1 //===-- llvm/GlobalVariable.h - GlobalVariable class ------------*- 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 GlobalVariable class, which 11 // represents a single global variable (or constant) in the VM. 12 // 13 // Global variables are constant pointers that refer to hunks of space that are 14 // allocated by either the VM, or by the linker in a static compiler. A global 15 // variable may have an initial value, which is copied into the executables .data 16 // area. Global Constants are required to have initializers. 17 // 18 //===----------------------------------------------------------------------===// 19 20 #ifndef LLVM_GLOBAL_VARIABLE_H 21 #define LLVM_GLOBAL_VARIABLE_H 22 23 #include "llvm/GlobalValue.h" 24 #include "llvm/OperandTraits.h" 25 #include "llvm/ADT/ilist_node.h" 26 #include "llvm/ADT/Twine.h" 27 28 namespace llvm { 29 30 class Module; 31 class Constant; 32 template<typename ValueSubClass, typename ItemParentClass> 33 class SymbolTableListTraits; 34 35 class GlobalVariable : public GlobalValue, public ilist_node<GlobalVariable> { 36 friend class SymbolTableListTraits<GlobalVariable, Module>; 37 void *operator new(size_t, unsigned); // Do not implement 38 void operator=(const GlobalVariable &); // Do not implement 39 GlobalVariable(const GlobalVariable &); // Do not implement 40 41 void setParent(Module *parent); 42 43 bool isConstantGlobal : 1; // Is this a global constant? 44 unsigned threadLocalMode : 3; // Is this symbol "Thread Local", 45 // if so, what is the desired model? 46 47 public: 48 // allocate space for exactly one operand 49 void *operator new(size_t s) { 50 return User::operator new(s, 1); 51 } 52 53 enum ThreadLocalMode { 54 NotThreadLocal = 0, 55 GeneralDynamicTLSModel, 56 LocalDynamicTLSModel, 57 InitialExecTLSModel, 58 LocalExecTLSModel 59 }; 60 61 /// GlobalVariable ctor - If a parent module is specified, the global is 62 /// automatically inserted into the end of the specified modules global list. 63 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage, 64 Constant *Initializer = 0, const Twine &Name = "", 65 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0); 66 /// GlobalVariable ctor - This creates a global and inserts it before the 67 /// specified other global. 68 GlobalVariable(Module &M, Type *Ty, bool isConstant, 69 LinkageTypes Linkage, Constant *Initializer, 70 const Twine &Name = "", 71 GlobalVariable *InsertBefore = 0, 72 ThreadLocalMode = NotThreadLocal, 73 unsigned AddressSpace = 0); 74 75 ~GlobalVariable() { 76 NumOperands = 1; // FIXME: needed by operator delete 77 } 78 79 /// Provide fast operand accessors 80 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value); 81 82 /// hasInitializer - Unless a global variable isExternal(), it has an 83 /// initializer. The initializer for the global variable/constant is held by 84 /// Initializer if an initializer is specified. 85 /// 86 inline bool hasInitializer() const { return !isDeclaration(); } 87 88 /// hasDefinitiveInitializer - Whether the global variable has an initializer, 89 /// and any other instances of the global (this can happen due to weak 90 /// linkage) are guaranteed to have the same initializer. 91 /// 92 /// Note that if you want to transform a global, you must use 93 /// hasUniqueInitializer() instead, because of the *_odr linkage type. 94 /// 95 /// Example: 96 /// 97 /// @a = global SomeType* null - Initializer is both definitive and unique. 98 /// 99 /// @b = global weak SomeType* null - Initializer is neither definitive nor 100 /// unique. 101 /// 102 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not 103 /// unique. 104 inline bool hasDefinitiveInitializer() const { 105 return hasInitializer() && 106 // The initializer of a global variable with weak linkage may change at 107 // link time. 108 !mayBeOverridden(); 109 } 110 111 /// hasUniqueInitializer - Whether the global variable has an initializer, and 112 /// any changes made to the initializer will turn up in the final executable. 113 inline bool hasUniqueInitializer() const { 114 return hasInitializer() && 115 // It's not safe to modify initializers of global variables with weak 116 // linkage, because the linker might choose to discard the initializer and 117 // use the initializer from another instance of the global variable 118 // instead. It is wrong to modify the initializer of a global variable 119 // with *_odr linkage because then different instances of the global may 120 // have different initializers, breaking the One Definition Rule. 121 !isWeakForLinker(); 122 } 123 124 /// getInitializer - Return the initializer for this global variable. It is 125 /// illegal to call this method if the global is external, because we cannot 126 /// tell what the value is initialized to! 127 /// 128 inline const Constant *getInitializer() const { 129 assert(hasInitializer() && "GV doesn't have initializer!"); 130 return static_cast<Constant*>(Op<0>().get()); 131 } 132 inline Constant *getInitializer() { 133 assert(hasInitializer() && "GV doesn't have initializer!"); 134 return static_cast<Constant*>(Op<0>().get()); 135 } 136 /// setInitializer - Sets the initializer for this global variable, removing 137 /// any existing initializer if InitVal==NULL. If this GV has type T*, the 138 /// initializer must have type T. 139 void setInitializer(Constant *InitVal); 140 141 /// If the value is a global constant, its value is immutable throughout the 142 /// runtime execution of the program. Assigning a value into the constant 143 /// leads to undefined behavior. 144 /// 145 bool isConstant() const { return isConstantGlobal; } 146 void setConstant(bool Val) { isConstantGlobal = Val; } 147 148 /// If the value is "Thread Local", its value isn't shared by the threads. 149 bool isThreadLocal() const { return threadLocalMode != NotThreadLocal; } 150 void setThreadLocal(bool Val) { 151 threadLocalMode = Val ? GeneralDynamicTLSModel : NotThreadLocal; 152 } 153 void setThreadLocalMode(ThreadLocalMode Val) { threadLocalMode = Val; } 154 ThreadLocalMode getThreadLocalMode() const { 155 return static_cast<ThreadLocalMode>(threadLocalMode); 156 } 157 158 /// copyAttributesFrom - copy all additional attributes (those not needed to 159 /// create a GlobalVariable) from the GlobalVariable Src to this one. 160 void copyAttributesFrom(const GlobalValue *Src); 161 162 /// removeFromParent - This method unlinks 'this' from the containing module, 163 /// but does not delete it. 164 /// 165 virtual void removeFromParent(); 166 167 /// eraseFromParent - This method unlinks 'this' from the containing module 168 /// and deletes it. 169 /// 170 virtual void eraseFromParent(); 171 172 /// Override Constant's implementation of this method so we can 173 /// replace constant initializers. 174 virtual void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U); 175 176 // Methods for support type inquiry through isa, cast, and dyn_cast: 177 static inline bool classof(const GlobalVariable *) { return true; } 178 static inline bool classof(const Value *V) { 179 return V->getValueID() == Value::GlobalVariableVal; 180 } 181 }; 182 183 template <> 184 struct OperandTraits<GlobalVariable> : 185 public OptionalOperandTraits<GlobalVariable> { 186 }; 187 188 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value) 189 190 } // End llvm namespace 191 192 #endif 193
