1 //===-- llvm/GlobalVariable.h - GlobalVariable class ------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains the declaration of the GlobalVariable class, which
11 // represents a single global variable (or constant) in the VM.
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.
18 //===----------------------------------------------------------------------===//
20 #ifndef LLVM_IR_GLOBALVARIABLE_H
21 #define LLVM_IR_GLOBALVARIABLE_H
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"
32 template<typename ValueSubClass, typename ItemParentClass>
33 class SymbolTableListTraits;
35 class GlobalVariable : public GlobalObject, 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;
41 void setParent(Module *parent);
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
47 bool isExternallyInitializedConstant : 1; // Is this a global whose value
48 // can change from its initial
49 // value before global
50 // initializers are run?
53 // allocate space for exactly one operand
54 void *operator new(size_t s) {
55 return User::operator new(s, 1);
58 enum ThreadLocalMode {
60 GeneralDynamicTLSModel,
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 = nullptr, 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 = nullptr,
77 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
78 bool isExternallyInitialized = false);
81 NumOperands = 1; // FIXME: needed by operator delete
84 /// Provide fast operand accessors
85 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
87 /// Definitions have initializers, declarations don't.
89 inline bool hasInitializer() const { return !isDeclaration(); }
91 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
92 /// and any other instances of the global (this can happen due to weak
93 /// linkage) are guaranteed to have the same initializer.
95 /// Note that if you want to transform a global, you must use
96 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
100 /// @a = global SomeType* null - Initializer is both definitive and unique.
102 /// @b = global weak SomeType* null - Initializer is neither definitive nor
105 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
107 inline bool hasDefinitiveInitializer() const {
108 return hasInitializer() &&
109 // The initializer of a global variable with weak linkage may change at
111 !mayBeOverridden() &&
112 // The initializer of a global variable with the externally_initialized
113 // marker may change at runtime before C++ initializers are evaluated.
114 !isExternallyInitialized();
117 /// hasUniqueInitializer - Whether the global variable has an initializer, and
118 /// any changes made to the initializer will turn up in the final executable.
119 inline bool hasUniqueInitializer() const {
120 return hasInitializer() &&
121 // It's not safe to modify initializers of global variables with weak
122 // linkage, because the linker might choose to discard the initializer and
123 // use the initializer from another instance of the global variable
124 // instead. It is wrong to modify the initializer of a global variable
125 // with *_odr linkage because then different instances of the global may
126 // have different initializers, breaking the One Definition Rule.
127 !isWeakForLinker() &&
128 // It is not safe to modify initializers of global variables with the
129 // external_initializer marker since the value may be changed at runtime
130 // before C++ initializers are evaluated.
131 !isExternallyInitialized();
134 /// getInitializer - Return the initializer for this global variable. It is
135 /// illegal to call this method if the global is external, because we cannot
136 /// tell what the value is initialized to!
138 inline const Constant *getInitializer() const {
139 assert(hasInitializer() && "GV doesn't have initializer!");
140 return static_cast<Constant*>(Op<0>().get());
142 inline Constant *getInitializer() {
143 assert(hasInitializer() && "GV doesn't have initializer!");
144 return static_cast<Constant*>(Op<0>().get());
146 /// setInitializer - Sets the initializer for this global variable, removing
147 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
148 /// initializer must have type T.
149 void setInitializer(Constant *InitVal);
151 /// If the value is a global constant, its value is immutable throughout the
152 /// runtime execution of the program. Assigning a value into the constant
153 /// leads to undefined behavior.
155 bool isConstant() const { return isConstantGlobal; }
156 void setConstant(bool Val) { isConstantGlobal = Val; }
158 /// If the value is "Thread Local", its value isn't shared by the threads.
159 bool isThreadLocal() const { return threadLocalMode != NotThreadLocal; }
160 void setThreadLocal(bool Val) {
161 threadLocalMode = Val ? GeneralDynamicTLSModel : NotThreadLocal;
163 void setThreadLocalMode(ThreadLocalMode Val) { threadLocalMode = Val; }
164 ThreadLocalMode getThreadLocalMode() const {
165 return static_cast<ThreadLocalMode>(threadLocalMode);
168 bool isExternallyInitialized() const {
169 return isExternallyInitializedConstant;
171 void setExternallyInitialized(bool Val) {
172 isExternallyInitializedConstant = Val;
175 /// copyAttributesFrom - copy all additional attributes (those not needed to
176 /// create a GlobalVariable) from the GlobalVariable Src to this one.
177 void copyAttributesFrom(const GlobalValue *Src) override;
179 /// removeFromParent - This method unlinks 'this' from the containing module,
180 /// but does not delete it.
182 void removeFromParent() override;
184 /// eraseFromParent - This method unlinks 'this' from the containing module
187 void eraseFromParent() override;
189 /// Override Constant's implementation of this method so we can
190 /// replace constant initializers.
191 void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U) override;
193 // Methods for support type inquiry through isa, cast, and dyn_cast:
194 static inline bool classof(const Value *V) {
195 return V->getValueID() == Value::GlobalVariableVal;
200 struct OperandTraits<GlobalVariable> :
201 public OptionalOperandTraits<GlobalVariable> {
204 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
206 } // End llvm namespace