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_GLOBAL_VARIABLE_H
21#define LLVM_GLOBAL_VARIABLE_H
22
23#include "llvm/GlobalValue.h"
24#include "llvm/OperandTraits.h"
25#include "llvm/ADT/ilist_node.h"
26#include "llvm/ADT/Twine.h"
27
28namespace llvm {
29
30class Module;
31class Constant;
32template<typename ValueSubClass, typename ItemParentClass>
33  class SymbolTableListTraits;
34
35class 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
40
41  void setParent(Module *parent);
42
43  bool isConstantGlobal : 1;           // Is this a global constant?
44  bool isThreadLocalSymbol : 1;        // Is this symbol "Thread Local"?
45
46public:
47  // allocate space for exactly one operand
48  void *operator new(size_t s) {
49    return User::operator new(s, 1);
50  }
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,
60                 const Twine &Name,
61                 GlobalVariable *InsertBefore = 0, bool ThreadLocal = false,
62                 unsigned AddressSpace = 0);
63
64  ~GlobalVariable() {
65    NumOperands = 1; // FIXME: needed by operator delete
66  }
67
68  /// Provide fast operand accessors
69  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
70
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.
74  ///
75  inline bool hasInitializer() const { return !isDeclaration(); }
76
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.
80  ///
81  /// Note that if you want to transform a global, you must use
82  /// hasUniqueInitializer() instead, because of the *_odr linkage type.
83  ///
84  /// Example:
85  ///
86  /// @a = global SomeType* null - Initializer is both definitive and unique.
87  ///
88  /// @b = global weak SomeType* null - Initializer is neither definitive nor
89  /// unique.
90  ///
91  /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
92  /// unique.
93  inline bool hasDefinitiveInitializer() const {
94    return hasInitializer() &&
95      // The initializer of a global variable with weak linkage may change at
96      // link time.
97      !mayBeOverridden();
98  }
99
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.
110      !isWeakForLinker();
111  }
112
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!
116  ///
117  inline const Constant *getInitializer() const {
118    assert(hasInitializer() && "GV doesn't have initializer!");
119    return static_cast<Constant*>(Op<0>().get());
120  }
121  inline Constant *getInitializer() {
122    assert(hasInitializer() && "GV doesn't have initializer!");
123    return static_cast<Constant*>(Op<0>().get());
124  }
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);
129
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.
133  ///
134  bool isConstant() const { return isConstantGlobal; }
135  void setConstant(bool Val) { isConstantGlobal = Val; }
136
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; }
140
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);
144
145  /// removeFromParent - This method unlinks 'this' from the containing module,
146  /// but does not delete it.
147  ///
148  virtual void removeFromParent();
149
150  /// eraseFromParent - This method unlinks 'this' from the containing module
151  /// and deletes it.
152  ///
153  virtual void eraseFromParent();
154
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);
158
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;
163  }
164};
165
166template <>
167struct OperandTraits<GlobalVariable> :
168  public OptionalOperandTraits<GlobalVariable> {
169};
170
171DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
172
173} // End llvm namespace
174
175#endif
176