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      1 //===-- llvm/GlobalValue.h - Class to represent a global value --*- 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 is a common base class of all globally definable objects.  As such,
     11 // it is subclassed by GlobalVariable, GlobalAlias and by Function.  This is
     12 // used because you can do certain things with these global objects that you
     13 // can't do to anything else.  For example, use the address of one as a
     14 // constant.
     15 //
     16 //===----------------------------------------------------------------------===//
     17 
     18 #ifndef LLVM_IR_GLOBALVALUE_H
     19 #define LLVM_IR_GLOBALVALUE_H
     20 
     21 #include "llvm/IR/Constant.h"
     22 #include "llvm/IR/DerivedTypes.h"
     23 #include <system_error>
     24 
     25 namespace llvm {
     26 
     27 class Comdat;
     28 class PointerType;
     29 class Module;
     30 
     31 class GlobalValue : public Constant {
     32   GlobalValue(const GlobalValue &) = delete;
     33 public:
     34   /// @brief An enumeration for the kinds of linkage for global values.
     35   enum LinkageTypes {
     36     ExternalLinkage = 0,///< Externally visible function
     37     AvailableExternallyLinkage, ///< Available for inspection, not emission.
     38     LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
     39     LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
     40     WeakAnyLinkage,     ///< Keep one copy of named function when linking (weak)
     41     WeakODRLinkage,     ///< Same, but only replaced by something equivalent.
     42     AppendingLinkage,   ///< Special purpose, only applies to global arrays
     43     InternalLinkage,    ///< Rename collisions when linking (static functions).
     44     PrivateLinkage,     ///< Like Internal, but omit from symbol table.
     45     ExternalWeakLinkage,///< ExternalWeak linkage description.
     46     CommonLinkage       ///< Tentative definitions.
     47   };
     48 
     49   /// @brief An enumeration for the kinds of visibility of global values.
     50   enum VisibilityTypes {
     51     DefaultVisibility = 0,  ///< The GV is visible
     52     HiddenVisibility,       ///< The GV is hidden
     53     ProtectedVisibility     ///< The GV is protected
     54   };
     55 
     56   /// @brief Storage classes of global values for PE targets.
     57   enum DLLStorageClassTypes {
     58     DefaultStorageClass   = 0,
     59     DLLImportStorageClass = 1, ///< Function to be imported from DLL
     60     DLLExportStorageClass = 2  ///< Function to be accessible from DLL.
     61   };
     62 
     63 protected:
     64   GlobalValue(PointerType *Ty, ValueTy VTy, Use *Ops, unsigned NumOps,
     65               LinkageTypes Linkage, const Twine &Name)
     66       : Constant(Ty, VTy, Ops, NumOps), Linkage(Linkage),
     67         Visibility(DefaultVisibility), UnnamedAddr(0),
     68         DllStorageClass(DefaultStorageClass),
     69         ThreadLocal(NotThreadLocal), Parent(nullptr) {
     70     setName(Name);
     71   }
     72 
     73   // Note: VC++ treats enums as signed, so an extra bit is required to prevent
     74   // Linkage and Visibility from turning into negative values.
     75   LinkageTypes Linkage : 5;   // The linkage of this global
     76   unsigned Visibility : 2;    // The visibility style of this global
     77   unsigned UnnamedAddr : 1;   // This value's address is not significant
     78   unsigned DllStorageClass : 2; // DLL storage class
     79 
     80   unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
     81                             // the desired model?
     82 
     83 private:
     84   // Give subclasses access to what otherwise would be wasted padding.
     85   // (19 + 3 + 2 + 1 + 2 + 5) == 32.
     86   unsigned SubClassData : 19;
     87 protected:
     88   static const unsigned GlobalValueSubClassDataBits = 19;
     89   unsigned getGlobalValueSubClassData() const {
     90     return SubClassData;
     91   }
     92   void setGlobalValueSubClassData(unsigned V) {
     93     assert(V < (1 << 19) && "It will not fit");
     94     SubClassData = V;
     95   }
     96 
     97   Module *Parent;             // The containing module.
     98 public:
     99   enum ThreadLocalMode {
    100     NotThreadLocal = 0,
    101     GeneralDynamicTLSModel,
    102     LocalDynamicTLSModel,
    103     InitialExecTLSModel,
    104     LocalExecTLSModel
    105   };
    106 
    107   ~GlobalValue() override {
    108     removeDeadConstantUsers();   // remove any dead constants using this.
    109   }
    110 
    111   unsigned getAlignment() const;
    112 
    113   bool hasUnnamedAddr() const { return UnnamedAddr; }
    114   void setUnnamedAddr(bool Val) { UnnamedAddr = Val; }
    115 
    116   bool hasComdat() const { return getComdat() != nullptr; }
    117   Comdat *getComdat();
    118   const Comdat *getComdat() const {
    119     return const_cast<GlobalValue *>(this)->getComdat();
    120   }
    121 
    122   VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
    123   bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
    124   bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
    125   bool hasProtectedVisibility() const {
    126     return Visibility == ProtectedVisibility;
    127   }
    128   void setVisibility(VisibilityTypes V) {
    129     assert((!hasLocalLinkage() || V == DefaultVisibility) &&
    130            "local linkage requires default visibility");
    131     Visibility = V;
    132   }
    133 
    134   /// If the value is "Thread Local", its value isn't shared by the threads.
    135   bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
    136   void setThreadLocal(bool Val) {
    137     setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
    138   }
    139   void setThreadLocalMode(ThreadLocalMode Val) {
    140     assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
    141     ThreadLocal = Val;
    142   }
    143   ThreadLocalMode getThreadLocalMode() const {
    144     return static_cast<ThreadLocalMode>(ThreadLocal);
    145   }
    146 
    147   DLLStorageClassTypes getDLLStorageClass() const {
    148     return DLLStorageClassTypes(DllStorageClass);
    149   }
    150   bool hasDLLImportStorageClass() const {
    151     return DllStorageClass == DLLImportStorageClass;
    152   }
    153   bool hasDLLExportStorageClass() const {
    154     return DllStorageClass == DLLExportStorageClass;
    155   }
    156   void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
    157 
    158   bool hasSection() const { return !StringRef(getSection()).empty(); }
    159   // It is unfortunate that we have to use "char *" in here since this is
    160   // always non NULL, but:
    161   // * The C API expects a null terminated string, so we cannot use StringRef.
    162   // * The C API expects us to own it, so we cannot use a std:string.
    163   // * For GlobalAliases we can fail to find the section and we have to
    164   //   return "", so we cannot use a "const std::string &".
    165   const char *getSection() const;
    166 
    167   /// Global values are always pointers.
    168   PointerType *getType() const { return cast<PointerType>(User::getType()); }
    169 
    170   Type *getValueType() const { return getType()->getElementType(); }
    171 
    172   static LinkageTypes getLinkOnceLinkage(bool ODR) {
    173     return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
    174   }
    175   static LinkageTypes getWeakLinkage(bool ODR) {
    176     return ODR ? WeakODRLinkage : WeakAnyLinkage;
    177   }
    178 
    179   static bool isExternalLinkage(LinkageTypes Linkage) {
    180     return Linkage == ExternalLinkage;
    181   }
    182   static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
    183     return Linkage == AvailableExternallyLinkage;
    184   }
    185   static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
    186     return Linkage == LinkOnceODRLinkage;
    187   }
    188   static bool isLinkOnceLinkage(LinkageTypes Linkage) {
    189     return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
    190   }
    191   static bool isWeakAnyLinkage(LinkageTypes Linkage) {
    192     return Linkage == WeakAnyLinkage;
    193   }
    194   static bool isWeakODRLinkage(LinkageTypes Linkage) {
    195     return Linkage == WeakODRLinkage;
    196   }
    197   static bool isWeakLinkage(LinkageTypes Linkage) {
    198     return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
    199   }
    200   static bool isAppendingLinkage(LinkageTypes Linkage) {
    201     return Linkage == AppendingLinkage;
    202   }
    203   static bool isInternalLinkage(LinkageTypes Linkage) {
    204     return Linkage == InternalLinkage;
    205   }
    206   static bool isPrivateLinkage(LinkageTypes Linkage) {
    207     return Linkage == PrivateLinkage;
    208   }
    209   static bool isLocalLinkage(LinkageTypes Linkage) {
    210     return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
    211   }
    212   static bool isExternalWeakLinkage(LinkageTypes Linkage) {
    213     return Linkage == ExternalWeakLinkage;
    214   }
    215   static bool isCommonLinkage(LinkageTypes Linkage) {
    216     return Linkage == CommonLinkage;
    217   }
    218 
    219   /// Whether the definition of this global may be discarded if it is not used
    220   /// in its compilation unit.
    221   static bool isDiscardableIfUnused(LinkageTypes Linkage) {
    222     return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage);
    223   }
    224 
    225   /// Whether the definition of this global may be replaced by something
    226   /// non-equivalent at link time. For example, if a function has weak linkage
    227   /// then the code defining it may be replaced by different code.
    228   static bool mayBeOverridden(LinkageTypes Linkage) {
    229     return Linkage == WeakAnyLinkage || Linkage == LinkOnceAnyLinkage ||
    230            Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
    231   }
    232 
    233   /// Whether the definition of this global may be replaced at link time.  NB:
    234   /// Using this method outside of the code generators is almost always a
    235   /// mistake: when working at the IR level use mayBeOverridden instead as it
    236   /// knows about ODR semantics.
    237   static bool isWeakForLinker(LinkageTypes Linkage)  {
    238     return Linkage == AvailableExternallyLinkage || Linkage == WeakAnyLinkage ||
    239            Linkage == WeakODRLinkage || Linkage == LinkOnceAnyLinkage ||
    240            Linkage == LinkOnceODRLinkage || Linkage == CommonLinkage ||
    241            Linkage == ExternalWeakLinkage;
    242   }
    243 
    244   bool hasExternalLinkage() const { return isExternalLinkage(Linkage); }
    245   bool hasAvailableExternallyLinkage() const {
    246     return isAvailableExternallyLinkage(Linkage);
    247   }
    248   bool hasLinkOnceLinkage() const {
    249     return isLinkOnceLinkage(Linkage);
    250   }
    251   bool hasLinkOnceODRLinkage() const { return isLinkOnceODRLinkage(Linkage); }
    252   bool hasWeakLinkage() const {
    253     return isWeakLinkage(Linkage);
    254   }
    255   bool hasWeakAnyLinkage() const {
    256     return isWeakAnyLinkage(Linkage);
    257   }
    258   bool hasWeakODRLinkage() const {
    259     return isWeakODRLinkage(Linkage);
    260   }
    261   bool hasAppendingLinkage() const { return isAppendingLinkage(Linkage); }
    262   bool hasInternalLinkage() const { return isInternalLinkage(Linkage); }
    263   bool hasPrivateLinkage() const { return isPrivateLinkage(Linkage); }
    264   bool hasLocalLinkage() const { return isLocalLinkage(Linkage); }
    265   bool hasExternalWeakLinkage() const { return isExternalWeakLinkage(Linkage); }
    266   bool hasCommonLinkage() const { return isCommonLinkage(Linkage); }
    267 
    268   void setLinkage(LinkageTypes LT) {
    269     if (isLocalLinkage(LT))
    270       Visibility = DefaultVisibility;
    271     Linkage = LT;
    272   }
    273   LinkageTypes getLinkage() const { return Linkage; }
    274 
    275   bool isDiscardableIfUnused() const {
    276     return isDiscardableIfUnused(Linkage);
    277   }
    278 
    279   bool mayBeOverridden() const { return mayBeOverridden(Linkage); }
    280 
    281   bool isWeakForLinker() const { return isWeakForLinker(Linkage); }
    282 
    283   /// Copy all additional attributes (those not needed to create a GlobalValue)
    284   /// from the GlobalValue Src to this one.
    285   virtual void copyAttributesFrom(const GlobalValue *Src);
    286 
    287   /// If special LLVM prefix that is used to inform the asm printer to not emit
    288   /// usual symbol prefix before the symbol name is used then return linkage
    289   /// name after skipping this special LLVM prefix.
    290   static StringRef getRealLinkageName(StringRef Name) {
    291     if (!Name.empty() && Name[0] == '\1')
    292       return Name.substr(1);
    293     return Name;
    294   }
    295 
    296 /// @name Materialization
    297 /// Materialization is used to construct functions only as they're needed. This
    298 /// is useful to reduce memory usage in LLVM or parsing work done by the
    299 /// BitcodeReader to load the Module.
    300 /// @{
    301 
    302   /// If this function's Module is being lazily streamed in functions from disk
    303   /// or some other source, this method can be used to check to see if the
    304   /// function has been read in yet or not.
    305   bool isMaterializable() const;
    306 
    307   /// Returns true if this function was loaded from a GVMaterializer that's
    308   /// still attached to its Module and that knows how to dematerialize the
    309   /// function.
    310   bool isDematerializable() const;
    311 
    312   /// Make sure this GlobalValue is fully read. If the module is corrupt, this
    313   /// returns true and fills in the optional string with information about the
    314   /// problem.  If successful, this returns false.
    315   std::error_code materialize();
    316 
    317   /// If this GlobalValue is read in, and if the GVMaterializer supports it,
    318   /// release the memory for the function, and set it up to be materialized
    319   /// lazily. If !isDematerializable(), this method is a noop.
    320   void Dematerialize();
    321 
    322 /// @}
    323 
    324   /// Override from Constant class.
    325   void destroyConstant() override;
    326 
    327   /// Return true if the primary definition of this global value is outside of
    328   /// the current translation unit.
    329   bool isDeclaration() const;
    330 
    331   bool isDeclarationForLinker() const {
    332     if (hasAvailableExternallyLinkage())
    333       return true;
    334 
    335     return isDeclaration();
    336   }
    337 
    338   /// This method unlinks 'this' from the containing module, but does not delete
    339   /// it.
    340   virtual void removeFromParent() = 0;
    341 
    342   /// This method unlinks 'this' from the containing module and deletes it.
    343   virtual void eraseFromParent() = 0;
    344 
    345   /// Get the module that this global value is contained inside of...
    346   Module *getParent() { return Parent; }
    347   const Module *getParent() const { return Parent; }
    348 
    349   // Methods for support type inquiry through isa, cast, and dyn_cast:
    350   static bool classof(const Value *V) {
    351     return V->getValueID() == Value::FunctionVal ||
    352            V->getValueID() == Value::GlobalVariableVal ||
    353            V->getValueID() == Value::GlobalAliasVal;
    354   }
    355 };
    356 
    357 } // End llvm namespace
    358 
    359 #endif
    360