1 //===-- llvm/GlobalValue.h - Class to represent a global value --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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
16 //===----------------------------------------------------------------------===//
18 #ifndef LLVM_IR_GLOBALVALUE_H
19 #define LLVM_IR_GLOBALVALUE_H
21 #include "llvm/ADT/StringRef.h"
22 #include "llvm/ADT/Twine.h"
23 #include "llvm/IR/Constant.h"
24 #include "llvm/IR/DerivedTypes.h"
25 #include "llvm/IR/Value.h"
26 #include "llvm/Support/MD5.h"
27 #include "llvm/Support/Casting.h"
28 #include "llvm/Support/ErrorHandling.h"
43 } // end namespace Intrinsic
45 class GlobalValue : public Constant {
47 /// @brief An enumeration for the kinds of linkage for global values.
49 ExternalLinkage = 0,///< Externally visible function
50 AvailableExternallyLinkage, ///< Available for inspection, not emission.
51 LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
52 LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
53 WeakAnyLinkage, ///< Keep one copy of named function when linking (weak)
54 WeakODRLinkage, ///< Same, but only replaced by something equivalent.
55 AppendingLinkage, ///< Special purpose, only applies to global arrays
56 InternalLinkage, ///< Rename collisions when linking (static functions).
57 PrivateLinkage, ///< Like Internal, but omit from symbol table.
58 ExternalWeakLinkage,///< ExternalWeak linkage description.
59 CommonLinkage ///< Tentative definitions.
62 /// @brief An enumeration for the kinds of visibility of global values.
63 enum VisibilityTypes {
64 DefaultVisibility = 0, ///< The GV is visible
65 HiddenVisibility, ///< The GV is hidden
66 ProtectedVisibility ///< The GV is protected
69 /// @brief Storage classes of global values for PE targets.
70 enum DLLStorageClassTypes {
71 DefaultStorageClass = 0,
72 DLLImportStorageClass = 1, ///< Function to be imported from DLL
73 DLLExportStorageClass = 2 ///< Function to be accessible from DLL.
77 GlobalValue(Type *Ty, ValueTy VTy, Use *Ops, unsigned NumOps,
78 LinkageTypes Linkage, const Twine &Name, unsigned AddressSpace)
79 : Constant(PointerType::get(Ty, AddressSpace), VTy, Ops, NumOps),
80 ValueType(Ty), Linkage(Linkage), Visibility(DefaultVisibility),
81 UnnamedAddrVal(unsigned(UnnamedAddr::None)),
82 DllStorageClass(DefaultStorageClass), ThreadLocal(NotThreadLocal),
83 HasLLVMReservedName(false), IntID((Intrinsic::ID)0U), Parent(nullptr) {
89 static const unsigned GlobalValueSubClassDataBits = 18;
91 // All bitfields use unsigned as the underlying type so that MSVC will pack
93 unsigned Linkage : 4; // The linkage of this global
94 unsigned Visibility : 2; // The visibility style of this global
95 unsigned UnnamedAddrVal : 2; // This value's address is not significant
96 unsigned DllStorageClass : 2; // DLL storage class
98 unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
101 /// True if the function's name starts with "llvm.". This corresponds to the
102 /// value of Function::isIntrinsic(), which may be true even if
103 /// Function::intrinsicID() returns Intrinsic::not_intrinsic.
104 unsigned HasLLVMReservedName : 1;
107 friend class Constant;
109 // Give subclasses access to what otherwise would be wasted padding.
110 // (18 + 4 + 2 + 2 + 2 + 3 + 1) == 32.
111 unsigned SubClassData : GlobalValueSubClassDataBits;
113 void destroyConstantImpl();
114 Value *handleOperandChangeImpl(Value *From, Value *To);
116 /// Returns true if the definition of this global may be replaced by a
117 /// differently optimized variant of the same source level function at link
119 bool mayBeDerefined() const {
120 switch (getLinkage()) {
122 case LinkOnceODRLinkage:
123 case AvailableExternallyLinkage:
127 case LinkOnceAnyLinkage:
129 case ExternalWeakLinkage:
130 case ExternalLinkage:
131 case AppendingLinkage:
132 case InternalLinkage:
134 return isInterposable();
137 llvm_unreachable("Fully covered switch above!");
141 /// \brief The intrinsic ID for this subclass (which must be a Function).
143 /// This member is defined by this class, but not used for anything.
144 /// Subclasses can use it to store their intrinsic ID, if they have one.
146 /// This is stored here to save space in Function on 64-bit hosts.
149 unsigned getGlobalValueSubClassData() const {
152 void setGlobalValueSubClassData(unsigned V) {
153 assert(V < (1 << GlobalValueSubClassDataBits) && "It will not fit");
157 Module *Parent; // The containing module.
159 // Used by SymbolTableListTraits.
160 void setParent(Module *parent) {
165 enum ThreadLocalMode {
167 GeneralDynamicTLSModel,
168 LocalDynamicTLSModel,
173 GlobalValue(const GlobalValue &) = delete;
175 ~GlobalValue() override {
176 removeDeadConstantUsers(); // remove any dead constants using this.
179 unsigned getAlignment() const;
181 enum class UnnamedAddr {
187 bool hasGlobalUnnamedAddr() const {
188 return getUnnamedAddr() == UnnamedAddr::Global;
191 /// Returns true if this value's address is not significant in this module.
192 /// This attribute is intended to be used only by the code generator and LTO
193 /// to allow the linker to decide whether the global needs to be in the symbol
194 /// table. It should probably not be used in optimizations, as the value may
195 /// have uses outside the module; use hasGlobalUnnamedAddr() instead.
196 bool hasAtLeastLocalUnnamedAddr() const {
197 return getUnnamedAddr() != UnnamedAddr::None;
200 UnnamedAddr getUnnamedAddr() const {
201 return UnnamedAddr(UnnamedAddrVal);
203 void setUnnamedAddr(UnnamedAddr Val) { UnnamedAddrVal = unsigned(Val); }
205 static UnnamedAddr getMinUnnamedAddr(UnnamedAddr A, UnnamedAddr B) {
206 if (A == UnnamedAddr::None || B == UnnamedAddr::None)
207 return UnnamedAddr::None;
208 if (A == UnnamedAddr::Local || B == UnnamedAddr::Local)
209 return UnnamedAddr::Local;
210 return UnnamedAddr::Global;
213 bool hasComdat() const { return getComdat() != nullptr; }
215 const Comdat *getComdat() const {
216 return const_cast<GlobalValue *>(this)->getComdat();
219 VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
220 bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
221 bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
222 bool hasProtectedVisibility() const {
223 return Visibility == ProtectedVisibility;
225 void setVisibility(VisibilityTypes V) {
226 assert((!hasLocalLinkage() || V == DefaultVisibility) &&
227 "local linkage requires default visibility");
231 /// If the value is "Thread Local", its value isn't shared by the threads.
232 bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
233 void setThreadLocal(bool Val) {
234 setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
236 void setThreadLocalMode(ThreadLocalMode Val) {
237 assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
240 ThreadLocalMode getThreadLocalMode() const {
241 return static_cast<ThreadLocalMode>(ThreadLocal);
244 DLLStorageClassTypes getDLLStorageClass() const {
245 return DLLStorageClassTypes(DllStorageClass);
247 bool hasDLLImportStorageClass() const {
248 return DllStorageClass == DLLImportStorageClass;
250 bool hasDLLExportStorageClass() const {
251 return DllStorageClass == DLLExportStorageClass;
253 void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
255 bool hasSection() const { return !getSection().empty(); }
256 StringRef getSection() const;
258 /// Global values are always pointers.
259 PointerType *getType() const { return cast<PointerType>(User::getType()); }
261 Type *getValueType() const { return ValueType; }
263 static LinkageTypes getLinkOnceLinkage(bool ODR) {
264 return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
266 static LinkageTypes getWeakLinkage(bool ODR) {
267 return ODR ? WeakODRLinkage : WeakAnyLinkage;
270 static bool isExternalLinkage(LinkageTypes Linkage) {
271 return Linkage == ExternalLinkage;
273 static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
274 return Linkage == AvailableExternallyLinkage;
276 static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
277 return Linkage == LinkOnceODRLinkage;
279 static bool isLinkOnceLinkage(LinkageTypes Linkage) {
280 return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
282 static bool isWeakAnyLinkage(LinkageTypes Linkage) {
283 return Linkage == WeakAnyLinkage;
285 static bool isWeakODRLinkage(LinkageTypes Linkage) {
286 return Linkage == WeakODRLinkage;
288 static bool isWeakLinkage(LinkageTypes Linkage) {
289 return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
291 static bool isAppendingLinkage(LinkageTypes Linkage) {
292 return Linkage == AppendingLinkage;
294 static bool isInternalLinkage(LinkageTypes Linkage) {
295 return Linkage == InternalLinkage;
297 static bool isPrivateLinkage(LinkageTypes Linkage) {
298 return Linkage == PrivateLinkage;
300 static bool isLocalLinkage(LinkageTypes Linkage) {
301 return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
303 static bool isExternalWeakLinkage(LinkageTypes Linkage) {
304 return Linkage == ExternalWeakLinkage;
306 static bool isCommonLinkage(LinkageTypes Linkage) {
307 return Linkage == CommonLinkage;
309 static bool isValidDeclarationLinkage(LinkageTypes Linkage) {
310 return isExternalWeakLinkage(Linkage) || isExternalLinkage(Linkage);
313 /// Whether the definition of this global may be replaced by something
314 /// non-equivalent at link time. For example, if a function has weak linkage
315 /// then the code defining it may be replaced by different code.
316 static bool isInterposableLinkage(LinkageTypes Linkage) {
319 case LinkOnceAnyLinkage:
321 case ExternalWeakLinkage:
324 case AvailableExternallyLinkage:
325 case LinkOnceODRLinkage:
327 // The above three cannot be overridden but can be de-refined.
329 case ExternalLinkage:
330 case AppendingLinkage:
331 case InternalLinkage:
335 llvm_unreachable("Fully covered switch above!");
338 /// Whether the definition of this global may be discarded if it is not used
339 /// in its compilation unit.
340 static bool isDiscardableIfUnused(LinkageTypes Linkage) {
341 return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage) ||
342 isAvailableExternallyLinkage(Linkage);
345 /// Whether the definition of this global may be replaced at link time. NB:
346 /// Using this method outside of the code generators is almost always a
347 /// mistake: when working at the IR level use isInterposable instead as it
348 /// knows about ODR semantics.
349 static bool isWeakForLinker(LinkageTypes Linkage) {
350 return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
351 Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
352 Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
355 /// Return true if the currently visible definition of this global (if any) is
356 /// exactly the definition we will see at runtime.
358 /// Non-exact linkage types inhibits most non-inlining IPO, since a
359 /// differently optimized variant of the same function can have different
360 /// observable or undefined behavior than in the variant currently visible.
361 /// For instance, we could have started with
363 /// void foo(int *v) {
364 /// int t = 5 / v[0];
368 /// and "refined" it to
370 /// void foo(int *v) { }
372 /// However, we cannot infer readnone for `foo`, since that would justify
373 /// DSE'ing a store to `v[0]` across a call to `foo`, which can cause
374 /// undefined behavior if the linker replaces the actual call destination with
375 /// the unoptimized `foo`.
377 /// Inlining is okay across non-exact linkage types as long as they're not
378 /// interposable (see \c isInterposable), since in such cases the currently
379 /// visible variant is *a* correct implementation of the original source
380 /// function; it just isn't the *only* correct implementation.
381 bool isDefinitionExact() const {
382 return !mayBeDerefined();
385 /// Return true if this global has an exact defintion.
386 bool hasExactDefinition() const {
387 // While this computes exactly the same thing as
388 // isStrongDefinitionForLinker, the intended uses are different. This
389 // function is intended to help decide if specific inter-procedural
390 // transforms are correct, while isStrongDefinitionForLinker's intended use
391 // is in low level code generation.
392 return !isDeclaration() && isDefinitionExact();
395 /// Return true if this global's definition can be substituted with an
396 /// *arbitrary* definition at link time. We cannot do any IPO or inlinining
397 /// across interposable call edges, since the callee can be replaced with
398 /// something arbitrary at link time.
399 bool isInterposable() const { return isInterposableLinkage(getLinkage()); }
401 bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
402 bool hasAvailableExternallyLinkage() const {
403 return isAvailableExternallyLinkage(getLinkage());
405 bool hasLinkOnceLinkage() const { return isLinkOnceLinkage(getLinkage()); }
406 bool hasLinkOnceODRLinkage() const {
407 return isLinkOnceODRLinkage(getLinkage());
409 bool hasWeakLinkage() const { return isWeakLinkage(getLinkage()); }
410 bool hasWeakAnyLinkage() const { return isWeakAnyLinkage(getLinkage()); }
411 bool hasWeakODRLinkage() const { return isWeakODRLinkage(getLinkage()); }
412 bool hasAppendingLinkage() const { return isAppendingLinkage(getLinkage()); }
413 bool hasInternalLinkage() const { return isInternalLinkage(getLinkage()); }
414 bool hasPrivateLinkage() const { return isPrivateLinkage(getLinkage()); }
415 bool hasLocalLinkage() const { return isLocalLinkage(getLinkage()); }
416 bool hasExternalWeakLinkage() const {
417 return isExternalWeakLinkage(getLinkage());
419 bool hasCommonLinkage() const { return isCommonLinkage(getLinkage()); }
420 bool hasValidDeclarationLinkage() const {
421 return isValidDeclarationLinkage(getLinkage());
424 void setLinkage(LinkageTypes LT) {
425 if (isLocalLinkage(LT))
426 Visibility = DefaultVisibility;
429 LinkageTypes getLinkage() const { return LinkageTypes(Linkage); }
431 bool isDiscardableIfUnused() const {
432 return isDiscardableIfUnused(getLinkage());
435 bool isWeakForLinker() const { return isWeakForLinker(getLinkage()); }
437 /// Copy all additional attributes (those not needed to create a GlobalValue)
438 /// from the GlobalValue Src to this one.
439 virtual void copyAttributesFrom(const GlobalValue *Src);
441 /// If special LLVM prefix that is used to inform the asm printer to not emit
442 /// usual symbol prefix before the symbol name is used then return linkage
443 /// name after skipping this special LLVM prefix.
444 static StringRef getRealLinkageName(StringRef Name) {
445 if (!Name.empty() && Name[0] == '\1')
446 return Name.substr(1);
450 /// Return the modified name for a global value suitable to be
451 /// used as the key for a global lookup (e.g. profile or ThinLTO).
452 /// The value's original name is \c Name and has linkage of type
453 /// \c Linkage. The value is defined in module \c FileName.
454 static std::string getGlobalIdentifier(StringRef Name,
455 GlobalValue::LinkageTypes Linkage,
458 /// Return the modified name for this global value suitable to be
459 /// used as the key for a global lookup (e.g. profile or ThinLTO).
460 std::string getGlobalIdentifier() const;
462 /// Declare a type to represent a global unique identifier for a global value.
463 /// This is a 64 bits hash that is used by PGO and ThinLTO to have a compact
464 /// unique way to identify a symbol.
465 using GUID = uint64_t;
467 /// Return a 64-bit global unique ID constructed from global value name
468 /// (i.e. returned by getGlobalIdentifier()).
469 static GUID getGUID(StringRef GlobalName) { return MD5Hash(GlobalName); }
471 /// Return a 64-bit global unique ID constructed from global value name
472 /// (i.e. returned by getGlobalIdentifier()).
473 GUID getGUID() const { return getGUID(getGlobalIdentifier()); }
475 /// @name Materialization
476 /// Materialization is used to construct functions only as they're needed.
478 /// is useful to reduce memory usage in LLVM or parsing work done by the
479 /// BitcodeReader to load the Module.
482 /// If this function's Module is being lazily streamed in functions from disk
483 /// or some other source, this method can be used to check to see if the
484 /// function has been read in yet or not.
485 bool isMaterializable() const;
487 /// Make sure this GlobalValue is fully read.
492 /// Return true if the primary definition of this global value is outside of
493 /// the current translation unit.
494 bool isDeclaration() const;
496 bool isDeclarationForLinker() const {
497 if (hasAvailableExternallyLinkage())
500 return isDeclaration();
503 /// Returns true if this global's definition will be the one chosen by the
506 /// NB! Ideally this should not be used at the IR level at all. If you're
507 /// interested in optimization constraints implied by the linker's ability to
508 /// choose an implementation, prefer using \c hasExactDefinition.
509 bool isStrongDefinitionForLinker() const {
510 return !(isDeclarationForLinker() || isWeakForLinker());
513 // Returns true if the alignment of the value can be unilaterally
515 bool canIncreaseAlignment() const;
517 const GlobalObject *getBaseObject() const {
518 return const_cast<GlobalValue *>(this)->getBaseObject();
520 GlobalObject *getBaseObject();
522 /// Returns whether this is a reference to an absolute symbol.
523 bool isAbsoluteSymbolRef() const;
525 /// If this is an absolute symbol reference, returns the range of the symbol,
526 /// otherwise returns None.
527 Optional<ConstantRange> getAbsoluteSymbolRange() const;
529 /// This method unlinks 'this' from the containing module, but does not delete
531 virtual void removeFromParent() = 0;
533 /// This method unlinks 'this' from the containing module and deletes it.
534 virtual void eraseFromParent() = 0;
536 /// Get the module that this global value is contained inside of...
537 Module *getParent() { return Parent; }
538 const Module *getParent() const { return Parent; }
540 // Methods for support type inquiry through isa, cast, and dyn_cast:
541 static bool classof(const Value *V) {
542 return V->getValueID() == Value::FunctionVal ||
543 V->getValueID() == Value::GlobalVariableVal ||
544 V->getValueID() == Value::GlobalAliasVal ||
545 V->getValueID() == Value::GlobalIFuncVal;
549 } // end namespace llvm
551 #endif // LLVM_IR_GLOBALVALUE_H