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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 public:
00051   /// isNullValue - Return true if this is the value that would be returned by
00052   /// getNullValue.
00053   bool isNullValue() const;
00054 
00055   /// \brief Returns true if the value is one.
00056   bool isOneValue() const;
00057 
00058   /// isAllOnesValue - Return true if this is the value that would be returned by
00059   /// getAllOnesValue.
00060   bool isAllOnesValue() const;
00061 
00062   /// isNegativeZeroValue - Return true if the value is what would be returned
00063   /// by getZeroValueForNegation.
00064   bool isNegativeZeroValue() const;
00065 
00066   /// Return true if the value is negative zero or null value.
00067   bool isZeroValue() const;
00068 
00069   /// \brief Return true if the value is not the smallest signed value.
00070   bool isNotMinSignedValue() const;
00071 
00072   /// \brief Return true if the value is the smallest signed value.
00073   bool isMinSignedValue() const;
00074 
00075   /// canTrap - Return true if evaluation of this constant could trap.  This is
00076   /// true for things like constant expressions that could divide by zero.
00077   bool canTrap() const;
00078 
00079   /// isThreadDependent - Return true if the value can vary between threads.
00080   bool isThreadDependent() const;
00081 
00082   /// Return true if the value is dependent on a dllimport variable.
00083   bool isDLLImportDependent() const;
00084 
00085   /// isConstantUsed - Return true if the constant has users other than constant
00086   /// exprs and other dangling things.
00087   bool isConstantUsed() const;
00088 
00089   /// This method classifies the entry according to whether or not it may
00090   /// generate a relocation entry.  This must be conservative, so if it might
00091   /// codegen to a relocatable entry, it should say so.
00092   ///
00093   /// FIXME: This really should not be in IR.
00094   bool needsRelocation() const;
00095 
00096   /// getAggregateElement - For aggregates (struct/array/vector) return the
00097   /// constant that corresponds to the specified element if possible, or null if
00098   /// not.  This can return null if the element index is a ConstantExpr, or if
00099   /// 'this' is a constant expr.
00100   Constant *getAggregateElement(unsigned Elt) const;
00101   Constant *getAggregateElement(Constant *Elt) const;
00102 
00103   /// getSplatValue - If this is a splat vector constant, meaning that all of
00104   /// the elements have the same value, return that value. Otherwise return 0.
00105   Constant *getSplatValue() const;
00106 
00107   /// If C is a constant integer then return its value, otherwise C must be a
00108   /// vector of constant integers, all equal, and the common value is returned.
00109   const APInt &getUniqueInteger() const;
00110 
00111   /// Called if some element of this constant is no longer valid.
00112   /// At this point only other constants may be on the use_list for this
00113   /// constant.  Any constants on our Use list must also be destroy'd.  The
00114   /// implementation must be sure to remove the constant from the list of
00115   /// available cached constants.  Implementations should implement
00116   /// destroyConstantImpl to remove constants from any pools/maps they are
00117   /// contained it.
00118   void destroyConstant();
00119 
00120   //// Methods for support type inquiry through isa, cast, and dyn_cast:
00121   static inline bool classof(const Value *V) {
00122     return V->getValueID() >= ConstantFirstVal &&
00123            V->getValueID() <= ConstantLastVal;
00124   }
00125 
00126   /// This method is a special form of User::replaceUsesOfWith
00127   /// (which does not work on constants) that does work
00128   /// on constants.  Basically this method goes through the trouble of building
00129   /// a new constant that is equivalent to the current one, with all uses of
00130   /// From replaced with uses of To.  After this construction is completed, all
00131   /// of the users of 'this' are replaced to use the new constant, and then
00132   /// 'this' is deleted.  In general, you should not call this method, instead,
00133   /// use Value::replaceAllUsesWith, which automatically dispatches to this
00134   /// method as needed.
00135   ///
00136   void handleOperandChange(Value *, Value *, Use *);
00137 
00138   static Constant *getNullValue(Type* Ty);
00139 
00140   /// @returns the value for an integer or vector of integer constant of the
00141   /// given type that has all its bits set to true.
00142   /// @brief Get the all ones value
00143   static Constant *getAllOnesValue(Type* Ty);
00144 
00145   /// getIntegerValue - Return the value for an integer or pointer constant,
00146   /// or a vector thereof, with the given scalar value.
00147   static Constant *getIntegerValue(Type *Ty, const APInt &V);
00148 
00149   /// removeDeadConstantUsers - If there are any dead constant users dangling
00150   /// off of this constant, remove them.  This method is useful for clients
00151   /// that want to check to see if a global is unused, but don't want to deal
00152   /// with potentially dead constants hanging off of the globals.
00153   void removeDeadConstantUsers() const;
00154 
00155   Constant *stripPointerCasts() {
00156     return cast<Constant>(Value::stripPointerCasts());
00157   }
00158 
00159   const Constant *stripPointerCasts() const {
00160     return const_cast<Constant*>(this)->stripPointerCasts();
00161   }
00162 };
00163 
00164 } // End llvm namespace
00165 
00166 #endif