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_IR_GLOBALVARIABLE_H 21 #define LLVM_IR_GLOBALVARIABLE_H 22 23 #include "llvm/ADT/Twine.h" 24 #include "llvm/ADT/ilist_node.h" 25 #include "llvm/IR/GlobalValue.h" 26 #include "llvm/IR/OperandTraits.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) LLVM_DELETED_FUNCTION; 38 void operator=(const GlobalVariable &) LLVM_DELETED_FUNCTION; 39 GlobalVariable(const GlobalVariable &) LLVM_DELETED_FUNCTION; 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 46 // model? 47 bool isExternallyInitializedConstant : 1; // Is this a global whose value 48 // can change from its initial 49 // value before global 50 // initializers are run? 51 52 public: 53 // allocate space for exactly one operand new(size_t s)54 void *operator new(size_t s) { 55 return User::operator new(s, 1); 56 } 57 58 enum ThreadLocalMode { 59 NotThreadLocal = 0, 60 GeneralDynamicTLSModel, 61 LocalDynamicTLSModel, 62 InitialExecTLSModel, 63 LocalExecTLSModel 64 }; 65 66 /// GlobalVariable ctor - If a parent module is specified, the global is 67 /// automatically inserted into the end of the specified modules global list. 68 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage, 69 Constant *Initializer = 0, const Twine &Name = "", 70 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 71 bool isExternallyInitialized = false); 72 /// GlobalVariable ctor - This creates a global and inserts it before the 73 /// specified other global. 74 GlobalVariable(Module &M, Type *Ty, bool isConstant, 75 LinkageTypes Linkage, Constant *Initializer, 76 const Twine &Name = "", GlobalVariable *InsertBefore = 0, 77 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 78 bool isExternallyInitialized = false); 79 ~GlobalVariable()80 ~GlobalVariable() { 81 NumOperands = 1; // FIXME: needed by operator delete 82 } 83 84 /// Provide fast operand accessors 85 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value); 86 87 /// hasInitializer - Unless a global variable isExternal(), it has an 88 /// initializer. The initializer for the global variable/constant is held by 89 /// Initializer if an initializer is specified. 90 /// hasInitializer()91 inline bool hasInitializer() const { return !isDeclaration(); } 92 93 /// hasDefinitiveInitializer - Whether the global variable has an initializer, 94 /// and any other instances of the global (this can happen due to weak 95 /// linkage) are guaranteed to have the same initializer. 96 /// 97 /// Note that if you want to transform a global, you must use 98 /// hasUniqueInitializer() instead, because of the *_odr linkage type. 99 /// 100 /// Example: 101 /// 102 /// @a = global SomeType* null - Initializer is both definitive and unique. 103 /// 104 /// @b = global weak SomeType* null - Initializer is neither definitive nor 105 /// unique. 106 /// 107 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not 108 /// unique. hasDefinitiveInitializer()109 inline bool hasDefinitiveInitializer() const { 110 return hasInitializer() && 111 // The initializer of a global variable with weak linkage may change at 112 // link time. 113 !mayBeOverridden() && 114 // The initializer of a global variable with the externally_initialized 115 // marker may change at runtime before C++ initializers are evaluated. 116 !isExternallyInitialized(); 117 } 118 119 /// hasUniqueInitializer - Whether the global variable has an initializer, and 120 /// any changes made to the initializer will turn up in the final executable. hasUniqueInitializer()121 inline bool hasUniqueInitializer() const { 122 return hasInitializer() && 123 // It's not safe to modify initializers of global variables with weak 124 // linkage, because the linker might choose to discard the initializer and 125 // use the initializer from another instance of the global variable 126 // instead. It is wrong to modify the initializer of a global variable 127 // with *_odr linkage because then different instances of the global may 128 // have different initializers, breaking the One Definition Rule. 129 !isWeakForLinker() && 130 // It is not safe to modify initializers of global variables with the 131 // external_initializer marker since the value may be changed at runtime 132 // before C++ initializers are evaluated. 133 !isExternallyInitialized(); 134 } 135 136 /// getInitializer - Return the initializer for this global variable. It is 137 /// illegal to call this method if the global is external, because we cannot 138 /// tell what the value is initialized to! 139 /// getInitializer()140 inline const Constant *getInitializer() const { 141 assert(hasInitializer() && "GV doesn't have initializer!"); 142 return static_cast<Constant*>(Op<0>().get()); 143 } getInitializer()144 inline Constant *getInitializer() { 145 assert(hasInitializer() && "GV doesn't have initializer!"); 146 return static_cast<Constant*>(Op<0>().get()); 147 } 148 /// setInitializer - Sets the initializer for this global variable, removing 149 /// any existing initializer if InitVal==NULL. If this GV has type T*, the 150 /// initializer must have type T. 151 void setInitializer(Constant *InitVal); 152 153 /// If the value is a global constant, its value is immutable throughout the 154 /// runtime execution of the program. Assigning a value into the constant 155 /// leads to undefined behavior. 156 /// isConstant()157 bool isConstant() const { return isConstantGlobal; } setConstant(bool Val)158 void setConstant(bool Val) { isConstantGlobal = Val; } 159 160 /// If the value is "Thread Local", its value isn't shared by the threads. isThreadLocal()161 bool isThreadLocal() const { return threadLocalMode != NotThreadLocal; } setThreadLocal(bool Val)162 void setThreadLocal(bool Val) { 163 threadLocalMode = Val ? GeneralDynamicTLSModel : NotThreadLocal; 164 } setThreadLocalMode(ThreadLocalMode Val)165 void setThreadLocalMode(ThreadLocalMode Val) { threadLocalMode = Val; } getThreadLocalMode()166 ThreadLocalMode getThreadLocalMode() const { 167 return static_cast<ThreadLocalMode>(threadLocalMode); 168 } 169 isExternallyInitialized()170 bool isExternallyInitialized() const { 171 return isExternallyInitializedConstant; 172 } setExternallyInitialized(bool Val)173 void setExternallyInitialized(bool Val) { 174 isExternallyInitializedConstant = Val; 175 } 176 177 /// copyAttributesFrom - copy all additional attributes (those not needed to 178 /// create a GlobalVariable) from the GlobalVariable Src to this one. 179 void copyAttributesFrom(const GlobalValue *Src); 180 181 /// removeFromParent - This method unlinks 'this' from the containing module, 182 /// but does not delete it. 183 /// 184 virtual void removeFromParent(); 185 186 /// eraseFromParent - This method unlinks 'this' from the containing module 187 /// and deletes it. 188 /// 189 virtual void eraseFromParent(); 190 191 /// Override Constant's implementation of this method so we can 192 /// replace constant initializers. 193 virtual void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U); 194 195 // Methods for support type inquiry through isa, cast, and dyn_cast: classof(const Value * V)196 static inline bool classof(const Value *V) { 197 return V->getValueID() == Value::GlobalVariableVal; 198 } 199 }; 200 201 template <> 202 struct OperandTraits<GlobalVariable> : 203 public OptionalOperandTraits<GlobalVariable> { 204 }; 205 206 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value) 207 208 } // End llvm namespace 209 210 #endif 211