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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 ConstantRange;
 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, AllocInfo AllocInfo)
       : User(ty, vty, AllocInfo) {}
 
   ~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 poison elements by setting
   /// AllowPoison to true.
   Constant *getSplatValue(bool AllowPoison = 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;
 
   /// Convert constant to an approximate constant range. For vectors, the
   /// range is the union over the element ranges. Poison elements are ignored.
   ConstantRange toConstantRange() 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

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