lib/Linker/LinkModules.cpp

   1 //===- lib/Linker/LinkModules.cpp - Module Linker Implementation ----------===//
   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 implements the LLVM module linker.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "LinkDiagnosticInfo.h"
  15 #include "llvm-c/Linker.h"
  16 #include "llvm/ADT/SetVector.h"
  17 #include "llvm/IR/Comdat.h"
  18 #include "llvm/IR/DiagnosticPrinter.h"
  19 #include "llvm/IR/GlobalValue.h"
  20 #include "llvm/IR/LLVMContext.h"
  21 #include "llvm/IR/Module.h"
  22 #include "llvm/Linker/Linker.h"
  23 #include "llvm/Support/Error.h"
  24 using namespace llvm;
  25
  26 namespace {
  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                                      bool &LinkFromSrc);
  72   std::map<const Comdat *, std::pair<Comdat::SelectionKind, bool>>
  73       ComdatsChosen;
  74   bool getComdatResult(const Comdat *SrcC, Comdat::SelectionKind &SK,
  75                        bool &LinkFromSrc);
  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);
 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 }
 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->getBaseObject();
 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                                                  bool &LinkFromSrc) {
 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     LinkFromSrc = false;
 180     break;
 181   case Comdat::SelectionKind::NoDuplicates:
 182     return emitError("Linking COMDATs named '" + ComdatName +
 183                      "': noduplicates has been violated!");
 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       LinkFromSrc = false;
 202     } else if (Result == Comdat::SelectionKind::Largest) {
 203       LinkFromSrc = SrcSize > DstSize;
 204     } else if (Result == Comdat::SelectionKind::SameSize) {
 205       if (SrcSize != DstSize)
 206         return emitError("Linking COMDATs named '" + ComdatName +
 207                          "': SameSize violated!");
 208       LinkFromSrc = false;
 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                                    bool &LinkFromSrc) {
 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     LinkFromSrc = true;
 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,
 238                                        LinkFromSrc);
 239 }
 240
 241 bool ModuleLinker::shouldLinkFromSource(bool &LinkFromSrc,
 242                                         const GlobalValue &Dest,
 243                                         const GlobalValue &Src) {
 244
 245   // Should we unconditionally use the Src?
 246   if (shouldOverrideFromSrc()) {
 247     LinkFromSrc = true;
 248     return false;
 249   }
 250
 251   // We always have to add Src if it has appending linkage.
 252   if (Src.hasAppendingLinkage()) {
 253     LinkFromSrc = true;
 254     return false;
 255   }
 256
 257   bool SrcIsDeclaration = Src.isDeclarationForLinker();
 258   bool DestIsDeclaration = Dest.isDeclarationForLinker();
 259
 260   if (SrcIsDeclaration) {
 261     // If Src is external or if both Src & Dest are external..  Just link the
 262     // external globals, we aren't adding anything.
 263     if (Src.hasDLLImportStorageClass()) {
 264       // If one of GVs is marked as DLLImport, result should be dllimport'ed.
 265       LinkFromSrc = DestIsDeclaration;
 266       return false;
 267     }
 268     // If the Dest is weak, use the source linkage.
 269     if (Dest.hasExternalWeakLinkage()) {
 270       LinkFromSrc = true;
 271       return false;
 272     }
 273     // Link an available_externally over a declaration.
 274     LinkFromSrc = !Src.isDeclaration() && Dest.isDeclaration();
 275     return false;
 276   }
 277
 278   if (DestIsDeclaration) {
 279     // If Dest is external but Src is not:
 280     LinkFromSrc = true;
 281     return false;
 282   }
 283
 284   if (Src.hasCommonLinkage()) {
 285     if (Dest.hasLinkOnceLinkage() || Dest.hasWeakLinkage()) {
 286       LinkFromSrc = true;
 287       return false;
 288     }
 289
 290     if (!Dest.hasCommonLinkage()) {
 291       LinkFromSrc = false;
 292       return false;
 293     }
 294
 295     const DataLayout &DL = Dest.getParent()->getDataLayout();
 296     uint64_t DestSize = DL.getTypeAllocSize(Dest.getValueType());
 297     uint64_t SrcSize = DL.getTypeAllocSize(Src.getValueType());
 298     LinkFromSrc = SrcSize > DestSize;
 299     return false;
 300   }
 301
 302   if (Src.isWeakForLinker()) {
 303     assert(!Dest.hasExternalWeakLinkage());
 304     assert(!Dest.hasAvailableExternallyLinkage());
 305
 306     if (Dest.hasLinkOnceLinkage() && Src.hasWeakLinkage()) {
 307       LinkFromSrc = true;
 308       return false;
 309     }
 310
 311     LinkFromSrc = false;
 312     return false;
 313   }
 314
 315   if (Dest.isWeakForLinker()) {
 316     assert(Src.hasExternalLinkage());
 317     LinkFromSrc = true;
 318     return false;
 319   }
 320
 321   assert(!Src.hasExternalWeakLinkage());
 322   assert(!Dest.hasExternalWeakLinkage());
 323   assert(Dest.hasExternalLinkage() && Src.hasExternalLinkage() &&
 324          "Unexpected linkage type!");
 325   return emitError("Linking globals named '" + Src.getName() +
 326                    "': symbol multiply defined!");
 327 }
 328
 329 bool ModuleLinker::linkIfNeeded(GlobalValue &GV) {
 330   GlobalValue *DGV = getLinkedToGlobal(&GV);
 331
 332   if (shouldLinkOnlyNeeded() && !(DGV && DGV->isDeclaration()))
 333     return false;
 334
 335   if (DGV && !GV.hasLocalLinkage() && !GV.hasAppendingLinkage()) {
 336     auto *DGVar = dyn_cast<GlobalVariable>(DGV);
 337     auto *SGVar = dyn_cast<GlobalVariable>(&GV);
 338     if (DGVar && SGVar) {
 339       if (DGVar->isDeclaration() && SGVar->isDeclaration() &&
 340           (!DGVar->isConstant() || !SGVar->isConstant())) {
 341         DGVar->setConstant(false);
 342         SGVar->setConstant(false);
 343       }
 344       if (DGVar->hasCommonLinkage() && SGVar->hasCommonLinkage()) {
 345         unsigned Align = std::max(DGVar->getAlignment(), SGVar->getAlignment());
 346         SGVar->setAlignment(Align);
 347         DGVar->setAlignment(Align);
 348       }
 349     }
 350
 351     GlobalValue::VisibilityTypes Visibility =
 352         getMinVisibility(DGV->getVisibility(), GV.getVisibility());
 353     DGV->setVisibility(Visibility);
 354     GV.setVisibility(Visibility);
 355
 356     GlobalValue::UnnamedAddr UnnamedAddr = GlobalValue::getMinUnnamedAddr(
 357         DGV->getUnnamedAddr(), GV.getUnnamedAddr());
 358     DGV->setUnnamedAddr(UnnamedAddr);
 359     GV.setUnnamedAddr(UnnamedAddr);
 360   }
 361
 362   if (!DGV && !shouldOverrideFromSrc() &&
 363       (GV.hasLocalLinkage() || GV.hasLinkOnceLinkage() ||
 364        GV.hasAvailableExternallyLinkage()))
 365     return false;
 366
 367   if (GV.isDeclaration())
 368     return false;
 369
 370   if (const Comdat *SC = GV.getComdat()) {
 371     bool LinkFromSrc;
 372     Comdat::SelectionKind SK;
 373     std::tie(SK, LinkFromSrc) = ComdatsChosen[SC];
 374     if (!LinkFromSrc)
 375       return false;
 376   }
 377
 378   bool LinkFromSrc = true;
 379   if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, GV))
 380     return true;
 381   if (LinkFromSrc)
 382     ValuesToLink.insert(&GV);
 383   return false;
 384 }
 385
 386 void ModuleLinker::addLazyFor(GlobalValue &GV, const IRMover::ValueAdder &Add) {
 387   // Add these to the internalize list
 388   if (!GV.hasLinkOnceLinkage() && !GV.hasAvailableExternallyLinkage() &&
 389       !shouldLinkOnlyNeeded())
 390     return;
 391
 392   if (InternalizeCallback)
 393     Internalize.insert(GV.getName());
 394   Add(GV);
 395
 396   const Comdat *SC = GV.getComdat();
 397   if (!SC)
 398     return;
 399   for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
 400     GlobalValue *DGV = getLinkedToGlobal(GV2);
 401     bool LinkFromSrc = true;
 402     if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
 403       return;
 404     if (!LinkFromSrc)
 405       continue;
 406     if (InternalizeCallback)
 407       Internalize.insert(GV2->getName());
 408     Add(*GV2);
 409   }
 410 }
 411
 412 void ModuleLinker::dropReplacedComdat(
 413     GlobalValue &GV, const DenseSet<const Comdat *> &ReplacedDstComdats) {
 414   Comdat *C = GV.getComdat();
 415   if (!C)
 416     return;
 417   if (!ReplacedDstComdats.count(C))
 418     return;
 419   if (GV.use_empty()) {
 420     GV.eraseFromParent();
 421     return;
 422   }
 423
 424   if (auto *F = dyn_cast<Function>(&GV)) {
 425     F->deleteBody();
 426   } else if (auto *Var = dyn_cast<GlobalVariable>(&GV)) {
 427     Var->setInitializer(nullptr);
 428   } else {
 429     auto &Alias = cast<GlobalAlias>(GV);
 430     Module &M = *Alias.getParent();
 431     PointerType &Ty = *cast<PointerType>(Alias.getType());
 432     GlobalValue *Declaration;
 433     if (auto *FTy = dyn_cast<FunctionType>(Alias.getValueType())) {
 434       Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage, "", &M);
 435     } else {
 436       Declaration =
 437           new GlobalVariable(M, Ty.getElementType(), /*isConstant*/ false,
 438                              GlobalValue::ExternalLinkage,
 439                              /*Initializer*/ nullptr);
 440     }
 441     Declaration->takeName(&Alias);
 442     Alias.replaceAllUsesWith(Declaration);
 443     Alias.eraseFromParent();
 444   }
 445 }
 446
 447 bool ModuleLinker::run() {
 448   Module &DstM = Mover.getModule();
 449   DenseSet<const Comdat *> ReplacedDstComdats;
 450
 451   for (const auto &SMEC : SrcM->getComdatSymbolTable()) {
 452     const Comdat &C = SMEC.getValue();
 453     if (ComdatsChosen.count(&C))
 454       continue;
 455     Comdat::SelectionKind SK;
 456     bool LinkFromSrc;
 457     if (getComdatResult(&C, SK, LinkFromSrc))
 458       return true;
 459     ComdatsChosen[&C] = std::make_pair(SK, LinkFromSrc);
 460
 461     if (!LinkFromSrc)
 462       continue;
 463
 464     Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
 465     Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(C.getName());
 466     if (DstCI == ComdatSymTab.end())
 467       continue;
 468
 469     // The source comdat is replacing the dest one.
 470     const Comdat *DstC = &DstCI->second;
 471     ReplacedDstComdats.insert(DstC);
 472   }
 473
 474   // Alias have to go first, since we are not able to find their comdats
 475   // otherwise.
 476   for (auto I = DstM.alias_begin(), E = DstM.alias_end(); I != E;) {
 477     GlobalAlias &GV = *I++;
 478     dropReplacedComdat(GV, ReplacedDstComdats);
 479   }
 480
 481   for (auto I = DstM.global_begin(), E = DstM.global_end(); I != E;) {
 482     GlobalVariable &GV = *I++;
 483     dropReplacedComdat(GV, ReplacedDstComdats);
 484   }
 485
 486   for (auto I = DstM.begin(), E = DstM.end(); I != E;) {
 487     Function &GV = *I++;
 488     dropReplacedComdat(GV, ReplacedDstComdats);
 489   }
 490
 491   for (GlobalVariable &GV : SrcM->globals())
 492     if (GV.hasLinkOnceLinkage())
 493       if (const Comdat *SC = GV.getComdat())
 494         LazyComdatMembers[SC].push_back(&GV);
 495
 496   for (Function &SF : *SrcM)
 497     if (SF.hasLinkOnceLinkage())
 498       if (const Comdat *SC = SF.getComdat())
 499         LazyComdatMembers[SC].push_back(&SF);
 500
 501   for (GlobalAlias &GA : SrcM->aliases())
 502     if (GA.hasLinkOnceLinkage())
 503       if (const Comdat *SC = GA.getComdat())
 504         LazyComdatMembers[SC].push_back(&GA);
 505
 506   // Insert all of the globals in src into the DstM module... without linking
 507   // initializers (which could refer to functions not yet mapped over).
 508   for (GlobalVariable &GV : SrcM->globals())
 509     if (linkIfNeeded(GV))
 510       return true;
 511
 512   for (Function &SF : *SrcM)
 513     if (linkIfNeeded(SF))
 514       return true;
 515
 516   for (GlobalAlias &GA : SrcM->aliases())
 517     if (linkIfNeeded(GA))
 518       return true;
 519
 520   for (unsigned I = 0; I < ValuesToLink.size(); ++I) {
 521     GlobalValue *GV = ValuesToLink[I];
 522     const Comdat *SC = GV->getComdat();
 523     if (!SC)
 524       continue;
 525     for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
 526       GlobalValue *DGV = getLinkedToGlobal(GV2);
 527       bool LinkFromSrc = true;
 528       if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
 529         return true;
 530       if (LinkFromSrc)
 531         ValuesToLink.insert(GV2);
 532     }
 533   }
 534
 535   if (InternalizeCallback) {
 536     for (GlobalValue *GV : ValuesToLink)
 537       Internalize.insert(GV->getName());
 538   }
 539
 540   // FIXME: Propagate Errors through to the caller instead of emitting
 541   // diagnostics.
 542   bool HasErrors = false;
 543   if (Error E = Mover.move(std::move(SrcM), ValuesToLink.getArrayRef(),
 544                            [this](GlobalValue &GV, IRMover::ValueAdder Add) {
 545                              addLazyFor(GV, Add);
 546                            },
 547                            /* IsPerformingImport */ false)) {
 548     handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
 549       DstM.getContext().diagnose(LinkDiagnosticInfo(DS_Error, EIB.message()));
 550       HasErrors = true;
 551     });
 552   }
 553   if (HasErrors)
 554     return true;
 555
 556   if (InternalizeCallback)
 557     InternalizeCallback(DstM, Internalize);
 558
 559   return false;
 560 }
 561
 562 Linker::Linker(Module &M) : Mover(M) {}
 563
 564 bool Linker::linkInModule(
 565     std::unique_ptr<Module> Src, unsigned Flags,
 566     std::function<void(Module &, const StringSet<> &)> InternalizeCallback) {
 567   ModuleLinker ModLinker(Mover, std::move(Src), Flags,
 568                          std::move(InternalizeCallback));
 569   return ModLinker.run();
 570 }
 571
 572 //===----------------------------------------------------------------------===//
 573 // LinkModules entrypoint.
 574 //===----------------------------------------------------------------------===//
 575
 576 /// This function links two modules together, with the resulting Dest module
 577 /// modified to be the composite of the two input modules. If an error occurs,
 578 /// true is returned and ErrorMsg (if not null) is set to indicate the problem.
 579 /// Upon failure, the Dest module could be in a modified state, and shouldn't be
 580 /// relied on to be consistent.
 581 bool Linker::linkModules(
 582     Module &Dest, std::unique_ptr<Module> Src, unsigned Flags,
 583     std::function<void(Module &, const StringSet<> &)> InternalizeCallback) {
 584   Linker L(Dest);
 585   return L.linkInModule(std::move(Src), Flags, std::move(InternalizeCallback));
 586 }
 587
 588 //===----------------------------------------------------------------------===//
 589 // C API.
 590 //===----------------------------------------------------------------------===//
 591
 592 LLVMBool LLVMLinkModules2(LLVMModuleRef Dest, LLVMModuleRef Src) {
 593   Module *D = unwrap(Dest);
 594   std::unique_ptr<Module> M(unwrap(Src));
 595   return Linker::linkModules(*D, std::move(M));
 596 }