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_CONSTANT_H 15 #define LLVM_CONSTANT_H 16 17 #include "llvm/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 &); // Do not implement 43 Constant(const Constant &); // Do not implement 44 virtual void anchor(); 45 46 protected: 47 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 48 : User(ty, vty, Ops, NumOps) {} 49 50 void destroyConstantImpl(); 51 public: 52 /// isNullValue - Return true if this is the value that would be returned by 53 /// getNullValue. 54 bool isNullValue() const; 55 56 /// isAllOnesValue - Return true if this is the value that would be returned by 57 /// getAllOnesValue. 58 bool isAllOnesValue() const; 59 60 /// isNegativeZeroValue - Return true if the value is what would be returned 61 /// by getZeroValueForNegation. 62 bool isNegativeZeroValue() const; 63 64 /// canTrap - Return true if evaluation of this constant could trap. This is 65 /// true for things like constant expressions that could divide by zero. 66 bool canTrap() const; 67 68 /// isConstantUsed - Return true if the constant has users other than constant 69 /// exprs and other dangling things. 70 bool isConstantUsed() const; 71 72 enum PossibleRelocationsTy { 73 NoRelocation = 0, 74 LocalRelocation = 1, 75 GlobalRelocations = 2 76 }; 77 78 /// getRelocationInfo - This method classifies the entry according to 79 /// whether or not it may generate a relocation entry. This must be 80 /// conservative, so if it might codegen to a relocatable entry, it should say 81 /// so. The return values are: 82 /// 83 /// NoRelocation: This constant pool entry is guaranteed to never have a 84 /// relocation applied to it (because it holds a simple constant like 85 /// '4'). 86 /// LocalRelocation: This entry has relocations, but the entries are 87 /// guaranteed to be resolvable by the static linker, so the dynamic 88 /// linker will never see them. 89 /// GlobalRelocations: This entry may have arbitrary relocations. 90 /// 91 /// FIXME: This really should not be in VMCore. 92 PossibleRelocationsTy getRelocationInfo() const; 93 94 /// getAggregateElement - For aggregates (struct/array/vector) return the 95 /// constant that corresponds to the specified element if possible, or null if 96 /// not. This can return null if the element index is a ConstantExpr, or if 97 /// 'this' is a constant expr. 98 Constant *getAggregateElement(unsigned Elt) const; 99 Constant *getAggregateElement(Constant *Elt) const; 100 101 /// destroyConstant - Called if some element of this constant is no longer 102 /// valid. At this point only other constants may be on the use_list for this 103 /// constant. Any constants on our Use list must also be destroy'd. The 104 /// implementation must be sure to remove the constant from the list of 105 /// available cached constants. Implementations should call 106 /// destroyConstantImpl as the last thing they do, to destroy all users and 107 /// delete this. 108 virtual void destroyConstant() { llvm_unreachable("Not reached!"); } 109 110 //// Methods for support type inquiry through isa, cast, and dyn_cast: 111 static inline bool classof(const Constant *) { return true; } 112 static inline bool classof(const GlobalValue *) { return true; } 113 static inline bool classof(const Value *V) { 114 return V->getValueID() >= ConstantFirstVal && 115 V->getValueID() <= ConstantLastVal; 116 } 117 118 /// replaceUsesOfWithOnConstant - This method is a special form of 119 /// User::replaceUsesOfWith (which does not work on constants) that does work 120 /// on constants. Basically this method goes through the trouble of building 121 /// a new constant that is equivalent to the current one, with all uses of 122 /// From replaced with uses of To. After this construction is completed, all 123 /// of the users of 'this' are replaced to use the new constant, and then 124 /// 'this' is deleted. In general, you should not call this method, instead, 125 /// use Value::replaceAllUsesWith, which automatically dispatches to this 126 /// method as needed. 127 /// 128 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) { 129 // Provide a default implementation for constants (like integers) that 130 // cannot use any other values. This cannot be called at runtime, but needs 131 // to be here to avoid link errors. 132 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be " 133 "implemented for all constants that have operands!"); 134 llvm_unreachable("Constants that do not have operands cannot be using " 135 "'From'!"); 136 } 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 }; 155 156 } // End llvm namespace 157 158 #endif 159
