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      1 //===-LTOBackend.cpp - LLVM Link Time Optimizer Backend -------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements the "backend" phase of LTO, i.e. it performs
     11 // optimization and code generation on a loaded module. It is generally used
     12 // internally by the LTO class but can also be used independently, for example
     13 // to implement a standalone ThinLTO backend.
     14 //
     15 //===----------------------------------------------------------------------===//
     16 
     17 #include "llvm/LTO/LTOBackend.h"
     18 #include "llvm/Analysis/AliasAnalysis.h"
     19 #include "llvm/Analysis/CGSCCPassManager.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/LegacyPassManager.h"
     25 #include "llvm/IR/PassManager.h"
     26 #include "llvm/IR/Verifier.h"
     27 #include "llvm/LTO/LTO.h"
     28 #include "llvm/MC/SubtargetFeature.h"
     29 #include "llvm/Object/ModuleSymbolTable.h"
     30 #include "llvm/Passes/PassBuilder.h"
     31 #include "llvm/Support/Error.h"
     32 #include "llvm/Support/FileSystem.h"
     33 #include "llvm/Support/MemoryBuffer.h"
     34 #include "llvm/Support/Path.h"
     35 #include "llvm/Support/Program.h"
     36 #include "llvm/Support/raw_ostream.h"
     37 #include "llvm/Support/TargetRegistry.h"
     38 #include "llvm/Support/ThreadPool.h"
     39 #include "llvm/Target/TargetMachine.h"
     40 #include "llvm/Transforms/IPO.h"
     41 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
     42 #include "llvm/Transforms/Scalar/LoopPassManager.h"
     43 #include "llvm/Transforms/Utils/FunctionImportUtils.h"
     44 #include "llvm/Transforms/Utils/SplitModule.h"
     45 
     46 using namespace llvm;
     47 using namespace lto;
     48 
     49 LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
     50   errs() << "failed to open " << Path << ": " << Msg << '\n';
     51   errs().flush();
     52   exit(1);
     53 }
     54 
     55 Error Config::addSaveTemps(std::string OutputFileName,
     56                            bool UseInputModulePath) {
     57   ShouldDiscardValueNames = false;
     58 
     59   std::error_code EC;
     60   ResolutionFile = llvm::make_unique<raw_fd_ostream>(
     61       OutputFileName + "resolution.txt", EC, sys::fs::OpenFlags::F_Text);
     62   if (EC)
     63     return errorCodeToError(EC);
     64 
     65   auto setHook = [&](std::string PathSuffix, ModuleHookFn &Hook) {
     66     // Keep track of the hook provided by the linker, which also needs to run.
     67     ModuleHookFn LinkerHook = Hook;
     68     Hook = [=](unsigned Task, const Module &M) {
     69       // If the linker's hook returned false, we need to pass that result
     70       // through.
     71       if (LinkerHook && !LinkerHook(Task, M))
     72         return false;
     73 
     74       std::string PathPrefix;
     75       // If this is the combined module (not a ThinLTO backend compile) or the
     76       // user hasn't requested using the input module's path, emit to a file
     77       // named from the provided OutputFileName with the Task ID appended.
     78       if (M.getModuleIdentifier() == "ld-temp.o" || !UseInputModulePath) {
     79         PathPrefix = OutputFileName;
     80         if (Task != (unsigned)-1)
     81           PathPrefix += utostr(Task) + ".";
     82       } else
     83         PathPrefix = M.getModuleIdentifier() + ".";
     84       std::string Path = PathPrefix + PathSuffix + ".bc";
     85       std::error_code EC;
     86       raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
     87       // Because -save-temps is a debugging feature, we report the error
     88       // directly and exit.
     89       if (EC)
     90         reportOpenError(Path, EC.message());
     91       WriteBitcodeToFile(M, OS, /*ShouldPreserveUseListOrder=*/false);
     92       return true;
     93     };
     94   };
     95 
     96   setHook("0.preopt", PreOptModuleHook);
     97   setHook("1.promote", PostPromoteModuleHook);
     98   setHook("2.internalize", PostInternalizeModuleHook);
     99   setHook("3.import", PostImportModuleHook);
    100   setHook("4.opt", PostOptModuleHook);
    101   setHook("5.precodegen", PreCodeGenModuleHook);
    102 
    103   CombinedIndexHook = [=](const ModuleSummaryIndex &Index) {
    104     std::string Path = OutputFileName + "index.bc";
    105     std::error_code EC;
    106     raw_fd_ostream OS(Path, EC, sys::fs::OpenFlags::F_None);
    107     // Because -save-temps is a debugging feature, we report the error
    108     // directly and exit.
    109     if (EC)
    110       reportOpenError(Path, EC.message());
    111     WriteIndexToFile(Index, OS);
    112 
    113     Path = OutputFileName + "index.dot";
    114     raw_fd_ostream OSDot(Path, EC, sys::fs::OpenFlags::F_None);
    115     if (EC)
    116       reportOpenError(Path, EC.message());
    117     Index.exportToDot(OSDot);
    118     return true;
    119   };
    120 
    121   return Error::success();
    122 }
    123 
    124 namespace {
    125 
    126 std::unique_ptr<TargetMachine>
    127 createTargetMachine(Config &Conf, const Target *TheTarget, Module &M) {
    128   StringRef TheTriple = M.getTargetTriple();
    129   SubtargetFeatures Features;
    130   Features.getDefaultSubtargetFeatures(Triple(TheTriple));
    131   for (const std::string &A : Conf.MAttrs)
    132     Features.AddFeature(A);
    133 
    134   Reloc::Model RelocModel;
    135   if (Conf.RelocModel)
    136     RelocModel = *Conf.RelocModel;
    137   else
    138     RelocModel =
    139         M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
    140 
    141   return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
    142       TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
    143       Conf.CodeModel, Conf.CGOptLevel));
    144 }
    145 
    146 static void runNewPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
    147                            unsigned OptLevel, bool IsThinLTO,
    148                            ModuleSummaryIndex *ExportSummary,
    149                            const ModuleSummaryIndex *ImportSummary) {
    150   Optional<PGOOptions> PGOOpt;
    151   if (!Conf.SampleProfile.empty())
    152     PGOOpt = PGOOptions("", "", Conf.SampleProfile, false, true);
    153 
    154   PassBuilder PB(TM, PGOOpt);
    155   AAManager AA;
    156 
    157   // Parse a custom AA pipeline if asked to.
    158   if (!PB.parseAAPipeline(AA, "default"))
    159     report_fatal_error("Error parsing default AA pipeline");
    160 
    161   LoopAnalysisManager LAM(Conf.DebugPassManager);
    162   FunctionAnalysisManager FAM(Conf.DebugPassManager);
    163   CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
    164   ModuleAnalysisManager MAM(Conf.DebugPassManager);
    165 
    166   // Register the AA manager first so that our version is the one used.
    167   FAM.registerPass([&] { return std::move(AA); });
    168 
    169   // Register all the basic analyses with the managers.
    170   PB.registerModuleAnalyses(MAM);
    171   PB.registerCGSCCAnalyses(CGAM);
    172   PB.registerFunctionAnalyses(FAM);
    173   PB.registerLoopAnalyses(LAM);
    174   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
    175 
    176   ModulePassManager MPM(Conf.DebugPassManager);
    177   // FIXME (davide): verify the input.
    178 
    179   PassBuilder::OptimizationLevel OL;
    180 
    181   switch (OptLevel) {
    182   default:
    183     llvm_unreachable("Invalid optimization level");
    184   case 0:
    185     OL = PassBuilder::O0;
    186     break;
    187   case 1:
    188     OL = PassBuilder::O1;
    189     break;
    190   case 2:
    191     OL = PassBuilder::O2;
    192     break;
    193   case 3:
    194     OL = PassBuilder::O3;
    195     break;
    196   }
    197 
    198   if (IsThinLTO)
    199     MPM = PB.buildThinLTODefaultPipeline(OL, Conf.DebugPassManager,
    200                                          ImportSummary);
    201   else
    202     MPM = PB.buildLTODefaultPipeline(OL, Conf.DebugPassManager, ExportSummary);
    203   MPM.run(Mod, MAM);
    204 
    205   // FIXME (davide): verify the output.
    206 }
    207 
    208 static void runNewPMCustomPasses(Module &Mod, TargetMachine *TM,
    209                                  std::string PipelineDesc,
    210                                  std::string AAPipelineDesc,
    211                                  bool DisableVerify) {
    212   PassBuilder PB(TM);
    213   AAManager AA;
    214 
    215   // Parse a custom AA pipeline if asked to.
    216   if (!AAPipelineDesc.empty())
    217     if (!PB.parseAAPipeline(AA, AAPipelineDesc))
    218       report_fatal_error("unable to parse AA pipeline description: " +
    219                          AAPipelineDesc);
    220 
    221   LoopAnalysisManager LAM;
    222   FunctionAnalysisManager FAM;
    223   CGSCCAnalysisManager CGAM;
    224   ModuleAnalysisManager MAM;
    225 
    226   // Register the AA manager first so that our version is the one used.
    227   FAM.registerPass([&] { return std::move(AA); });
    228 
    229   // Register all the basic analyses with the managers.
    230   PB.registerModuleAnalyses(MAM);
    231   PB.registerCGSCCAnalyses(CGAM);
    232   PB.registerFunctionAnalyses(FAM);
    233   PB.registerLoopAnalyses(LAM);
    234   PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
    235 
    236   ModulePassManager MPM;
    237 
    238   // Always verify the input.
    239   MPM.addPass(VerifierPass());
    240 
    241   // Now, add all the passes we've been requested to.
    242   if (!PB.parsePassPipeline(MPM, PipelineDesc))
    243     report_fatal_error("unable to parse pass pipeline description: " +
    244                        PipelineDesc);
    245 
    246   if (!DisableVerify)
    247     MPM.addPass(VerifierPass());
    248   MPM.run(Mod, MAM);
    249 }
    250 
    251 static void runOldPMPasses(Config &Conf, Module &Mod, TargetMachine *TM,
    252                            bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
    253                            const ModuleSummaryIndex *ImportSummary) {
    254   legacy::PassManager passes;
    255   passes.add(createTargetTransformInfoWrapperPass(TM->getTargetIRAnalysis()));
    256 
    257   PassManagerBuilder PMB;
    258   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
    259   PMB.Inliner = createFunctionInliningPass();
    260   PMB.ExportSummary = ExportSummary;
    261   PMB.ImportSummary = ImportSummary;
    262   // Unconditionally verify input since it is not verified before this
    263   // point and has unknown origin.
    264   PMB.VerifyInput = true;
    265   PMB.VerifyOutput = !Conf.DisableVerify;
    266   PMB.LoopVectorize = true;
    267   PMB.SLPVectorize = true;
    268   PMB.OptLevel = Conf.OptLevel;
    269   PMB.PGOSampleUse = Conf.SampleProfile;
    270   if (IsThinLTO)
    271     PMB.populateThinLTOPassManager(passes);
    272   else
    273     PMB.populateLTOPassManager(passes);
    274   passes.run(Mod);
    275 }
    276 
    277 bool opt(Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
    278          bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
    279          const ModuleSummaryIndex *ImportSummary) {
    280   // FIXME: Plumb the combined index into the new pass manager.
    281   if (!Conf.OptPipeline.empty())
    282     runNewPMCustomPasses(Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
    283                          Conf.DisableVerify);
    284   else if (Conf.UseNewPM)
    285     runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
    286                    ImportSummary);
    287   else
    288     runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
    289   return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
    290 }
    291 
    292 void codegen(Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
    293              unsigned Task, Module &Mod) {
    294   if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
    295     return;
    296 
    297   std::unique_ptr<ToolOutputFile> DwoOut;
    298   SmallString<1024> DwoFile(Conf.DwoPath);
    299   if (!Conf.DwoDir.empty()) {
    300     std::error_code EC;
    301     if (auto EC = llvm::sys::fs::create_directories(Conf.DwoDir))
    302       report_fatal_error("Failed to create directory " + Conf.DwoDir + ": " +
    303                          EC.message());
    304 
    305     DwoFile = Conf.DwoDir;
    306     sys::path::append(DwoFile, std::to_string(Task) + ".dwo");
    307   }
    308 
    309   if (!DwoFile.empty()) {
    310     std::error_code EC;
    311     TM->Options.MCOptions.SplitDwarfFile = DwoFile.str().str();
    312     DwoOut = llvm::make_unique<ToolOutputFile>(DwoFile, EC, sys::fs::F_None);
    313     if (EC)
    314       report_fatal_error("Failed to open " + DwoFile + ": " + EC.message());
    315   }
    316 
    317   auto Stream = AddStream(Task);
    318   legacy::PassManager CodeGenPasses;
    319   if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
    320                               DwoOut ? &DwoOut->os() : nullptr,
    321                               Conf.CGFileType))
    322     report_fatal_error("Failed to setup codegen");
    323   CodeGenPasses.run(Mod);
    324 
    325   if (DwoOut)
    326     DwoOut->keep();
    327 }
    328 
    329 void splitCodeGen(Config &C, TargetMachine *TM, AddStreamFn AddStream,
    330                   unsigned ParallelCodeGenParallelismLevel,
    331                   std::unique_ptr<Module> Mod) {
    332   ThreadPool CodegenThreadPool(ParallelCodeGenParallelismLevel);
    333   unsigned ThreadCount = 0;
    334   const Target *T = &TM->getTarget();
    335 
    336   SplitModule(
    337       std::move(Mod), ParallelCodeGenParallelismLevel,
    338       [&](std::unique_ptr<Module> MPart) {
    339         // We want to clone the module in a new context to multi-thread the
    340         // codegen. We do it by serializing partition modules to bitcode
    341         // (while still on the main thread, in order to avoid data races) and
    342         // spinning up new threads which deserialize the partitions into
    343         // separate contexts.
    344         // FIXME: Provide a more direct way to do this in LLVM.
    345         SmallString<0> BC;
    346         raw_svector_ostream BCOS(BC);
    347         WriteBitcodeToFile(*MPart, BCOS);
    348 
    349         // Enqueue the task
    350         CodegenThreadPool.async(
    351             [&](const SmallString<0> &BC, unsigned ThreadId) {
    352               LTOLLVMContext Ctx(C);
    353               Expected<std::unique_ptr<Module>> MOrErr = parseBitcodeFile(
    354                   MemoryBufferRef(StringRef(BC.data(), BC.size()), "ld-temp.o"),
    355                   Ctx);
    356               if (!MOrErr)
    357                 report_fatal_error("Failed to read bitcode");
    358               std::unique_ptr<Module> MPartInCtx = std::move(MOrErr.get());
    359 
    360               std::unique_ptr<TargetMachine> TM =
    361                   createTargetMachine(C, T, *MPartInCtx);
    362 
    363               codegen(C, TM.get(), AddStream, ThreadId, *MPartInCtx);
    364             },
    365             // Pass BC using std::move to ensure that it get moved rather than
    366             // copied into the thread's context.
    367             std::move(BC), ThreadCount++);
    368       },
    369       false);
    370 
    371   // Because the inner lambda (which runs in a worker thread) captures our local
    372   // variables, we need to wait for the worker threads to terminate before we
    373   // can leave the function scope.
    374   CodegenThreadPool.wait();
    375 }
    376 
    377 Expected<const Target *> initAndLookupTarget(Config &C, Module &Mod) {
    378   if (!C.OverrideTriple.empty())
    379     Mod.setTargetTriple(C.OverrideTriple);
    380   else if (Mod.getTargetTriple().empty())
    381     Mod.setTargetTriple(C.DefaultTriple);
    382 
    383   std::string Msg;
    384   const Target *T = TargetRegistry::lookupTarget(Mod.getTargetTriple(), Msg);
    385   if (!T)
    386     return make_error<StringError>(Msg, inconvertibleErrorCode());
    387   return T;
    388 }
    389 
    390 }
    391 
    392 static Error
    393 finalizeOptimizationRemarks(std::unique_ptr<ToolOutputFile> DiagOutputFile) {
    394   // Make sure we flush the diagnostic remarks file in case the linker doesn't
    395   // call the global destructors before exiting.
    396   if (!DiagOutputFile)
    397     return Error::success();
    398   DiagOutputFile->keep();
    399   DiagOutputFile->os().flush();
    400   return Error::success();
    401 }
    402 
    403 Error lto::backend(Config &C, AddStreamFn AddStream,
    404                    unsigned ParallelCodeGenParallelismLevel,
    405                    std::unique_ptr<Module> Mod,
    406                    ModuleSummaryIndex &CombinedIndex) {
    407   Expected<const Target *> TOrErr = initAndLookupTarget(C, *Mod);
    408   if (!TOrErr)
    409     return TOrErr.takeError();
    410 
    411   std::unique_ptr<TargetMachine> TM = createTargetMachine(C, *TOrErr, *Mod);
    412 
    413   // Setup optimization remarks.
    414   auto DiagFileOrErr = lto::setupOptimizationRemarks(
    415       Mod->getContext(), C.RemarksFilename, C.RemarksWithHotness);
    416   if (!DiagFileOrErr)
    417     return DiagFileOrErr.takeError();
    418   auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
    419 
    420   if (!C.CodeGenOnly) {
    421     if (!opt(C, TM.get(), 0, *Mod, /*IsThinLTO=*/false,
    422              /*ExportSummary=*/&CombinedIndex, /*ImportSummary=*/nullptr))
    423       return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    424   }
    425 
    426   if (ParallelCodeGenParallelismLevel == 1) {
    427     codegen(C, TM.get(), AddStream, 0, *Mod);
    428   } else {
    429     splitCodeGen(C, TM.get(), AddStream, ParallelCodeGenParallelismLevel,
    430                  std::move(Mod));
    431   }
    432   return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    433 }
    434 
    435 static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
    436                             const ModuleSummaryIndex &Index) {
    437   std::vector<GlobalValue*> DeadGVs;
    438   for (auto &GV : Mod.global_values())
    439     if (GlobalValueSummary *GVS = DefinedGlobals.lookup(GV.getGUID()))
    440       if (!Index.isGlobalValueLive(GVS)) {
    441         DeadGVs.push_back(&GV);
    442         convertToDeclaration(GV);
    443       }
    444 
    445   // Now that all dead bodies have been dropped, delete the actual objects
    446   // themselves when possible.
    447   for (GlobalValue *GV : DeadGVs) {
    448     GV->removeDeadConstantUsers();
    449     // Might reference something defined in native object (i.e. dropped a
    450     // non-prevailing IR def, but we need to keep the declaration).
    451     if (GV->use_empty())
    452       GV->eraseFromParent();
    453   }
    454 }
    455 
    456 Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
    457                        Module &Mod, const ModuleSummaryIndex &CombinedIndex,
    458                        const FunctionImporter::ImportMapTy &ImportList,
    459                        const GVSummaryMapTy &DefinedGlobals,
    460                        MapVector<StringRef, BitcodeModule> &ModuleMap) {
    461   Expected<const Target *> TOrErr = initAndLookupTarget(Conf, Mod);
    462   if (!TOrErr)
    463     return TOrErr.takeError();
    464 
    465   std::unique_ptr<TargetMachine> TM = createTargetMachine(Conf, *TOrErr, Mod);
    466 
    467   // Setup optimization remarks.
    468   auto DiagFileOrErr = lto::setupOptimizationRemarks(
    469       Mod.getContext(), Conf.RemarksFilename, Conf.RemarksWithHotness, Task);
    470   if (!DiagFileOrErr)
    471     return DiagFileOrErr.takeError();
    472   auto DiagnosticOutputFile = std::move(*DiagFileOrErr);
    473 
    474   if (Conf.CodeGenOnly) {
    475     codegen(Conf, TM.get(), AddStream, Task, Mod);
    476     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    477   }
    478 
    479   if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
    480     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    481 
    482   renameModuleForThinLTO(Mod, CombinedIndex);
    483 
    484   dropDeadSymbols(Mod, DefinedGlobals, CombinedIndex);
    485 
    486   thinLTOResolveWeakForLinkerModule(Mod, DefinedGlobals);
    487 
    488   if (Conf.PostPromoteModuleHook && !Conf.PostPromoteModuleHook(Task, Mod))
    489     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    490 
    491   if (!DefinedGlobals.empty())
    492     thinLTOInternalizeModule(Mod, DefinedGlobals);
    493 
    494   if (Conf.PostInternalizeModuleHook &&
    495       !Conf.PostInternalizeModuleHook(Task, Mod))
    496     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    497 
    498   auto ModuleLoader = [&](StringRef Identifier) {
    499     assert(Mod.getContext().isODRUniquingDebugTypes() &&
    500            "ODR Type uniquing should be enabled on the context");
    501     auto I = ModuleMap.find(Identifier);
    502     assert(I != ModuleMap.end());
    503     return I->second.getLazyModule(Mod.getContext(),
    504                                    /*ShouldLazyLoadMetadata=*/true,
    505                                    /*IsImporting*/ true);
    506   };
    507 
    508   FunctionImporter Importer(CombinedIndex, ModuleLoader);
    509   if (Error Err = Importer.importFunctions(Mod, ImportList).takeError())
    510     return Err;
    511 
    512   if (Conf.PostImportModuleHook && !Conf.PostImportModuleHook(Task, Mod))
    513     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    514 
    515   if (!opt(Conf, TM.get(), Task, Mod, /*IsThinLTO=*/true,
    516            /*ExportSummary=*/nullptr, /*ImportSummary=*/&CombinedIndex))
    517     return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    518 
    519   codegen(Conf, TM.get(), AddStream, Task, Mod);
    520   return finalizeOptimizationRemarks(std::move(DiagnosticOutputFile));
    521 }
    522