 0;

  // The caller should check this is an external node.  Just more  efficient...
  assert((OldNode->NodeType & ExternalTypeBits) && "Non-external node");

  // If a clone has already been created for OldNode, return it.
  DSNode*& CacheEntry = NodeCache[OldNode];
  if (CacheEntry != 0)
    return CacheEntry;

  // The result value...
  DSNode* NewNode = 0;

  // If nodes already exist for any of the globals of OldNode,
  // merge all such nodes together since they are merged in OldNode.
  // If ValueCacheIsFinal==true, look for an existing node that has
  // an identical list of globals and return it if it exists.
  //
  for (unsigned j = 0, N = OldNode->getGlobals().size(); j != N; ++j)
    if (DSNode *PrevNode = ScalarMap[OldNode->getGlobals()[j]].getNode()) {
      if (NewNode == 0) {
        NewNode = PrevNode;             // first existing node found
        if (GlobalsAreFinal && j == 0)
          if (OldNode->getGlobals() == PrevNode->getGlobals()) {
            CacheEntry = NewNode;
            return NewNode;
          }
      }
      else if (NewNode != PrevNode) {   // found another, different from prev
        // update ValMap *before* merging PrevNode into NewNode
        for (unsigned k = 0, NK = PrevNode->getGlobals().size(); k < NK; ++k)
          ScalarMap[PrevNode->getGlobals()[k]] = NewNode;
        NewNode->mergeWith(PrevNode);
      }
    } else if (NewNode != 0) {
      ScalarMap[OldNode->getGlobals()[j]] = NewNode; // add the merged node
    }

  // If no existing node was found, clone the node and update the ValMap.
  if (NewNode == 0) {
    NewNode = new DSNode(*OldNode);
    Nodes.push_back(NewNode);
    for (unsigned j = 0, e = NewNode->getNumLinks(); j != e; ++j)
      NewNode->setLink(j, 0);
    for (unsigned j = 0, N = NewNode->getGlobals().size(); j < N; ++j)
      ScalarMap[NewNode->getGlobals()[j]] = NewNode;
  }
  else
    NewNode->NodeType |= OldNode->NodeType; // Markers may be different!

  // Add the entry to NodeCache
  CacheEntry = NewNode;

  // Rewrite the links in the new node to point into the current graph,
  // but only for links to external nodes.  Set other links to NULL.
  for (unsigned j = 0, e = OldNode->getNumLinks(); j != e; ++j) {
    DSNode* OldTarget = OldNode->getLink(j);
    if (OldTarget && (OldTarget->NodeType & ExternalTypeBits)) {
      DSNode* NewLink = this->cloneNodeInto(OldTarget, NodeCache);
      if (NewNode->getLink(j))
        NewNode->getLink(j)->mergeWith(NewLink);
      else
        NewNode->setLink(j, NewLink);
    }
  }

  // Remove all local markers
  NewNode->NodeType &= ~(DSNode::AllocaNode | DSNode::ScalarNode);

  return NewNode;
}


// GlobalDSGraph::cloneCalls - Clone function calls and their visible target
// links (and recursively their such links) into this graph.
// 
void GlobalDSGraph::cloneCalls(DSGraph& Graph) {
  hash_map<const DSNode*, DSNode*> NodeCache;
  std::vector<DSCallSite >& FromCalls =Graph.FunctionCalls;

  FunctionCalls.reserve(FunctionCalls.size() + FromCalls.size());

  for (int i = 0, ei = FromCalls.size(); i < ei; ++i) {
    DSCallSite& callCopy = FunctionCalls.back();
    callCopy.reserve(FromCalls[i].size());
    for (unsigned j = 0, ej = FromCalls[i].size(); j != ej; ++j)
      callCopy.push_back
        ((FromCalls[i][j] && (FromCalls[i][j]->NodeType & ExternalTypeBits))
         ? cloneNodeInto(FromCalls[i][j], NodeCache, true)
         : 0);
  }

  // remove trivially identical function calls
  removeIdenticalCalls(FunctionCalls, "Globals Graph");
}
#endif

#endif