path: root/lib/Transforms/ExprTypeConvert.cpp

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

#include "TransformInternals.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include <algorithm>
using namespace llvm;

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

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


// ExpressionConvertibleToType - Return true if it is possible
bool llvm::ExpressionConvertibleToType(Value *V, const Type *Ty,
                                 ValueTypeCache &CTMap, const TargetData &TD) {
  // Expression type must be holdable in a register.
  if (!Ty->isFirstClassType())
    return false;

  ValueTypeCache::iterator CTMI = CTMap.find(V);
  if (CTMI != CTMap.end()) return CTMI->second == Ty;

  // If it's a constant... all constants can be converted to a different
  // type.
  //
  if (isa<Constant>(V) && !isa<GlobalValue>(V))
    return true;

  CTMap[V] = Ty;
  if (V->getType() == Ty) return true;  // Expression already correct type!

  Instruction *I = dyn_cast<Instruction>(V);
  if (I == 0) return false;              // Otherwise, we can't convert!

  switch (I->getOpcode()) {
  case Instruction::BitCast:
    if (!cast<BitCastInst>(I)->isLosslessCast())
      return false;
    // We 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 (const PointerType *SPT =
        dyn_cast<PointerType>(I->getOperand(0)->getType()))
      if (const PointerType *DPT = dyn_cast<PointerType>(I->getType()))
        if (const ArrayType *AT = dyn_cast<ArrayType>(SPT->getElementType()))
          if (AT->getElementType() == DPT->getElementType())
            return false;
    // Otherwise it is a lossless cast and we can allow it
    break;

  case Instruction::Add:
  case Instruction::Sub:
    if (!Ty->isInteger() && !Ty->isFloatingPoint()) return false;
    if (!ExpressionConvertibleToType(I->getOperand(0), Ty, CTMap, TD) ||
        !ExpressionConvertibleToType(I->getOperand(1), Ty, CTMap, TD))
      return false;
    break;
  case Instruction::LShr:
  case Instruction::AShr:
    if (!Ty->isInteger()) return false;
    if (!ExpressionConvertibleToType(I->getOperand(0), Ty, CTMap, TD))
      return false;
    break;
  case Instruction::Shl:
    if (!Ty->isInteger()) return false;
    if (!ExpressionConvertibleToType(I->getOperand(0), Ty, CTMap, TD))
      return false;
    break;

  case Instruction::Load: {
    LoadInst *LI = cast<LoadInst>(I);
    if (!ExpressionConvertibleToType(LI->getPointerOperand(),
                                     PointerType::get(Ty), CTMap, TD))
      return false;
    break;
  }
  case Instruction::PHI: {
    PHINode *PN = cast<PHINode>(I);
    // Be conservative if we find a giant PHI node.
    if (PN->getNumIncomingValues() > 32) return false;

    for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i)
      if (!ExpressionConvertibleToType(PN->getIncomingValue(i), Ty, CTMap, TD))
        return false;
    break;
  }

  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertible 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;  // GEP must always return a pointer...
    const Type *PVTy = PTy->getElementType();

    // 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...
    //
    std::vector<Value*> Indices(GEP->idx_begin(), GEP->idx_end());
    const Type *BaseType = GEP->getPointerOperand()->getType();
    const Type *ElTy = 0;

    while (!Indices.empty() &&
           Indices.back() == Constant::getNullValue(Indices.back()->getType())){
      Indices.pop_back();
      ElTy = GetElementPtrInst::getIndexedType(BaseType, Indices, true);
      if (ElTy == PVTy)
        break;  // Found a match!!
      ElTy = 0;
    }

    if (ElTy) break;   // Found a number of zeros we can strip off!

    // Otherwise, it could be that we have something like this:
    //     getelementptr [[sbyte] *] * %reg115, long %reg138    ; [sbyte]**
    // and want to convert it into something like this:
    //     getelemenptr [[int] *] * %reg115, long %reg138      ; [int]**
    //
    if (GEP->getNumOperands() == 2 &&
        PTy->getElementType()->isSized() &&
        TD.getTypeSize(PTy->getElementType()) ==
        TD.getTypeSize(GEP->getType()->getElementType())) {
      const PointerType *NewSrcTy = PointerType::get(PVTy);
      if (!ExpressionConvertibleToType(I->getOperand(0), NewSrcTy, CTMap, TD))
        return false;
      break;
    }

    return false;   // No match, maybe next time.
  }

  case Instruction::Call: {
    if (isa<Function>(I->getOperand(0)))
      return false;  // Don't even try to change direct calls.

    // If this is a function pointer, we can convert the return type if we can
    // convert the source function pointer.
    //
    const PointerType *PT = cast<PointerType>(I->getOperand(0)->getType());
    const FunctionType *FT = cast<FunctionType>(PT->getElementType());
    std::vector<const Type *> ArgTys(FT->param_begin(), FT->param_end());
    const FunctionType *NewTy =
      FunctionType::get(Ty, ArgTys, FT->isVarArg());
    if (!ExpressionConvertibleToType(I->getOperand(0),
                                     PointerType::get(NewTy), CTMap, TD))
      return false;
    break;
  }
  default:
    return false;
  }

  // Expressions are only convertible if all of the users of the expression can
  // have this value converted.  This makes use of the map to avoid infinite
  // recursion.
  //
  for (Value::use_iterator It = I->use_begin(), E = I->use_end(); It != E; ++It)
    if (!OperandConvertibleToType(*It, I, Ty, CTMap, TD))
      return false;

  return true;
}


Value *llvm::ConvertExpressionToType(Value *V, const Type *Ty,
                                     ValueMapCache &VMC, const TargetData &TD) {
  if (V->getType() == Ty) return V;  // Already where we need to be?

  ValueMapCache::ExprMapTy::iterator VMCI = VMC.ExprMap.find(V);
  if (VMCI != VMC.ExprMap.end()) {
    assert(VMCI->second->getType() == Ty);

    if (Instruction *I = dyn_cast<Instruction>(V))
      ValueHandle IHandle(VMC, I);  // Remove I if it is unused now!

    return VMCI->second;
  }

  DOUT << "CETT: " << (void*)V << " " << *V;

  Instruction *I = dyn_cast<Instruction>(V);
  if (I == 0) {
    Constant *CPV = cast<Constant>(V);
    // Constants are converted by constant folding the cast that is required.
    // We assume here that all casts are implemented for constant prop.
    // FIXME: This seems to work, but it is unclear why ZEXT is always the
    // right choice here.
    Instruction::CastOps opcode = CastInst::getCastOpcode(CPV, false, Ty,false);
    Value *Result = ConstantExpr::getCast(opcode, CPV, Ty);
    // Add the instruction to the expression map
    //VMC.ExprMap[V] = Result;
    return Result;
  }


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

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

  Constant *Dummy = Constant::getNullValue(Ty);

  switch (I->getOpcode()) {
  case Instruction::BitCast: {
    assert(VMC.NewCasts.count(ValueHandle(VMC, I)) == 0);
    Instruction::CastOps opcode = CastInst::getCastOpcode(I->getOperand(0),
        false, Ty, false);
    Res = CastInst::create(opcode, I->getOperand(0), Ty, Name);
    VMC.NewCasts.insert(ValueHandle(VMC, Res));
    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, TD));
    Res->setOperand(1, ConvertExpressionToType(I->getOperand(1), Ty, VMC, TD));
    break;

  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
    Res = BinaryOperator::create(cast<BinaryOperator>(I)->getOpcode(), Dummy,
                                 I->getOperand(1), Name);
    VMC.ExprMap[I] = Res;
    Res->setOperand(0, ConvertExpressionToType(I->getOperand(0), Ty, VMC, TD));
    break;

  case Instruction::Load: {
    LoadInst *LI = cast<LoadInst>(I);

    Res = new LoadInst(Constant::getNullValue(PointerType::get(Ty)), Name);
    VMC.ExprMap[I] = Res;
    Res->setOperand(0, ConvertExpressionToType(LI->getPointerOperand(),
                                               PointerType::get(Ty), VMC, TD));
    assert(Res->getOperand(0)->getType() == PointerType::get(Ty));
    assert(Ty == Res->getType());
    assert(Res->getType()->isFirstClassType() && "Load of structure or array!");
    break;
  }

  case Instruction::PHI: {
    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, false);
      Value *V = ConvertExpressionToType(OldVal, Ty, VMC, TD);
      NewPN->addIncoming(V, BB);
    }
    Res = NewPN;
    break;
  }

  case Instruction::GetElementPtr: {
    // GetElementPtr's are directly convertible 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...
    //
    std::vector<Value*> Indices(GEP->idx_begin(), GEP->idx_end());
    const Type *BaseType = GEP->getPointerOperand()->getType();
    const Type *PVTy = cast<PointerType>(Ty)->getElementType();
    Res = 0;
    while (!Indices.empty() &&
           Indices.back() == Constant::getNullValue(Indices.back()->getType())){
      Indices.pop_back();
      if (GetElementPtrInst::getIndexedType(BaseType, Indices, true) == PVTy) {
        if (Indices.size() == 0)
          // We want to no-op cast this so use BitCast
          Res = new BitCastInst(GEP->getPointerOperand(), BaseType);
        else
          Res = new GetElementPtrInst(GEP->getPointerOperand(), Indices, Name);
        break;
      }
    }

    // Otherwise, it could be that we have something like this:
    //     getelementptr [[sbyte] *] * %reg115, uint %reg138    ; [sbyte]**
    // and want to convert it into something like this:
    //     getelemenptr [[int] *] * %reg115, uint %reg138      ; [int]**
    //
    if (Res == 0) {
      const PointerType *NewSrcTy = PointerType::get(PVTy);
      std::vector<Value*> Indices(GEP->idx_begin(), GEP->idx_end());
      Res = new GetElementPtrInst(Constant::getNullValue(NewSrcTy),
                                  Indices, Name);
      VMC.ExprMap[I] = Res;
      Res->setOperand(0, ConvertExpressionToType(I->getOperand(0),
                                                 NewSrcTy, VMC, TD));
    }


    assert(Res && "Didn't find match!");
    break;
  }

  case Instruction::Call: {
    assert(!isa<Function>(I->getOperand(0)));

    // If this is a function pointer, we can convert the return type if we can
    // convert the source function pointer.
    //
    const PointerType *PT = cast<PointerType>(I->getOperand(0)->getType());
    const FunctionType *FT = cast<FunctionType>(PT->getElementType());
    std::vector<const Type *> ArgTys(FT->param_begin(), FT->param_end());
    const FunctionType *NewTy =
      FunctionType::get(Ty, ArgTys, FT->isVarArg());
    const PointerType *NewPTy = PointerType::get(NewTy);
    if (Ty == Type::VoidTy)
      Name = "";  // Make sure not to name calls that now return void!

    Res = new CallInst(Constant::getNullValue(NewPTy),
                       std::vector<Value*>(I->op_begin()+1, I->op_end()),
                       Name);
    if (cast<CallInst>(I)->isTailCall())
      cast<CallInst>(Res)->setTailCall();
    cast<CallInst>(Res)->setCallingConv(cast<CallInst>(I)->getCallingConv());
    VMC.ExprMap[I] = Res;
    Res->setOperand(0, ConvertExpressionToType(I->getOperand(0),NewPTy,VMC,TD));
    break;
  }
  default:
    assert(0 && "Expression convertible, but don't know how to convert?");
    return 0;
  }

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

  BB->getInstList().insert(I, Res);

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


  //// WTF is this code!  FIXME: remove this.
  unsigned NumUses = I->getNumUses();
  for (unsigned It = 0; It < NumUses; ) {
    unsigned OldSize = NumUses;
    Value::use_iterator UI = I->use_begin();
    std::advance(UI, It);
    ConvertOperandToType(*UI, I, Res, VMC, TD);
    NumUses = I->getNumUses();
    if (NumUses == OldSize) ++It;
  }

  DOUT << "ExpIn: " << (void*)I << " " << *I
       << "ExpOut: " << (void*)Res << " " << *Res;

  return Res;
}



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

  // 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.
  //
  if (V->getType() != Ty) {
    for (Value::use_iterator I = V->use_begin(), E = V->use_end(); I != E; ++I)
      if (!OperandConvertibleToType(*I, V, Ty, ConvertedTypes, TD))
        return false;
  }

  return true;
}

// OperandConvertibleToType - 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 OperandConvertibleToType(User *U, Value *V, const Type *Ty,
                                     ValueTypeCache &CTMap,
                                     const TargetData &TD) {
  //  if (V->getType() == Ty) return true;   // Operand already the right type?

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

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

  switch (I->getOpcode()) {
  case Instruction::BitCast:
    assert(I->getOperand(0) == V);
    // We can convert the expr if the cast destination type is losslessly
    // convertible to the requested type.  Also, do not change a cast that 
    // is a noop cast.  For all intents and purposes it should be eliminated.
    if (!cast<BitCastInst>(I)->isLosslessCast() || 
        I->getType() == I->getOperand(0)->getType())
      return false;

    // 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 (const PointerType *SPT =
        dyn_cast<PointerType>(I->getOperand(0)->getType()))
      if (const PointerType *DPT = dyn_cast<PointerType>(I->getType()))
        if (const ArrayType *AT = dyn_cast<ArrayType>(SPT->getElementType()))
          if (AT->getElementType() == DPT->getElementType())
            return false;
    return true;

  case Instruction::Add:
  case Instruction::Sub: {
    if (!Ty->isInteger() && !Ty->isFloatingPoint()) return false;

    Value *OtherOp = I->getOperand((V == I->getOperand(0)) ? 1 : 0);
    return ValueConvertibleToType(I, Ty, CTMap, TD) &&
           ExpressionConvertibleToType(OtherOp, Ty, CTMap, TD);
  }
  case Instruction::ICmp: {
    if (cast<ICmpInst>(I)->getPredicate() == ICmpInst::ICMP_EQ ||
        cast<ICmpInst>(I)->getPredicate() == ICmpInst::ICMP_NE) {
      Value *OtherOp = I->getOperand((V == I->getOperand(0)) ? 1 : 0);
      return ExpressionConvertibleToType(OtherOp, Ty, CTMap, TD);
    }
    return false;
  }
  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
    if (I->getOperand(1) == V) return false;  // Cannot change shift amount type
    if (!Ty->isInteger()) return false;
    return ValueConvertibleToType(I, Ty, CTMap, TD);

  case Instruction::Free:
    assert(I->getOperand(0) == V);
    return isa<PointerType>(Ty);    // Free can free any pointer type!

  case Instruction::Load:
    // Cannot convert the types of any subscripts...
    if (I->getOperand(0) != V) return false;

    if (const PointerType *PT = dyn_cast<PointerType>(Ty)) {
      LoadInst *LI = cast<LoadInst>(I);

      const Type *LoadedTy = PT->getElementType();

      // They could be loading the first element of a composite type...
      if (const CompositeType *CT = dyn_cast<CompositeType>(LoadedTy)) {
        unsigned Offset = 0;     // No offset, get first leaf.
        std::vector<Value*> Indices;  // Discarded...
        LoadedTy = getStructOffsetType(CT, Offset, Indices, TD, false);
        assert(Offset == 0 && "Offset changed from zero???");
      }

      if (!LoadedTy->isFirstClassType())
        return false;

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

      return ValueConvertibleToType(LI, LoadedTy, CTMap, TD);
    }
    return false;

  case Instruction::Store: {
    if (V == I->getOperand(0)) {
      ValueTypeCache::iterator CTMI = CTMap.find(I->getOperand(1));
      if (CTMI != CTMap.end()) {   // Operand #1 is in the table already?
        // If so, check to see if it's Ty*, or, more importantly, if it is a
        // pointer to a structure where the first element is a Ty... this code
        // is necessary because we might be trying to change the source and
        // destination type of the store (they might be related) and the dest
        // pointer type might be a pointer to structure.  Below we allow pointer
        // to structures where the 0th element is compatible with the value,
        // now we have to support the symmetrical part of this.
        //
        const Type *ElTy = cast<PointerType>(CTMI->second)->getElementType();

        // Already a pointer to what we want?  Trivially accept...
        if (ElTy == Ty) return true;

        // Tricky case now, if the destination is a pointer to structure,
        // obviously the source is not allowed to be a structure (cannot copy
        // a whole structure at a time), so the level raiser must be trying to
        // store into the first field.  Check for this and allow it now:
        //
        if (isa<StructType>(ElTy)) {
          unsigned Offset = 0;
          std::vector<Value*> Indices;
          ElTy = getStructOffsetType(ElTy, Offset, Indices, TD, false);
          assert(Offset == 0 && "Offset changed!");
          if (ElTy == 0)    // Element at offset zero in struct doesn't exist!
            return false;   // Can only happen for {}*

          if (ElTy == Ty)   // Looks like the 0th element of structure is
            return true;    // compatible!  Accept now!

          // Otherwise we know that we can't work, so just stop trying now.
          return false;
        }
      }

      // Can convert the store if we can convert the pointer operand to match
      // the new  value type...
      return ExpressionConvertibleToType(I->getOperand(1), PointerType::get(Ty),
                                         CTMap, TD);
    } else if (const PointerType *PT = dyn_cast<PointerType>(Ty)) {
      const Type *ElTy = PT->getElementType();
      assert(V == I->getOperand(1));

      if (isa<StructType>(ElTy)) {
        // We can change the destination pointer if we can store our first
        // argument into the first element of the structure...
        //
        unsigned Offset = 0;
        std::vector<Value*> Indices;
        ElTy = getStructOffsetType(ElTy, Offset, Indices, TD, false);
        assert(Offset == 0 && "Offset changed!");
        if (ElTy == 0)    // Element at offset zero in struct doesn't exist!
          return false;   // Can only happen for {}*
      }

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

      // Can convert store if the incoming value is convertible and if the
      // result will preserve semantics...
      const Type *Op0Ty = I->getOperand(0)->getType();
      if (Op0Ty->isInteger() == ElTy->isInteger() &&
          Op0Ty->isFloatingPoint() == ElTy->isFloatingPoint())
        return ExpressionConvertibleToType(I->getOperand(0), ElTy, CTMap, TD);
    }
    return false;
  }

  case Instruction::PHI: {
    PHINode *PN = cast<PHINode>(I);
    // Be conservative if we find a giant PHI node.
    if (PN->getNumIncomingValues() > 32) return false;

    for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i)
      if (!ExpressionConvertibleToType(PN->getIncomingValue(i), Ty, CTMap, TD))
        return false;
    return ValueConvertibleToType(PN, Ty, CTMap, TD);
  }

  case Instruction::Call: {
    User::op_iterator OI = std::find(I->op_begin(), I->op_end(), V);
    assert (OI != I->op_end() && "Not using value!");
    unsigned OpNum = OI - I->op_begin();

    // Are we trying to change the function pointer value to a new type?
    if (OpNum == 0) {
      const PointerType *PTy = dyn_cast<PointerType>(Ty);
      if (PTy == 0) return false;  // Can't convert to a non-pointer type...
      const FunctionType *FTy = dyn_cast<FunctionType>(PTy->getElementType());
      if (FTy == 0) return false;  // Can't convert to a non ptr to function...

      // Do not allow converting to a call where all of the operands are ...'s
      if (FTy->getNumParams() == 0 && FTy->isVarArg())
        return false;              // Do not permit this conversion!

      // Perform sanity checks to make sure that new function type has the
      // correct number of arguments...
      //
      unsigned NumArgs = I->getNumOperands()-1;  // Don't include function ptr

      // Cannot convert to a type that requires more fixed arguments than
      // the call provides...
      //
      if (NumArgs < FTy->getNumParams()) return false;

      // Unless this is a vararg function type, we cannot provide more arguments
      // than are desired...
      //
      if (!FTy->isVarArg() && NumArgs > FTy->getNumParams())
        return false;

      // Okay, at this point, we know that the call and the function type match
      // number of arguments.  Now we see if we can convert the arguments
      // themselves.  Note that we do not require operands to be convertible,
      // we can insert casts if they are convertible but not compatible.  The
      // reason for this is that we prefer to have resolved functions but casted
      // arguments if possible.
      //
      for (unsigned i = 0, NA = FTy->getNumParams(); i < NA; ++i)
        if (FTy->getParamType(i) != I->getOperand(i+1)->getType())
          return false;   // Operands must have compatible types!

      // Okay, at this point, we know that all of the arguments can be
      // converted.  We succeed if we can change the return type if
      // necessary...
      //
      return ValueConvertibleToType(I, FTy->getReturnType(), CTMap, TD);
    }

    const PointerType *MPtr = cast<PointerType>(I->getOperand(0)->getType());
    const FunctionType *FTy = cast<FunctionType>(MPtr->getElementType());
    if (!FTy->isVarArg()) return false;

    if ((OpNum-1) < FTy->getNumParams())
      return false;  // It's not in the varargs section...

    // If we get this far, we know the value is in the varargs section of the
    // function!  We can convert if we don't reinterpret the value...
    //
    return isa<PointerType>(Ty) && isa<PointerType>(V->getType());
  }
  }
  return false;
}


void llvm::ConvertValueToNewType(Value *V, Value *NewVal, ValueMapCache &VMC,
                                 const TargetData &TD) {
  ValueHandle VH(VMC, V);

  // FIXME: This is horrible!
  unsigned NumUses = V->getNumUses();
  for (unsigned It = 0; It < NumUses; ) {
    unsigned OldSize = NumUses;
    Value::use_iterator UI = V->use_begin();
    std::advance(UI, It);
    ConvertOperandToType(*UI, V, NewVal, VMC, TD);
    NumUses = V->getNumUses();
    if (NumUses == OldSize) ++It;
  }
}



static void ConvertOperandToType(User *U, Value *OldVal, Value *NewVal,
                                 ValueMapCache &VMC, const TargetData &TD) {
  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 convertible

  BasicBlock *BB = I->getParent();
  assert(BB != 0 && "Instruction not embedded in basic block!");
  std::string Name = I->getName();
  I->setName("");
  Instruction *Res = 0;     // 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();
  Constant *Dummy = (NewTy != Type::VoidTy) ?
                  Constant::getNullValue(NewTy) : 0;

  switch (I->getOpcode()) {
  case Instruction::BitCast: {
    Instruction::CastOps opcode = CastInst::getCastOpcode(NewVal, false, 
                                                          I->getType(), false);
    Res = CastInst::create(opcode, NewVal, I->getType(), 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

    unsigned OtherIdx = (OldVal == I->getOperand(0)) ? 1 : 0;
    Value *OtherOp    = I->getOperand(OtherIdx);
    Res->setOperand(!OtherIdx, NewVal);
    Value *NewOther   = ConvertExpressionToType(OtherOp, NewTy, VMC, TD);
    Res->setOperand(OtherIdx, NewOther);
    break;
  }
  case Instruction::ICmp: {
    ICmpInst::Predicate pred = cast<ICmpInst>(I)->getPredicate();
    if (pred == ICmpInst::ICMP_EQ || pred == ICmpInst::ICMP_NE) {
      Res = new ICmpInst(pred, 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);
      Res->setOperand(!OtherIdx, NewVal);
      Value *NewOther   = ConvertExpressionToType(OtherOp, NewTy, VMC, TD);
      Res->setOperand(OtherIdx, NewOther);
    }
    break;
  }
  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
    assert(I->getOperand(0) == OldVal);
    Res = BinaryOperator::create(cast<BinaryOperator>(I)->getOpcode(), NewVal,
                                 I->getOperand(1), Name);
    break;

  case Instruction::Free:            // Free can free any pointer type!
    assert(I->getOperand(0) == OldVal);
    Res = new FreeInst(NewVal);
    break;


  case Instruction::Load: {
    assert(I->getOperand(0) == OldVal && isa<PointerType>(NewVal->getType()));
    const Type *LoadedTy =
      cast<PointerType>(NewVal->getType())->getElementType();

    Value *Src = NewVal;

    if (const CompositeType *CT = dyn_cast<CompositeType>(LoadedTy)) {
      std::vector<Value*> Indices;
      Indices.push_back(Constant::getNullValue(Type::Int32Ty));

      unsigned Offset = 0;   // No offset, get first leaf.
      LoadedTy = getStructOffsetType(CT, Offset, Indices, TD, false);
      assert(LoadedTy->isFirstClassType());

      if (Indices.size() != 1) {     // Do not generate load X, 0
        // Insert the GEP instruction before this load.
        Src = new GetElementPtrInst(Src, Indices, Name+".idx", I);
      }
    }

    Res = new LoadInst(Src, Name);
    assert(Res->getType()->isFirstClassType() && "Load of structure or array!");
    break;
  }

  case Instruction::Store: {
    if (I->getOperand(0) == OldVal) {  // Replace the source value
      // Check to see if operand #1 has already been converted...
      ValueMapCache::ExprMapTy::iterator VMCI =
        VMC.ExprMap.find(I->getOperand(1));
      if (VMCI != VMC.ExprMap.end()) {
        // Comments describing this stuff are in the OperandConvertibleToType
        // switch statement for Store...
        //
        const Type *ElTy =
          cast<PointerType>(VMCI->second->getType())->getElementType();

        Value *SrcPtr = VMCI->second;

        if (ElTy != NewTy) {
          std::vector<Value*> Indices;
          Indices.push_back(Constant::getNullValue(Type::Int32Ty));

          unsigned Offset = 0;
          const Type *Ty = getStructOffsetType(ElTy, Offset, Indices, TD,false);
          assert(Offset == 0 && "Offset changed!");
          assert(NewTy == Ty && "Did not convert to correct type!");

          // Insert the GEP instruction before this store.
          SrcPtr = new GetElementPtrInst(SrcPtr, Indices,
                                         SrcPtr->getName()+".idx", I);
        }
        Res = new StoreInst(NewVal, SrcPtr);

        VMC.ExprMap[I] = Res;
      } else {
        // Otherwise, we haven't converted Operand #1 over yet...
        const PointerType *NewPT = PointerType::get(NewTy);
        Res = new StoreInst(NewVal, Constant::getNullValue(NewPT));
        VMC.ExprMap[I] = Res;
        Res->setOperand(1, ConvertExpressionToType(I->getOperand(1),
                                                   NewPT, VMC, TD));
      }
    } else {                           // Replace the source pointer
      const Type *ValTy = cast<PointerType>(NewTy)->getElementType();

      Value *SrcPtr = NewVal;

      if (isa<StructType>(ValTy)) {
        std::vector<Value*> Indices;
        Indices.push_back(Constant::getNullValue(Type::Int32Ty));

        unsigned Offset = 0;
        ValTy = getStructOffsetType(ValTy, Offset, Indices, TD, false);

        assert(Offset == 0 && ValTy);

        // Insert the GEP instruction before this store.
        SrcPtr = new GetElementPtrInst(SrcPtr, Indices,
                                       SrcPtr->getName()+".idx", I);
      }

      Res = new StoreInst(Constant::getNullValue(ValTy), SrcPtr);
      VMC.ExprMap[I] = Res;
      Res->setOperand(0, ConvertExpressionToType(I->getOperand(0),
                                                 ValTy, VMC, TD));
    }
    break;
  }

  case Instruction::PHI: {
    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);
      ValueHandle OldValHandle(VMC, OldVal);
      OldPN->removeIncomingValue(BB, false);
      Value *V = ConvertExpressionToType(OldVal, NewTy, VMC, TD);
      NewPN->addIncoming(V, BB);
    }
    Res = NewPN;
    break;
  }

  case Instruction::Call: {
    Value *Meth = I->getOperand(0);
    std::vector<Value*> Params(I->op_begin()+1, I->op_end());

    if (Meth == OldVal) {   // Changing the function pointer?
      const PointerType *NewPTy = cast<PointerType>(NewVal->getType());
      const FunctionType *NewTy = cast<FunctionType>(NewPTy->getElementType());

      if (NewTy->getReturnType() == Type::VoidTy)
        Name = "";  // Make sure not to name a void call!

      // Get an iterator to the call instruction so that we can insert casts for
      // operands if need be.  Note that we do not require operands to be
      // convertible, we can insert casts if they are convertible but not
      // compatible.  The reason for this is that we prefer to have resolved
      // functions but casted arguments if possible.
      //
      BasicBlock::iterator It = I;

      // Convert over all of the call operands to their new types... but only
      // convert over the part that is not in the vararg section of the call.
      //
      for (unsigned i = 0; i != NewTy->getNumParams(); ++i)
        if (Params[i]->getType() != NewTy->getParamType(i)) {
          // Create a cast to convert it to the right type, we know that this
          // is a no-op cast...
          //
          Params[i] = new BitCastInst(Params[i], NewTy->getParamType(i),
                                   "callarg.cast." +
                                   Params[i]->getName(), It);
        }
      Meth = NewVal;  // Update call destination to new value

    } else {                   // Changing an argument, must be in vararg area
      std::vector<Value*>::iterator OI =
        std::find(Params.begin(), Params.end(), OldVal);
      assert (OI != Params.end() && "Not using value!");

      *OI = NewVal;
    }

    Res = new CallInst(Meth, Params, Name);
    if (cast<CallInst>(I)->isTailCall())
      cast<CallInst>(Res)->setTailCall();
    cast<CallInst>(Res)->setCallingConv(cast<CallInst>(I)->getCallingConv());
    break;
  }
  default:
    assert(0 && "Expression convertible, but don't know how to convert?");
    return;
  }

  assert(Res != 0 && "We didn't get a result conversion?");

  // If the instruction was newly created, insert it into the instruction
  // stream.
  //
  BasicBlock::iterator It = I;
  assert(It != BB->end() && "Instruction not in own basic block??");
  BB->getInstList().insert(It, Res);   // Keep It pointing to old instruction

  DOUT << "COT CREATED: "  << (void*)Res << " " << *Res
       << "In: " << (void*)I << " " << *I << "Out: " << (void*)Res
       << " " << *Res;

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

  if (I->getType() != Res->getType())
    ConvertValueToNewType(I, Res, VMC, TD);
  else {
    for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
         UI != E; )
      if (isa<ValueHandle>(*UI)) {
        ++UI;
      } else {
        Use &U = UI.getUse();
        ++UI;  // Do not invalidate UI.
        U.set(Res);
      }
  }
}


ValueHandle::ValueHandle(ValueMapCache &VMC, Value *V)
  : Instruction(Type::VoidTy, UserOp1, &Op, 1, ""), Op(V, this), Cache(VMC) {
  //DOUT << "VH AQUIRING: " << (void*)V << " " << V;
}

ValueHandle::ValueHandle(const ValueHandle &VH)
  : Instruction(Type::VoidTy, UserOp1, &Op, 1, ""),
    Op(VH.Op, this), Cache(VH.Cache) {
  //DOUT << "VH AQUIRING: " << (void*)V << " " << V;
}

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

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

  //DOUT << "VH DELETING: " << (void*)I << " " << I;

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

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

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

ValueHandle::~ValueHandle() {
  if (Op->hasOneUse()) {
    Value *V = Op;
    Op.set(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 {
    //DOUT << "VH RELEASING: " << (void*)Operands[0].get() << " "
    //     << Operands[0]->getNumUses() << " " << Operands[0];
  }
}