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/GlobalObject.h" 26 #include "llvm/IR/OperandTraits.h" 27 28 namespace llvm { 29 30 class Module; 31 class Constant; 32 template <typename ValueSubClass> class SymbolTableListTraits; 33 34 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> { 35 friend class SymbolTableListTraits<GlobalVariable>; 36 void *operator new(size_t, unsigned) = delete; 37 void operator=(const GlobalVariable &) = delete; 38 GlobalVariable(const GlobalVariable &) = delete; 39 40 void setParent(Module *parent); 41 42 bool isConstantGlobal : 1; // Is this a global constant? 43 bool isExternallyInitializedConstant : 1; // Is this a global whose value 44 // can change from its initial 45 // value before global 46 // initializers are run? 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 /// GlobalVariable ctor - If a parent module is specified, the global is 54 /// automatically inserted into the end of the specified modules global list. 55 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage, 56 Constant *Initializer = nullptr, const Twine &Name = "", 57 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 58 bool isExternallyInitialized = false); 59 /// GlobalVariable ctor - This creates a global and inserts it before the 60 /// specified other global. 61 GlobalVariable(Module &M, Type *Ty, bool isConstant, 62 LinkageTypes Linkage, Constant *Initializer, 63 const Twine &Name = "", GlobalVariable *InsertBefore = nullptr, 64 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 65 bool isExternallyInitialized = false); 66 67 ~GlobalVariable() override { 68 // FIXME: needed by operator delete 69 setGlobalVariableNumOperands(1); 70 } 71 72 /// Provide fast operand accessors 73 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value); 74 75 /// Definitions have initializers, declarations don't. 76 /// 77 inline bool hasInitializer() const { return !isDeclaration(); } 78 79 /// hasDefinitiveInitializer - Whether the global variable has an initializer, 80 /// and any other instances of the global (this can happen due to weak 81 /// linkage) are guaranteed to have the same initializer. 82 /// 83 /// Note that if you want to transform a global, you must use 84 /// hasUniqueInitializer() instead, because of the *_odr linkage type. 85 /// 86 /// Example: 87 /// 88 /// @a = global SomeType* null - Initializer is both definitive and unique. 89 /// 90 /// @b = global weak SomeType* null - Initializer is neither definitive nor 91 /// unique. 92 /// 93 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not 94 /// unique. 95 inline bool hasDefinitiveInitializer() const { 96 return hasInitializer() && 97 // The initializer of a global variable with weak linkage may change at 98 // link time. 99 !mayBeOverridden() && 100 // The initializer of a global variable with the externally_initialized 101 // marker may change at runtime before C++ initializers are evaluated. 102 !isExternallyInitialized(); 103 } 104 105 /// hasUniqueInitializer - Whether the global variable has an initializer, and 106 /// any changes made to the initializer will turn up in the final executable. 107 inline bool hasUniqueInitializer() const { 108 return 109 // We need to be sure this is the definition that will actually be used 110 isStrongDefinitionForLinker() && 111 // It is not safe to modify initializers of global variables with the 112 // external_initializer marker since the value may be changed at runtime 113 // before C++ initializers are evaluated. 114 !isExternallyInitialized(); 115 } 116 117 /// getInitializer - Return the initializer for this global variable. It is 118 /// illegal to call this method if the global is external, because we cannot 119 /// tell what the value is initialized to! 120 /// 121 inline const Constant *getInitializer() const { 122 assert(hasInitializer() && "GV doesn't have initializer!"); 123 return static_cast<Constant*>(Op<0>().get()); 124 } 125 inline Constant *getInitializer() { 126 assert(hasInitializer() && "GV doesn't have initializer!"); 127 return static_cast<Constant*>(Op<0>().get()); 128 } 129 /// setInitializer - Sets the initializer for this global variable, removing 130 /// any existing initializer if InitVal==NULL. If this GV has type T*, the 131 /// initializer must have type T. 132 void setInitializer(Constant *InitVal); 133 134 /// If the value is a global constant, its value is immutable throughout the 135 /// runtime execution of the program. Assigning a value into the constant 136 /// leads to undefined behavior. 137 /// 138 bool isConstant() const { return isConstantGlobal; } 139 void setConstant(bool Val) { isConstantGlobal = Val; } 140 141 bool isExternallyInitialized() const { 142 return isExternallyInitializedConstant; 143 } 144 void setExternallyInitialized(bool Val) { 145 isExternallyInitializedConstant = Val; 146 } 147 148 /// copyAttributesFrom - copy all additional attributes (those not needed to 149 /// create a GlobalVariable) from the GlobalVariable Src to this one. 150 void copyAttributesFrom(const GlobalValue *Src) override; 151 152 /// removeFromParent - This method unlinks 'this' from the containing module, 153 /// but does not delete it. 154 /// 155 void removeFromParent() override; 156 157 /// eraseFromParent - This method unlinks 'this' from the containing module 158 /// and deletes it. 159 /// 160 void eraseFromParent() override; 161 162 // Methods for support type inquiry through isa, cast, and dyn_cast: 163 static inline bool classof(const Value *V) { 164 return V->getValueID() == Value::GlobalVariableVal; 165 } 166 }; 167 168 template <> 169 struct OperandTraits<GlobalVariable> : 170 public OptionalOperandTraits<GlobalVariable> { 171 }; 172 173 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value) 174 175 } // End llvm namespace 176 177 #endif 178
