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Constant.h
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00001 //===-- llvm/Constant.h - Constant class definition -------------*- C++ -*-===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file contains the declaration of the Constant class.
00011 //
00012 //===----------------------------------------------------------------------===//
00013 
00014 #ifndef LLVM_IR_CONSTANT_H
00015 #define LLVM_IR_CONSTANT_H
00016 
00017 #include "llvm/IR/User.h"
00018 
00019 namespace llvm {
00020   class APInt;
00021 
00022   template<typename T> class SmallVectorImpl;
00023 
00024 /// This is an important base class in LLVM. It provides the common facilities
00025 /// of all constant values in an LLVM program. A constant is a value that is
00026 /// immutable at runtime. Functions are constants because their address is
00027 /// immutable. Same with global variables. 
00028 /// 
00029 /// All constants share the capabilities provided in this class. All constants
00030 /// can have a null value. They can have an operand list. Constants can be
00031 /// simple (integer and floating point values), complex (arrays and structures),
00032 /// or expression based (computations yielding a constant value composed of 
00033 /// only certain operators and other constant values).
00034 /// 
00035 /// Note that Constants are immutable (once created they never change) 
00036 /// and are fully shared by structural equivalence.  This means that two 
00037 /// structurally equivalent constants will always have the same address.  
00038 /// Constants are created on demand as needed and never deleted: thus clients 
00039 /// don't have to worry about the lifetime of the objects.
00040 /// @brief LLVM Constant Representation
00041 class Constant : public User {
00042   void operator=(const Constant &) = delete;
00043   Constant(const Constant &) = delete;
00044   void anchor() override;
00045 
00046 protected:
00047   Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps)
00048     : User(ty, vty, Ops, NumOps) {}
00049 
00050   void replaceUsesOfWithOnConstantImpl(Constant *Replacement);
00051 
00052 public:
00053   /// isNullValue - Return true if this is the value that would be returned by
00054   /// getNullValue.
00055   bool isNullValue() const;
00056 
00057   /// \brief Returns true if the value is one.
00058   bool isOneValue() const;
00059 
00060   /// isAllOnesValue - Return true if this is the value that would be returned by
00061   /// getAllOnesValue.
00062   bool isAllOnesValue() const;
00063 
00064   /// isNegativeZeroValue - Return true if the value is what would be returned 
00065   /// by getZeroValueForNegation.
00066   bool isNegativeZeroValue() const;
00067 
00068   /// Return true if the value is negative zero or null value.
00069   bool isZeroValue() const;
00070 
00071   /// \brief Return true if the value is not the smallest signed value.
00072   bool isNotMinSignedValue() const;
00073 
00074   /// \brief Return true if the value is the smallest signed value.
00075   bool isMinSignedValue() const;
00076 
00077   /// canTrap - Return true if evaluation of this constant could trap.  This is
00078   /// true for things like constant expressions that could divide by zero.
00079   bool canTrap() const;
00080 
00081   /// isThreadDependent - Return true if the value can vary between threads.
00082   bool isThreadDependent() const;
00083 
00084   /// Return true if the value is dependent on a dllimport variable.
00085   bool isDLLImportDependent() const;
00086 
00087   /// isConstantUsed - Return true if the constant has users other than constant
00088   /// exprs and other dangling things.
00089   bool isConstantUsed() const;
00090   
00091   enum PossibleRelocationsTy {
00092     NoRelocation = 0,
00093     LocalRelocation = 1,
00094     GlobalRelocations = 2
00095   };
00096   
00097   /// getRelocationInfo - This method classifies the entry according to
00098   /// whether or not it may generate a relocation entry.  This must be
00099   /// conservative, so if it might codegen to a relocatable entry, it should say
00100   /// so.  The return values are:
00101   /// 
00102   ///  NoRelocation: This constant pool entry is guaranteed to never have a
00103   ///     relocation applied to it (because it holds a simple constant like
00104   ///     '4').
00105   ///  LocalRelocation: This entry has relocations, but the entries are
00106   ///     guaranteed to be resolvable by the static linker, so the dynamic
00107   ///     linker will never see them.
00108   ///  GlobalRelocations: This entry may have arbitrary relocations.
00109   ///
00110   /// FIXME: This really should not be in VMCore.
00111   PossibleRelocationsTy getRelocationInfo() const;
00112   
00113   /// getAggregateElement - For aggregates (struct/array/vector) return the
00114   /// constant that corresponds to the specified element if possible, or null if
00115   /// not.  This can return null if the element index is a ConstantExpr, or if
00116   /// 'this' is a constant expr.
00117   Constant *getAggregateElement(unsigned Elt) const;
00118   Constant *getAggregateElement(Constant *Elt) const;
00119 
00120   /// getSplatValue - If this is a splat vector constant, meaning that all of
00121   /// the elements have the same value, return that value. Otherwise return 0.
00122   Constant *getSplatValue() const;
00123 
00124   /// If C is a constant integer then return its value, otherwise C must be a
00125   /// vector of constant integers, all equal, and the common value is returned.
00126   const APInt &getUniqueInteger() const;
00127 
00128   /// Called if some element of this constant is no longer valid.
00129   /// At this point only other constants may be on the use_list for this
00130   /// constant.  Any constants on our Use list must also be destroy'd.  The
00131   /// implementation must be sure to remove the constant from the list of
00132   /// available cached constants.  Implementations should implement
00133   /// destroyConstantImpl to remove constants from any pools/maps they are
00134   /// contained it.
00135   void destroyConstant();
00136 
00137   //// Methods for support type inquiry through isa, cast, and dyn_cast:
00138   static inline bool classof(const Value *V) {
00139     return V->getValueID() >= ConstantFirstVal &&
00140            V->getValueID() <= ConstantLastVal;
00141   }
00142 
00143   /// replaceUsesOfWithOnConstant - This method is a special form of
00144   /// User::replaceUsesOfWith (which does not work on constants) that does work
00145   /// on constants.  Basically this method goes through the trouble of building
00146   /// a new constant that is equivalent to the current one, with all uses of
00147   /// From replaced with uses of To.  After this construction is completed, all
00148   /// of the users of 'this' are replaced to use the new constant, and then
00149   /// 'this' is deleted.  In general, you should not call this method, instead,
00150   /// use Value::replaceAllUsesWith, which automatically dispatches to this
00151   /// method as needed.
00152   ///
00153   virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) {
00154     // Provide a default implementation for constants (like integers) that
00155     // cannot use any other values.  This cannot be called at runtime, but needs
00156     // to be here to avoid link errors.
00157     assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be "
00158            "implemented for all constants that have operands!");
00159     llvm_unreachable("Constants that do not have operands cannot be using "
00160                      "'From'!");
00161   }
00162 
00163   static Constant *getNullValue(Type* Ty);
00164 
00165   /// @returns the value for an integer or vector of integer constant of the
00166   /// given type that has all its bits set to true.
00167   /// @brief Get the all ones value
00168   static Constant *getAllOnesValue(Type* Ty);
00169 
00170   /// getIntegerValue - Return the value for an integer or pointer constant,
00171   /// or a vector thereof, with the given scalar value.
00172   static Constant *getIntegerValue(Type* Ty, const APInt &V);
00173   
00174   /// removeDeadConstantUsers - If there are any dead constant users dangling
00175   /// off of this constant, remove them.  This method is useful for clients
00176   /// that want to check to see if a global is unused, but don't want to deal
00177   /// with potentially dead constants hanging off of the globals.
00178   void removeDeadConstantUsers() const;
00179 
00180   Constant *stripPointerCasts() {
00181     return cast<Constant>(Value::stripPointerCasts());
00182   }
00183 
00184   const Constant *stripPointerCasts() const {
00185     return const_cast<Constant*>(this)->stripPointerCasts();
00186   }
00187 };
00188 
00189 } // End llvm namespace
00190 
00191 #endif