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/PointerUnion.h" 24 #include "llvm/ADT/Twine.h" 25 #include "llvm/ADT/ilist_node.h" 26 #include "llvm/IR/GlobalObject.h" 27 #include "llvm/IR/OperandTraits.h" 28 #include "llvm/IR/Value.h" 29 #include <cassert> 30 #include <cstddef> 31 32 namespace llvm { 33 34 class Constant; 35 class Module; 36 37 template <typename ValueSubClass> class SymbolTableListTraits; 38 class DIGlobalVariable; 39 class DIGlobalVariableExpression; 40 41 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> { 42 friend class SymbolTableListTraits<GlobalVariable>; 43 44 bool isConstantGlobal : 1; // Is this a global constant? 45 bool isExternallyInitializedConstant : 1; // Is this a global whose value 46 // can change from its initial 47 // value before global 48 // initializers are run? 49 50 public: 51 /// GlobalVariable ctor - If a parent module is specified, the global is 52 /// automatically inserted into the end of the specified modules global list. 53 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage, 54 Constant *Initializer = nullptr, const Twine &Name = "", 55 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 56 bool isExternallyInitialized = false); 57 /// GlobalVariable ctor - This creates a global and inserts it before the 58 /// specified other global. 59 GlobalVariable(Module &M, Type *Ty, bool isConstant, 60 LinkageTypes Linkage, Constant *Initializer, 61 const Twine &Name = "", GlobalVariable *InsertBefore = nullptr, 62 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0, 63 bool isExternallyInitialized = false); 64 GlobalVariable(const GlobalVariable &) = delete; 65 GlobalVariable &operator=(const GlobalVariable &) = delete; 66 67 ~GlobalVariable() override { 68 dropAllReferences(); 69 70 // FIXME: needed by operator delete 71 setGlobalVariableNumOperands(1); 72 } 73 74 // allocate space for exactly one operand 75 void *operator new(size_t s) { 76 return User::operator new(s, 1); 77 } 78 79 void *operator new(size_t, unsigned) = delete; 80 81 /// Provide fast operand accessors 82 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value); 83 84 /// Definitions have initializers, declarations don't. 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 may change to something arbitrary 107 // at link time. 108 !isInterposable() && 109 // The initializer of a global variable with the externally_initialized 110 // marker may change at runtime before C++ initializers are evaluated. 111 !isExternallyInitialized(); 112 } 113 114 /// hasUniqueInitializer - Whether the global variable has an initializer, and 115 /// any changes made to the initializer will turn up in the final executable. 116 inline bool hasUniqueInitializer() const { 117 return 118 // We need to be sure this is the definition that will actually be used 119 isStrongDefinitionForLinker() && 120 // It is not safe to modify initializers of global variables with the 121 // external_initializer marker since the value may be changed at runtime 122 // before C++ initializers are evaluated. 123 !isExternallyInitialized(); 124 } 125 126 /// getInitializer - Return the initializer for this global variable. It is 127 /// illegal to call this method if the global is external, because we cannot 128 /// tell what the value is initialized to! 129 /// 130 inline const Constant *getInitializer() const { 131 assert(hasInitializer() && "GV doesn't have initializer!"); 132 return static_cast<Constant*>(Op<0>().get()); 133 } 134 inline Constant *getInitializer() { 135 assert(hasInitializer() && "GV doesn't have initializer!"); 136 return static_cast<Constant*>(Op<0>().get()); 137 } 138 /// setInitializer - Sets the initializer for this global variable, removing 139 /// any existing initializer if InitVal==NULL. If this GV has type T*, the 140 /// initializer must have type T. 141 void setInitializer(Constant *InitVal); 142 143 /// If the value is a global constant, its value is immutable throughout the 144 /// runtime execution of the program. Assigning a value into the constant 145 /// leads to undefined behavior. 146 /// 147 bool isConstant() const { return isConstantGlobal; } 148 void setConstant(bool Val) { isConstantGlobal = Val; } 149 150 bool isExternallyInitialized() const { 151 return isExternallyInitializedConstant; 152 } 153 void setExternallyInitialized(bool Val) { 154 isExternallyInitializedConstant = Val; 155 } 156 157 /// copyAttributesFrom - copy all additional attributes (those not needed to 158 /// create a GlobalVariable) from the GlobalVariable Src to this one. 159 void copyAttributesFrom(const GlobalValue *Src) override; 160 161 /// removeFromParent - This method unlinks 'this' from the containing module, 162 /// but does not delete it. 163 /// 164 void removeFromParent() override; 165 166 /// eraseFromParent - This method unlinks 'this' from the containing module 167 /// and deletes it. 168 /// 169 void eraseFromParent() override; 170 171 /// Drop all references in preparation to destroy the GlobalVariable. This 172 /// drops not only the reference to the initializer but also to any metadata. 173 void dropAllReferences(); 174 175 /// Attach a DIGlobalVariableExpression. 176 void addDebugInfo(DIGlobalVariableExpression *GV); 177 178 /// Fill the vector with all debug info attachements. 179 void getDebugInfo(SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const; 180 181 // Methods for support type inquiry through isa, cast, and dyn_cast: 182 static inline bool classof(const Value *V) { 183 return V->getValueID() == Value::GlobalVariableVal; 184 } 185 }; 186 187 template <> 188 struct OperandTraits<GlobalVariable> : 189 public OptionalOperandTraits<GlobalVariable> { 190 }; 191 192 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value) 193 194 } // end namespace llvm 195 196 #endif // LLVM_IR_GLOBALVARIABLE_H 197