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/Attributes.h" 27 #include "llvm/IR/GlobalObject.h" 28 #include "llvm/IR/OperandTraits.h" 29 #include "llvm/IR/Value.h" 30 #include <cassert> 31 #include <cstddef> 32 33 namespace llvm { 34 35 class Constant; 36 class Module; 37 38 template <typename ValueSubClass> class SymbolTableListTraits; 39 class DIGlobalVariable; 40 class DIGlobalVariableExpression; 41 42 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> { 43 friend class SymbolTableListTraits<GlobalVariable>; 44 45 AttributeSet Attrs; 46 bool isConstantGlobal : 1; // Is this a global constant? 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 /// 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 GlobalVariable(const GlobalVariable &) = delete; 67 GlobalVariable &operator=(const GlobalVariable &) = delete; 68 69 ~GlobalVariable() { 70 dropAllReferences(); 71 72 // FIXME: needed by operator delete 73 setGlobalVariableNumOperands(1); 74 } 75 76 // allocate space for exactly one operand 77 void *operator new(size_t s) { 78 return User::operator new(s, 1); 79 } 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 GlobalVariable *Src); 160 161 /// removeFromParent - This method unlinks 'this' from the containing module, 162 /// but does not delete it. 163 /// 164 void removeFromParent(); 165 166 /// eraseFromParent - This method unlinks 'this' from the containing module 167 /// and deletes it. 168 /// 169 void eraseFromParent(); 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 /// Add attribute to this global. 182 void addAttribute(Attribute::AttrKind Kind) { 183 Attrs = Attrs.addAttribute(getContext(), Kind); 184 } 185 186 /// Add attribute to this global. 187 void addAttribute(StringRef Kind, StringRef Val = StringRef()) { 188 Attrs = Attrs.addAttribute(getContext(), Kind, Val); 189 } 190 191 /// Return true if the attribute exists. 192 bool hasAttribute(Attribute::AttrKind Kind) const { 193 return Attrs.hasAttribute(Kind); 194 } 195 196 /// Return true if the attribute exists. 197 bool hasAttribute(StringRef Kind) const { 198 return Attrs.hasAttribute(Kind); 199 } 200 201 /// Return true if any attributes exist. 202 bool hasAttributes() const { 203 return Attrs.hasAttributes(); 204 } 205 206 /// Return the attribute object. 207 Attribute getAttribute(Attribute::AttrKind Kind) const { 208 return Attrs.getAttribute(Kind); 209 } 210 211 /// Return the attribute object. 212 Attribute getAttribute(StringRef Kind) const { 213 return Attrs.getAttribute(Kind); 214 } 215 216 /// Return the attribute set for this global 217 AttributeSet getAttributes() const { 218 return Attrs; 219 } 220 221 /// Return attribute set as list with index. 222 /// FIXME: This may not be required once ValueEnumerators 223 /// in bitcode-writer can enumerate attribute-set. 224 AttributeList getAttributesAsList(unsigned index) const { 225 if (!hasAttributes()) 226 return AttributeList(); 227 std::pair<unsigned, AttributeSet> AS[1] = {{index, Attrs}}; 228 return AttributeList::get(getContext(), AS); 229 } 230 231 /// Set attribute list for this global 232 void setAttributes(AttributeSet A) { 233 Attrs = A; 234 } 235 236 /// Check if section name is present 237 bool hasImplicitSection() const { 238 return getAttributes().hasAttribute("bss-section") || 239 getAttributes().hasAttribute("data-section") || 240 getAttributes().hasAttribute("rodata-section"); 241 } 242 243 // Methods for support type inquiry through isa, cast, and dyn_cast: 244 static bool classof(const Value *V) { 245 return V->getValueID() == Value::GlobalVariableVal; 246 } 247 }; 248 249 template <> 250 struct OperandTraits<GlobalVariable> : 251 public OptionalOperandTraits<GlobalVariable> { 252 }; 253 254 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value) 255 256 } // end namespace llvm 257 258 #endif // LLVM_IR_GLOBALVARIABLE_H 259
