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 45 protected: 46 Constant(Type *ty, ValueTy vty, Use *Ops, unsigned NumOps) 47 : User(ty, vty, Ops, NumOps) {} 48 49 void destroyConstantImpl(); 50 public: 51 /// isNullValue - Return true if this is the value that would be returned by 52 /// getNullValue. 53 bool isNullValue() const; 54 55 /// isAllOnesValue - Return true if this is the value that would be returned by 56 /// getAllOnesValue. 57 bool isAllOnesValue() const; 58 59 /// isNegativeZeroValue - Return true if the value is what would be returned 60 /// by getZeroValueForNegation. 61 bool isNegativeZeroValue() const; 62 63 /// canTrap - Return true if evaluation of this constant could trap. This is 64 /// true for things like constant expressions that could divide by zero. 65 bool canTrap() const; 66 67 /// isConstantUsed - Return true if the constant has users other than constant 68 /// exprs and other dangling things. 69 bool isConstantUsed() const; 70 71 enum PossibleRelocationsTy { 72 NoRelocation = 0, 73 LocalRelocation = 1, 74 GlobalRelocations = 2 75 }; 76 77 /// getRelocationInfo - This method classifies the entry according to 78 /// whether or not it may generate a relocation entry. This must be 79 /// conservative, so if it might codegen to a relocatable entry, it should say 80 /// so. The return values are: 81 /// 82 /// NoRelocation: This constant pool entry is guaranteed to never have a 83 /// relocation applied to it (because it holds a simple constant like 84 /// '4'). 85 /// LocalRelocation: This entry has relocations, but the entries are 86 /// guaranteed to be resolvable by the static linker, so the dynamic 87 /// linker will never see them. 88 /// GlobalRelocations: This entry may have arbitrary relocations. 89 /// 90 /// FIXME: This really should not be in VMCore. 91 PossibleRelocationsTy getRelocationInfo() const; 92 93 /// getVectorElements - This method, which is only valid on constant of vector 94 /// type, returns the elements of the vector in the specified smallvector. 95 /// This handles breaking down a vector undef into undef elements, etc. For 96 /// constant exprs and other cases we can't handle, we return an empty vector. 97 void getVectorElements(SmallVectorImpl<Constant*> &Elts) const; 98 99 /// destroyConstant - Called if some element of this constant is no longer 100 /// valid. At this point only other constants may be on the use_list for this 101 /// constant. Any constants on our Use list must also be destroy'd. The 102 /// implementation must be sure to remove the constant from the list of 103 /// available cached constants. Implementations should call 104 /// destroyConstantImpl as the last thing they do, to destroy all users and 105 /// delete this. 106 virtual void destroyConstant() { assert(0 && "Not reached!"); } 107 108 //// Methods for support type inquiry through isa, cast, and dyn_cast: 109 static inline bool classof(const Constant *) { return true; } 110 static inline bool classof(const GlobalValue *) { return true; } 111 static inline bool classof(const Value *V) { 112 return V->getValueID() >= ConstantFirstVal && 113 V->getValueID() <= ConstantLastVal; 114 } 115 116 /// replaceUsesOfWithOnConstant - This method is a special form of 117 /// User::replaceUsesOfWith (which does not work on constants) that does work 118 /// on constants. Basically this method goes through the trouble of building 119 /// a new constant that is equivalent to the current one, with all uses of 120 /// From replaced with uses of To. After this construction is completed, all 121 /// of the users of 'this' are replaced to use the new constant, and then 122 /// 'this' is deleted. In general, you should not call this method, instead, 123 /// use Value::replaceAllUsesWith, which automatically dispatches to this 124 /// method as needed. 125 /// 126 virtual void replaceUsesOfWithOnConstant(Value *, Value *, Use *) { 127 // Provide a default implementation for constants (like integers) that 128 // cannot use any other values. This cannot be called at runtime, but needs 129 // to be here to avoid link errors. 130 assert(getNumOperands() == 0 && "replaceUsesOfWithOnConstant must be " 131 "implemented for all constants that have operands!"); 132 assert(0 && "Constants that do not have operands cannot be using 'From'!"); 133 } 134 135 static Constant *getNullValue(Type* Ty); 136 137 /// @returns the value for an integer constant of the given type that has all 138 /// its bits set to true. 139 /// @brief Get the all ones value 140 static Constant *getAllOnesValue(Type* Ty); 141 142 /// getIntegerValue - Return the value for an integer or pointer constant, 143 /// or a vector thereof, with the given scalar value. 144 static Constant *getIntegerValue(Type* Ty, const APInt &V); 145 146 /// removeDeadConstantUsers - If there are any dead constant users dangling 147 /// off of this constant, remove them. This method is useful for clients 148 /// that want to check to see if a global is unused, but don't want to deal 149 /// with potentially dead constants hanging off of the globals. 150 void removeDeadConstantUsers() const; 151 }; 152 153 } // End llvm namespace 154 155 #endif 156
