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/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/Casting.h"
27#include "llvm/Support/ErrorHandling.h"
28#include "llvm/Support/MD5.h"
29#include <cassert>
30#include <cstdint>
31#include <string>
32
33namespace llvm {
34
35class Comdat;
36class ConstantRange;
37class Error;
38class GlobalObject;
39class Module;
40
41namespace Intrinsic {
42 enum ID : unsigned;
43} // end namespace Intrinsic
44
45class GlobalValue : public Constant {
46public:
47 /// An enumeration for the kinds of linkage for global values.
48 enum LinkageTypes {
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.
60 };
61
62 /// 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
67 };
68
69 /// 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.
74 };
75
76protected:
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), Visibility(DefaultVisibility),
81 UnnamedAddrVal(unsigned(UnnamedAddr::None)),
82 DllStorageClass(DefaultStorageClass), ThreadLocal(NotThreadLocal),
83 HasLLVMReservedName(false), IsDSOLocal(false), IntID((Intrinsic::ID)0U),
84 Parent(nullptr) {
85 setLinkage(Linkage);
86 setName(Name);
87 }
88
89 Type *ValueType;
90
91 static const unsigned GlobalValueSubClassDataBits = 17;
92
93 // All bitfields use unsigned as the underlying type so that MSVC will pack
94 // them.
95 unsigned Linkage : 4; // The linkage of this global
96 unsigned Visibility : 2; // The visibility style of this global
97 unsigned UnnamedAddrVal : 2; // This value's address is not significant
98 unsigned DllStorageClass : 2; // DLL storage class
99
100 unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
101 // the desired model?
102
103 /// True if the function's name starts with "llvm.". This corresponds to the
104 /// value of Function::isIntrinsic(), which may be true even if
105 /// Function::intrinsicID() returns Intrinsic::not_intrinsic.
106 unsigned HasLLVMReservedName : 1;
107
108 /// If true then there is a definition within the same linkage unit and that
109 /// definition cannot be runtime preempted.
110 unsigned IsDSOLocal : 1;
111
112private:
113 // Give subclasses access to what otherwise would be wasted padding.
114 // (17 + 4 + 2 + 2 + 2 + 3 + 1 + 1) == 32.
115 unsigned SubClassData : GlobalValueSubClassDataBits;
116
117 friend class Constant;
118
119 void destroyConstantImpl();
120 Value *handleOperandChangeImpl(Value *From, Value *To);
121
122 /// Returns true if the definition of this global may be replaced by a
123 /// differently optimized variant of the same source level function at link
124 /// time.
125 bool mayBeDerefined() const {
126 switch (getLinkage()) {
127 case WeakODRLinkage:
128 case LinkOnceODRLinkage:
129 case AvailableExternallyLinkage:
130 return true;
131
132 case WeakAnyLinkage:
133 case LinkOnceAnyLinkage:
134 case CommonLinkage:
135 case ExternalWeakLinkage:
136 case ExternalLinkage:
137 case AppendingLinkage:
138 case InternalLinkage:
139 case PrivateLinkage:
140 return isInterposable();
141 }
142
143 llvm_unreachable("Fully covered switch above!");
144 }
145
146 void maybeSetDsoLocal() {
147 if (hasLocalLinkage() ||
148 (!hasDefaultVisibility() && !hasExternalWeakLinkage()))
149 setDSOLocal(true);
150 }
151
152protected:
153 /// The intrinsic ID for this subclass (which must be a Function).
154 ///
155 /// This member is defined by this class, but not used for anything.
156 /// Subclasses can use it to store their intrinsic ID, if they have one.
157 ///
158 /// This is stored here to save space in Function on 64-bit hosts.
159 Intrinsic::ID IntID;
160
161 unsigned getGlobalValueSubClassData() const {
162 return SubClassData;
163 }
164 void setGlobalValueSubClassData(unsigned V) {
165 assert(V < (1 << GlobalValueSubClassDataBits) && "It will not fit");
166 SubClassData = V;
167 }
168
169 Module *Parent; // The containing module.
170
171 // Used by SymbolTableListTraits.
172 void setParent(Module *parent) {
173 Parent = parent;
174 }
175
176 ~GlobalValue() {
177 removeDeadConstantUsers(); // remove any dead constants using this.
178 }
179
180public:
181 enum ThreadLocalMode {
182 NotThreadLocal = 0,
183 GeneralDynamicTLSModel,
184 LocalDynamicTLSModel,
185 InitialExecTLSModel,
186 LocalExecTLSModel
187 };
188
189 GlobalValue(const GlobalValue &) = delete;
190
191 unsigned getAlignment() const;
192 unsigned getAddressSpace() const;
193
194 enum class UnnamedAddr {
195 None,
196 Local,
197 Global,
198 };
199
200 bool hasGlobalUnnamedAddr() const {
201 return getUnnamedAddr() == UnnamedAddr::Global;
202 }
203
204 /// Returns true if this value's address is not significant in this module.
205 /// This attribute is intended to be used only by the code generator and LTO
206 /// to allow the linker to decide whether the global needs to be in the symbol
207 /// table. It should probably not be used in optimizations, as the value may
208 /// have uses outside the module; use hasGlobalUnnamedAddr() instead.
209 bool hasAtLeastLocalUnnamedAddr() const {
210 return getUnnamedAddr() != UnnamedAddr::None;
211 }
212
213 UnnamedAddr getUnnamedAddr() const {
214 return UnnamedAddr(UnnamedAddrVal);
215 }
216 void setUnnamedAddr(UnnamedAddr Val) { UnnamedAddrVal = unsigned(Val); }
217
218 static UnnamedAddr getMinUnnamedAddr(UnnamedAddr A, UnnamedAddr B) {
219 if (A == UnnamedAddr::None || B == UnnamedAddr::None)
220 return UnnamedAddr::None;
221 if (A == UnnamedAddr::Local || B == UnnamedAddr::Local)
222 return UnnamedAddr::Local;
223 return UnnamedAddr::Global;
224 }
225
226 bool hasComdat() const { return getComdat() != nullptr; }
227 const Comdat *getComdat() const;
228 Comdat *getComdat() {
229 return const_cast<Comdat *>(
230 static_cast<const GlobalValue *>(this)->getComdat());
231 }
232
233 VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
234 bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
235 bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
236 bool hasProtectedVisibility() const {
237 return Visibility == ProtectedVisibility;
238 }
239 void setVisibility(VisibilityTypes V) {
240 assert((!hasLocalLinkage() || V == DefaultVisibility) &&
241 "local linkage requires default visibility");
242 Visibility = V;
243 maybeSetDsoLocal();
244 }
245
246 /// If the value is "Thread Local", its value isn't shared by the threads.
247 bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
248 void setThreadLocal(bool Val) {
249 setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
250 }
251 void setThreadLocalMode(ThreadLocalMode Val) {
252 assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
253 ThreadLocal = Val;
254 }
255 ThreadLocalMode getThreadLocalMode() const {
256 return static_cast<ThreadLocalMode>(ThreadLocal);
257 }
258
259 DLLStorageClassTypes getDLLStorageClass() const {
260 return DLLStorageClassTypes(DllStorageClass);
261 }
262 bool hasDLLImportStorageClass() const {
263 return DllStorageClass == DLLImportStorageClass;
264 }
265 bool hasDLLExportStorageClass() const {
266 return DllStorageClass == DLLExportStorageClass;
267 }
268 void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
269
270 bool hasSection() const { return !getSection().empty(); }
271 StringRef getSection() const;
272
273 /// Global values are always pointers.
274 PointerType *getType() const { return cast<PointerType>(User::getType()); }
275
276 Type *getValueType() const { return ValueType; }
277
278 void setDSOLocal(bool Local) { IsDSOLocal = Local; }
279
280 bool isDSOLocal() const {
281 return IsDSOLocal;
282 }
283
284 static LinkageTypes getLinkOnceLinkage(bool ODR) {
285 return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
286 }
287 static LinkageTypes getWeakLinkage(bool ODR) {
288 return ODR ? WeakODRLinkage : WeakAnyLinkage;
289 }
290
291 static bool isExternalLinkage(LinkageTypes Linkage) {
292 return Linkage == ExternalLinkage;
293 }
294 static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
295 return Linkage == AvailableExternallyLinkage;
296 }
297 static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
298 return Linkage == LinkOnceODRLinkage;
299 }
300 static bool isLinkOnceLinkage(LinkageTypes Linkage) {
301 return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
302 }
303 static bool isWeakAnyLinkage(LinkageTypes Linkage) {
304 return Linkage == WeakAnyLinkage;
305 }
306 static bool isWeakODRLinkage(LinkageTypes Linkage) {
307 return Linkage == WeakODRLinkage;
308 }
309 static bool isWeakLinkage(LinkageTypes Linkage) {
310 return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
311 }
312 static bool isAppendingLinkage(LinkageTypes Linkage) {
313 return Linkage == AppendingLinkage;
314 }
315 static bool isInternalLinkage(LinkageTypes Linkage) {
316 return Linkage == InternalLinkage;
317 }
318 static bool isPrivateLinkage(LinkageTypes Linkage) {
319 return Linkage == PrivateLinkage;
320 }
321 static bool isLocalLinkage(LinkageTypes Linkage) {
322 return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
323 }
324 static bool isExternalWeakLinkage(LinkageTypes Linkage) {
325 return Linkage == ExternalWeakLinkage;
326 }
327 static bool isCommonLinkage(LinkageTypes Linkage) {
328 return Linkage == CommonLinkage;
329 }
330 static bool isValidDeclarationLinkage(LinkageTypes Linkage) {
331 return isExternalWeakLinkage(Linkage) || isExternalLinkage(Linkage);
332 }
333
334 /// Whether the definition of this global may be replaced by something
335 /// non-equivalent at link time. For example, if a function has weak linkage
336 /// then the code defining it may be replaced by different code.
337 static bool isInterposableLinkage(LinkageTypes Linkage) {
338 switch (Linkage) {
339 case WeakAnyLinkage:
340 case LinkOnceAnyLinkage:
341 case CommonLinkage:
342 case ExternalWeakLinkage:
343 return true;
344
345 case AvailableExternallyLinkage:
346 case LinkOnceODRLinkage:
347 case WeakODRLinkage:
348 // The above three cannot be overridden but can be de-refined.
349
350 case ExternalLinkage:
351 case AppendingLinkage:
352 case InternalLinkage:
353 case PrivateLinkage:
354 return false;
355 }
356 llvm_unreachable("Fully covered switch above!");
357 }
358
359 /// Whether the definition of this global may be discarded if it is not used
360 /// in its compilation unit.
361 static bool isDiscardableIfUnused(LinkageTypes Linkage) {
362 return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage) ||
363 isAvailableExternallyLinkage(Linkage);
364 }
365
366 /// Whether the definition of this global may be replaced at link time. NB:
367 /// Using this method outside of the code generators is almost always a
368 /// mistake: when working at the IR level use isInterposable instead as it
369 /// knows about ODR semantics.
370 static bool isWeakForLinker(LinkageTypes Linkage) {
371 return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
372 Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
373 Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
374 }
375
376 /// Return true if the currently visible definition of this global (if any) is
377 /// exactly the definition we will see at runtime.
378 ///
379 /// Non-exact linkage types inhibits most non-inlining IPO, since a
380 /// differently optimized variant of the same function can have different
381 /// observable or undefined behavior than in the variant currently visible.
382 /// For instance, we could have started with
383 ///
384 /// void foo(int *v) {
385 /// int t = 5 / v[0];
386 /// (void) t;
387 /// }
388 ///
389 /// and "refined" it to
390 ///
391 /// void foo(int *v) { }
392 ///
393 /// However, we cannot infer readnone for `foo`, since that would justify
394 /// DSE'ing a store to `v[0]` across a call to `foo`, which can cause
395 /// undefined behavior if the linker replaces the actual call destination with
396 /// the unoptimized `foo`.
397 ///
398 /// Inlining is okay across non-exact linkage types as long as they're not
399 /// interposable (see \c isInterposable), since in such cases the currently
400 /// visible variant is *a* correct implementation of the original source
401 /// function; it just isn't the *only* correct implementation.
402 bool isDefinitionExact() const {
403 return !mayBeDerefined();
404 }
405
406 /// Return true if this global has an exact defintion.
407 bool hasExactDefinition() const {
408 // While this computes exactly the same thing as
409 // isStrongDefinitionForLinker, the intended uses are different. This
410 // function is intended to help decide if specific inter-procedural
411 // transforms are correct, while isStrongDefinitionForLinker's intended use
412 // is in low level code generation.
413 return !isDeclaration() && isDefinitionExact();
414 }
415
416 /// Return true if this global's definition can be substituted with an
417 /// *arbitrary* definition at link time. We cannot do any IPO or inlinining
418 /// across interposable call edges, since the callee can be replaced with
419 /// something arbitrary at link time.
420 bool isInterposable() const { return isInterposableLinkage(getLinkage()); }
421
422 bool hasExternalLinkage() const { return isExternalLinkage(getLinkage()); }
423 bool hasAvailableExternallyLinkage() const {
424 return isAvailableExternallyLinkage(getLinkage());
425 }
426 bool hasLinkOnceLinkage() const { return isLinkOnceLinkage(getLinkage()); }
427 bool hasLinkOnceODRLinkage() const {
428 return isLinkOnceODRLinkage(getLinkage());
429 }
430 bool hasWeakLinkage() const { return isWeakLinkage(getLinkage()); }
431 bool hasWeakAnyLinkage() const { return isWeakAnyLinkage(getLinkage()); }
432 bool hasWeakODRLinkage() const { return isWeakODRLinkage(getLinkage()); }
433 bool hasAppendingLinkage() const { return isAppendingLinkage(getLinkage()); }
434 bool hasInternalLinkage() const { return isInternalLinkage(getLinkage()); }
435 bool hasPrivateLinkage() const { return isPrivateLinkage(getLinkage()); }
436 bool hasLocalLinkage() const { return isLocalLinkage(getLinkage()); }
437 bool hasExternalWeakLinkage() const {
438 return isExternalWeakLinkage(getLinkage());
439 }
440 bool hasCommonLinkage() const { return isCommonLinkage(getLinkage()); }
441 bool hasValidDeclarationLinkage() const {
442 return isValidDeclarationLinkage(getLinkage());
443 }
444
445 void setLinkage(LinkageTypes LT) {
446 if (isLocalLinkage(LT))
447 Visibility = DefaultVisibility;
448 Linkage = LT;
449 maybeSetDsoLocal();
450 }
451 LinkageTypes getLinkage() const { return LinkageTypes(Linkage); }
452
453 bool isDiscardableIfUnused() const {
454 return isDiscardableIfUnused(getLinkage());
455 }
456
457 bool isWeakForLinker() const { return isWeakForLinker(getLinkage()); }
458
459protected:
460 /// Copy all additional attributes (those not needed to create a GlobalValue)
461 /// from the GlobalValue Src to this one.
462 void copyAttributesFrom(const GlobalValue *Src);
463
464public:
465 /// If the given string begins with the GlobalValue name mangling escape
466 /// character '\1', drop it.
467 ///
468 /// This function applies a specific mangling that is used in PGO profiles,
469 /// among other things. If you're trying to get a symbol name for an
470 /// arbitrary GlobalValue, this is not the function you're looking for; see
471 /// Mangler.h.
472 static StringRef dropLLVMManglingEscape(StringRef Name) {
473 if (!Name.empty() && Name[0] == '\1')
474 return Name.substr(1);
475 return Name;
476 }
477
478 /// Return the modified name for a global value suitable to be
479 /// used as the key for a global lookup (e.g. profile or ThinLTO).
480 /// The value's original name is \c Name and has linkage of type
481 /// \c Linkage. The value is defined in module \c FileName.
482 static std::string getGlobalIdentifier(StringRef Name,
483 GlobalValue::LinkageTypes Linkage,
484 StringRef FileName);
485
486 /// Return the modified name for this global value suitable to be
487 /// used as the key for a global lookup (e.g. profile or ThinLTO).
488 std::string getGlobalIdentifier() const;
489
490 /// Declare a type to represent a global unique identifier for a global value.
491 /// This is a 64 bits hash that is used by PGO and ThinLTO to have a compact
492 /// unique way to identify a symbol.
493 using GUID = uint64_t;
494
495 /// Return a 64-bit global unique ID constructed from global value name
496 /// (i.e. returned by getGlobalIdentifier()).
497 static GUID getGUID(StringRef GlobalName) { return MD5Hash(GlobalName); }
498
499 /// Return a 64-bit global unique ID constructed from global value name
500 /// (i.e. returned by getGlobalIdentifier()).
501 GUID getGUID() const { return getGUID(getGlobalIdentifier()); }
502
503 /// @name Materialization
504 /// Materialization is used to construct functions only as they're needed.
505 /// This
506 /// is useful to reduce memory usage in LLVM or parsing work done by the
507 /// BitcodeReader to load the Module.
508 /// @{
509
510 /// If this function's Module is being lazily streamed in functions from disk
511 /// or some other source, this method can be used to check to see if the
512 /// function has been read in yet or not.
513 bool isMaterializable() const;
514
515 /// Make sure this GlobalValue is fully read.
516 Error materialize();
517
518/// @}
519
520 /// Return true if the primary definition of this global value is outside of
521 /// the current translation unit.
522 bool isDeclaration() const;
523
524 bool isDeclarationForLinker() const {
525 if (hasAvailableExternallyLinkage())
526 return true;
527
528 return isDeclaration();
529 }
530
531 /// Returns true if this global's definition will be the one chosen by the
532 /// linker.
533 ///
534 /// NB! Ideally this should not be used at the IR level at all. If you're
535 /// interested in optimization constraints implied by the linker's ability to
536 /// choose an implementation, prefer using \c hasExactDefinition.
537 bool isStrongDefinitionForLinker() const {
538 return !(isDeclarationForLinker() || isWeakForLinker());
539 }
540
541 // Returns true if the alignment of the value can be unilaterally
542 // increased.
543 bool canIncreaseAlignment() const;
544
545 const GlobalObject *getBaseObject() const;
546 GlobalObject *getBaseObject() {
547 return const_cast<GlobalObject *>(
548 static_cast<const GlobalValue *>(this)->getBaseObject());
549 }
550
551 /// Returns whether this is a reference to an absolute symbol.
552 bool isAbsoluteSymbolRef() const;
553
554 /// If this is an absolute symbol reference, returns the range of the symbol,
555 /// otherwise returns None.
556 Optional<ConstantRange> getAbsoluteSymbolRange() const;
557
558 /// This method unlinks 'this' from the containing module, but does not delete
559 /// it.
560 void removeFromParent();
561
562 /// This method unlinks 'this' from the containing module and deletes it.
563 void eraseFromParent();
564
565 /// Get the module that this global value is contained inside of...
566 Module *getParent() { return Parent; }
567 const Module *getParent() const { return Parent; }
568
569 // Methods for support type inquiry through isa, cast, and dyn_cast:
570 static bool classof(const Value *V) {
571 return V->getValueID() == Value::FunctionVal ||
572 V->getValueID() == Value::GlobalVariableVal ||
573 V->getValueID() == Value::GlobalAliasVal ||
574 V->getValueID() == Value::GlobalIFuncVal;
575 }
576
577 /// True if GV can be left out of the object symbol table. This is the case
578 /// for linkonce_odr values whose address is not significant. While legal, it
579 /// is not normally profitable to omit them from the .o symbol table. Using
580 /// this analysis makes sense when the information can be passed down to the
581 /// linker or we are in LTO.
582 bool canBeOmittedFromSymbolTable() const;
583};
584
585} // end namespace llvm
586
587#endif // LLVM_IR_GLOBALVALUE_H
588