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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 
28 namespace llvm {
29 
30 class Module;
31 class Constant;
32 template<typename ValueSubClass, typename ItemParentClass>
33   class SymbolTableListTraits;
34 
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
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 
46 public:
47   // allocate space for exactly one operand
new(size_t s)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 
~GlobalVariable()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   ///
hasInitializer()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.
hasDefinitiveInitializer()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.
hasUniqueInitializer()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   ///
getInitializer()117   inline const Constant *getInitializer() const {
118     assert(hasInitializer() && "GV doesn't have initializer!");
119     return static_cast<Constant*>(Op<0>().get());
120   }
getInitializer()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   ///
isConstant()134   bool isConstant() const { return isConstantGlobal; }
setConstant(bool Val)135   void setConstant(bool Val) { isConstantGlobal = Val; }
136 
137   /// If the value is "Thread Local", its value isn't shared by the threads.
isThreadLocal()138   bool isThreadLocal() const { return isThreadLocalSymbol; }
setThreadLocal(bool Val)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:
classof(const GlobalVariable *)160   static inline bool classof(const GlobalVariable *) { return true; }
classof(const Value * V)161   static inline bool classof(const Value *V) {
162     return V->getValueID() == Value::GlobalVariableVal;
163   }
164 };
165 
166 template <>
167 struct OperandTraits<GlobalVariable> :
168   public OptionalOperandTraits<GlobalVariable> {
169 };
170 
171 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
172 
173 } // End llvm namespace
174 
175 #endif
176