lib/LTO/LTOBackend.cpp

   1 //===-LTOBackend.cpp - LLVM Link Time Optimizer Backend -------------------===//
   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 "backend" phase of LTO, i.e. it performs
  10 // optimization and code generation on a loaded module. It is generally used
  11 // internally by the LTO class but can also be used independently, for example
  12 // to implement a standalone ThinLTO backend.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/LTO/LTOBackend.h"
  17 #include "llvm/Analysis/AliasAnalysis.h"
  18 #include "llvm/Analysis/CGSCCPassManager.h"
  19 #include "llvm/Analysis/TargetLibraryInfo.h"
  20 #include "llvm/Analysis/TargetTransformInfo.h"
  21 #include "llvm/Bitcode/BitcodeReader.h"
  22 #include "llvm/Bitcode/BitcodeWriter.h"
  23 #include "llvm/IR/LegacyPassManager.h"
  24 #include "llvm/IR/PassManager.h"
  25 #include "llvm/IR/Verifier.h"
  26 #include "llvm/LTO/LTO.h"
  27 #include "llvm/MC/SubtargetFeature.h"
  28 #include "llvm/Object/ModuleSymbolTable.h"
  29 #include "llvm/Passes/PassBuilder.h"
  30 #include "llvm/Support/Error.h"
  31 #include "llvm/Support/FileSystem.h"
  32 #include "llvm/Support/MemoryBuffer.h"
  33 #include "llvm/Support/Path.h"
  34 #include "llvm/Support/Program.h"
  35 #include "llvm/Support/raw_ostream.h"
  36 #include "llvm/Support/TargetRegistry.h"
  37 #include "llvm/Support/ThreadPool.h"
  38 #include "llvm/Target/TargetMachine.h"
  39 #include "llvm/Transforms/IPO.h"
  40 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
  41 #include "llvm/Transforms/Scalar/LoopPassManager.h"
  42 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
  43 #include "llvm/Transforms/Utils/SplitModule.h"
  44
  45 using namespace llvm;
  46 using namespace lto;
  47
  48 LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
  49   errs() << "failed to open " << Path << ": " << Msg << '\n';
  50   errs().flush();
  51   exit(1);
  52 }
  53
  54 Error Config::addSaveTemps(std::string OutputFileName,
  55                            bool UseInputModulePath) {
  56   ShouldDiscardValueNames = false;
  57
  58   std::error_code EC;
  59   ResolutionFile = llvm::make_unique<raw_fd_ostream>(
  60       OutputFileName + "resolution.txt", EC, sys::fs::OpenFlags::F_Text);
  61   if (EC)
  62     return errorCodeToError(EC);
  63
  64   auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
  65     // Keep track of the hook provided by the linker, which also needs to run.
  66     ModuleHookFn LinkerHook = Hook;
  67     Hook = [=](unsigned Task, const Module &M) {
  68       // If the linker's hook returned false, we need to pass that result
  69       // through.
  70       if (LinkerHook && !LinkerHook(Task, M))
  71         return false;
  72
  73       std::string PathPrefix;
  74       // If this is the combined module (not a ThinLTO backend compile) or the
  75       // user hasn't requested using the input module's path, emit to a file
  76       // named from the provided OutputFileName with the Task ID appended.
  77       if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
  78         PathPrefix = OutputFileName;
  79         if (Task != (unsigned)-1)
  80           PathPrefix += utostr(Task) + ".";
  81       } else
  82         PathPrefix = M.getModuleIdentifier() + ".";
  83       std::string Path = PathPrefix + PathSuffix + ".bc";
  84       std::error_code EC;
  85       raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
  86       // Because -save-temps is a debugging feature, we report the error
  87       // directly and exit.
  88       if (EC)
  89         reportOpenError(Path, EC.message());
  90       WriteBitcodeToFile(M, OS, /*ShouldPreserveUseListOrder=*/false);
  91       return true;
  92     };
  93   };
  94
  95   setHook("0.preopt", PreOptModuleHook);
  96   setHook("1.promote", PostPromoteModuleHook);
  97   setHook("2.internalize", PostInternalizeModuleHook);
  98   setHook("3.import", PostImportModuleHook);
  99   setHook("4.opt", PostOptModuleHook);
 100   setHook("5.precodegen", PreCodeGenModuleHook);
 101
 102   CombinedIndexHook = [=](const ModuleSummaryIndex &Index) {
 103     std::string Path = OutputFileName + "index.bc";
 104     std::error_code EC;
 105     raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
 106     // Because -save-temps is a debugging feature, we report the error
 107     // directly and exit.
 108     if (EC)
 109       reportOpenError(Path, EC.message());
 110     WriteIndexToFile(Index, OS);
 111
 112     Path = OutputFileName + "index.dot";
 113     raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::F_None);
 114     if (EC)
 115       reportOpenError(Path, EC.message());
 116     Index.exportToDot(OSDot);
 117     return true;
 118   };
 119
 120   return Error::success();
 121 }
 122
 123 namespace {
 124
 125 std::unique_ptr<TargetMachine>
 126 createTargetMachine(Config &Conf, const Target *TheTarget, Module &M) {
 127   StringRef TheTriple = M.getTargetTriple();
 128   SubtargetFeatures Features;
 129   Features.getDefaultSubtargetFeatures(Triple(TheTriple));
 130   for (const std::string &A : Conf.MAttrs)
 131     Features.AddFeature(A);
 132
 133   Reloc::Model RelocModel;
 134   if (Conf.RelocModel)
 135     RelocModel = *Conf.RelocModel;
 136   else
 137     RelocModel =
 138         M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
 139
 140   Optional<CodeModel::Model> CodeModel;
 141   if (Conf.CodeModel)
 142     CodeModel = *Conf.CodeModel;
 143   else
 144     CodeModel = M.getCodeModel();
 145
 146   return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
 147       TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
 148       CodeModel, Conf.CGOptLevel));
 149 }
 150
 151 static void runNewPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
 152                            unsigned OptLevel, bool IsThinLTO,
 153                            ModuleSummaryIndex *ExportSummary,
 154                            const ModuleSummaryIndex *ImportSummary) {
 155   Optional<PGOOptions> PGOOpt;
 156   if (!Conf.SampleProfile.empty())
 157     PGOOpt = PGOOptions(Conf.SampleProfile, "", Conf.ProfileRemapping,
 158                         PGOOptions::SampleUse, PGOOptions::NoCSAction, true);
 159   else if (Conf.RunCSIRInstr) {
 160     PGOOpt = PGOOptions("", Conf.CSIRProfile, Conf.ProfileRemapping,
 161                         PGOOptions::IRUse, PGOOptions::CSIRInstr);
 162   } else if (!Conf.CSIRProfile.empty()) {
 163     PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
 164                         PGOOptions::IRUse, PGOOptions::CSIRUse);
 165   }
 166
 167   PassBuilder PB(TM, PipelineTuningOptions(), PGOOpt);
 168   AAManager AA;
 169
 170   // Parse a custom AA pipeline if asked to.
 171   if (auto Err = PB.parseAAPipeline(AA, "default"))
 172     report_fatal_error("Error parsing default AA pipeline");
 173
 174   LoopAnalysisManager LAM(Conf.DebugPassManager);
 175   FunctionAnalysisManager FAM(Conf.DebugPassManager);
 176   CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
 177   ModuleAnalysisManager MAM(Conf.DebugPassManager);
 178
 179   // Register the AA manager first so that our version is the one used.
 180   FAM.registerPass([&] { return std::move(AA); });
 181
 182   // Register all the basic analyses with the managers.
 183   PB.registerModuleAnalyses(MAM);
 184   PB.registerCGSCCAnalyses(CGAM);
 185   PB.registerFunctionAnalyses(FAM);
 186   PB.registerLoopAnalyses(LAM);
 187   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 188
 189   ModulePassManager MPM(Conf.DebugPassManager);
 190   // FIXME (davide): verify the input.
 191
 192   PassBuilder::OptimizationLevel OL;
 193
 194   switch (OptLevel) {
 195   default:
 196     llvm_unreachable("Invalid optimization level");
 197   case 0:
 198     OL = PassBuilder::O0;
 199     break;
 200   case 1:
 201     OL = PassBuilder::O1;
 202     break;
 203   case 2:
 204     OL = PassBuilder::O2;
 205     break;
 206   case 3:
 207     OL = PassBuilder::O3;
 208     break;
 209   }
 210
 211   if (IsThinLTO)
 212     MPM = PB.buildThinLTODefaultPipeline(OL, Conf.DebugPassManager,
 213                                          ImportSummary);
 214   else
 215     MPM = PB.buildLTODefaultPipeline(OL, Conf.DebugPassManager, ExportSummary);
 216   MPM.run(Mod, MAM);
 217
 218   // FIXME (davide): verify the output.
 219 }
 220
 221 static void runNewPMCustomPasses(Module &Mod, TargetMachine *TM,
 222                                  std::string PipelineDesc,
 223                                  std::string AAPipelineDesc,
 224                                  bool DisableVerify) {
 225   PassBuilder PB(TM);
 226   AAManager AA;
 227
 228   // Parse a custom AA pipeline if asked to.
 229   if (!AAPipelineDesc.empty())
 230     if (auto Err = PB.parseAAPipeline(AA, AAPipelineDesc))
 231       report_fatal_error("unable to parse AA pipeline description '" +
 232                          AAPipelineDesc + "': " + toString(std::move(Err)));
 233
 234   LoopAnalysisManager LAM;
 235   FunctionAnalysisManager FAM;
 236   CGSCCAnalysisManager CGAM;
 237   ModuleAnalysisManager MAM;
 238
 239   // Register the AA manager first so that our version is the one used.
 240   FAM.registerPass([&] { return std::move(AA); });
 241
 242   // Register all the basic analyses with the managers.
 243   PB.registerModuleAnalyses(MAM);
 244   PB.registerCGSCCAnalyses(CGAM);
 245   PB.registerFunctionAnalyses(FAM);
 246   PB.registerLoopAnalyses(LAM);
 247   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
 248
 249   ModulePassManager MPM;
 250
 251   // Always verify the input.
 252   MPM.addPass(VerifierPass());
 253
 254   // Now, add all the passes we've been requested to.
 255   if (auto Err = PB.parsePassPipeline(MPM, PipelineDesc))
 256     report_fatal_error("unable to parse pass pipeline description '" +
 257                        PipelineDesc + "': " + toString(std::move(Err)));
 258
 259   if (!DisableVerify)
 260     MPM.addPass(VerifierPass());
 261   MPM.run(Mod, MAM);
 262 }
 263
 264 static void runOldPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
 265                            bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
 266                            const ModuleSummaryIndex *ImportSummary) {
 267   legacy::PassManager passes;
 268   passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
 269
 270   PassManagerBuilder PMB;
 271   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
 272   PMB.Inliner = createFunctionInliningPass();
 273   PMB.ExportSummary = ExportSummary;
 274   PMB.ImportSummary = ImportSummary;
 275   // Unconditionally verify input since it is not verified before this
 276   // point and has unknown origin.
 277   PMB.VerifyInput = true;
 278   PMB.VerifyOutput = !Conf.DisableVerify;
 279   PMB.LoopVectorize = true;
 280   PMB.SLPVectorize = true;
 281   PMB.OptLevel = Conf.OptLevel;
 282   PMB.PGOSampleUse = Conf.SampleProfile;
 283   PMB.EnablePGOCSInstrGen = Conf.RunCSIRInstr;
 284   if (!Conf.RunCSIRInstr && !Conf.CSIRProfile.empty()) {
 285     PMB.EnablePGOCSInstrUse = true;
 286     PMB.PGOInstrUse = Conf.CSIRProfile;
 287   }
 288   if (IsThinLTO)
 289     PMB.populateThinLTOPassManager(passes);
 290   else
 291     PMB.populateLTOPassManager(passes);
 292   passes.run(Mod);
 293 }
 294
 295 bool opt(Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
 296          bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
 297          const ModuleSummaryIndex *ImportSummary) {
 298   // FIXME: Plumb the combined index into the new pass manager.
 299   if (!Conf.OptPipeline.empty())
 300     runNewPMCustomPasses(Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
 301                          Conf.DisableVerify);
 302   else if (Conf.UseNewPM)
 303     runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
 304                    ImportSummary);
 305   else
 306     runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
 307   return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
 308 }
 309
 310 void codegen(Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
 311              unsigned Task, Module &Mod) {
 312   if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
 313     return;
 314
 315   std::unique_ptr<ToolOutputFile> DwoOut;
 316   SmallString<1024> DwoFile(Conf.DwoPath);
 317   if (!Conf.DwoDir.empty()) {
 318     std::error_code EC;
 319     if (auto EC = llvm::sys::fs::create_directories(Conf.DwoDir))
 320       report_fatal_error("Failed to create directory " + Conf.DwoDir + ": " +
 321                          EC.message());
 322
 323     DwoFile = Conf.DwoDir;
 324     sys::path::append(DwoFile, std::to_string(Task) + ".dwo");
 325   }
 326
 327   if (!DwoFile.empty()) {
 328     std::error_code EC;
 329     TM->Options.MCOptions.SplitDwarfFile = DwoFile.str().str();
 330     DwoOut = llvm::make_unique<ToolOutputFile>(DwoFile, EC, sys::fs::F_None);
 331     if (EC)
 332       report_fatal_error("Failed to open " + DwoFile + ": " + EC.message());
 333   }
 334
 335   auto Stream = AddStream(Task);
 336   legacy::PassManager CodeGenPasses;
 337   if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
 338                               DwoOut ? &DwoOut->os() : nullptr,
 339                               Conf.CGFileType))
 340     report_fatal_error("Failed to setup codegen");
 341   CodeGenPasses.run(Mod);
 342
 343   if (DwoOut)
 344     DwoOut->keep();
 345 }
 346
 347 void splitCodeGen(Config &C, TargetMachine *TM, AddStreamFn AddStream,
 348                   unsigned ParallelCodeGenParallelismLevel,
 349                   std::unique_ptr<Module> Mod) {
 350   ThreadPool CodegenThreadPool(ParallelCodeGenParallelismLevel);
 351   unsigned ThreadCount = 0;
 352   const Target *T = &TM->getTarget();
 353
 354   SplitModule(
 355       std::move(Mod), ParallelCodeGenParallelismLevel,
 356       [&](std::unique_ptr<Module> MPart) {
 357         // We want to clone the module in a new context to multi-thread the
 358         // codegen. We do it by serializing partition modules to bitcode
 359         // (while still on the main thread, in order to avoid data races) and
 360         // spinning up new threads which deserialize the partitions into
 361         // separate contexts.
 362         // FIXME: Provide a more direct way to do this in LLVM.
 363         SmallString<0> BC;
 364         raw_svector_ostream BCOS(BC);
 365         WriteBitcodeToFile(*MPart, BCOS);
 366
 367         // Enqueue the task
 368         CodegenThreadPool.async(
 369             [&](const SmallString<0> &BC, unsigned ThreadId) {
 370               LTOLLVMContext Ctx(C);
 371               Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
 372                   MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
 373                   Ctx);
 374               if (!MOrErr)
 375                 report_fatal_error("Failed to read bitcode");
 376               std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
 377
 378               std::unique_ptr<TargetMachine> TM =
 379                   createTargetMachine(C, T, *MPartInCtx);
 380
 381               codegen(C, TM.get(), AddStream, ThreadId, *MPartInCtx);
 382             },
 383             // Pass BC using std::move to ensure that it get moved rather than
 384             // copied into the thread's context.
 385             std::move(BC), ThreadCount++);
 386       },
 387       false);
 388
 389   // Because the inner lambda (which runs in a worker thread) captures our local
 390   // variables, we need to wait for the worker threads to terminate before we
 391   // can leave the function scope.
 392   CodegenThreadPool.wait();
 393 }
 394
 395 Expected<const Target *> initAndLookupTarget(Config &C, Module &Mod) {
 396   if (!C.OverrideTriple.empty())
 397     Mod.setTargetTriple(C.OverrideTriple);
 398   else if (Mod.getTargetTriple().empty())
 399     Mod.setTargetTriple(C.DefaultTriple);
 400
 401   std::string Msg;
 402   const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
 403   if (!T)
 404     return make_error<StringError>(Msg, inconvertibleErrorCode());
 405   return T;
 406 }
 407
 408 }
 409
 410 static Error
 411 finalizeOptimizationRemarks(std::unique_ptr<ToolOutputFile> DiagOutputFile) {
 412   // Make sure we flush the diagnostic remarks file in case the linker doesn't
 413   // call the global destructors before exiting.
 414   if (!DiagOutputFile)
 415     return Error::success();
 416   DiagOutputFile->keep();
 417   DiagOutputFile->os().flush();
 418   return Error::success();
 419 }
 420
 421 Error lto::backend(Config &C, AddStreamFn AddStream,
 422                    unsigned ParallelCodeGenParallelismLevel,
 423                    std::unique_ptr<Module> Mod,
 424                    ModuleSummaryIndex &CombinedIndex) {
 425   Expected<const Target *> TOrErr = initAndLookupTarget(C, *Mod);
 426   if (!TOrErr)
 427     return TOrErr.takeError();
 428
 429   std::unique_ptr<TargetMachine> TM = createTargetMachine(C, *TOrErr, *Mod);
 430
 431   // Setup optimization remarks.
 432   auto DiagFileOrErr =
 433       lto::setupOptimizationRemarks(Mod->getContext(), C.RemarksFilename,
 434                                     C.RemarksPasses, C.RemarksWithHotness);
 435   if (!DiagFileOrErr)
 436     return DiagFileOrErr.takeError();
 437   auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
 438
 439   if (!C.CodeGenOnly) {
 440     if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false,
 441              /*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr))
 442       return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 443   }
 444
 445   if (ParallelCodeGenParallelismLevel == 1) {
 446     codegen(C, TM.get(), AddStream, 0, *Mod);
 447   } else {
 448     splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
 449                  std::move(Mod));
 450   }
 451   return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 452 }
 453
 454 static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
 455                             const ModuleSummaryIndex &Index) {
 456   std::vector<GlobalValue*> DeadGVs;
 457   for (auto &GV : Mod.global_values())
 458     if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
 459       if (!Index.isGlobalValueLive(GVS)) {
 460         DeadGVs.push_back(&GV);
 461         convertToDeclaration(GV);
 462       }
 463
 464   // Now that all dead bodies have been dropped, delete the actual objects
 465   // themselves when possible.
 466   for (GlobalValue *GV : DeadGVs) {
 467     GV->removeDeadConstantUsers();
 468     // Might reference something defined in native object (i.e. dropped a
 469     // non-prevailing IR def, but we need to keep the declaration).
 470     if (GV->use_empty())
 471       GV->eraseFromParent();
 472   }
 473 }
 474
 475 Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
 476                        Module &Mod, const ModuleSummaryIndex &CombinedIndex,
 477                        const FunctionImporter::ImportMapTy &ImportList,
 478                        const GVSummaryMapTy &DefinedGlobals,
 479                        MapVector<StringRef, BitcodeModule> &ModuleMap) {
 480   Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
 481   if (!TOrErr)
 482     return TOrErr.takeError();
 483
 484   std::unique_ptr<TargetMachine> TM = createTargetMachine(Conf, *TOrErr, Mod);
 485
 486   // Setup optimization remarks.
 487   auto DiagFileOrErr = lto::setupOptimizationRemarks(
 488       Mod.getContext(), Conf.RemarksFilename, Conf.RemarksPasses,
 489       Conf.RemarksWithHotness, Task);
 490   if (!DiagFileOrErr)
 491     return DiagFileOrErr.takeError();
 492   auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
 493
 494   if (Conf.CodeGenOnly) {
 495     codegen(Conf, TM.get(), AddStream, Task, Mod);
 496     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 497   }
 498
 499   if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
 500     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 501
 502   renameModuleForThinLTO(Mod, CombinedIndex);
 503
 504   dropDeadSymbols(Mod, DefinedGlobals, CombinedIndex);
 505
 506   thinLTOResolvePrevailingInModule(Mod, DefinedGlobals);
 507
 508   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
 509     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 510
 511   if (!DefinedGlobals.empty())
 512     thinLTOInternalizeModule(Mod, DefinedGlobals);
 513
 514   if (Conf.PostInternalizeModuleHook &&
 515       !Conf.PostInternalizeModuleHook(Task, Mod))
 516     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 517
 518   auto ModuleLoader = [&](StringRef Identifier) {
 519     assert(Mod.getContext().isODRUniquingDebugTypes() &&
 520            "ODR Type uniquing should be enabled on the context");
 521     auto I = ModuleMap.find(Identifier);
 522     assert(I != ModuleMap.end());
 523     return I->second.getLazyModule(Mod.getContext(),
 524                                    /*ShouldLazyLoadMetadata=*/true,
 525                                    /*IsImporting*/ true);
 526   };
 527
 528   FunctionImporter Importer(CombinedIndex, ModuleLoader);
 529   if (Error Err = Importer.importFunctions(Mod, ImportList).takeError())
 530     return Err;
 531
 532   if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
 533     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 534
 535   if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true,
 536            /*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex))
 537     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 538
 539   codegen(Conf, TM.get(), AddStream, Task, Mod);
 540   return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
 541 }