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_GLOBAL_VARIABLE_H
21 #define LLVM_GLOBAL_VARIABLE_H
23 #include "llvm/GlobalValue.h"
24 #include "llvm/OperandTraits.h"
25 #include "llvm/ADT/ilist_node.h"
26 #include "llvm/ADT/Twine.h"
32 template<typename ValueSubClass, typename ItemParentClass>
33 class SymbolTableListTraits;
35 class GlobalVariable : public GlobalValue, public ilist_node<GlobalVariable> {
36 friend class SymbolTableListTraits<GlobalVariable, Module>;
37 void *operator new(size_t, unsigned); // Do not implement
38 void operator=(const GlobalVariable &); // Do not implement
39 GlobalVariable(const GlobalVariable &); // Do not implement
41 void setParent(Module *parent);
43 bool isConstantGlobal : 1; // Is this a global constant?
44 bool isThreadLocalSymbol : 1; // Is this symbol "Thread Local"?
47 // allocate space for exactly one operand
48 void *operator new(size_t s) {
49 return User::operator new(s, 1);
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 = 0, const Twine &Name = "",
55 bool ThreadLocal = false, unsigned AddressSpace = 0);
56 /// GlobalVariable ctor - This creates a global and inserts it before the
57 /// specified other global.
58 GlobalVariable(Module &M, Type *Ty, bool isConstant,
59 LinkageTypes Linkage, Constant *Initializer,
61 GlobalVariable *InsertBefore = 0, bool ThreadLocal = false,
62 unsigned AddressSpace = 0);
65 NumOperands = 1; // FIXME: needed by operator delete
68 /// Provide fast operand accessors
69 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
71 /// hasInitializer - Unless a global variable isExternal(), it has an
72 /// initializer. The initializer for the global variable/constant is held by
73 /// Initializer if an initializer is specified.
75 inline bool hasInitializer() const { return !isDeclaration(); }
77 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
78 /// and any other instances of the global (this can happen due to weak
79 /// linkage) are guaranteed to have the same initializer.
81 /// Note that if you want to transform a global, you must use
82 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
86 /// @a = global SomeType* null - Initializer is both definitive and unique.
88 /// @b = global weak SomeType* null - Initializer is neither definitive nor
91 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
93 inline bool hasDefinitiveInitializer() const {
94 return hasInitializer() &&
95 // The initializer of a global variable with weak linkage may change at
100 /// hasUniqueInitializer - Whether the global variable has an initializer, and
101 /// any changes made to the initializer will turn up in the final executable.
102 inline bool hasUniqueInitializer() const {
103 return hasInitializer() &&
104 // It's not safe to modify initializers of global variables with weak
105 // linkage, because the linker might choose to discard the initializer and
106 // use the initializer from another instance of the global variable
107 // instead. It is wrong to modify the initializer of a global variable
108 // with *_odr linkage because then different instances of the global may
109 // have different initializers, breaking the One Definition Rule.
113 /// getInitializer - Return the initializer for this global variable. It is
114 /// illegal to call this method if the global is external, because we cannot
115 /// tell what the value is initialized to!
117 inline const Constant *getInitializer() const {
118 assert(hasInitializer() && "GV doesn't have initializer!");
119 return static_cast<Constant*>(Op<0>().get());
121 inline Constant *getInitializer() {
122 assert(hasInitializer() && "GV doesn't have initializer!");
123 return static_cast<Constant*>(Op<0>().get());
125 /// setInitializer - Sets the initializer for this global variable, removing
126 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
127 /// initializer must have type T.
128 void setInitializer(Constant *InitVal);
130 /// If the value is a global constant, its value is immutable throughout the
131 /// runtime execution of the program. Assigning a value into the constant
132 /// leads to undefined behavior.
134 bool isConstant() const { return isConstantGlobal; }
135 void setConstant(bool Val) { isConstantGlobal = Val; }
137 /// If the value is "Thread Local", its value isn't shared by the threads.
138 bool isThreadLocal() const { return isThreadLocalSymbol; }
139 void setThreadLocal(bool Val) { isThreadLocalSymbol = Val; }
141 /// copyAttributesFrom - copy all additional attributes (those not needed to
142 /// create a GlobalVariable) from the GlobalVariable Src to this one.
143 void copyAttributesFrom(const GlobalValue *Src);
145 /// removeFromParent - This method unlinks 'this' from the containing module,
146 /// but does not delete it.
148 virtual void removeFromParent();
150 /// eraseFromParent - This method unlinks 'this' from the containing module
153 virtual void eraseFromParent();
155 /// Override Constant's implementation of this method so we can
156 /// replace constant initializers.
157 virtual void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U);
159 // Methods for support type inquiry through isa, cast, and dyn_cast:
160 static inline bool classof(const GlobalVariable *) { return true; }
161 static inline bool classof(const Value *V) {
162 return V->getValueID() == Value::GlobalVariableVal;
167 struct OperandTraits<GlobalVariable> :
168 public OptionalOperandTraits<GlobalVariable> {
171 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
173 } // End llvm namespace