1//===-- llvm/GlobalVariable.h - GlobalVariable class ------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file contains the declaration of the GlobalVariable class, which
10// represents a single global variable (or constant) in the VM.
11//
12// Global variables are constant pointers that refer to hunks of space that are
13// allocated by either the VM, or by the linker in a static compiler. A global
14// variable may have an initial value, which is copied into the executables .data
15// area. Global Constants are required to have initializers.
16//
17//===----------------------------------------------------------------------===//
18
19#ifndef LLVM_IR_GLOBALVARIABLE_H
20#define LLVM_IR_GLOBALVARIABLE_H
21
22#include "llvm/ADT/Twine.h"
23#include "llvm/ADT/ilist_node.h"
24#include "llvm/IR/Attributes.h"
25#include "llvm/IR/GlobalObject.h"
26#include "llvm/IR/OperandTraits.h"
27#include "llvm/IR/Value.h"
28#include <cassert>
29#include <cstddef>
30
31namespace llvm {
32
33class Constant;
34class Module;
35
36template <typename ValueSubClass> class SymbolTableListTraits;
37class DIGlobalVariable;
38class DIGlobalVariableExpression;
39
40class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
41 friend class SymbolTableListTraits<GlobalVariable>;
42
43 AttributeSet Attrs;
44 bool isConstantGlobal : 1; // Is this a global constant?
45 bool isExternallyInitializedConstant : 1; // Is this a global whose value
46 // can change from its initial
47 // value before global
48 // initializers are run?
49
50public:
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 = nullptr, const Twine &Name = "",
55 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
56 bool isExternallyInitialized = false);
57 /// GlobalVariable ctor - This creates a global and inserts it before the
58 /// specified other global.
59 GlobalVariable(Module &M, Type *Ty, bool isConstant, LinkageTypes Linkage,
60 Constant *Initializer, const Twine &Name = "",
61 GlobalVariable *InsertBefore = nullptr,
62 ThreadLocalMode = NotThreadLocal,
63 Optional<unsigned> AddressSpace = None,
64 bool isExternallyInitialized = false);
65 GlobalVariable(const GlobalVariable &) = delete;
66 GlobalVariable &operator=(const GlobalVariable &) = delete;
67
68 ~GlobalVariable() {
69 dropAllReferences();
70 }
71
72 // allocate space for exactly one operand
73 void *operator new(size_t s) {
74 return User::operator new(s, 1);
75 }
76
77 // delete space for exactly one operand as created in the corresponding new operator
78 void operator delete(void *ptr){
79 assert(ptr != nullptr && "must not be nullptr");
80 User *Obj = static_cast<User *>(ptr);
81 // Number of operands can be set to 0 after construction and initialization. Make sure
82 // that number of operands is reset to 1, as this is needed in User::operator delete
83 Obj->setGlobalVariableNumOperands(1);
84 User::operator delete(Obj);
85 }
86
87 /// Provide fast operand accessors
88 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
89
90 /// Definitions have initializers, declarations don't.
91 ///
92 inline bool hasInitializer() const { return !isDeclaration(); }
93
94 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
95 /// and any other instances of the global (this can happen due to weak
96 /// linkage) are guaranteed to have the same initializer.
97 ///
98 /// Note that if you want to transform a global, you must use
99 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
100 ///
101 /// Example:
102 ///
103 /// @a = global SomeType* null - Initializer is both definitive and unique.
104 ///
105 /// @b = global weak SomeType* null - Initializer is neither definitive nor
106 /// unique.
107 ///
108 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
109 /// unique.
110 inline bool hasDefinitiveInitializer() const {
111 return hasInitializer() &&
112 // The initializer of a global variable may change to something arbitrary
113 // at link time.
114 !isInterposable() &&
115 // The initializer of a global variable with the externally_initialized
116 // marker may change at runtime before C++ initializers are evaluated.
117 !isExternallyInitialized();
118 }
119
120 /// hasUniqueInitializer - Whether the global variable has an initializer, and
121 /// any changes made to the initializer will turn up in the final executable.
122 inline bool hasUniqueInitializer() const {
123 return
124 // We need to be sure this is the definition that will actually be used
125 isStrongDefinitionForLinker() &&
126 // It is not safe to modify initializers of global variables with the
127 // external_initializer marker since the value may be changed at runtime
128 // before C++ initializers are evaluated.
129 !isExternallyInitialized();
130 }
131
132 /// getInitializer - Return the initializer for this global variable. It is
133 /// illegal to call this method if the global is external, because we cannot
134 /// tell what the value is initialized to!
135 ///
136 inline const Constant *getInitializer() const {
137 assert(hasInitializer() && "GV doesn't have initializer!");
138 return static_cast<Constant*>(Op<0>().get());
139 }
140 inline Constant *getInitializer() {
141 assert(hasInitializer() && "GV doesn't have initializer!");
142 return static_cast<Constant*>(Op<0>().get());
143 }
144 /// setInitializer - Sets the initializer for this global variable, removing
145 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
146 /// initializer must have type T.
147 void setInitializer(Constant *InitVal);
148
149 /// If the value is a global constant, its value is immutable throughout the
150 /// runtime execution of the program. Assigning a value into the constant
151 /// leads to undefined behavior.
152 ///
153 bool isConstant() const { return isConstantGlobal; }
154 void setConstant(bool Val) { isConstantGlobal = Val; }
155
156 bool isExternallyInitialized() const {
157 return isExternallyInitializedConstant;
158 }
159 void setExternallyInitialized(bool Val) {
160 isExternallyInitializedConstant = Val;
161 }
162
163 /// copyAttributesFrom - copy all additional attributes (those not needed to
164 /// create a GlobalVariable) from the GlobalVariable Src to this one.
165 void copyAttributesFrom(const GlobalVariable *Src);
166
167 /// removeFromParent - This method unlinks 'this' from the containing module,
168 /// but does not delete it.
169 ///
170 void removeFromParent();
171
172 /// eraseFromParent - This method unlinks 'this' from the containing module
173 /// and deletes it.
174 ///
175 void eraseFromParent();
176
177 /// Drop all references in preparation to destroy the GlobalVariable. This
178 /// drops not only the reference to the initializer but also to any metadata.
179 void dropAllReferences();
180
181 /// Attach a DIGlobalVariableExpression.
182 void addDebugInfo(DIGlobalVariableExpression *GV);
183
184 /// Fill the vector with all debug info attachements.
185 void getDebugInfo(SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const;
186
187 /// Add attribute to this global.
188 void addAttribute(Attribute::AttrKind Kind) {
189 Attrs = Attrs.addAttribute(getContext(), Kind);
190 }
191
192 /// Add attribute to this global.
193 void addAttribute(StringRef Kind, StringRef Val = StringRef()) {
194 Attrs = Attrs.addAttribute(getContext(), Kind, Val);
195 }
196
197 /// Return true if the attribute exists.
198 bool hasAttribute(Attribute::AttrKind Kind) const {
199 return Attrs.hasAttribute(Kind);
200 }
201
202 /// Return true if the attribute exists.
203 bool hasAttribute(StringRef Kind) const {
204 return Attrs.hasAttribute(Kind);
205 }
206
207 /// Return true if any attributes exist.
208 bool hasAttributes() const {
209 return Attrs.hasAttributes();
210 }
211
212 /// Return the attribute object.
213 Attribute getAttribute(Attribute::AttrKind Kind) const {
214 return Attrs.getAttribute(Kind);
215 }
216
217 /// Return the attribute object.
218 Attribute getAttribute(StringRef Kind) const {
219 return Attrs.getAttribute(Kind);
220 }
221
222 /// Return the attribute set for this global
223 AttributeSet getAttributes() const {
224 return Attrs;
225 }
226
227 /// Return attribute set as list with index.
228 /// FIXME: This may not be required once ValueEnumerators
229 /// in bitcode-writer can enumerate attribute-set.
230 AttributeList getAttributesAsList(unsigned index) const {
231 if (!hasAttributes())
232 return AttributeList();
233 std::pair<unsigned, AttributeSet> AS[1] = {{index, Attrs}};
234 return AttributeList::get(getContext(), AS);
235 }
236
237 /// Set attribute list for this global
238 void setAttributes(AttributeSet A) {
239 Attrs = A;
240 }
241
242 /// Check if section name is present
243 bool hasImplicitSection() const {
244 return getAttributes().hasAttribute("bss-section") ||
245 getAttributes().hasAttribute("data-section") ||
246 getAttributes().hasAttribute("relro-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