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      1 //===-LTOCodeGenerator.cpp - LLVM Link Time Optimizer ---------------------===//
      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 Link Time Optimization library. This library is
     11 // intended to be used by linker to optimize code at link time.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "llvm/LTO/legacy/LTOCodeGenerator.h"
     16 
     17 #include "llvm/ADT/Statistic.h"
     18 #include "llvm/ADT/StringExtras.h"
     19 #include "llvm/Analysis/Passes.h"
     20 #include "llvm/Analysis/TargetLibraryInfo.h"
     21 #include "llvm/Analysis/TargetTransformInfo.h"
     22 #include "llvm/Bitcode/BitcodeWriter.h"
     23 #include "llvm/CodeGen/ParallelCG.h"
     24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
     25 #include "llvm/Config/config.h"
     26 #include "llvm/IR/Constants.h"
     27 #include "llvm/IR/DataLayout.h"
     28 #include "llvm/IR/DebugInfo.h"
     29 #include "llvm/IR/DerivedTypes.h"
     30 #include "llvm/IR/DiagnosticInfo.h"
     31 #include "llvm/IR/DiagnosticPrinter.h"
     32 #include "llvm/IR/LLVMContext.h"
     33 #include "llvm/IR/LegacyPassManager.h"
     34 #include "llvm/IR/Mangler.h"
     35 #include "llvm/IR/Module.h"
     36 #include "llvm/IR/Verifier.h"
     37 #include "llvm/InitializePasses.h"
     38 #include "llvm/LTO/LTO.h"
     39 #include "llvm/LTO/legacy/LTOModule.h"
     40 #include "llvm/LTO/legacy/UpdateCompilerUsed.h"
     41 #include "llvm/Linker/Linker.h"
     42 #include "llvm/MC/MCAsmInfo.h"
     43 #include "llvm/MC/MCContext.h"
     44 #include "llvm/MC/SubtargetFeature.h"
     45 #include "llvm/Support/CommandLine.h"
     46 #include "llvm/Support/FileSystem.h"
     47 #include "llvm/Support/Host.h"
     48 #include "llvm/Support/MemoryBuffer.h"
     49 #include "llvm/Support/Signals.h"
     50 #include "llvm/Support/TargetRegistry.h"
     51 #include "llvm/Support/TargetSelect.h"
     52 #include "llvm/Support/ToolOutputFile.h"
     53 #include "llvm/Support/YAMLTraits.h"
     54 #include "llvm/Support/raw_ostream.h"
     55 #include "llvm/Target/TargetOptions.h"
     56 #include "llvm/Transforms/IPO.h"
     57 #include "llvm/Transforms/IPO/Internalize.h"
     58 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
     59 #include "llvm/Transforms/ObjCARC.h"
     60 #include "llvm/Transforms/Utils/ModuleUtils.h"
     61 #include <system_error>
     62 using namespace llvm;
     63 
     64 const char* LTOCodeGenerator::getVersionString() {
     65 #ifdef LLVM_VERSION_INFO
     66   return PACKAGE_NAME " version " PACKAGE_VERSION ", " LLVM_VERSION_INFO;
     67 #else
     68   return PACKAGE_NAME " version " PACKAGE_VERSION;
     69 #endif
     70 }
     71 
     72 namespace llvm {
     73 cl::opt<bool> LTODiscardValueNames(
     74     "lto-discard-value-names",
     75     cl::desc("Strip names from Value during LTO (other than GlobalValue)."),
     76 #ifdef NDEBUG
     77     cl::init(true),
     78 #else
     79     cl::init(false),
     80 #endif
     81     cl::Hidden);
     82 
     83 cl::opt<std::string>
     84     LTORemarksFilename("lto-pass-remarks-output",
     85                        cl::desc("Output filename for pass remarks"),
     86                        cl::value_desc("filename"));
     87 
     88 cl::opt<bool> LTOPassRemarksWithHotness(
     89     "lto-pass-remarks-with-hotness",
     90     cl::desc("With PGO, include profile count in optimization remarks"),
     91     cl::Hidden);
     92 }
     93 
     94 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
     95     : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
     96       TheLinker(new Linker(*MergedModule)) {
     97   Context.setDiscardValueNames(LTODiscardValueNames);
     98   Context.enableDebugTypeODRUniquing();
     99   initializeLTOPasses();
    100 }
    101 
    102 LTOCodeGenerator::~LTOCodeGenerator() {}
    103 
    104 // Initialize LTO passes. Please keep this function in sync with
    105 // PassManagerBuilder::populateLTOPassManager(), and make sure all LTO
    106 // passes are initialized.
    107 void LTOCodeGenerator::initializeLTOPasses() {
    108   PassRegistry &R = *PassRegistry::getPassRegistry();
    109 
    110   initializeInternalizeLegacyPassPass(R);
    111   initializeIPSCCPLegacyPassPass(R);
    112   initializeGlobalOptLegacyPassPass(R);
    113   initializeConstantMergeLegacyPassPass(R);
    114   initializeDAHPass(R);
    115   initializeInstructionCombiningPassPass(R);
    116   initializeSimpleInlinerPass(R);
    117   initializePruneEHPass(R);
    118   initializeGlobalDCELegacyPassPass(R);
    119   initializeArgPromotionPass(R);
    120   initializeJumpThreadingPass(R);
    121   initializeSROALegacyPassPass(R);
    122   initializePostOrderFunctionAttrsLegacyPassPass(R);
    123   initializeReversePostOrderFunctionAttrsLegacyPassPass(R);
    124   initializeGlobalsAAWrapperPassPass(R);
    125   initializeLegacyLICMPassPass(R);
    126   initializeMergedLoadStoreMotionLegacyPassPass(R);
    127   initializeGVNLegacyPassPass(R);
    128   initializeMemCpyOptLegacyPassPass(R);
    129   initializeDCELegacyPassPass(R);
    130   initializeCFGSimplifyPassPass(R);
    131 }
    132 
    133 void LTOCodeGenerator::setAsmUndefinedRefs(LTOModule *Mod) {
    134   const std::vector<StringRef> &undefs = Mod->getAsmUndefinedRefs();
    135   for (int i = 0, e = undefs.size(); i != e; ++i)
    136     AsmUndefinedRefs[undefs[i]] = 1;
    137 }
    138 
    139 bool LTOCodeGenerator::addModule(LTOModule *Mod) {
    140   assert(&Mod->getModule().getContext() == &Context &&
    141          "Expected module in same context");
    142 
    143   bool ret = TheLinker->linkInModule(Mod->takeModule());
    144   setAsmUndefinedRefs(Mod);
    145 
    146   // We've just changed the input, so let's make sure we verify it.
    147   HasVerifiedInput = false;
    148 
    149   return !ret;
    150 }
    151 
    152 void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
    153   assert(&Mod->getModule().getContext() == &Context &&
    154          "Expected module in same context");
    155 
    156   AsmUndefinedRefs.clear();
    157 
    158   MergedModule = Mod->takeModule();
    159   TheLinker = make_unique<Linker>(*MergedModule);
    160   setAsmUndefinedRefs(&*Mod);
    161 
    162   // We've just changed the input, so let's make sure we verify it.
    163   HasVerifiedInput = false;
    164 }
    165 
    166 void LTOCodeGenerator::setTargetOptions(const TargetOptions &Options) {
    167   this->Options = Options;
    168 }
    169 
    170 void LTOCodeGenerator::setDebugInfo(lto_debug_model Debug) {
    171   switch (Debug) {
    172   case LTO_DEBUG_MODEL_NONE:
    173     EmitDwarfDebugInfo = false;
    174     return;
    175 
    176   case LTO_DEBUG_MODEL_DWARF:
    177     EmitDwarfDebugInfo = true;
    178     return;
    179   }
    180   llvm_unreachable("Unknown debug format!");
    181 }
    182 
    183 void LTOCodeGenerator::setOptLevel(unsigned Level) {
    184   OptLevel = Level;
    185   switch (OptLevel) {
    186   case 0:
    187     CGOptLevel = CodeGenOpt::None;
    188     return;
    189   case 1:
    190     CGOptLevel = CodeGenOpt::Less;
    191     return;
    192   case 2:
    193     CGOptLevel = CodeGenOpt::Default;
    194     return;
    195   case 3:
    196     CGOptLevel = CodeGenOpt::Aggressive;
    197     return;
    198   }
    199   llvm_unreachable("Unknown optimization level!");
    200 }
    201 
    202 bool LTOCodeGenerator::writeMergedModules(StringRef Path) {
    203   if (!determineTarget())
    204     return false;
    205 
    206   // We always run the verifier once on the merged module.
    207   verifyMergedModuleOnce();
    208 
    209   // mark which symbols can not be internalized
    210   applyScopeRestrictions();
    211 
    212   // create output file
    213   std::error_code EC;
    214   ToolOutputFile Out(Path, EC, sys::fs::F_None);
    215   if (EC) {
    216     std::string ErrMsg = "could not open bitcode file for writing: ";
    217     ErrMsg += Path.str() + ": " + EC.message();
    218     emitError(ErrMsg);
    219     return false;
    220   }
    221 
    222   // write bitcode to it
    223   WriteBitcodeToFile(*MergedModule, Out.os(), ShouldEmbedUselists);
    224   Out.os().close();
    225 
    226   if (Out.os().has_error()) {
    227     std::string ErrMsg = "could not write bitcode file: ";
    228     ErrMsg += Path.str() + ": " + Out.os().error().message();
    229     emitError(ErrMsg);
    230     Out.os().clear_error();
    231     return false;
    232   }
    233 
    234   Out.keep();
    235   return true;
    236 }
    237 
    238 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
    239   // make unique temp output file to put generated code
    240   SmallString<128> Filename;
    241   int FD;
    242 
    243   StringRef Extension
    244       (FileType == TargetMachine::CGFT_AssemblyFile ? "s" : "o");
    245 
    246   std::error_code EC =
    247       sys::fs::createTemporaryFile("lto-llvm", Extension, FD, Filename);
    248   if (EC) {
    249     emitError(EC.message());
    250     return false;
    251   }
    252 
    253   // generate object file
    254   ToolOutputFile objFile(Filename, FD);
    255 
    256   bool genResult = compileOptimized(&objFile.os());
    257   objFile.os().close();
    258   if (objFile.os().has_error()) {
    259     emitError((Twine("could not write object file: ") + Filename + ": " +
    260                objFile.os().error().message())
    261                   .str());
    262     objFile.os().clear_error();
    263     sys::fs::remove(Twine(Filename));
    264     return false;
    265   }
    266 
    267   objFile.keep();
    268   if (!genResult) {
    269     sys::fs::remove(Twine(Filename));
    270     return false;
    271   }
    272 
    273   NativeObjectPath = Filename.c_str();
    274   *Name = NativeObjectPath.c_str();
    275   return true;
    276 }
    277 
    278 std::unique_ptr<MemoryBuffer>
    279 LTOCodeGenerator::compileOptimized() {
    280   const char *name;
    281   if (!compileOptimizedToFile(&name))
    282     return nullptr;
    283 
    284   // read .o file into memory buffer
    285   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
    286       MemoryBuffer::getFile(name, -1, false);
    287   if (std::error_code EC = BufferOrErr.getError()) {
    288     emitError(EC.message());
    289     sys::fs::remove(NativeObjectPath);
    290     return nullptr;
    291   }
    292 
    293   // remove temp files
    294   sys::fs::remove(NativeObjectPath);
    295 
    296   return std::move(*BufferOrErr);
    297 }
    298 
    299 bool LTOCodeGenerator::compile_to_file(const char **Name, bool DisableVerify,
    300                                        bool DisableInline,
    301                                        bool DisableGVNLoadPRE,
    302                                        bool DisableVectorization) {
    303   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
    304                 DisableVectorization))
    305     return false;
    306 
    307   return compileOptimizedToFile(Name);
    308 }
    309 
    310 std::unique_ptr<MemoryBuffer>
    311 LTOCodeGenerator::compile(bool DisableVerify, bool DisableInline,
    312                           bool DisableGVNLoadPRE, bool DisableVectorization) {
    313   if (!optimize(DisableVerify, DisableInline, DisableGVNLoadPRE,
    314                 DisableVectorization))
    315     return nullptr;
    316 
    317   return compileOptimized();
    318 }
    319 
    320 bool LTOCodeGenerator::determineTarget() {
    321   if (TargetMach)
    322     return true;
    323 
    324   TripleStr = MergedModule->getTargetTriple();
    325   if (TripleStr.empty()) {
    326     TripleStr = sys::getDefaultTargetTriple();
    327     MergedModule->setTargetTriple(TripleStr);
    328   }
    329   llvm::Triple Triple(TripleStr);
    330 
    331   // create target machine from info for merged modules
    332   std::string ErrMsg;
    333   MArch = TargetRegistry::lookupTarget(TripleStr, ErrMsg);
    334   if (!MArch) {
    335     emitError(ErrMsg);
    336     return false;
    337   }
    338 
    339   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
    340   // the default set of features.
    341   SubtargetFeatures Features(MAttr);
    342   Features.getDefaultSubtargetFeatures(Triple);
    343   FeatureStr = Features.getString();
    344   // Set a default CPU for Darwin triples.
    345   if (MCpu.empty() && Triple.isOSDarwin()) {
    346     if (Triple.getArch() == llvm::Triple::x86_64)
    347       MCpu = "core2";
    348     else if (Triple.getArch() == llvm::Triple::x86)
    349       MCpu = "yonah";
    350     else if (Triple.getArch() == llvm::Triple::aarch64)
    351       MCpu = "cyclone";
    352   }
    353 
    354   TargetMach = createTargetMachine();
    355   return true;
    356 }
    357 
    358 std::unique_ptr<TargetMachine> LTOCodeGenerator::createTargetMachine() {
    359   return std::unique_ptr<TargetMachine>(MArch->createTargetMachine(
    360       TripleStr, MCpu, FeatureStr, Options, RelocModel, None, CGOptLevel));
    361 }
    362 
    363 // If a linkonce global is present in the MustPreserveSymbols, we need to make
    364 // sure we honor this. To force the compiler to not drop it, we add it to the
    365 // "llvm.compiler.used" global.
    366 void LTOCodeGenerator::preserveDiscardableGVs(
    367     Module &TheModule,
    368     llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {
    369   std::vector<GlobalValue *> Used;
    370   auto mayPreserveGlobal = [&](GlobalValue &GV) {
    371     if (!GV.isDiscardableIfUnused() || GV.isDeclaration() ||
    372         !mustPreserveGV(GV))
    373       return;
    374     if (GV.hasAvailableExternallyLinkage())
    375       return emitWarning(
    376           (Twine("Linker asked to preserve available_externally global: '") +
    377            GV.getName() + "'").str());
    378     if (GV.hasInternalLinkage())
    379       return emitWarning((Twine("Linker asked to preserve internal global: '") +
    380                    GV.getName() + "'").str());
    381     Used.push_back(&GV);
    382   };
    383   for (auto &GV : TheModule)
    384     mayPreserveGlobal(GV);
    385   for (auto &GV : TheModule.globals())
    386     mayPreserveGlobal(GV);
    387   for (auto &GV : TheModule.aliases())
    388     mayPreserveGlobal(GV);
    389 
    390   if (Used.empty())
    391     return;
    392 
    393   appendToCompilerUsed(TheModule, Used);
    394 }
    395 
    396 void LTOCodeGenerator::applyScopeRestrictions() {
    397   if (ScopeRestrictionsDone)
    398     return;
    399 
    400   // Declare a callback for the internalize pass that will ask for every
    401   // candidate GlobalValue if it can be internalized or not.
    402   Mangler Mang;
    403   SmallString<64> MangledName;
    404   auto mustPreserveGV = [&](const GlobalValue &GV) -> bool {
    405     // Unnamed globals can't be mangled, but they can't be preserved either.
    406     if (!GV.hasName())
    407       return false;
    408 
    409     // Need to mangle the GV as the "MustPreserveSymbols" StringSet is filled
    410     // with the linker supplied name, which on Darwin includes a leading
    411     // underscore.
    412     MangledName.clear();
    413     MangledName.reserve(GV.getName().size() + 1);
    414     Mang.getNameWithPrefix(MangledName, &GV, /*CannotUsePrivateLabel=*/false);
    415     return MustPreserveSymbols.count(MangledName);
    416   };
    417 
    418   // Preserve linkonce value on linker request
    419   preserveDiscardableGVs(*MergedModule, mustPreserveGV);
    420 
    421   if (!ShouldInternalize)
    422     return;
    423 
    424   if (ShouldRestoreGlobalsLinkage) {
    425     // Record the linkage type of non-local symbols so they can be restored
    426     // prior
    427     // to module splitting.
    428     auto RecordLinkage = [&](const GlobalValue &GV) {
    429       if (!GV.hasAvailableExternallyLinkage() && !GV.hasLocalLinkage() &&
    430           GV.hasName())
    431         ExternalSymbols.insert(std::make_pair(GV.getName(), GV.getLinkage()));
    432     };
    433     for (auto &GV : *MergedModule)
    434       RecordLinkage(GV);
    435     for (auto &GV : MergedModule->globals())
    436       RecordLinkage(GV);
    437     for (auto &GV : MergedModule->aliases())
    438       RecordLinkage(GV);
    439   }
    440 
    441   // Update the llvm.compiler_used globals to force preserving libcalls and
    442   // symbols referenced from asm
    443   updateCompilerUsed(*MergedModule, *TargetMach, AsmUndefinedRefs);
    444 
    445   internalizeModule(*MergedModule, mustPreserveGV);
    446 
    447   ScopeRestrictionsDone = true;
    448 }
    449 
    450 /// Restore original linkage for symbols that may have been internalized
    451 void LTOCodeGenerator::restoreLinkageForExternals() {
    452   if (!ShouldInternalize || !ShouldRestoreGlobalsLinkage)
    453     return;
    454 
    455   assert(ScopeRestrictionsDone &&
    456          "Cannot externalize without internalization!");
    457 
    458   if (ExternalSymbols.empty())
    459     return;
    460 
    461   auto externalize = [this](GlobalValue &GV) {
    462     if (!GV.hasLocalLinkage() || !GV.hasName())
    463       return;
    464 
    465     auto I = ExternalSymbols.find(GV.getName());
    466     if (I == ExternalSymbols.end())
    467       return;
    468 
    469     GV.setLinkage(I->second);
    470   };
    471 
    472   llvm::for_each(MergedModule->functions(), externalize);
    473   llvm::for_each(MergedModule->globals(), externalize);
    474   llvm::for_each(MergedModule->aliases(), externalize);
    475 }
    476 
    477 void LTOCodeGenerator::verifyMergedModuleOnce() {
    478   // Only run on the first call.
    479   if (HasVerifiedInput)
    480     return;
    481   HasVerifiedInput = true;
    482 
    483   bool BrokenDebugInfo = false;
    484   if (verifyModule(*MergedModule, &dbgs(), &BrokenDebugInfo))
    485     report_fatal_error("Broken module found, compilation aborted!");
    486   if (BrokenDebugInfo) {
    487     emitWarning("Invalid debug info found, debug info will be stripped");
    488     StripDebugInfo(*MergedModule);
    489   }
    490 }
    491 
    492 void LTOCodeGenerator::finishOptimizationRemarks() {
    493   if (DiagnosticOutputFile) {
    494     DiagnosticOutputFile->keep();
    495     // FIXME: LTOCodeGenerator dtor is not invoked on Darwin
    496     DiagnosticOutputFile->os().flush();
    497   }
    498 }
    499 
    500 /// Optimize merged modules using various IPO passes
    501 bool LTOCodeGenerator::optimize(bool DisableVerify, bool DisableInline,
    502                                 bool DisableGVNLoadPRE,
    503                                 bool DisableVectorization) {
    504   if (!this->determineTarget())
    505     return false;
    506 
    507   auto DiagFileOrErr = lto::setupOptimizationRemarks(
    508       Context, LTORemarksFilename, LTOPassRemarksWithHotness);
    509   if (!DiagFileOrErr) {
    510     errs() << "Error: " << toString(DiagFileOrErr.takeError()) << "\n";
    511     report_fatal_error("Can't get an output file for the remarks");
    512   }
    513   DiagnosticOutputFile = std::move(*DiagFileOrErr);
    514 
    515   // We always run the verifier once on the merged module, the `DisableVerify`
    516   // parameter only applies to subsequent verify.
    517   verifyMergedModuleOnce();
    518 
    519   // Mark which symbols can not be internalized
    520   this->applyScopeRestrictions();
    521 
    522   // Instantiate the pass manager to organize the passes.
    523   legacy::PassManager passes;
    524 
    525   // Add an appropriate DataLayout instance for this module...
    526   MergedModule->setDataLayout(TargetMach->createDataLayout());
    527 
    528   passes.add(
    529       createTargetTransformInfoWrapperPass(TargetMach->getTargetIRAnalysis()));
    530 
    531   Triple TargetTriple(TargetMach->getTargetTriple());
    532   PassManagerBuilder PMB;
    533   PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
    534   PMB.LoopVectorize = !DisableVectorization;
    535   PMB.SLPVectorize = !DisableVectorization;
    536   if (!DisableInline)
    537     PMB.Inliner = createFunctionInliningPass();
    538   PMB.LibraryInfo = new TargetLibraryInfoImpl(TargetTriple);
    539   if (Freestanding)
    540     PMB.LibraryInfo->disableAllFunctions();
    541   PMB.OptLevel = OptLevel;
    542   PMB.VerifyInput = !DisableVerify;
    543   PMB.VerifyOutput = !DisableVerify;
    544 
    545   PMB.populateLTOPassManager(passes);
    546 
    547   // Run our queue of passes all at once now, efficiently.
    548   passes.run(*MergedModule);
    549 
    550   return true;
    551 }
    552 
    553 bool LTOCodeGenerator::compileOptimized(ArrayRef<raw_pwrite_stream *> Out) {
    554   if (!this->determineTarget())
    555     return false;
    556 
    557   // We always run the verifier once on the merged module.  If it has already
    558   // been called in optimize(), this call will return early.
    559   verifyMergedModuleOnce();
    560 
    561   legacy::PassManager preCodeGenPasses;
    562 
    563   // If the bitcode files contain ARC code and were compiled with optimization,
    564   // the ObjCARCContractPass must be run, so do it unconditionally here.
    565   preCodeGenPasses.add(createObjCARCContractPass());
    566   preCodeGenPasses.run(*MergedModule);
    567 
    568   // Re-externalize globals that may have been internalized to increase scope
    569   // for splitting
    570   restoreLinkageForExternals();
    571 
    572   // Do code generation. We need to preserve the module in case the client calls
    573   // writeMergedModules() after compilation, but we only need to allow this at
    574   // parallelism level 1. This is achieved by having splitCodeGen return the
    575   // original module at parallelism level 1 which we then assign back to
    576   // MergedModule.
    577   MergedModule = splitCodeGen(std::move(MergedModule), Out, {},
    578                               [&]() { return createTargetMachine(); }, FileType,
    579                               ShouldRestoreGlobalsLinkage);
    580 
    581   // If statistics were requested, print them out after codegen.
    582   if (llvm::AreStatisticsEnabled())
    583     llvm::PrintStatistics();
    584   reportAndResetTimings();
    585 
    586   finishOptimizationRemarks();
    587 
    588   return true;
    589 }
    590 
    591 /// setCodeGenDebugOptions - Set codegen debugging options to aid in debugging
    592 /// LTO problems.
    593 void LTOCodeGenerator::setCodeGenDebugOptions(StringRef Options) {
    594   for (std::pair<StringRef, StringRef> o = getToken(Options); !o.first.empty();
    595        o = getToken(o.second))
    596     CodegenOptions.push_back(o.first);
    597 }
    598 
    599 void LTOCodeGenerator::parseCodeGenDebugOptions() {
    600   // if options were requested, set them
    601   if (!CodegenOptions.empty()) {
    602     // ParseCommandLineOptions() expects argv[0] to be program name.
    603     std::vector<const char *> CodegenArgv(1, "libLLVMLTO");
    604     for (std::string &Arg : CodegenOptions)
    605       CodegenArgv.push_back(Arg.c_str());
    606     cl::ParseCommandLineOptions(CodegenArgv.size(), CodegenArgv.data());
    607   }
    608 }
    609 
    610 
    611 void LTOCodeGenerator::DiagnosticHandler(const DiagnosticInfo &DI) {
    612   // Map the LLVM internal diagnostic severity to the LTO diagnostic severity.
    613   lto_codegen_diagnostic_severity_t Severity;
    614   switch (DI.getSeverity()) {
    615   case DS_Error:
    616     Severity = LTO_DS_ERROR;
    617     break;
    618   case DS_Warning:
    619     Severity = LTO_DS_WARNING;
    620     break;
    621   case DS_Remark:
    622     Severity = LTO_DS_REMARK;
    623     break;
    624   case DS_Note:
    625     Severity = LTO_DS_NOTE;
    626     break;
    627   }
    628   // Create the string that will be reported to the external diagnostic handler.
    629   std::string MsgStorage;
    630   raw_string_ostream Stream(MsgStorage);
    631   DiagnosticPrinterRawOStream DP(Stream);
    632   DI.print(DP);
    633   Stream.flush();
    634 
    635   // If this method has been called it means someone has set up an external
    636   // diagnostic handler. Assert on that.
    637   assert(DiagHandler && "Invalid diagnostic handler");
    638   (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
    639 }
    640 
    641 namespace {
    642 struct LTODiagnosticHandler : public DiagnosticHandler {
    643   LTOCodeGenerator *CodeGenerator;
    644   LTODiagnosticHandler(LTOCodeGenerator *CodeGenPtr)
    645       : CodeGenerator(CodeGenPtr) {}
    646   bool handleDiagnostics(const DiagnosticInfo &DI) override {
    647     CodeGenerator->DiagnosticHandler(DI);
    648     return true;
    649   }
    650 };
    651 }
    652 
    653 void
    654 LTOCodeGenerator::setDiagnosticHandler(lto_diagnostic_handler_t DiagHandler,
    655                                        void *Ctxt) {
    656   this->DiagHandler = DiagHandler;
    657   this->DiagContext = Ctxt;
    658   if (!DiagHandler)
    659     return Context.setDiagnosticHandler(nullptr);
    660   // Register the LTOCodeGenerator stub in the LLVMContext to forward the
    661   // diagnostic to the external DiagHandler.
    662   Context.setDiagnosticHandler(llvm::make_unique<LTODiagnosticHandler>(this),
    663                                true);
    664 }
    665 
    666 namespace {
    667 class LTODiagnosticInfo : public DiagnosticInfo {
    668   const Twine &Msg;
    669 public:
    670   LTODiagnosticInfo(const Twine &DiagMsg, DiagnosticSeverity Severity=DS_Error)
    671       : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
    672   void print(DiagnosticPrinter &DP) const override { DP << Msg; }
    673 };
    674 }
    675 
    676 void LTOCodeGenerator::emitError(const std::string &ErrMsg) {
    677   if (DiagHandler)
    678     (*DiagHandler)(LTO_DS_ERROR, ErrMsg.c_str(), DiagContext);
    679   else
    680     Context.diagnose(LTODiagnosticInfo(ErrMsg));
    681 }
    682 
    683 void LTOCodeGenerator::emitWarning(const std::string &ErrMsg) {
    684   if (DiagHandler)
    685     (*DiagHandler)(LTO_DS_WARNING, ErrMsg.c_str(), DiagContext);
    686   else
    687     Context.diagnose(LTODiagnosticInfo(ErrMsg, DS_Warning));
    688 }
    689