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/Twine.h"
24#include "llvm/ADT/ilist_node.h"
25#include "llvm/IR/GlobalObject.h"
26#include "llvm/IR/OperandTraits.h"
27
28namespace llvm {
29
30class Module;
31class Constant;
32template <typename ValueSubClass> class SymbolTableListTraits;
33
34class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
35  friend class SymbolTableListTraits<GlobalVariable>;
36  void *operator new(size_t, unsigned) = delete;
37  void operator=(const GlobalVariable &) = delete;
38  GlobalVariable(const GlobalVariable &) = delete;
39
40  void setParent(Module *parent);
41
42  bool isConstantGlobal : 1;                   // Is this a global constant?
43  bool isExternallyInitializedConstant : 1;    // Is this a global whose value
44                                               // can change from its initial
45                                               // value before global
46                                               // initializers are run?
47public:
48  // allocate space for exactly one operand
49  void *operator new(size_t s) {
50    return User::operator new(s, 1);
51  }
52
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
67  ~GlobalVariable() override {
68    dropAllReferences();
69
70    // FIXME: needed by operator delete
71    setGlobalVariableNumOperands(1);
72  }
73
74  /// Provide fast operand accessors
75  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
76
77  /// Definitions have initializers, declarations don't.
78  ///
79  inline bool hasInitializer() const { return !isDeclaration(); }
80
81  /// hasDefinitiveInitializer - Whether the global variable has an initializer,
82  /// and any other instances of the global (this can happen due to weak
83  /// linkage) are guaranteed to have the same initializer.
84  ///
85  /// Note that if you want to transform a global, you must use
86  /// hasUniqueInitializer() instead, because of the *_odr linkage type.
87  ///
88  /// Example:
89  ///
90  /// @a = global SomeType* null - Initializer is both definitive and unique.
91  ///
92  /// @b = global weak SomeType* null - Initializer is neither definitive nor
93  /// unique.
94  ///
95  /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
96  /// unique.
97  inline bool hasDefinitiveInitializer() const {
98    return hasInitializer() &&
99      // The initializer of a global variable may change to something arbitrary
100      // at link time.
101      !isInterposable() &&
102      // The initializer of a global variable with the externally_initialized
103      // marker may change at runtime before C++ initializers are evaluated.
104      !isExternallyInitialized();
105  }
106
107  /// hasUniqueInitializer - Whether the global variable has an initializer, and
108  /// any changes made to the initializer will turn up in the final executable.
109  inline bool hasUniqueInitializer() const {
110    return
111        // We need to be sure this is the definition that will actually be used
112        isStrongDefinitionForLinker() &&
113        // It is not safe to modify initializers of global variables with the
114        // external_initializer marker since the value may be changed at runtime
115        // before C++ initializers are evaluated.
116        !isExternallyInitialized();
117  }
118
119  /// getInitializer - Return the initializer for this global variable.  It is
120  /// illegal to call this method if the global is external, because we cannot
121  /// tell what the value is initialized to!
122  ///
123  inline const Constant *getInitializer() const {
124    assert(hasInitializer() && "GV doesn't have initializer!");
125    return static_cast<Constant*>(Op<0>().get());
126  }
127  inline Constant *getInitializer() {
128    assert(hasInitializer() && "GV doesn't have initializer!");
129    return static_cast<Constant*>(Op<0>().get());
130  }
131  /// setInitializer - Sets the initializer for this global variable, removing
132  /// any existing initializer if InitVal==NULL.  If this GV has type T*, the
133  /// initializer must have type T.
134  void setInitializer(Constant *InitVal);
135
136  /// If the value is a global constant, its value is immutable throughout the
137  /// runtime execution of the program.  Assigning a value into the constant
138  /// leads to undefined behavior.
139  ///
140  bool isConstant() const { return isConstantGlobal; }
141  void setConstant(bool Val) { isConstantGlobal = Val; }
142
143  bool isExternallyInitialized() const {
144    return isExternallyInitializedConstant;
145  }
146  void setExternallyInitialized(bool Val) {
147    isExternallyInitializedConstant = Val;
148  }
149
150  /// copyAttributesFrom - copy all additional attributes (those not needed to
151  /// create a GlobalVariable) from the GlobalVariable Src to this one.
152  void copyAttributesFrom(const GlobalValue *Src) override;
153
154  /// removeFromParent - This method unlinks 'this' from the containing module,
155  /// but does not delete it.
156  ///
157  void removeFromParent() override;
158
159  /// eraseFromParent - This method unlinks 'this' from the containing module
160  /// and deletes it.
161  ///
162  void eraseFromParent() override;
163
164  /// Drop all references in preparation to destroy the GlobalVariable. This
165  /// drops not only the reference to the initializer but also to any metadata.
166  void dropAllReferences();
167
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;
171  }
172};
173
174template <>
175struct OperandTraits<GlobalVariable> :
176  public OptionalOperandTraits<GlobalVariable> {
177};
178
179DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
180
181} // End llvm namespace
182
183#endif
184