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/ModuleSummaryAnalysis.h"
20#include "llvm/Analysis/TargetLibraryInfo.h"
21#include "llvm/Analysis/TargetTransformInfo.h"
22#include "llvm/Bitcode/BitcodeReader.h"
23#include "llvm/Bitcode/BitcodeWriter.h"
24#include "llvm/IR/LLVMRemarkStreamer.h"
25#include "llvm/IR/LegacyPassManager.h"
26#include "llvm/IR/PassManager.h"
27#include "llvm/IR/Verifier.h"
28#include "llvm/LTO/LTO.h"
29#include "llvm/MC/SubtargetFeature.h"
30#include "llvm/Object/ModuleSymbolTable.h"
31#include "llvm/Passes/PassBuilder.h"
32#include "llvm/Passes/PassPlugin.h"
33#include "llvm/Passes/StandardInstrumentations.h"
34#include "llvm/Support/Error.h"
35#include "llvm/Support/FileSystem.h"
36#include "llvm/Support/MemoryBuffer.h"
37#include "llvm/Support/Path.h"
38#include "llvm/Support/Program.h"
39#include "llvm/Support/SmallVectorMemoryBuffer.h"
40#include "llvm/Support/TargetRegistry.h"
41#include "llvm/Support/ThreadPool.h"
42#include "llvm/Support/raw_ostream.h"
43#include "llvm/Target/TargetMachine.h"
44#include "llvm/Transforms/IPO.h"
45#include "llvm/Transforms/IPO/PassManagerBuilder.h"
46#include "llvm/Transforms/Scalar/LoopPassManager.h"
47#include "llvm/Transforms/Utils/FunctionImportUtils.h"
48#include "llvm/Transforms/Utils/SplitModule.h"
49
50using namespace llvm;
51using namespace lto;
52
53LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
54  errs() << "failed to open " << Path << ": " << Msg << '\n';
55  errs().flush();
56  exit(1);
57}
58
59Error Config::addSaveTemps(std::string OutputFileName,
60                           bool UseInputModulePath) {
61  ShouldDiscardValueNames = false;
62
63  std::error_code EC;
64  ResolutionFile = std::make_unique<raw_fd_ostream>(
65      OutputFileName + "resolution.txt", EC, sys::fs::OpenFlags::OF_Text);
66  if (EC) {
67    ResolutionFile.reset();
68    return errorCodeToError(EC);
69  }
70
71  auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
72    // Keep track of the hook provided by the linker, which also needs to run.
73    ModuleHookFn LinkerHook = Hook;
74    Hook = [=](unsigned Task, const Module &M) {
75      // If the linker's hook returned false, we need to pass that result
76      // through.
77      if (LinkerHook && !LinkerHook(Task, M))
78        return false;
79
80      std::string PathPrefix;
81      // If this is the combined module (not a ThinLTO backend compile) or the
82      // user hasn't requested using the input module's path, emit to a file
83      // named from the provided OutputFileName with the Task ID appended.
84      if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
85        PathPrefix = OutputFileName;
86        if (Task != (unsigned)-1)
87          PathPrefix += utostr(Task) + ".";
88      } else
89        PathPrefix = M.getModuleIdentifier() + ".";
90      std::string Path = PathPrefix + PathSuffix + ".bc";
91      std::error_code EC;
92      raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
93      // Because -save-temps is a debugging feature, we report the error
94      // directly and exit.
95      if (EC)
96        reportOpenError(Path, EC.message());
97      WriteBitcodeToFile(M, OS, /*ShouldPreserveUseListOrder=*/false);
98      return true;
99    };
100  };
101
102  setHook("0.preopt", PreOptModuleHook);
103  setHook("1.promote", PostPromoteModuleHook);
104  setHook("2.internalize", PostInternalizeModuleHook);
105  setHook("3.import", PostImportModuleHook);
106  setHook("4.opt", PostOptModuleHook);
107  setHook("5.precodegen", PreCodeGenModuleHook);
108
109  CombinedIndexHook =
110      [=](const ModuleSummaryIndex &Index,
111          const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
112        std::string Path = OutputFileName + "index.bc";
113        std::error_code EC;
114        raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::OF_None);
115        // Because -save-temps is a debugging feature, we report the error
116        // directly and exit.
117        if (EC)
118          reportOpenError(Path, EC.message());
119        WriteIndexToFile(Index, OS);
120
121        Path = OutputFileName + "index.dot";
122        raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::OF_None);
123        if (EC)
124          reportOpenError(Path, EC.message());
125        Index.exportToDot(OSDot, GUIDPreservedSymbols);
126        return true;
127      };
128
129  return Error::success();
130}
131
132#define HANDLE_EXTENSION(Ext)                                                  \
133  llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
134#include "llvm/Support/Extension.def"
135
136static void RegisterPassPlugins(ArrayRef<std::string> PassPlugins,
137                                PassBuilder &PB) {
138#define HANDLE_EXTENSION(Ext)                                                  \
139  get##Ext##PluginInfo().RegisterPassBuilderCallbacks(PB);
140#include "llvm/Support/Extension.def"
141
142  // Load requested pass plugins and let them register pass builder callbacks
143  for (auto &PluginFN : PassPlugins) {
144    auto PassPlugin = PassPlugin::Load(PluginFN);
145    if (!PassPlugin) {
146      errs() << "Failed to load passes from '" << PluginFN
147             << "'. Request ignored.\n";
148      continue;
149    }
150
151    PassPlugin->registerPassBuilderCallbacks(PB);
152  }
153}
154
155namespace {
156
157std::unique_ptr<TargetMachine>
158createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
159  StringRef TheTriple = M.getTargetTriple();
160  SubtargetFeatures Features;
161  Features.getDefaultSubtargetFeatures(Triple(TheTriple));
162  for (const std::string &A : Conf.MAttrs)
163    Features.AddFeature(A);
164
165  Reloc::Model RelocModel;
166  if (Conf.RelocModel)
167    RelocModel = *Conf.RelocModel;
168  else
169    RelocModel =
170        M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
171
172  Optional<CodeModel::Model> CodeModel;
173  if (Conf.CodeModel)
174    CodeModel = *Conf.CodeModel;
175  else
176    CodeModel = M.getCodeModel();
177
178  return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
179      TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
180      CodeModel, Conf.CGOptLevel));
181}
182
183static void runNewPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
184                           unsigned OptLevel, bool IsThinLTO,
185                           ModuleSummaryIndex *ExportSummary,
186                           const ModuleSummaryIndex *ImportSummary) {
187  Optional<PGOOptions> PGOOpt;
188  if (!Conf.SampleProfile.empty())
189    PGOOpt = PGOOptions(Conf.SampleProfile, "", Conf.ProfileRemapping,
190                        PGOOptions::SampleUse, PGOOptions::NoCSAction, true);
191  else if (Conf.RunCSIRInstr) {
192    PGOOpt = PGOOptions("", Conf.CSIRProfile, Conf.ProfileRemapping,
193                        PGOOptions::IRUse, PGOOptions::CSIRInstr);
194  } else if (!Conf.CSIRProfile.empty()) {
195    PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
196                        PGOOptions::IRUse, PGOOptions::CSIRUse);
197  }
198
199  PassInstrumentationCallbacks PIC;
200  StandardInstrumentations SI;
201  SI.registerCallbacks(PIC);
202  PassBuilder PB(TM, Conf.PTO, PGOOpt, &PIC);
203  AAManager AA;
204
205  // Parse a custom AA pipeline if asked to.
206  if (auto Err = PB.parseAAPipeline(AA, "default"))
207    report_fatal_error("Error parsing default AA pipeline");
208
209  RegisterPassPlugins(Conf.PassPlugins, PB);
210
211  LoopAnalysisManager LAM(Conf.DebugPassManager);
212  FunctionAnalysisManager FAM(Conf.DebugPassManager);
213  CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
214  ModuleAnalysisManager MAM(Conf.DebugPassManager);
215
216  // Register the AA manager first so that our version is the one used.
217  FAM.registerPass([&] { return std::move(AA); });
218
219  // Register all the basic analyses with the managers.
220  PB.registerModuleAnalyses(MAM);
221  PB.registerCGSCCAnalyses(CGAM);
222  PB.registerFunctionAnalyses(FAM);
223  PB.registerLoopAnalyses(LAM);
224  PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
225
226  ModulePassManager MPM(Conf.DebugPassManager);
227  // FIXME (davide): verify the input.
228
229  PassBuilder::OptimizationLevel OL;
230
231  switch (OptLevel) {
232  default:
233    llvm_unreachable("Invalid optimization level");
234  case 0:
235    OL = PassBuilder::OptimizationLevel::O0;
236    break;
237  case 1:
238    OL = PassBuilder::OptimizationLevel::O1;
239    break;
240  case 2:
241    OL = PassBuilder::OptimizationLevel::O2;
242    break;
243  case 3:
244    OL = PassBuilder::OptimizationLevel::O3;
245    break;
246  }
247
248  if (IsThinLTO)
249    MPM = PB.buildThinLTODefaultPipeline(OL, Conf.DebugPassManager,
250                                         ImportSummary);
251  else
252    MPM = PB.buildLTODefaultPipeline(OL, Conf.DebugPassManager, ExportSummary);
253  MPM.run(Mod, MAM);
254
255  // FIXME (davide): verify the output.
256}
257
258static void runNewPMCustomPasses(const Config &Conf, Module &Mod,
259                                 TargetMachine *TM, std::string PipelineDesc,
260                                 std::string AAPipelineDesc,
261                                 bool DisableVerify) {
262  PassBuilder PB(TM);
263  AAManager AA;
264
265  // Parse a custom AA pipeline if asked to.
266  if (!AAPipelineDesc.empty())
267    if (auto Err = PB.parseAAPipeline(AA, AAPipelineDesc))
268      report_fatal_error("unable to parse AA pipeline description '" +
269                         AAPipelineDesc + "': " + toString(std::move(Err)));
270
271  RegisterPassPlugins(Conf.PassPlugins, PB);
272
273  LoopAnalysisManager LAM;
274  FunctionAnalysisManager FAM;
275  CGSCCAnalysisManager CGAM;
276  ModuleAnalysisManager MAM;
277
278  // Register the AA manager first so that our version is the one used.
279  FAM.registerPass([&] { return std::move(AA); });
280
281  // Register all the basic analyses with the managers.
282  PB.registerModuleAnalyses(MAM);
283  PB.registerCGSCCAnalyses(CGAM);
284  PB.registerFunctionAnalyses(FAM);
285  PB.registerLoopAnalyses(LAM);
286  PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
287
288  ModulePassManager MPM;
289
290  // Always verify the input.
291  MPM.addPass(VerifierPass());
292
293  // Now, add all the passes we've been requested to.
294  if (auto Err = PB.parsePassPipeline(MPM, PipelineDesc))
295    report_fatal_error("unable to parse pass pipeline description '" +
296                       PipelineDesc + "': " + toString(std::move(Err)));
297
298  if (!DisableVerify)
299    MPM.addPass(VerifierPass());
300  MPM.run(Mod, MAM);
301}
302
303static void runOldPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
304                           bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
305                           const ModuleSummaryIndex *ImportSummary) {
306  legacy::PassManager passes;
307  passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
308
309  PassManagerBuilder PMB;
310  PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
311  PMB.Inliner = createFunctionInliningPass();
312  PMB.ExportSummary = ExportSummary;
313  PMB.ImportSummary = ImportSummary;
314  // Unconditionally verify input since it is not verified before this
315  // point and has unknown origin.
316  PMB.VerifyInput = true;
317  PMB.VerifyOutput = !Conf.DisableVerify;
318  PMB.LoopVectorize = true;
319  PMB.SLPVectorize = true;
320  PMB.OptLevel = Conf.OptLevel;
321  PMB.PGOSampleUse = Conf.SampleProfile;
322  PMB.EnablePGOCSInstrGen = Conf.RunCSIRInstr;
323  if (!Conf.RunCSIRInstr && !Conf.CSIRProfile.empty()) {
324    PMB.EnablePGOCSInstrUse = true;
325    PMB.PGOInstrUse = Conf.CSIRProfile;
326  }
327  if (IsThinLTO)
328    PMB.populateThinLTOPassManager(passes);
329  else
330    PMB.populateLTOPassManager(passes);
331  passes.run(Mod);
332}
333
334bool opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
335         bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
336         const ModuleSummaryIndex *ImportSummary) {
337  // FIXME: Plumb the combined index into the new pass manager.
338  if (!Conf.OptPipeline.empty())
339    runNewPMCustomPasses(Conf, Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
340                         Conf.DisableVerify);
341  else if (Conf.UseNewPM)
342    runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
343                   ImportSummary);
344  else
345    runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
346  return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
347}
348
349static cl::opt<bool> EmbedBitcode(
350    "lto-embed-bitcode", cl::init(false),
351    cl::desc("Embed LLVM bitcode in object files produced by LTO"));
352
353static void EmitBitcodeSection(Module &M, const Config &Conf) {
354  if (!EmbedBitcode)
355    return;
356  SmallVector<char, 0> Buffer;
357  raw_svector_ostream OS(Buffer);
358  WriteBitcodeToFile(M, OS);
359
360  std::unique_ptr<MemoryBuffer> Buf(
361      new SmallVectorMemoryBuffer(std::move(Buffer)));
362  llvm::EmbedBitcodeInModule(M, Buf->getMemBufferRef(), /*EmbedBitcode*/ true,
363                             /*EmbedMarker*/ false, /*CmdArgs*/ nullptr);
364}
365
366void codegen(const Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
367             unsigned Task, Module &Mod,
368             const ModuleSummaryIndex &CombinedIndex) {
369  if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
370    return;
371
372  EmitBitcodeSection(Mod, Conf);
373
374  std::unique_ptr<ToolOutputFile> DwoOut;
375  SmallString<1024> DwoFile(Conf.SplitDwarfOutput);
376  if (!Conf.DwoDir.empty()) {
377    std::error_code EC;
378    if (auto EC = llvm::sys::fs::create_directories(Conf.DwoDir))
379      report_fatal_error("Failed to create directory " + Conf.DwoDir + ": " +
380                         EC.message());
381
382    DwoFile = Conf.DwoDir;
383    sys::path::append(DwoFile, std::to_string(Task) + ".dwo");
384    TM->Options.MCOptions.SplitDwarfFile = std::string(DwoFile);
385  } else
386    TM->Options.MCOptions.SplitDwarfFile = Conf.SplitDwarfFile;
387
388  if (!DwoFile.empty()) {
389    std::error_code EC;
390    DwoOut = std::make_unique<ToolOutputFile>(DwoFile, EC, sys::fs::OF_None);
391    if (EC)
392      report_fatal_error("Failed to open " + DwoFile + ": " + EC.message());
393  }
394
395  auto Stream = AddStream(Task);
396  legacy::PassManager CodeGenPasses;
397  CodeGenPasses.add(
398      createImmutableModuleSummaryIndexWrapperPass(&CombinedIndex));
399  if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
400                              DwoOut ? &DwoOut->os() : nullptr,
401                              Conf.CGFileType))
402    report_fatal_error("Failed to setup codegen");
403  CodeGenPasses.run(Mod);
404
405  if (DwoOut)
406    DwoOut->keep();
407}
408
409void splitCodeGen(const Config &C, TargetMachine *TM, AddStreamFn AddStream,
410                  unsigned ParallelCodeGenParallelismLevel,
411                  std::unique_ptr<Module> Mod,
412                  const ModuleSummaryIndex &CombinedIndex) {
413  ThreadPool CodegenThreadPool(
414      heavyweight_hardware_concurrency(ParallelCodeGenParallelismLevel));
415  unsigned ThreadCount = 0;
416  const Target *T = &TM->getTarget();
417
418  SplitModule(
419      std::move(Mod), ParallelCodeGenParallelismLevel,
420      [&](std::unique_ptr<Module> MPart) {
421        // We want to clone the module in a new context to multi-thread the
422        // codegen. We do it by serializing partition modules to bitcode
423        // (while still on the main thread, in order to avoid data races) and
424        // spinning up new threads which deserialize the partitions into
425        // separate contexts.
426        // FIXME: Provide a more direct way to do this in LLVM.
427        SmallString<0> BC;
428        raw_svector_ostream BCOS(BC);
429        WriteBitcodeToFile(*MPart, BCOS);
430
431        // Enqueue the task
432        CodegenThreadPool.async(
433            [&](const SmallString<0> &BC, unsigned ThreadId) {
434              LTOLLVMContext Ctx(C);
435              Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
436                  MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
437                  Ctx);
438              if (!MOrErr)
439                report_fatal_error("Failed to read bitcode");
440              std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
441
442              std::unique_ptr<TargetMachine> TM =
443                  createTargetMachine(C, T, *MPartInCtx);
444
445              codegen(C, TM.get(), AddStream, ThreadId, *MPartInCtx,
446                      CombinedIndex);
447            },
448            // Pass BC using std::move to ensure that it get moved rather than
449            // copied into the thread's context.
450            std::move(BC), ThreadCount++);
451      },
452      false);
453
454  // Because the inner lambda (which runs in a worker thread) captures our local
455  // variables, we need to wait for the worker threads to terminate before we
456  // can leave the function scope.
457  CodegenThreadPool.wait();
458}
459
460Expected<const Target *> initAndLookupTarget(const Config &C, Module &Mod) {
461  if (!C.OverrideTriple.empty())
462    Mod.setTargetTriple(C.OverrideTriple);
463  else if (Mod.getTargetTriple().empty())
464    Mod.setTargetTriple(C.DefaultTriple);
465
466  std::string Msg;
467  const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
468  if (!T)
469    return make_error<StringError>(Msg, inconvertibleErrorCode());
470  return T;
471}
472}
473
474Error lto::finalizeOptimizationRemarks(
475    std::unique_ptr<ToolOutputFile> DiagOutputFile) {
476  // Make sure we flush the diagnostic remarks file in case the linker doesn't
477  // call the global destructors before exiting.
478  if (!DiagOutputFile)
479    return Error::success();
480  DiagOutputFile->keep();
481  DiagOutputFile->os().flush();
482  return Error::success();
483}
484
485Error lto::backend(const Config &C, AddStreamFn AddStream,
486                   unsigned ParallelCodeGenParallelismLevel,
487                   std::unique_ptr<Module> Mod,
488                   ModuleSummaryIndex &CombinedIndex) {
489  Expected<const Target *> TOrErr = initAndLookupTarget(C, *Mod);
490  if (!TOrErr)
491    return TOrErr.takeError();
492
493  std::unique_ptr<TargetMachine> TM = createTargetMachine(C, *TOrErr, *Mod);
494
495  if (!C.CodeGenOnly) {
496    if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false,
497             /*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr))
498      return Error::success();
499  }
500
501  if (ParallelCodeGenParallelismLevel == 1) {
502    codegen(C, TM.get(), AddStream, 0, *Mod, CombinedIndex);
503  } else {
504    splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
505                 std::move(Mod), CombinedIndex);
506  }
507  return Error::success();
508}
509
510static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
511                            const ModuleSummaryIndex &Index) {
512  std::vector<GlobalValue*> DeadGVs;
513  for (auto &GV : Mod.global_values())
514    if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
515      if (!Index.isGlobalValueLive(GVS)) {
516        DeadGVs.push_back(&GV);
517        convertToDeclaration(GV);
518      }
519
520  // Now that all dead bodies have been dropped, delete the actual objects
521  // themselves when possible.
522  for (GlobalValue *GV : DeadGVs) {
523    GV->removeDeadConstantUsers();
524    // Might reference something defined in native object (i.e. dropped a
525    // non-prevailing IR def, but we need to keep the declaration).
526    if (GV->use_empty())
527      GV->eraseFromParent();
528  }
529}
530
531Error lto::thinBackend(const Config &Conf, unsigned Task, AddStreamFn AddStream,
532                       Module &Mod, const ModuleSummaryIndex &CombinedIndex,
533                       const FunctionImporter::ImportMapTy &ImportList,
534                       const GVSummaryMapTy &DefinedGlobals,
535                       MapVector<StringRef, BitcodeModule> &ModuleMap) {
536  Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
537  if (!TOrErr)
538    return TOrErr.takeError();
539
540  std::unique_ptr<TargetMachine> TM = createTargetMachine(Conf, *TOrErr, Mod);
541
542  // Setup optimization remarks.
543  auto DiagFileOrErr = lto::setupLLVMOptimizationRemarks(
544      Mod.getContext(), Conf.RemarksFilename, Conf.RemarksPasses,
545      Conf.RemarksFormat, Conf.RemarksWithHotness, Task);
546  if (!DiagFileOrErr)
547    return DiagFileOrErr.takeError();
548  auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
549
550  // Set the partial sample profile ratio in the profile summary module flag of
551  // the module, if applicable.
552  Mod.setPartialSampleProfileRatio(CombinedIndex);
553
554  if (Conf.CodeGenOnly) {
555    codegen(Conf, TM.get(), AddStream, Task, Mod, CombinedIndex);
556    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
557  }
558
559  if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
560    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
561
562  // When linking an ELF shared object, dso_local should be dropped. We
563  // conservatively do this for -fpic.
564  bool ClearDSOLocalOnDeclarations =
565      TM->getTargetTriple().isOSBinFormatELF() &&
566      TM->getRelocationModel() != Reloc::Static &&
567      Mod.getPIELevel() == PIELevel::Default;
568  renameModuleForThinLTO(Mod, CombinedIndex, ClearDSOLocalOnDeclarations);
569
570  dropDeadSymbols(Mod, DefinedGlobals, CombinedIndex);
571
572  thinLTOResolvePrevailingInModule(Mod, DefinedGlobals);
573
574  if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
575    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
576
577  if (!DefinedGlobals.empty())
578    thinLTOInternalizeModule(Mod, DefinedGlobals);
579
580  if (Conf.PostInternalizeModuleHook &&
581      !Conf.PostInternalizeModuleHook(Task, Mod))
582    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
583
584  auto ModuleLoader = [&](StringRef Identifier) {
585    assert(Mod.getContext().isODRUniquingDebugTypes() &&
586           "ODR Type uniquing should be enabled on the context");
587    auto I = ModuleMap.find(Identifier);
588    assert(I != ModuleMap.end());
589    return I->second.getLazyModule(Mod.getContext(),
590                                   /*ShouldLazyLoadMetadata=*/true,
591                                   /*IsImporting*/ true);
592  };
593
594  FunctionImporter Importer(CombinedIndex, ModuleLoader,
595                            ClearDSOLocalOnDeclarations);
596  if (Error Err = Importer.importFunctions(Mod, ImportList).takeError())
597    return Err;
598
599  if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
600    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
601
602  if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true,
603           /*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex))
604    return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
605
606  codegen(Conf, TM.get(), AddStream, Task, Mod, CombinedIndex);
607  return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
608}
609