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 &) LLVM_DELETED_FUNCTION;
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:
GlobalValue(Type * Ty,ValueTy VTy,Use * Ops,unsigned NumOps,LinkageTypes Linkage,const Twine & Name)64   GlobalValue(Type *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;
getGlobalValueSubClassData()89   unsigned getGlobalValueSubClassData() const {
90     return SubClassData;
91   }
setGlobalValueSubClassData(unsigned V)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 
~GlobalValue()107   ~GlobalValue() {
108     removeDeadConstantUsers();   // remove any dead constants using this.
109   }
110 
111   unsigned getAlignment() const;
112 
hasUnnamedAddr()113   bool hasUnnamedAddr() const { return UnnamedAddr; }
setUnnamedAddr(bool Val)114   void setUnnamedAddr(bool Val) { UnnamedAddr = Val; }
115 
hasComdat()116   bool hasComdat() const { return getComdat() != nullptr; }
117   Comdat *getComdat();
getComdat()118   const Comdat *getComdat() const {
119     return const_cast<GlobalValue *>(this)->getComdat();
120   }
121 
getVisibility()122   VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
hasDefaultVisibility()123   bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
hasHiddenVisibility()124   bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
hasProtectedVisibility()125   bool hasProtectedVisibility() const {
126     return Visibility == ProtectedVisibility;
127   }
setVisibility(VisibilityTypes V)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.
isThreadLocal()135   bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
setThreadLocal(bool Val)136   void setThreadLocal(bool Val) {
137     setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
138   }
setThreadLocalMode(ThreadLocalMode Val)139   void setThreadLocalMode(ThreadLocalMode Val) {
140     assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
141     ThreadLocal = Val;
142   }
getThreadLocalMode()143   ThreadLocalMode getThreadLocalMode() const {
144     return static_cast<ThreadLocalMode>(ThreadLocal);
145   }
146 
getDLLStorageClass()147   DLLStorageClassTypes getDLLStorageClass() const {
148     return DLLStorageClassTypes(DllStorageClass);
149   }
hasDLLImportStorageClass()150   bool hasDLLImportStorageClass() const {
151     return DllStorageClass == DLLImportStorageClass;
152   }
hasDLLExportStorageClass()153   bool hasDLLExportStorageClass() const {
154     return DllStorageClass == DLLExportStorageClass;
155   }
setDLLStorageClass(DLLStorageClassTypes C)156   void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
157 
hasSection()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.
getType()168   inline PointerType *getType() const {
169     return cast<PointerType>(User::getType());
170   }
171 
getLinkOnceLinkage(bool ODR)172   static LinkageTypes getLinkOnceLinkage(bool ODR) {
173     return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
174   }
getWeakLinkage(bool ODR)175   static LinkageTypes getWeakLinkage(bool ODR) {
176     return ODR ? WeakODRLinkage : WeakAnyLinkage;
177   }
178 
isExternalLinkage(LinkageTypes Linkage)179   static bool isExternalLinkage(LinkageTypes Linkage) {
180     return Linkage == ExternalLinkage;
181   }
isAvailableExternallyLinkage(LinkageTypes Linkage)182   static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
183     return Linkage == AvailableExternallyLinkage;
184   }
isLinkOnceODRLinkage(LinkageTypes Linkage)185   static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
186     return Linkage == LinkOnceODRLinkage;
187   }
isLinkOnceLinkage(LinkageTypes Linkage)188   static bool isLinkOnceLinkage(LinkageTypes Linkage) {
189     return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
190   }
isWeakAnyLinkage(LinkageTypes Linkage)191   static bool isWeakAnyLinkage(LinkageTypes Linkage) {
192     return Linkage == WeakAnyLinkage;
193   }
isWeakODRLinkage(LinkageTypes Linkage)194   static bool isWeakODRLinkage(LinkageTypes Linkage) {
195     return Linkage == WeakODRLinkage;
196   }
isWeakLinkage(LinkageTypes Linkage)197   static bool isWeakLinkage(LinkageTypes Linkage) {
198     return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
199   }
isAppendingLinkage(LinkageTypes Linkage)200   static bool isAppendingLinkage(LinkageTypes Linkage) {
201     return Linkage == AppendingLinkage;
202   }
isInternalLinkage(LinkageTypes Linkage)203   static bool isInternalLinkage(LinkageTypes Linkage) {
204     return Linkage == InternalLinkage;
205   }
isPrivateLinkage(LinkageTypes Linkage)206   static bool isPrivateLinkage(LinkageTypes Linkage) {
207     return Linkage == PrivateLinkage;
208   }
isLocalLinkage(LinkageTypes Linkage)209   static bool isLocalLinkage(LinkageTypes Linkage) {
210     return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
211   }
isExternalWeakLinkage(LinkageTypes Linkage)212   static bool isExternalWeakLinkage(LinkageTypes Linkage) {
213     return Linkage == ExternalWeakLinkage;
214   }
isCommonLinkage(LinkageTypes Linkage)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.
isDiscardableIfUnused(LinkageTypes Linkage)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.
mayBeOverridden(LinkageTypes Linkage)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.
isWeakForLinker(LinkageTypes Linkage)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 
hasExternalLinkage()244   bool hasExternalLinkage() const { return isExternalLinkage(Linkage); }
hasAvailableExternallyLinkage()245   bool hasAvailableExternallyLinkage() const {
246     return isAvailableExternallyLinkage(Linkage);
247   }
hasLinkOnceLinkage()248   bool hasLinkOnceLinkage() const {
249     return isLinkOnceLinkage(Linkage);
250   }
hasLinkOnceODRLinkage()251   bool hasLinkOnceODRLinkage() const { return isLinkOnceODRLinkage(Linkage); }
hasWeakLinkage()252   bool hasWeakLinkage() const {
253     return isWeakLinkage(Linkage);
254   }
hasWeakAnyLinkage()255   bool hasWeakAnyLinkage() const {
256     return isWeakAnyLinkage(Linkage);
257   }
hasWeakODRLinkage()258   bool hasWeakODRLinkage() const {
259     return isWeakODRLinkage(Linkage);
260   }
hasAppendingLinkage()261   bool hasAppendingLinkage() const { return isAppendingLinkage(Linkage); }
hasInternalLinkage()262   bool hasInternalLinkage() const { return isInternalLinkage(Linkage); }
hasPrivateLinkage()263   bool hasPrivateLinkage() const { return isPrivateLinkage(Linkage); }
hasLocalLinkage()264   bool hasLocalLinkage() const { return isLocalLinkage(Linkage); }
hasExternalWeakLinkage()265   bool hasExternalWeakLinkage() const { return isExternalWeakLinkage(Linkage); }
hasCommonLinkage()266   bool hasCommonLinkage() const { return isCommonLinkage(Linkage); }
267 
setLinkage(LinkageTypes LT)268   void setLinkage(LinkageTypes LT) {
269     if (isLocalLinkage(LT))
270       Visibility = DefaultVisibility;
271     Linkage = LT;
272   }
getLinkage()273   LinkageTypes getLinkage() const { return Linkage; }
274 
isDiscardableIfUnused()275   bool isDiscardableIfUnused() const {
276     return isDiscardableIfUnused(Linkage);
277   }
278 
mayBeOverridden()279   bool mayBeOverridden() const { return mayBeOverridden(Linkage); }
280 
isWeakForLinker()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.
getRealLinkageName(StringRef Name)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 
isDeclarationForLinker()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...
getParent()346   inline Module *getParent() { return Parent; }
getParent()347   inline const Module *getParent() const { return Parent; }
348 
349   const DataLayout *getDataLayout() const;
350 
351   // Methods for support type inquiry through isa, cast, and dyn_cast:
classof(const Value * V)352   static inline bool classof(const Value *V) {
353     return V->getValueID() == Value::FunctionVal ||
354            V->getValueID() == Value::GlobalVariableVal ||
355            V->getValueID() == Value::GlobalAliasVal;
356   }
357 };
358 
359 } // End llvm namespace
360 
361 #endif
362