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//===-- llvm/Constant.h - Constant class definition -------------*- 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

//

//===----------------------------------------------------------------------===//

//

// This file contains the declaration of the Constant class.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_IR_CONSTANT_H

#define LLVM_IR_CONSTANT_H

#include "llvm/IR/User.h"

#include "llvm/IR/Value.h"

#include "llvm/Support/Casting.h"

namespace llvm {

class APInt;

/// This is an important base class in LLVM. It provides the common facilities

/// of all constant values in an LLVM program. A constant is a value that is

/// immutable at runtime. Functions are constants because their address is

/// immutable. Same with global variables.

///

/// All constants share the capabilities provided in this class. All constants

/// can have a null value. They can have an operand list. Constants can be

/// simple (integer and floating point values), complex (arrays and structures),

/// or expression based (computations yielding a constant value composed of

/// only certain operators and other constant values).

///

/// 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.

/// LLVM Constant Representation

class Constant : public User {

protected:

  Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)

    : User(ty, vty, Ops, NumOps) {}

  ~Constant() = default;

public:

  void operator=(const Constant &) = delete;

  Constant(const Constant &) = delete;

  /// Return true if this is the value that would be returned by getNullValue.

  bool isNullValue() const;

  /// Returns true if the value is one.

  bool isOneValue() const;

  /// Return true if the value is not the one value, or,

  /// for vectors, does not contain one value elements.

  bool isNotOneValue() const;

  /// Return true if this is the value that would be returned by

  /// getAllOnesValue.

  bool isAllOnesValue() const;

  /// Return true if the value is what would be returned by

  /// getZeroValueForNegation.

  bool isNegativeZeroValue() const;

  /// Return true if the value is negative zero or null value.

  bool isZeroValue() const;

  /// Return true if the value is not the smallest signed value, or,

  /// for vectors, does not contain smallest signed value elements.

  bool isNotMinSignedValue() const;

  /// Return true if the value is the smallest signed value.

  bool isMinSignedValue() const;

  /// Return true if this is a finite and non-zero floating-point scalar

  /// constant or a fixed width vector constant with all finite and non-zero

  /// elements.

  bool isFiniteNonZeroFP() const;

  /// Return true if this is a normal (as opposed to denormal, infinity, nan,

  /// or zero) floating-point scalar constant or a vector constant with all

  /// normal elements. See APFloat::isNormal.

  bool isNormalFP() const;

  /// Return true if this scalar has an exact multiplicative inverse or this

  /// vector has an exact multiplicative inverse for each element in the vector.

  bool hasExactInverseFP() const;

  /// Return true if this is a floating-point NaN constant or a vector

  /// floating-point constant with all NaN elements.

  bool isNaN() const;

  /// Return true if this constant and a constant 'Y' are element-wise equal.

  /// This is identical to just comparing the pointers, with the exception that

  /// for vectors, if only one of the constants has an `undef` element in some

  /// lane, the constants still match.

  bool isElementWiseEqual(Value *Y) const;

  /// Return true if this is a vector constant that includes any undef or

  /// poison elements. Since it is impossible to inspect a scalable vector

  /// element- wise at compile time, this function returns true only if the

  /// entire vector is undef or poison.

  bool containsUndefOrPoisonElement() const;

  /// Return true if this is a vector constant that includes any poison

  /// elements.

  bool containsPoisonElement() const;

  /// Return true if this is a vector constant that includes any strictly undef

  /// (not poison) elements.

  bool containsUndefElement() const;

  /// Return true if this is a fixed width vector constant that includes

  /// any constant expressions.

  bool containsConstantExpression() const;

  /// Return true if the value can vary between threads.

  bool isThreadDependent() const;

  /// Return true if the value is dependent on a dllimport variable.

  bool isDLLImportDependent() const;

  /// Return true if the constant has users other than constant expressions and

  /// other dangling things.

  bool isConstantUsed() const;

  /// This method classifies the entry according to whether or not it may

  /// generate a relocation entry (either static or dynamic). This must be

  /// conservative, so if it might codegen to a relocatable entry, it should say

  /// so.

  ///

  /// FIXME: This really should not be in IR.

  bool needsRelocation() const;

  bool needsDynamicRelocation() const;

  /// For aggregates (struct/array/vector) return the constant that corresponds

  /// to the specified element if possible, or null if not. This can return null

  /// if the element index is a ConstantExpr, if 'this' is a constant expr or

  /// if the constant does not fit into an uint64_t.

  Constant *getAggregateElement(unsigned Elt) const;

  Constant *getAggregateElement(Constant *Elt) const;

  /// 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;

  /// If C is a constant integer then return its value, otherwise C must be a

  /// vector of constant integers, all equal, and the common value is returned.

  const APInt &getUniqueInteger() const;

  /// Called if some element of this constant is no longer valid.

  /// At this point only other constants may be on the use_list for this

  /// constant.  Any constants on our Use list must also be destroy'd.  The

  /// implementation must be sure to remove the constant from the list of

  /// available cached constants.  Implementations should implement

  /// destroyConstantImpl to remove constants from any pools/maps they are

  /// contained it.

  void destroyConstant();

  //// Methods for support type inquiry through isa, cast, and dyn_cast:

  static bool classof(const Value *V) {

    static_assert(ConstantFirstVal == 0, "V->getValueID() >= ConstantFirstVal always succeeds");

    return V->getValueID() <= ConstantLastVal;

  }

  /// This method is a special form of User::replaceUsesOfWith

  /// (which does not work on constants) that does work

  /// on constants.  Basically this method goes through the trouble of building

  /// a new constant that is equivalent to the current one, with all uses of

  /// From replaced with uses of To.  After this construction is completed, all

  /// of the users of 'this' are replaced to use the new constant, and then

  /// 'this' is deleted.  In general, you should not call this method, instead,

  /// use Value::replaceAllUsesWith, which automatically dispatches to this

  /// method as needed.

  ///

  void handleOperandChange(Value *, Value *);

  static Constant *getNullValue(Type* Ty);

  /// @returns the value for an integer or vector of integer constant of the

  /// given type that has all its bits set to true.

  /// Get the all ones value

  static Constant *getAllOnesValue(Type* Ty);

  /// Return the value for an integer or pointer constant, or a vector thereof,

  /// with the given scalar value.

  static Constant *getIntegerValue(Type *Ty, const APInt &V);

  /// If there are any dead constant users dangling off of this constant, remove

  /// them. This method is useful for clients that want to check to see if a

  /// global is unused, but don't want to deal with potentially dead constants

  /// hanging off of the globals.

  void removeDeadConstantUsers() const;

  /// Return true if the constant has exactly one live use.

  ///

  /// This returns the same result as calling Value::hasOneUse after

  /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.

  bool hasOneLiveUse() const;

  /// Return true if the constant has no live uses.

  ///

  /// This returns the same result as calling Value::use_empty after

  /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.

  bool hasZeroLiveUses() const;

  const Constant *stripPointerCasts() const {

    return cast<Constant>(Value::stripPointerCasts());

  }

  Constant *stripPointerCasts() {

    return const_cast<Constant*>(

                      static_cast<const Constant *>(this)->stripPointerCasts());

  }

  /// Try to replace undefined constant C or undefined elements in C with

  /// Replacement. If no changes are made, the constant C is returned.

  static Constant *replaceUndefsWith(Constant *C, Constant *Replacement);

  /// Merges undefs of a Constant with another Constant, along with the

  /// undefs already present. Other doesn't have to be the same type as C, but

  /// both must either be scalars or vectors with the same element count. If no

  /// changes are made, the constant C is returned.

  static Constant *mergeUndefsWith(Constant *C, Constant *Other);

  /// Return true if a constant is ConstantData or a ConstantAggregate or

  /// ConstantExpr that contain only ConstantData.

  bool isManifestConstant() const;

private:

  enum PossibleRelocationsTy {

    /// This constant requires no relocations. That is, it holds simple

    /// constants (like integrals).

    NoRelocation = 0,

    /// This constant holds static relocations that can be resolved by the

    /// static linker.

    LocalRelocation = 1,

    /// This constant holds dynamic relocations that the dynamic linker will

    /// need to resolve.

    GlobalRelocation = 2,

  };

  /// Determine what potential relocations may be needed by this constant.

  PossibleRelocationsTy getRelocationInfo() const;

  bool hasNLiveUses(unsigned N) const;

};

} // end namespace llvm

#endif // LLVM_IR_CONSTANT_H