//===- ExprTypeConvert.cpp - Code to change an LLVM Expr Type ---------------=//
//
// This file implements the part of level raising that checks to see if it is
// possible to coerce an entire expression tree into a different type.  If
// convertable, other routines from this file will do the conversion.
//
//===----------------------------------------------------------------------===//

#include "TransformInternals.h"
#include "llvm/Method.h"
#include "llvm/Support/STLExtras.h"
#include "llvm/iOther.h"
#include "llvm/iMemory.h"
#include "llvm/ConstPoolVals.h"
#include "llvm/Optimizations/ConstantHandling.h"
#include "llvm/Optimizations/DCE.h"
#include <map>
#include <algorithm>

#include "llvm/Assembly/Writer.h"

//#define DEBUG_EXPR_CONVERT 1

static inline const Type *getTy(const Value *V, ValueTypeCache &CT) {
  ValueTypeCache::iterator I = CT.find(V);
  if (I == CT.end()) return V->getType();
  return I->second;
}

GetElementPtrInst *getAddToGEPResult(const Type *Ty, const Value *V) {
  const StructType *StructTy = getPointedToStruct(Ty);
  if (StructTy == 0) return 0;    // Must be a pointer to a struct...

  // Must be a constant unsigned offset value... get it now...
  if (!isa<ConstPoolUInt>(V)) return 0;
  unsigned Offset = cast<ConstPoolUInt>(V)->getValue();
 
  // Check to make sure the offset is somewhat legitiment w.r.t the struct
  // type...
  if (Offset >= TD.getTypeSize(StructTy)) return 0;
  
  // If we get this far, we have succeeded... TODO: We need to handle array
  // indexing as well...
  const StructLayout *SL = TD.getStructLayout(StructTy);
  vector<ConstPoolVal*> Offsets;
  unsigned ActualOffset = Offset;
  const Type *ElTy = getStructOffsetType(StructTy, ActualOffset, Offsets);

  if (ActualOffset != Offset) return 0;  // TODO: Handle Array indexing...
 
  // Success!  Return the GEP instruction, with a dummy first argument.
  ConstPoolVal *Dummy = ConstPoolVal::getNullConstant(Ty);
  return new GetElementPtrInst(Dummy, Offsets);
}



static bool OperandConvertableToType(User *U, Value *V, const Type *Ty,
                                     ValueTypeCache &ConvertedTypes);

static void ConvertOperandToType(User *U, Value *OldVal, Value *NewVal,
                                 ValueMapCache &VMC);


// ExpressionConvertableToType - Return true if it is possible
bool ExpressionConvertableToType(Value *V, const Type *Ty,
                                 ValueTypeCache &CTMap) {
  if (V->getType() == Ty) return true;  // Expression already correct type!

  // Expression type must be holdable in a register.
  if (!isFirstClassType(Ty))
    return false;
  
  ValueTypeCache::iterator CTMI = CTMap.find(V);
  if (CTMI != CTMap.end()) return CTMI->second == Ty;

  CTMap[V] = Ty;

  Instruction *I = dyn_cast<Instruction>(V);
  if (I == 0) {
    // It's not an instruction, check to see if it's a constant... all constants
    // can be converted to an equivalent value (except pointers, they can't be
    // const prop'd in general).  We just ask the constant propogator to see if
    // it can convert the value...
    //
    if (ConstPoolVal *CPV = dyn_cast<ConstPoolVal>(V))
      if (opt::ConstantFoldCastInstruction(CPV, Ty))
        return true;  // Don't worry about deallocating, it's a constant.

    return false;              // Otherwise, we can't convert!
  }

  switch (I->getOpcode()) {
  case Instruction::Cast:
    // We can convert the expr if the cast destination type is losslessly
    // convertable to the requested type.
    if (!losslessCastableTypes(Ty, I->getType())) return false;
#if 1
    // We also do not allow conversion of a cast that casts from a ptr to array
    // of X to a *X.  For example: cast [4 x %List *] * %val to %List * *
    //
    if (PointerType *SPT = dyn_cast<PointerType>(I->getOperand(0)->getType()))
      if (PointerType *DPT = dyn_cast<PointerType>(I->getType()))
        if (ArrayType *AT = dyn_cast<ArrayType>(SPT->getValueType()))
          if (AT->getElementType() == DPT->getValueType())
            return false;
#endif
    return true;

  case Instruction::Add:
  case Instruction::Sub:
    if (!ExpressionConvertableToType(I->getOperand(0), Ty, CTMap) ||
        !ExpressionConvertableToType(I->getOperand(1), Ty, CTMap))
      return false;
    break;
  case Instruction::Shr:
    if (Ty->isSigned() != V->getType()->isSigned()) return false;
    // FALL THROUGH
  case Instruction::Shl:
    if (!ExpressionConvertableToType(I->getOperand(0), Ty, CTMap))
      return false;
    break;

  case Instruction::Load: {
    LoadInst *LI = cast<LoadInst>(I);
    if (LI->hasIndices()) {
      // We can't convert a load expression if it has indices... unless they are
      // all zero.
      const vector<ConstPoolVal*> &CPV = LI->getIndices();
      for (unsigned i = 0; i < CPV.size(); ++i)
        if (!CPV[i]->isNullValue()) return false;
    }

    if (!ExpressionConvertableToType(LI->getPointerOperand(),
                                     PointerType::get(Ty), CTMap))
      return false;
    break;                                     
  }
  case Instruction::PHINode: {
    PHINode *PN = cast<PHINode>(I);
    for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i)
      if (!ExpressionConvertableToType(PN->getIncomingValue(i), Ty, CTMap))
        return false;
    break;
  }

  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertable to a pointer type if they have
    // a number of zeros at the end.  Because removing these values does not
    // change the logical offset of the GEP, it is okay and fair to remove them.
    // This can change this:
    //   %t1 = getelementptr %Hosp * %hosp, ubyte 4, ubyte 0  ; <%List **>
    //   %t2 = cast %List * * %t1 to %List *
    // into
    //   %t2 = getelementptr %Hosp * %hosp, ubyte 4           ; <%List *>
    // 
    GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);
    const PointerType *PTy = dyn_cast<PointerType>(Ty);
    if (!PTy) return false;

    // Check to see if there are zero elements that we can remove from the
    // index array.  If there are, check to see if removing them causes us to
    // get to the right type...
    //
    vector<ConstPoolVal*> Indices = GEP->getIndices();
    const Type *BaseType = GEP->getPointerOperand()->getType();

    while (Indices.size() &&
           cast<ConstPoolUInt>(Indices.back())->getValue() == 0) {
      Indices.pop_back();
      const Type *ElTy = GetElementPtrInst::getIndexedType(BaseType, Indices,
                                                           true);
      if (ElTy == PTy->getValueType())
        break;  // Found a match!!
    }
    return false;   // No match, maybe next time.
  }

  default:
    return false;
  }

  // Expressions are only convertable if all of the users of the expression can
  // have this value converted.  This makes use of the map to avoid infinite
  // recursion.
  //
  if (isa<Instruction>(V)) {
    for (Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I)
      if (!OperandConvertableToType(*I, V, Ty, CTMap))
        return false;
  }

  return true;
}


Value *ConvertExpressionToType(Value *V, const Type *Ty, ValueMapCache &VMC) {
  ValueMapCache::ExprMapTy::iterator VMCI = VMC.ExprMap.find(V);
  if (VMCI != VMC.ExprMap.end()) {
    assert(VMCI->second->getType() == Ty);
    return VMCI->second;
  }

#ifdef DEBUG_EXPR_CONVERT
  cerr << "CETT: " << (void*)V << " " << V;
#endif

  Instruction *I = dyn_cast<Instruction>(V);
  if (I == 0)
    if (ConstPoolVal *CPV = cast<ConstPoolVal>(V)) {
      // Constants are converted by constant folding the cast that is required.
      // We assume here that all casts are implemented for constant prop.
      Value *Result = opt::ConstantFoldCastInstruction(CPV, Ty);
      assert(Result && "ConstantFoldCastInstruction Failed!!!");
      assert(Result->getType() == Ty && "Const prop of cast failed!");

      // Add the instruction to the expression map
      VMC.ExprMap[V] = Result;
      return Result;
    }


  BasicBlock *BB = I->getParent();
  BasicBlock::InstListType &BIL = BB->getInstList();
  string Name = I->getName();  if (!Name.empty()) I->setName("");
  Instruction *Res;     // Result of conversion

  ValueHandle IHandle(VMC, I);  // Prevent I from being removed!
  
  ConstPoolVal *Dummy = ConstPoolVal::getNullConstant(Ty);

  //cerr << endl << endl << "Type:\t" << Ty << "\nInst: " << I << "BB Before: " << BB << endl;

  switch (I->getOpcode()) {
  case Instruction::Cast:
    Res = new CastInst(I->getOperand(0), Ty, Name);
    break;
    
  case Instruction::Add:
  case Instruction::Sub:
    Res = BinaryOperator::create(cast<BinaryOperator>(I)->getOpcode(),
                                 Dummy, Dummy, Name);
    VMC.ExprMap[I] = Res;   // Add node to expression eagerly

    Res->setOperand(0, ConvertExpressionToType(I->getOperand(0), Ty, VMC));
    Res->setOperand(1, ConvertExpressionToType(I->getOperand(1), Ty, VMC));
    break;

  case Instruction::Shl:
  case Instruction::Shr:
    Res = new ShiftInst(cast<ShiftInst>(I)->getOpcode(), Dummy,
                        I->getOperand(1), Name);
    VMC.ExprMap[I] = Res;
    Res->setOperand(0, ConvertExpressionToType(I->getOperand(0), Ty, VMC));
    break;

  case Instruction::Load: {
    LoadInst *LI = cast<LoadInst>(I);
#ifndef NDEBUG
    if (LI->hasIndices()) {
      // We can't convert a load expression if it has indices... unless they are
      // all zero.
      const vector<ConstPoolVal*> &CPV = LI->getIndices();
      for (unsigned i = 0; i < CPV.size(); ++i)
        assert(CPV[i]->isNullValue() && "Load index not 0!");
    }
#endif
    Res = new LoadInst(ConstPoolVal::getNullConstant(PointerType::get(Ty)), 
                       Name);
    VMC.ExprMap[I] = Res;
    Res->setOperand(0, ConvertExpressionToType(LI->getPointerOperand(),
                                               PointerType::get(Ty), VMC));
    assert(Res->getOperand(0)->getType() == PointerType::get(Ty));
    assert(Ty == Res->getType());
    assert(isFirstClassType(Res->getType()) && "Load of structure or array!");
    break;
  }

  case Instruction::PHINode: {
    PHINode *OldPN = cast<PHINode>(I);
    PHINode *NewPN = new PHINode(Ty, Name);

    VMC.ExprMap[I] = NewPN;   // Add node to expression eagerly
    while (OldPN->getNumOperands()) {
      BasicBlock *BB = OldPN->getIncomingBlock(0);
      Value *OldVal = OldPN->getIncomingValue(0);
      ValueHandle OldValHandle(VMC, OldVal);
      OldPN->removeIncomingValue(BB);
      Value *V = ConvertExpressionToType(OldVal, Ty, VMC);
      NewPN->addIncoming(V, BB);
    }
    Res = NewPN;
    break;
  }

  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertable to a pointer type if they have
    // a number of zeros at the end.  Because removing these values does not
    // change the logical offset of the GEP, it is okay and fair to remove them.
    // This can change this:
    //   %t1 = getelementptr %Hosp * %hosp, ubyte 4, ubyte 0  ; <%List **>
    //   %t2 = cast %List * * %t1 to %List *
    // into
    //   %t2 = getelementptr %Hosp * %hosp, ubyte 4           ; <%List *>
    // 
    GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);

    // Check to see if there are zero elements that we can remove from the
    // index array.  If there are, check to see if removing them causes us to
    // get to the right type...
    //
    vector<ConstPoolVal*> Indices = GEP->getIndices();
    const Type *BaseType = GEP->getPointerOperand()->getType();
    const Type *PVTy = cast<PointerType>(Ty)->getValueType();
    Res = 0;
    while (Indices.size() &&
           cast<ConstPoolUInt>(Indices.back())->getValue() == 0) {
      Indices.pop_back();
      if (GetElementPtrInst::getIndexedType(BaseType, Indices, true) == PVTy) {
        if (Indices.size() == 0) {
          Res = new CastInst(GEP->getPointerOperand(), BaseType); // NOOP
        } else {
          Res = new GetElementPtrInst(GEP->getPointerOperand(), Indices, Name);
        }
        break;
      }
    }
    assert(Res && "Didn't find match!");
    break;   // No match, maybe next time.
  }

  default:
    assert(0 && "Expression convertable, but don't know how to convert?");
    return 0;
  }

  assert(Res->getType() == Ty && "Didn't convert expr to correct type!");

  BasicBlock::iterator It = find(BIL.begin(), BIL.end(), I);
  assert(It != BIL.end() && "Instruction not in own basic block??");
  BIL.insert(It, Res);

  // Add the instruction to the expression map
  VMC.ExprMap[I] = Res;

  // Expressions are only convertable if all of the users of the expression can
  // have this value converted.  This makes use of the map to avoid infinite
  // recursion.
  //
  unsigned NumUses = I->use_size();
  for (unsigned It = 0; It < NumUses; ) {
    unsigned OldSize = NumUses;
    ConvertOperandToType(*(I->use_begin()+It), I, Res, VMC);
    NumUses = I->use_size();
    if (NumUses == OldSize) ++It;
  }

#ifdef DEBUG_EXPR_CONVERT
  cerr << "ExpIn: " << (void*)I << " " << I
       << "ExpOut: " << (void*)Res << " " << Res;
  cerr << "ExpCREATED: " << (void*)Res << " " << Res;
#endif

  if (I->use_empty()) {
#ifdef DEBUG_EXPR_CONVERT
    cerr << "EXPR DELETING: " << (void*)I << " " << I;
#endif
    BIL.remove(I);
    delete I;
  }

  return Res;
}



// RetValConvertableToType - Return true if it is possible
bool RetValConvertableToType(Value *V, const Type *Ty,
                             ValueTypeCache &ConvertedTypes) {
  ValueTypeCache::iterator I = ConvertedTypes.find(V);
  if (I != ConvertedTypes.end()) return I->second == Ty;
  ConvertedTypes[V] = Ty;

  assert(isa<Instruction>(V) && "Can't convert ret val of non instruction");

  // It is safe to convert the specified value to the specified type IFF all of
  // the uses of the value can be converted to accept the new typed value.
  //
  for (Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I)
    if (!OperandConvertableToType(*I, V, Ty, ConvertedTypes))
      return false;

  return true;
}





// OperandConvertableToType - Return true if it is possible to convert operand
// V of User (instruction) U to the specified type.  This is true iff it is
// possible to change the specified instruction to accept this.  CTMap is a map
// of converted types, so that circular definitions will see the future type of
// the expression, not the static current type.
//
static bool OperandConvertableToType(User *U, Value *V, const Type *Ty,
                                     ValueTypeCache &CTMap) {
  // TODO: IS THIS A BUG????
  if (V->getType() == Ty) return true;   // Already the right type?

  // Expression type must be holdable in a register.
  if (!isFirstClassType(Ty))
    return false;

  Instruction *I = dyn_cast<Instruction>(U);
  if (I == 0) return false;              // We can't convert!

  switch (I->getOpcode()) {
  case Instruction::Cast:
    assert(I->getOperand(0) == V);
    // We can convert the expr if the cast destination type is losslessly
    // convertable to the requested type.
    if (!losslessCastableTypes(Ty, I->getOperand(0)->getType()))
      return false;
#if 1
    // We also do not allow conversion of a cast that casts from a ptr to array
    // of X to a *X.  For example: cast [4 x %List *] * %val to %List * *
    //
    if (PointerType *SPT = dyn_cast<PointerType>(I->getOperand(0)->getType()))
      if (PointerType *DPT = dyn_cast<PointerType>(I->getType()))
        if (ArrayType *AT = dyn_cast<ArrayType>(SPT->getValueType()))
          if (AT->getElementType() == DPT->getValueType())
            return false;
#endif
    return true;

  case Instruction::Add:
    if (V == I->getOperand(0) && isa<CastInst>(I->getOperand(1))) {
      Instruction *GEP =
        getAddToGEPResult(Ty, cast<CastInst>(I->getOperand(1))->getOperand(0));
      if (GEP) {  // If successful, this Add can be converted to a GEP.
        const Type *RetTy = GEP->getType();  // Get the new type...
        delete GEP;  // We don't want the actual instruction yet...
        // Only successful if we can convert this type to the required type
        return RetValConvertableToType(I, RetTy, CTMap);
      }
    }
    // FALLTHROUGH
  case Instruction::Sub: {
    Value *OtherOp = I->getOperand((V == I->getOperand(0)) ? 1 : 0);
    return RetValConvertableToType(I, Ty, CTMap) &&
           ExpressionConvertableToType(OtherOp, Ty, CTMap);
  }
  case Instruction::SetEQ:
  case Instruction::SetNE: {
    Value *OtherOp = I->getOperand((V == I->getOperand(0)) ? 1 : 0);
    return ExpressionConvertableToType(OtherOp, Ty, CTMap);
  }
  case Instruction::Shr:
    if (Ty->isSigned() != V->getType()->isSigned()) return false;
    // FALL THROUGH
  case Instruction::Shl:
    assert(I->getOperand(0) == V);
    return RetValConvertableToType(I, Ty, CTMap);

  case Instruction::Load:
    assert(I->getOperand(0) == V);
    if (const PointerType *PT = dyn_cast<PointerType>(Ty)) {
      LoadInst *LI = cast<LoadInst>(I);
      const Type *PVTy = PT->getValueType();

      if (LI->hasIndices() || isa<ArrayType>(PVTy))
        return false;

      if (!isFirstClassType(PVTy)) {
        // They could be loading the first element of a structure type...
        if (const StructType *ST = dyn_cast<StructType>(PVTy)) {
          unsigned Offset = 0;   // No offset, get first leaf.
          vector<ConstPoolVal*> Offsets;  // Discarded...
          const Type *Ty = getStructOffsetType(ST, Offset, Offsets, false);
          assert(Offset == 0 && "Offset changed from zero???");
          if (!isFirstClassType(Ty)) return false;

          // See if the leaf type is compatible with the old return type...
          if (TD.getTypeSize(Ty) != TD.getTypeSize(LI->getType()))
            return false;
          return RetValConvertableToType(LI, Ty, CTMap);
        }
        return false;
      }

      if (TD.getTypeSize(PVTy) != TD.getTypeSize(LI->getType()))
        return false;

      return RetValConvertableToType(LI, PVTy, CTMap);
    }
    return false;

  case Instruction::Store: {
    StoreInst *SI = cast<StoreInst>(I);
    if (SI->hasIndices()) return false;

    if (V == I->getOperand(0)) {
      // Can convert the store if we can convert the pointer operand to match
      // the new  value type...
      return ExpressionConvertableToType(I->getOperand(1), PointerType::get(Ty),
                                         CTMap);
    } else if (const PointerType *PT = dyn_cast<PointerType>(Ty)) {
      if (isa<ArrayType>(PT->getValueType()))
        return false;  // Avoid getDataSize on unsized array type!
      assert(V == I->getOperand(1));

      // Must move the same amount of data...
      if (TD.getTypeSize(PT->getValueType()) != 
          TD.getTypeSize(I->getOperand(0)->getType())) return false;

      // Can convert store if the incoming value is convertable...
      return ExpressionConvertableToType(I->getOperand(0), PT->getValueType(),
                                         CTMap);
    }
    return false;
  }

  case Instruction::PHINode: {
    PHINode *PN = cast<PHINode>(I);
    for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i)
      if (!ExpressionConvertableToType(PN->getIncomingValue(i), Ty, CTMap))
        return false;
    return RetValConvertableToType(PN, Ty, CTMap);
  }

#if 0
  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertable to a pointer type if they have
    // a number of zeros at the end.  Because removing these values does not
    // change the logical offset of the GEP, it is okay and fair to remove them.
    // This can change this:
    //   %t1 = getelementptr %Hosp * %hosp, ubyte 4, ubyte 0  ; <%List **>
    //   %t2 = cast %List * * %t1 to %List *
    // into
    //   %t2 = getelementptr %Hosp * %hosp, ubyte 4           ; <%List *>
    // 
    GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);
    const PointerType *PTy = dyn_cast<PointerType>(Ty);
    if (!PTy) return false;

    // Check to see if there are zero elements that we can remove from the
    // index array.  If there are, check to see if removing them causes us to
    // get to the right type...
    //
    vector<ConstPoolVal*> Indices = GEP->getIndices();
    const Type *BaseType = GEP->getPointerOperand()->getType();

    while (Indices.size() &&
           cast<ConstPoolUInt>(Indices.back())->getValue() == 0) {
      Indices.pop_back();
      const Type *ElTy = GetElementPtrInst::getIndexedType(BaseType, Indices,
                                                           true);
      if (ElTy == PTy->getValueType())
        return true;  // Found a match!!
    }
    break;   // No match, maybe next time.
  }
#endif
  }
  return false;
}


void ConvertUsersType(Value *V, Value *NewVal, ValueMapCache &VMC) {
  ValueHandle VH(VMC, V);

  unsigned NumUses = V->use_size();
  for (unsigned It = 0; It < NumUses; ) {
    unsigned OldSize = NumUses;
    ConvertOperandToType(*(V->use_begin()+It), V, NewVal, VMC);
    NumUses = V->use_size();
    if (NumUses == OldSize) ++It;
  }
}



static void ConvertOperandToType(User *U, Value *OldVal, Value *NewVal,
                                 ValueMapCache &VMC) {
  if (isa<ValueHandle>(U)) return;  // Valuehandles don't let go of operands...

  if (VMC.OperandsMapped.count(U)) return;
  VMC.OperandsMapped.insert(U);

  ValueMapCache::ExprMapTy::iterator VMCI = VMC.ExprMap.find(U);
  if (VMCI != VMC.ExprMap.end())
    return;


  Instruction *I = cast<Instruction>(U);  // Only Instructions convertable

  BasicBlock *BB = I->getParent();
  BasicBlock::InstListType &BIL = BB->getInstList();
  string Name = I->getName();  if (!Name.empty()) I->setName("");
  Instruction *Res;     // Result of conversion

  //cerr << endl << endl << "Type:\t" << Ty << "\nInst: " << I << "BB Before: " << BB << endl;

  // Prevent I from being removed...
  ValueHandle IHandle(VMC, I);

  const Type *NewTy = NewVal->getType();
  ConstPoolVal *Dummy = (NewTy != Type::VoidTy) ? 
                  ConstPoolVal::getNullConstant(NewTy) : 0;

  switch (I->getOpcode()) {
  case Instruction::Cast:
    assert(I->getOperand(0) == OldVal);
    Res = new CastInst(NewVal, I->getType(), Name);
    break;

  case Instruction::Add:
    if (OldVal == I->getOperand(0) && isa<CastInst>(I->getOperand(1))) {
      Res = getAddToGEPResult(NewVal->getType(),
                              cast<CastInst>(I->getOperand(1))->getOperand(0));
      if (Res) {  // If successful, this Add should be converted to a GEP.
        // First operand is actually the given pointer...
        Res->setOperand(0, NewVal);
        break;
      }
    }
    // FALLTHROUGH

  case Instruction::Sub:
  case Instruction::SetEQ:
  case Instruction::SetNE: {
    Res = BinaryOperator::create(cast<BinaryOperator>(I)->getOpcode(),
                                 Dummy, Dummy, Name);
    VMC.ExprMap[I] = Res;   // Add node to expression eagerly

    unsigned OtherIdx = (OldVal == I->getOperand(0)) ? 1 : 0;
    Value *OtherOp    = I->getOperand(OtherIdx);
    Value *NewOther   = ConvertExpressionToType(OtherOp, NewTy, VMC);

    Res->setOperand(OtherIdx, NewOther);
    Res->setOperand(!OtherIdx, NewVal);
    break;
  }
  case Instruction::Shl:
  case Instruction::Shr:
    assert(I->getOperand(0) == OldVal);
    Res = new ShiftInst(cast<ShiftInst>(I)->getOpcode(), NewVal,
                        I->getOperand(1), Name);
    break;

  case Instruction::Load: {
    assert(I->getOperand(0) == OldVal && isa<PointerType>(NewVal->getType()));
    const Type *PVTy = cast<PointerType>(NewVal->getType())->getValueType();
    if (!isFirstClassType(PVTy)) {  // Must be an indirect load then...
      assert(isa<StructType>(PVTy));
      unsigned Offset = 0;   // No offset, get first leaf.
      vector<ConstPoolVal*> Offsets;  // Discarded...
      const Type *Ty = getStructOffsetType(PVTy, Offset, Offsets, false);
      Res = new LoadInst(NewVal, Offsets, Name);
    } else {
      Res = new LoadInst(NewVal, Name);
    }
    assert(isFirstClassType(Res->getType()) && "Load of structure or array!");
    break;
  }
  case Instruction::Store: {
    if (I->getOperand(0) == OldVal) {  // Replace the source value
      const PointerType *NewPT = PointerType::get(NewTy);
      Res = new StoreInst(NewVal, ConstPoolVal::getNullConstant(NewPT));
      VMC.ExprMap[I] = Res;
      Res->setOperand(1, ConvertExpressionToType(I->getOperand(1), NewPT, VMC));
    } else {                           // Replace the source pointer
      const Type *ValTy = cast<PointerType>(NewTy)->getValueType();
      Res = new StoreInst(ConstPoolVal::getNullConstant(ValTy), NewVal);
      VMC.ExprMap[I] = Res;
      Res->setOperand(0, ConvertExpressionToType(I->getOperand(0), ValTy, VMC));
    }
    break;
  }

  case Instruction::PHINode: {
    PHINode *OldPN = cast<PHINode>(I);
    PHINode *NewPN = new PHINode(NewTy, Name);
    VMC.ExprMap[I] = NewPN;

    while (OldPN->getNumOperands()) {
      BasicBlock *BB = OldPN->getIncomingBlock(0);
      Value *OldVal = OldPN->getIncomingValue(0);
      OldPN->removeIncomingValue(BB);
      Value *V = ConvertExpressionToType(OldVal, NewTy, VMC);
      NewPN->addIncoming(V, BB);
    }
    Res = NewPN;
    break;
  }

#if 0
  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertable to a pointer type if they have
    // a number of zeros at the end.  Because removing these values does not
    // change the logical offset of the GEP, it is okay and fair to remove them.
    // This can change this:
    //   %t1 = getelementptr %Hosp * %hosp, ubyte 4, ubyte 0  ; <%List **>
    //   %t2 = cast %List * * %t1 to %List *
    // into
    //   %t2 = getelementptr %Hosp * %hosp, ubyte 4           ; <%List *>
    // 
    GetElementPtrInst *GEP = cast<GetElementPtrInst>(I);

    // Check to see if there are zero elements that we can remove from the
    // index array.  If there are, check to see if removing them causes us to
    // get to the right type...
    //
    vector<ConstPoolVal*> Indices = GEP->getIndices();
    const Type *BaseType = GEP->getPointerOperand()->getType();
    const Type *PVTy = cast<PointerType>(Ty)->getValueType();
    Res = 0;
    while (Indices.size() &&
           cast<ConstPoolUInt>(Indices.back())->getValue() == 0) {
      Indices.pop_back();
      if (GetElementPtrInst::getIndexedType(BaseType, Indices, true) == PVTy) {
        if (Indices.size() == 0) {
          Res = new CastInst(GEP->getPointerOperand(), BaseType); // NOOP
        } else {
          Res = new GetElementPtrInst(GEP->getPointerOperand(), Indices, Name);
        }
        break;
      }
    }
    assert(Res && "Didn't find match!");
    break;   // No match, maybe next time.
  }
#endif

  default:
    assert(0 && "Expression convertable, but don't know how to convert?");
    return;
  }

  BasicBlock::iterator It = find(BIL.begin(), BIL.end(), I);
  assert(It != BIL.end() && "Instruction not in own basic block??");
  BIL.insert(It, Res);   // Keep It pointing to old instruction

#ifdef DEBUG_EXPR_CONVERT
  cerr << "COT CREATED: "  << (void*)Res << " " << Res;
  cerr << "In: " << (void*)I << " " << I << "Out: " << (void*)Res << " " << Res;
#endif

  // Add the instruction to the expression map
  VMC.ExprMap[I] = Res;

  if (I->getType() != Res->getType())
    ConvertUsersType(I, Res, VMC);
  else {
    for (unsigned It = 0; It < I->use_size(); ) {
      User *Use = *(I->use_begin()+It);
      if (isa<ValueHandle>(Use))            // Don't remove ValueHandles!
        ++It;
      else
        Use->replaceUsesOfWith(I, Res);
    }

    if (I->use_empty()) {
      // Now we just need to remove the old instruction so we don't get infinite
      // loops.  Note that we cannot use DCE because DCE won't remove a store
      // instruction, for example.
      //
#ifdef DEBUG_EXPR_CONVERT
      cerr << "DELETING: " << (void*)I << " " << I;
#endif
      BIL.remove(I);
      delete I;
    } else {
      for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
           UI != UE; ++UI)
        assert(isa<ValueHandle>((Value*)*UI) &&"Uses of Instruction remain!!!");
    }
  }
}


ValueHandle::ValueHandle(ValueMapCache &VMC, Value *V) : Instruction(Type::VoidTy, UserOp1, ""), 
                                                         Cache(VMC) {
#ifdef DEBUG_EXPR_CONVERT
  cerr << "VH AQUIRING: " << (void*)V << " " << V;
#endif
  Operands.push_back(Use(V, this));
}

static void RecursiveDelete(ValueMapCache &Cache, Instruction *I) {
  if (!I || !I->use_empty()) return;

  assert(I->getParent() && "Inst not in basic block!");

#ifdef DEBUG_EXPR_CONVERT
  cerr << "VH DELETING: " << (void*)I << " " << I;
#endif

  for (User::op_iterator OI = I->op_begin(), OE = I->op_end(); 
       OI != OE; ++OI) {
    Instruction *U = dyn_cast<Instruction>(*OI);
    if (U) {
      *OI = 0;
      RecursiveDelete(Cache, dyn_cast<Instruction>(U));
    }
  }

  I->getParent()->getInstList().remove(I);

  Cache.OperandsMapped.erase(I);
  Cache.ExprMap.erase(I);
  delete I;
}

ValueHandle::~ValueHandle() {
  if (Operands[0]->use_size() == 1) {
    Value *V = Operands[0];
    Operands[0] = 0;   // Drop use!

    // Now we just need to remove the old instruction so we don't get infinite
    // loops.  Note that we cannot use DCE because DCE won't remove a store
    // instruction, for example.
    //
    RecursiveDelete(Cache, dyn_cast<Instruction>(V));
  } else {
#ifdef DEBUG_EXPR_CONVERT
    cerr << "VH RELEASING: " << (void*)Operands[0].get() << " " << Operands[0]->use_size() << " " << Operands[0];
#endif
  }
}