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) = delete;
38 void operator=(const GlobalVariable &) = delete;
39 GlobalVariable(const GlobalVariable &) = delete;
41 void setParent(Module *parent);
43 bool isConstantGlobal : 1; // Is this a global constant?
44 bool isExternallyInitializedConstant : 1; // Is this a global whose value
45 // can change from its initial
46 // value before global
47 // initializers are run?
49 // allocate space for exactly one operand
50 void *operator new(size_t s) {
51 return User::operator new(s, 1);
54 /// GlobalVariable ctor - If a parent module is specified, the global is
55 /// automatically inserted into the end of the specified modules global list.
56 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage,
57 Constant *Initializer = nullptr, const Twine &Name = "",
58 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
59 bool isExternallyInitialized = false);
60 /// GlobalVariable ctor - This creates a global and inserts it before the
61 /// specified other global.
62 GlobalVariable(Module &M, Type *Ty, bool isConstant,
63 LinkageTypes Linkage, Constant *Initializer,
64 const Twine &Name = "", GlobalVariable *InsertBefore = nullptr,
65 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
66 bool isExternallyInitialized = false);
68 ~GlobalVariable() override {
69 // FIXME: needed by operator delete
70 setGlobalVariableNumOperands(1);
73 /// Provide fast operand accessors
74 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
76 /// Definitions have initializers, declarations don't.
78 inline bool hasInitializer() const { return !isDeclaration(); }
80 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
81 /// and any other instances of the global (this can happen due to weak
82 /// linkage) are guaranteed to have the same initializer.
84 /// Note that if you want to transform a global, you must use
85 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
89 /// @a = global SomeType* null - Initializer is both definitive and unique.
91 /// @b = global weak SomeType* null - Initializer is neither definitive nor
94 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
96 inline bool hasDefinitiveInitializer() const {
97 return hasInitializer() &&
98 // The initializer of a global variable with weak linkage may change at
100 !mayBeOverridden() &&
101 // The initializer of a global variable with the externally_initialized
102 // marker may change at runtime before C++ initializers are evaluated.
103 !isExternallyInitialized();
106 /// hasUniqueInitializer - Whether the global variable has an initializer, and
107 /// any changes made to the initializer will turn up in the final executable.
108 inline bool hasUniqueInitializer() const {
109 return hasInitializer() &&
110 // It's not safe to modify initializers of global variables with weak
111 // linkage, because the linker might choose to discard the initializer and
112 // use the initializer from another instance of the global variable
113 // instead. It is wrong to modify the initializer of a global variable
114 // with *_odr linkage because then different instances of the global may
115 // have different initializers, breaking the One Definition Rule.
116 !isWeakForLinker() &&
117 // It is not safe to modify initializers of global variables with the
118 // external_initializer marker since the value may be changed at runtime
119 // before C++ initializers are evaluated.
120 !isExternallyInitialized();
123 /// getInitializer - Return the initializer for this global variable. It is
124 /// illegal to call this method if the global is external, because we cannot
125 /// tell what the value is initialized to!
127 inline const Constant *getInitializer() const {
128 assert(hasInitializer() && "GV doesn't have initializer!");
129 return static_cast<Constant*>(Op<0>().get());
131 inline Constant *getInitializer() {
132 assert(hasInitializer() && "GV doesn't have initializer!");
133 return static_cast<Constant*>(Op<0>().get());
135 /// setInitializer - Sets the initializer for this global variable, removing
136 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
137 /// initializer must have type T.
138 void setInitializer(Constant *InitVal);
140 /// If the value is a global constant, its value is immutable throughout the
141 /// runtime execution of the program. Assigning a value into the constant
142 /// leads to undefined behavior.
144 bool isConstant() const { return isConstantGlobal; }
145 void setConstant(bool Val) { isConstantGlobal = Val; }
147 bool isExternallyInitialized() const {
148 return isExternallyInitializedConstant;
150 void setExternallyInitialized(bool Val) {
151 isExternallyInitializedConstant = Val;
154 /// copyAttributesFrom - copy all additional attributes (those not needed to
155 /// create a GlobalVariable) from the GlobalVariable Src to this one.
156 void copyAttributesFrom(const GlobalValue *Src) override;
158 /// removeFromParent - This method unlinks 'this' from the containing module,
159 /// but does not delete it.
161 void removeFromParent() override;
163 /// eraseFromParent - This method unlinks 'this' from the containing module
166 void eraseFromParent() override;
168 // Methods for support type inquiry through isa, cast, and dyn_cast:
169 static inline bool classof(const Value *V) {
170 return V->getValueID() == Value::GlobalVariableVal;
175 struct OperandTraits<GlobalVariable> :
176 public OptionalOperandTraits<GlobalVariable> {
179 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
181 } // End llvm namespace