llvm-mirror/lib/VMCore/Constants.cpp

//===-- Constants.cpp - Implement Constant nodes --------------------------===//
//
// This file implements the Constant* classes...
//
//===----------------------------------------------------------------------===//

#include "llvm/Constants.h"
#include "llvm/ConstantHandling.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iMemory.h"
#include "llvm/SymbolTable.h"
#include "llvm/Module.h"
#include "Support/StringExtras.h"
#include <algorithm>

ConstantBool *ConstantBool::True  = new ConstantBool(true);
ConstantBool *ConstantBool::False = new ConstantBool(false);


//===----------------------------------------------------------------------===//
//                              Constant Class
//===----------------------------------------------------------------------===//

// Specialize setName to take care of symbol table majik
void Constant::setName(const std::string &Name, SymbolTable *ST) {
  assert(ST && "Type::setName - Must provide symbol table argument!");

  if (Name.size()) ST->insert(Name, this);
}

void Constant::destroyConstantImpl() {
  // When a Constant is destroyed, there may be lingering
  // references to the constant by other constants in the constant pool.  These
  // constants are implicitly dependant on the module that is being deleted,
  // but they don't know that.  Because we only find out when the CPV is
  // deleted, we must now notify all of our users (that should only be
  // Constants) that they are, in fact, invalid now and should be deleted.
  //
  while (!use_empty()) {
    Value *V = use_back();
#ifndef NDEBUG      // Only in -g mode...
    if (!isa<Constant>(V))
      std::cerr << "While deleting: " << *this
                << "\n\nUse still stuck around after Def is destroyed: "
                << *V << "\n\n";
#endif
    assert(isa<Constant>(V) && "References remain to Constant being destroyed");
    Constant *CPV = cast<Constant>(V);
    CPV->destroyConstant();

    // The constant should remove itself from our use list...
    assert((use_empty() || use_back() != V) && "Constant not removed!");
  }

  // Value has no outstanding references it is safe to delete it now...
  delete this;
}

// Static constructor to create a '0' constant of arbitrary type...
Constant *Constant::getNullValue(const Type *Ty) {
  switch (Ty->getPrimitiveID()) {
  case Type::BoolTyID:   return ConstantBool::get(false);
  case Type::SByteTyID:
  case Type::ShortTyID:
  case Type::IntTyID:
  case Type::LongTyID:   return ConstantSInt::get(Ty, 0);

  case Type::UByteTyID:
  case Type::UShortTyID:
  case Type::UIntTyID:
  case Type::ULongTyID:  return ConstantUInt::get(Ty, 0);

  case Type::FloatTyID:
  case Type::DoubleTyID: return ConstantFP::get(Ty, 0);

  case Type::PointerTyID: 
    return ConstantPointerNull::get(cast<PointerType>(Ty));
  case Type::StructTyID: {
    const StructType *ST = cast<StructType>(Ty);

    const StructType::ElementTypes &ETs = ST->getElementTypes();
    std::vector<Constant*> Elements;
    Elements.resize(ETs.size());
    for (unsigned i = 0, e = ETs.size(); i != e; ++i)
      Elements[i] = Constant::getNullValue(ETs[i]);
    return ConstantStruct::get(ST, Elements);
  }
  case Type::ArrayTyID: {
    const ArrayType *AT = cast<ArrayType>(Ty);
    Constant *El = Constant::getNullValue(AT->getElementType());
    unsigned NumElements = AT->getNumElements();
    return ConstantArray::get(AT, std::vector<Constant*>(NumElements, El));
  }
  default:
    // Function, Type, Label, or Opaque type?
    assert(0 && "Cannot create a null constant of that type!");
    return 0;
  }
}

// Static constructor to create the maximum constant of an integral type...
ConstantIntegral *ConstantIntegral::getMaxValue(const Type *Ty) {
  switch (Ty->getPrimitiveID()) {
  case Type::BoolTyID:   return ConstantBool::True;
  case Type::SByteTyID:
  case Type::ShortTyID:
  case Type::IntTyID:
  case Type::LongTyID: {
    // Calculate 011111111111111... 
    unsigned TypeBits = Ty->getPrimitiveSize()*8;
    int64_t Val = INT64_MAX;             // All ones
    Val >>= 64-TypeBits;                 // Shift out unwanted 1 bits...
    return ConstantSInt::get(Ty, Val);
  }

  case Type::UByteTyID:
  case Type::UShortTyID:
  case Type::UIntTyID:
  case Type::ULongTyID:  return getAllOnesValue(Ty);

  default: return 0;
  }
}

// Static constructor to create the minimum constant for an integral type...
ConstantIntegral *ConstantIntegral::getMinValue(const Type *Ty) {
  switch (Ty->getPrimitiveID()) {
  case Type::BoolTyID:   return ConstantBool::False;
  case Type::SByteTyID:
  case Type::ShortTyID:
  case Type::IntTyID:
  case Type::LongTyID: {
     // Calculate 1111111111000000000000 
     unsigned TypeBits = Ty->getPrimitiveSize()*8;
     int64_t Val = -1;                    // All ones
     Val <<= TypeBits-1;                  // Shift over to the right spot
     return ConstantSInt::get(Ty, Val);
  }

  case Type::UByteTyID:
  case Type::UShortTyID:
  case Type::UIntTyID:
  case Type::ULongTyID:  return ConstantUInt::get(Ty, 0);

  default: return 0;
  }
}

// Static constructor to create an integral constant with all bits set
ConstantIntegral *ConstantIntegral::getAllOnesValue(const Type *Ty) {
  switch (Ty->getPrimitiveID()) {
  case Type::BoolTyID:   return ConstantBool::True;
  case Type::SByteTyID:
  case Type::ShortTyID:
  case Type::IntTyID:
  case Type::LongTyID:   return ConstantSInt::get(Ty, -1);

  case Type::UByteTyID:
  case Type::UShortTyID:
  case Type::UIntTyID:
  case Type::ULongTyID: {
    // Calculate ~0 of the right type...
    unsigned TypeBits = Ty->getPrimitiveSize()*8;
    uint64_t Val = ~0ULL;                // All ones
    Val >>= 64-TypeBits;                 // Shift out unwanted 1 bits...
    return ConstantUInt::get(Ty, Val);
  }
  default: return 0;
  }
}

bool ConstantUInt::isAllOnesValue() const {
  unsigned TypeBits = getType()->getPrimitiveSize()*8;
  uint64_t Val = ~0ULL;                // All ones
  Val >>= 64-TypeBits;                 // Shift out inappropriate bits
  return getValue() == Val;
}


//===----------------------------------------------------------------------===//
//                            ConstantXXX Classes
//===----------------------------------------------------------------------===//

//===----------------------------------------------------------------------===//
//                             Normal Constructors

ConstantBool::ConstantBool(bool V) : ConstantIntegral(Type::BoolTy) {
  Val = V;
}

ConstantInt::ConstantInt(const Type *Ty, uint64_t V) : ConstantIntegral(Ty) {
  Val.Unsigned = V;
}

ConstantSInt::ConstantSInt(const Type *Ty, int64_t V) : ConstantInt(Ty, V) {
  assert(Ty->isInteger() && Ty->isSigned() &&
         "Illegal type for unsigned integer constant!");
  assert(isValueValidForType(Ty, V) && "Value too large for type!");
}

ConstantUInt::ConstantUInt(const Type *Ty, uint64_t V) : ConstantInt(Ty, V) {
  assert(Ty->isInteger() && Ty->isUnsigned() &&
         "Illegal type for unsigned integer constant!");
  assert(isValueValidForType(Ty, V) && "Value too large for type!");
}

ConstantFP::ConstantFP(const Type *Ty, double V) : Constant(Ty) {
  assert(isValueValidForType(Ty, V) && "Value too large for type!");
  Val = V;
}

ConstantArray::ConstantArray(const ArrayType *T,
                             const std::vector<Constant*> &V) : Constant(T) {
  Operands.reserve(V.size());
  for (unsigned i = 0, e = V.size(); i != e; ++i) {
    assert(V[i]->getType() == T->getElementType());
    Operands.push_back(Use(V[i], this));
  }
}

ConstantStruct::ConstantStruct(const StructType *T,
                               const std::vector<Constant*> &V) : Constant(T) {
  const StructType::ElementTypes &ETypes = T->getElementTypes();
  assert(V.size() == ETypes.size() &&
         "Invalid initializer vector for constant structure");
  Operands.reserve(V.size());
  for (unsigned i = 0, e = V.size(); i != e; ++i) {
    assert((V[i]->getType() == ETypes[i] ||
            (ETypes[i]->isAbstract() &&
             ETypes[i]->getPrimitiveID()==V[i]->getType()->getPrimitiveID())) &&
           "Initializer for struct element doesn't match struct element type!");
    Operands.push_back(Use(V[i], this));
  }
}

ConstantPointerRef::ConstantPointerRef(GlobalValue *GV)
  : ConstantPointer(GV->getType()) {
  Operands.push_back(Use(GV, this));
}

ConstantExpr::ConstantExpr(unsigned Opcode, Constant *C, const Type *Ty)
  : Constant(Ty), iType(Opcode) {
  Operands.push_back(Use(C, this));
}

static bool isSetCC(unsigned Opcode) {
  return Opcode == Instruction::SetEQ || Opcode == Instruction::SetNE ||
         Opcode == Instruction::SetLT || Opcode == Instruction::SetGT ||
         Opcode == Instruction::SetLE || Opcode == Instruction::SetGE;
}

ConstantExpr::ConstantExpr(unsigned Opcode, Constant *C1, Constant *C2)
  : Constant(isSetCC(Opcode) ? Type::BoolTy : C1->getType()), iType(Opcode) {
  Operands.push_back(Use(C1, this));
  Operands.push_back(Use(C2, this));
}

ConstantExpr::ConstantExpr(Constant *C, const std::vector<Constant*> &IdxList,
                           const Type *DestTy)
  : Constant(DestTy), iType(Instruction::GetElementPtr) {
  Operands.reserve(1+IdxList.size());
  Operands.push_back(Use(C, this));
  for (unsigned i = 0, E = IdxList.size(); i != E; ++i)
    Operands.push_back(Use(IdxList[i], this));
}



//===----------------------------------------------------------------------===//
//                           classof implementations

bool ConstantIntegral::classof(const Constant *CPV) {
  return CPV->getType()->isIntegral() && !isa<ConstantExpr>(CPV);
}

bool ConstantInt::classof(const Constant *CPV) {
  return CPV->getType()->isInteger() && !isa<ConstantExpr>(CPV);
}
bool ConstantSInt::classof(const Constant *CPV) {
  return CPV->getType()->isSigned() && !isa<ConstantExpr>(CPV);
}
bool ConstantUInt::classof(const Constant *CPV) {
  return CPV->getType()->isUnsigned() && !isa<ConstantExpr>(CPV);
}
bool ConstantFP::classof(const Constant *CPV) {
  const Type *Ty = CPV->getType();
  return ((Ty == Type::FloatTy || Ty == Type::DoubleTy) &&
          !isa<ConstantExpr>(CPV));
}
bool ConstantArray::classof(const Constant *CPV) {
  return isa<ArrayType>(CPV->getType()) && !isa<ConstantExpr>(CPV);
}
bool ConstantStruct::classof(const Constant *CPV) {
  return isa<StructType>(CPV->getType()) && !isa<ConstantExpr>(CPV);
}
bool ConstantPointer::classof(const Constant *CPV) {
  return (isa<PointerType>(CPV->getType()) && !isa<ConstantExpr>(CPV));
}



//===----------------------------------------------------------------------===//
//                      isValueValidForType implementations

bool ConstantSInt::isValueValidForType(const Type *Ty, int64_t Val) {
  switch (Ty->getPrimitiveID()) {
  default:
    return false;         // These can't be represented as integers!!!

    // Signed types...
  case Type::SByteTyID:
    return (Val <= INT8_MAX && Val >= INT8_MIN);
  case Type::ShortTyID:
    return (Val <= INT16_MAX && Val >= INT16_MIN);
  case Type::IntTyID:
    return (Val <= INT32_MAX && Val >= INT32_MIN);
  case Type::LongTyID:
    return true;          // This is the largest type...
  }
  assert(0 && "WTF?");
  return false;
}

bool ConstantUInt::isValueValidForType(const Type *Ty, uint64_t Val) {
  switch (Ty->getPrimitiveID()) {
  default:
    return false;         // These can't be represented as integers!!!

    // Unsigned types...
  case Type::UByteTyID:
    return (Val <= UINT8_MAX);
  case Type::UShortTyID:
    return (Val <= UINT16_MAX);
  case Type::UIntTyID:
    return (Val <= UINT32_MAX);
  case Type::ULongTyID:
    return true;          // This is the largest type...
  }
  assert(0 && "WTF?");
  return false;
}

bool ConstantFP::isValueValidForType(const Type *Ty, double Val) {
  switch (Ty->getPrimitiveID()) {
  default:
    return false;         // These can't be represented as floating point!

    // TODO: Figure out how to test if a double can be cast to a float!
  case Type::FloatTyID:
    /*
    return (Val <= UINT8_MAX);
    */
  case Type::DoubleTyID:
    return true;          // This is the largest type...
  }
};

//===----------------------------------------------------------------------===//
//                replaceUsesOfWithOnConstant implementations

void ConstantArray::replaceUsesOfWithOnConstant(Value *From, Value *To) {
  assert(isa<Constant>(To) && "Cannot make Constant refer to non-constant!");

  std::vector<Constant*> Values;
  Values.reserve(getValues().size());  // Build replacement array...
  for (unsigned i = 0, e = getValues().size(); i != e; ++i) {
    Constant *Val = cast<Constant>(getValues()[i]);
    if (Val == From) Val = cast<Constant>(To);
    Values.push_back(Val);
  }
  
  ConstantArray *Replacement = ConstantArray::get(getType(), Values);
  assert(Replacement != this && "I didn't contain From!");

  // Everyone using this now uses the replacement...
  replaceAllUsesWith(Replacement);
  
  // Delete the old constant!
  destroyConstant();  
}

void ConstantStruct::replaceUsesOfWithOnConstant(Value *From, Value *To) {
  assert(isa<Constant>(To) && "Cannot make Constant refer to non-constant!");

  std::vector<Constant*> Values;
  Values.reserve(getValues().size());
  for (unsigned i = 0, e = getValues().size(); i != e; ++i) {
    Constant *Val = cast<Constant>(getValues()[i]);
    if (Val == From) Val = cast<Constant>(To);
    Values.push_back(Val);
  }
  
  ConstantStruct *Replacement = ConstantStruct::get(getType(), Values);
  assert(Replacement != this && "I didn't contain From!");

  // Everyone using this now uses the replacement...
  replaceAllUsesWith(Replacement);
  
  // Delete the old constant!
  destroyConstant();
}

void ConstantPointerRef::replaceUsesOfWithOnConstant(Value *From, Value *To) {
  if (isa<GlobalValue>(To)) {
    assert(From == getOperand(0) && "Doesn't contain from!");
    ConstantPointerRef *Replacement =
      ConstantPointerRef::get(cast<GlobalValue>(To));
    
    // Everyone using this now uses the replacement...
    replaceAllUsesWith(Replacement);
    
    // Delete the old constant!
    destroyConstant();
  } else {
    // Just replace ourselves with the To value specified.
    replaceAllUsesWith(To);
  
    // Delete the old constant!
    destroyConstant();
  }
}

void ConstantExpr::replaceUsesOfWithOnConstant(Value *From, Value *ToV) {
  assert(isa<Constant>(ToV) && "Cannot make Constant refer to non-constant!");
  Constant *To = cast<Constant>(ToV);

  Constant *Replacement = 0;
  if (getOpcode() == Instruction::GetElementPtr) {
    std::vector<Constant*> Indices;
    Constant *Pointer = getOperand(0);
    Indices.reserve(getNumOperands()-1);
    if (Pointer == From) Pointer = To;
    
    for (unsigned i = 1, e = getNumOperands(); i != e; ++i) {
      Constant *Val = getOperand(i);
      if (Val == From) Val = To;
      Indices.push_back(Val);
    }
    Replacement = ConstantExpr::getGetElementPtr(Pointer, Indices);
  } else if (getOpcode() == Instruction::Cast) {
    assert(getOperand(0) == From && "Cast only has one use!");
    Replacement = ConstantExpr::getCast(To, getType());
  } else if (getNumOperands() == 2) {
    Constant *C1 = getOperand(0);
    Constant *C2 = getOperand(1);
    if (C1 == From) C1 = To;
    if (C2 == From) C2 = To;
    Replacement = ConstantExpr::get(getOpcode(), C1, C2);
  } else {
    assert(0 && "Unknown ConstantExpr type!");
    return;
  }
  
  assert(Replacement != this && "I didn't contain From!");

  // Everyone using this now uses the replacement...
  replaceAllUsesWith(Replacement);
  
  // Delete the old constant!
  destroyConstant();
}

//===----------------------------------------------------------------------===//
//                      Factory Function Implementation

// ReplaceUsesOfWith - This is exactly the same as Value::replaceAllUsesWith,
// except that it doesn't have all of the asserts.  The asserts fail because we
// are half-way done resolving types, which causes some types to exist as two
// different Type*'s at the same time.  This is a sledgehammer to work around
// this problem.
//
static void ReplaceUsesOfWith(Value *Old, Value *New) {
  while (!Old->use_empty()) {
    User *Use = Old->use_back();
    // Must handle Constants specially, we cannot call replaceUsesOfWith on a
    // constant!
    if (Constant *C = dyn_cast<Constant>(Use)) {
      C->replaceUsesOfWithOnConstant(Old, New);
    } else {
      Use->replaceUsesOfWith(Old, New);
    }
  }
}


// ConstantCreator - A class that is used to create constants by
// ValueMap*.  This class should be partially specialized if there is
// something strange that needs to be done to interface to the ctor for the
// constant.
//
template<class ConstantClass, class TypeClass, class ValType>
struct ConstantCreator {
  static ConstantClass *create(const TypeClass *Ty, const ValType &V) {
    return new ConstantClass(Ty, V);
  }
};

namespace {
  template<class ValType, class TypeClass, class ConstantClass>
  class ValueMap {
  protected:
    typedef std::pair<const TypeClass*, ValType> ConstHashKey;
    std::map<ConstHashKey, ConstantClass *> Map;
  public:
    // getOrCreate - Return the specified constant from the map, creating it if
    // necessary.
    ConstantClass *getOrCreate(const TypeClass *Ty, const ValType &V) {
      ConstHashKey Lookup(Ty, V);
      typename std::map<ConstHashKey,ConstantClass *>::iterator I =
        Map.lower_bound(Lookup);
      if (I != Map.end() && I->first == Lookup)
        return I->second;  // Is it in the map?

      // If no preexisting value, create one now...
      ConstantClass *Result =
        ConstantCreator<ConstantClass,TypeClass,ValType>::create(Ty, V);

      Map.insert(I, std::make_pair(ConstHashKey(Ty, V), Result));
      return Result;
    }
    
    void remove(ConstantClass *CP) {
      // FIXME: This could be sped up a LOT.  If this gets to be a performance
      // problem, someone should look at this.
      for (typename std::map<ConstHashKey, ConstantClass*>::iterator
             I = Map.begin(), E = Map.end(); I != E; ++I)
        if (I->second == CP) {
          Map.erase(I);
          return;
        }
      assert(0 && "Constant not found in constant table!");
    }
  };
}



//---- ConstantUInt::get() and ConstantSInt::get() implementations...
//
static ValueMap< int64_t, Type, ConstantSInt> SIntConstants;
static ValueMap<uint64_t, Type, ConstantUInt> UIntConstants;

ConstantSInt *ConstantSInt::get(const Type *Ty, int64_t V) {
  return SIntConstants.getOrCreate(Ty, V);
}

ConstantUInt *ConstantUInt::get(const Type *Ty, uint64_t V) {
  return UIntConstants.getOrCreate(Ty, V);
}

ConstantInt *ConstantInt::get(const Type *Ty, unsigned char V) {
  assert(V <= 127 && "Can only be used with very small positive constants!");
  if (Ty->isSigned()) return ConstantSInt::get(Ty, V);
  return ConstantUInt::get(Ty, V);
}

//---- ConstantFP::get() implementation...
//
static ValueMap<double, Type, ConstantFP> FPConstants;

ConstantFP *ConstantFP::get(const Type *Ty, double V) {
  return FPConstants.getOrCreate(Ty, V);
}

//---- ConstantArray::get() implementation...
//
static ValueMap<std::vector<Constant*>, ArrayType,
                ConstantArray> ArrayConstants;

ConstantArray *ConstantArray::get(const ArrayType *Ty,
                                  const std::vector<Constant*> &V) {
  return ArrayConstants.getOrCreate(Ty, V);
}

// destroyConstant - Remove the constant from the constant table...
//
void ConstantArray::destroyConstant() {
  ArrayConstants.remove(this);
  destroyConstantImpl();
}

/// refineAbstractType - If this callback is invoked, then this constant is of a
/// derived type, change all users to use a concrete constant of the new type.
///
void ConstantArray::refineAbstractType(const DerivedType *OldTy,
                                       const Type *NewTy) {
  Value::refineAbstractType(OldTy, NewTy);
  if (OldTy == NewTy) return;

  // Make everyone now use a constant of the new type...
  std::vector<Constant*> C;
  for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
    C.push_back(cast<Constant>(getOperand(i)));
  Constant *New = ConstantArray::get(cast<ArrayType>(NewTy), C);
  if (New != this) {
    ReplaceUsesOfWith(this, New);
    destroyConstant();    // This constant is now dead, destroy it.
  }
}


// ConstantArray::get(const string&) - Return an array that is initialized to
// contain the specified string.  A null terminator is added to the specified
// string so that it may be used in a natural way...
//
ConstantArray *ConstantArray::get(const std::string &Str) {
  std::vector<Constant*> ElementVals;

  for (unsigned i = 0; i < Str.length(); ++i)
    ElementVals.push_back(ConstantSInt::get(Type::SByteTy, Str[i]));

  // Add a null terminator to the string...
  ElementVals.push_back(ConstantSInt::get(Type::SByteTy, 0));

  ArrayType *ATy = ArrayType::get(Type::SByteTy, Str.length()+1);
  return ConstantArray::get(ATy, ElementVals);
}

// getAsString - If the sub-element type of this array is either sbyte or ubyte,
// then this method converts the array to an std::string and returns it.
// Otherwise, it asserts out.
//
std::string ConstantArray::getAsString() const {
  assert((getType()->getElementType() == Type::UByteTy ||
          getType()->getElementType() == Type::SByteTy) && "Not a string!");

  std::string Result;
  for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
    Result += (char)cast<ConstantInt>(getOperand(i))->getRawValue();
  return Result;
}


//---- ConstantStruct::get() implementation...
//
static ValueMap<std::vector<Constant*>, StructType, 
                ConstantStruct> StructConstants;

ConstantStruct *ConstantStruct::get(const StructType *Ty,
                                    const std::vector<Constant*> &V) {
  return StructConstants.getOrCreate(Ty, V);
}

// destroyConstant - Remove the constant from the constant table...
//
void ConstantStruct::destroyConstant() {
  StructConstants.remove(this);
  destroyConstantImpl();
}

/// refineAbstractType - If this callback is invoked, then this constant is of a
/// derived type, change all users to use a concrete constant of the new type.
///
void ConstantStruct::refineAbstractType(const DerivedType *OldTy,
                                        const Type *NewTy) {
  Value::refineAbstractType(OldTy, NewTy);
  if (OldTy == NewTy) return;

  // Make everyone now use a constant of the new type...
  std::vector<Constant*> C;
  for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
    C.push_back(cast<Constant>(getOperand(i)));
  Constant *New = ConstantStruct::get(cast<StructType>(NewTy), C);
  if (New != this) {
    ReplaceUsesOfWith(this, New);
    destroyConstant();    // This constant is now dead, destroy it.
  }
}


//---- ConstantPointerNull::get() implementation...
//

// ConstantPointerNull does not take extra "value" argument...
template<class ValType>
struct ConstantCreator<ConstantPointerNull, PointerType, ValType> {
  static ConstantPointerNull *create(const PointerType *Ty, const ValType &V){
    return new ConstantPointerNull(Ty);
  }
};

static ValueMap<char, PointerType, ConstantPointerNull> NullPtrConstants;

ConstantPointerNull *ConstantPointerNull::get(const PointerType *Ty) {
  return NullPtrConstants.getOrCreate(Ty, 0);
}

// destroyConstant - Remove the constant from the constant table...
//
void ConstantPointerNull::destroyConstant() {
  NullPtrConstants.remove(this);
  destroyConstantImpl();
}

/// refineAbstractType - If this callback is invoked, then this constant is of a
/// derived type, change all users to use a concrete constant of the new type.
///
void ConstantPointerNull::refineAbstractType(const DerivedType *OldTy,
                                             const Type *NewTy) {
  Value::refineAbstractType(OldTy, NewTy);
  if (OldTy == NewTy) return;

  // Make everyone now use a constant of the new type...
  Constant *New = ConstantPointerNull::get(cast<PointerType>(NewTy));
  if (New != this) {
    ReplaceUsesOfWith(this, New);
    
    // This constant is now dead, destroy it.
    destroyConstant();
  }
}



//---- ConstantPointerRef::get() implementation...
//
ConstantPointerRef *ConstantPointerRef::get(GlobalValue *GV) {
  assert(GV->getParent() && "Global Value must be attached to a module!");
  
  // The Module handles the pointer reference sharing...
  return GV->getParent()->getConstantPointerRef(GV);
}

// destroyConstant - Remove the constant from the constant table...
//
void ConstantPointerRef::destroyConstant() {
  getValue()->getParent()->destroyConstantPointerRef(this);
  destroyConstantImpl();
}


//---- ConstantExpr::get() implementations...
//
typedef std::pair<unsigned, std::vector<Constant*> > ExprMapKeyType;

template<>
struct ConstantCreator<ConstantExpr, Type, ExprMapKeyType> {
  static ConstantExpr *create(const Type *Ty, const ExprMapKeyType &V) {
    if (V.first == Instruction::Cast)
      return new ConstantExpr(Instruction::Cast, V.second[0], Ty);
    if ((V.first >= Instruction::BinaryOpsBegin &&
         V.first < Instruction::BinaryOpsEnd) ||
        V.first == Instruction::Shl || V.first == Instruction::Shr)
      return new ConstantExpr(V.first, V.second[0], V.second[1]);
    
    assert(V.first == Instruction::GetElementPtr && "Invalid ConstantExpr!");
    
    // Check that the indices list is valid...
    std::vector<Value*> ValIdxList(V.second.begin()+1, V.second.end());
    const Type *DestTy = GetElementPtrInst::getIndexedType(Ty, ValIdxList,
                                                           true);
    assert(DestTy && "Invalid index list for GetElementPtr expression");
    
    std::vector<Constant*> IdxList(V.second.begin()+1, V.second.end());
    return new ConstantExpr(V.second[0], IdxList, PointerType::get(DestTy));
  }
};

static ValueMap<ExprMapKeyType, Type, ConstantExpr> ExprConstants;

Constant *ConstantExpr::getCast(Constant *C, const Type *Ty) {
  if (Constant *FC = ConstantFoldCastInstruction(C, Ty))
    return FC;          // Fold a few common cases...

  // Look up the constant in the table first to ensure uniqueness
  std::vector<Constant*> argVec(1, C);
  ExprMapKeyType Key = std::make_pair(Instruction::Cast, argVec);
  return ExprConstants.getOrCreate(Ty, Key);
}

Constant *ConstantExpr::get(unsigned Opcode, Constant *C1, Constant *C2) {
  // Check the operands for consistency first
  assert((Opcode >= Instruction::BinaryOpsBegin &&
          Opcode < Instruction::BinaryOpsEnd) &&
         "Invalid opcode in binary constant expression");
  assert(C1->getType() == C2->getType() &&
         "Operand types in binary constant expression should match");
  
  if (Constant *FC = ConstantFoldBinaryInstruction(Opcode, C1, C2))
    return FC;          // Fold a few common cases...

  std::vector<Constant*> argVec(1, C1); argVec.push_back(C2);
  ExprMapKeyType Key = std::make_pair(Opcode, argVec);
  return ExprConstants.getOrCreate(C1->getType(), Key);
}

/// getShift - Return a shift left or shift right constant expr
Constant *ConstantExpr::getShift(unsigned Opcode, Constant *C1, Constant *C2) {
  // Check the operands for consistency first
  assert((Opcode == Instruction::Shl ||
          Opcode == Instruction::Shr) &&
         "Invalid opcode in binary constant expression");
  assert(C1->getType()->isIntegral() && C2->getType() == Type::UByteTy &&
         "Invalid operand types for Shift constant expr!");

  if (Constant *FC = ConstantFoldShiftInstruction(Opcode, C1, C2))
    return FC;          // Fold a few common cases...

  // Look up the constant in the table first to ensure uniqueness
  std::vector<Constant*> argVec(1, C1); argVec.push_back(C2);
  ExprMapKeyType Key = std::make_pair(Opcode, argVec);
  return ExprConstants.getOrCreate(C1->getType(), Key);
}


Constant *ConstantExpr::getGetElementPtr(Constant *C,
                                         const std::vector<Constant*> &IdxList){
  if (Constant *FC = ConstantFoldGetElementPtr(C, IdxList))
    return FC;          // Fold a few common cases...
  const Type *Ty = C->getType();
  assert(isa<PointerType>(Ty) &&
         "Non-pointer type for constant GetElementPtr expression");

  // Look up the constant in the table first to ensure uniqueness
  std::vector<Constant*> argVec(1, C);
  argVec.insert(argVec.end(), IdxList.begin(), IdxList.end());
  
  const ExprMapKeyType &Key = std::make_pair(Instruction::GetElementPtr,argVec);
  return ExprConstants.getOrCreate(Ty, Key);
}

// destroyConstant - Remove the constant from the constant table...
//
void ConstantExpr::destroyConstant() {
  ExprConstants.remove(this);
  destroyConstantImpl();
}

/// refineAbstractType - If this callback is invoked, then this constant is of a
/// derived type, change all users to use a concrete constant of the new type.
///
void ConstantExpr::refineAbstractType(const DerivedType *OldTy,
                                      const Type *NewTy) {
  Value::refineAbstractType(OldTy, NewTy);
  if (OldTy == NewTy) return;

  // FIXME: These need to use a lower-level implementation method, because the
  // ::get methods intuit the type of the result based on the types of the
  // operands.  The operand types may not have had their types resolved yet.
  //
  Constant *New;
  if (getOpcode() == Instruction::Cast) {
    New = getCast(getOperand(0), NewTy);
  } else if (getOpcode() >= Instruction::BinaryOpsBegin &&
             getOpcode() < Instruction::BinaryOpsEnd) {
    New = get(getOpcode(), getOperand(0), getOperand(0));
  } else if (getOpcode() == Instruction::Shl || getOpcode() ==Instruction::Shr){
    New = getShift(getOpcode(), getOperand(0), getOperand(0));
  } else {
    assert(getOpcode() == Instruction::GetElementPtr);

    // Make everyone now use a constant of the new type...
    std::vector<Constant*> C;
    for (unsigned i = 1, e = getNumOperands(); i != e; ++i)
      C.push_back(cast<Constant>(getOperand(i)));
    New = ConstantExpr::getGetElementPtr(getOperand(0), C);
  }
  if (New != this) {
    ReplaceUsesOfWith(this, New);
    destroyConstant();    // This constant is now dead, destroy it.
  }
}




const char *ConstantExpr::getOpcodeName() const {
  return Instruction::getOpcodeName(getOpcode());
}

unsigned Constant::mutateReferences(Value *OldV, Value *NewV) {
  // Uses of constant pointer refs are global values, not constants!
  if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(this)) {
    GlobalValue *NewGV = cast<GlobalValue>(NewV);
    GlobalValue *OldGV = CPR->getValue();

    assert(OldGV == OldV && "Cannot mutate old value if I'm not using it!");
    Operands[0] = NewGV;
    OldGV->getParent()->mutateConstantPointerRef(OldGV, NewGV);
    return 1;
  } else {
    Constant *NewC = cast<Constant>(NewV);
    unsigned NumReplaced = 0;
    for (unsigned i = 0, N = getNumOperands(); i != N; ++i)
      if (Operands[i] == OldV) {
        ++NumReplaced;
        Operands[i] = NewC;
      }
    return NumReplaced;
  }
}