include/llvm/IR/GlobalVariable.h

   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/PointerUnion.h"
  23 #include "llvm/ADT/Twine.h"
  24 #include "llvm/ADT/ilist_node.h"
  25 #include "llvm/IR/Attributes.h"
  26 #include "llvm/IR/GlobalObject.h"
  27 #include "llvm/IR/OperandTraits.h"
  28 #include "llvm/IR/Value.h"
  29 #include <cassert>
  30 #include <cstddef>
  31
  32 namespace llvm {
  33
  34 class Constant;
  35 class Module;
  36
  37 template <typename ValueSubClass> class SymbolTableListTraits;
  38 class DIGlobalVariable;
  39 class DIGlobalVariableExpression;
  40
  41 class GlobalVariable : public GlobalObject, public ilist_node<GlobalVariable> {
  42   friend class SymbolTableListTraits<GlobalVariable>;
  43
  44   AttributeSet Attrs;
  45   bool isConstantGlobal : 1;                   // Is this a global constant?
  46   bool isExternallyInitializedConstant : 1;    // Is this a global whose value
  47                                                // can change from its initial
  48                                                // value before global
  49                                                // initializers are run?
  50
  51 public:
  52   /// GlobalVariable ctor - If a parent module is specified, the global is
  53   /// automatically inserted into the end of the specified modules global list.
  54   GlobalVariable(Type *Ty, bool isConstant, LinkageTypes Linkage,
  55                  Constant *Initializer = nullptr, const Twine &Name = "",
  56                  ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
  57                  bool isExternallyInitialized = false);
  58   /// GlobalVariable ctor - This creates a global and inserts it before the
  59   /// specified other global.
  60   GlobalVariable(Module &M, Type *Ty, bool isConstant,
  61                  LinkageTypes Linkage, Constant *Initializer,
  62                  const Twine &Name = "", GlobalVariable *InsertBefore = nullptr,
  63                  ThreadLocalMode = NotThreadLocal, unsigned AddressSpace = 0,
  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
 256 template <>
 257 struct OperandTraits<GlobalVariable> :
 258   public OptionalOperandTraits<GlobalVariable> {
 259 };
 260
 261 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalVariable, Value)
 262
 263 } // end namespace llvm
 264
 265 #endif // LLVM_IR_GLOBALVARIABLE_H