xref: /freebsd/contrib/llvm-project/llvm/lib/LTO/ThinLTOCodeGenerator.cpp (revision 7ef62cebc2f965b0f640263e179276928885e33d) 
1 //===-ThinLTOCodeGenerator.cpp - LLVM Link Time Optimizer -----------------===//
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 Thin Link Time Optimization library. This library is
10 // intended to be used by linker to optimize code at link time.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/LTO/legacy/ThinLTOCodeGenerator.h"
15 #include "llvm/Support/CommandLine.h"
16 
17 #include "llvm/ADT/ScopeExit.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/ADT/StringExtras.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/Analysis/ModuleSummaryAnalysis.h"
22 #include "llvm/Analysis/ProfileSummaryInfo.h"
23 #include "llvm/Analysis/TargetLibraryInfo.h"
24 #include "llvm/Bitcode/BitcodeReader.h"
25 #include "llvm/Bitcode/BitcodeWriter.h"
26 #include "llvm/Bitcode/BitcodeWriterPass.h"
27 #include "llvm/Config/llvm-config.h"
28 #include "llvm/IR/DebugInfo.h"
29 #include "llvm/IR/DiagnosticPrinter.h"
30 #include "llvm/IR/LegacyPassManager.h"
31 #include "llvm/IR/LLVMContext.h"
32 #include "llvm/IR/LLVMRemarkStreamer.h"
33 #include "llvm/IR/Mangler.h"
34 #include "llvm/IR/PassTimingInfo.h"
35 #include "llvm/IR/Verifier.h"
36 #include "llvm/IRReader/IRReader.h"
37 #include "llvm/LTO/LTO.h"
38 #include "llvm/LTO/SummaryBasedOptimizations.h"
39 #include "llvm/MC/SubtargetFeature.h"
40 #include "llvm/MC/TargetRegistry.h"
41 #include "llvm/Object/IRObjectFile.h"
42 #include "llvm/Passes/PassBuilder.h"
43 #include "llvm/Passes/StandardInstrumentations.h"
44 #include "llvm/Remarks/HotnessThresholdParser.h"
45 #include "llvm/Support/CachePruning.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/Error.h"
48 #include "llvm/Support/FileUtilities.h"
49 #include "llvm/Support/Path.h"
50 #include "llvm/Support/SHA1.h"
51 #include "llvm/Support/SmallVectorMemoryBuffer.h"
52 #include "llvm/Support/ThreadPool.h"
53 #include "llvm/Support/Threading.h"
54 #include "llvm/Support/ToolOutputFile.h"
55 #include "llvm/Target/TargetMachine.h"
56 #include "llvm/Transforms/IPO/FunctionAttrs.h"
57 #include "llvm/Transforms/IPO/FunctionImport.h"
58 #include "llvm/Transforms/IPO/Internalize.h"
59 #include "llvm/Transforms/IPO/WholeProgramDevirt.h"
60 #include "llvm/Transforms/ObjCARC.h"
61 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
62 
63 #include <numeric>
64 
65 #if !defined(_MSC_VER) && !defined(__MINGW32__)
66 #include <unistd.h>
67 #else
68 #include <io.h>
69 #endif
70 
71 using namespace llvm;
72 
73 #define DEBUG_TYPE "thinlto"
74 
75 namespace llvm {
76 // Flags -discard-value-names, defined in LTOCodeGenerator.cpp
77 extern cl::opt<bool> LTODiscardValueNames;
78 extern cl::opt<std::string> RemarksFilename;
79 extern cl::opt<std::string> RemarksPasses;
80 extern cl::opt<bool> RemarksWithHotness;
81 extern cl::opt<std::optional<uint64_t>, false, remarks::HotnessThresholdParser>
82     RemarksHotnessThreshold;
83 extern cl::opt<std::string> RemarksFormat;
84 }
85 
86 namespace {
87 
88 // Default to using all available threads in the system, but using only one
89 // thred per core, as indicated by the usage of
90 // heavyweight_hardware_concurrency() below.
91 static cl::opt<int> ThreadCount("threads", cl::init(0));
92 
93 // Simple helper to save temporary files for debug.
94 static void saveTempBitcode(const Module &TheModule, StringRef TempDir,
95                             unsigned count, StringRef Suffix) {
96   if (TempDir.empty())
97     return;
98   // User asked to save temps, let dump the bitcode file after import.
99   std::string SaveTempPath = (TempDir + llvm::Twine(count) + Suffix).str();
100   std::error_code EC;
101   raw_fd_ostream OS(SaveTempPath, EC, sys::fs::OF_None);
102   if (EC)
103     report_fatal_error(Twine("Failed to open ") + SaveTempPath +
104                        " to save optimized bitcode\n");
105   WriteBitcodeToFile(TheModule, OS, /* ShouldPreserveUseListOrder */ true);
106 }
107 
108 static const GlobalValueSummary *
109 getFirstDefinitionForLinker(const GlobalValueSummaryList &GVSummaryList) {
110   // If there is any strong definition anywhere, get it.
111   auto StrongDefForLinker = llvm::find_if(
112       GVSummaryList, [](const std::unique_ptr<GlobalValueSummary> &Summary) {
113         auto Linkage = Summary->linkage();
114         return !GlobalValue::isAvailableExternallyLinkage(Linkage) &&
115                !GlobalValue::isWeakForLinker(Linkage);
116       });
117   if (StrongDefForLinker != GVSummaryList.end())
118     return StrongDefForLinker->get();
119   // Get the first *linker visible* definition for this global in the summary
120   // list.
121   auto FirstDefForLinker = llvm::find_if(
122       GVSummaryList, [](const std::unique_ptr<GlobalValueSummary> &Summary) {
123         auto Linkage = Summary->linkage();
124         return !GlobalValue::isAvailableExternallyLinkage(Linkage);
125       });
126   // Extern templates can be emitted as available_externally.
127   if (FirstDefForLinker == GVSummaryList.end())
128     return nullptr;
129   return FirstDefForLinker->get();
130 }
131 
132 // Populate map of GUID to the prevailing copy for any multiply defined
133 // symbols. Currently assume first copy is prevailing, or any strong
134 // definition. Can be refined with Linker information in the future.
135 static void computePrevailingCopies(
136     const ModuleSummaryIndex &Index,
137     DenseMap<GlobalValue::GUID, const GlobalValueSummary *> &PrevailingCopy) {
138   auto HasMultipleCopies = [&](const GlobalValueSummaryList &GVSummaryList) {
139     return GVSummaryList.size() > 1;
140   };
141 
142   for (auto &I : Index) {
143     if (HasMultipleCopies(I.second.SummaryList))
144       PrevailingCopy[I.first] =
145           getFirstDefinitionForLinker(I.second.SummaryList);
146   }
147 }
148 
149 static StringMap<lto::InputFile *>
150 generateModuleMap(std::vector<std::unique_ptr<lto::InputFile>> &Modules) {
151   StringMap<lto::InputFile *> ModuleMap;
152   for (auto &M : Modules) {
153     assert(ModuleMap.find(M->getName()) == ModuleMap.end() &&
154            "Expect unique Buffer Identifier");
155     ModuleMap[M->getName()] = M.get();
156   }
157   return ModuleMap;
158 }
159 
160 static void promoteModule(Module &TheModule, const ModuleSummaryIndex &Index,
161                           bool ClearDSOLocalOnDeclarations) {
162   if (renameModuleForThinLTO(TheModule, Index, ClearDSOLocalOnDeclarations))
163     report_fatal_error("renameModuleForThinLTO failed");
164 }
165 
166 namespace {
167 class ThinLTODiagnosticInfo : public DiagnosticInfo {
168   const Twine &Msg;
169 public:
170   ThinLTODiagnosticInfo(const Twine &DiagMsg,
171                         DiagnosticSeverity Severity = DS_Error)
172       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
173   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
174 };
175 }
176 
177 /// Verify the module and strip broken debug info.
178 static void verifyLoadedModule(Module &TheModule) {
179   bool BrokenDebugInfo = false;
180   if (verifyModule(TheModule, &dbgs(), &BrokenDebugInfo))
181     report_fatal_error("Broken module found, compilation aborted!");
182   if (BrokenDebugInfo) {
183     TheModule.getContext().diagnose(ThinLTODiagnosticInfo(
184         "Invalid debug info found, debug info will be stripped", DS_Warning));
185     StripDebugInfo(TheModule);
186   }
187 }
188 
189 static std::unique_ptr<Module> loadModuleFromInput(lto::InputFile *Input,
190                                                    LLVMContext &Context,
191                                                    bool Lazy,
192                                                    bool IsImporting) {
193   auto &Mod = Input->getSingleBitcodeModule();
194   SMDiagnostic Err;
195   Expected<std::unique_ptr<Module>> ModuleOrErr =
196       Lazy ? Mod.getLazyModule(Context,
197                                /* ShouldLazyLoadMetadata */ true, IsImporting)
198            : Mod.parseModule(Context);
199   if (!ModuleOrErr) {
200     handleAllErrors(ModuleOrErr.takeError(), [&](ErrorInfoBase &EIB) {
201       SMDiagnostic Err = SMDiagnostic(Mod.getModuleIdentifier(),
202                                       SourceMgr::DK_Error, EIB.message());
203       Err.print("ThinLTO", errs());
204     });
205     report_fatal_error("Can't load module, abort.");
206   }
207   if (!Lazy)
208     verifyLoadedModule(*ModuleOrErr.get());
209   return std::move(*ModuleOrErr);
210 }
211 
212 static void
213 crossImportIntoModule(Module &TheModule, const ModuleSummaryIndex &Index,
214                       StringMap<lto::InputFile *> &ModuleMap,
215                       const FunctionImporter::ImportMapTy &ImportList,
216                       bool ClearDSOLocalOnDeclarations) {
217   auto Loader = [&](StringRef Identifier) {
218     auto &Input = ModuleMap[Identifier];
219     return loadModuleFromInput(Input, TheModule.getContext(),
220                                /*Lazy=*/true, /*IsImporting*/ true);
221   };
222 
223   FunctionImporter Importer(Index, Loader, ClearDSOLocalOnDeclarations);
224   Expected<bool> Result = Importer.importFunctions(TheModule, ImportList);
225   if (!Result) {
226     handleAllErrors(Result.takeError(), [&](ErrorInfoBase &EIB) {
227       SMDiagnostic Err = SMDiagnostic(TheModule.getModuleIdentifier(),
228                                       SourceMgr::DK_Error, EIB.message());
229       Err.print("ThinLTO", errs());
230     });
231     report_fatal_error("importFunctions failed");
232   }
233   // Verify again after cross-importing.
234   verifyLoadedModule(TheModule);
235 }
236 
237 static void optimizeModule(Module &TheModule, TargetMachine &TM,
238                            unsigned OptLevel, bool Freestanding,
239                            bool DebugPassManager, ModuleSummaryIndex *Index) {
240   std::optional<PGOOptions> PGOOpt;
241   LoopAnalysisManager LAM;
242   FunctionAnalysisManager FAM;
243   CGSCCAnalysisManager CGAM;
244   ModuleAnalysisManager MAM;
245 
246   PassInstrumentationCallbacks PIC;
247   StandardInstrumentations SI(TheModule.getContext(), DebugPassManager);
248   SI.registerCallbacks(PIC, &FAM);
249   PipelineTuningOptions PTO;
250   PTO.LoopVectorization = true;
251   PTO.SLPVectorization = true;
252   PassBuilder PB(&TM, PTO, PGOOpt, &PIC);
253 
254   std::unique_ptr<TargetLibraryInfoImpl> TLII(
255       new TargetLibraryInfoImpl(Triple(TM.getTargetTriple())));
256   if (Freestanding)
257     TLII->disableAllFunctions();
258   FAM.registerPass([&] { return TargetLibraryAnalysis(*TLII); });
259 
260   // Register all the basic analyses with the managers.
261   PB.registerModuleAnalyses(MAM);
262   PB.registerCGSCCAnalyses(CGAM);
263   PB.registerFunctionAnalyses(FAM);
264   PB.registerLoopAnalyses(LAM);
265   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
266 
267   ModulePassManager MPM;
268 
269   OptimizationLevel OL;
270 
271   switch (OptLevel) {
272   default:
273     llvm_unreachable("Invalid optimization level");
274   case 0:
275     OL = OptimizationLevel::O0;
276     break;
277   case 1:
278     OL = OptimizationLevel::O1;
279     break;
280   case 2:
281     OL = OptimizationLevel::O2;
282     break;
283   case 3:
284     OL = OptimizationLevel::O3;
285     break;
286   }
287 
288   MPM.addPass(PB.buildThinLTODefaultPipeline(OL, Index));
289 
290   MPM.run(TheModule, MAM);
291 }
292 
293 static void
294 addUsedSymbolToPreservedGUID(const lto::InputFile &File,
295                              DenseSet<GlobalValue::GUID> &PreservedGUID) {
296   for (const auto &Sym : File.symbols()) {
297     if (Sym.isUsed())
298       PreservedGUID.insert(GlobalValue::getGUID(Sym.getIRName()));
299   }
300 }
301 
302 // Convert the PreservedSymbols map from "Name" based to "GUID" based.
303 static void computeGUIDPreservedSymbols(const lto::InputFile &File,
304                                         const StringSet<> &PreservedSymbols,
305                                         const Triple &TheTriple,
306                                         DenseSet<GlobalValue::GUID> &GUIDs) {
307   // Iterate the symbols in the input file and if the input has preserved symbol
308   // compute the GUID for the symbol.
309   for (const auto &Sym : File.symbols()) {
310     if (PreservedSymbols.count(Sym.getName()) && !Sym.getIRName().empty())
311       GUIDs.insert(GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
312           Sym.getIRName(), GlobalValue::ExternalLinkage, "")));
313   }
314 }
315 
316 static DenseSet<GlobalValue::GUID>
317 computeGUIDPreservedSymbols(const lto::InputFile &File,
318                             const StringSet<> &PreservedSymbols,
319                             const Triple &TheTriple) {
320   DenseSet<GlobalValue::GUID> GUIDPreservedSymbols(PreservedSymbols.size());
321   computeGUIDPreservedSymbols(File, PreservedSymbols, TheTriple,
322                               GUIDPreservedSymbols);
323   return GUIDPreservedSymbols;
324 }
325 
326 std::unique_ptr<MemoryBuffer> codegenModule(Module &TheModule,
327                                             TargetMachine &TM) {
328   SmallVector<char, 128> OutputBuffer;
329 
330   // CodeGen
331   {
332     raw_svector_ostream OS(OutputBuffer);
333     legacy::PassManager PM;
334 
335     // If the bitcode files contain ARC code and were compiled with optimization,
336     // the ObjCARCContractPass must be run, so do it unconditionally here.
337     PM.add(createObjCARCContractPass());
338 
339     // Setup the codegen now.
340     if (TM.addPassesToEmitFile(PM, OS, nullptr, CGFT_ObjectFile,
341                                /* DisableVerify */ true))
342       report_fatal_error("Failed to setup codegen");
343 
344     // Run codegen now. resulting binary is in OutputBuffer.
345     PM.run(TheModule);
346   }
347   return std::make_unique<SmallVectorMemoryBuffer>(
348       std::move(OutputBuffer), /*RequiresNullTerminator=*/false);
349 }
350 
351 /// Manage caching for a single Module.
352 class ModuleCacheEntry {
353   SmallString<128> EntryPath;
354 
355 public:
356   // Create a cache entry. This compute a unique hash for the Module considering
357   // the current list of export/import, and offer an interface to query to
358   // access the content in the cache.
359   ModuleCacheEntry(
360       StringRef CachePath, const ModuleSummaryIndex &Index, StringRef ModuleID,
361       const FunctionImporter::ImportMapTy &ImportList,
362       const FunctionImporter::ExportSetTy &ExportList,
363       const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes> &ResolvedODR,
364       const GVSummaryMapTy &DefinedGVSummaries, unsigned OptLevel,
365       bool Freestanding, const TargetMachineBuilder &TMBuilder) {
366     if (CachePath.empty())
367       return;
368 
369     if (!Index.modulePaths().count(ModuleID))
370       // The module does not have an entry, it can't have a hash at all
371       return;
372 
373     if (all_of(Index.getModuleHash(ModuleID),
374                [](uint32_t V) { return V == 0; }))
375       // No hash entry, no caching!
376       return;
377 
378     llvm::lto::Config Conf;
379     Conf.OptLevel = OptLevel;
380     Conf.Options = TMBuilder.Options;
381     Conf.CPU = TMBuilder.MCpu;
382     Conf.MAttrs.push_back(TMBuilder.MAttr);
383     Conf.RelocModel = TMBuilder.RelocModel;
384     Conf.CGOptLevel = TMBuilder.CGOptLevel;
385     Conf.Freestanding = Freestanding;
386     SmallString<40> Key;
387     computeLTOCacheKey(Key, Conf, Index, ModuleID, ImportList, ExportList,
388                        ResolvedODR, DefinedGVSummaries);
389 
390     // This choice of file name allows the cache to be pruned (see pruneCache()
391     // in include/llvm/Support/CachePruning.h).
392     sys::path::append(EntryPath, CachePath, "llvmcache-" + Key);
393   }
394 
395   // Access the path to this entry in the cache.
396   StringRef getEntryPath() { return EntryPath; }
397 
398   // Try loading the buffer for this cache entry.
399   ErrorOr<std::unique_ptr<MemoryBuffer>> tryLoadingBuffer() {
400     if (EntryPath.empty())
401       return std::error_code();
402     SmallString<64> ResultPath;
403     Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
404         Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
405     if (!FDOrErr)
406       return errorToErrorCode(FDOrErr.takeError());
407     ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = MemoryBuffer::getOpenFile(
408         *FDOrErr, EntryPath, /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
409     sys::fs::closeFile(*FDOrErr);
410     return MBOrErr;
411   }
412 
413   // Cache the Produced object file
414   void write(const MemoryBuffer &OutputBuffer) {
415     if (EntryPath.empty())
416       return;
417 
418     // Write to a temporary to avoid race condition
419     SmallString<128> TempFilename;
420     SmallString<128> CachePath(EntryPath);
421     llvm::sys::path::remove_filename(CachePath);
422     sys::path::append(TempFilename, CachePath, "Thin-%%%%%%.tmp.o");
423 
424     if (auto Err = handleErrors(
425             llvm::writeFileAtomically(TempFilename, EntryPath,
426                                       OutputBuffer.getBuffer()),
427             [](const llvm::AtomicFileWriteError &E) {
428               std::string ErrorMsgBuffer;
429               llvm::raw_string_ostream S(ErrorMsgBuffer);
430               E.log(S);
431 
432               if (E.Error ==
433                   llvm::atomic_write_error::failed_to_create_uniq_file) {
434                 errs() << "Error: " << ErrorMsgBuffer << "\n";
435                 report_fatal_error("ThinLTO: Can't get a temporary file");
436               }
437             })) {
438       // FIXME
439       consumeError(std::move(Err));
440     }
441   }
442 };
443 
444 static std::unique_ptr<MemoryBuffer>
445 ProcessThinLTOModule(Module &TheModule, ModuleSummaryIndex &Index,
446                      StringMap<lto::InputFile *> &ModuleMap, TargetMachine &TM,
447                      const FunctionImporter::ImportMapTy &ImportList,
448                      const FunctionImporter::ExportSetTy &ExportList,
449                      const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
450                      const GVSummaryMapTy &DefinedGlobals,
451                      const ThinLTOCodeGenerator::CachingOptions &CacheOptions,
452                      bool DisableCodeGen, StringRef SaveTempsDir,
453                      bool Freestanding, unsigned OptLevel, unsigned count,
454                      bool DebugPassManager) {
455   // See comment at call to updateVCallVisibilityInIndex() for why
456   // WholeProgramVisibilityEnabledInLTO is false.
457   updatePublicTypeTestCalls(TheModule,
458                             /* WholeProgramVisibilityEnabledInLTO */ false);
459 
460   // "Benchmark"-like optimization: single-source case
461   bool SingleModule = (ModuleMap.size() == 1);
462 
463   // When linking an ELF shared object, dso_local should be dropped. We
464   // conservatively do this for -fpic.
465   bool ClearDSOLocalOnDeclarations =
466       TM.getTargetTriple().isOSBinFormatELF() &&
467       TM.getRelocationModel() != Reloc::Static &&
468       TheModule.getPIELevel() == PIELevel::Default;
469 
470   if (!SingleModule) {
471     promoteModule(TheModule, Index, ClearDSOLocalOnDeclarations);
472 
473     // Apply summary-based prevailing-symbol resolution decisions.
474     thinLTOFinalizeInModule(TheModule, DefinedGlobals, /*PropagateAttrs=*/true);
475 
476     // Save temps: after promotion.
477     saveTempBitcode(TheModule, SaveTempsDir, count, ".1.promoted.bc");
478   }
479 
480   // Be friendly and don't nuke totally the module when the client didn't
481   // supply anything to preserve.
482   if (!ExportList.empty() || !GUIDPreservedSymbols.empty()) {
483     // Apply summary-based internalization decisions.
484     thinLTOInternalizeModule(TheModule, DefinedGlobals);
485   }
486 
487   // Save internalized bitcode
488   saveTempBitcode(TheModule, SaveTempsDir, count, ".2.internalized.bc");
489 
490   if (!SingleModule) {
491     crossImportIntoModule(TheModule, Index, ModuleMap, ImportList,
492                           ClearDSOLocalOnDeclarations);
493 
494     // Save temps: after cross-module import.
495     saveTempBitcode(TheModule, SaveTempsDir, count, ".3.imported.bc");
496   }
497 
498   optimizeModule(TheModule, TM, OptLevel, Freestanding, DebugPassManager,
499                  &Index);
500 
501   saveTempBitcode(TheModule, SaveTempsDir, count, ".4.opt.bc");
502 
503   if (DisableCodeGen) {
504     // Configured to stop before CodeGen, serialize the bitcode and return.
505     SmallVector<char, 128> OutputBuffer;
506     {
507       raw_svector_ostream OS(OutputBuffer);
508       ProfileSummaryInfo PSI(TheModule);
509       auto Index = buildModuleSummaryIndex(TheModule, nullptr, &PSI);
510       WriteBitcodeToFile(TheModule, OS, true, &Index);
511     }
512     return std::make_unique<SmallVectorMemoryBuffer>(
513         std::move(OutputBuffer), /*RequiresNullTerminator=*/false);
514   }
515 
516   return codegenModule(TheModule, TM);
517 }
518 
519 /// Resolve prevailing symbols. Record resolutions in the \p ResolvedODR map
520 /// for caching, and in the \p Index for application during the ThinLTO
521 /// backends. This is needed for correctness for exported symbols (ensure
522 /// at least one copy kept) and a compile-time optimization (to drop duplicate
523 /// copies when possible).
524 static void resolvePrevailingInIndex(
525     ModuleSummaryIndex &Index,
526     StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>>
527         &ResolvedODR,
528     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
529     const DenseMap<GlobalValue::GUID, const GlobalValueSummary *>
530         &PrevailingCopy) {
531 
532   auto isPrevailing = [&](GlobalValue::GUID GUID, const GlobalValueSummary *S) {
533     const auto &Prevailing = PrevailingCopy.find(GUID);
534     // Not in map means that there was only one copy, which must be prevailing.
535     if (Prevailing == PrevailingCopy.end())
536       return true;
537     return Prevailing->second == S;
538   };
539 
540   auto recordNewLinkage = [&](StringRef ModuleIdentifier,
541                               GlobalValue::GUID GUID,
542                               GlobalValue::LinkageTypes NewLinkage) {
543     ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
544   };
545 
546   // TODO Conf.VisibilityScheme can be lto::Config::ELF for ELF.
547   lto::Config Conf;
548   thinLTOResolvePrevailingInIndex(Conf, Index, isPrevailing, recordNewLinkage,
549                                   GUIDPreservedSymbols);
550 }
551 
552 // Initialize the TargetMachine builder for a given Triple
553 static void initTMBuilder(TargetMachineBuilder &TMBuilder,
554                           const Triple &TheTriple) {
555   // Set a default CPU for Darwin triples (copied from LTOCodeGenerator).
556   // FIXME this looks pretty terrible...
557   if (TMBuilder.MCpu.empty() && TheTriple.isOSDarwin()) {
558     if (TheTriple.getArch() == llvm::Triple::x86_64)
559       TMBuilder.MCpu = "core2";
560     else if (TheTriple.getArch() == llvm::Triple::x86)
561       TMBuilder.MCpu = "yonah";
562     else if (TheTriple.getArch() == llvm::Triple::aarch64 ||
563              TheTriple.getArch() == llvm::Triple::aarch64_32)
564       TMBuilder.MCpu = "cyclone";
565   }
566   TMBuilder.TheTriple = std::move(TheTriple);
567 }
568 
569 } // end anonymous namespace
570 
571 void ThinLTOCodeGenerator::addModule(StringRef Identifier, StringRef Data) {
572   MemoryBufferRef Buffer(Data, Identifier);
573 
574   auto InputOrError = lto::InputFile::create(Buffer);
575   if (!InputOrError)
576     report_fatal_error(Twine("ThinLTO cannot create input file: ") +
577                        toString(InputOrError.takeError()));
578 
579   auto TripleStr = (*InputOrError)->getTargetTriple();
580   Triple TheTriple(TripleStr);
581 
582   if (Modules.empty())
583     initTMBuilder(TMBuilder, Triple(TheTriple));
584   else if (TMBuilder.TheTriple != TheTriple) {
585     if (!TMBuilder.TheTriple.isCompatibleWith(TheTriple))
586       report_fatal_error("ThinLTO modules with incompatible triples not "
587                          "supported");
588     initTMBuilder(TMBuilder, Triple(TMBuilder.TheTriple.merge(TheTriple)));
589   }
590 
591   Modules.emplace_back(std::move(*InputOrError));
592 }
593 
594 void ThinLTOCodeGenerator::preserveSymbol(StringRef Name) {
595   PreservedSymbols.insert(Name);
596 }
597 
598 void ThinLTOCodeGenerator::crossReferenceSymbol(StringRef Name) {
599   // FIXME: At the moment, we don't take advantage of this extra information,
600   // we're conservatively considering cross-references as preserved.
601   //  CrossReferencedSymbols.insert(Name);
602   PreservedSymbols.insert(Name);
603 }
604 
605 // TargetMachine factory
606 std::unique_ptr<TargetMachine> TargetMachineBuilder::create() const {
607   std::string ErrMsg;
608   const Target *TheTarget =
609       TargetRegistry::lookupTarget(TheTriple.str(), ErrMsg);
610   if (!TheTarget) {
611     report_fatal_error(Twine("Can't load target for this Triple: ") + ErrMsg);
612   }
613 
614   // Use MAttr as the default set of features.
615   SubtargetFeatures Features(MAttr);
616   Features.getDefaultSubtargetFeatures(TheTriple);
617   std::string FeatureStr = Features.getString();
618 
619   std::unique_ptr<TargetMachine> TM(
620       TheTarget->createTargetMachine(TheTriple.str(), MCpu, FeatureStr, Options,
621                                      RelocModel, std::nullopt, CGOptLevel));
622   assert(TM && "Cannot create target machine");
623 
624   return TM;
625 }
626 
627 /**
628  * Produce the combined summary index from all the bitcode files:
629  * "thin-link".
630  */
631 std::unique_ptr<ModuleSummaryIndex> ThinLTOCodeGenerator::linkCombinedIndex() {
632   std::unique_ptr<ModuleSummaryIndex> CombinedIndex =
633       std::make_unique<ModuleSummaryIndex>(/*HaveGVs=*/false);
634   uint64_t NextModuleId = 0;
635   for (auto &Mod : Modules) {
636     auto &M = Mod->getSingleBitcodeModule();
637     if (Error Err =
638             M.readSummary(*CombinedIndex, Mod->getName(), NextModuleId++)) {
639       // FIXME diagnose
640       logAllUnhandledErrors(
641           std::move(Err), errs(),
642           "error: can't create module summary index for buffer: ");
643       return nullptr;
644     }
645   }
646   return CombinedIndex;
647 }
648 
649 namespace {
650 struct IsExported {
651   const StringMap<FunctionImporter::ExportSetTy> &ExportLists;
652   const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols;
653 
654   IsExported(const StringMap<FunctionImporter::ExportSetTy> &ExportLists,
655              const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols)
656       : ExportLists(ExportLists), GUIDPreservedSymbols(GUIDPreservedSymbols) {}
657 
658   bool operator()(StringRef ModuleIdentifier, ValueInfo VI) const {
659     const auto &ExportList = ExportLists.find(ModuleIdentifier);
660     return (ExportList != ExportLists.end() && ExportList->second.count(VI)) ||
661            GUIDPreservedSymbols.count(VI.getGUID());
662   }
663 };
664 
665 struct IsPrevailing {
666   const DenseMap<GlobalValue::GUID, const GlobalValueSummary *> &PrevailingCopy;
667   IsPrevailing(const DenseMap<GlobalValue::GUID, const GlobalValueSummary *>
668                    &PrevailingCopy)
669       : PrevailingCopy(PrevailingCopy) {}
670 
671   bool operator()(GlobalValue::GUID GUID, const GlobalValueSummary *S) const {
672     const auto &Prevailing = PrevailingCopy.find(GUID);
673     // Not in map means that there was only one copy, which must be prevailing.
674     if (Prevailing == PrevailingCopy.end())
675       return true;
676     return Prevailing->second == S;
677   };
678 };
679 } // namespace
680 
681 static void computeDeadSymbolsInIndex(
682     ModuleSummaryIndex &Index,
683     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
684   // We have no symbols resolution available. And can't do any better now in the
685   // case where the prevailing symbol is in a native object. It can be refined
686   // with linker information in the future.
687   auto isPrevailing = [&](GlobalValue::GUID G) {
688     return PrevailingType::Unknown;
689   };
690   computeDeadSymbolsWithConstProp(Index, GUIDPreservedSymbols, isPrevailing,
691                                   /* ImportEnabled = */ true);
692 }
693 
694 /**
695  * Perform promotion and renaming of exported internal functions.
696  * Index is updated to reflect linkage changes from weak resolution.
697  */
698 void ThinLTOCodeGenerator::promote(Module &TheModule, ModuleSummaryIndex &Index,
699                                    const lto::InputFile &File) {
700   auto ModuleCount = Index.modulePaths().size();
701   auto ModuleIdentifier = TheModule.getModuleIdentifier();
702 
703   // Collect for each module the list of function it defines (GUID -> Summary).
704   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries;
705   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
706 
707   // Convert the preserved symbols set from string to GUID
708   auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
709       File, PreservedSymbols, Triple(TheModule.getTargetTriple()));
710 
711   // Add used symbol to the preserved symbols.
712   addUsedSymbolToPreservedGUID(File, GUIDPreservedSymbols);
713 
714   // Compute "dead" symbols, we don't want to import/export these!
715   computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
716 
717   // Generate import/export list
718   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
719   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
720   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
721                            ExportLists);
722 
723   DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
724   computePrevailingCopies(Index, PrevailingCopy);
725 
726   // Resolve prevailing symbols
727   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
728   resolvePrevailingInIndex(Index, ResolvedODR, GUIDPreservedSymbols,
729                            PrevailingCopy);
730 
731   thinLTOFinalizeInModule(TheModule,
732                           ModuleToDefinedGVSummaries[ModuleIdentifier],
733                           /*PropagateAttrs=*/false);
734 
735   // Promote the exported values in the index, so that they are promoted
736   // in the module.
737   thinLTOInternalizeAndPromoteInIndex(
738       Index, IsExported(ExportLists, GUIDPreservedSymbols),
739       IsPrevailing(PrevailingCopy));
740 
741   // FIXME Set ClearDSOLocalOnDeclarations.
742   promoteModule(TheModule, Index, /*ClearDSOLocalOnDeclarations=*/false);
743 }
744 
745 /**
746  * Perform cross-module importing for the module identified by ModuleIdentifier.
747  */
748 void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
749                                              ModuleSummaryIndex &Index,
750                                              const lto::InputFile &File) {
751   auto ModuleMap = generateModuleMap(Modules);
752   auto ModuleCount = Index.modulePaths().size();
753 
754   // Collect for each module the list of function it defines (GUID -> Summary).
755   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
756   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
757 
758   // Convert the preserved symbols set from string to GUID
759   auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
760       File, PreservedSymbols, Triple(TheModule.getTargetTriple()));
761 
762   addUsedSymbolToPreservedGUID(File, GUIDPreservedSymbols);
763 
764   // Compute "dead" symbols, we don't want to import/export these!
765   computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
766 
767   // Generate import/export list
768   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
769   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
770   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
771                            ExportLists);
772   auto &ImportList = ImportLists[TheModule.getModuleIdentifier()];
773 
774   // FIXME Set ClearDSOLocalOnDeclarations.
775   crossImportIntoModule(TheModule, Index, ModuleMap, ImportList,
776                         /*ClearDSOLocalOnDeclarations=*/false);
777 }
778 
779 /**
780  * Compute the list of summaries needed for importing into module.
781  */
782 void ThinLTOCodeGenerator::gatherImportedSummariesForModule(
783     Module &TheModule, ModuleSummaryIndex &Index,
784     std::map<std::string, GVSummaryMapTy> &ModuleToSummariesForIndex,
785     const lto::InputFile &File) {
786   auto ModuleCount = Index.modulePaths().size();
787   auto ModuleIdentifier = TheModule.getModuleIdentifier();
788 
789   // Collect for each module the list of function it defines (GUID -> Summary).
790   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
791   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
792 
793   // Convert the preserved symbols set from string to GUID
794   auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
795       File, PreservedSymbols, Triple(TheModule.getTargetTriple()));
796 
797   addUsedSymbolToPreservedGUID(File, GUIDPreservedSymbols);
798 
799   // Compute "dead" symbols, we don't want to import/export these!
800   computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
801 
802   // Generate import/export list
803   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
804   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
805   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
806                            ExportLists);
807 
808   llvm::gatherImportedSummariesForModule(
809       ModuleIdentifier, ModuleToDefinedGVSummaries,
810       ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
811 }
812 
813 /**
814  * Emit the list of files needed for importing into module.
815  */
816 void ThinLTOCodeGenerator::emitImports(Module &TheModule, StringRef OutputName,
817                                        ModuleSummaryIndex &Index,
818                                        const lto::InputFile &File) {
819   auto ModuleCount = Index.modulePaths().size();
820   auto ModuleIdentifier = TheModule.getModuleIdentifier();
821 
822   // Collect for each module the list of function it defines (GUID -> Summary).
823   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
824   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
825 
826   // Convert the preserved symbols set from string to GUID
827   auto GUIDPreservedSymbols = computeGUIDPreservedSymbols(
828       File, PreservedSymbols, Triple(TheModule.getTargetTriple()));
829 
830   addUsedSymbolToPreservedGUID(File, GUIDPreservedSymbols);
831 
832   // Compute "dead" symbols, we don't want to import/export these!
833   computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
834 
835   // Generate import/export list
836   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
837   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
838   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
839                            ExportLists);
840 
841   std::map<std::string, GVSummaryMapTy> ModuleToSummariesForIndex;
842   llvm::gatherImportedSummariesForModule(
843       ModuleIdentifier, ModuleToDefinedGVSummaries,
844       ImportLists[ModuleIdentifier], ModuleToSummariesForIndex);
845 
846   std::error_code EC;
847   if ((EC = EmitImportsFiles(ModuleIdentifier, OutputName,
848                              ModuleToSummariesForIndex)))
849     report_fatal_error(Twine("Failed to open ") + OutputName +
850                        " to save imports lists\n");
851 }
852 
853 /**
854  * Perform internalization. Runs promote and internalization together.
855  * Index is updated to reflect linkage changes.
856  */
857 void ThinLTOCodeGenerator::internalize(Module &TheModule,
858                                        ModuleSummaryIndex &Index,
859                                        const lto::InputFile &File) {
860   initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
861   auto ModuleCount = Index.modulePaths().size();
862   auto ModuleIdentifier = TheModule.getModuleIdentifier();
863 
864   // Convert the preserved symbols set from string to GUID
865   auto GUIDPreservedSymbols =
866       computeGUIDPreservedSymbols(File, PreservedSymbols, TMBuilder.TheTriple);
867 
868   addUsedSymbolToPreservedGUID(File, GUIDPreservedSymbols);
869 
870   // Collect for each module the list of function it defines (GUID -> Summary).
871   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
872   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
873 
874   // Compute "dead" symbols, we don't want to import/export these!
875   computeDeadSymbolsInIndex(Index, GUIDPreservedSymbols);
876 
877   // Generate import/export list
878   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
879   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
880   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
881                            ExportLists);
882   auto &ExportList = ExportLists[ModuleIdentifier];
883 
884   // Be friendly and don't nuke totally the module when the client didn't
885   // supply anything to preserve.
886   if (ExportList.empty() && GUIDPreservedSymbols.empty())
887     return;
888 
889   DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
890   computePrevailingCopies(Index, PrevailingCopy);
891 
892   // Resolve prevailing symbols
893   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
894   resolvePrevailingInIndex(Index, ResolvedODR, GUIDPreservedSymbols,
895                            PrevailingCopy);
896 
897   // Promote the exported values in the index, so that they are promoted
898   // in the module.
899   thinLTOInternalizeAndPromoteInIndex(
900       Index, IsExported(ExportLists, GUIDPreservedSymbols),
901       IsPrevailing(PrevailingCopy));
902 
903   // FIXME Set ClearDSOLocalOnDeclarations.
904   promoteModule(TheModule, Index, /*ClearDSOLocalOnDeclarations=*/false);
905 
906   // Internalization
907   thinLTOFinalizeInModule(TheModule,
908                           ModuleToDefinedGVSummaries[ModuleIdentifier],
909                           /*PropagateAttrs=*/false);
910 
911   thinLTOInternalizeModule(TheModule,
912                            ModuleToDefinedGVSummaries[ModuleIdentifier]);
913 }
914 
915 /**
916  * Perform post-importing ThinLTO optimizations.
917  */
918 void ThinLTOCodeGenerator::optimize(Module &TheModule) {
919   initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
920 
921   // Optimize now
922   optimizeModule(TheModule, *TMBuilder.create(), OptLevel, Freestanding,
923                  DebugPassManager, nullptr);
924 }
925 
926 /// Write out the generated object file, either from CacheEntryPath or from
927 /// OutputBuffer, preferring hard-link when possible.
928 /// Returns the path to the generated file in SavedObjectsDirectoryPath.
929 std::string
930 ThinLTOCodeGenerator::writeGeneratedObject(int count, StringRef CacheEntryPath,
931                                            const MemoryBuffer &OutputBuffer) {
932   auto ArchName = TMBuilder.TheTriple.getArchName();
933   SmallString<128> OutputPath(SavedObjectsDirectoryPath);
934   llvm::sys::path::append(OutputPath,
935                           Twine(count) + "." + ArchName + ".thinlto.o");
936   OutputPath.c_str(); // Ensure the string is null terminated.
937   if (sys::fs::exists(OutputPath))
938     sys::fs::remove(OutputPath);
939 
940   // We don't return a memory buffer to the linker, just a list of files.
941   if (!CacheEntryPath.empty()) {
942     // Cache is enabled, hard-link the entry (or copy if hard-link fails).
943     auto Err = sys::fs::create_hard_link(CacheEntryPath, OutputPath);
944     if (!Err)
945       return std::string(OutputPath.str());
946     // Hard linking failed, try to copy.
947     Err = sys::fs::copy_file(CacheEntryPath, OutputPath);
948     if (!Err)
949       return std::string(OutputPath.str());
950     // Copy failed (could be because the CacheEntry was removed from the cache
951     // in the meantime by another process), fall back and try to write down the
952     // buffer to the output.
953     errs() << "remark: can't link or copy from cached entry '" << CacheEntryPath
954            << "' to '" << OutputPath << "'\n";
955   }
956   // No cache entry, just write out the buffer.
957   std::error_code Err;
958   raw_fd_ostream OS(OutputPath, Err, sys::fs::OF_None);
959   if (Err)
960     report_fatal_error(Twine("Can't open output '") + OutputPath + "'\n");
961   OS << OutputBuffer.getBuffer();
962   return std::string(OutputPath.str());
963 }
964 
965 // Main entry point for the ThinLTO processing
966 void ThinLTOCodeGenerator::run() {
967   timeTraceProfilerBegin("ThinLink", StringRef(""));
968   auto TimeTraceScopeExit = llvm::make_scope_exit([]() {
969     if (llvm::timeTraceProfilerEnabled())
970       llvm::timeTraceProfilerEnd();
971   });
972   // Prepare the resulting object vector
973   assert(ProducedBinaries.empty() && "The generator should not be reused");
974   if (SavedObjectsDirectoryPath.empty())
975     ProducedBinaries.resize(Modules.size());
976   else {
977     sys::fs::create_directories(SavedObjectsDirectoryPath);
978     bool IsDir;
979     sys::fs::is_directory(SavedObjectsDirectoryPath, IsDir);
980     if (!IsDir)
981       report_fatal_error(Twine("Unexistent dir: '") + SavedObjectsDirectoryPath + "'");
982     ProducedBinaryFiles.resize(Modules.size());
983   }
984 
985   if (CodeGenOnly) {
986     // Perform only parallel codegen and return.
987     ThreadPool Pool;
988     int count = 0;
989     for (auto &Mod : Modules) {
990       Pool.async([&](int count) {
991         LLVMContext Context;
992         Context.setDiscardValueNames(LTODiscardValueNames);
993 
994         // Parse module now
995         auto TheModule = loadModuleFromInput(Mod.get(), Context, false,
996                                              /*IsImporting*/ false);
997 
998         // CodeGen
999         auto OutputBuffer = codegenModule(*TheModule, *TMBuilder.create());
1000         if (SavedObjectsDirectoryPath.empty())
1001           ProducedBinaries[count] = std::move(OutputBuffer);
1002         else
1003           ProducedBinaryFiles[count] =
1004               writeGeneratedObject(count, "", *OutputBuffer);
1005       }, count++);
1006     }
1007 
1008     return;
1009   }
1010 
1011   // Sequential linking phase
1012   auto Index = linkCombinedIndex();
1013 
1014   // Save temps: index.
1015   if (!SaveTempsDir.empty()) {
1016     auto SaveTempPath = SaveTempsDir + "index.bc";
1017     std::error_code EC;
1018     raw_fd_ostream OS(SaveTempPath, EC, sys::fs::OF_None);
1019     if (EC)
1020       report_fatal_error(Twine("Failed to open ") + SaveTempPath +
1021                          " to save optimized bitcode\n");
1022     writeIndexToFile(*Index, OS);
1023   }
1024 
1025 
1026   // Prepare the module map.
1027   auto ModuleMap = generateModuleMap(Modules);
1028   auto ModuleCount = Modules.size();
1029 
1030   // Collect for each module the list of function it defines (GUID -> Summary).
1031   StringMap<GVSummaryMapTy> ModuleToDefinedGVSummaries(ModuleCount);
1032   Index->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
1033 
1034   // Convert the preserved symbols set from string to GUID, this is needed for
1035   // computing the caching hash and the internalization.
1036   DenseSet<GlobalValue::GUID> GUIDPreservedSymbols;
1037   for (const auto &M : Modules)
1038     computeGUIDPreservedSymbols(*M, PreservedSymbols, TMBuilder.TheTriple,
1039                                 GUIDPreservedSymbols);
1040 
1041   // Add used symbol from inputs to the preserved symbols.
1042   for (const auto &M : Modules)
1043     addUsedSymbolToPreservedGUID(*M, GUIDPreservedSymbols);
1044 
1045   // Compute "dead" symbols, we don't want to import/export these!
1046   computeDeadSymbolsInIndex(*Index, GUIDPreservedSymbols);
1047 
1048   // Synthesize entry counts for functions in the combined index.
1049   computeSyntheticCounts(*Index);
1050 
1051   // Currently there is no support for enabling whole program visibility via a
1052   // linker option in the old LTO API, but this call allows it to be specified
1053   // via the internal option. Must be done before WPD below.
1054   if (hasWholeProgramVisibility(/* WholeProgramVisibilityEnabledInLTO */ false))
1055     Index->setWithWholeProgramVisibility();
1056   updateVCallVisibilityInIndex(*Index,
1057                                /* WholeProgramVisibilityEnabledInLTO */ false,
1058                                // FIXME: This needs linker information via a
1059                                // TBD new interface.
1060                                /* DynamicExportSymbols */ {});
1061 
1062   // Perform index-based WPD. This will return immediately if there are
1063   // no index entries in the typeIdMetadata map (e.g. if we are instead
1064   // performing IR-based WPD in hybrid regular/thin LTO mode).
1065   std::map<ValueInfo, std::vector<VTableSlotSummary>> LocalWPDTargetsMap;
1066   std::set<GlobalValue::GUID> ExportedGUIDs;
1067   runWholeProgramDevirtOnIndex(*Index, ExportedGUIDs, LocalWPDTargetsMap);
1068   for (auto GUID : ExportedGUIDs)
1069     GUIDPreservedSymbols.insert(GUID);
1070 
1071   // Collect the import/export lists for all modules from the call-graph in the
1072   // combined index.
1073   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
1074   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
1075   ComputeCrossModuleImport(*Index, ModuleToDefinedGVSummaries, ImportLists,
1076                            ExportLists);
1077 
1078   // We use a std::map here to be able to have a defined ordering when
1079   // producing a hash for the cache entry.
1080   // FIXME: we should be able to compute the caching hash for the entry based
1081   // on the index, and nuke this map.
1082   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
1083 
1084   DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
1085   computePrevailingCopies(*Index, PrevailingCopy);
1086 
1087   // Resolve prevailing symbols, this has to be computed early because it
1088   // impacts the caching.
1089   resolvePrevailingInIndex(*Index, ResolvedODR, GUIDPreservedSymbols,
1090                            PrevailingCopy);
1091 
1092   // Use global summary-based analysis to identify symbols that can be
1093   // internalized (because they aren't exported or preserved as per callback).
1094   // Changes are made in the index, consumed in the ThinLTO backends.
1095   updateIndexWPDForExports(*Index,
1096                            IsExported(ExportLists, GUIDPreservedSymbols),
1097                            LocalWPDTargetsMap);
1098   thinLTOInternalizeAndPromoteInIndex(
1099       *Index, IsExported(ExportLists, GUIDPreservedSymbols),
1100       IsPrevailing(PrevailingCopy));
1101 
1102   thinLTOPropagateFunctionAttrs(*Index, IsPrevailing(PrevailingCopy));
1103 
1104   // Make sure that every module has an entry in the ExportLists, ImportList,
1105   // GVSummary and ResolvedODR maps to enable threaded access to these maps
1106   // below.
1107   for (auto &Module : Modules) {
1108     auto ModuleIdentifier = Module->getName();
1109     ExportLists[ModuleIdentifier];
1110     ImportLists[ModuleIdentifier];
1111     ResolvedODR[ModuleIdentifier];
1112     ModuleToDefinedGVSummaries[ModuleIdentifier];
1113   }
1114 
1115   std::vector<BitcodeModule *> ModulesVec;
1116   ModulesVec.reserve(Modules.size());
1117   for (auto &Mod : Modules)
1118     ModulesVec.push_back(&Mod->getSingleBitcodeModule());
1119   std::vector<int> ModulesOrdering = lto::generateModulesOrdering(ModulesVec);
1120 
1121   if (llvm::timeTraceProfilerEnabled())
1122     llvm::timeTraceProfilerEnd();
1123 
1124   TimeTraceScopeExit.release();
1125 
1126   // Parallel optimizer + codegen
1127   {
1128     ThreadPool Pool(heavyweight_hardware_concurrency(ThreadCount));
1129     for (auto IndexCount : ModulesOrdering) {
1130       auto &Mod = Modules[IndexCount];
1131       Pool.async([&](int count) {
1132         auto ModuleIdentifier = Mod->getName();
1133         auto &ExportList = ExportLists[ModuleIdentifier];
1134 
1135         auto &DefinedGVSummaries = ModuleToDefinedGVSummaries[ModuleIdentifier];
1136 
1137         // The module may be cached, this helps handling it.
1138         ModuleCacheEntry CacheEntry(CacheOptions.Path, *Index, ModuleIdentifier,
1139                                     ImportLists[ModuleIdentifier], ExportList,
1140                                     ResolvedODR[ModuleIdentifier],
1141                                     DefinedGVSummaries, OptLevel, Freestanding,
1142                                     TMBuilder);
1143         auto CacheEntryPath = CacheEntry.getEntryPath();
1144 
1145         {
1146           auto ErrOrBuffer = CacheEntry.tryLoadingBuffer();
1147           LLVM_DEBUG(dbgs() << "Cache " << (ErrOrBuffer ? "hit" : "miss")
1148                             << " '" << CacheEntryPath << "' for buffer "
1149                             << count << " " << ModuleIdentifier << "\n");
1150 
1151           if (ErrOrBuffer) {
1152             // Cache Hit!
1153             if (SavedObjectsDirectoryPath.empty())
1154               ProducedBinaries[count] = std::move(ErrOrBuffer.get());
1155             else
1156               ProducedBinaryFiles[count] = writeGeneratedObject(
1157                   count, CacheEntryPath, *ErrOrBuffer.get());
1158             return;
1159           }
1160         }
1161 
1162         LLVMContext Context;
1163         Context.setDiscardValueNames(LTODiscardValueNames);
1164         Context.enableDebugTypeODRUniquing();
1165         auto DiagFileOrErr = lto::setupLLVMOptimizationRemarks(
1166             Context, RemarksFilename, RemarksPasses, RemarksFormat,
1167             RemarksWithHotness, RemarksHotnessThreshold, count);
1168         if (!DiagFileOrErr) {
1169           errs() << "Error: " << toString(DiagFileOrErr.takeError()) << "\n";
1170           report_fatal_error("ThinLTO: Can't get an output file for the "
1171                              "remarks");
1172         }
1173 
1174         // Parse module now
1175         auto TheModule = loadModuleFromInput(Mod.get(), Context, false,
1176                                              /*IsImporting*/ false);
1177 
1178         // Save temps: original file.
1179         saveTempBitcode(*TheModule, SaveTempsDir, count, ".0.original.bc");
1180 
1181         auto &ImportList = ImportLists[ModuleIdentifier];
1182         // Run the main process now, and generates a binary
1183         auto OutputBuffer = ProcessThinLTOModule(
1184             *TheModule, *Index, ModuleMap, *TMBuilder.create(), ImportList,
1185             ExportList, GUIDPreservedSymbols,
1186             ModuleToDefinedGVSummaries[ModuleIdentifier], CacheOptions,
1187             DisableCodeGen, SaveTempsDir, Freestanding, OptLevel, count,
1188             DebugPassManager);
1189 
1190         // Commit to the cache (if enabled)
1191         CacheEntry.write(*OutputBuffer);
1192 
1193         if (SavedObjectsDirectoryPath.empty()) {
1194           // We need to generated a memory buffer for the linker.
1195           if (!CacheEntryPath.empty()) {
1196             // When cache is enabled, reload from the cache if possible.
1197             // Releasing the buffer from the heap and reloading it from the
1198             // cache file with mmap helps us to lower memory pressure.
1199             // The freed memory can be used for the next input file.
1200             // The final binary link will read from the VFS cache (hopefully!)
1201             // or from disk (if the memory pressure was too high).
1202             auto ReloadedBufferOrErr = CacheEntry.tryLoadingBuffer();
1203             if (auto EC = ReloadedBufferOrErr.getError()) {
1204               // On error, keep the preexisting buffer and print a diagnostic.
1205               errs() << "remark: can't reload cached file '" << CacheEntryPath
1206                      << "': " << EC.message() << "\n";
1207             } else {
1208               OutputBuffer = std::move(*ReloadedBufferOrErr);
1209             }
1210           }
1211           ProducedBinaries[count] = std::move(OutputBuffer);
1212           return;
1213         }
1214         ProducedBinaryFiles[count] = writeGeneratedObject(
1215             count, CacheEntryPath, *OutputBuffer);
1216       }, IndexCount);
1217     }
1218   }
1219 
1220   pruneCache(CacheOptions.Path, CacheOptions.Policy, ProducedBinaries);
1221 
1222   // If statistics were requested, print them out now.
1223   if (llvm::AreStatisticsEnabled())
1224     llvm::PrintStatistics();
1225   reportAndResetTimings();
1226 }
1227