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