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 protected: 44 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 45 : User(ty, vty, Ops, NumOps) {} 46 47 public: 48 void operator=(const Constant &) = delete; 49 Constant(const Constant &) = delete; 50 51 /// Return true if this is the value that would be returned by getNullValue. 52 bool isNullValue() const; 53 54 /// Returns true if the value is one. 55 bool isOneValue() const; 56 57 /// Return true if this is the value that would be returned by 58 /// getAllOnesValue. 59 bool isAllOnesValue() const; 60 61 /// Return true if the value is what would be returned by 62 /// getZeroValueForNegation. 63 bool isNegativeZeroValue() const; 64 65 /// Return true if the value is negative zero or null value. 66 bool isZeroValue() const; 67 68 /// Return true if the value is not the smallest signed value. 69 bool isNotMinSignedValue() const; 70 71 /// Return true if the value is the smallest signed value. 72 bool isMinSignedValue() const; 73 74 /// Return true if evaluation of this constant could trap. This is true for 75 /// things like constant expressions that could divide by zero. 76 bool canTrap() const; 77 78 /// Return true if the value can vary between threads. 79 bool isThreadDependent() const; 80 81 /// Return true if the value is dependent on a dllimport variable. 82 bool isDLLImportDependent() const; 83 84 /// Return true if the constant has users other than constant expressions and 85 /// other dangling things. 86 bool isConstantUsed() const; 87 88 /// This method classifies the entry according to whether or not it may 89 /// generate a relocation entry. This must be conservative, so if it might 90 /// codegen to a relocatable entry, it should say so. 91 /// 92 /// FIXME: This really should not be in IR. 93 bool needsRelocation() const; 94 95 /// For aggregates (struct/array/vector) return the constant that corresponds 96 /// to the specified element if possible, or null if not. This can return null 97 /// if the element index is a ConstantExpr, or if 'this' is a constant expr. 98 Constant *getAggregateElement(unsigned Elt) const; 99 Constant *getAggregateElement(Constant *Elt) const; 100 101 /// If this is a splat vector constant, meaning that all of the elements have 102 /// the same value, return that value. Otherwise return 0. 103 Constant *getSplatValue() const; 104 105 /// If C is a constant integer then return its value, otherwise C must be a 106 /// vector of constant integers, all equal, and the common value is returned. 107 const APInt &getUniqueInteger() const; 108 109 /// Called if some element of this constant is no longer valid. 110 /// At this point only other constants may be on the use_list for this 111 /// constant. Any constants on our Use list must also be destroy'd. The 112 /// implementation must be sure to remove the constant from the list of 113 /// available cached constants. Implementations should implement 114 /// destroyConstantImpl to remove constants from any pools/maps they are 115 /// contained it. 116 void destroyConstant(); 117 118 //// Methods for support type inquiry through isa, cast, and dyn_cast: 119 static inline bool classof(const Value *V) { 120 return V->getValueID() >= ConstantFirstVal && 121 V->getValueID() <= ConstantLastVal; 122 } 123 124 /// This method is a special form of User::replaceUsesOfWith 125 /// (which does not work on constants) that does work 126 /// on constants. Basically this method goes through the trouble of building 127 /// a new constant that is equivalent to the current one, with all uses of 128 /// From replaced with uses of To. After this construction is completed, all 129 /// of the users of 'this' are replaced to use the new constant, and then 130 /// 'this' is deleted. In general, you should not call this method, instead, 131 /// use Value::replaceAllUsesWith, which automatically dispatches to this 132 /// method as needed. 133 /// 134 void handleOperandChange(Value *, Value *); 135 136 static Constant *getNullValue(Type* Ty); 137 138 /// @returns the value for an integer or vector of integer constant of the 139 /// given type that has all its bits set to true. 140 /// @brief Get the all ones value 141 static Constant *getAllOnesValue(Type* Ty); 142 143 /// Return the value for an integer or pointer constant, or a vector thereof, 144 /// with the given scalar value. 145 static Constant *getIntegerValue(Type *Ty, const APInt &V); 146 147 /// If there are any dead constant users dangling off of this constant, remove 148 /// them. This method is useful for clients that want to check to see if a 149 /// global is unused, but don't want to deal with potentially dead constants 150 /// hanging off of the globals. 151 void removeDeadConstantUsers() const; 152 153 const Constant *stripPointerCasts() const { 154 return cast<Constant>(Value::stripPointerCasts()); 155 } 156 157 Constant *stripPointerCasts() { 158 return const_cast<Constant*>( 159 static_cast<const Constant *>(this)->stripPointerCasts()); 160 } 161 }; 162 163 } // end namespace llvm 164 165 #endif // LLVM_IR_CONSTANT_H 166
