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 #include "llvm/IR/Value.h" 19 #include "llvm/Support/Casting.h" 20 21 namespace llvm { 22 23 class APInt; 24 25 /// This is an important base class in LLVM. It provides the common facilities 26 /// of all constant values in an LLVM program. A constant is a value that is 27 /// immutable at runtime. Functions are constants because their address is 28 /// immutable. Same with global variables. 29 /// 30 /// All constants share the capabilities provided in this class. All constants 31 /// can have a null value. They can have an operand list. Constants can be 32 /// simple (integer and floating point values), complex (arrays and structures), 33 /// or expression based (computations yielding a constant value composed of 34 /// only certain operators and other constant values). 35 /// 36 /// Note that Constants are immutable (once created they never change) 37 /// and are fully shared by structural equivalence. This means that two 38 /// structurally equivalent constants will always have the same address. 39 /// Constants are created on demand as needed and never deleted: thus clients 40 /// don't have to worry about the lifetime of the objects. 41 /// @brief LLVM Constant Representation 42 class Constant : public User { 43 void anchor() override; 44 45 protected: 46 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 47 : User(ty, vty, Ops, NumOps) {} 48 49 public: 50 void operator=(const Constant &) = delete; 51 Constant(const Constant &) = delete; 52 53 /// Return true if this is the value that would be returned by getNullValue. 54 bool isNullValue() const; 55 56 /// Returns true if the value is one. 57 bool isOneValue() const; 58 59 /// Return true if this is the value that would be returned by 60 /// getAllOnesValue. 61 bool isAllOnesValue() const; 62 63 /// Return true if the value is what would be returned by 64 /// getZeroValueForNegation. 65 bool isNegativeZeroValue() const; 66 67 /// Return true if the value is negative zero or null value. 68 bool isZeroValue() const; 69 70 /// Return true if the value is not the smallest signed value. 71 bool isNotMinSignedValue() const; 72 73 /// Return true if the value is the smallest signed value. 74 bool isMinSignedValue() const; 75 76 /// Return true if evaluation of this constant could trap. This is true for 77 /// things like constant expressions that could divide by zero. 78 bool canTrap() const; 79 80 /// Return true if the value can vary between threads. 81 bool isThreadDependent() const; 82 83 /// Return true if the value is dependent on a dllimport variable. 84 bool isDLLImportDependent() const; 85 86 /// Return true if the constant has users other than constant expressions and 87 /// other dangling things. 88 bool isConstantUsed() const; 89 90 /// This method classifies the entry according to whether or not it may 91 /// generate a relocation entry. This must be conservative, so if it might 92 /// codegen to a relocatable entry, it should say so. 93 /// 94 /// FIXME: This really should not be in IR. 95 bool needsRelocation() const; 96 97 /// For aggregates (struct/array/vector) return the constant that corresponds 98 /// to the specified element if possible, or null if not. This can return null 99 /// if the element index is a ConstantExpr, or if 'this' is a constant expr. 100 Constant *getAggregateElement(unsigned Elt) const; 101 Constant *getAggregateElement(Constant *Elt) const; 102 103 /// If this is a splat vector constant, meaning that all of the elements have 104 /// 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: 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 *); 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 /// Return the value for an integer or pointer constant, or a vector thereof, 146 /// with the given scalar value. 147 static Constant *getIntegerValue(Type *Ty, const APInt &V); 148 149 /// If there are any dead constant users dangling off of this constant, remove 150 /// them. This method is useful for clients that want to check to see if a 151 /// global is unused, but don't want to deal with potentially dead constants 152 /// hanging off of the globals. 153 void removeDeadConstantUsers() const; 154 155 const Constant *stripPointerCasts() const { 156 return cast<Constant>(Value::stripPointerCasts()); 157 } 158 159 Constant *stripPointerCasts() { 160 return const_cast<Constant*>( 161 static_cast<const Constant *>(this)->stripPointerCasts()); 162 } 163 }; 164 165 } // end namespace llvm 166 167 #endif // LLVM_IR_CONSTANT_H 168
