xref: /freebsd/contrib/llvm-project/llvm/lib/Linker/LinkModules.cpp (revision e6bfd18d21b225af6a0ed67ceeaf1293b7b9eba5)
1 //===- lib/Linker/LinkModules.cpp - Module Linker Implementation ----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the LLVM module linker.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "LinkDiagnosticInfo.h"
14 #include "llvm-c/Linker.h"
15 #include "llvm/ADT/SetVector.h"
16 #include "llvm/IR/Comdat.h"
17 #include "llvm/IR/GlobalValue.h"
18 #include "llvm/IR/LLVMContext.h"
19 #include "llvm/IR/Module.h"
20 #include "llvm/Linker/Linker.h"
21 #include "llvm/Support/Error.h"
22 using namespace llvm;
23 
24 namespace {
25 
26 enum class LinkFrom { Dst, Src, Both };
27 
28 /// This is an implementation class for the LinkModules function, which is the
29 /// entrypoint for this file.
30 class ModuleLinker {
31   IRMover &Mover;
32   std::unique_ptr<Module> SrcM;
33 
34   SetVector<GlobalValue *> ValuesToLink;
35 
36   /// For symbol clashes, prefer those from Src.
37   unsigned Flags;
38 
39   /// List of global value names that should be internalized.
40   StringSet<> Internalize;
41 
42   /// Function that will perform the actual internalization. The reason for a
43   /// callback is that the linker cannot call internalizeModule without
44   /// creating a circular dependency between IPO and the linker.
45   std::function<void(Module &, const StringSet<> &)> InternalizeCallback;
46 
47   /// Used as the callback for lazy linking.
48   /// The mover has just hit GV and we have to decide if it, and other members
49   /// of the same comdat, should be linked. Every member to be linked is passed
50   /// to Add.
51   void addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add);
52 
53   bool shouldOverrideFromSrc() { return Flags & Linker::OverrideFromSrc; }
54   bool shouldLinkOnlyNeeded() { return Flags & Linker::LinkOnlyNeeded; }
55 
56   bool shouldLinkFromSource(bool &LinkFromSrc, const GlobalValue &Dest,
57                             const GlobalValue &Src);
58 
59   /// Should we have mover and linker error diag info?
60   bool emitError(const Twine &Message) {
61     SrcM->getContext().diagnose(LinkDiagnosticInfo(DS_Error, Message));
62     return true;
63   }
64 
65   bool getComdatLeader(Module &M, StringRef ComdatName,
66                        const GlobalVariable *&GVar);
67   bool computeResultingSelectionKind(StringRef ComdatName,
68                                      Comdat::SelectionKind Src,
69                                      Comdat::SelectionKind Dst,
70                                      Comdat::SelectionKind &Result,
71                                      LinkFrom &From);
72   DenseMap<const Comdat *, std::pair<Comdat::SelectionKind, LinkFrom>>
73       ComdatsChosen;
74   bool getComdatResult(const Comdat *SrcC, Comdat::SelectionKind &SK,
75                        LinkFrom &From);
76   // Keep track of the lazy linked global members of each comdat in source.
77   DenseMap<const Comdat *, std::vector<GlobalValue *>> LazyComdatMembers;
78 
79   /// Given a global in the source module, return the global in the
80   /// destination module that is being linked to, if any.
81   GlobalValue *getLinkedToGlobal(const GlobalValue *SrcGV) {
82     Module &DstM = Mover.getModule();
83     // If the source has no name it can't link.  If it has local linkage,
84     // there is no name match-up going on.
85     if (!SrcGV->hasName() || GlobalValue::isLocalLinkage(SrcGV->getLinkage()))
86       return nullptr;
87 
88     // Otherwise see if we have a match in the destination module's symtab.
89     GlobalValue *DGV = DstM.getNamedValue(SrcGV->getName());
90     if (!DGV)
91       return nullptr;
92 
93     // If we found a global with the same name in the dest module, but it has
94     // internal linkage, we are really not doing any linkage here.
95     if (DGV->hasLocalLinkage())
96       return nullptr;
97 
98     // Otherwise, we do in fact link to the destination global.
99     return DGV;
100   }
101 
102   /// Drop GV if it is a member of a comdat that we are dropping.
103   /// This can happen with COFF's largest selection kind.
104   void dropReplacedComdat(GlobalValue &GV,
105                           const DenseSet<const Comdat *> &ReplacedDstComdats);
106 
107   bool linkIfNeeded(GlobalValue &GV, SmallVectorImpl<GlobalValue *> &GVToClone);
108 
109 public:
110   ModuleLinker(IRMover &Mover, std::unique_ptr<Module> SrcM, unsigned Flags,
111                std::function<void(Module &, const StringSet<> &)>
112                    InternalizeCallback = {})
113       : Mover(Mover), SrcM(std::move(SrcM)), Flags(Flags),
114         InternalizeCallback(std::move(InternalizeCallback)) {}
115 
116   bool run();
117 };
118 } // namespace
119 
120 static GlobalValue::VisibilityTypes
121 getMinVisibility(GlobalValue::VisibilityTypes A,
122                  GlobalValue::VisibilityTypes B) {
123   if (A == GlobalValue::HiddenVisibility || B == GlobalValue::HiddenVisibility)
124     return GlobalValue::HiddenVisibility;
125   if (A == GlobalValue::ProtectedVisibility ||
126       B == GlobalValue::ProtectedVisibility)
127     return GlobalValue::ProtectedVisibility;
128   return GlobalValue::DefaultVisibility;
129 }
130 
131 bool ModuleLinker::getComdatLeader(Module &M, StringRef ComdatName,
132                                    const GlobalVariable *&GVar) {
133   const GlobalValue *GVal = M.getNamedValue(ComdatName);
134   if (const auto *GA = dyn_cast_or_null<GlobalAlias>(GVal)) {
135     GVal = GA->getAliaseeObject();
136     if (!GVal)
137       // We cannot resolve the size of the aliasee yet.
138       return emitError("Linking COMDATs named '" + ComdatName +
139                        "': COMDAT key involves incomputable alias size.");
140   }
141 
142   GVar = dyn_cast_or_null<GlobalVariable>(GVal);
143   if (!GVar)
144     return emitError(
145         "Linking COMDATs named '" + ComdatName +
146         "': GlobalVariable required for data dependent selection!");
147 
148   return false;
149 }
150 
151 bool ModuleLinker::computeResultingSelectionKind(StringRef ComdatName,
152                                                  Comdat::SelectionKind Src,
153                                                  Comdat::SelectionKind Dst,
154                                                  Comdat::SelectionKind &Result,
155                                                  LinkFrom &From) {
156   Module &DstM = Mover.getModule();
157   // The ability to mix Comdat::SelectionKind::Any with
158   // Comdat::SelectionKind::Largest is a behavior that comes from COFF.
159   bool DstAnyOrLargest = Dst == Comdat::SelectionKind::Any ||
160                          Dst == Comdat::SelectionKind::Largest;
161   bool SrcAnyOrLargest = Src == Comdat::SelectionKind::Any ||
162                          Src == Comdat::SelectionKind::Largest;
163   if (DstAnyOrLargest && SrcAnyOrLargest) {
164     if (Dst == Comdat::SelectionKind::Largest ||
165         Src == Comdat::SelectionKind::Largest)
166       Result = Comdat::SelectionKind::Largest;
167     else
168       Result = Comdat::SelectionKind::Any;
169   } else if (Src == Dst) {
170     Result = Dst;
171   } else {
172     return emitError("Linking COMDATs named '" + ComdatName +
173                      "': invalid selection kinds!");
174   }
175 
176   switch (Result) {
177   case Comdat::SelectionKind::Any:
178     // Go with Dst.
179     From = LinkFrom::Dst;
180     break;
181   case Comdat::SelectionKind::NoDeduplicate:
182     From = LinkFrom::Both;
183     break;
184   case Comdat::SelectionKind::ExactMatch:
185   case Comdat::SelectionKind::Largest:
186   case Comdat::SelectionKind::SameSize: {
187     const GlobalVariable *DstGV;
188     const GlobalVariable *SrcGV;
189     if (getComdatLeader(DstM, ComdatName, DstGV) ||
190         getComdatLeader(*SrcM, ComdatName, SrcGV))
191       return true;
192 
193     const DataLayout &DstDL = DstM.getDataLayout();
194     const DataLayout &SrcDL = SrcM->getDataLayout();
195     uint64_t DstSize = DstDL.getTypeAllocSize(DstGV->getValueType());
196     uint64_t SrcSize = SrcDL.getTypeAllocSize(SrcGV->getValueType());
197     if (Result == Comdat::SelectionKind::ExactMatch) {
198       if (SrcGV->getInitializer() != DstGV->getInitializer())
199         return emitError("Linking COMDATs named '" + ComdatName +
200                          "': ExactMatch violated!");
201       From = LinkFrom::Dst;
202     } else if (Result == Comdat::SelectionKind::Largest) {
203       From = SrcSize > DstSize ? LinkFrom::Src : LinkFrom::Dst;
204     } else if (Result == Comdat::SelectionKind::SameSize) {
205       if (SrcSize != DstSize)
206         return emitError("Linking COMDATs named '" + ComdatName +
207                          "': SameSize violated!");
208       From = LinkFrom::Dst;
209     } else {
210       llvm_unreachable("unknown selection kind");
211     }
212     break;
213   }
214   }
215 
216   return false;
217 }
218 
219 bool ModuleLinker::getComdatResult(const Comdat *SrcC,
220                                    Comdat::SelectionKind &Result,
221                                    LinkFrom &From) {
222   Module &DstM = Mover.getModule();
223   Comdat::SelectionKind SSK = SrcC->getSelectionKind();
224   StringRef ComdatName = SrcC->getName();
225   Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
226   Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(ComdatName);
227 
228   if (DstCI == ComdatSymTab.end()) {
229     // Use the comdat if it is only available in one of the modules.
230     From = LinkFrom::Src;
231     Result = SSK;
232     return false;
233   }
234 
235   const Comdat *DstC = &DstCI->second;
236   Comdat::SelectionKind DSK = DstC->getSelectionKind();
237   return computeResultingSelectionKind(ComdatName, SSK, DSK, Result, From);
238 }
239 
240 bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
241                                         const GlobalValue &Dest,
242                                         const GlobalValue &Src) {
243 
244   // Should we unconditionally use the Src?
245   if (shouldOverrideFromSrc()) {
246     LinkFromSrc = true;
247     return false;
248   }
249 
250   // We always have to add Src if it has appending linkage.
251   if (Src.hasAppendingLinkage() || Dest.hasAppendingLinkage()) {
252     LinkFromSrc = true;
253     return false;
254   }
255 
256   bool SrcIsDeclaration = Src.isDeclarationForLinker();
257   bool DestIsDeclaration = Dest.isDeclarationForLinker();
258 
259   if (SrcIsDeclaration) {
260     // If Src is external or if both Src & Dest are external..  Just link the
261     // external globals, we aren't adding anything.
262     if (Src.hasDLLImportStorageClass()) {
263       // If one of GVs is marked as DLLImport, result should be dllimport'ed.
264       LinkFromSrc = DestIsDeclaration;
265       return false;
266     }
267     // If the Dest is weak, use the source linkage.
268     if (Dest.hasExternalWeakLinkage()) {
269       LinkFromSrc = true;
270       return false;
271     }
272     // Link an available_externally over a declaration.
273     LinkFromSrc = !Src.isDeclaration() && Dest.isDeclaration();
274     return false;
275   }
276 
277   if (DestIsDeclaration) {
278     // If Dest is external but Src is not:
279     LinkFromSrc = true;
280     return false;
281   }
282 
283   if (Src.hasCommonLinkage()) {
284     if (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage()) {
285       LinkFromSrc = true;
286       return false;
287     }
288 
289     if (!Dest.hasCommonLinkage()) {
290       LinkFromSrc = false;
291       return false;
292     }
293 
294     const DataLayout &DL = Dest.getParent()->getDataLayout();
295     uint64_t DestSize = DL.getTypeAllocSize(Dest.getValueType());
296     uint64_t SrcSize = DL.getTypeAllocSize(Src.getValueType());
297     LinkFromSrc = SrcSize > DestSize;
298     return false;
299   }
300 
301   if (Src.isWeakForLinker()) {
302     assert(!Dest.hasExternalWeakLinkage());
303     assert(!Dest.hasAvailableExternallyLinkage());
304 
305     if (Dest.hasLinkOnceLinkage() && Src.hasWeakLinkage()) {
306       LinkFromSrc = true;
307       return false;
308     }
309 
310     LinkFromSrc = false;
311     return false;
312   }
313 
314   if (Dest.isWeakForLinker()) {
315     assert(Src.hasExternalLinkage());
316     LinkFromSrc = true;
317     return false;
318   }
319 
320   assert(!Src.hasExternalWeakLinkage());
321   assert(!Dest.hasExternalWeakLinkage());
322   assert(Dest.hasExternalLinkage() && Src.hasExternalLinkage() &&
323          "Unexpected linkage type!");
324   return emitError("Linking globals named '" + Src.getName() +
325                    "': symbol multiply defined!");
326 }
327 
328 bool ModuleLinker::linkIfNeeded(GlobalValue &GV,
329                                 SmallVectorImpl<GlobalValue *> &GVToClone) {
330   GlobalValue *DGV = getLinkedToGlobal(&GV);
331 
332   if (shouldLinkOnlyNeeded()) {
333     // Always import variables with appending linkage.
334     if (!GV.hasAppendingLinkage()) {
335       // Don't import globals unless they are referenced by the destination
336       // module.
337       if (!DGV)
338         return false;
339       // Don't import globals that are already defined in the destination module
340       if (!DGV->isDeclaration())
341         return false;
342     }
343   }
344 
345   if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
346     auto *DGVar = dyn_cast<GlobalVariable>(DGV);
347     auto *SGVar = dyn_cast<GlobalVariable>(&GV);
348     if (DGVar && SGVar) {
349       if (DGVar->isDeclaration() && SGVar->isDeclaration() &&
350           (!DGVar->isConstant() || !SGVar->isConstant())) {
351         DGVar->setConstant(false);
352         SGVar->setConstant(false);
353       }
354       if (DGVar->hasCommonLinkage() && SGVar->hasCommonLinkage()) {
355         MaybeAlign Align(
356             std::max(DGVar->getAlignment(), SGVar->getAlignment()));
357         SGVar->setAlignment(Align);
358         DGVar->setAlignment(Align);
359       }
360     }
361 
362     GlobalValue::VisibilityTypes Visibility =
363         getMinVisibility(DGV->getVisibility(), GV.getVisibility());
364     DGV->setVisibility(Visibility);
365     GV.setVisibility(Visibility);
366 
367     GlobalValue::UnnamedAddr UnnamedAddr = GlobalValue::getMinUnnamedAddr(
368         DGV->getUnnamedAddr(), GV.getUnnamedAddr());
369     DGV->setUnnamedAddr(UnnamedAddr);
370     GV.setUnnamedAddr(UnnamedAddr);
371   }
372 
373   if (!DGV && !shouldOverrideFromSrc() &&
374       (GV.hasLocalLinkage() || GV.hasLinkOnceLinkage() ||
375        GV.hasAvailableExternallyLinkage()))
376     return false;
377 
378   if (GV.isDeclaration())
379     return false;
380 
381   LinkFrom ComdatFrom = LinkFrom::Dst;
382   if (const Comdat *SC = GV.getComdat()) {
383     std::tie(std::ignore, ComdatFrom) = ComdatsChosen[SC];
384     if (ComdatFrom == LinkFrom::Dst)
385       return false;
386   }
387 
388   bool LinkFromSrc = true;
389   if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, GV))
390     return true;
391   if (DGV && ComdatFrom == LinkFrom::Both)
392     GVToClone.push_back(LinkFromSrc ? DGV : &GV);
393   if (LinkFromSrc)
394     ValuesToLink.insert(&GV);
395   return false;
396 }
397 
398 void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
399   // Add these to the internalize list
400   if (!GV.hasLinkOnceLinkage() && !GV.hasAvailableExternallyLinkage() &&
401       !shouldLinkOnlyNeeded())
402     return;
403 
404   if (InternalizeCallback)
405     Internalize.insert(GV.getName());
406   Add(GV);
407 
408   const Comdat *SC = GV.getComdat();
409   if (!SC)
410     return;
411   for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
412     GlobalValue *DGV = getLinkedToGlobal(GV2);
413     bool LinkFromSrc = true;
414     if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
415       return;
416     if (!LinkFromSrc)
417       continue;
418     if (InternalizeCallback)
419       Internalize.insert(GV2->getName());
420     Add(*GV2);
421   }
422 }
423 
424 void ModuleLinker::dropReplacedComdat(
425     GlobalValue &GV, const DenseSet<const Comdat *> &ReplacedDstComdats) {
426   Comdat *C = GV.getComdat();
427   if (!C)
428     return;
429   if (!ReplacedDstComdats.count(C))
430     return;
431   if (GV.use_empty()) {
432     GV.eraseFromParent();
433     return;
434   }
435 
436   if (auto *F = dyn_cast<Function>(&GV)) {
437     F->deleteBody();
438   } else if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
439     Var->setInitializer(nullptr);
440   } else {
441     auto &Alias = cast<GlobalAlias>(GV);
442     Module &M = *Alias.getParent();
443     GlobalValue *Declaration;
444     if (auto *FTy = dyn_cast<FunctionType>(Alias.getValueType())) {
445       Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage, "", &M);
446     } else {
447       Declaration =
448           new GlobalVariable(M, Alias.getValueType(), /*isConstant*/ false,
449                              GlobalValue::ExternalLinkage,
450                              /*Initializer*/ nullptr);
451     }
452     Declaration->takeName(&Alias);
453     Alias.replaceAllUsesWith(Declaration);
454     Alias.eraseFromParent();
455   }
456 }
457 
458 bool ModuleLinker::run() {
459   Module &DstM = Mover.getModule();
460   DenseSet<const Comdat *> ReplacedDstComdats;
461 
462   for (const auto &SMEC : SrcM->getComdatSymbolTable()) {
463     const Comdat &C = SMEC.getValue();
464     if (ComdatsChosen.count(&C))
465       continue;
466     Comdat::SelectionKind SK;
467     LinkFrom From;
468     if (getComdatResult(&C, SK, From))
469       return true;
470     ComdatsChosen[&C] = std::make_pair(SK, From);
471 
472     if (From != LinkFrom::Src)
473       continue;
474 
475     Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
476     Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(C.getName());
477     if (DstCI == ComdatSymTab.end())
478       continue;
479 
480     // The source comdat is replacing the dest one.
481     const Comdat *DstC = &DstCI->second;
482     ReplacedDstComdats.insert(DstC);
483   }
484 
485   // Alias have to go first, since we are not able to find their comdats
486   // otherwise.
487   for (GlobalAlias &GV : llvm::make_early_inc_range(DstM.aliases()))
488     dropReplacedComdat(GV, ReplacedDstComdats);
489 
490   for (GlobalVariable &GV : llvm::make_early_inc_range(DstM.globals()))
491     dropReplacedComdat(GV, ReplacedDstComdats);
492 
493   for (Function &GV : llvm::make_early_inc_range(DstM))
494     dropReplacedComdat(GV, ReplacedDstComdats);
495 
496   for (GlobalVariable &GV : SrcM->globals())
497     if (GV.hasLinkOnceLinkage())
498       if (const Comdat *SC = GV.getComdat())
499         LazyComdatMembers[SC].push_back(&GV);
500 
501   for (Function &SF : *SrcM)
502     if (SF.hasLinkOnceLinkage())
503       if (const Comdat *SC = SF.getComdat())
504         LazyComdatMembers[SC].push_back(&SF);
505 
506   for (GlobalAlias &GA : SrcM->aliases())
507     if (GA.hasLinkOnceLinkage())
508       if (const Comdat *SC = GA.getComdat())
509         LazyComdatMembers[SC].push_back(&GA);
510 
511   // Insert all of the globals in src into the DstM module... without linking
512   // initializers (which could refer to functions not yet mapped over).
513   SmallVector<GlobalValue *, 0> GVToClone;
514   for (GlobalVariable &GV : SrcM->globals())
515     if (linkIfNeeded(GV, GVToClone))
516       return true;
517 
518   for (Function &SF : *SrcM)
519     if (linkIfNeeded(SF, GVToClone))
520       return true;
521 
522   for (GlobalAlias &GA : SrcM->aliases())
523     if (linkIfNeeded(GA, GVToClone))
524       return true;
525 
526   for (GlobalIFunc &GI : SrcM->ifuncs())
527     if (linkIfNeeded(GI, GVToClone))
528       return true;
529 
530   // For a variable in a comdat nodeduplicate, its initializer should be
531   // preserved (its content may be implicitly used by other members) even if
532   // symbol resolution does not pick it. Clone it into an unnamed private
533   // variable.
534   for (GlobalValue *GV : GVToClone) {
535     if (auto *Var = dyn_cast<GlobalVariable>(GV)) {
536       auto *NewVar = new GlobalVariable(*Var->getParent(), Var->getValueType(),
537                                         Var->isConstant(), Var->getLinkage(),
538                                         Var->getInitializer());
539       NewVar->copyAttributesFrom(Var);
540       NewVar->setVisibility(GlobalValue::DefaultVisibility);
541       NewVar->setLinkage(GlobalValue::PrivateLinkage);
542       NewVar->setDSOLocal(true);
543       NewVar->setComdat(Var->getComdat());
544       if (Var->getParent() != &Mover.getModule())
545         ValuesToLink.insert(NewVar);
546     } else {
547       emitError("linking '" + GV->getName() +
548                 "': non-variables in comdat nodeduplicate are not handled");
549     }
550   }
551 
552   for (unsigned I = 0; I < ValuesToLink.size(); ++I) {
553     GlobalValue *GV = ValuesToLink[I];
554     const Comdat *SC = GV->getComdat();
555     if (!SC)
556       continue;
557     for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
558       GlobalValue *DGV = getLinkedToGlobal(GV2);
559       bool LinkFromSrc = true;
560       if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
561         return true;
562       if (LinkFromSrc)
563         ValuesToLink.insert(GV2);
564     }
565   }
566 
567   if (InternalizeCallback) {
568     for (GlobalValue *GV : ValuesToLink)
569       Internalize.insert(GV->getName());
570   }
571 
572   // FIXME: Propagate Errors through to the caller instead of emitting
573   // diagnostics.
574   bool HasErrors = false;
575   if (Error E =
576           Mover.move(std::move(SrcM), ValuesToLink.getArrayRef(),
577                      IRMover::LazyCallback(
578                          [this](GlobalValue &GV, IRMover::ValueAdder Add) {
579                            addLazyFor(GV, Add);
580                          }),
581                      /* IsPerformingImport */ false)) {
582     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
583       DstM.getContext().diagnose(LinkDiagnosticInfo(DS_Error, EIB.message()));
584       HasErrors = true;
585     });
586   }
587   if (HasErrors)
588     return true;
589 
590   if (InternalizeCallback)
591     InternalizeCallback(DstM, Internalize);
592 
593   return false;
594 }
595 
596 Linker::Linker(Module &M) : Mover(M) {}
597 
598 bool Linker::linkInModule(
599     std::unique_ptr<Module> Src, unsigned Flags,
600     std::function<void(Module &, const StringSet<> &)> InternalizeCallback) {
601   ModuleLinker ModLinker(Mover, std::move(Src), Flags,
602                          std::move(InternalizeCallback));
603   return ModLinker.run();
604 }
605 
606 //===----------------------------------------------------------------------===//
607 // LinkModules entrypoint.
608 //===----------------------------------------------------------------------===//
609 
610 /// This function links two modules together, with the resulting Dest module
611 /// modified to be the composite of the two input modules. If an error occurs,
612 /// true is returned and ErrorMsg (if not null) is set to indicate the problem.
613 /// Upon failure, the Dest module could be in a modified state, and shouldn't be
614 /// relied on to be consistent.
615 bool Linker::linkModules(
616     Module &Dest, std::unique_ptr<Module> Src, unsigned Flags,
617     std::function<void(Module &, const StringSet<> &)> InternalizeCallback) {
618   Linker L(Dest);
619   return L.linkInModule(std::move(Src), Flags, std::move(InternalizeCallback));
620 }
621 
622 //===----------------------------------------------------------------------===//
623 // C API.
624 //===----------------------------------------------------------------------===//
625 
626 LLVMBool LLVMLinkModules2(LLVMModuleRef Dest, LLVMModuleRef Src) {
627   Module *D = unwrap(Dest);
628   std::unique_ptr<Module> M(unwrap(Src));
629   return Linker::linkModules(*D, std::move(M));
630 }
631