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/GlobalValue.h"
26#include "llvm/IR/OperandTraits.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) LLVM_DELETED_FUNCTION;
38  void operator=(const GlobalVariable &) LLVM_DELETED_FUNCTION;
39  GlobalVariable(const GlobalVariable &) LLVM_DELETED_FUNCTION;
40
41  void setParent(Module *parent);
42
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
46                                               // model?
47  bool isExternallyInitializedConstant : 1;    // Is this a global whose value
48                                               // can change from its initial
49                                               // value before global
50                                               // initializers are run?
51
52public:
53  // allocate space for exactly one operand
54  void *operator new(size_t s) {
55    return User::operator new(s, 1);
56  }
57
58  enum ThreadLocalMode {
59    NotThreadLocal = 0,
60    GeneralDynamicTLSModel,
61    LocalDynamicTLSModel,
62    InitialExecTLSModel,
63    LocalExecTLSModel
64  };
65
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 = 0, 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 = 0,
77                 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
78                 bool isExternallyInitialized = false);
79
80  ~GlobalVariable() {
81    NumOperands = 1; // FIXME: needed by operator delete
82  }
83
84  /// Provide fast operand accessors
85  DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
86
87  /// hasInitializer - Unless a global variable isExternal(), it has an
88  /// initializer.  The initializer for the global variable/constant is held by
89  /// Initializer if an initializer is specified.
90  ///
91  inline bool hasInitializer() const { return !isDeclaration(); }
92
93  /// hasDefinitiveInitializer - Whether the global variable has an initializer,
94  /// and any other instances of the global (this can happen due to weak
95  /// linkage) are guaranteed to have the same initializer.
96  ///
97  /// Note that if you want to transform a global, you must use
98  /// hasUniqueInitializer() instead, because of the *_odr linkage type.
99  ///
100  /// Example:
101  ///
102  /// @a = global SomeType* null - Initializer is both definitive and unique.
103  ///
104  /// @b = global weak SomeType* null - Initializer is neither definitive nor
105  /// unique.
106  ///
107  /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
108  /// unique.
109  inline bool hasDefinitiveInitializer() const {
110    return hasInitializer() &&
111      // The initializer of a global variable with weak linkage may change at
112      // link time.
113      !mayBeOverridden() &&
114      // The initializer of a global variable with the externally_initialized
115      // marker may change at runtime before C++ initializers are evaluated.
116      !isExternallyInitialized();
117  }
118
119  /// hasUniqueInitializer - Whether the global variable has an initializer, and
120  /// any changes made to the initializer will turn up in the final executable.
121  inline bool hasUniqueInitializer() const {
122    return hasInitializer() &&
123      // It's not safe to modify initializers of global variables with weak
124      // linkage, because the linker might choose to discard the initializer and
125      // use the initializer from another instance of the global variable
126      // instead. It is wrong to modify the initializer of a global variable
127      // with *_odr linkage because then different instances of the global may
128      // have different initializers, breaking the One Definition Rule.
129      !isWeakForLinker() &&
130      // It is not safe to modify initializers of global variables with the
131      // external_initializer marker since the value may be changed at runtime
132      // before C++ initializers are evaluated.
133      !isExternallyInitialized();
134  }
135
136  /// getInitializer - Return the initializer for this global variable.  It is
137  /// illegal to call this method if the global is external, because we cannot
138  /// tell what the value is initialized to!
139  ///
140  inline const Constant *getInitializer() const {
141    assert(hasInitializer() && "GV doesn't have initializer!");
142    return static_cast<Constant*>(Op<0>().get());
143  }
144  inline Constant *getInitializer() {
145    assert(hasInitializer() && "GV doesn't have initializer!");
146    return static_cast<Constant*>(Op<0>().get());
147  }
148  /// setInitializer - Sets the initializer for this global variable, removing
149  /// any existing initializer if InitVal==NULL.  If this GV has type T*, the
150  /// initializer must have type T.
151  void setInitializer(Constant *InitVal);
152
153  /// If the value is a global constant, its value is immutable throughout the
154  /// runtime execution of the program.  Assigning a value into the constant
155  /// leads to undefined behavior.
156  ///
157  bool isConstant() const { return isConstantGlobal; }
158  void setConstant(bool Val) { isConstantGlobal = Val; }
159
160  /// If the value is "Thread Local", its value isn't shared by the threads.
161  bool isThreadLocal() const { return threadLocalMode != NotThreadLocal; }
162  void setThreadLocal(bool Val) {
163    threadLocalMode = Val ? GeneralDynamicTLSModel : NotThreadLocal;
164  }
165  void setThreadLocalMode(ThreadLocalMode Val) { threadLocalMode = Val; }
166  ThreadLocalMode getThreadLocalMode() const {
167    return static_cast<ThreadLocalMode>(threadLocalMode);
168  }
169
170  bool isExternallyInitialized() const {
171    return isExternallyInitializedConstant;
172  }
173  void setExternallyInitialized(bool Val) {
174    isExternallyInitializedConstant = Val;
175  }
176
177  /// copyAttributesFrom - copy all additional attributes (those not needed to
178  /// create a GlobalVariable) from the GlobalVariable Src to this one.
179  void copyAttributesFrom(const GlobalValue *Src);
180
181  /// removeFromParent - This method unlinks 'this' from the containing module,
182  /// but does not delete it.
183  ///
184  virtual void removeFromParent();
185
186  /// eraseFromParent - This method unlinks 'this' from the containing module
187  /// and deletes it.
188  ///
189  virtual void eraseFromParent();
190
191  /// Override Constant's implementation of this method so we can
192  /// replace constant initializers.
193  virtual void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U);
194
195  // Methods for support type inquiry through isa, cast, and dyn_cast:
196  static inline bool classof(const Value *V) {
197    return V->getValueID() == Value::GlobalVariableVal;
198  }
199};
200
201template <>
202struct OperandTraits<GlobalVariable> :
203  public OptionalOperandTraits<GlobalVariable> {
204};
205
206DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
207
208} // End llvm namespace
209
210#endif
211