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/PointerUnion.h"
24#include "llvm/ADT/Twine.h"
25#include "llvm/ADT/ilist_node.h"
26#include "llvm/IR/Attributes.h"
27#include "llvm/IR/GlobalObject.h"
28#include "llvm/IR/OperandTraits.h"
29#include "llvm/IR/Value.h"
30#include <cassert>
31#include <cstddef>
32
33namespace llvm {
34
35class Constant;
36class Module;
37
38template <typename ValueSubClass> class SymbolTableListTraits;
39class DIGlobalVariable;
40class DIGlobalVariableExpression;
41
42class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
43 friend class SymbolTableListTraits<GlobalVariable>;
44
45 AttributeSet Attrs;
46 bool isConstantGlobal : 1; // Is this a global constant?
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 /// 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 GlobalVariable(const GlobalVariable &) = delete;
67 GlobalVariable &operator=(const GlobalVariable &) = delete;
68
69 ~GlobalVariable() {
70 dropAllReferences();
71 }
72
73 // allocate space for exactly one operand
74 void *operator new(size_t s) {
75 return User::operator new(s, 1);
76 }
77
78 // delete space for exactly one operand as created in the corresponding new operator
79 void operator delete(void *ptr){
80 assert(ptr != nullptr && "must not be nullptr");
81 User *Obj = static_cast<User *>(ptr);
82 // Number of operands can be set to 0 after construction and initialization. Make sure
83 // that number of operands is reset to 1, as this is needed in User::operator delete
84 Obj->setGlobalVariableNumOperands(1);
85 User::operator delete(Obj);
86 }
87
88 /// Provide fast operand accessors
89 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
90
91 /// Definitions have initializers, declarations don't.
92 ///
93 inline bool hasInitializer() const { return !isDeclaration(); }
94
95 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
96 /// and any other instances of the global (this can happen due to weak
97 /// linkage) are guaranteed to have the same initializer.
98 ///
99 /// Note that if you want to transform a global, you must use
100 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
101 ///
102 /// Example:
103 ///
104 /// @a = global SomeType* null - Initializer is both definitive and unique.
105 ///
106 /// @b = global weak SomeType* null - Initializer is neither definitive nor
107 /// unique.
108 ///
109 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
110 /// unique.
111 inline bool hasDefinitiveInitializer() const {
112 return hasInitializer() &&
113 // The initializer of a global variable may change to something arbitrary
114 // at link time.
115 !isInterposable() &&
116 // The initializer of a global variable with the externally_initialized
117 // marker may change at runtime before C++ initializers are evaluated.
118 !isExternallyInitialized();
119 }
120
121 /// hasUniqueInitializer - Whether the global variable has an initializer, and
122 /// any changes made to the initializer will turn up in the final executable.
123 inline bool hasUniqueInitializer() const {
124 return
125 // We need to be sure this is the definition that will actually be used
126 isStrongDefinitionForLinker() &&
127 // It is not safe to modify initializers of global variables with the
128 // external_initializer marker since the value may be changed at runtime
129 // before C++ initializers are evaluated.
130 !isExternallyInitialized();
131 }
132
133 /// getInitializer - Return the initializer for this global variable. It is
134 /// illegal to call this method if the global is external, because we cannot
135 /// tell what the value is initialized to!
136 ///
137 inline const Constant *getInitializer() const {
138 assert(hasInitializer() && "GV doesn't have initializer!");
139 return static_cast<Constant*>(Op<0>().get());
140 }
141 inline Constant *getInitializer() {
142 assert(hasInitializer() && "GV doesn't have initializer!");
143 return static_cast<Constant*>(Op<0>().get());
144 }
145 /// setInitializer - Sets the initializer for this global variable, removing
146 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
147 /// initializer must have type T.
148 void setInitializer(Constant *InitVal);
149
150 /// If the value is a global constant, its value is immutable throughout the
151 /// runtime execution of the program. Assigning a value into the constant
152 /// leads to undefined behavior.
153 ///
154 bool isConstant() const { return isConstantGlobal; }
155 void setConstant(bool Val) { isConstantGlobal = Val; }
156
157 bool isExternallyInitialized() const {
158 return isExternallyInitializedConstant;
159 }
160 void setExternallyInitialized(bool Val) {
161 isExternallyInitializedConstant = Val;
162 }
163
164 /// copyAttributesFrom - copy all additional attributes (those not needed to
165 /// create a GlobalVariable) from the GlobalVariable Src to this one.
166 void copyAttributesFrom(const GlobalVariable *Src);
167
168 /// removeFromParent - This method unlinks 'this' from the containing module,
169 /// but does not delete it.
170 ///
171 void removeFromParent();
172
173 /// eraseFromParent - This method unlinks 'this' from the containing module
174 /// and deletes it.
175 ///
176 void eraseFromParent();
177
178 /// Drop all references in preparation to destroy the GlobalVariable. This
179 /// drops not only the reference to the initializer but also to any metadata.
180 void dropAllReferences();
181
182 /// Attach a DIGlobalVariableExpression.
183 void addDebugInfo(DIGlobalVariableExpression *GV);
184
185 /// Fill the vector with all debug info attachements.
186 void getDebugInfo(SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const;
187
188 /// Add attribute to this global.
189 void addAttribute(Attribute::AttrKind Kind) {
190 Attrs = Attrs.addAttribute(getContext(), Kind);
191 }
192
193 /// Add attribute to this global.
194 void addAttribute(StringRef Kind, StringRef Val = StringRef()) {
195 Attrs = Attrs.addAttribute(getContext(), Kind, Val);
196 }
197
198 /// Return true if the attribute exists.
199 bool hasAttribute(Attribute::AttrKind Kind) const {
200 return Attrs.hasAttribute(Kind);
201 }
202
203 /// Return true if the attribute exists.
204 bool hasAttribute(StringRef Kind) const {
205 return Attrs.hasAttribute(Kind);
206 }
207
208 /// Return true if any attributes exist.
209 bool hasAttributes() const {
210 return Attrs.hasAttributes();
211 }
212
213 /// Return the attribute object.
214 Attribute getAttribute(Attribute::AttrKind Kind) const {
215 return Attrs.getAttribute(Kind);
216 }
217
218 /// Return the attribute object.
219 Attribute getAttribute(StringRef Kind) const {
220 return Attrs.getAttribute(Kind);
221 }
222
223 /// Return the attribute set for this global
224 AttributeSet getAttributes() const {
225 return Attrs;
226 }
227
228 /// Return attribute set as list with index.
229 /// FIXME: This may not be required once ValueEnumerators
230 /// in bitcode-writer can enumerate attribute-set.
231 AttributeList getAttributesAsList(unsigned index) const {
232 if (!hasAttributes())
233 return AttributeList();
234 std::pair<unsigned, AttributeSet> AS[1] = {{index, Attrs}};
235 return AttributeList::get(getContext(), AS);
236 }
237
238 /// Set attribute list for this global
239 void setAttributes(AttributeSet A) {
240 Attrs = A;
241 }
242
243 /// Check if section name is present
244 bool hasImplicitSection() const {
245 return getAttributes().hasAttribute("bss-section") ||
246 getAttributes().hasAttribute("data-section") ||
247 getAttributes().hasAttribute("rodata-section");
248 }
249
250 // Methods for support type inquiry through isa, cast, and dyn_cast:
251 static bool classof(const Value *V) {
252 return V->getValueID() == Value::GlobalVariableVal;
253 }
254};
255
256template <>
257struct OperandTraits<GlobalVariable> :
258 public OptionalOperandTraits<GlobalVariable> {
259};
260
261DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
262
263} // end namespace llvm
264
265#endif // LLVM_IR_GLOBALVARIABLE_H
266