lib/Frontend/CompilerInstance.cpp

//===--- CompilerInstance.cpp ---------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "clang/Frontend/CompilerInstance.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/Version.h"
#include "clang/Config/config.h"
#include "clang/Frontend/ChainedDiagnosticConsumer.h"
#include "clang/Frontend/FrontendAction.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Frontend/FrontendDiagnostic.h"
#include "clang/Frontend/LogDiagnosticPrinter.h"
#include "clang/Frontend/SerializedDiagnosticPrinter.h"
#include "clang/Frontend/TextDiagnosticPrinter.h"
#include "clang/Frontend/Utils.h"
#include "clang/Frontend/VerifyDiagnosticConsumer.h"
#include "clang/Lex/HeaderSearch.h"
#include "clang/Lex/PTHManager.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/CodeCompleteConsumer.h"
#include "clang/Sema/Sema.h"
#include "clang/Serialization/ASTReader.h"
#include "clang/Serialization/GlobalModuleIndex.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/LockFileManager.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Program.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
#include <sys/stat.h>
#include <system_error>
#include <time.h>

using namespace clang;

CompilerInstance::CompilerInstance(bool BuildingModule)
  : ModuleLoader(BuildingModule),
    Invocation(new CompilerInvocation()), ModuleManager(nullptr),
    BuildGlobalModuleIndex(false), HaveFullGlobalModuleIndex(false),
    ModuleBuildFailed(false) {
}

CompilerInstance::~CompilerInstance() {
  assert(OutputFiles.empty() && "Still output files in flight?");
}

void CompilerInstance::setInvocation(CompilerInvocation *Value) {
  Invocation = Value;
}

bool CompilerInstance::shouldBuildGlobalModuleIndex() const {
  return (BuildGlobalModuleIndex ||
          (ModuleManager && ModuleManager->isGlobalIndexUnavailable() &&
           getFrontendOpts().GenerateGlobalModuleIndex)) &&
         !ModuleBuildFailed;
}

void CompilerInstance::setDiagnostics(DiagnosticsEngine *Value) {
  Diagnostics = Value;
}

void CompilerInstance::setTarget(TargetInfo *Value) {
  Target = Value;
}

void CompilerInstance::setFileManager(FileManager *Value) {
  FileMgr = Value;
  if (Value)
    VirtualFileSystem = Value->getVirtualFileSystem();
  else
    VirtualFileSystem.reset();
}

void CompilerInstance::setSourceManager(SourceManager *Value) {
  SourceMgr = Value;
}

void CompilerInstance::setPreprocessor(Preprocessor *Value) { PP = Value; }

void CompilerInstance::setASTContext(ASTContext *Value) { Context = Value; }

void CompilerInstance::setSema(Sema *S) {
  TheSema.reset(S);
}

void CompilerInstance::setASTConsumer(ASTConsumer *Value) {
  Consumer.reset(Value);
}

void CompilerInstance::setCodeCompletionConsumer(CodeCompleteConsumer *Value) {
  CompletionConsumer.reset(Value);
}

IntrusiveRefCntPtr<ASTReader> CompilerInstance::getModuleManager() const {
  return ModuleManager;
}
void CompilerInstance::setModuleManager(IntrusiveRefCntPtr<ASTReader> Reader) {
  ModuleManager = Reader;
}

std::shared_ptr<ModuleDependencyCollector>
CompilerInstance::getModuleDepCollector() const {
  return ModuleDepCollector;
}

void CompilerInstance::setModuleDepCollector(
    std::shared_ptr<ModuleDependencyCollector> Collector) {
  ModuleDepCollector = Collector;
}

// Diagnostics
static void SetUpDiagnosticLog(DiagnosticOptions *DiagOpts,
                               const CodeGenOptions *CodeGenOpts,
                               DiagnosticsEngine &Diags) {
  std::string ErrorInfo;
  bool OwnsStream = false;
  raw_ostream *OS = &llvm::errs();
  if (DiagOpts->DiagnosticLogFile != "-") {
    // Create the output stream.
    llvm::raw_fd_ostream *FileOS(new llvm::raw_fd_ostream(
        DiagOpts->DiagnosticLogFile.c_str(), ErrorInfo,
        llvm::sys::fs::F_Append | llvm::sys::fs::F_Text));
    if (!ErrorInfo.empty()) {
      Diags.Report(diag::warn_fe_cc_log_diagnostics_failure)
        << DiagOpts->DiagnosticLogFile << ErrorInfo;
    } else {
      FileOS->SetUnbuffered();
      FileOS->SetUseAtomicWrites(true);
      OS = FileOS;
      OwnsStream = true;
    }
  }

  // Chain in the diagnostic client which will log the diagnostics.
  LogDiagnosticPrinter *Logger = new LogDiagnosticPrinter(*OS, DiagOpts,
                                                          OwnsStream);
  if (CodeGenOpts)
    Logger->setDwarfDebugFlags(CodeGenOpts->DwarfDebugFlags);
  Diags.setClient(new ChainedDiagnosticConsumer(Diags.takeClient(), Logger));
}

static void SetupSerializedDiagnostics(DiagnosticOptions *DiagOpts,
                                       DiagnosticsEngine &Diags,
                                       StringRef OutputFile) {
  std::string ErrorInfo;
  std::unique_ptr<llvm::raw_fd_ostream> OS;
  OS.reset(new llvm::raw_fd_ostream(OutputFile.str().c_str(), ErrorInfo,
                                    llvm::sys::fs::F_None));

  if (!ErrorInfo.empty()) {
    Diags.Report(diag::warn_fe_serialized_diag_failure)
      << OutputFile << ErrorInfo;
    return;
  }

  DiagnosticConsumer *SerializedConsumer =
      clang::serialized_diags::create(OS.release(), DiagOpts);

  Diags.setClient(new ChainedDiagnosticConsumer(Diags.takeClient(),
                                                SerializedConsumer));
}

void CompilerInstance::createDiagnostics(DiagnosticConsumer *Client,
                                         bool ShouldOwnClient) {
  Diagnostics = createDiagnostics(&getDiagnosticOpts(), Client,
                                  ShouldOwnClient, &getCodeGenOpts());
}

IntrusiveRefCntPtr<DiagnosticsEngine>
CompilerInstance::createDiagnostics(DiagnosticOptions *Opts,
                                    DiagnosticConsumer *Client,
                                    bool ShouldOwnClient,
                                    const CodeGenOptions *CodeGenOpts) {
  IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
  IntrusiveRefCntPtr<DiagnosticsEngine>
      Diags(new DiagnosticsEngine(DiagID, Opts));

  // Create the diagnostic client for reporting errors or for
  // implementing -verify.
  if (Client) {
    Diags->setClient(Client, ShouldOwnClient);
  } else
    Diags->setClient(new TextDiagnosticPrinter(llvm::errs(), Opts));

  // Chain in -verify checker, if requested.
  if (Opts->VerifyDiagnostics)
    Diags->setClient(new VerifyDiagnosticConsumer(*Diags));

  // Chain in -diagnostic-log-file dumper, if requested.
  if (!Opts->DiagnosticLogFile.empty())
    SetUpDiagnosticLog(Opts, CodeGenOpts, *Diags);

  if (!Opts->DiagnosticSerializationFile.empty())
    SetupSerializedDiagnostics(Opts, *Diags,
                               Opts->DiagnosticSerializationFile);

  // Configure our handling of diagnostics.
  ProcessWarningOptions(*Diags, *Opts);

  return Diags;
}

// File Manager

void CompilerInstance::createFileManager() {
  if (!hasVirtualFileSystem()) {
    // TODO: choose the virtual file system based on the CompilerInvocation.
    setVirtualFileSystem(vfs::getRealFileSystem());
  }
  FileMgr = new FileManager(getFileSystemOpts(), VirtualFileSystem);
}

// Source Manager

void CompilerInstance::createSourceManager(FileManager &FileMgr) {
  SourceMgr = new SourceManager(getDiagnostics(), FileMgr);
}

// Initialize the remapping of files to alternative contents, e.g.,
// those specified through other files.
static void InitializeFileRemapping(DiagnosticsEngine &Diags,
                                    SourceManager &SourceMgr,
                                    FileManager &FileMgr,
                                    const PreprocessorOptions &InitOpts) {
  // Remap files in the source manager (with buffers).
  for (PreprocessorOptions::const_remapped_file_buffer_iterator
           Remap = InitOpts.remapped_file_buffer_begin(),
           RemapEnd = InitOpts.remapped_file_buffer_end();
       Remap != RemapEnd; ++Remap) {
    // Create the file entry for the file that we're mapping from.
    const FileEntry *FromFile =
        FileMgr.getVirtualFile(Remap->first, Remap->second->getBufferSize(), 0);
    if (!FromFile) {
      Diags.Report(diag::err_fe_remap_missing_from_file) << Remap->first;
      if (!InitOpts.RetainRemappedFileBuffers)
        delete Remap->second;
      continue;
    }

    // Override the contents of the "from" file with the contents of
    // the "to" file.
    SourceMgr.overrideFileContents(FromFile, Remap->second,
                                   InitOpts.RetainRemappedFileBuffers);
  }

  // Remap files in the source manager (with other files).
  for (PreprocessorOptions::const_remapped_file_iterator
           Remap = InitOpts.remapped_file_begin(),
           RemapEnd = InitOpts.remapped_file_end();
       Remap != RemapEnd; ++Remap) {
    // Find the file that we're mapping to.
    const FileEntry *ToFile = FileMgr.getFile(Remap->second);
    if (!ToFile) {
      Diags.Report(diag::err_fe_remap_missing_to_file) << Remap->first
                                                       << Remap->second;
      continue;
    }

    // Create the file entry for the file that we're mapping from.
    const FileEntry *FromFile =
        FileMgr.getVirtualFile(Remap->first, ToFile->getSize(), 0);
    if (!FromFile) {
      Diags.Report(diag::err_fe_remap_missing_from_file) << Remap->first;
      continue;
    }

    // Override the contents of the "from" file with the contents of
    // the "to" file.
    SourceMgr.overrideFileContents(FromFile, ToFile);
  }

  SourceMgr.setOverridenFilesKeepOriginalName(
      InitOpts.RemappedFilesKeepOriginalName);
}

// Preprocessor

void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
  const PreprocessorOptions &PPOpts = getPreprocessorOpts();

  // Create a PTH manager if we are using some form of a token cache.
  PTHManager *PTHMgr = nullptr;
  if (!PPOpts.TokenCache.empty())
    PTHMgr = PTHManager::Create(PPOpts.TokenCache, getDiagnostics());

  // Create the Preprocessor.
  HeaderSearch *HeaderInfo = new HeaderSearch(&getHeaderSearchOpts(),
                                              getSourceManager(),
                                              getDiagnostics(),
                                              getLangOpts(),
                                              &getTarget());
  PP = new Preprocessor(&getPreprocessorOpts(), getDiagnostics(), getLangOpts(),
                        getSourceManager(), *HeaderInfo, *this, PTHMgr,
                        /*OwnsHeaderSearch=*/true, TUKind);
  PP->Initialize(getTarget());

  // Note that this is different then passing PTHMgr to Preprocessor's ctor.
  // That argument is used as the IdentifierInfoLookup argument to
  // IdentifierTable's ctor.
  if (PTHMgr) {
    PTHMgr->setPreprocessor(&*PP);
    PP->setPTHManager(PTHMgr);
  }

  if (PPOpts.DetailedRecord)
    PP->createPreprocessingRecord();

  // Apply remappings to the source manager.
  InitializeFileRemapping(PP->getDiagnostics(), PP->getSourceManager(),
                          PP->getFileManager(), PPOpts);

  // Predefine macros and configure the preprocessor.
  InitializePreprocessor(*PP, PPOpts, getFrontendOpts());

  // Initialize the header search object.
  ApplyHeaderSearchOptions(PP->getHeaderSearchInfo(), getHeaderSearchOpts(),
                           PP->getLangOpts(), PP->getTargetInfo().getTriple());

  PP->setPreprocessedOutput(getPreprocessorOutputOpts().ShowCPP);

  // Set up the module path, including the hash for the
  // module-creation options.
  SmallString<256> SpecificModuleCache(
                           getHeaderSearchOpts().ModuleCachePath);
  if (!getHeaderSearchOpts().DisableModuleHash)
    llvm::sys::path::append(SpecificModuleCache,
                            getInvocation().getModuleHash());
  PP->getHeaderSearchInfo().setModuleCachePath(SpecificModuleCache);

  // Handle generating dependencies, if requested.
  const DependencyOutputOptions &DepOpts = getDependencyOutputOpts();
  if (!DepOpts.OutputFile.empty())
    TheDependencyFileGenerator.reset(
        DependencyFileGenerator::CreateAndAttachToPreprocessor(*PP, DepOpts));
  if (!DepOpts.DOTOutputFile.empty())
    AttachDependencyGraphGen(*PP, DepOpts.DOTOutputFile,
                             getHeaderSearchOpts().Sysroot);

  for (auto &Listener : DependencyCollectors)
    Listener->attachToPreprocessor(*PP);

  // If we don't have a collector, but we are collecting module dependencies,
  // then we're the top level compiler instance and need to create one.
  if (!ModuleDepCollector && !DepOpts.ModuleDependencyOutputDir.empty())
    ModuleDepCollector = std::make_shared<ModuleDependencyCollector>(
        DepOpts.ModuleDependencyOutputDir);

  // Handle generating header include information, if requested.
  if (DepOpts.ShowHeaderIncludes)
    AttachHeaderIncludeGen(*PP);
  if (!DepOpts.HeaderIncludeOutputFile.empty()) {
    StringRef OutputPath = DepOpts.HeaderIncludeOutputFile;
    if (OutputPath == "-")
      OutputPath = "";
    AttachHeaderIncludeGen(*PP, /*ShowAllHeaders=*/true, OutputPath,
                           /*ShowDepth=*/false);
  }

  if (DepOpts.PrintShowIncludes) {
    AttachHeaderIncludeGen(*PP, /*ShowAllHeaders=*/false, /*OutputPath=*/"",
                           /*ShowDepth=*/true, /*MSStyle=*/true);
  }
}

// ASTContext

void CompilerInstance::createASTContext() {
  Preprocessor &PP = getPreprocessor();
  Context = new ASTContext(getLangOpts(), PP.getSourceManager(),
                           PP.getIdentifierTable(), PP.getSelectorTable(),
                           PP.getBuiltinInfo());
  Context->InitBuiltinTypes(getTarget());
}

// ExternalASTSource

void CompilerInstance::createPCHExternalASTSource(
    StringRef Path, bool DisablePCHValidation, bool AllowPCHWithCompilerErrors,
    void *DeserializationListener, bool OwnDeserializationListener) {
  IntrusiveRefCntPtr<ExternalASTSource> Source;
  bool Preamble = getPreprocessorOpts().PrecompiledPreambleBytes.first != 0;
  Source = createPCHExternalASTSource(
      Path, getHeaderSearchOpts().Sysroot, DisablePCHValidation,
      AllowPCHWithCompilerErrors, getPreprocessor(), getASTContext(),
      DeserializationListener, OwnDeserializationListener, Preamble,
      getFrontendOpts().UseGlobalModuleIndex);
  ModuleManager = static_cast<ASTReader*>(Source.get());
  getASTContext().setExternalSource(Source);
}

ExternalASTSource *CompilerInstance::createPCHExternalASTSource(
    StringRef Path, const std::string &Sysroot, bool DisablePCHValidation,
    bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
    void *DeserializationListener, bool OwnDeserializationListener,
    bool Preamble, bool UseGlobalModuleIndex) {
  HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();

  std::unique_ptr<ASTReader> Reader;
  Reader.reset(new ASTReader(PP, Context,
                             Sysroot.empty() ? "" : Sysroot.c_str(),
                             DisablePCHValidation,
                             AllowPCHWithCompilerErrors,
                             /*AllowConfigurationMismatch*/false,
                             HSOpts.ModulesValidateSystemHeaders,
                             UseGlobalModuleIndex));

  Reader->setDeserializationListener(
      static_cast<ASTDeserializationListener *>(DeserializationListener),
      /*TakeOwnership=*/OwnDeserializationListener);
  switch (Reader->ReadAST(Path,
                          Preamble ? serialization::MK_Preamble
                                   : serialization::MK_PCH,
                          SourceLocation(),
                          ASTReader::ARR_None)) {
  case ASTReader::Success:
    // Set the predefines buffer as suggested by the PCH reader. Typically, the
    // predefines buffer will be empty.
    PP.setPredefines(Reader->getSuggestedPredefines());
    return Reader.release();

  case ASTReader::Failure:
    // Unrecoverable failure: don't even try to process the input file.
    break;

  case ASTReader::Missing:
  case ASTReader::OutOfDate:
  case ASTReader::VersionMismatch:
  case ASTReader::ConfigurationMismatch:
  case ASTReader::HadErrors:
    // No suitable PCH file could be found. Return an error.
    break;
  }

  return nullptr;
}

// Code Completion

static bool EnableCodeCompletion(Preprocessor &PP,
                                 const std::string &Filename,
                                 unsigned Line,
                                 unsigned Column) {
  // Tell the source manager to chop off the given file at a specific
  // line and column.
  const FileEntry *Entry = PP.getFileManager().getFile(Filename);
  if (!Entry) {
    PP.getDiagnostics().Report(diag::err_fe_invalid_code_complete_file)
      << Filename;
    return true;
  }

  // Truncate the named file at the given line/column.
  PP.SetCodeCompletionPoint(Entry, Line, Column);
  return false;
}

void CompilerInstance::createCodeCompletionConsumer() {
  const ParsedSourceLocation &Loc = getFrontendOpts().CodeCompletionAt;
  if (!CompletionConsumer) {
    setCodeCompletionConsumer(
      createCodeCompletionConsumer(getPreprocessor(),
                                   Loc.FileName, Loc.Line, Loc.Column,
                                   getFrontendOpts().CodeCompleteOpts,
                                   llvm::outs()));
    if (!CompletionConsumer)
      return;
  } else if (EnableCodeCompletion(getPreprocessor(), Loc.FileName,
                                  Loc.Line, Loc.Column)) {
    setCodeCompletionConsumer(nullptr);
    return;
  }

  if (CompletionConsumer->isOutputBinary() &&
      llvm::sys::ChangeStdoutToBinary()) {
    getPreprocessor().getDiagnostics().Report(diag::err_fe_stdout_binary);
    setCodeCompletionConsumer(nullptr);
  }
}

void CompilerInstance::createFrontendTimer() {
  FrontendTimer.reset(new llvm::Timer("Clang front-end timer"));
}

CodeCompleteConsumer *
CompilerInstance::createCodeCompletionConsumer(Preprocessor &PP,
                                               const std::string &Filename,
                                               unsigned Line,
                                               unsigned Column,
                                               const CodeCompleteOptions &Opts,
                                               raw_ostream &OS) {
  if (EnableCodeCompletion(PP, Filename, Line, Column))
    return nullptr;

  // Set up the creation routine for code-completion.
  return new PrintingCodeCompleteConsumer(Opts, OS);
}

void CompilerInstance::createSema(TranslationUnitKind TUKind,
                                  CodeCompleteConsumer *CompletionConsumer) {
  TheSema.reset(new Sema(getPreprocessor(), getASTContext(), getASTConsumer(),
                         TUKind, CompletionConsumer));
}

// Output Files

void CompilerInstance::addOutputFile(const OutputFile &OutFile) {
  assert(OutFile.OS && "Attempt to add empty stream to output list!");
  OutputFiles.push_back(OutFile);
}

void CompilerInstance::clearOutputFiles(bool EraseFiles) {
  for (std::list<OutputFile>::iterator
         it = OutputFiles.begin(), ie = OutputFiles.end(); it != ie; ++it) {
    delete it->OS;
    if (!it->TempFilename.empty()) {
      if (EraseFiles) {
        llvm::sys::fs::remove(it->TempFilename);
      } else {
        SmallString<128> NewOutFile(it->Filename);

        // If '-working-directory' was passed, the output filename should be
        // relative to that.
        FileMgr->FixupRelativePath(NewOutFile);
        if (std::error_code ec =
                llvm::sys::fs::rename(it->TempFilename, NewOutFile.str())) {
          getDiagnostics().Report(diag::err_unable_to_rename_temp)
            << it->TempFilename << it->Filename << ec.message();

          llvm::sys::fs::remove(it->TempFilename);
        }
      }
    } else if (!it->Filename.empty() && EraseFiles)
      llvm::sys::fs::remove(it->Filename);

  }
  OutputFiles.clear();
}

llvm::raw_fd_ostream *
CompilerInstance::createDefaultOutputFile(bool Binary,
                                          StringRef InFile,
                                          StringRef Extension) {
  return createOutputFile(getFrontendOpts().OutputFile, Binary,
                          /*RemoveFileOnSignal=*/true, InFile, Extension,
                          /*UseTemporary=*/true);
}

llvm::raw_null_ostream *CompilerInstance::createNullOutputFile() {
  llvm::raw_null_ostream *OS = new llvm::raw_null_ostream();
  addOutputFile(OutputFile("", "", OS));
  return OS;
}

llvm::raw_fd_ostream *
CompilerInstance::createOutputFile(StringRef OutputPath,
                                   bool Binary, bool RemoveFileOnSignal,
                                   StringRef InFile,
                                   StringRef Extension,
                                   bool UseTemporary,
                                   bool CreateMissingDirectories) {
  std::string Error, OutputPathName, TempPathName;
  llvm::raw_fd_ostream *OS = createOutputFile(OutputPath, Error, Binary,
                                              RemoveFileOnSignal,
                                              InFile, Extension,
                                              UseTemporary,
                                              CreateMissingDirectories,
                                              &OutputPathName,
                                              &TempPathName);
  if (!OS) {
    getDiagnostics().Report(diag::err_fe_unable_to_open_output)
      << OutputPath << Error;
    return nullptr;
  }

  // Add the output file -- but don't try to remove "-", since this means we are
  // using stdin.
  addOutputFile(OutputFile((OutputPathName != "-") ? OutputPathName : "",
                TempPathName, OS));

  return OS;
}

llvm::raw_fd_ostream *
CompilerInstance::createOutputFile(StringRef OutputPath,
                                   std::string &Error,
                                   bool Binary,
                                   bool RemoveFileOnSignal,
                                   StringRef InFile,
                                   StringRef Extension,
                                   bool UseTemporary,
                                   bool CreateMissingDirectories,
                                   std::string *ResultPathName,
                                   std::string *TempPathName) {
  assert((!CreateMissingDirectories || UseTemporary) &&
         "CreateMissingDirectories is only allowed when using temporary files");

  std::string OutFile, TempFile;
  if (!OutputPath.empty()) {
    OutFile = OutputPath;
  } else if (InFile == "-") {
    OutFile = "-";
  } else if (!Extension.empty()) {
    SmallString<128> Path(InFile);
    llvm::sys::path::replace_extension(Path, Extension);
    OutFile = Path.str();
  } else {
    OutFile = "-";
  }

  std::unique_ptr<llvm::raw_fd_ostream> OS;
  std::string OSFile;

  if (UseTemporary) {
    if (OutFile == "-")
      UseTemporary = false;
    else {
      llvm::sys::fs::file_status Status;
      llvm::sys::fs::status(OutputPath, Status);
      if (llvm::sys::fs::exists(Status)) {
        // Fail early if we can't write to the final destination.
        if (!llvm::sys::fs::can_write(OutputPath))
          return nullptr;

        // Don't use a temporary if the output is a special file. This handles
        // things like '-o /dev/null'
        if (!llvm::sys::fs::is_regular_file(Status))
          UseTemporary = false;
      }
    }
  }

  if (UseTemporary) {
    // Create a temporary file.
    SmallString<128> TempPath;
    TempPath = OutFile;
    TempPath += "-%%%%%%%%";
    int fd;
    std::error_code EC =
        llvm::sys::fs::createUniqueFile(TempPath.str(), fd, TempPath);

    if (CreateMissingDirectories &&
        EC == llvm::errc::no_such_file_or_directory) {
      StringRef Parent = llvm::sys::path::parent_path(OutputPath);
      EC = llvm::sys::fs::create_directories(Parent);
      if (!EC) {
        EC = llvm::sys::fs::createUniqueFile(TempPath.str(), fd, TempPath);
      }
    }

    if (!EC) {
      OS.reset(new llvm::raw_fd_ostream(fd, /*shouldClose=*/true));
      OSFile = TempFile = TempPath.str();
    }
    // If we failed to create the temporary, fallback to writing to the file
    // directly. This handles the corner case where we cannot write to the
    // directory, but can write to the file.
  }

  if (!OS) {
    OSFile = OutFile;
    OS.reset(new llvm::raw_fd_ostream(
        OSFile.c_str(), Error,
        (Binary ? llvm::sys::fs::F_None : llvm::sys::fs::F_Text)));
    if (!Error.empty())
      return nullptr;
  }

  // Make sure the out stream file gets removed if we crash.
  if (RemoveFileOnSignal)
    llvm::sys::RemoveFileOnSignal(OSFile);

  if (ResultPathName)
    *ResultPathName = OutFile;
  if (TempPathName)
    *TempPathName = TempFile;

  return OS.release();
}

// Initialization Utilities

bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input){
  return InitializeSourceManager(Input, getDiagnostics(),
                                 getFileManager(), getSourceManager(),
                                 getFrontendOpts());
}

bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input,
                                               DiagnosticsEngine &Diags,
                                               FileManager &FileMgr,
                                               SourceManager &SourceMgr,
                                               const FrontendOptions &Opts) {
  SrcMgr::CharacteristicKind
    Kind = Input.isSystem() ? SrcMgr::C_System : SrcMgr::C_User;

  if (Input.isBuffer()) {
    SourceMgr.setMainFileID(SourceMgr.createFileID(Input.getBuffer(), Kind));
    assert(!SourceMgr.getMainFileID().isInvalid() &&
           "Couldn't establish MainFileID!");
    return true;
  }

  StringRef InputFile = Input.getFile();

  // Figure out where to get and map in the main file.
  if (InputFile != "-") {
    const FileEntry *File = FileMgr.getFile(InputFile, /*OpenFile=*/true);
    if (!File) {
      Diags.Report(diag::err_fe_error_reading) << InputFile;
      return false;
    }

    // The natural SourceManager infrastructure can't currently handle named
    // pipes, but we would at least like to accept them for the main
    // file. Detect them here, read them with the volatile flag so FileMgr will
    // pick up the correct size, and simply override their contents as we do for
    // STDIN.
    if (File->isNamedPipe()) {
      std::string ErrorStr;
      if (llvm::MemoryBuffer *MB =
              FileMgr.getBufferForFile(File, &ErrorStr, /*isVolatile=*/true)) {
        // Create a new virtual file that will have the correct size.
        File = FileMgr.getVirtualFile(InputFile, MB->getBufferSize(), 0);
        SourceMgr.overrideFileContents(File, MB);
      } else {
        Diags.Report(diag::err_cannot_open_file) << InputFile << ErrorStr;
        return false;
      }
    }

    SourceMgr.setMainFileID(
        SourceMgr.createFileID(File, SourceLocation(), Kind));
  } else {
    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> SBOrErr =
        llvm::MemoryBuffer::getSTDIN();
    if (std::error_code EC = SBOrErr.getError()) {
      Diags.Report(diag::err_fe_error_reading_stdin) << EC.message();
      return false;
    }
    std::unique_ptr<llvm::MemoryBuffer> SB = std::move(SBOrErr.get());

    const FileEntry *File = FileMgr.getVirtualFile(SB->getBufferIdentifier(),
                                                   SB->getBufferSize(), 0);
    SourceMgr.setMainFileID(
        SourceMgr.createFileID(File, SourceLocation(), Kind));
    SourceMgr.overrideFileContents(File, SB.release());
  }

  assert(!SourceMgr.getMainFileID().isInvalid() &&
         "Couldn't establish MainFileID!");
  return true;
}

// High-Level Operations

bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
  assert(hasDiagnostics() && "Diagnostics engine is not initialized!");
  assert(!getFrontendOpts().ShowHelp && "Client must handle '-help'!");
  assert(!getFrontendOpts().ShowVersion && "Client must handle '-version'!");

  // FIXME: Take this as an argument, once all the APIs we used have moved to
  // taking it as an input instead of hard-coding llvm::errs.
  raw_ostream &OS = llvm::errs();

  // Create the target instance.
  setTarget(TargetInfo::CreateTargetInfo(getDiagnostics(),
                                         getInvocation().TargetOpts));
  if (!hasTarget())
    return false;

  // Inform the target of the language options.
  //
  // FIXME: We shouldn't need to do this, the target should be immutable once
  // created. This complexity should be lifted elsewhere.
  getTarget().adjust(getLangOpts());

  // rewriter project will change target built-in bool type from its default.
  if (getFrontendOpts().ProgramAction == frontend::RewriteObjC)
    getTarget().noSignedCharForObjCBool();

  // Validate/process some options.
  if (getHeaderSearchOpts().Verbose)
    OS << "clang -cc1 version " CLANG_VERSION_STRING
       << " based upon " << BACKEND_PACKAGE_STRING
       << " default target " << llvm::sys::getDefaultTargetTriple() << "\n";

  if (getFrontendOpts().ShowTimers)
    createFrontendTimer();

  if (getFrontendOpts().ShowStats)
    llvm::EnableStatistics();

  for (unsigned i = 0, e = getFrontendOpts().Inputs.size(); i != e; ++i) {
    // Reset the ID tables if we are reusing the SourceManager.
    if (hasSourceManager())
      getSourceManager().clearIDTables();

    if (Act.BeginSourceFile(*this, getFrontendOpts().Inputs[i])) {
      Act.Execute();
      Act.EndSourceFile();
    }
  }

  // Notify the diagnostic client that all files were processed.
  getDiagnostics().getClient()->finish();

  if (getDiagnosticOpts().ShowCarets) {
    // We can have multiple diagnostics sharing one diagnostic client.
    // Get the total number of warnings/errors from the client.
    unsigned NumWarnings = getDiagnostics().getClient()->getNumWarnings();
    unsigned NumErrors = getDiagnostics().getClient()->getNumErrors();

    if (NumWarnings)
      OS << NumWarnings << " warning" << (NumWarnings == 1 ? "" : "s");
    if (NumWarnings && NumErrors)
      OS << " and ";
    if (NumErrors)
      OS << NumErrors << " error" << (NumErrors == 1 ? "" : "s");
    if (NumWarnings || NumErrors)
      OS << " generated.\n";
  }

  if (getFrontendOpts().ShowStats && hasFileManager()) {
    getFileManager().PrintStats();
    OS << "\n";
  }

  return !getDiagnostics().getClient()->getNumErrors();
}

/// \brief Determine the appropriate source input kind based on language
/// options.
static InputKind getSourceInputKindFromOptions(const LangOptions &LangOpts) {
  if (LangOpts.OpenCL)
    return IK_OpenCL;
  if (LangOpts.CUDA)
    return IK_CUDA;
  if (LangOpts.ObjC1)
    return LangOpts.CPlusPlus? IK_ObjCXX : IK_ObjC;
  return LangOpts.CPlusPlus? IK_CXX : IK_C;
}

/// \brief Compile a module file for the given module, using the options
/// provided by the importing compiler instance.
static void compileModuleImpl(CompilerInstance &ImportingInstance,
                          SourceLocation ImportLoc,
                          Module *Module,
                          StringRef ModuleFileName) {
  ModuleMap &ModMap
    = ImportingInstance.getPreprocessor().getHeaderSearchInfo().getModuleMap();

  // Construct a compiler invocation for creating this module.
  IntrusiveRefCntPtr<CompilerInvocation> Invocation
    (new CompilerInvocation(ImportingInstance.getInvocation()));

  PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();

  // For any options that aren't intended to affect how a module is built,
  // reset them to their default values.
  Invocation->getLangOpts()->resetNonModularOptions();
  PPOpts.resetNonModularOptions();

  // Remove any macro definitions that are explicitly ignored by the module.
  // They aren't supposed to affect how the module is built anyway.
  const HeaderSearchOptions &HSOpts = Invocation->getHeaderSearchOpts();
  PPOpts.Macros.erase(
      std::remove_if(PPOpts.Macros.begin(), PPOpts.Macros.end(),
                     [&HSOpts](const std::pair<std::string, bool> &def) {
        StringRef MacroDef = def.first;
        return HSOpts.ModulesIgnoreMacros.count(MacroDef.split('=').first) > 0;
      }),
      PPOpts.Macros.end());

  // Note the name of the module we're building.
  Invocation->getLangOpts()->CurrentModule = Module->getTopLevelModuleName();

  // Make sure that the failed-module structure has been allocated in
  // the importing instance, and propagate the pointer to the newly-created
  // instance.
  PreprocessorOptions &ImportingPPOpts
    = ImportingInstance.getInvocation().getPreprocessorOpts();
  if (!ImportingPPOpts.FailedModules)
    ImportingPPOpts.FailedModules = new PreprocessorOptions::FailedModulesSet;
  PPOpts.FailedModules = ImportingPPOpts.FailedModules;

  // If there is a module map file, build the module using the module map.
  // Set up the inputs/outputs so that we build the module from its umbrella
  // header.
  FrontendOptions &FrontendOpts = Invocation->getFrontendOpts();
  FrontendOpts.OutputFile = ModuleFileName.str();
  FrontendOpts.DisableFree = false;
  FrontendOpts.GenerateGlobalModuleIndex = false;
  FrontendOpts.Inputs.clear();
  InputKind IK = getSourceInputKindFromOptions(*Invocation->getLangOpts());

  // Don't free the remapped file buffers; they are owned by our caller.
  PPOpts.RetainRemappedFileBuffers = true;

  Invocation->getDiagnosticOpts().VerifyDiagnostics = 0;
  assert(ImportingInstance.getInvocation().getModuleHash() ==
         Invocation->getModuleHash() && "Module hash mismatch!");

  // Construct a compiler instance that will be used to actually create the
  // module.
  CompilerInstance Instance(/*BuildingModule=*/true);
  Instance.setInvocation(&*Invocation);

  Instance.createDiagnostics(new ForwardingDiagnosticConsumer(
                                   ImportingInstance.getDiagnosticClient()),
                             /*ShouldOwnClient=*/true);

  Instance.setVirtualFileSystem(&ImportingInstance.getVirtualFileSystem());

  // Note that this module is part of the module build stack, so that we
  // can detect cycles in the module graph.
  Instance.setFileManager(&ImportingInstance.getFileManager());
  Instance.createSourceManager(Instance.getFileManager());
  SourceManager &SourceMgr = Instance.getSourceManager();
  SourceMgr.setModuleBuildStack(
    ImportingInstance.getSourceManager().getModuleBuildStack());
  SourceMgr.pushModuleBuildStack(Module->getTopLevelModuleName(),
    FullSourceLoc(ImportLoc, ImportingInstance.getSourceManager()));

  // If we're collecting module dependencies, we need to share a collector
  // between all of the module CompilerInstances.
  Instance.setModuleDepCollector(ImportingInstance.getModuleDepCollector());

  // Get or create the module map that we'll use to build this module.
  std::string InferredModuleMapContent;
  if (const FileEntry *ModuleMapFile =
          ModMap.getContainingModuleMapFile(Module)) {
    // Use the module map where this module resides.
    FrontendOpts.Inputs.push_back(
        FrontendInputFile(ModuleMapFile->getName(), IK));
  } else {
    llvm::raw_string_ostream OS(InferredModuleMapContent);
    Module->print(OS);
    OS.flush();
    FrontendOpts.Inputs.push_back(
        FrontendInputFile("__inferred_module.map", IK));

    llvm::MemoryBuffer *ModuleMapBuffer =
        llvm::MemoryBuffer::getMemBuffer(InferredModuleMapContent);
    ModuleMapFile = Instance.getFileManager().getVirtualFile(
        "__inferred_module.map", InferredModuleMapContent.size(), 0);
    SourceMgr.overrideFileContents(ModuleMapFile, ModuleMapBuffer);
  }

  // Construct a module-generating action. Passing through Module->ModuleMap is
  // safe because the FileManager is shared between the compiler instances.
  GenerateModuleAction CreateModuleAction(Module->ModuleMap, Module->IsSystem);

  // Execute the action to actually build the module in-place. Use a separate
  // thread so that we get a stack large enough.
  const unsigned ThreadStackSize = 8 << 20;
  llvm::CrashRecoveryContext CRC;
  CRC.RunSafelyOnThread([&]() { Instance.ExecuteAction(CreateModuleAction); },
                        ThreadStackSize);

  // Delete the temporary module map file.
  // FIXME: Even though we're executing under crash protection, it would still
  // be nice to do this with RemoveFileOnSignal when we can. However, that
  // doesn't make sense for all clients, so clean this up manually.
  Instance.clearOutputFiles(/*EraseFiles=*/true);

  // We've rebuilt a module. If we're allowed to generate or update the global
  // module index, record that fact in the importing compiler instance.
  if (ImportingInstance.getFrontendOpts().GenerateGlobalModuleIndex) {
    ImportingInstance.setBuildGlobalModuleIndex(true);
  }
}

static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
                                 SourceLocation ImportLoc,
                                 SourceLocation ModuleNameLoc,
                                 Module *Module,
                                 StringRef ModuleFileName) {
  // FIXME: have LockFileManager return an error_code so that we can
  // avoid the mkdir when the directory already exists.
  StringRef Dir = llvm::sys::path::parent_path(ModuleFileName);
  llvm::sys::fs::create_directories(Dir);

  while (1) {
    unsigned ModuleLoadCapabilities = ASTReader::ARR_Missing;
    llvm::LockFileManager Locked(ModuleFileName);
    switch (Locked) {
    case llvm::LockFileManager::LFS_Error:
      return false;

    case llvm::LockFileManager::LFS_Owned:
      // We're responsible for building the module ourselves.
      // FIXME: if there are errors, don't attempt to load the module.
      compileModuleImpl(ImportingInstance, ModuleNameLoc, Module,
                        ModuleFileName);
      break;

    case llvm::LockFileManager::LFS_Shared:
      // Someone else is responsible for building the module. Wait for them to
      // finish.
      if (Locked.waitForUnlock() == llvm::LockFileManager::Res_OwnerDied)
        continue; // try again to get the lock.
      ModuleLoadCapabilities |= ASTReader::ARR_OutOfDate;
      break;
    }

    // Try to read the module file, now that we've compiled it.
    ASTReader::ASTReadResult ReadResult =
        ImportingInstance.getModuleManager()->ReadAST(
            ModuleFileName, serialization::MK_Module, ImportLoc,
            ModuleLoadCapabilities);

    if (ReadResult == ASTReader::OutOfDate &&
        Locked == llvm::LockFileManager::LFS_Shared) {
      // The module may be out of date in the presence of file system races,
      // or if one of its imports depends on header search paths that are not
      // consistent with this ImportingInstance.  Try again...
      continue;
    } else if (ReadResult == ASTReader::Missing) {
      ImportingInstance.getDiagnostics().Report(ModuleNameLoc,
                                                diag::err_module_not_built)
          << Module->Name << SourceRange(ImportLoc, ModuleNameLoc);
    }
    return ReadResult == ASTReader::Success;
  }
}

/// \brief Diagnose differences between the current definition of the given
/// configuration macro and the definition provided on the command line.
static void checkConfigMacro(Preprocessor &PP, StringRef ConfigMacro,
                             Module *Mod, SourceLocation ImportLoc) {
  IdentifierInfo *Id = PP.getIdentifierInfo(ConfigMacro);
  SourceManager &SourceMgr = PP.getSourceManager();

  // If this identifier has never had a macro definition, then it could
  // not have changed.
  if (!Id->hadMacroDefinition())
    return;

  // If this identifier does not currently have a macro definition,
  // check whether it had one on the command line.
  if (!Id->hasMacroDefinition()) {
    MacroDirective::DefInfo LatestDef =
        PP.getMacroDirectiveHistory(Id)->getDefinition();
    for (MacroDirective::DefInfo Def = LatestDef; Def;
           Def = Def.getPreviousDefinition()) {
      FileID FID = SourceMgr.getFileID(Def.getLocation());
      if (FID.isInvalid())
        continue;

      // We only care about the predefines buffer.
      if (FID != PP.getPredefinesFileID())
        continue;

      // This macro was defined on the command line, then #undef'd later.
      // Complain.
      PP.Diag(ImportLoc, diag::warn_module_config_macro_undef)
        << true << ConfigMacro << Mod->getFullModuleName();
      if (LatestDef.isUndefined())
        PP.Diag(LatestDef.getUndefLocation(), diag::note_module_def_undef_here)
          << true;
      return;
    }

    // Okay: no definition in the predefines buffer.
    return;
  }

  // This identifier has a macro definition. Check whether we had a definition
  // on the command line.
  MacroDirective::DefInfo LatestDef =
      PP.getMacroDirectiveHistory(Id)->getDefinition();
  MacroDirective::DefInfo PredefinedDef;
  for (MacroDirective::DefInfo Def = LatestDef; Def;
         Def = Def.getPreviousDefinition()) {
    FileID FID = SourceMgr.getFileID(Def.getLocation());
    if (FID.isInvalid())
      continue;

    // We only care about the predefines buffer.
    if (FID != PP.getPredefinesFileID())
      continue;

    PredefinedDef = Def;
    break;
  }

  // If there was no definition for this macro in the predefines buffer,
  // complain.
  if (!PredefinedDef ||
      (!PredefinedDef.getLocation().isValid() &&
       PredefinedDef.getUndefLocation().isValid())) {
    PP.Diag(ImportLoc, diag::warn_module_config_macro_undef)
      << false << ConfigMacro << Mod->getFullModuleName();
    PP.Diag(LatestDef.getLocation(), diag::note_module_def_undef_here)
      << false;
    return;
  }

  // If the current macro definition is the same as the predefined macro
  // definition, it's okay.
  if (LatestDef.getMacroInfo() == PredefinedDef.getMacroInfo() ||
      LatestDef.getMacroInfo()->isIdenticalTo(*PredefinedDef.getMacroInfo(),PP,
                                              /*Syntactically=*/true))
    return;

  // The macro definitions differ.
  PP.Diag(ImportLoc, diag::warn_module_config_macro_undef)
    << false << ConfigMacro << Mod->getFullModuleName();
  PP.Diag(LatestDef.getLocation(), diag::note_module_def_undef_here)
    << false;
}

/// \brief Write a new timestamp file with the given path.
static void writeTimestampFile(StringRef TimestampFile) {
  std::string ErrorInfo;
  llvm::raw_fd_ostream Out(TimestampFile.str().c_str(), ErrorInfo,
                           llvm::sys::fs::F_None);
}

/// \brief Prune the module cache of modules that haven't been accessed in
/// a long time.
static void pruneModuleCache(const HeaderSearchOptions &HSOpts) {
  struct stat StatBuf;
  llvm::SmallString<128> TimestampFile;
  TimestampFile = HSOpts.ModuleCachePath;
  llvm::sys::path::append(TimestampFile, "modules.timestamp");

  // Try to stat() the timestamp file.
  if (::stat(TimestampFile.c_str(), &StatBuf)) {
    // If the timestamp file wasn't there, create one now.
    if (errno == ENOENT) {
      writeTimestampFile(TimestampFile);
    }
    return;
  }

  // Check whether the time stamp is older than our pruning interval.
  // If not, do nothing.
  time_t TimeStampModTime = StatBuf.st_mtime;
  time_t CurrentTime = time(nullptr);
  if (CurrentTime - TimeStampModTime <= time_t(HSOpts.ModuleCachePruneInterval))
    return;

  // Write a new timestamp file so that nobody else attempts to prune.
  // There is a benign race condition here, if two Clang instances happen to
  // notice at the same time that the timestamp is out-of-date.
  writeTimestampFile(TimestampFile);

  // Walk the entire module cache, looking for unused module files and module
  // indices.
  std::error_code EC;
  SmallString<128> ModuleCachePathNative;
  llvm::sys::path::native(HSOpts.ModuleCachePath, ModuleCachePathNative);
  for (llvm::sys::fs::directory_iterator
         Dir(ModuleCachePathNative.str(), EC), DirEnd;
       Dir != DirEnd && !EC; Dir.increment(EC)) {
    // If we don't have a directory, there's nothing to look into.
    if (!llvm::sys::fs::is_directory(Dir->path()))
      continue;

    // Walk all of the files within this directory.
    for (llvm::sys::fs::directory_iterator File(Dir->path(), EC), FileEnd;
         File != FileEnd && !EC; File.increment(EC)) {
      // We only care about module and global module index files.
      StringRef Extension = llvm::sys::path::extension(File->path());
      if (Extension != ".pcm" && Extension != ".timestamp" &&
          llvm::sys::path::filename(File->path()) != "modules.idx")
        continue;

      // Look at this file. If we can't stat it, there's nothing interesting
      // there.
      if (::stat(File->path().c_str(), &StatBuf))
        continue;

      // If the file has been used recently enough, leave it there.
      time_t FileAccessTime = StatBuf.st_atime;
      if (CurrentTime - FileAccessTime <=
              time_t(HSOpts.ModuleCachePruneAfter)) {
        continue;
      }

      // Remove the file.
      llvm::sys::fs::remove(File->path());

      // Remove the timestamp file.
      std::string TimpestampFilename = File->path() + ".timestamp";
      llvm::sys::fs::remove(TimpestampFilename);
    }

    // If we removed all of the files in the directory, remove the directory
    // itself.
    if (llvm::sys::fs::directory_iterator(Dir->path(), EC) ==
            llvm::sys::fs::directory_iterator() && !EC)
      llvm::sys::fs::remove(Dir->path());
  }
}

void CompilerInstance::createModuleManager() {
  if (!ModuleManager) {
    if (!hasASTContext())
      createASTContext();

    // If we're not recursively building a module, check whether we
    // need to prune the module cache.
    if (getSourceManager().getModuleBuildStack().empty() &&
        getHeaderSearchOpts().ModuleCachePruneInterval > 0 &&
        getHeaderSearchOpts().ModuleCachePruneAfter > 0) {
      pruneModuleCache(getHeaderSearchOpts());
    }

    HeaderSearchOptions &HSOpts = getHeaderSearchOpts();
    std::string Sysroot = HSOpts.Sysroot;
    const PreprocessorOptions &PPOpts = getPreprocessorOpts();
    ModuleManager = new ASTReader(getPreprocessor(), *Context,
                                  Sysroot.empty() ? "" : Sysroot.c_str(),
                                  PPOpts.DisablePCHValidation,
                                  /*AllowASTWithCompilerErrors=*/false,
                                  /*AllowConfigurationMismatch=*/false,
                                  HSOpts.ModulesValidateSystemHeaders,
                                  getFrontendOpts().UseGlobalModuleIndex);
    if (hasASTConsumer()) {
      ModuleManager->setDeserializationListener(
        getASTConsumer().GetASTDeserializationListener());
      getASTContext().setASTMutationListener(
        getASTConsumer().GetASTMutationListener());
    }
    getASTContext().setExternalSource(ModuleManager);
    if (hasSema())
      ModuleManager->InitializeSema(getSema());
    if (hasASTConsumer())
      ModuleManager->StartTranslationUnit(&getASTConsumer());
  }
}

ModuleLoadResult
CompilerInstance::loadModule(SourceLocation ImportLoc,
                             ModuleIdPath Path,
                             Module::NameVisibilityKind Visibility,
                             bool IsInclusionDirective) {
  // Determine what file we're searching from.
  StringRef ModuleName = Path[0].first->getName();
  SourceLocation ModuleNameLoc = Path[0].second;

  // If we've already handled this import, just return the cached result.
  // This one-element cache is important to eliminate redundant diagnostics
  // when both the preprocessor and parser see the same import declaration.
  if (!ImportLoc.isInvalid() && LastModuleImportLoc == ImportLoc) {
    // Make the named module visible.
    if (LastModuleImportResult && ModuleName != getLangOpts().CurrentModule)
      ModuleManager->makeModuleVisible(LastModuleImportResult, Visibility,
                                       ImportLoc, /*Complain=*/false);
    return LastModuleImportResult;
  }

  clang::Module *Module = nullptr;

  // If we don't already have information on this module, load the module now.
  llvm::DenseMap<const IdentifierInfo *, clang::Module *>::iterator Known
    = KnownModules.find(Path[0].first);
  if (Known != KnownModules.end()) {
    // Retrieve the cached top-level module.
    Module = Known->second;
  } else if (ModuleName == getLangOpts().CurrentModule) {
    // This is the module we're building.
    Module = PP->getHeaderSearchInfo().lookupModule(ModuleName);
    Known = KnownModules.insert(std::make_pair(Path[0].first, Module)).first;
  } else {
    // Search for a module with the given name.
    Module = PP->getHeaderSearchInfo().lookupModule(ModuleName);
    if (!Module) {
      getDiagnostics().Report(ModuleNameLoc, diag::err_module_not_found)
      << ModuleName
      << SourceRange(ImportLoc, ModuleNameLoc);
      ModuleBuildFailed = true;
      return ModuleLoadResult();
    }

    std::string ModuleFileName =
        PP->getHeaderSearchInfo().getModuleFileName(Module);

    // If we don't already have an ASTReader, create one now.
    if (!ModuleManager)
      createModuleManager();

    if (TheDependencyFileGenerator)
      TheDependencyFileGenerator->AttachToASTReader(*ModuleManager);

    if (ModuleDepCollector)
      ModuleDepCollector->attachToASTReader(*ModuleManager);

    for (auto &Listener : DependencyCollectors)
      Listener->attachToASTReader(*ModuleManager);

    // Try to load the module file.
    unsigned ARRFlags = ASTReader::ARR_OutOfDate | ASTReader::ARR_Missing;
    switch (ModuleManager->ReadAST(ModuleFileName, serialization::MK_Module,
                                   ImportLoc, ARRFlags)) {
    case ASTReader::Success:
      break;

    case ASTReader::OutOfDate:
    case ASTReader::Missing: {
      // The module file is missing or out-of-date. Build it.
      assert(Module && "missing module file");
      // Check whether there is a cycle in the module graph.
      ModuleBuildStack ModPath = getSourceManager().getModuleBuildStack();
      ModuleBuildStack::iterator Pos = ModPath.begin(), PosEnd = ModPath.end();
      for (; Pos != PosEnd; ++Pos) {
        if (Pos->first == ModuleName)
          break;
      }

      if (Pos != PosEnd) {
        SmallString<256> CyclePath;
        for (; Pos != PosEnd; ++Pos) {
          CyclePath += Pos->first;
          CyclePath += " -> ";
        }
        CyclePath += ModuleName;

        getDiagnostics().Report(ModuleNameLoc, diag::err_module_cycle)
          << ModuleName << CyclePath;
        return ModuleLoadResult();
      }

      getDiagnostics().Report(ImportLoc, diag::remark_module_build)
          << ModuleName << ModuleFileName;

      // Check whether we have already attempted to build this module (but
      // failed).
      if (getPreprocessorOpts().FailedModules &&
          getPreprocessorOpts().FailedModules->hasAlreadyFailed(ModuleName)) {
        getDiagnostics().Report(ModuleNameLoc, diag::err_module_not_built)
          << ModuleName
          << SourceRange(ImportLoc, ModuleNameLoc);
        ModuleBuildFailed = true;
        return ModuleLoadResult();
      }

      // Try to compile and then load the module.
      if (!compileAndLoadModule(*this, ImportLoc, ModuleNameLoc, Module,
                                ModuleFileName)) {
        if (getPreprocessorOpts().FailedModules)
          getPreprocessorOpts().FailedModules->addFailed(ModuleName);
        KnownModules[Path[0].first] = nullptr;
        ModuleBuildFailed = true;
        return ModuleLoadResult();
      }

      // Okay, we've rebuilt and now loaded the module.
      break;
    }

    case ASTReader::VersionMismatch:
    case ASTReader::ConfigurationMismatch:
    case ASTReader::HadErrors:
      ModuleLoader::HadFatalFailure = true;
      // FIXME: The ASTReader will already have complained, but can we showhorn
      // that diagnostic information into a more useful form?
      KnownModules[Path[0].first] = nullptr;
      return ModuleLoadResult();

    case ASTReader::Failure:
      ModuleLoader::HadFatalFailure = true;
      // Already complained, but note now that we failed.
      KnownModules[Path[0].first] = nullptr;
      ModuleBuildFailed = true;
      return ModuleLoadResult();
    }

    // Cache the result of this top-level module lookup for later.
    Known = KnownModules.insert(std::make_pair(Path[0].first, Module)).first;
  }

  // If we never found the module, fail.
  if (!Module)
    return ModuleLoadResult();

  // Verify that the rest of the module path actually corresponds to
  // a submodule.
  if (Path.size() > 1) {
    for (unsigned I = 1, N = Path.size(); I != N; ++I) {
      StringRef Name = Path[I].first->getName();
      clang::Module *Sub = Module->findSubmodule(Name);

      if (!Sub) {
        // Attempt to perform typo correction to find a module name that works.
        SmallVector<StringRef, 2> Best;
        unsigned BestEditDistance = (std::numeric_limits<unsigned>::max)();

        for (clang::Module::submodule_iterator J = Module->submodule_begin(),
                                            JEnd = Module->submodule_end();
             J != JEnd; ++J) {
          unsigned ED = Name.edit_distance((*J)->Name,
                                           /*AllowReplacements=*/true,
                                           BestEditDistance);
          if (ED <= BestEditDistance) {
            if (ED < BestEditDistance) {
              Best.clear();
              BestEditDistance = ED;
            }

            Best.push_back((*J)->Name);
          }
        }

        // If there was a clear winner, user it.
        if (Best.size() == 1) {
          getDiagnostics().Report(Path[I].second,
                                  diag::err_no_submodule_suggest)
            << Path[I].first << Module->getFullModuleName() << Best[0]
            << SourceRange(Path[0].second, Path[I-1].second)
            << FixItHint::CreateReplacement(SourceRange(Path[I].second),
                                            Best[0]);

          Sub = Module->findSubmodule(Best[0]);
        }
      }

      if (!Sub) {
        // No submodule by this name. Complain, and don't look for further
        // submodules.
        getDiagnostics().Report(Path[I].second, diag::err_no_submodule)
          << Path[I].first << Module->getFullModuleName()
          << SourceRange(Path[0].second, Path[I-1].second);
        break;
      }

      Module = Sub;
    }
  }

  // Make the named module visible, if it's not already part of the module
  // we are parsing.
  if (ModuleName != getLangOpts().CurrentModule) {
    if (!Module->IsFromModuleFile) {
      // We have an umbrella header or directory that doesn't actually include
      // all of the headers within the directory it covers. Complain about
      // this missing submodule and recover by forgetting that we ever saw
      // this submodule.
      // FIXME: Should we detect this at module load time? It seems fairly
      // expensive (and rare).
      getDiagnostics().Report(ImportLoc, diag::warn_missing_submodule)
        << Module->getFullModuleName()
        << SourceRange(Path.front().second, Path.back().second);

      return ModuleLoadResult(nullptr, true);
    }

    // Check whether this module is available.
    clang::Module::Requirement Requirement;
    clang::Module::HeaderDirective MissingHeader;
    if (!Module->isAvailable(getLangOpts(), getTarget(), Requirement,
                             MissingHeader)) {
      if (MissingHeader.FileNameLoc.isValid()) {
        getDiagnostics().Report(MissingHeader.FileNameLoc,
                                diag::err_module_header_missing)
          << MissingHeader.IsUmbrella << MissingHeader.FileName;
      } else {
        getDiagnostics().Report(ImportLoc, diag::err_module_unavailable)
          << Module->getFullModuleName()
          << Requirement.second << Requirement.first
          << SourceRange(Path.front().second, Path.back().second);
      }
      LastModuleImportLoc = ImportLoc;
      LastModuleImportResult = ModuleLoadResult();
      return ModuleLoadResult();
    }

    ModuleManager->makeModuleVisible(Module, Visibility, ImportLoc,
                                     /*Complain=*/true);
  }

  // Check for any configuration macros that have changed.
  clang::Module *TopModule = Module->getTopLevelModule();
  for (unsigned I = 0, N = TopModule->ConfigMacros.size(); I != N; ++I) {
    checkConfigMacro(getPreprocessor(), TopModule->ConfigMacros[I],
                     Module, ImportLoc);
  }

  // If this module import was due to an inclusion directive, create an
  // implicit import declaration to capture it in the AST.
  if (IsInclusionDirective && hasASTContext()) {
    TranslationUnitDecl *TU = getASTContext().getTranslationUnitDecl();
    ImportDecl *ImportD = ImportDecl::CreateImplicit(getASTContext(), TU,
                                                     ImportLoc, Module,
                                                     Path.back().second);
    TU->addDecl(ImportD);
    if (Consumer)
      Consumer->HandleImplicitImportDecl(ImportD);
  }

  LastModuleImportLoc = ImportLoc;
  LastModuleImportResult = ModuleLoadResult(Module, false);
  return LastModuleImportResult;
}

void CompilerInstance::makeModuleVisible(Module *Mod,
                                         Module::NameVisibilityKind Visibility,
                                         SourceLocation ImportLoc,
                                         bool Complain){
  ModuleManager->makeModuleVisible(Mod, Visibility, ImportLoc, Complain);
}

GlobalModuleIndex *CompilerInstance::loadGlobalModuleIndex(
    SourceLocation TriggerLoc) {
  if (!ModuleManager)
    createModuleManager();
  // Can't do anything if we don't have the module manager.
  if (!ModuleManager)
    return nullptr;
  // Get an existing global index.  This loads it if not already
  // loaded.
  ModuleManager->loadGlobalIndex();
  GlobalModuleIndex *GlobalIndex = ModuleManager->getGlobalIndex();
  // If the global index doesn't exist, create it.
  if (!GlobalIndex && shouldBuildGlobalModuleIndex() && hasFileManager() &&
      hasPreprocessor()) {
    llvm::sys::fs::create_directories(
      getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
    GlobalModuleIndex::writeIndex(
      getFileManager(),
      getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
    ModuleManager->resetForReload();
    ModuleManager->loadGlobalIndex();
    GlobalIndex = ModuleManager->getGlobalIndex();
  }
  // For finding modules needing to be imported for fixit messages,
  // we need to make the global index cover all modules, so we do that here.
  if (!HaveFullGlobalModuleIndex && GlobalIndex && !buildingModule()) {
    ModuleMap &MMap = getPreprocessor().getHeaderSearchInfo().getModuleMap();
    bool RecreateIndex = false;
    for (ModuleMap::module_iterator I = MMap.module_begin(),
        E = MMap.module_end(); I != E; ++I) {
      Module *TheModule = I->second;
      const FileEntry *Entry = TheModule->getASTFile();
      if (!Entry) {
        SmallVector<std::pair<IdentifierInfo *, SourceLocation>, 2> Path;
        Path.push_back(std::make_pair(
				  getPreprocessor().getIdentifierInfo(TheModule->Name), TriggerLoc));
        std::reverse(Path.begin(), Path.end());
		    // Load a module as hidden.  This also adds it to the global index.
        loadModule(TheModule->DefinitionLoc, Path,
                                             Module::Hidden, false);
        RecreateIndex = true;
      }
    }
    if (RecreateIndex) {
      GlobalModuleIndex::writeIndex(
        getFileManager(),
        getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
      ModuleManager->resetForReload();
      ModuleManager->loadGlobalIndex();
      GlobalIndex = ModuleManager->getGlobalIndex();
    }
    HaveFullGlobalModuleIndex = true;
  }
  return GlobalIndex;
}

// Check global module index for missing imports.
bool
CompilerInstance::lookupMissingImports(StringRef Name,
                                       SourceLocation TriggerLoc) {
  // Look for the symbol in non-imported modules, but only if an error
  // actually occurred.
  if (!buildingModule()) {
    // Load global module index, or retrieve a previously loaded one.
    GlobalModuleIndex *GlobalIndex = loadGlobalModuleIndex(
      TriggerLoc);

    // Only if we have a global index.
    if (GlobalIndex) {
      GlobalModuleIndex::HitSet FoundModules;

      // Find the modules that reference the identifier.
      // Note that this only finds top-level modules.
      // We'll let diagnoseTypo find the actual declaration module.
      if (GlobalIndex->lookupIdentifier(Name, FoundModules))
        return true;
    }
  }

  return false;
}