1 //===-- llvm/Constant.h - Constant class definition -------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file contains the declaration of the Constant class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_IR_CONSTANT_H 15 #define LLVM_IR_CONSTANT_H 16 17 #include "llvm/IR/User.h" 18 19 namespace llvm { 20 class APInt; 21 22 template<typename T> class SmallVectorImpl; 23 24 /// This is an important base class in LLVM. It provides the common facilities 25 /// of all constant values in an LLVM program. A constant is a value that is 26 /// immutable at runtime. Functions are constants because their address is 27 /// immutable. Same with global variables. 28 /// 29 /// All constants share the capabilities provided in this class. All constants 30 /// can have a null value. They can have an operand list. Constants can be 31 /// simple (integer and floating point values), complex (arrays and structures), 32 /// or expression based (computations yielding a constant value composed of 33 /// only certain operators and other constant values). 34 /// 35 /// Note that Constants are immutable (once created they never change) 36 /// and are fully shared by structural equivalence. This means that two 37 /// structurally equivalent constants will always have the same address. 38 /// Constants are created on demand as needed and never deleted: thus clients 39 /// don't have to worry about the lifetime of the objects. 40 /// @brief LLVM Constant Representation 41 class Constant : public User { 42 void operator=(const Constant &) = delete; 43 Constant(const Constant &) = delete; 44 void anchor() override; 45 46 protected: Constant(Type * ty,ValueTy vty,Use * Ops,unsigned NumOps)47 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 48 : User(ty, vty, Ops, NumOps) {} 49 50 public: 51 /// isNullValue - Return true if this is the value that would be returned by 52 /// getNullValue. 53 bool isNullValue() const; 54 55 /// \brief Returns true if the value is one. 56 bool isOneValue() const; 57 58 /// isAllOnesValue - Return true if this is the value that would be returned by 59 /// getAllOnesValue. 60 bool isAllOnesValue() const; 61 62 /// isNegativeZeroValue - Return true if the value is what would be returned 63 /// by getZeroValueForNegation. 64 bool isNegativeZeroValue() const; 65 66 /// Return true if the value is negative zero or null value. 67 bool isZeroValue() const; 68 69 /// \brief Return true if the value is not the smallest signed value. 70 bool isNotMinSignedValue() const; 71 72 /// \brief Return true if the value is the smallest signed value. 73 bool isMinSignedValue() const; 74 75 /// canTrap - Return true if evaluation of this constant could trap. This is 76 /// true for things like constant expressions that could divide by zero. 77 bool canTrap() const; 78 79 /// isThreadDependent - Return true if the value can vary between threads. 80 bool isThreadDependent() const; 81 82 /// Return true if the value is dependent on a dllimport variable. 83 bool isDLLImportDependent() const; 84 85 /// isConstantUsed - Return true if the constant has users other than constant 86 /// exprs and other dangling things. 87 bool isConstantUsed() const; 88 89 /// This method classifies the entry according to whether or not it may 90 /// generate a relocation entry. This must be conservative, so if it might 91 /// codegen to a relocatable entry, it should say so. 92 /// 93 /// FIXME: This really should not be in IR. 94 bool needsRelocation() const; 95 96 /// getAggregateElement - For aggregates (struct/array/vector) return the 97 /// constant that corresponds to the specified element if possible, or null if 98 /// not. This can return null if the element index is a ConstantExpr, or if 99 /// 'this' is a constant expr. 100 Constant *getAggregateElement(unsigned Elt) const; 101 Constant *getAggregateElement(Constant *Elt) const; 102 103 /// getSplatValue - If this is a splat vector constant, meaning that all of 104 /// the elements have the same value, return that value. Otherwise return 0. 105 Constant *getSplatValue() const; 106 107 /// If C is a constant integer then return its value, otherwise C must be a 108 /// vector of constant integers, all equal, and the common value is returned. 109 const APInt &getUniqueInteger() const; 110 111 /// Called if some element of this constant is no longer valid. 112 /// At this point only other constants may be on the use_list for this 113 /// constant. Any constants on our Use list must also be destroy'd. The 114 /// implementation must be sure to remove the constant from the list of 115 /// available cached constants. Implementations should implement 116 /// destroyConstantImpl to remove constants from any pools/maps they are 117 /// contained it. 118 void destroyConstant(); 119 120 //// Methods for support type inquiry through isa, cast, and dyn_cast: classof(const Value * V)121 static inline bool classof(const Value *V) { 122 return V->getValueID() >= ConstantFirstVal && 123 V->getValueID() <= ConstantLastVal; 124 } 125 126 /// This method is a special form of User::replaceUsesOfWith 127 /// (which does not work on constants) that does work 128 /// on constants. Basically this method goes through the trouble of building 129 /// a new constant that is equivalent to the current one, with all uses of 130 /// From replaced with uses of To. After this construction is completed, all 131 /// of the users of 'this' are replaced to use the new constant, and then 132 /// 'this' is deleted. In general, you should not call this method, instead, 133 /// use Value::replaceAllUsesWith, which automatically dispatches to this 134 /// method as needed. 135 /// 136 void handleOperandChange(Value *, Value *, Use *); 137 138 static Constant *getNullValue(Type* Ty); 139 140 /// @returns the value for an integer or vector of integer constant of the 141 /// given type that has all its bits set to true. 142 /// @brief Get the all ones value 143 static Constant *getAllOnesValue(Type* Ty); 144 145 /// getIntegerValue - Return the value for an integer or pointer constant, 146 /// or a vector thereof, with the given scalar value. 147 static Constant *getIntegerValue(Type *Ty, const APInt &V); 148 149 /// removeDeadConstantUsers - If there are any dead constant users dangling 150 /// off of this constant, remove them. This method is useful for clients 151 /// that want to check to see if a global is unused, but don't want to deal 152 /// with potentially dead constants hanging off of the globals. 153 void removeDeadConstantUsers() const; 154 stripPointerCasts()155 Constant *stripPointerCasts() { 156 return cast<Constant>(Value::stripPointerCasts()); 157 } 158 stripPointerCasts()159 const Constant *stripPointerCasts() const { 160 return const_cast<Constant*>(this)->stripPointerCasts(); 161 } 162 }; 163 164 } // End llvm namespace 165 166 #endif 167