GlobalVariable.h revision 263508 
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  /// Definitions have initializers, declarations don't.
88  ///
89  inline bool hasInitializer() const { return !isDeclaration(); }
90
91  /// hasDefinitiveInitializer - Whether the global variable has an initializer,
92  /// and any other instances of the global (this can happen due to weak
93  /// linkage) are guaranteed to have the same initializer.
94  ///
95  /// Note that if you want to transform a global, you must use
96  /// hasUniqueInitializer() instead, because of the *_odr linkage type.
97  ///
98  /// Example:
99  ///
100  /// @a = global SomeType* null - Initializer is both definitive and unique.
101  ///
102  /// @b = global weak SomeType* null - Initializer is neither definitive nor
103  /// unique.
104  ///
105  /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
106  /// unique.
107  inline bool hasDefinitiveInitializer() const {
108    return hasInitializer() &&
109      // The initializer of a global variable with weak linkage may change at
110      // link time.
111      !mayBeOverridden() &&
112      // The initializer of a global variable with the externally_initialized
113      // marker may change at runtime before C++ initializers are evaluated.
114      !isExternallyInitialized();
115  }
116
117  /// hasUniqueInitializer - Whether the global variable has an initializer, and
118  /// any changes made to the initializer will turn up in the final executable.
119  inline bool hasUniqueInitializer() const {
120    return hasInitializer() &&
121      // It's not safe to modify initializers of global variables with weak
122      // linkage, because the linker might choose to discard the initializer and
123      // use the initializer from another instance of the global variable
124      // instead. It is wrong to modify the initializer of a global variable
125      // with *_odr linkage because then different instances of the global may
126      // have different initializers, breaking the One Definition Rule.
127      !isWeakForLinker() &&
128      // It is not safe to modify initializers of global variables with the
129      // external_initializer marker since the value may be changed at runtime
130      // before C++ initializers are evaluated.
131      !isExternallyInitialized();
132  }
133
134  /// getInitializer - Return the initializer for this global variable.  It is
135  /// illegal to call this method if the global is external, because we cannot
136  /// tell what the value is initialized to!
137  ///
138  inline const Constant *getInitializer() const {
139    assert(hasInitializer() && "GV doesn't have initializer!");
140    return static_cast<Constant*>(Op<0>().get());
141  }
142  inline Constant *getInitializer() {
143    assert(hasInitializer() && "GV doesn't have initializer!");
144    return static_cast<Constant*>(Op<0>().get());
145  }
146  /// setInitializer - Sets the initializer for this global variable, removing
147  /// any existing initializer if InitVal==NULL.  If this GV has type T*, the
148  /// initializer must have type T.
149  void setInitializer(Constant *InitVal);
150
151  /// If the value is a global constant, its value is immutable throughout the
152  /// runtime execution of the program.  Assigning a value into the constant
153  /// leads to undefined behavior.
154  ///
155  bool isConstant() const { return isConstantGlobal; }
156  void setConstant(bool Val) { isConstantGlobal = Val; }
157
158  /// If the value is "Thread Local", its value isn't shared by the threads.
159  bool isThreadLocal() const { return threadLocalMode != NotThreadLocal; }
160  void setThreadLocal(bool Val) {
161    threadLocalMode = Val ? GeneralDynamicTLSModel : NotThreadLocal;
162  }
163  void setThreadLocalMode(ThreadLocalMode Val) { threadLocalMode = Val; }
164  ThreadLocalMode getThreadLocalMode() const {
165    return static_cast<ThreadLocalMode>(threadLocalMode);
166  }
167
168  bool isExternallyInitialized() const {
169    return isExternallyInitializedConstant;
170  }
171  void setExternallyInitialized(bool Val) {
172    isExternallyInitializedConstant = Val;
173  }
174
175  /// copyAttributesFrom - copy all additional attributes (those not needed to
176  /// create a GlobalVariable) from the GlobalVariable Src to this one.
177  void copyAttributesFrom(const GlobalValue *Src);
178
179  /// removeFromParent - This method unlinks 'this' from the containing module,
180  /// but does not delete it.
181  ///
182  virtual void removeFromParent();
183
184  /// eraseFromParent - This method unlinks 'this' from the containing module
185  /// and deletes it.
186  ///
187  virtual void eraseFromParent();
188
189  /// Override Constant's implementation of this method so we can
190  /// replace constant initializers.
191  virtual void replaceUsesOfWithOnConstant(Value *From, Value *To, Use *U);
192
193  // Methods for support type inquiry through isa, cast, and dyn_cast:
194  static inline bool classof(const Value *V) {
195    return V->getValueID() == Value::GlobalVariableVal;
196  }
197};
198
199template <>
200struct OperandTraits<GlobalVariable> :
201  public OptionalOperandTraits<GlobalVariable> {
202};
203
204DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
205
206} // End llvm namespace
207
208#endif
209