llvm-for-llvmta/include/llvm/IR/Constants.h

//===-- llvm/Constants.h - Constant class subclass definitions --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// @file
/// This file contains the declarations for the subclasses of Constant,
/// which represent the different flavors of constant values that live in LLVM.
/// Note that Constants are immutable (once created they never change) and are
/// fully shared by structural equivalence.  This means that two structurally
/// equivalent constants will always have the same address.  Constants are
/// created on demand as needed and never deleted: thus clients don't have to
/// worry about the lifetime of the objects.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_CONSTANTS_H
#define LLVM_IR_CONSTANTS_H

#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/OperandTraits.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <cstddef>
#include <cstdint>

namespace llvm {

template <class ConstantClass> struct ConstantAggrKeyType;

/// Base class for constants with no operands.
///
/// These constants have no operands; they represent their data directly.
/// Since they can be in use by unrelated modules (and are never based on
/// GlobalValues), it never makes sense to RAUW them.
class ConstantData : public Constant {
  friend class Constant;

  Value *handleOperandChangeImpl(Value *From, Value *To) {
    llvm_unreachable("Constant data does not have operands!");
  }

protected:
  explicit ConstantData(Type *Ty, ValueTy VT) : Constant(Ty, VT, nullptr, 0) {}

  void *operator new(size_t s) { return User::operator new(s, 0); }

public:
  ConstantData(const ConstantData &) = delete;

  /// Methods to support type inquiry through isa, cast, and dyn_cast.
  static bool classof(const Value *V) {
    return V->getValueID() >= ConstantDataFirstVal &&
           V->getValueID() <= ConstantDataLastVal;
  }
};

//===----------------------------------------------------------------------===//
/// This is the shared class of boolean and integer constants. This class
/// represents both boolean and integral constants.
/// Class for constant integers.
class ConstantInt final : public ConstantData {
  friend class Constant;

  APInt Val;

  ConstantInt(IntegerType *Ty, const APInt& V);

  void destroyConstantImpl();

public:
  ConstantInt(const ConstantInt &) = delete;

  static ConstantInt *getTrue(LLVMContext &Context);
  static ConstantInt *getFalse(LLVMContext &Context);
  static ConstantInt *getBool(LLVMContext &Context, bool V);
  static Constant *getTrue(Type *Ty);
  static Constant *getFalse(Type *Ty);
  static Constant *getBool(Type *Ty, bool V);

  /// If Ty is a vector type, return a Constant with a splat of the given
  /// value. Otherwise return a ConstantInt for the given value.
  static Constant *get(Type *Ty, uint64_t V, bool isSigned = false);

  /// Return a ConstantInt with the specified integer value for the specified
  /// type. If the type is wider than 64 bits, the value will be zero-extended
  /// to fit the type, unless isSigned is true, in which case the value will
  /// be interpreted as a 64-bit signed integer and sign-extended to fit
  /// the type.
  /// Get a ConstantInt for a specific value.
  static ConstantInt *get(IntegerType *Ty, uint64_t V,
                          bool isSigned = false);

  /// Return a ConstantInt with the specified value for the specified type. The
  /// value V will be canonicalized to a an unsigned APInt. Accessing it with
  /// either getSExtValue() or getZExtValue() will yield a correctly sized and
  /// signed value for the type Ty.
  /// Get a ConstantInt for a specific signed value.
  static ConstantInt *getSigned(IntegerType *Ty, int64_t V);
  static Constant *getSigned(Type *Ty, int64_t V);

  /// Return a ConstantInt with the specified value and an implied Type. The
  /// type is the integer type that corresponds to the bit width of the value.
  static ConstantInt *get(LLVMContext &Context, const APInt &V);

  /// Return a ConstantInt constructed from the string strStart with the given
  /// radix.
  static ConstantInt *get(IntegerType *Ty, StringRef Str,
                          uint8_t radix);

  /// If Ty is a vector type, return a Constant with a splat of the given
  /// value. Otherwise return a ConstantInt for the given value.
  static Constant *get(Type* Ty, const APInt& V);

  /// Return the constant as an APInt value reference. This allows clients to
  /// obtain a full-precision copy of the value.
  /// Return the constant's value.
  inline const APInt &getValue() const {
    return Val;
  }

  /// getBitWidth - Return the bitwidth of this constant.
  unsigned getBitWidth() const { return Val.getBitWidth(); }

  /// Return the constant as a 64-bit unsigned integer value after it
  /// has been zero extended as appropriate for the type of this constant. Note
  /// that this method can assert if the value does not fit in 64 bits.
  /// Return the zero extended value.
  inline uint64_t getZExtValue() const {
    return Val.getZExtValue();
  }

  /// Return the constant as a 64-bit integer value after it has been sign
  /// extended as appropriate for the type of this constant. Note that
  /// this method can assert if the value does not fit in 64 bits.
  /// Return the sign extended value.
  inline int64_t getSExtValue() const {
    return Val.getSExtValue();
  }

  /// Return the constant as an llvm::MaybeAlign.
  /// Note that this method can assert if the value does not fit in 64 bits or
  /// is not a power of two.
  inline MaybeAlign getMaybeAlignValue() const {
    return MaybeAlign(getZExtValue());
  }

  /// Return the constant as an llvm::Align, interpreting `0` as `Align(1)`.
  /// Note that this method can assert if the value does not fit in 64 bits or
  /// is not a power of two.
  inline Align getAlignValue() const {
    return getMaybeAlignValue().valueOrOne();
  }

  /// A helper method that can be used to determine if the constant contained
  /// within is equal to a constant.  This only works for very small values,
  /// because this is all that can be represented with all types.
  /// Determine if this constant's value is same as an unsigned char.
  bool equalsInt(uint64_t V) const {
    return Val == V;
  }

  /// getType - Specialize the getType() method to always return an IntegerType,
  /// which reduces the amount of casting needed in parts of the compiler.
  ///
  inline IntegerType *getType() const {
    return cast<IntegerType>(Value::getType());
  }

  /// This static method returns true if the type Ty is big enough to
  /// represent the value V. This can be used to avoid having the get method
  /// assert when V is larger than Ty can represent. Note that there are two
  /// versions of this method, one for unsigned and one for signed integers.
  /// Although ConstantInt canonicalizes everything to an unsigned integer,
  /// the signed version avoids callers having to convert a signed quantity
  /// to the appropriate unsigned type before calling the method.
  /// @returns true if V is a valid value for type Ty
  /// Determine if the value is in range for the given type.
  static bool isValueValidForType(Type *Ty, uint64_t V);
  static bool isValueValidForType(Type *Ty, int64_t V);

  bool isNegative() const { return Val.isNegative(); }

  /// This is just a convenience method to make client code smaller for a
  /// common code. It also correctly performs the comparison without the
  /// potential for an assertion from getZExtValue().
  bool isZero() const {
    return Val.isNullValue();
  }

  /// This is just a convenience method to make client code smaller for a
  /// common case. It also correctly performs the comparison without the
  /// potential for an assertion from getZExtValue().
  /// Determine if the value is one.
  bool isOne() const {
    return Val.isOneValue();
  }

  /// This function will return true iff every bit in this constant is set
  /// to true.
  /// @returns true iff this constant's bits are all set to true.
  /// Determine if the value is all ones.
  bool isMinusOne() const {
    return Val.isAllOnesValue();
  }

  /// This function will return true iff this constant represents the largest
  /// value that may be represented by the constant's type.
  /// @returns true iff this is the largest value that may be represented
  /// by this type.
  /// Determine if the value is maximal.
  bool isMaxValue(bool isSigned) const {
    if (isSigned)
      return Val.isMaxSignedValue();
    else
      return Val.isMaxValue();
  }

  /// This function will return true iff this constant represents the smallest
  /// value that may be represented by this constant's type.
  /// @returns true if this is the smallest value that may be represented by
  /// this type.
  /// Determine if the value is minimal.
  bool isMinValue(bool isSigned) const {
    if (isSigned)
      return Val.isMinSignedValue();
    else
      return Val.isMinValue();
  }

  /// This function will return true iff this constant represents a value with
  /// active bits bigger than 64 bits or a value greater than the given uint64_t
  /// value.
  /// @returns true iff this constant is greater or equal to the given number.
  /// Determine if the value is greater or equal to the given number.
  bool uge(uint64_t Num) const {
    return Val.uge(Num);
  }

  /// getLimitedValue - If the value is smaller than the specified limit,
  /// return it, otherwise return the limit value.  This causes the value
  /// to saturate to the limit.
  /// @returns the min of the value of the constant and the specified value
  /// Get the constant's value with a saturation limit
  uint64_t getLimitedValue(uint64_t Limit = ~0ULL) const {
    return Val.getLimitedValue(Limit);
  }

  /// Methods to support type inquiry through isa, cast, and dyn_cast.
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantIntVal;
  }
};

//===----------------------------------------------------------------------===//
/// ConstantFP - Floating Point Values [float, double]
///
class ConstantFP final : public ConstantData {
  friend class Constant;

  APFloat Val;

  ConstantFP(Type *Ty, const APFloat& V);

  void destroyConstantImpl();

public:
  ConstantFP(const ConstantFP &) = delete;

  /// Floating point negation must be implemented with f(x) = -0.0 - x. This
  /// method returns the negative zero constant for floating point or vector
  /// floating point types; for all other types, it returns the null value.
  static Constant *getZeroValueForNegation(Type *Ty);

  /// This returns a ConstantFP, or a vector containing a splat of a ConstantFP,
  /// for the specified value in the specified type. This should only be used
  /// for simple constant values like 2.0/1.0 etc, that are known-valid both as
  /// host double and as the target format.
  static Constant *get(Type* Ty, double V);

  /// If Ty is a vector type, return a Constant with a splat of the given
  /// value. Otherwise return a ConstantFP for the given value.
  static Constant *get(Type *Ty, const APFloat &V);

  static Constant *get(Type* Ty, StringRef Str);
  static ConstantFP *get(LLVMContext &Context, const APFloat &V);
  static Constant *getNaN(Type *Ty, bool Negative = false, uint64_t Payload = 0);
  static Constant *getQNaN(Type *Ty, bool Negative = false,
                           APInt *Payload = nullptr);
  static Constant *getSNaN(Type *Ty, bool Negative = false,
                           APInt *Payload = nullptr);
  static Constant *getNegativeZero(Type *Ty);
  static Constant *getInfinity(Type *Ty, bool Negative = false);

  /// Return true if Ty is big enough to represent V.
  static bool isValueValidForType(Type *Ty, const APFloat &V);
  inline const APFloat &getValueAPF() const { return Val; }
  inline const APFloat &getValue() const { return Val; }

  /// Return true if the value is positive or negative zero.
  bool isZero() const { return Val.isZero(); }

  /// Return true if the sign bit is set.
  bool isNegative() const { return Val.isNegative(); }

  /// Return true if the value is infinity
  bool isInfinity() const { return Val.isInfinity(); }

  /// Return true if the value is a NaN.
  bool isNaN() const { return Val.isNaN(); }

  /// We don't rely on operator== working on double values, as it returns true
  /// for things that are clearly not equal, like -0.0 and 0.0.
  /// As such, this method can be used to do an exact bit-for-bit comparison of
  /// two floating point values.  The version with a double operand is retained
  /// because it's so convenient to write isExactlyValue(2.0), but please use
  /// it only for simple constants.
  bool isExactlyValue(const APFloat &V) const;

  bool isExactlyValue(double V) const {
    bool ignored;
    APFloat FV(V);
    FV.convert(Val.getSemantics(), APFloat::rmNearestTiesToEven, &ignored);
    return isExactlyValue(FV);
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantFPVal;
  }
};

//===----------------------------------------------------------------------===//
/// All zero aggregate value
///
class ConstantAggregateZero final : public ConstantData {
  friend class Constant;

  explicit ConstantAggregateZero(Type *Ty)
      : ConstantData(Ty, ConstantAggregateZeroVal) {}

  void destroyConstantImpl();

public:
  ConstantAggregateZero(const ConstantAggregateZero &) = delete;

  static ConstantAggregateZero *get(Type *Ty);

  /// If this CAZ has array or vector type, return a zero with the right element
  /// type.
  Constant *getSequentialElement() const;

  /// If this CAZ has struct type, return a zero with the right element type for
  /// the specified element.
  Constant *getStructElement(unsigned Elt) const;

  /// Return a zero of the right value for the specified GEP index if we can,
  /// otherwise return null (e.g. if C is a ConstantExpr).
  Constant *getElementValue(Constant *C) const;

  /// Return a zero of the right value for the specified GEP index.
  Constant *getElementValue(unsigned Idx) const;

  /// Return the number of elements in the array, vector, or struct.
  unsigned getNumElements() const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  ///
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantAggregateZeroVal;
  }
};

/// Base class for aggregate constants (with operands).
///
/// These constants are aggregates of other constants, which are stored as
/// operands.
///
/// Subclasses are \a ConstantStruct, \a ConstantArray, and \a
/// ConstantVector.
///
/// \note Some subclasses of \a ConstantData are semantically aggregates --
/// such as \a ConstantDataArray -- but are not subclasses of this because they
/// use operands.
class ConstantAggregate : public Constant {
protected:
  ConstantAggregate(Type *T, ValueTy VT, ArrayRef<Constant *> V);

public:
  /// Transparently provide more efficient getOperand methods.
  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() >= ConstantAggregateFirstVal &&
           V->getValueID() <= ConstantAggregateLastVal;
  }
};

template <>
struct OperandTraits<ConstantAggregate>
    : public VariadicOperandTraits<ConstantAggregate> {};

DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantAggregate, Constant)

//===----------------------------------------------------------------------===//
/// ConstantArray - Constant Array Declarations
///
class ConstantArray final : public ConstantAggregate {
  friend struct ConstantAggrKeyType<ConstantArray>;
  friend class Constant;

  ConstantArray(ArrayType *T, ArrayRef<Constant *> Val);

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

public:
  // ConstantArray accessors
  static Constant *get(ArrayType *T, ArrayRef<Constant*> V);

private:
  static Constant *getImpl(ArrayType *T, ArrayRef<Constant *> V);

public:
  /// Specialize the getType() method to always return an ArrayType,
  /// which reduces the amount of casting needed in parts of the compiler.
  inline ArrayType *getType() const {
    return cast<ArrayType>(Value::getType());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantArrayVal;
  }
};

//===----------------------------------------------------------------------===//
// Constant Struct Declarations
//
class ConstantStruct final : public ConstantAggregate {
  friend struct ConstantAggrKeyType<ConstantStruct>;
  friend class Constant;

  ConstantStruct(StructType *T, ArrayRef<Constant *> Val);

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

public:
  // ConstantStruct accessors
  static Constant *get(StructType *T, ArrayRef<Constant*> V);

  template <typename... Csts>
  static std::enable_if_t<are_base_of<Constant, Csts...>::value, Constant *>
  get(StructType *T, Csts *... Vs) {
    SmallVector<Constant *, 8> Values({Vs...});
    return get(T, Values);
  }

  /// Return an anonymous struct that has the specified elements.
  /// If the struct is possibly empty, then you must specify a context.
  static Constant *getAnon(ArrayRef<Constant*> V, bool Packed = false) {
    return get(getTypeForElements(V, Packed), V);
  }
  static Constant *getAnon(LLVMContext &Ctx,
                           ArrayRef<Constant*> V, bool Packed = false) {
    return get(getTypeForElements(Ctx, V, Packed), V);
  }

  /// Return an anonymous struct type to use for a constant with the specified
  /// set of elements. The list must not be empty.
  static StructType *getTypeForElements(ArrayRef<Constant*> V,
                                        bool Packed = false);
  /// This version of the method allows an empty list.
  static StructType *getTypeForElements(LLVMContext &Ctx,
                                        ArrayRef<Constant*> V,
                                        bool Packed = false);

  /// Specialization - reduce amount of casting.
  inline StructType *getType() const {
    return cast<StructType>(Value::getType());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantStructVal;
  }
};

//===----------------------------------------------------------------------===//
/// Constant Vector Declarations
///
class ConstantVector final : public ConstantAggregate {
  friend struct ConstantAggrKeyType<ConstantVector>;
  friend class Constant;

  ConstantVector(VectorType *T, ArrayRef<Constant *> Val);

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

public:
  // ConstantVector accessors
  static Constant *get(ArrayRef<Constant*> V);

private:
  static Constant *getImpl(ArrayRef<Constant *> V);

public:
  /// Return a ConstantVector with the specified constant in each element.
  /// Note that this might not return an instance of ConstantVector
  static Constant *getSplat(ElementCount EC, Constant *Elt);

  /// Specialize the getType() method to always return a FixedVectorType,
  /// which reduces the amount of casting needed in parts of the compiler.
  inline FixedVectorType *getType() const {
    return cast<FixedVectorType>(Value::getType());
  }

  /// If all elements of the vector constant have the same value, return that
  /// value. Otherwise, return nullptr. Ignore undefined elements by setting
  /// AllowUndefs to true.
  Constant *getSplatValue(bool AllowUndefs = false) const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantVectorVal;
  }
};

//===----------------------------------------------------------------------===//
/// A constant pointer value that points to null
///
class ConstantPointerNull final : public ConstantData {
  friend class Constant;

  explicit ConstantPointerNull(PointerType *T)
      : ConstantData(T, Value::ConstantPointerNullVal) {}

  void destroyConstantImpl();

public:
  ConstantPointerNull(const ConstantPointerNull &) = delete;

  /// Static factory methods - Return objects of the specified value
  static ConstantPointerNull *get(PointerType *T);

  /// Specialize the getType() method to always return an PointerType,
  /// which reduces the amount of casting needed in parts of the compiler.
  inline PointerType *getType() const {
    return cast<PointerType>(Value::getType());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantPointerNullVal;
  }
};

//===----------------------------------------------------------------------===//
/// ConstantDataSequential - A vector or array constant whose element type is a
/// simple 1/2/4/8-byte integer or float/double, and whose elements are just
/// simple data values (i.e. ConstantInt/ConstantFP).  This Constant node has no
/// operands because it stores all of the elements of the constant as densely
/// packed data, instead of as Value*'s.
///
/// This is the common base class of ConstantDataArray and ConstantDataVector.
///
class ConstantDataSequential : public ConstantData {
  friend class LLVMContextImpl;
  friend class Constant;

  /// A pointer to the bytes underlying this constant (which is owned by the
  /// uniquing StringMap).
  const char *DataElements;

  /// This forms a link list of ConstantDataSequential nodes that have
  /// the same value but different type.  For example, 0,0,0,1 could be a 4
  /// element array of i8, or a 1-element array of i32.  They'll both end up in
  /// the same StringMap bucket, linked up.
  std::unique_ptr<ConstantDataSequential> Next;

  void destroyConstantImpl();

protected:
  explicit ConstantDataSequential(Type *ty, ValueTy VT, const char *Data)
      : ConstantData(ty, VT), DataElements(Data) {}

  static Constant *getImpl(StringRef Bytes, Type *Ty);

public:
  ConstantDataSequential(const ConstantDataSequential &) = delete;

  /// Return true if a ConstantDataSequential can be formed with a vector or
  /// array of the specified element type.
  /// ConstantDataArray only works with normal float and int types that are
  /// stored densely in memory, not with things like i42 or x86_f80.
  static bool isElementTypeCompatible(Type *Ty);

  /// If this is a sequential container of integers (of any size), return the
  /// specified element in the low bits of a uint64_t.
  uint64_t getElementAsInteger(unsigned i) const;

  /// If this is a sequential container of integers (of any size), return the
  /// specified element as an APInt.
  APInt getElementAsAPInt(unsigned i) const;

  /// If this is a sequential container of floating point type, return the
  /// specified element as an APFloat.
  APFloat getElementAsAPFloat(unsigned i) const;

  /// If this is an sequential container of floats, return the specified element
  /// as a float.
  float getElementAsFloat(unsigned i) const;

  /// If this is an sequential container of doubles, return the specified
  /// element as a double.
  double getElementAsDouble(unsigned i) const;

  /// Return a Constant for a specified index's element.
  /// Note that this has to compute a new constant to return, so it isn't as
  /// efficient as getElementAsInteger/Float/Double.
  Constant *getElementAsConstant(unsigned i) const;

  /// Return the element type of the array/vector.
  Type *getElementType() const;

  /// Return the number of elements in the array or vector.
  unsigned getNumElements() const;

  /// Return the size (in bytes) of each element in the array/vector.
  /// The size of the elements is known to be a multiple of one byte.
  uint64_t getElementByteSize() const;

  /// This method returns true if this is an array of \p CharSize integers.
  bool isString(unsigned CharSize = 8) const;

  /// This method returns true if the array "isString", ends with a null byte,
  /// and does not contains any other null bytes.
  bool isCString() const;

  /// If this array is isString(), then this method returns the array as a
  /// StringRef. Otherwise, it asserts out.
  StringRef getAsString() const {
    assert(isString() && "Not a string");
    return getRawDataValues();
  }

  /// If this array is isCString(), then this method returns the array (without
  /// the trailing null byte) as a StringRef. Otherwise, it asserts out.
  StringRef getAsCString() const {
    assert(isCString() && "Isn't a C string");
    StringRef Str = getAsString();
    return Str.substr(0, Str.size()-1);
  }

  /// Return the raw, underlying, bytes of this data. Note that this is an
  /// extremely tricky thing to work with, as it exposes the host endianness of
  /// the data elements.
  StringRef getRawDataValues() const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantDataArrayVal ||
           V->getValueID() == ConstantDataVectorVal;
  }

private:
  const char *getElementPointer(unsigned Elt) const;
};

//===----------------------------------------------------------------------===//
/// An array constant whose element type is a simple 1/2/4/8-byte integer or
/// float/double, and whose elements are just simple data values
/// (i.e. ConstantInt/ConstantFP). This Constant node has no operands because it
/// stores all of the elements of the constant as densely packed data, instead
/// of as Value*'s.
class ConstantDataArray final : public ConstantDataSequential {
  friend class ConstantDataSequential;

  explicit ConstantDataArray(Type *ty, const char *Data)
      : ConstantDataSequential(ty, ConstantDataArrayVal, Data) {}

public:
  ConstantDataArray(const ConstantDataArray &) = delete;

  /// get() constructor - Return a constant with array type with an element
  /// count and element type matching the ArrayRef passed in.  Note that this
  /// can return a ConstantAggregateZero object.
  template <typename ElementTy>
  static Constant *get(LLVMContext &Context, ArrayRef<ElementTy> Elts) {
    const char *Data = reinterpret_cast<const char *>(Elts.data());
    return getRaw(StringRef(Data, Elts.size() * sizeof(ElementTy)), Elts.size(),
                  Type::getScalarTy<ElementTy>(Context));
  }

  /// get() constructor - ArrayTy needs to be compatible with
  /// ArrayRef<ElementTy>. Calls get(LLVMContext, ArrayRef<ElementTy>).
  template <typename ArrayTy>
  static Constant *get(LLVMContext &Context, ArrayTy &Elts) {
    return ConstantDataArray::get(Context, makeArrayRef(Elts));
  }

  /// get() constructor - Return a constant with array type with an element
  /// count and element type matching the NumElements and ElementTy parameters
  /// passed in. Note that this can return a ConstantAggregateZero object.
  /// ElementTy needs to be one of i8/i16/i32/i64/float/double. Data is the
  /// buffer containing the elements. Be careful to make sure Data uses the
  /// right endianness, the buffer will be used as-is.
  static Constant *getRaw(StringRef Data, uint64_t NumElements, Type *ElementTy) {
    Type *Ty = ArrayType::get(ElementTy, NumElements);
    return getImpl(Data, Ty);
  }

  /// getFP() constructors - Return a constant of array type with a float
  /// element type taken from argument `ElementType', and count taken from
  /// argument `Elts'.  The amount of bits of the contained type must match the
  /// number of bits of the type contained in the passed in ArrayRef.
  /// (i.e. half or bfloat for 16bits, float for 32bits, double for 64bits) Note
  /// that this can return a ConstantAggregateZero object.
  static Constant *getFP(Type *ElementType, ArrayRef<uint16_t> Elts);
  static Constant *getFP(Type *ElementType, ArrayRef<uint32_t> Elts);
  static Constant *getFP(Type *ElementType, ArrayRef<uint64_t> Elts);

  /// This method constructs a CDS and initializes it with a text string.
  /// The default behavior (AddNull==true) causes a null terminator to
  /// be placed at the end of the array (increasing the length of the string by
  /// one more than the StringRef would normally indicate.  Pass AddNull=false
  /// to disable this behavior.
  static Constant *getString(LLVMContext &Context, StringRef Initializer,
                             bool AddNull = true);

  /// Specialize the getType() method to always return an ArrayType,
  /// which reduces the amount of casting needed in parts of the compiler.
  inline ArrayType *getType() const {
    return cast<ArrayType>(Value::getType());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantDataArrayVal;
  }
};

//===----------------------------------------------------------------------===//
/// A vector constant whose element type is a simple 1/2/4/8-byte integer or
/// float/double, and whose elements are just simple data values
/// (i.e. ConstantInt/ConstantFP). This Constant node has no operands because it
/// stores all of the elements of the constant as densely packed data, instead
/// of as Value*'s.
class ConstantDataVector final : public ConstantDataSequential {
  friend class ConstantDataSequential;

  explicit ConstantDataVector(Type *ty, const char *Data)
      : ConstantDataSequential(ty, ConstantDataVectorVal, Data),
        IsSplatSet(false) {}
  // Cache whether or not the constant is a splat.
  mutable bool IsSplatSet : 1;
  mutable bool IsSplat : 1;
  bool isSplatData() const;

public:
  ConstantDataVector(const ConstantDataVector &) = delete;

  /// get() constructors - Return a constant with vector type with an element
  /// count and element type matching the ArrayRef passed in.  Note that this
  /// can return a ConstantAggregateZero object.
  static Constant *get(LLVMContext &Context, ArrayRef<uint8_t> Elts);
  static Constant *get(LLVMContext &Context, ArrayRef<uint16_t> Elts);
  static Constant *get(LLVMContext &Context, ArrayRef<uint32_t> Elts);
  static Constant *get(LLVMContext &Context, ArrayRef<uint64_t> Elts);
  static Constant *get(LLVMContext &Context, ArrayRef<float> Elts);
  static Constant *get(LLVMContext &Context, ArrayRef<double> Elts);

  /// getFP() constructors - Return a constant of vector type with a float
  /// element type taken from argument `ElementType', and count taken from
  /// argument `Elts'.  The amount of bits of the contained type must match the
  /// number of bits of the type contained in the passed in ArrayRef.
  /// (i.e. half or bfloat for 16bits, float for 32bits, double for 64bits) Note
  /// that this can return a ConstantAggregateZero object.
  static Constant *getFP(Type *ElementType, ArrayRef<uint16_t> Elts);
  static Constant *getFP(Type *ElementType, ArrayRef<uint32_t> Elts);
  static Constant *getFP(Type *ElementType, ArrayRef<uint64_t> Elts);

  /// Return a ConstantVector with the specified constant in each element.
  /// The specified constant has to be a of a compatible type (i8/i16/
  /// i32/i64/float/double) and must be a ConstantFP or ConstantInt.
  static Constant *getSplat(unsigned NumElts, Constant *Elt);

  /// Returns true if this is a splat constant, meaning that all elements have
  /// the same value.
  bool isSplat() const;

  /// If this is a splat constant, meaning that all of the elements have the
  /// same value, return that value. Otherwise return NULL.
  Constant *getSplatValue() const;

  /// Specialize the getType() method to always return a FixedVectorType,
  /// which reduces the amount of casting needed in parts of the compiler.
  inline FixedVectorType *getType() const {
    return cast<FixedVectorType>(Value::getType());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantDataVectorVal;
  }
};

//===----------------------------------------------------------------------===//
/// A constant token which is empty
///
class ConstantTokenNone final : public ConstantData {
  friend class Constant;

  explicit ConstantTokenNone(LLVMContext &Context)
      : ConstantData(Type::getTokenTy(Context), ConstantTokenNoneVal) {}

  void destroyConstantImpl();

public:
  ConstantTokenNone(const ConstantTokenNone &) = delete;

  /// Return the ConstantTokenNone.
  static ConstantTokenNone *get(LLVMContext &Context);

  /// Methods to support type inquiry through isa, cast, and dyn_cast.
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantTokenNoneVal;
  }
};

/// The address of a basic block.
///
class BlockAddress final : public Constant {
  friend class Constant;

  BlockAddress(Function *F, BasicBlock *BB);

  void *operator new(size_t s) { return User::operator new(s, 2); }

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

public:
  /// Return a BlockAddress for the specified function and basic block.
  static BlockAddress *get(Function *F, BasicBlock *BB);

  /// Return a BlockAddress for the specified basic block.  The basic
  /// block must be embedded into a function.
  static BlockAddress *get(BasicBlock *BB);

  /// Lookup an existing \c BlockAddress constant for the given BasicBlock.
  ///
  /// \returns 0 if \c !BB->hasAddressTaken(), otherwise the \c BlockAddress.
  static BlockAddress *lookup(const BasicBlock *BB);

  /// Transparently provide more efficient getOperand methods.
  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);

  Function *getFunction() const { return (Function*)Op<0>().get(); }
  BasicBlock *getBasicBlock() const { return (BasicBlock*)Op<1>().get(); }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == BlockAddressVal;
  }
};

template <>
struct OperandTraits<BlockAddress> :
  public FixedNumOperandTraits<BlockAddress, 2> {
};

DEFINE_TRANSPARENT_OPERAND_ACCESSORS(BlockAddress, Value)

/// Wrapper for a function that represents a value that
/// functionally represents the original function. This can be a function,
/// global alias to a function, or an ifunc.
class DSOLocalEquivalent final : public Constant {
  friend class Constant;

  DSOLocalEquivalent(GlobalValue *GV);

  void *operator new(size_t s) { return User::operator new(s, 1); }

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

public:
  /// Return a DSOLocalEquivalent for the specified global value.
  static DSOLocalEquivalent *get(GlobalValue *GV);

  /// Transparently provide more efficient getOperand methods.
  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);

  GlobalValue *getGlobalValue() const {
    return cast<GlobalValue>(Op<0>().get());
  }

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == DSOLocalEquivalentVal;
  }
};

template <>
struct OperandTraits<DSOLocalEquivalent>
    : public FixedNumOperandTraits<DSOLocalEquivalent, 1> {};

DEFINE_TRANSPARENT_OPERAND_ACCESSORS(DSOLocalEquivalent, Value)

//===----------------------------------------------------------------------===//
/// A constant value that is initialized with an expression using
/// other constant values.
///
/// This class uses the standard Instruction opcodes to define the various
/// constant expressions.  The Opcode field for the ConstantExpr class is
/// maintained in the Value::SubclassData field.
class ConstantExpr : public Constant {
  friend struct ConstantExprKeyType;
  friend class Constant;

  void destroyConstantImpl();
  Value *handleOperandChangeImpl(Value *From, Value *To);

protected:
  ConstantExpr(Type *ty, unsigned Opcode, Use *Ops, unsigned NumOps)
      : Constant(ty, ConstantExprVal, Ops, NumOps) {
    // Operation type (an Instruction opcode) is stored as the SubclassData.
    setValueSubclassData(Opcode);
  }

  ~ConstantExpr() = default;

public:
  // Static methods to construct a ConstantExpr of different kinds.  Note that
  // these methods may return a object that is not an instance of the
  // ConstantExpr class, because they will attempt to fold the constant
  // expression into something simpler if possible.

  /// getAlignOf constant expr - computes the alignment of a type in a target
  /// independent way (Note: the return type is an i64).
  static Constant *getAlignOf(Type *Ty);

  /// getSizeOf constant expr - computes the (alloc) size of a type (in
  /// address-units, not bits) in a target independent way (Note: the return
  /// type is an i64).
  ///
  static Constant *getSizeOf(Type *Ty);

  /// getOffsetOf constant expr - computes the offset of a struct field in a
  /// target independent way (Note: the return type is an i64).
  ///
  static Constant *getOffsetOf(StructType *STy, unsigned FieldNo);

  /// getOffsetOf constant expr - This is a generalized form of getOffsetOf,
  /// which supports any aggregate type, and any Constant index.
  ///
  static Constant *getOffsetOf(Type *Ty, Constant *FieldNo);

  static Constant *getNeg(Constant *C, bool HasNUW = false, bool HasNSW =false);
  static Constant *getFNeg(Constant *C);
  static Constant *getNot(Constant *C);
  static Constant *getAdd(Constant *C1, Constant *C2,
                          bool HasNUW = false, bool HasNSW = false);
  static Constant *getFAdd(Constant *C1, Constant *C2);
  static Constant *getSub(Constant *C1, Constant *C2,
                          bool HasNUW = false, bool HasNSW = false);
  static Constant *getFSub(Constant *C1, Constant *C2);
  static Constant *getMul(Constant *C1, Constant *C2,
                          bool HasNUW = false, bool HasNSW = false);
  static Constant *getFMul(Constant *C1, Constant *C2);
  static Constant *getUDiv(Constant *C1, Constant *C2, bool isExact = false);
  static Constant *getSDiv(Constant *C1, Constant *C2, bool isExact = false);
  static Constant *getFDiv(Constant *C1, Constant *C2);
  static Constant *getURem(Constant *C1, Constant *C2);
  static Constant *getSRem(Constant *C1, Constant *C2);
  static Constant *getFRem(Constant *C1, Constant *C2);
  static Constant *getAnd(Constant *C1, Constant *C2);
  static Constant *getOr(Constant *C1, Constant *C2);
  static Constant *getXor(Constant *C1, Constant *C2);
  static Constant *getUMin(Constant *C1, Constant *C2);
  static Constant *getShl(Constant *C1, Constant *C2,
                          bool HasNUW = false, bool HasNSW = false);
  static Constant *getLShr(Constant *C1, Constant *C2, bool isExact = false);
  static Constant *getAShr(Constant *C1, Constant *C2, bool isExact = false);
  static Constant *getTrunc(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getSExt(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getZExt(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getFPTrunc(Constant *C, Type *Ty,
                              bool OnlyIfReduced = false);
  static Constant *getFPExtend(Constant *C, Type *Ty,
                               bool OnlyIfReduced = false);
  static Constant *getUIToFP(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getSIToFP(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getFPToUI(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getFPToSI(Constant *C, Type *Ty, bool OnlyIfReduced = false);
  static Constant *getPtrToInt(Constant *C, Type *Ty,
                               bool OnlyIfReduced = false);
  static Constant *getIntToPtr(Constant *C, Type *Ty,
                               bool OnlyIfReduced = false);
  static Constant *getBitCast(Constant *C, Type *Ty,
                              bool OnlyIfReduced = false);
  static Constant *getAddrSpaceCast(Constant *C, Type *Ty,
                                    bool OnlyIfReduced = false);

  static Constant *getNSWNeg(Constant *C) { return getNeg(C, false, true); }
  static Constant *getNUWNeg(Constant *C) { return getNeg(C, true, false); }

  static Constant *getNSWAdd(Constant *C1, Constant *C2) {
    return getAdd(C1, C2, false, true);
  }

  static Constant *getNUWAdd(Constant *C1, Constant *C2) {
    return getAdd(C1, C2, true, false);
  }

  static Constant *getNSWSub(Constant *C1, Constant *C2) {
    return getSub(C1, C2, false, true);
  }

  static Constant *getNUWSub(Constant *C1, Constant *C2) {
    return getSub(C1, C2, true, false);
  }

  static Constant *getNSWMul(Constant *C1, Constant *C2) {
    return getMul(C1, C2, false, true);
  }

  static Constant *getNUWMul(Constant *C1, Constant *C2) {
    return getMul(C1, C2, true, false);
  }

  static Constant *getNSWShl(Constant *C1, Constant *C2) {
    return getShl(C1, C2, false, true);
  }

  static Constant *getNUWShl(Constant *C1, Constant *C2) {
    return getShl(C1, C2, true, false);
  }

  static Constant *getExactSDiv(Constant *C1, Constant *C2) {
    return getSDiv(C1, C2, true);
  }

  static Constant *getExactUDiv(Constant *C1, Constant *C2) {
    return getUDiv(C1, C2, true);
  }

  static Constant *getExactAShr(Constant *C1, Constant *C2) {
    return getAShr(C1, C2, true);
  }

  static Constant *getExactLShr(Constant *C1, Constant *C2) {
    return getLShr(C1, C2, true);
  }

  /// If C is a scalar/fixed width vector of known powers of 2, then this
  /// function returns a new scalar/fixed width vector obtained from logBase2
  /// of C. Undef vector elements are set to zero.
  /// Return a null pointer otherwise.
  static Constant *getExactLogBase2(Constant *C);

  /// Return the identity constant for a binary opcode.
  /// The identity constant C is defined as X op C = X and C op X = X for every
  /// X when the binary operation is commutative. If the binop is not
  /// commutative, callers can acquire the operand 1 identity constant by
  /// setting AllowRHSConstant to true. For example, any shift has a zero
  /// identity constant for operand 1: X shift 0 = X.
  /// Return nullptr if the operator does not have an identity constant.
  static Constant *getBinOpIdentity(unsigned Opcode, Type *Ty,
                                    bool AllowRHSConstant = false);

  /// Return the absorbing element for the given binary
  /// operation, i.e. a constant C such that X op C = C and C op X = C for
  /// every X.  For example, this returns zero for integer multiplication.
  /// It returns null if the operator doesn't have an absorbing element.
  static Constant *getBinOpAbsorber(unsigned Opcode, Type *Ty);

  /// Transparently provide more efficient getOperand methods.
  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Constant);

  /// Convenience function for getting a Cast operation.
  ///
  /// \param ops The opcode for the conversion
  /// \param C  The constant to be converted
  /// \param Ty The type to which the constant is converted
  /// \param OnlyIfReduced see \a getWithOperands() docs.
  static Constant *getCast(unsigned ops, Constant *C, Type *Ty,
                           bool OnlyIfReduced = false);

  // Create a ZExt or BitCast cast constant expression
  static Constant *getZExtOrBitCast(
    Constant *C,   ///< The constant to zext or bitcast
    Type *Ty ///< The type to zext or bitcast C to
  );

  // Create a SExt or BitCast cast constant expression
  static Constant *getSExtOrBitCast(
    Constant *C,   ///< The constant to sext or bitcast
    Type *Ty ///< The type to sext or bitcast C to
  );

  // Create a Trunc or BitCast cast constant expression
  static Constant *getTruncOrBitCast(
    Constant *C,   ///< The constant to trunc or bitcast
    Type *Ty ///< The type to trunc or bitcast C to
  );

  /// Create a BitCast, AddrSpaceCast, or a PtrToInt cast constant
  /// expression.
  static Constant *getPointerCast(
    Constant *C,   ///< The pointer value to be casted (operand 0)
    Type *Ty ///< The type to which cast should be made
  );

  /// Create a BitCast or AddrSpaceCast for a pointer type depending on
  /// the address space.
  static Constant *getPointerBitCastOrAddrSpaceCast(
    Constant *C,   ///< The constant to addrspacecast or bitcast
    Type *Ty ///< The type to bitcast or addrspacecast C to
  );

  /// Create a ZExt, Bitcast or Trunc for integer -> integer casts
  static Constant *getIntegerCast(
    Constant *C,    ///< The integer constant to be casted
    Type *Ty, ///< The integer type to cast to
    bool isSigned   ///< Whether C should be treated as signed or not
  );

  /// Create a FPExt, Bitcast or FPTrunc for fp -> fp casts
  static Constant *getFPCast(
    Constant *C,    ///< The integer constant to be casted
    Type *Ty ///< The integer type to cast to
  );

  /// Return true if this is a convert constant expression
  bool isCast() const;

  /// Return true if this is a compare constant expression
  bool isCompare() const;

  /// Return true if this is an insertvalue or extractvalue expression,
  /// and the getIndices() method may be used.
  bool hasIndices() const;

  /// Return true if this is a getelementptr expression and all
  /// the index operands are compile-time known integers within the
  /// corresponding notional static array extents. Note that this is
  /// not equivalant to, a subset of, or a superset of the "inbounds"
  /// property.
  bool isGEPWithNoNotionalOverIndexing() const;

  /// Select constant expr
  ///
  /// \param OnlyIfReducedTy see \a getWithOperands() docs.
  static Constant *getSelect(Constant *C, Constant *V1, Constant *V2,
                             Type *OnlyIfReducedTy = nullptr);

  /// get - Return a unary operator constant expression,
  /// folding if possible.
  ///
  /// \param OnlyIfReducedTy see \a getWithOperands() docs.
  static Constant *get(unsigned Opcode, Constant *C1, unsigned Flags = 0, 
                       Type *OnlyIfReducedTy = nullptr);

  /// get - Return a binary or shift operator constant expression,
  /// folding if possible.
  ///
  /// \param OnlyIfReducedTy see \a getWithOperands() docs.
  static Constant *get(unsigned Opcode, Constant *C1, Constant *C2,
                       unsigned Flags = 0, Type *OnlyIfReducedTy = nullptr);

  /// Return an ICmp or FCmp comparison operator constant expression.
  ///
  /// \param OnlyIfReduced see \a getWithOperands() docs.
  static Constant *getCompare(unsigned short pred, Constant *C1, Constant *C2,
                              bool OnlyIfReduced = false);

  /// get* - Return some common constants without having to
  /// specify the full Instruction::OPCODE identifier.
  ///
  static Constant *getICmp(unsigned short pred, Constant *LHS, Constant *RHS,
                           bool OnlyIfReduced = false);
  static Constant *getFCmp(unsigned short pred, Constant *LHS, Constant *RHS,
                           bool OnlyIfReduced = false);

  /// Getelementptr form.  Value* is only accepted for convenience;
  /// all elements must be Constants.
  ///
  /// \param InRangeIndex the inrange index if present or None.
  /// \param OnlyIfReducedTy see \a getWithOperands() docs.
  static Constant *getGetElementPtr(Type *Ty, Constant *C,
                                    ArrayRef<Constant *> IdxList,
                                    bool InBounds = false,
                                    Optional<unsigned> InRangeIndex = None,
                                    Type *OnlyIfReducedTy = nullptr) {
    return getGetElementPtr(
        Ty, C, makeArrayRef((Value * const *)IdxList.data(), IdxList.size()),
        InBounds, InRangeIndex, OnlyIfReducedTy);
  }
  static Constant *getGetElementPtr(Type *Ty, Constant *C, Constant *Idx,
                                    bool InBounds = false,
                                    Optional<unsigned> InRangeIndex = None,
                                    Type *OnlyIfReducedTy = nullptr) {
    // This form of the function only exists to avoid ambiguous overload
    // warnings about whether to convert Idx to ArrayRef<Constant *> or
    // ArrayRef<Value *>.
    return getGetElementPtr(Ty, C, cast<Value>(Idx), InBounds, InRangeIndex,
                            OnlyIfReducedTy);
  }
  static Constant *getGetElementPtr(Type *Ty, Constant *C,
                                    ArrayRef<Value *> IdxList,
                                    bool InBounds = false,
                                    Optional<unsigned> InRangeIndex = None,
                                    Type *OnlyIfReducedTy = nullptr);

  /// Create an "inbounds" getelementptr. See the documentation for the
  /// "inbounds" flag in LangRef.html for details.
  static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
                                            ArrayRef<Constant *> IdxList) {
    return getGetElementPtr(Ty, C, IdxList, true);
  }
  static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
                                            Constant *Idx) {
    // This form of the function only exists to avoid ambiguous overload
    // warnings about whether to convert Idx to ArrayRef<Constant *> or
    // ArrayRef<Value *>.
    return getGetElementPtr(Ty, C, Idx, true);
  }
  static Constant *getInBoundsGetElementPtr(Type *Ty, Constant *C,
                                            ArrayRef<Value *> IdxList) {
    return getGetElementPtr(Ty, C, IdxList, true);
  }

  static Constant *getExtractElement(Constant *Vec, Constant *Idx,
                                     Type *OnlyIfReducedTy = nullptr);
  static Constant *getInsertElement(Constant *Vec, Constant *Elt, Constant *Idx,
                                    Type *OnlyIfReducedTy = nullptr);
  static Constant *getShuffleVector(Constant *V1, Constant *V2,
                                    ArrayRef<int> Mask,
                                    Type *OnlyIfReducedTy = nullptr);
  static Constant *getExtractValue(Constant *Agg, ArrayRef<unsigned> Idxs,
                                   Type *OnlyIfReducedTy = nullptr);
  static Constant *getInsertValue(Constant *Agg, Constant *Val,
                                  ArrayRef<unsigned> Idxs,
                                  Type *OnlyIfReducedTy = nullptr);

  /// Return the opcode at the root of this constant expression
  unsigned getOpcode() const { return getSubclassDataFromValue(); }

  /// Return the ICMP or FCMP predicate value. Assert if this is not an ICMP or
  /// FCMP constant expression.
  unsigned getPredicate() const;

  /// Assert that this is an insertvalue or exactvalue
  /// expression and return the list of indices.
  ArrayRef<unsigned> getIndices() const;

  /// Assert that this is a shufflevector and return the mask. See class
  /// ShuffleVectorInst for a description of the mask representation.
  ArrayRef<int> getShuffleMask() const;

  /// Assert that this is a shufflevector and return the mask.
  ///
  /// TODO: This is a temporary hack until we update the bitcode format for
  /// shufflevector.
  Constant *getShuffleMaskForBitcode() const;

  /// Return a string representation for an opcode.
  const char *getOpcodeName() const;

  /// Return a constant expression identical to this one, but with the specified
  /// operand set to the specified value.
  Constant *getWithOperandReplaced(unsigned OpNo, Constant *Op) const;

  /// This returns the current constant expression with the operands replaced
  /// with the specified values. The specified array must have the same number
  /// of operands as our current one.
  Constant *getWithOperands(ArrayRef<Constant*> Ops) const {
    return getWithOperands(Ops, getType());
  }

  /// Get the current expression with the operands replaced.
  ///
  /// Return the current constant expression with the operands replaced with \c
  /// Ops and the type with \c Ty.  The new operands must have the same number
  /// as the current ones.
  ///
  /// If \c OnlyIfReduced is \c true, nullptr will be returned unless something
  /// gets constant-folded, the type changes, or the expression is otherwise
  /// canonicalized.  This parameter should almost always be \c false.
  Constant *getWithOperands(ArrayRef<Constant *> Ops, Type *Ty,
                            bool OnlyIfReduced = false,
                            Type *SrcTy = nullptr) const;

  /// Returns an Instruction which implements the same operation as this
  /// ConstantExpr. The instruction is not linked to any basic block.
  ///
  /// A better approach to this could be to have a constructor for Instruction
  /// which would take a ConstantExpr parameter, but that would have spread
  /// implementation details of ConstantExpr outside of Constants.cpp, which
  /// would make it harder to remove ConstantExprs altogether.
  Instruction *getAsInstruction() const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == ConstantExprVal;
  }

private:
  // Shadow Value::setValueSubclassData with a private forwarding method so that
  // subclasses cannot accidentally use it.
  void setValueSubclassData(unsigned short D) {
    Value::setValueSubclassData(D);
  }
};

template <>
struct OperandTraits<ConstantExpr> :
  public VariadicOperandTraits<ConstantExpr, 1> {
};

DEFINE_TRANSPARENT_OPERAND_ACCESSORS(ConstantExpr, Constant)

//===----------------------------------------------------------------------===//
/// 'undef' values are things that do not have specified contents.
/// These are used for a variety of purposes, including global variable
/// initializers and operands to instructions.  'undef' values can occur with
/// any first-class type.
///
/// Undef values aren't exactly constants; if they have multiple uses, they
/// can appear to have different bit patterns at each use. See
/// LangRef.html#undefvalues for details.
///
class UndefValue : public ConstantData {
  friend class Constant;

  explicit UndefValue(Type *T) : ConstantData(T, UndefValueVal) {}

  void destroyConstantImpl();

protected:
  explicit UndefValue(Type *T, ValueTy vty) : ConstantData(T, vty) {}

public:
  UndefValue(const UndefValue &) = delete;

  /// Static factory methods - Return an 'undef' object of the specified type.
  static UndefValue *get(Type *T);

  /// If this Undef has array or vector type, return a undef with the right
  /// element type.
  UndefValue *getSequentialElement() const;

  /// If this undef has struct type, return a undef with the right element type
  /// for the specified element.
  UndefValue *getStructElement(unsigned Elt) const;

  /// Return an undef of the right value for the specified GEP index if we can,
  /// otherwise return null (e.g. if C is a ConstantExpr).
  UndefValue *getElementValue(Constant *C) const;

  /// Return an undef of the right value for the specified GEP index.
  UndefValue *getElementValue(unsigned Idx) const;

  /// Return the number of elements in the array, vector, or struct.
  unsigned getNumElements() const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == UndefValueVal ||
           V->getValueID() == PoisonValueVal;
  }
};

//===----------------------------------------------------------------------===//
/// In order to facilitate speculative execution, many instructions do not
/// invoke immediate undefined behavior when provided with illegal operands,
/// and return a poison value instead.
///
/// see LangRef.html#poisonvalues for details.
///
class PoisonValue final : public UndefValue {
  friend class Constant;

  explicit PoisonValue(Type *T) : UndefValue(T, PoisonValueVal) {}

  void destroyConstantImpl();

public:
  PoisonValue(const PoisonValue &) = delete;

  /// Static factory methods - Return an 'poison' object of the specified type.
  static PoisonValue *get(Type *T);

  /// If this poison has array or vector type, return a poison with the right
  /// element type.
  PoisonValue *getSequentialElement() const;

  /// If this poison has struct type, return a poison with the right element
  /// type for the specified element.
  PoisonValue *getStructElement(unsigned Elt) const;

  /// Return an poison of the right value for the specified GEP index if we can,
  /// otherwise return null (e.g. if C is a ConstantExpr).
  PoisonValue *getElementValue(Constant *C) const;

  /// Return an poison of the right value for the specified GEP index.
  PoisonValue *getElementValue(unsigned Idx) const;

  /// Methods for support type inquiry through isa, cast, and dyn_cast:
  static bool classof(const Value *V) {
    return V->getValueID() == PoisonValueVal;
  }
};

} // end namespace llvm

#endif // LLVM_IR_CONSTANTS_H