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, typename... Args> class SymbolTableListTraits;
37class DIGlobalVariableExpression;
38
39class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
40 friend class SymbolTableListTraits<GlobalVariable>;
41
42 AttributeSet Attrs;
43
44 // Is this a global constant?
45 bool isConstantGlobal : 1;
46 // Is this a global whose value can change from its initial value before
47 // global initializers are run?
48 bool isExternallyInitializedConstant : 1;
49
50private:
51 static const unsigned CodeModelBits = LastCodeModelBit - LastAlignmentBit;
52 static const unsigned CodeModelMask = (1 << CodeModelBits) - 1;
53 static const unsigned CodeModelShift = LastAlignmentBit + 1;
54
55public:
56 /// GlobalVariable ctor - If a parent module is specified, the global is
57 /// automatically inserted into the end of the specified modules global list.
58 GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage,
59 Constant *Initializer = nullptr, const Twine &Name = "",
60 ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
61 bool isExternallyInitialized = false);
62 /// GlobalVariable ctor - This creates a global and inserts it before the
63 /// specified other global.
64 GlobalVariable(Module &M, Type *Ty, bool isConstant, LinkageTypes Linkage,
65 Constant *Initializer, const Twine &Name = "",
66 GlobalVariable *InsertBefore = nullptr,
67 ThreadLocalMode = NotThreadLocal,
68 std::optional<unsigned> AddressSpace = std::nullopt,
69 bool isExternallyInitialized = false);
70 GlobalVariable(const GlobalVariable &) = delete;
71 GlobalVariable &operator=(const GlobalVariable &) = delete;
72
73 ~GlobalVariable() {
74 dropAllReferences();
75 }
76
77 // allocate space for exactly one operand
78 void *operator new(size_t s) {
79 return User::operator new(Size: s, Us: 1);
80 }
81
82 // delete space for exactly one operand as created in the corresponding new operator
83 void operator delete(void *ptr){
84 assert(ptr != nullptr && "must not be nullptr");
85 User *Obj = static_cast<User *>(ptr);
86 // Number of operands can be set to 0 after construction and initialization. Make sure
87 // that number of operands is reset to 1, as this is needed in User::operator delete
88 Obj->setGlobalVariableNumOperands(1);
89 User::operator delete(Usr: Obj);
90 }
91
92 /// Provide fast operand accessors
93 DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
94
95 /// Definitions have initializers, declarations don't.
96 ///
97 inline bool hasInitializer() const { return !isDeclaration(); }
98
99 /// hasDefinitiveInitializer - Whether the global variable has an initializer,
100 /// and any other instances of the global (this can happen due to weak
101 /// linkage) are guaranteed to have the same initializer.
102 ///
103 /// Note that if you want to transform a global, you must use
104 /// hasUniqueInitializer() instead, because of the *_odr linkage type.
105 ///
106 /// Example:
107 ///
108 /// @a = global SomeType* null - Initializer is both definitive and unique.
109 ///
110 /// @b = global weak SomeType* null - Initializer is neither definitive nor
111 /// unique.
112 ///
113 /// @c = global weak_odr SomeType* null - Initializer is definitive, but not
114 /// unique.
115 inline bool hasDefinitiveInitializer() const {
116 return hasInitializer() &&
117 // The initializer of a global variable may change to something arbitrary
118 // at link time.
119 !isInterposable() &&
120 // The initializer of a global variable with the externally_initialized
121 // marker may change at runtime before C++ initializers are evaluated.
122 !isExternallyInitialized();
123 }
124
125 /// hasUniqueInitializer - Whether the global variable has an initializer, and
126 /// any changes made to the initializer will turn up in the final executable.
127 inline bool hasUniqueInitializer() const {
128 return
129 // We need to be sure this is the definition that will actually be used
130 isStrongDefinitionForLinker() &&
131 // It is not safe to modify initializers of global variables with the
132 // external_initializer marker since the value may be changed at runtime
133 // before C++ initializers are evaluated.
134 !isExternallyInitialized();
135 }
136
137 /// getInitializer - Return the initializer for this global variable. It is
138 /// illegal to call this method if the global is external, because we cannot
139 /// tell what the value is initialized to!
140 ///
141 inline const Constant *getInitializer() const {
142 assert(hasInitializer() && "GV doesn't have initializer!");
143 return static_cast<Constant*>(Op<0>().get());
144 }
145 inline Constant *getInitializer() {
146 assert(hasInitializer() && "GV doesn't have initializer!");
147 return static_cast<Constant*>(Op<0>().get());
148 }
149 /// setInitializer - Sets the initializer for this global variable, removing
150 /// any existing initializer if InitVal==NULL. If this GV has type T*, the
151 /// initializer must have type T.
152 void setInitializer(Constant *InitVal);
153
154 /// If the value is a global constant, its value is immutable throughout the
155 /// runtime execution of the program. Assigning a value into the constant
156 /// leads to undefined behavior.
157 ///
158 bool isConstant() const { return isConstantGlobal; }
159 void setConstant(bool Val) { isConstantGlobal = Val; }
160
161 bool isExternallyInitialized() const {
162 return isExternallyInitializedConstant;
163 }
164 void setExternallyInitialized(bool Val) {
165 isExternallyInitializedConstant = Val;
166 }
167
168 /// copyAttributesFrom - copy all additional attributes (those not needed to
169 /// create a GlobalVariable) from the GlobalVariable Src to this one.
170 void copyAttributesFrom(const GlobalVariable *Src);
171
172 /// removeFromParent - This method unlinks 'this' from the containing module,
173 /// but does not delete it.
174 ///
175 void removeFromParent();
176
177 /// eraseFromParent - This method unlinks 'this' from the containing module
178 /// and deletes it.
179 ///
180 void eraseFromParent();
181
182 /// Drop all references in preparation to destroy the GlobalVariable. This
183 /// drops not only the reference to the initializer but also to any metadata.
184 void dropAllReferences();
185
186 /// Attach a DIGlobalVariableExpression.
187 void addDebugInfo(DIGlobalVariableExpression *GV);
188
189 /// Fill the vector with all debug info attachements.
190 void getDebugInfo(SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const;
191
192 /// Add attribute to this global.
193 void addAttribute(Attribute::AttrKind Kind) {
194 Attrs = Attrs.addAttribute(C&: getContext(), Kind);
195 }
196
197 /// Add attribute to this global.
198 void addAttribute(StringRef Kind, StringRef Val = StringRef()) {
199 Attrs = Attrs.addAttribute(C&: getContext(), Kind, Value: Val);
200 }
201
202 /// Return true if the attribute exists.
203 bool hasAttribute(Attribute::AttrKind Kind) const {
204 return Attrs.hasAttribute(Kind);
205 }
206
207 /// Return true if the attribute exists.
208 bool hasAttribute(StringRef Kind) const {
209 return Attrs.hasAttribute(Kind);
210 }
211
212 /// Return true if any attributes exist.
213 bool hasAttributes() const {
214 return Attrs.hasAttributes();
215 }
216
217 /// Return the attribute object.
218 Attribute getAttribute(Attribute::AttrKind Kind) const {
219 return Attrs.getAttribute(Kind);
220 }
221
222 /// Return the attribute object.
223 Attribute getAttribute(StringRef Kind) const {
224 return Attrs.getAttribute(Kind);
225 }
226
227 /// Return the attribute set for this global
228 AttributeSet getAttributes() const {
229 return Attrs;
230 }
231
232 /// Return attribute set as list with index.
233 /// FIXME: This may not be required once ValueEnumerators
234 /// in bitcode-writer can enumerate attribute-set.
235 AttributeList getAttributesAsList(unsigned index) const {
236 if (!hasAttributes())
237 return AttributeList();
238 std::pair<unsigned, AttributeSet> AS[1] = {{index, Attrs}};
239 return AttributeList::get(C&: getContext(), Attrs: AS);
240 }
241
242 /// Set attribute list for this global
243 void setAttributes(AttributeSet A) {
244 Attrs = A;
245 }
246
247 /// Check if section name is present
248 bool hasImplicitSection() const {
249 return getAttributes().hasAttribute(Kind: "bss-section") ||
250 getAttributes().hasAttribute(Kind: "data-section") ||
251 getAttributes().hasAttribute(Kind: "relro-section") ||
252 getAttributes().hasAttribute(Kind: "rodata-section");
253 }
254
255 /// Get the custom code model raw value of this global.
256 ///
257 unsigned getCodeModelRaw() const {
258 unsigned Data = getGlobalValueSubClassData();
259 return (Data >> CodeModelShift) & CodeModelMask;
260 }
261
262 /// Get the custom code model of this global if it has one.
263 ///
264 /// If this global does not have a custom code model, the empty instance
265 /// will be returned.
266 std::optional<CodeModel::Model> getCodeModel() const {
267 unsigned CodeModelData = getCodeModelRaw();
268 if (CodeModelData > 0)
269 return static_cast<CodeModel::Model>(CodeModelData - 1);
270 return {};
271 }
272
273 /// Change the code model for this global.
274 ///
275 void setCodeModel(CodeModel::Model CM);
276
277 // Methods for support type inquiry through isa, cast, and dyn_cast:
278 static bool classof(const Value *V) {
279 return V->getValueID() == Value::GlobalVariableVal;
280 }
281};
282
283template <>
284struct OperandTraits<GlobalVariable> :
285 public OptionalOperandTraits<GlobalVariable> {
286};
287
288DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
289
290} // end namespace llvm
291
292#endif // LLVM_IR_GLOBALVARIABLE_H
293