xref: /llvm-project-15.0.7/clang/lib/Frontend/ASTUnit.cpp (revision 2c5e91e2)

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

#include "clang/Frontend/ASTUnit.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/AST/TypeOrdering.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/Driver/Compilation.h"
#include "clang/Driver/Driver.h"
#include "clang/Driver/Job.h"
#include "clang/Driver/ArgList.h"
#include "clang/Driver/Options.h"
#include "clang/Driver/Tool.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Frontend/FrontendActions.h"
#include "clang/Frontend/FrontendDiagnostic.h"
#include "clang/Frontend/FrontendOptions.h"
#include "clang/Frontend/Utils.h"
#include "clang/Serialization/ASTReader.h"
#include "clang/Serialization/ASTWriter.h"
#include "clang/Lex/HeaderSearch.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Basic/TargetOptions.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/Diagnostic.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/Atomic.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/CrashRecoveryContext.h"
#include <cstdlib>
#include <cstdio>
#include <sys/stat.h>
using namespace clang;

using llvm::TimeRecord;

namespace {
  class SimpleTimer {
    bool WantTiming;
    TimeRecord Start;
    std::string Output;

  public:
    explicit SimpleTimer(bool WantTiming) : WantTiming(WantTiming) {
      if (WantTiming)
        Start = TimeRecord::getCurrentTime();
    }

    void setOutput(const Twine &Output) {
      if (WantTiming)
        this->Output = Output.str();
    }

    ~SimpleTimer() {
      if (WantTiming) {
        TimeRecord Elapsed = TimeRecord::getCurrentTime();
        Elapsed -= Start;
        llvm::errs() << Output << ':';
        Elapsed.print(Elapsed, llvm::errs());
        llvm::errs() << '\n';
      }
    }
  };
}

/// \brief After failing to build a precompiled preamble (due to
/// errors in the source that occurs in the preamble), the number of
/// reparses during which we'll skip even trying to precompile the
/// preamble.
const unsigned DefaultPreambleRebuildInterval = 5;

/// \brief Tracks the number of ASTUnit objects that are currently active.
///
/// Used for debugging purposes only.
static llvm::sys::cas_flag ActiveASTUnitObjects;

ASTUnit::ASTUnit(bool _MainFileIsAST)
  : OnlyLocalDecls(false), CaptureDiagnostics(false),
    MainFileIsAST(_MainFileIsAST),
    TUKind(TU_Complete), WantTiming(getenv("LIBCLANG_TIMING")),
    OwnsRemappedFileBuffers(true),
    NumStoredDiagnosticsFromDriver(0),
    ConcurrencyCheckValue(CheckUnlocked),
    PreambleRebuildCounter(0), SavedMainFileBuffer(0), PreambleBuffer(0),
    ShouldCacheCodeCompletionResults(false),
    NestedMacroExpansions(true),
    CompletionCacheTopLevelHashValue(0),
    PreambleTopLevelHashValue(0),
    CurrentTopLevelHashValue(0),
    UnsafeToFree(false) {
  if (getenv("LIBCLANG_OBJTRACKING")) {
    llvm::sys::AtomicIncrement(&ActiveASTUnitObjects);
    fprintf(stderr, "+++ %d translation units\n", ActiveASTUnitObjects);
  }
}

ASTUnit::~ASTUnit() {
  ConcurrencyCheckValue = CheckLocked;
  CleanTemporaryFiles();
  if (!PreambleFile.empty())
    llvm::sys::Path(PreambleFile).eraseFromDisk();

  // Free the buffers associated with remapped files. We are required to
  // perform this operation here because we explicitly request that the
  // compiler instance *not* free these buffers for each invocation of the
  // parser.
  if (Invocation.getPtr() && OwnsRemappedFileBuffers) {
    PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();
    for (PreprocessorOptions::remapped_file_buffer_iterator
           FB = PPOpts.remapped_file_buffer_begin(),
           FBEnd = PPOpts.remapped_file_buffer_end();
         FB != FBEnd;
         ++FB)
      delete FB->second;
  }

  delete SavedMainFileBuffer;
  delete PreambleBuffer;

  ClearCachedCompletionResults();

  if (getenv("LIBCLANG_OBJTRACKING")) {
    llvm::sys::AtomicDecrement(&ActiveASTUnitObjects);
    fprintf(stderr, "--- %d translation units\n", ActiveASTUnitObjects);
  }
}

void ASTUnit::CleanTemporaryFiles() {
  for (unsigned I = 0, N = TemporaryFiles.size(); I != N; ++I)
    TemporaryFiles[I].eraseFromDisk();
  TemporaryFiles.clear();
}

/// \brief Determine the set of code-completion contexts in which this
/// declaration should be shown.
static unsigned getDeclShowContexts(NamedDecl *ND,
                                    const LangOptions &LangOpts,
                                    bool &IsNestedNameSpecifier) {
  IsNestedNameSpecifier = false;

  if (isa<UsingShadowDecl>(ND))
    ND = dyn_cast<NamedDecl>(ND->getUnderlyingDecl());
  if (!ND)
    return 0;

  unsigned Contexts = 0;
  if (isa<TypeDecl>(ND) || isa<ObjCInterfaceDecl>(ND) ||
      isa<ClassTemplateDecl>(ND) || isa<TemplateTemplateParmDecl>(ND)) {
    // Types can appear in these contexts.
    if (LangOpts.CPlusPlus || !isa<TagDecl>(ND))
      Contexts |= (1 << (CodeCompletionContext::CCC_TopLevel - 1))
                | (1 << (CodeCompletionContext::CCC_ObjCIvarList - 1))
                | (1 << (CodeCompletionContext::CCC_ClassStructUnion - 1))
                | (1 << (CodeCompletionContext::CCC_Statement - 1))
                | (1 << (CodeCompletionContext::CCC_Type - 1))
              | (1 << (CodeCompletionContext::CCC_ParenthesizedExpression - 1));

    // In C++, types can appear in expressions contexts (for functional casts).
    if (LangOpts.CPlusPlus)
      Contexts |= (1 << (CodeCompletionContext::CCC_Expression - 1));

    // In Objective-C, message sends can send interfaces. In Objective-C++,
    // all types are available due to functional casts.
    if (LangOpts.CPlusPlus || isa<ObjCInterfaceDecl>(ND))
      Contexts |= (1 << (CodeCompletionContext::CCC_ObjCMessageReceiver - 1));

    // In Objective-C, you can only be a subclass of another Objective-C class
    if (isa<ObjCInterfaceDecl>(ND))
      Contexts |= (1 << (CodeCompletionContext::CCC_ObjCInterfaceName - 1));

    // Deal with tag names.
    if (isa<EnumDecl>(ND)) {
      Contexts |= (1 << (CodeCompletionContext::CCC_EnumTag - 1));

      // Part of the nested-name-specifier in C++0x.
      if (LangOpts.CPlusPlus0x)
        IsNestedNameSpecifier = true;
    } else if (RecordDecl *Record = dyn_cast<RecordDecl>(ND)) {
      if (Record->isUnion())
        Contexts |= (1 << (CodeCompletionContext::CCC_UnionTag - 1));
      else
        Contexts |= (1 << (CodeCompletionContext::CCC_ClassOrStructTag - 1));

      if (LangOpts.CPlusPlus)
        IsNestedNameSpecifier = true;
    } else if (isa<ClassTemplateDecl>(ND))
      IsNestedNameSpecifier = true;
  } else if (isa<ValueDecl>(ND) || isa<FunctionTemplateDecl>(ND)) {
    // Values can appear in these contexts.
    Contexts = (1 << (CodeCompletionContext::CCC_Statement - 1))
             | (1 << (CodeCompletionContext::CCC_Expression - 1))
             | (1 << (CodeCompletionContext::CCC_ParenthesizedExpression - 1))
             | (1 << (CodeCompletionContext::CCC_ObjCMessageReceiver - 1));
  } else if (isa<ObjCProtocolDecl>(ND)) {
    Contexts = (1 << (CodeCompletionContext::CCC_ObjCProtocolName - 1));
  } else if (isa<ObjCCategoryDecl>(ND)) {
    Contexts = (1 << (CodeCompletionContext::CCC_ObjCCategoryName - 1));
  } else if (isa<NamespaceDecl>(ND) || isa<NamespaceAliasDecl>(ND)) {
    Contexts = (1 << (CodeCompletionContext::CCC_Namespace - 1));

    // Part of the nested-name-specifier.
    IsNestedNameSpecifier = true;
  }

  return Contexts;
}

void ASTUnit::CacheCodeCompletionResults() {
  if (!TheSema)
    return;

  SimpleTimer Timer(WantTiming);
  Timer.setOutput("Cache global code completions for " + getMainFileName());

  // Clear out the previous results.
  ClearCachedCompletionResults();

  // Gather the set of global code completions.
  typedef CodeCompletionResult Result;
  SmallVector<Result, 8> Results;
  CachedCompletionAllocator = new GlobalCodeCompletionAllocator;
  TheSema->GatherGlobalCodeCompletions(*CachedCompletionAllocator, Results);

  // Translate global code completions into cached completions.
  llvm::DenseMap<CanQualType, unsigned> CompletionTypes;

  for (unsigned I = 0, N = Results.size(); I != N; ++I) {
    switch (Results[I].Kind) {
    case Result::RK_Declaration: {
      bool IsNestedNameSpecifier = false;
      CachedCodeCompletionResult CachedResult;
      CachedResult.Completion = Results[I].CreateCodeCompletionString(*TheSema,
                                                    *CachedCompletionAllocator);
      CachedResult.ShowInContexts = getDeclShowContexts(Results[I].Declaration,
                                                        Ctx->getLangOptions(),
                                                        IsNestedNameSpecifier);
      CachedResult.Priority = Results[I].Priority;
      CachedResult.Kind = Results[I].CursorKind;
      CachedResult.Availability = Results[I].Availability;

      // Keep track of the type of this completion in an ASTContext-agnostic
      // way.
      QualType UsageType = getDeclUsageType(*Ctx, Results[I].Declaration);
      if (UsageType.isNull()) {
        CachedResult.TypeClass = STC_Void;
        CachedResult.Type = 0;
      } else {
        CanQualType CanUsageType
          = Ctx->getCanonicalType(UsageType.getUnqualifiedType());
        CachedResult.TypeClass = getSimplifiedTypeClass(CanUsageType);

        // Determine whether we have already seen this type. If so, we save
        // ourselves the work of formatting the type string by using the
        // temporary, CanQualType-based hash table to find the associated value.
        unsigned &TypeValue = CompletionTypes[CanUsageType];
        if (TypeValue == 0) {
          TypeValue = CompletionTypes.size();
          CachedCompletionTypes[QualType(CanUsageType).getAsString()]
            = TypeValue;
        }

        CachedResult.Type = TypeValue;
      }

      CachedCompletionResults.push_back(CachedResult);

      /// Handle nested-name-specifiers in C++.
      if (TheSema->Context.getLangOptions().CPlusPlus &&
          IsNestedNameSpecifier && !Results[I].StartsNestedNameSpecifier) {
        // The contexts in which a nested-name-specifier can appear in C++.
        unsigned NNSContexts
          = (1 << (CodeCompletionContext::CCC_TopLevel - 1))
          | (1 << (CodeCompletionContext::CCC_ObjCIvarList - 1))
          | (1 << (CodeCompletionContext::CCC_ClassStructUnion - 1))
          | (1 << (CodeCompletionContext::CCC_Statement - 1))
          | (1 << (CodeCompletionContext::CCC_Expression - 1))
          | (1 << (CodeCompletionContext::CCC_ObjCMessageReceiver - 1))
          | (1 << (CodeCompletionContext::CCC_EnumTag - 1))
          | (1 << (CodeCompletionContext::CCC_UnionTag - 1))
          | (1 << (CodeCompletionContext::CCC_ClassOrStructTag - 1))
          | (1 << (CodeCompletionContext::CCC_Type - 1))
          | (1 << (CodeCompletionContext::CCC_PotentiallyQualifiedName - 1))
          | (1 << (CodeCompletionContext::CCC_ParenthesizedExpression - 1));

        if (isa<NamespaceDecl>(Results[I].Declaration) ||
            isa<NamespaceAliasDecl>(Results[I].Declaration))
          NNSContexts |= (1 << (CodeCompletionContext::CCC_Namespace - 1));

        if (unsigned RemainingContexts
                                = NNSContexts & ~CachedResult.ShowInContexts) {
          // If there any contexts where this completion can be a
          // nested-name-specifier but isn't already an option, create a
          // nested-name-specifier completion.
          Results[I].StartsNestedNameSpecifier = true;
          CachedResult.Completion
            = Results[I].CreateCodeCompletionString(*TheSema,
                                                    *CachedCompletionAllocator);
          CachedResult.ShowInContexts = RemainingContexts;
          CachedResult.Priority = CCP_NestedNameSpecifier;
          CachedResult.TypeClass = STC_Void;
          CachedResult.Type = 0;
          CachedCompletionResults.push_back(CachedResult);
        }
      }
      break;
    }

    case Result::RK_Keyword:
    case Result::RK_Pattern:
      // Ignore keywords and patterns; we don't care, since they are so
      // easily regenerated.
      break;

    case Result::RK_Macro: {
      CachedCodeCompletionResult CachedResult;
      CachedResult.Completion
        = Results[I].CreateCodeCompletionString(*TheSema,
                                                *CachedCompletionAllocator);
      CachedResult.ShowInContexts
        = (1 << (CodeCompletionContext::CCC_TopLevel - 1))
        | (1 << (CodeCompletionContext::CCC_ObjCInterface - 1))
        | (1 << (CodeCompletionContext::CCC_ObjCImplementation - 1))
        | (1 << (CodeCompletionContext::CCC_ObjCIvarList - 1))
        | (1 << (CodeCompletionContext::CCC_ClassStructUnion - 1))
        | (1 << (CodeCompletionContext::CCC_Statement - 1))
        | (1 << (CodeCompletionContext::CCC_Expression - 1))
        | (1 << (CodeCompletionContext::CCC_ObjCMessageReceiver - 1))
        | (1 << (CodeCompletionContext::CCC_MacroNameUse - 1))
        | (1 << (CodeCompletionContext::CCC_PreprocessorExpression - 1))
        | (1 << (CodeCompletionContext::CCC_ParenthesizedExpression - 1))
        | (1 << (CodeCompletionContext::CCC_OtherWithMacros - 1));

      CachedResult.Priority = Results[I].Priority;
      CachedResult.Kind = Results[I].CursorKind;
      CachedResult.Availability = Results[I].Availability;
      CachedResult.TypeClass = STC_Void;
      CachedResult.Type = 0;
      CachedCompletionResults.push_back(CachedResult);
      break;
    }
    }
  }

  // Save the current top-level hash value.
  CompletionCacheTopLevelHashValue = CurrentTopLevelHashValue;
}

void ASTUnit::ClearCachedCompletionResults() {
  CachedCompletionResults.clear();
  CachedCompletionTypes.clear();
  CachedCompletionAllocator = 0;
}

namespace {

/// \brief Gathers information from ASTReader that will be used to initialize
/// a Preprocessor.
class ASTInfoCollector : public ASTReaderListener {
  Preprocessor &PP;
  ASTContext &Context;
  LangOptions &LangOpt;
  HeaderSearch &HSI;
  llvm::IntrusiveRefCntPtr<TargetInfo> &Target;
  std::string &Predefines;
  unsigned &Counter;

  unsigned NumHeaderInfos;

  bool InitializedLanguage;
public:
  ASTInfoCollector(Preprocessor &PP, ASTContext &Context, LangOptions &LangOpt,
                   HeaderSearch &HSI,
                   llvm::IntrusiveRefCntPtr<TargetInfo> &Target,
                   std::string &Predefines,
                   unsigned &Counter)
    : PP(PP), Context(Context), LangOpt(LangOpt), HSI(HSI), Target(Target),
      Predefines(Predefines), Counter(Counter), NumHeaderInfos(0),
      InitializedLanguage(false) {}

  virtual bool ReadLanguageOptions(const LangOptions &LangOpts) {
    if (InitializedLanguage)
      return false;

    LangOpt = LangOpts;

    // Initialize the preprocessor.
    PP.Initialize(*Target);

    // Initialize the ASTContext
    Context.InitBuiltinTypes(*Target);

    InitializedLanguage = true;
    return false;
  }

  virtual bool ReadTargetTriple(StringRef Triple) {
    // If we've already initialized the target, don't do it again.
    if (Target)
      return false;

    // FIXME: This is broken, we should store the TargetOptions in the AST file.
    TargetOptions TargetOpts;
    TargetOpts.ABI = "";
    TargetOpts.CXXABI = "";
    TargetOpts.CPU = "";
    TargetOpts.Features.clear();
    TargetOpts.Triple = Triple;
    Target = TargetInfo::CreateTargetInfo(PP.getDiagnostics(), TargetOpts);
    return false;
  }

  virtual bool ReadPredefinesBuffer(const PCHPredefinesBlocks &Buffers,
                                    StringRef OriginalFileName,
                                    std::string &SuggestedPredefines,
                                    FileManager &FileMgr) {
    Predefines = Buffers[0].Data;
    for (unsigned I = 1, N = Buffers.size(); I != N; ++I) {
      Predefines += Buffers[I].Data;
    }
    return false;
  }

  virtual void ReadHeaderFileInfo(const HeaderFileInfo &HFI, unsigned ID) {
    HSI.setHeaderFileInfoForUID(HFI, NumHeaderInfos++);
  }

  virtual void ReadCounter(unsigned Value) {
    Counter = Value;
  }
};

class StoredDiagnosticConsumer : public DiagnosticConsumer {
  SmallVectorImpl<StoredDiagnostic> &StoredDiags;

public:
  explicit StoredDiagnosticConsumer(
                          SmallVectorImpl<StoredDiagnostic> &StoredDiags)
    : StoredDiags(StoredDiags) { }

  virtual void HandleDiagnostic(DiagnosticsEngine::Level Level,
                                const Diagnostic &Info);

  DiagnosticConsumer *clone(DiagnosticsEngine &Diags) const {
    // Just drop any diagnostics that come from cloned consumers; they'll
    // have different source managers anyway.
    return new IgnoringDiagConsumer();
  }
};

/// \brief RAII object that optionally captures diagnostics, if
/// there is no diagnostic client to capture them already.
class CaptureDroppedDiagnostics {
  DiagnosticsEngine &Diags;
  StoredDiagnosticConsumer Client;
  DiagnosticConsumer *PreviousClient;

public:
  CaptureDroppedDiagnostics(bool RequestCapture, DiagnosticsEngine &Diags,
                          SmallVectorImpl<StoredDiagnostic> &StoredDiags)
    : Diags(Diags), Client(StoredDiags), PreviousClient(0)
  {
    if (RequestCapture || Diags.getClient() == 0) {
      PreviousClient = Diags.takeClient();
      Diags.setClient(&Client);
    }
  }

  ~CaptureDroppedDiagnostics() {
    if (Diags.getClient() == &Client) {
      Diags.takeClient();
      Diags.setClient(PreviousClient);
    }
  }
};

} // anonymous namespace

void StoredDiagnosticConsumer::HandleDiagnostic(DiagnosticsEngine::Level Level,
                                              const Diagnostic &Info) {
  // Default implementation (Warnings/errors count).
  DiagnosticConsumer::HandleDiagnostic(Level, Info);

  StoredDiags.push_back(StoredDiagnostic(Level, Info));
}

const std::string &ASTUnit::getOriginalSourceFileName() {
  return OriginalSourceFile;
}

llvm::MemoryBuffer *ASTUnit::getBufferForFile(StringRef Filename,
                                              std::string *ErrorStr) {
  assert(FileMgr);
  return FileMgr->getBufferForFile(Filename, ErrorStr);
}

/// \brief Configure the diagnostics object for use with ASTUnit.
void ASTUnit::ConfigureDiags(llvm::IntrusiveRefCntPtr<DiagnosticsEngine> &Diags,
                             const char **ArgBegin, const char **ArgEnd,
                             ASTUnit &AST, bool CaptureDiagnostics) {
  if (!Diags.getPtr()) {
    // No diagnostics engine was provided, so create our own diagnostics object
    // with the default options.
    DiagnosticOptions DiagOpts;
    DiagnosticConsumer *Client = 0;
    if (CaptureDiagnostics)
      Client = new StoredDiagnosticConsumer(AST.StoredDiagnostics);
    Diags = CompilerInstance::createDiagnostics(DiagOpts, ArgEnd- ArgBegin,
                                                ArgBegin, Client);
  } else if (CaptureDiagnostics) {
    Diags->setClient(new StoredDiagnosticConsumer(AST.StoredDiagnostics));
  }
}

ASTUnit *ASTUnit::LoadFromASTFile(const std::string &Filename,
                              llvm::IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
                                  const FileSystemOptions &FileSystemOpts,
                                  bool OnlyLocalDecls,
                                  RemappedFile *RemappedFiles,
                                  unsigned NumRemappedFiles,
                                  bool CaptureDiagnostics) {
  llvm::OwningPtr<ASTUnit> AST(new ASTUnit(true));

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<ASTUnit>
    ASTUnitCleanup(AST.get());
  llvm::CrashRecoveryContextCleanupRegistrar<DiagnosticsEngine,
    llvm::CrashRecoveryContextReleaseRefCleanup<DiagnosticsEngine> >
    DiagCleanup(Diags.getPtr());

  ConfigureDiags(Diags, 0, 0, *AST, CaptureDiagnostics);

  AST->OnlyLocalDecls = OnlyLocalDecls;
  AST->CaptureDiagnostics = CaptureDiagnostics;
  AST->Diagnostics = Diags;
  AST->FileMgr = new FileManager(FileSystemOpts);
  AST->SourceMgr = new SourceManager(AST->getDiagnostics(),
                                     AST->getFileManager());
  AST->HeaderInfo.reset(new HeaderSearch(AST->getFileManager()));

  for (unsigned I = 0; I != NumRemappedFiles; ++I) {
    FilenameOrMemBuf fileOrBuf = RemappedFiles[I].second;
    if (const llvm::MemoryBuffer *
          memBuf = fileOrBuf.dyn_cast<const llvm::MemoryBuffer *>()) {
      // Create the file entry for the file that we're mapping from.
      const FileEntry *FromFile
        = AST->getFileManager().getVirtualFile(RemappedFiles[I].first,
                                               memBuf->getBufferSize(),
                                               0);
      if (!FromFile) {
        AST->getDiagnostics().Report(diag::err_fe_remap_missing_from_file)
          << RemappedFiles[I].first;
        delete memBuf;
        continue;
      }

      // Override the contents of the "from" file with the contents of
      // the "to" file.
      AST->getSourceManager().overrideFileContents(FromFile, memBuf);

    } else {
      const char *fname = fileOrBuf.get<const char *>();
      const FileEntry *ToFile = AST->FileMgr->getFile(fname);
      if (!ToFile) {
        AST->getDiagnostics().Report(diag::err_fe_remap_missing_to_file)
        << RemappedFiles[I].first << fname;
        continue;
      }

      // Create the file entry for the file that we're mapping from.
      const FileEntry *FromFile
        = AST->getFileManager().getVirtualFile(RemappedFiles[I].first,
                                               ToFile->getSize(),
                                               0);
      if (!FromFile) {
        AST->getDiagnostics().Report(diag::err_fe_remap_missing_from_file)
          << RemappedFiles[I].first;
        delete memBuf;
        continue;
      }

      // Override the contents of the "from" file with the contents of
      // the "to" file.
      AST->getSourceManager().overrideFileContents(FromFile, ToFile);
    }
  }

  // Gather Info for preprocessor construction later on.

  HeaderSearch &HeaderInfo = *AST->HeaderInfo.get();
  std::string Predefines;
  unsigned Counter;

  llvm::OwningPtr<ASTReader> Reader;

  AST->PP = new Preprocessor(AST->getDiagnostics(), AST->ASTFileLangOpts,
                             /*Target=*/0, AST->getSourceManager(), HeaderInfo,
                             *AST,
                             /*IILookup=*/0,
                             /*OwnsHeaderSearch=*/false,
                             /*DelayInitialization=*/true);
  Preprocessor &PP = *AST->PP;

  AST->Ctx = new ASTContext(AST->ASTFileLangOpts,
                            AST->getSourceManager(),
                            /*Target=*/0,
                            PP.getIdentifierTable(),
                            PP.getSelectorTable(),
                            PP.getBuiltinInfo(),
                            /* size_reserve = */0,
                            /*DelayInitialization=*/true);
  ASTContext &Context = *AST->Ctx;

  Reader.reset(new ASTReader(PP, Context));

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<ASTReader>
    ReaderCleanup(Reader.get());

  Reader->setListener(new ASTInfoCollector(*AST->PP, Context,
                                           AST->ASTFileLangOpts, HeaderInfo,
                                           AST->Target, Predefines, Counter));

  switch (Reader->ReadAST(Filename, serialization::MK_MainFile)) {
  case ASTReader::Success:
    break;

  case ASTReader::Failure:
  case ASTReader::IgnorePCH:
    AST->getDiagnostics().Report(diag::err_fe_unable_to_load_pch);
    return NULL;
  }

  AST->OriginalSourceFile = Reader->getOriginalSourceFile();

  PP.setPredefines(Reader->getSuggestedPredefines());
  PP.setCounterValue(Counter);

  // Attach the AST reader to the AST context as an external AST
  // source, so that declarations will be deserialized from the
  // AST file as needed.
  ASTReader *ReaderPtr = Reader.get();
  llvm::OwningPtr<ExternalASTSource> Source(Reader.take());

  // Unregister the cleanup for ASTReader.  It will get cleaned up
  // by the ASTUnit cleanup.
  ReaderCleanup.unregister();

  Context.setExternalSource(Source);

  // Create an AST consumer, even though it isn't used.
  AST->Consumer.reset(new ASTConsumer);

  // Create a semantic analysis object and tell the AST reader about it.
  AST->TheSema.reset(new Sema(PP, Context, *AST->Consumer));
  AST->TheSema->Initialize();
  ReaderPtr->InitializeSema(*AST->TheSema);

  return AST.take();
}

namespace {

/// \brief Preprocessor callback class that updates a hash value with the names
/// of all macros that have been defined by the translation unit.
class MacroDefinitionTrackerPPCallbacks : public PPCallbacks {
  unsigned &Hash;

public:
  explicit MacroDefinitionTrackerPPCallbacks(unsigned &Hash) : Hash(Hash) { }

  virtual void MacroDefined(const Token &MacroNameTok, const MacroInfo *MI) {
    Hash = llvm::HashString(MacroNameTok.getIdentifierInfo()->getName(), Hash);
  }
};

/// \brief Add the given declaration to the hash of all top-level entities.
void AddTopLevelDeclarationToHash(Decl *D, unsigned &Hash) {
  if (!D)
    return;

  DeclContext *DC = D->getDeclContext();
  if (!DC)
    return;

  if (!(DC->isTranslationUnit() || DC->getLookupParent()->isTranslationUnit()))
    return;

  if (NamedDecl *ND = dyn_cast<NamedDecl>(D)) {
    if (ND->getIdentifier())
      Hash = llvm::HashString(ND->getIdentifier()->getName(), Hash);
    else if (DeclarationName Name = ND->getDeclName()) {
      std::string NameStr = Name.getAsString();
      Hash = llvm::HashString(NameStr, Hash);
    }
    return;
  }

  if (ObjCForwardProtocolDecl *Forward
      = dyn_cast<ObjCForwardProtocolDecl>(D)) {
    for (ObjCForwardProtocolDecl::protocol_iterator
         P = Forward->protocol_begin(),
         PEnd = Forward->protocol_end();
         P != PEnd; ++P)
      AddTopLevelDeclarationToHash(*P, Hash);
    return;
  }

  if (ObjCClassDecl *Class = dyn_cast<ObjCClassDecl>(D)) {
    AddTopLevelDeclarationToHash(Class->getForwardInterfaceDecl(), Hash);
    return;
  }
}

class TopLevelDeclTrackerConsumer : public ASTConsumer {
  ASTUnit &Unit;
  unsigned &Hash;

public:
  TopLevelDeclTrackerConsumer(ASTUnit &_Unit, unsigned &Hash)
    : Unit(_Unit), Hash(Hash) {
    Hash = 0;
  }

  void HandleTopLevelDecl(DeclGroupRef D) {
    for (DeclGroupRef::iterator it = D.begin(), ie = D.end(); it != ie; ++it) {
      Decl *D = *it;
      // FIXME: Currently ObjC method declarations are incorrectly being
      // reported as top-level declarations, even though their DeclContext
      // is the containing ObjC @interface/@implementation.  This is a
      // fundamental problem in the parser right now.
      if (isa<ObjCMethodDecl>(D))
        continue;

      AddTopLevelDeclarationToHash(D, Hash);
      Unit.addTopLevelDecl(D);
    }
  }

  // We're not interested in "interesting" decls.
  void HandleInterestingDecl(DeclGroupRef) {}
};

class TopLevelDeclTrackerAction : public ASTFrontendAction {
public:
  ASTUnit &Unit;

  virtual ASTConsumer *CreateASTConsumer(CompilerInstance &CI,
                                         StringRef InFile) {
    CI.getPreprocessor().addPPCallbacks(
     new MacroDefinitionTrackerPPCallbacks(Unit.getCurrentTopLevelHashValue()));
    return new TopLevelDeclTrackerConsumer(Unit,
                                           Unit.getCurrentTopLevelHashValue());
  }

public:
  TopLevelDeclTrackerAction(ASTUnit &_Unit) : Unit(_Unit) {}

  virtual bool hasCodeCompletionSupport() const { return false; }
  virtual TranslationUnitKind getTranslationUnitKind()  {
    return Unit.getTranslationUnitKind();
  }
};

class PrecompilePreambleConsumer : public PCHGenerator {
  ASTUnit &Unit;
  unsigned &Hash;
  std::vector<Decl *> TopLevelDecls;

public:
  PrecompilePreambleConsumer(ASTUnit &Unit, const Preprocessor &PP,
                             StringRef isysroot, raw_ostream *Out)
    : PCHGenerator(PP, "", /*IsModule=*/false, isysroot, Out), Unit(Unit),
      Hash(Unit.getCurrentTopLevelHashValue()) {
    Hash = 0;
  }

  virtual void HandleTopLevelDecl(DeclGroupRef D) {
    for (DeclGroupRef::iterator it = D.begin(), ie = D.end(); it != ie; ++it) {
      Decl *D = *it;
      // FIXME: Currently ObjC method declarations are incorrectly being
      // reported as top-level declarations, even though their DeclContext
      // is the containing ObjC @interface/@implementation.  This is a
      // fundamental problem in the parser right now.
      if (isa<ObjCMethodDecl>(D))
        continue;
      AddTopLevelDeclarationToHash(D, Hash);
      TopLevelDecls.push_back(D);
    }
  }

  virtual void HandleTranslationUnit(ASTContext &Ctx) {
    PCHGenerator::HandleTranslationUnit(Ctx);
    if (!Unit.getDiagnostics().hasErrorOccurred()) {
      // Translate the top-level declarations we captured during
      // parsing into declaration IDs in the precompiled
      // preamble. This will allow us to deserialize those top-level
      // declarations when requested.
      for (unsigned I = 0, N = TopLevelDecls.size(); I != N; ++I)
        Unit.addTopLevelDeclFromPreamble(
                                      getWriter().getDeclID(TopLevelDecls[I]));
    }
  }
};

class PrecompilePreambleAction : public ASTFrontendAction {
  ASTUnit &Unit;

public:
  explicit PrecompilePreambleAction(ASTUnit &Unit) : Unit(Unit) {}

  virtual ASTConsumer *CreateASTConsumer(CompilerInstance &CI,
                                         StringRef InFile) {
    std::string Sysroot;
    std::string OutputFile;
    raw_ostream *OS = 0;
    if (GeneratePCHAction::ComputeASTConsumerArguments(CI, InFile, Sysroot,
                                                       OutputFile,
                                                       OS))
      return 0;

    if (!CI.getFrontendOpts().RelocatablePCH)
      Sysroot.clear();

    CI.getPreprocessor().addPPCallbacks(
     new MacroDefinitionTrackerPPCallbacks(Unit.getCurrentTopLevelHashValue()));
    return new PrecompilePreambleConsumer(Unit, CI.getPreprocessor(), Sysroot,
                                          OS);
  }

  virtual bool hasCodeCompletionSupport() const { return false; }
  virtual bool hasASTFileSupport() const { return false; }
  virtual TranslationUnitKind getTranslationUnitKind() { return TU_Prefix; }
};

}

/// Parse the source file into a translation unit using the given compiler
/// invocation, replacing the current translation unit.
///
/// \returns True if a failure occurred that causes the ASTUnit not to
/// contain any translation-unit information, false otherwise.
bool ASTUnit::Parse(llvm::MemoryBuffer *OverrideMainBuffer) {
  delete SavedMainFileBuffer;
  SavedMainFileBuffer = 0;

  if (!Invocation) {
    delete OverrideMainBuffer;
    return true;
  }

  // Create the compiler instance to use for building the AST.
  llvm::OwningPtr<CompilerInstance> Clang(new CompilerInstance());

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance>
    CICleanup(Clang.get());

  llvm::IntrusiveRefCntPtr<CompilerInvocation>
    CCInvocation(new CompilerInvocation(*Invocation));

  Clang->setInvocation(CCInvocation.getPtr());
  OriginalSourceFile = Clang->getFrontendOpts().Inputs[0].second;

  // Set up diagnostics, capturing any diagnostics that would
  // otherwise be dropped.
  Clang->setDiagnostics(&getDiagnostics());

  // Create the target instance.
  Clang->getTargetOpts().Features = TargetFeatures;
  Clang->setTarget(TargetInfo::CreateTargetInfo(Clang->getDiagnostics(),
                   Clang->getTargetOpts()));
  if (!Clang->hasTarget()) {
    delete OverrideMainBuffer;
    return true;
  }

  // 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.
  Clang->getTarget().setForcedLangOptions(Clang->getLangOpts());

  assert(Clang->getFrontendOpts().Inputs.size() == 1 &&
         "Invocation must have exactly one source file!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_AST &&
         "FIXME: AST inputs not yet supported here!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_LLVM_IR &&
         "IR inputs not support here!");

  // Configure the various subsystems.
  // FIXME: Should we retain the previous file manager?
  FileSystemOpts = Clang->getFileSystemOpts();
  FileMgr = new FileManager(FileSystemOpts);
  SourceMgr = new SourceManager(getDiagnostics(), *FileMgr);
  TheSema.reset();
  Ctx = 0;
  PP = 0;

  // Clear out old caches and data.
  TopLevelDecls.clear();
  CleanTemporaryFiles();

  if (!OverrideMainBuffer) {
    StoredDiagnostics.erase(
                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
                            StoredDiagnostics.end());
    TopLevelDeclsInPreamble.clear();
  }

  // Create a file manager object to provide access to and cache the filesystem.
  Clang->setFileManager(&getFileManager());

  // Create the source manager.
  Clang->setSourceManager(&getSourceManager());

  // If the main file has been overridden due to the use of a preamble,
  // make that override happen and introduce the preamble.
  PreprocessorOptions &PreprocessorOpts = Clang->getPreprocessorOpts();
  PreprocessorOpts.DetailedRecordIncludesNestedMacroExpansions
    = NestedMacroExpansions;
  if (OverrideMainBuffer) {
    PreprocessorOpts.addRemappedFile(OriginalSourceFile, OverrideMainBuffer);
    PreprocessorOpts.PrecompiledPreambleBytes.first = Preamble.size();
    PreprocessorOpts.PrecompiledPreambleBytes.second
                                                    = PreambleEndsAtStartOfLine;
    PreprocessorOpts.ImplicitPCHInclude = PreambleFile;
    PreprocessorOpts.DisablePCHValidation = true;

    // The stored diagnostic has the old source manager in it; update
    // the locations to refer into the new source manager. Since we've
    // been careful to make sure that the source manager's state
    // before and after are identical, so that we can reuse the source
    // location itself.
    for (unsigned I = NumStoredDiagnosticsFromDriver,
                  N = StoredDiagnostics.size();
         I < N; ++I) {
      FullSourceLoc Loc(StoredDiagnostics[I].getLocation(),
                        getSourceManager());
      StoredDiagnostics[I].setLocation(Loc);
    }

    // Keep track of the override buffer;
    SavedMainFileBuffer = OverrideMainBuffer;
  }

  llvm::OwningPtr<TopLevelDeclTrackerAction> Act(
    new TopLevelDeclTrackerAction(*this));

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<TopLevelDeclTrackerAction>
    ActCleanup(Act.get());

  if (!Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0].second,
                            Clang->getFrontendOpts().Inputs[0].first))
    goto error;

  if (OverrideMainBuffer) {
    std::string ModName = PreambleFile;
    TranslateStoredDiagnostics(Clang->getModuleManager(), ModName,
                               getSourceManager(), PreambleDiagnostics,
                               StoredDiagnostics);
  }

  Act->Execute();

  // Steal the created target, context, and preprocessor.
  TheSema.reset(Clang->takeSema());
  Consumer.reset(Clang->takeASTConsumer());
  Ctx = &Clang->getASTContext();
  PP = &Clang->getPreprocessor();
  Clang->setSourceManager(0);
  Clang->setFileManager(0);
  Target = &Clang->getTarget();

  Act->EndSourceFile();

  return false;

error:
  // Remove the overridden buffer we used for the preamble.
  if (OverrideMainBuffer) {
    delete OverrideMainBuffer;
    SavedMainFileBuffer = 0;
  }

  StoredDiagnostics.clear();
  return true;
}

/// \brief Simple function to retrieve a path for a preamble precompiled header.
static std::string GetPreamblePCHPath() {
  // FIXME: This is lame; sys::Path should provide this function (in particular,
  // it should know how to find the temporary files dir).
  // FIXME: This is really lame. I copied this code from the Driver!
  // FIXME: This is a hack so that we can override the preamble file during
  // crash-recovery testing, which is the only case where the preamble files
  // are not necessarily cleaned up.
  const char *TmpFile = ::getenv("CINDEXTEST_PREAMBLE_FILE");
  if (TmpFile)
    return TmpFile;

  std::string Error;
  const char *TmpDir = ::getenv("TMPDIR");
  if (!TmpDir)
    TmpDir = ::getenv("TEMP");
  if (!TmpDir)
    TmpDir = ::getenv("TMP");
#ifdef LLVM_ON_WIN32
  if (!TmpDir)
    TmpDir = ::getenv("USERPROFILE");
#endif
  if (!TmpDir)
    TmpDir = "/tmp";
  llvm::sys::Path P(TmpDir);
  P.createDirectoryOnDisk(true);
  P.appendComponent("preamble");
  P.appendSuffix("pch");
  if (P.makeUnique(/*reuse_current=*/false, /*ErrMsg*/0))
    return std::string();

  return P.str();
}

/// \brief Compute the preamble for the main file, providing the source buffer
/// that corresponds to the main file along with a pair (bytes, start-of-line)
/// that describes the preamble.
std::pair<llvm::MemoryBuffer *, std::pair<unsigned, bool> >
ASTUnit::ComputePreamble(CompilerInvocation &Invocation,
                         unsigned MaxLines, bool &CreatedBuffer) {
  FrontendOptions &FrontendOpts = Invocation.getFrontendOpts();
  PreprocessorOptions &PreprocessorOpts = Invocation.getPreprocessorOpts();
  CreatedBuffer = false;

  // Try to determine if the main file has been remapped, either from the
  // command line (to another file) or directly through the compiler invocation
  // (to a memory buffer).
  llvm::MemoryBuffer *Buffer = 0;
  llvm::sys::PathWithStatus MainFilePath(FrontendOpts.Inputs[0].second);
  if (const llvm::sys::FileStatus *MainFileStatus = MainFilePath.getFileStatus()) {
    // Check whether there is a file-file remapping of the main file
    for (PreprocessorOptions::remapped_file_iterator
          M = PreprocessorOpts.remapped_file_begin(),
          E = PreprocessorOpts.remapped_file_end();
         M != E;
         ++M) {
      llvm::sys::PathWithStatus MPath(M->first);
      if (const llvm::sys::FileStatus *MStatus = MPath.getFileStatus()) {
        if (MainFileStatus->uniqueID == MStatus->uniqueID) {
          // We found a remapping. Try to load the resulting, remapped source.
          if (CreatedBuffer) {
            delete Buffer;
            CreatedBuffer = false;
          }

          Buffer = getBufferForFile(M->second);
          if (!Buffer)
            return std::make_pair((llvm::MemoryBuffer*)0,
                                  std::make_pair(0, true));
          CreatedBuffer = true;
        }
      }
    }

    // Check whether there is a file-buffer remapping. It supercedes the
    // file-file remapping.
    for (PreprocessorOptions::remapped_file_buffer_iterator
           M = PreprocessorOpts.remapped_file_buffer_begin(),
           E = PreprocessorOpts.remapped_file_buffer_end();
         M != E;
         ++M) {
      llvm::sys::PathWithStatus MPath(M->first);
      if (const llvm::sys::FileStatus *MStatus = MPath.getFileStatus()) {
        if (MainFileStatus->uniqueID == MStatus->uniqueID) {
          // We found a remapping.
          if (CreatedBuffer) {
            delete Buffer;
            CreatedBuffer = false;
          }

          Buffer = const_cast<llvm::MemoryBuffer *>(M->second);
        }
      }
    }
  }

  // If the main source file was not remapped, load it now.
  if (!Buffer) {
    Buffer = getBufferForFile(FrontendOpts.Inputs[0].second);
    if (!Buffer)
      return std::make_pair((llvm::MemoryBuffer*)0, std::make_pair(0, true));

    CreatedBuffer = true;
  }

  return std::make_pair(Buffer, Lexer::ComputePreamble(Buffer,
                                                       Invocation.getLangOpts(),
                                                       MaxLines));
}

static llvm::MemoryBuffer *CreatePaddedMainFileBuffer(llvm::MemoryBuffer *Old,
                                                      unsigned NewSize,
                                                      StringRef NewName) {
  llvm::MemoryBuffer *Result
    = llvm::MemoryBuffer::getNewUninitMemBuffer(NewSize, NewName);
  memcpy(const_cast<char*>(Result->getBufferStart()),
         Old->getBufferStart(), Old->getBufferSize());
  memset(const_cast<char*>(Result->getBufferStart()) + Old->getBufferSize(),
         ' ', NewSize - Old->getBufferSize() - 1);
  const_cast<char*>(Result->getBufferEnd())[-1] = '\n';

  return Result;
}

/// \brief Attempt to build or re-use a precompiled preamble when (re-)parsing
/// the source file.
///
/// This routine will compute the preamble of the main source file. If a
/// non-trivial preamble is found, it will precompile that preamble into a
/// precompiled header so that the precompiled preamble can be used to reduce
/// reparsing time. If a precompiled preamble has already been constructed,
/// this routine will determine if it is still valid and, if so, avoid
/// rebuilding the precompiled preamble.
///
/// \param AllowRebuild When true (the default), this routine is
/// allowed to rebuild the precompiled preamble if it is found to be
/// out-of-date.
///
/// \param MaxLines When non-zero, the maximum number of lines that
/// can occur within the preamble.
///
/// \returns If the precompiled preamble can be used, returns a newly-allocated
/// buffer that should be used in place of the main file when doing so.
/// Otherwise, returns a NULL pointer.
llvm::MemoryBuffer *ASTUnit::getMainBufferWithPrecompiledPreamble(
                              const CompilerInvocation &PreambleInvocationIn,
                                                           bool AllowRebuild,
                                                           unsigned MaxLines) {

  llvm::IntrusiveRefCntPtr<CompilerInvocation>
    PreambleInvocation(new CompilerInvocation(PreambleInvocationIn));
  FrontendOptions &FrontendOpts = PreambleInvocation->getFrontendOpts();
  PreprocessorOptions &PreprocessorOpts
    = PreambleInvocation->getPreprocessorOpts();

  bool CreatedPreambleBuffer = false;
  std::pair<llvm::MemoryBuffer *, std::pair<unsigned, bool> > NewPreamble
    = ComputePreamble(*PreambleInvocation, MaxLines, CreatedPreambleBuffer);

  // If ComputePreamble() Take ownership of the preamble buffer.
  llvm::OwningPtr<llvm::MemoryBuffer> OwnedPreambleBuffer;
  if (CreatedPreambleBuffer)
    OwnedPreambleBuffer.reset(NewPreamble.first);

  if (!NewPreamble.second.first) {
    // We couldn't find a preamble in the main source. Clear out the current
    // preamble, if we have one. It's obviously no good any more.
    Preamble.clear();
    if (!PreambleFile.empty()) {
      llvm::sys::Path(PreambleFile).eraseFromDisk();
      PreambleFile.clear();
    }

    // The next time we actually see a preamble, precompile it.
    PreambleRebuildCounter = 1;
    return 0;
  }

  if (!Preamble.empty()) {
    // We've previously computed a preamble. Check whether we have the same
    // preamble now that we did before, and that there's enough space in
    // the main-file buffer within the precompiled preamble to fit the
    // new main file.
    if (Preamble.size() == NewPreamble.second.first &&
        PreambleEndsAtStartOfLine == NewPreamble.second.second &&
        NewPreamble.first->getBufferSize() < PreambleReservedSize-2 &&
        memcmp(Preamble.getBufferStart(), NewPreamble.first->getBufferStart(),
               NewPreamble.second.first) == 0) {
      // The preamble has not changed. We may be able to re-use the precompiled
      // preamble.

      // Check that none of the files used by the preamble have changed.
      bool AnyFileChanged = false;

      // First, make a record of those files that have been overridden via
      // remapping or unsaved_files.
      llvm::StringMap<std::pair<off_t, time_t> > OverriddenFiles;
      for (PreprocessorOptions::remapped_file_iterator
                R = PreprocessorOpts.remapped_file_begin(),
             REnd = PreprocessorOpts.remapped_file_end();
           !AnyFileChanged && R != REnd;
           ++R) {
        struct stat StatBuf;
        if (FileMgr->getNoncachedStatValue(R->second, StatBuf)) {
          // If we can't stat the file we're remapping to, assume that something
          // horrible happened.
          AnyFileChanged = true;
          break;
        }

        OverriddenFiles[R->first] = std::make_pair(StatBuf.st_size,
                                                   StatBuf.st_mtime);
      }
      for (PreprocessorOptions::remapped_file_buffer_iterator
                R = PreprocessorOpts.remapped_file_buffer_begin(),
             REnd = PreprocessorOpts.remapped_file_buffer_end();
           !AnyFileChanged && R != REnd;
           ++R) {
        // FIXME: Should we actually compare the contents of file->buffer
        // remappings?
        OverriddenFiles[R->first] = std::make_pair(R->second->getBufferSize(),
                                                   0);
      }

      // Check whether anything has changed.
      for (llvm::StringMap<std::pair<off_t, time_t> >::iterator
             F = FilesInPreamble.begin(), FEnd = FilesInPreamble.end();
           !AnyFileChanged && F != FEnd;
           ++F) {
        llvm::StringMap<std::pair<off_t, time_t> >::iterator Overridden
          = OverriddenFiles.find(F->first());
        if (Overridden != OverriddenFiles.end()) {
          // This file was remapped; check whether the newly-mapped file
          // matches up with the previous mapping.
          if (Overridden->second != F->second)
            AnyFileChanged = true;
          continue;
        }

        // The file was not remapped; check whether it has changed on disk.
        struct stat StatBuf;
        if (FileMgr->getNoncachedStatValue(F->first(), StatBuf)) {
          // If we can't stat the file, assume that something horrible happened.
          AnyFileChanged = true;
        } else if (StatBuf.st_size != F->second.first ||
                   StatBuf.st_mtime != F->second.second)
          AnyFileChanged = true;
      }

      if (!AnyFileChanged) {
        // Okay! We can re-use the precompiled preamble.

        // Set the state of the diagnostic object to mimic its state
        // after parsing the preamble.
        // FIXME: This won't catch any #pragma push warning changes that
        // have occurred in the preamble.
        getDiagnostics().Reset();
        ProcessWarningOptions(getDiagnostics(),
                              PreambleInvocation->getDiagnosticOpts());
        getDiagnostics().setNumWarnings(NumWarningsInPreamble);

        // Create a version of the main file buffer that is padded to
        // buffer size we reserved when creating the preamble.
        return CreatePaddedMainFileBuffer(NewPreamble.first,
                                          PreambleReservedSize,
                                          FrontendOpts.Inputs[0].second);
      }
    }

    // If we aren't allowed to rebuild the precompiled preamble, just
    // return now.
    if (!AllowRebuild)
      return 0;

    // We can't reuse the previously-computed preamble. Build a new one.
    Preamble.clear();
    PreambleDiagnostics.clear();
    llvm::sys::Path(PreambleFile).eraseFromDisk();
    PreambleRebuildCounter = 1;
  } else if (!AllowRebuild) {
    // We aren't allowed to rebuild the precompiled preamble; just
    // return now.
    return 0;
  }

  // If the preamble rebuild counter > 1, it's because we previously
  // failed to build a preamble and we're not yet ready to try
  // again. Decrement the counter and return a failure.
  if (PreambleRebuildCounter > 1) {
    --PreambleRebuildCounter;
    return 0;
  }

  // Create a temporary file for the precompiled preamble. In rare
  // circumstances, this can fail.
  std::string PreamblePCHPath = GetPreamblePCHPath();
  if (PreamblePCHPath.empty()) {
    // Try again next time.
    PreambleRebuildCounter = 1;
    return 0;
  }

  // We did not previously compute a preamble, or it can't be reused anyway.
  SimpleTimer PreambleTimer(WantTiming);
  PreambleTimer.setOutput("Precompiling preamble");

  // Create a new buffer that stores the preamble. The buffer also contains
  // extra space for the original contents of the file (which will be present
  // when we actually parse the file) along with more room in case the file
  // grows.
  PreambleReservedSize = NewPreamble.first->getBufferSize();
  if (PreambleReservedSize < 4096)
    PreambleReservedSize = 8191;
  else
    PreambleReservedSize *= 2;

  // Save the preamble text for later; we'll need to compare against it for
  // subsequent reparses.
  StringRef MainFilename = PreambleInvocation->getFrontendOpts().Inputs[0].second;
  Preamble.assign(FileMgr->getFile(MainFilename),
                  NewPreamble.first->getBufferStart(),
                  NewPreamble.first->getBufferStart()
                                                  + NewPreamble.second.first);
  PreambleEndsAtStartOfLine = NewPreamble.second.second;

  delete PreambleBuffer;
  PreambleBuffer
    = llvm::MemoryBuffer::getNewUninitMemBuffer(PreambleReservedSize,
                                                FrontendOpts.Inputs[0].second);
  memcpy(const_cast<char*>(PreambleBuffer->getBufferStart()),
         NewPreamble.first->getBufferStart(), Preamble.size());
  memset(const_cast<char*>(PreambleBuffer->getBufferStart()) + Preamble.size(),
         ' ', PreambleReservedSize - Preamble.size() - 1);
  const_cast<char*>(PreambleBuffer->getBufferEnd())[-1] = '\n';

  // Remap the main source file to the preamble buffer.
  llvm::sys::PathWithStatus MainFilePath(FrontendOpts.Inputs[0].second);
  PreprocessorOpts.addRemappedFile(MainFilePath.str(), PreambleBuffer);

  // Tell the compiler invocation to generate a temporary precompiled header.
  FrontendOpts.ProgramAction = frontend::GeneratePCH;
  // FIXME: Generate the precompiled header into memory?
  FrontendOpts.OutputFile = PreamblePCHPath;
  PreprocessorOpts.PrecompiledPreambleBytes.first = 0;
  PreprocessorOpts.PrecompiledPreambleBytes.second = false;

  // Create the compiler instance to use for building the precompiled preamble.
  llvm::OwningPtr<CompilerInstance> Clang(new CompilerInstance());

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance>
    CICleanup(Clang.get());

  Clang->setInvocation(&*PreambleInvocation);
  OriginalSourceFile = Clang->getFrontendOpts().Inputs[0].second;

  // Set up diagnostics, capturing all of the diagnostics produced.
  Clang->setDiagnostics(&getDiagnostics());

  // Create the target instance.
  Clang->getTargetOpts().Features = TargetFeatures;
  Clang->setTarget(TargetInfo::CreateTargetInfo(Clang->getDiagnostics(),
                                               Clang->getTargetOpts()));
  if (!Clang->hasTarget()) {
    llvm::sys::Path(FrontendOpts.OutputFile).eraseFromDisk();
    Preamble.clear();
    PreambleRebuildCounter = DefaultPreambleRebuildInterval;
    PreprocessorOpts.eraseRemappedFile(
                               PreprocessorOpts.remapped_file_buffer_end() - 1);
    return 0;
  }

  // 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.
  Clang->getTarget().setForcedLangOptions(Clang->getLangOpts());

  assert(Clang->getFrontendOpts().Inputs.size() == 1 &&
         "Invocation must have exactly one source file!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_AST &&
         "FIXME: AST inputs not yet supported here!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_LLVM_IR &&
         "IR inputs not support here!");

  // Clear out old caches and data.
  getDiagnostics().Reset();
  ProcessWarningOptions(getDiagnostics(), Clang->getDiagnosticOpts());
  StoredDiagnostics.erase(
                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
                          StoredDiagnostics.end());
  TopLevelDecls.clear();
  TopLevelDeclsInPreamble.clear();

  // Create a file manager object to provide access to and cache the filesystem.
  Clang->setFileManager(new FileManager(Clang->getFileSystemOpts()));

  // Create the source manager.
  Clang->setSourceManager(new SourceManager(getDiagnostics(),
                                            Clang->getFileManager()));

  llvm::OwningPtr<PrecompilePreambleAction> Act;
  Act.reset(new PrecompilePreambleAction(*this));
  if (!Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0].second,
                            Clang->getFrontendOpts().Inputs[0].first)) {
    llvm::sys::Path(FrontendOpts.OutputFile).eraseFromDisk();
    Preamble.clear();
    PreambleRebuildCounter = DefaultPreambleRebuildInterval;
    PreprocessorOpts.eraseRemappedFile(
                               PreprocessorOpts.remapped_file_buffer_end() - 1);
    return 0;
  }

  Act->Execute();
  Act->EndSourceFile();

  if (Diagnostics->hasErrorOccurred()) {
    // There were errors parsing the preamble, so no precompiled header was
    // generated. Forget that we even tried.
    // FIXME: Should we leave a note for ourselves to try again?
    llvm::sys::Path(FrontendOpts.OutputFile).eraseFromDisk();
    Preamble.clear();
    TopLevelDeclsInPreamble.clear();
    PreambleRebuildCounter = DefaultPreambleRebuildInterval;
    PreprocessorOpts.eraseRemappedFile(
                               PreprocessorOpts.remapped_file_buffer_end() - 1);
    return 0;
  }

  // Transfer any diagnostics generated when parsing the preamble into the set
  // of preamble diagnostics.
  PreambleDiagnostics.clear();
  PreambleDiagnostics.insert(PreambleDiagnostics.end(),
                   StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
                             StoredDiagnostics.end());
  StoredDiagnostics.erase(
                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
                          StoredDiagnostics.end());

  // Keep track of the preamble we precompiled.
  PreambleFile = FrontendOpts.OutputFile;
  NumWarningsInPreamble = getDiagnostics().getNumWarnings();

  // Keep track of all of the files that the source manager knows about,
  // so we can verify whether they have changed or not.
  FilesInPreamble.clear();
  SourceManager &SourceMgr = Clang->getSourceManager();
  const llvm::MemoryBuffer *MainFileBuffer
    = SourceMgr.getBuffer(SourceMgr.getMainFileID());
  for (SourceManager::fileinfo_iterator F = SourceMgr.fileinfo_begin(),
                                     FEnd = SourceMgr.fileinfo_end();
       F != FEnd;
       ++F) {
    const FileEntry *File = F->second->OrigEntry;
    if (!File || F->second->getRawBuffer() == MainFileBuffer)
      continue;

    FilesInPreamble[File->getName()]
      = std::make_pair(F->second->getSize(), File->getModificationTime());
  }

  PreambleRebuildCounter = 1;
  PreprocessorOpts.eraseRemappedFile(
                               PreprocessorOpts.remapped_file_buffer_end() - 1);

  // If the hash of top-level entities differs from the hash of the top-level
  // entities the last time we rebuilt the preamble, clear out the completion
  // cache.
  if (CurrentTopLevelHashValue != PreambleTopLevelHashValue) {
    CompletionCacheTopLevelHashValue = 0;
    PreambleTopLevelHashValue = CurrentTopLevelHashValue;
  }

  return CreatePaddedMainFileBuffer(NewPreamble.first,
                                    PreambleReservedSize,
                                    FrontendOpts.Inputs[0].second);
}

void ASTUnit::RealizeTopLevelDeclsFromPreamble() {
  std::vector<Decl *> Resolved;
  Resolved.reserve(TopLevelDeclsInPreamble.size());
  ExternalASTSource &Source = *getASTContext().getExternalSource();
  for (unsigned I = 0, N = TopLevelDeclsInPreamble.size(); I != N; ++I) {
    // Resolve the declaration ID to an actual declaration, possibly
    // deserializing the declaration in the process.
    Decl *D = Source.GetExternalDecl(TopLevelDeclsInPreamble[I]);
    if (D)
      Resolved.push_back(D);
  }
  TopLevelDeclsInPreamble.clear();
  TopLevelDecls.insert(TopLevelDecls.begin(), Resolved.begin(), Resolved.end());
}

StringRef ASTUnit::getMainFileName() const {
  return Invocation->getFrontendOpts().Inputs[0].second;
}

ASTUnit *ASTUnit::create(CompilerInvocation *CI,
                         llvm::IntrusiveRefCntPtr<DiagnosticsEngine> Diags) {
  llvm::OwningPtr<ASTUnit> AST;
  AST.reset(new ASTUnit(false));
  ConfigureDiags(Diags, 0, 0, *AST, /*CaptureDiagnostics=*/false);
  AST->Diagnostics = Diags;
  AST->Invocation = CI;
  AST->FileSystemOpts = CI->getFileSystemOpts();
  AST->FileMgr = new FileManager(AST->FileSystemOpts);
  AST->SourceMgr = new SourceManager(*Diags, *AST->FileMgr);

  return AST.take();
}

ASTUnit *ASTUnit::LoadFromCompilerInvocationAction(CompilerInvocation *CI,
                              llvm::IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
                                             ASTFrontendAction *Action) {
  assert(CI && "A CompilerInvocation is required");

  // Create the AST unit.
  llvm::OwningPtr<ASTUnit> AST;
  AST.reset(new ASTUnit(false));
  ConfigureDiags(Diags, 0, 0, *AST, /*CaptureDiagnostics*/false);
  AST->Diagnostics = Diags;
  AST->OnlyLocalDecls = false;
  AST->CaptureDiagnostics = false;
  AST->TUKind = Action ? Action->getTranslationUnitKind() : TU_Complete;
  AST->ShouldCacheCodeCompletionResults = false;
  AST->Invocation = CI;

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<ASTUnit>
    ASTUnitCleanup(AST.get());
  llvm::CrashRecoveryContextCleanupRegistrar<DiagnosticsEngine,
    llvm::CrashRecoveryContextReleaseRefCleanup<DiagnosticsEngine> >
    DiagCleanup(Diags.getPtr());

  // We'll manage file buffers ourselves.
  CI->getPreprocessorOpts().RetainRemappedFileBuffers = true;
  CI->getFrontendOpts().DisableFree = false;
  ProcessWarningOptions(AST->getDiagnostics(), CI->getDiagnosticOpts());

  // Save the target features.
  AST->TargetFeatures = CI->getTargetOpts().Features;

  // Create the compiler instance to use for building the AST.
  llvm::OwningPtr<CompilerInstance> Clang(new CompilerInstance());

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance>
    CICleanup(Clang.get());

  Clang->setInvocation(CI);
  AST->OriginalSourceFile = Clang->getFrontendOpts().Inputs[0].second;

  // Set up diagnostics, capturing any diagnostics that would
  // otherwise be dropped.
  Clang->setDiagnostics(&AST->getDiagnostics());

  // Create the target instance.
  Clang->getTargetOpts().Features = AST->TargetFeatures;
  Clang->setTarget(TargetInfo::CreateTargetInfo(Clang->getDiagnostics(),
                   Clang->getTargetOpts()));
  if (!Clang->hasTarget())
    return 0;

  // 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.
  Clang->getTarget().setForcedLangOptions(Clang->getLangOpts());

  assert(Clang->getFrontendOpts().Inputs.size() == 1 &&
         "Invocation must have exactly one source file!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_AST &&
         "FIXME: AST inputs not yet supported here!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_LLVM_IR &&
         "IR inputs not supported here!");

  // Configure the various subsystems.
  AST->FileSystemOpts = Clang->getFileSystemOpts();
  AST->FileMgr = new FileManager(AST->FileSystemOpts);
  AST->SourceMgr = new SourceManager(AST->getDiagnostics(), *AST->FileMgr);
  AST->TheSema.reset();
  AST->Ctx = 0;
  AST->PP = 0;

  // Create a file manager object to provide access to and cache the filesystem.
  Clang->setFileManager(&AST->getFileManager());

  // Create the source manager.
  Clang->setSourceManager(&AST->getSourceManager());

  ASTFrontendAction *Act = Action;

  llvm::OwningPtr<TopLevelDeclTrackerAction> TrackerAct;
  if (!Act) {
    TrackerAct.reset(new TopLevelDeclTrackerAction(*AST));
    Act = TrackerAct.get();
  }

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<TopLevelDeclTrackerAction>
    ActCleanup(TrackerAct.get());

  if (!Act->BeginSourceFile(*Clang.get(),
                            Clang->getFrontendOpts().Inputs[0].second,
                            Clang->getFrontendOpts().Inputs[0].first))
    return 0;

  Act->Execute();

  // Steal the created target, context, and preprocessor.
  AST->TheSema.reset(Clang->takeSema());
  AST->Consumer.reset(Clang->takeASTConsumer());
  AST->Ctx = &Clang->getASTContext();
  AST->PP = &Clang->getPreprocessor();
  Clang->setSourceManager(0);
  Clang->setFileManager(0);
  AST->Target = &Clang->getTarget();

  Act->EndSourceFile();

  return AST.take();
}

bool ASTUnit::LoadFromCompilerInvocation(bool PrecompilePreamble) {
  if (!Invocation)
    return true;

  // We'll manage file buffers ourselves.
  Invocation->getPreprocessorOpts().RetainRemappedFileBuffers = true;
  Invocation->getFrontendOpts().DisableFree = false;
  ProcessWarningOptions(getDiagnostics(), Invocation->getDiagnosticOpts());

  // Save the target features.
  TargetFeatures = Invocation->getTargetOpts().Features;

  llvm::MemoryBuffer *OverrideMainBuffer = 0;
  if (PrecompilePreamble) {
    PreambleRebuildCounter = 2;
    OverrideMainBuffer
      = getMainBufferWithPrecompiledPreamble(*Invocation);
  }

  SimpleTimer ParsingTimer(WantTiming);
  ParsingTimer.setOutput("Parsing " + getMainFileName());

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<llvm::MemoryBuffer>
    MemBufferCleanup(OverrideMainBuffer);

  return Parse(OverrideMainBuffer);
}

ASTUnit *ASTUnit::LoadFromCompilerInvocation(CompilerInvocation *CI,
                              llvm::IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
                                             bool OnlyLocalDecls,
                                             bool CaptureDiagnostics,
                                             bool PrecompilePreamble,
                                             TranslationUnitKind TUKind,
                                             bool CacheCodeCompletionResults,
                                             bool NestedMacroExpansions) {
  // Create the AST unit.
  llvm::OwningPtr<ASTUnit> AST;
  AST.reset(new ASTUnit(false));
  ConfigureDiags(Diags, 0, 0, *AST, CaptureDiagnostics);
  AST->Diagnostics = Diags;
  AST->OnlyLocalDecls = OnlyLocalDecls;
  AST->CaptureDiagnostics = CaptureDiagnostics;
  AST->TUKind = TUKind;
  AST->ShouldCacheCodeCompletionResults = CacheCodeCompletionResults;
  AST->Invocation = CI;
  AST->NestedMacroExpansions = NestedMacroExpansions;

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<ASTUnit>
    ASTUnitCleanup(AST.get());
  llvm::CrashRecoveryContextCleanupRegistrar<DiagnosticsEngine,
    llvm::CrashRecoveryContextReleaseRefCleanup<DiagnosticsEngine> >
    DiagCleanup(Diags.getPtr());

  return AST->LoadFromCompilerInvocation(PrecompilePreamble)? 0 : AST.take();
}

ASTUnit *ASTUnit::LoadFromCommandLine(const char **ArgBegin,
                                      const char **ArgEnd,
                                    llvm::IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
                                      StringRef ResourceFilesPath,
                                      bool OnlyLocalDecls,
                                      bool CaptureDiagnostics,
                                      RemappedFile *RemappedFiles,
                                      unsigned NumRemappedFiles,
                                      bool RemappedFilesKeepOriginalName,
                                      bool PrecompilePreamble,
                                      TranslationUnitKind TUKind,
                                      bool CacheCodeCompletionResults,
                                      bool NestedMacroExpansions) {
  if (!Diags.getPtr()) {
    // No diagnostics engine was provided, so create our own diagnostics object
    // with the default options.
    DiagnosticOptions DiagOpts;
    Diags = CompilerInstance::createDiagnostics(DiagOpts, ArgEnd - ArgBegin,
                                                ArgBegin);
  }

  SmallVector<StoredDiagnostic, 4> StoredDiagnostics;

  llvm::IntrusiveRefCntPtr<CompilerInvocation> CI;

  {

    CaptureDroppedDiagnostics Capture(CaptureDiagnostics, *Diags,
                                      StoredDiagnostics);

    CI = clang::createInvocationFromCommandLine(
                                           llvm::makeArrayRef(ArgBegin, ArgEnd),
                                           Diags);
    if (!CI)
      return 0;
  }

  // Override any files that need remapping
  for (unsigned I = 0; I != NumRemappedFiles; ++I) {
    FilenameOrMemBuf fileOrBuf = RemappedFiles[I].second;
    if (const llvm::MemoryBuffer *
            memBuf = fileOrBuf.dyn_cast<const llvm::MemoryBuffer *>()) {
      CI->getPreprocessorOpts().addRemappedFile(RemappedFiles[I].first, memBuf);
    } else {
      const char *fname = fileOrBuf.get<const char *>();
      CI->getPreprocessorOpts().addRemappedFile(RemappedFiles[I].first, fname);
    }
  }
  CI->getPreprocessorOpts().RemappedFilesKeepOriginalName =
                                                  RemappedFilesKeepOriginalName;

  // Override the resources path.
  CI->getHeaderSearchOpts().ResourceDir = ResourceFilesPath;

  // Create the AST unit.
  llvm::OwningPtr<ASTUnit> AST;
  AST.reset(new ASTUnit(false));
  ConfigureDiags(Diags, ArgBegin, ArgEnd, *AST, CaptureDiagnostics);
  AST->Diagnostics = Diags;

  AST->FileSystemOpts = CI->getFileSystemOpts();
  AST->FileMgr = new FileManager(AST->FileSystemOpts);
  AST->OnlyLocalDecls = OnlyLocalDecls;
  AST->CaptureDiagnostics = CaptureDiagnostics;
  AST->TUKind = TUKind;
  AST->ShouldCacheCodeCompletionResults = CacheCodeCompletionResults;
  AST->NumStoredDiagnosticsFromDriver = StoredDiagnostics.size();
  AST->StoredDiagnostics.swap(StoredDiagnostics);
  AST->Invocation = CI;
  AST->NestedMacroExpansions = NestedMacroExpansions;

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<ASTUnit>
    ASTUnitCleanup(AST.get());
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInvocation,
    llvm::CrashRecoveryContextReleaseRefCleanup<CompilerInvocation> >
    CICleanup(CI.getPtr());
  llvm::CrashRecoveryContextCleanupRegistrar<DiagnosticsEngine,
    llvm::CrashRecoveryContextReleaseRefCleanup<DiagnosticsEngine> >
    DiagCleanup(Diags.getPtr());

  return AST->LoadFromCompilerInvocation(PrecompilePreamble) ? 0 : AST.take();
}

bool ASTUnit::Reparse(RemappedFile *RemappedFiles, unsigned NumRemappedFiles) {
  if (!Invocation)
    return true;

  SimpleTimer ParsingTimer(WantTiming);
  ParsingTimer.setOutput("Reparsing " + getMainFileName());

  // Remap files.
  PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();
  PPOpts.DisableStatCache = true;
  for (PreprocessorOptions::remapped_file_buffer_iterator
         R = PPOpts.remapped_file_buffer_begin(),
         REnd = PPOpts.remapped_file_buffer_end();
       R != REnd;
       ++R) {
    delete R->second;
  }
  Invocation->getPreprocessorOpts().clearRemappedFiles();
  for (unsigned I = 0; I != NumRemappedFiles; ++I) {
    FilenameOrMemBuf fileOrBuf = RemappedFiles[I].second;
    if (const llvm::MemoryBuffer *
            memBuf = fileOrBuf.dyn_cast<const llvm::MemoryBuffer *>()) {
      Invocation->getPreprocessorOpts().addRemappedFile(RemappedFiles[I].first,
                                                        memBuf);
    } else {
      const char *fname = fileOrBuf.get<const char *>();
      Invocation->getPreprocessorOpts().addRemappedFile(RemappedFiles[I].first,
                                                        fname);
    }
  }

  // If we have a preamble file lying around, or if we might try to
  // build a precompiled preamble, do so now.
  llvm::MemoryBuffer *OverrideMainBuffer = 0;
  if (!PreambleFile.empty() || PreambleRebuildCounter > 0)
    OverrideMainBuffer = getMainBufferWithPrecompiledPreamble(*Invocation);

  // Clear out the diagnostics state.
  if (!OverrideMainBuffer) {
    getDiagnostics().Reset();
    ProcessWarningOptions(getDiagnostics(), Invocation->getDiagnosticOpts());
  }

  // Parse the sources
  bool Result = Parse(OverrideMainBuffer);

  // If we're caching global code-completion results, and the top-level
  // declarations have changed, clear out the code-completion cache.
  if (!Result && ShouldCacheCodeCompletionResults &&
      CurrentTopLevelHashValue != CompletionCacheTopLevelHashValue)
    CacheCodeCompletionResults();

  // We now need to clear out the completion allocator for
  // clang_getCursorCompletionString; it'll be recreated if necessary.
  CursorCompletionAllocator = 0;

  return Result;
}

//----------------------------------------------------------------------------//
// Code completion
//----------------------------------------------------------------------------//

namespace {
  /// \brief Code completion consumer that combines the cached code-completion
  /// results from an ASTUnit with the code-completion results provided to it,
  /// then passes the result on to
  class AugmentedCodeCompleteConsumer : public CodeCompleteConsumer {
    unsigned long long NormalContexts;
    ASTUnit &AST;
    CodeCompleteConsumer &Next;

  public:
    AugmentedCodeCompleteConsumer(ASTUnit &AST, CodeCompleteConsumer &Next,
                                  bool IncludeMacros, bool IncludeCodePatterns,
                                  bool IncludeGlobals)
      : CodeCompleteConsumer(IncludeMacros, IncludeCodePatterns, IncludeGlobals,
                             Next.isOutputBinary()), AST(AST), Next(Next)
    {
      // Compute the set of contexts in which we will look when we don't have
      // any information about the specific context.
      NormalContexts
        = (1LL << (CodeCompletionContext::CCC_TopLevel - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCInterface - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCImplementation - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCIvarList - 1))
        | (1LL << (CodeCompletionContext::CCC_Statement - 1))
        | (1LL << (CodeCompletionContext::CCC_Expression - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCMessageReceiver - 1))
        | (1LL << (CodeCompletionContext::CCC_DotMemberAccess - 1))
        | (1LL << (CodeCompletionContext::CCC_ArrowMemberAccess - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCPropertyAccess - 1))
        | (1LL << (CodeCompletionContext::CCC_ObjCProtocolName - 1))
        | (1LL << (CodeCompletionContext::CCC_ParenthesizedExpression - 1))
        | (1LL << (CodeCompletionContext::CCC_Recovery - 1));

      if (AST.getASTContext().getLangOptions().CPlusPlus)
        NormalContexts |= (1LL << (CodeCompletionContext::CCC_EnumTag - 1))
                   | (1LL << (CodeCompletionContext::CCC_UnionTag - 1))
                   | (1LL << (CodeCompletionContext::CCC_ClassOrStructTag - 1));
    }

    virtual void ProcessCodeCompleteResults(Sema &S,
                                            CodeCompletionContext Context,
                                            CodeCompletionResult *Results,
                                            unsigned NumResults);

    virtual void ProcessOverloadCandidates(Sema &S, unsigned CurrentArg,
                                           OverloadCandidate *Candidates,
                                           unsigned NumCandidates) {
      Next.ProcessOverloadCandidates(S, CurrentArg, Candidates, NumCandidates);
    }

    virtual CodeCompletionAllocator &getAllocator() {
      return Next.getAllocator();
    }
  };
}

/// \brief Helper function that computes which global names are hidden by the
/// local code-completion results.
static void CalculateHiddenNames(const CodeCompletionContext &Context,
                                 CodeCompletionResult *Results,
                                 unsigned NumResults,
                                 ASTContext &Ctx,
                          llvm::StringSet<llvm::BumpPtrAllocator> &HiddenNames){
  bool OnlyTagNames = false;
  switch (Context.getKind()) {
  case CodeCompletionContext::CCC_Recovery:
  case CodeCompletionContext::CCC_TopLevel:
  case CodeCompletionContext::CCC_ObjCInterface:
  case CodeCompletionContext::CCC_ObjCImplementation:
  case CodeCompletionContext::CCC_ObjCIvarList:
  case CodeCompletionContext::CCC_ClassStructUnion:
  case CodeCompletionContext::CCC_Statement:
  case CodeCompletionContext::CCC_Expression:
  case CodeCompletionContext::CCC_ObjCMessageReceiver:
  case CodeCompletionContext::CCC_DotMemberAccess:
  case CodeCompletionContext::CCC_ArrowMemberAccess:
  case CodeCompletionContext::CCC_ObjCPropertyAccess:
  case CodeCompletionContext::CCC_Namespace:
  case CodeCompletionContext::CCC_Type:
  case CodeCompletionContext::CCC_Name:
  case CodeCompletionContext::CCC_PotentiallyQualifiedName:
  case CodeCompletionContext::CCC_ParenthesizedExpression:
  case CodeCompletionContext::CCC_ObjCInterfaceName:
    break;

  case CodeCompletionContext::CCC_EnumTag:
  case CodeCompletionContext::CCC_UnionTag:
  case CodeCompletionContext::CCC_ClassOrStructTag:
    OnlyTagNames = true;
    break;

  case CodeCompletionContext::CCC_ObjCProtocolName:
  case CodeCompletionContext::CCC_MacroName:
  case CodeCompletionContext::CCC_MacroNameUse:
  case CodeCompletionContext::CCC_PreprocessorExpression:
  case CodeCompletionContext::CCC_PreprocessorDirective:
  case CodeCompletionContext::CCC_NaturalLanguage:
  case CodeCompletionContext::CCC_SelectorName:
  case CodeCompletionContext::CCC_TypeQualifiers:
  case CodeCompletionContext::CCC_Other:
  case CodeCompletionContext::CCC_OtherWithMacros:
  case CodeCompletionContext::CCC_ObjCInstanceMessage:
  case CodeCompletionContext::CCC_ObjCClassMessage:
  case CodeCompletionContext::CCC_ObjCCategoryName:
    // We're looking for nothing, or we're looking for names that cannot
    // be hidden.
    return;
  }

  typedef CodeCompletionResult Result;
  for (unsigned I = 0; I != NumResults; ++I) {
    if (Results[I].Kind != Result::RK_Declaration)
      continue;

    unsigned IDNS
      = Results[I].Declaration->getUnderlyingDecl()->getIdentifierNamespace();

    bool Hiding = false;
    if (OnlyTagNames)
      Hiding = (IDNS & Decl::IDNS_Tag);
    else {
      unsigned HiddenIDNS = (Decl::IDNS_Type | Decl::IDNS_Member |
                             Decl::IDNS_Namespace | Decl::IDNS_Ordinary |
                             Decl::IDNS_NonMemberOperator);
      if (Ctx.getLangOptions().CPlusPlus)
        HiddenIDNS |= Decl::IDNS_Tag;
      Hiding = (IDNS & HiddenIDNS);
    }

    if (!Hiding)
      continue;

    DeclarationName Name = Results[I].Declaration->getDeclName();
    if (IdentifierInfo *Identifier = Name.getAsIdentifierInfo())
      HiddenNames.insert(Identifier->getName());
    else
      HiddenNames.insert(Name.getAsString());
  }
}


void AugmentedCodeCompleteConsumer::ProcessCodeCompleteResults(Sema &S,
                                            CodeCompletionContext Context,
                                            CodeCompletionResult *Results,
                                            unsigned NumResults) {
  // Merge the results we were given with the results we cached.
  bool AddedResult = false;
  unsigned InContexts
    = (Context.getKind() == CodeCompletionContext::CCC_Recovery? NormalContexts
                                        : (1ULL << (Context.getKind() - 1)));
  // Contains the set of names that are hidden by "local" completion results.
  llvm::StringSet<llvm::BumpPtrAllocator> HiddenNames;
  typedef CodeCompletionResult Result;
  SmallVector<Result, 8> AllResults;
  for (ASTUnit::cached_completion_iterator
            C = AST.cached_completion_begin(),
         CEnd = AST.cached_completion_end();
       C != CEnd; ++C) {
    // If the context we are in matches any of the contexts we are
    // interested in, we'll add this result.
    if ((C->ShowInContexts & InContexts) == 0)
      continue;

    // If we haven't added any results previously, do so now.
    if (!AddedResult) {
      CalculateHiddenNames(Context, Results, NumResults, S.Context,
                           HiddenNames);
      AllResults.insert(AllResults.end(), Results, Results + NumResults);
      AddedResult = true;
    }

    // Determine whether this global completion result is hidden by a local
    // completion result. If so, skip it.
    if (C->Kind != CXCursor_MacroDefinition &&
        HiddenNames.count(C->Completion->getTypedText()))
      continue;

    // Adjust priority based on similar type classes.
    unsigned Priority = C->Priority;
    CXCursorKind CursorKind = C->Kind;
    CodeCompletionString *Completion = C->Completion;
    if (!Context.getPreferredType().isNull()) {
      if (C->Kind == CXCursor_MacroDefinition) {
        Priority = getMacroUsagePriority(C->Completion->getTypedText(),
                                         S.getLangOptions(),
                               Context.getPreferredType()->isAnyPointerType());
      } else if (C->Type) {
        CanQualType Expected
          = S.Context.getCanonicalType(
                               Context.getPreferredType().getUnqualifiedType());
        SimplifiedTypeClass ExpectedSTC = getSimplifiedTypeClass(Expected);
        if (ExpectedSTC == C->TypeClass) {
          // We know this type is similar; check for an exact match.
          llvm::StringMap<unsigned> &CachedCompletionTypes
            = AST.getCachedCompletionTypes();
          llvm::StringMap<unsigned>::iterator Pos
            = CachedCompletionTypes.find(QualType(Expected).getAsString());
          if (Pos != CachedCompletionTypes.end() && Pos->second == C->Type)
            Priority /= CCF_ExactTypeMatch;
          else
            Priority /= CCF_SimilarTypeMatch;
        }
      }
    }

    // Adjust the completion string, if required.
    if (C->Kind == CXCursor_MacroDefinition &&
        Context.getKind() == CodeCompletionContext::CCC_MacroNameUse) {
      // Create a new code-completion string that just contains the
      // macro name, without its arguments.
      CodeCompletionBuilder Builder(getAllocator(), CCP_CodePattern,
                                    C->Availability);
      Builder.AddTypedTextChunk(C->Completion->getTypedText());
      CursorKind = CXCursor_NotImplemented;
      Priority = CCP_CodePattern;
      Completion = Builder.TakeString();
    }

    AllResults.push_back(Result(Completion, Priority, CursorKind,
                                C->Availability));
  }

  // If we did not add any cached completion results, just forward the
  // results we were given to the next consumer.
  if (!AddedResult) {
    Next.ProcessCodeCompleteResults(S, Context, Results, NumResults);
    return;
  }

  Next.ProcessCodeCompleteResults(S, Context, AllResults.data(),
                                  AllResults.size());
}



void ASTUnit::CodeComplete(StringRef File, unsigned Line, unsigned Column,
                           RemappedFile *RemappedFiles,
                           unsigned NumRemappedFiles,
                           bool IncludeMacros,
                           bool IncludeCodePatterns,
                           CodeCompleteConsumer &Consumer,
                           DiagnosticsEngine &Diag, LangOptions &LangOpts,
                           SourceManager &SourceMgr, FileManager &FileMgr,
                   SmallVectorImpl<StoredDiagnostic> &StoredDiagnostics,
             SmallVectorImpl<const llvm::MemoryBuffer *> &OwnedBuffers) {
  if (!Invocation)
    return;

  SimpleTimer CompletionTimer(WantTiming);
  CompletionTimer.setOutput("Code completion @ " + File + ":" +
                            Twine(Line) + ":" + Twine(Column));

  llvm::IntrusiveRefCntPtr<CompilerInvocation>
    CCInvocation(new CompilerInvocation(*Invocation));

  FrontendOptions &FrontendOpts = CCInvocation->getFrontendOpts();
  PreprocessorOptions &PreprocessorOpts = CCInvocation->getPreprocessorOpts();

  FrontendOpts.ShowMacrosInCodeCompletion
    = IncludeMacros && CachedCompletionResults.empty();
  FrontendOpts.ShowCodePatternsInCodeCompletion = IncludeCodePatterns;
  FrontendOpts.ShowGlobalSymbolsInCodeCompletion
    = CachedCompletionResults.empty();
  FrontendOpts.CodeCompletionAt.FileName = File;
  FrontendOpts.CodeCompletionAt.Line = Line;
  FrontendOpts.CodeCompletionAt.Column = Column;

  // Set the language options appropriately.
  LangOpts = CCInvocation->getLangOpts();

  llvm::OwningPtr<CompilerInstance> Clang(new CompilerInstance());

  // Recover resources if we crash before exiting this method.
  llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance>
    CICleanup(Clang.get());

  Clang->setInvocation(&*CCInvocation);
  OriginalSourceFile = Clang->getFrontendOpts().Inputs[0].second;

  // Set up diagnostics, capturing any diagnostics produced.
  Clang->setDiagnostics(&Diag);
  ProcessWarningOptions(Diag, CCInvocation->getDiagnosticOpts());
  CaptureDroppedDiagnostics Capture(true,
                                    Clang->getDiagnostics(),
                                    StoredDiagnostics);

  // Create the target instance.
  Clang->getTargetOpts().Features = TargetFeatures;
  Clang->setTarget(TargetInfo::CreateTargetInfo(Clang->getDiagnostics(),
                                               Clang->getTargetOpts()));
  if (!Clang->hasTarget()) {
    Clang->setInvocation(0);
    return;
  }

  // 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.
  Clang->getTarget().setForcedLangOptions(Clang->getLangOpts());

  assert(Clang->getFrontendOpts().Inputs.size() == 1 &&
         "Invocation must have exactly one source file!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_AST &&
         "FIXME: AST inputs not yet supported here!");
  assert(Clang->getFrontendOpts().Inputs[0].first != IK_LLVM_IR &&
         "IR inputs not support here!");


  // Use the source and file managers that we were given.
  Clang->setFileManager(&FileMgr);
  Clang->setSourceManager(&SourceMgr);

  // Remap files.
  PreprocessorOpts.clearRemappedFiles();
  PreprocessorOpts.RetainRemappedFileBuffers = true;
  for (unsigned I = 0; I != NumRemappedFiles; ++I) {
    FilenameOrMemBuf fileOrBuf = RemappedFiles[I].second;
    if (const llvm::MemoryBuffer *
            memBuf = fileOrBuf.dyn_cast<const llvm::MemoryBuffer *>()) {
      PreprocessorOpts.addRemappedFile(RemappedFiles[I].first, memBuf);
      OwnedBuffers.push_back(memBuf);
    } else {
      const char *fname = fileOrBuf.get<const char *>();
      PreprocessorOpts.addRemappedFile(RemappedFiles[I].first, fname);
    }
  }

  // Use the code completion consumer we were given, but adding any cached
  // code-completion results.
  AugmentedCodeCompleteConsumer *AugmentedConsumer
    = new AugmentedCodeCompleteConsumer(*this, Consumer,
                                        FrontendOpts.ShowMacrosInCodeCompletion,
                                FrontendOpts.ShowCodePatternsInCodeCompletion,
                                FrontendOpts.ShowGlobalSymbolsInCodeCompletion);
  Clang->setCodeCompletionConsumer(AugmentedConsumer);

  // If we have a precompiled preamble, try to use it. We only allow
  // the use of the precompiled preamble if we're if the completion
  // point is within the main file, after the end of the precompiled
  // preamble.
  llvm::MemoryBuffer *OverrideMainBuffer = 0;
  if (!PreambleFile.empty()) {
    using llvm::sys::FileStatus;
    llvm::sys::PathWithStatus CompleteFilePath(File);
    llvm::sys::PathWithStatus MainPath(OriginalSourceFile);
    if (const FileStatus *CompleteFileStatus = CompleteFilePath.getFileStatus())
      if (const FileStatus *MainStatus = MainPath.getFileStatus())
        if (CompleteFileStatus->getUniqueID() == MainStatus->getUniqueID() &&
            Line > 1)
          OverrideMainBuffer
            = getMainBufferWithPrecompiledPreamble(*CCInvocation, false,
                                                   Line - 1);
  }

  // If the main file has been overridden due to the use of a preamble,
  // make that override happen and introduce the preamble.
  PreprocessorOpts.DisableStatCache = true;
  StoredDiagnostics.insert(StoredDiagnostics.end(),
                           this->StoredDiagnostics.begin(),
             this->StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver);
  if (OverrideMainBuffer) {
    PreprocessorOpts.addRemappedFile(OriginalSourceFile, OverrideMainBuffer);
    PreprocessorOpts.PrecompiledPreambleBytes.first = Preamble.size();
    PreprocessorOpts.PrecompiledPreambleBytes.second
                                                    = PreambleEndsAtStartOfLine;
    PreprocessorOpts.ImplicitPCHInclude = PreambleFile;
    PreprocessorOpts.DisablePCHValidation = true;

    OwnedBuffers.push_back(OverrideMainBuffer);
  } else {
    PreprocessorOpts.PrecompiledPreambleBytes.first = 0;
    PreprocessorOpts.PrecompiledPreambleBytes.second = false;
  }

  // Disable the preprocessing record
  PreprocessorOpts.DetailedRecord = false;

  llvm::OwningPtr<SyntaxOnlyAction> Act;
  Act.reset(new SyntaxOnlyAction);
  if (Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0].second,
                           Clang->getFrontendOpts().Inputs[0].first)) {
    if (OverrideMainBuffer) {
      std::string ModName = PreambleFile;
      TranslateStoredDiagnostics(Clang->getModuleManager(), ModName,
                                 getSourceManager(), PreambleDiagnostics,
                                 StoredDiagnostics);
    }
    Act->Execute();
    Act->EndSourceFile();
  }
}

CXSaveError ASTUnit::Save(StringRef File) {
  if (getDiagnostics().hasUnrecoverableErrorOccurred())
    return CXSaveError_TranslationErrors;

  // Write to a temporary file and later rename it to the actual file, to avoid
  // possible race conditions.
  llvm::SmallString<128> TempPath;
  TempPath = File;
  TempPath += "-%%%%%%%%";
  int fd;
  if (llvm::sys::fs::unique_file(TempPath.str(), fd, TempPath,
                                 /*makeAbsolute=*/false))
    return CXSaveError_Unknown;

  // FIXME: Can we somehow regenerate the stat cache here, or do we need to
  // unconditionally create a stat cache when we parse the file?
  llvm::raw_fd_ostream Out(fd, /*shouldClose=*/true);

  serialize(Out);
  Out.close();
  if (Out.has_error())
    return CXSaveError_Unknown;

  if (llvm::error_code ec = llvm::sys::fs::rename(TempPath.str(), File)) {
    bool exists;
    llvm::sys::fs::remove(TempPath.str(), exists);
    return CXSaveError_Unknown;
  }

  return CXSaveError_None;
}

bool ASTUnit::serialize(raw_ostream &OS) {
  if (getDiagnostics().hasErrorOccurred())
    return true;

  std::vector<unsigned char> Buffer;
  llvm::BitstreamWriter Stream(Buffer);
  ASTWriter Writer(Stream);
  // FIXME: Handle modules
  Writer.WriteAST(getSema(), 0, std::string(), /*IsModule=*/false, "");

  // Write the generated bitstream to "Out".
  if (!Buffer.empty())
    OS.write((char *)&Buffer.front(), Buffer.size());

  return false;
}

typedef ContinuousRangeMap<unsigned, int, 2> SLocRemap;

static void TranslateSLoc(SourceLocation &L, SLocRemap &Remap) {
  unsigned Raw = L.getRawEncoding();
  const unsigned MacroBit = 1U << 31;
  L = SourceLocation::getFromRawEncoding((Raw & MacroBit) |
      ((Raw & ~MacroBit) + Remap.find(Raw & ~MacroBit)->second));
}

void ASTUnit::TranslateStoredDiagnostics(
                          ASTReader *MMan,
                          StringRef ModName,
                          SourceManager &SrcMgr,
                          const SmallVectorImpl<StoredDiagnostic> &Diags,
                          SmallVectorImpl<StoredDiagnostic> &Out) {
  // The stored diagnostic has the old source manager in it; update
  // the locations to refer into the new source manager. We also need to remap
  // all the locations to the new view. This includes the diag location, any
  // associated source ranges, and the source ranges of associated fix-its.
  // FIXME: There should be a cleaner way to do this.

  SmallVector<StoredDiagnostic, 4> Result;
  Result.reserve(Diags.size());
  assert(MMan && "Don't have a module manager");
  serialization::Module *Mod = MMan->ModuleMgr.lookup(ModName);
  assert(Mod && "Don't have preamble module");
  SLocRemap &Remap = Mod->SLocRemap;
  for (unsigned I = 0, N = Diags.size(); I != N; ++I) {
    // Rebuild the StoredDiagnostic.
    const StoredDiagnostic &SD = Diags[I];
    SourceLocation L = SD.getLocation();
    TranslateSLoc(L, Remap);
    FullSourceLoc Loc(L, SrcMgr);

    SmallVector<CharSourceRange, 4> Ranges;
    Ranges.reserve(SD.range_size());
    for (StoredDiagnostic::range_iterator I = SD.range_begin(),
                                          E = SD.range_end();
         I != E; ++I) {
      SourceLocation BL = I->getBegin();
      TranslateSLoc(BL, Remap);
      SourceLocation EL = I->getEnd();
      TranslateSLoc(EL, Remap);
      Ranges.push_back(CharSourceRange(SourceRange(BL, EL), I->isTokenRange()));
    }

    SmallVector<FixItHint, 2> FixIts;
    FixIts.reserve(SD.fixit_size());
    for (StoredDiagnostic::fixit_iterator I = SD.fixit_begin(),
                                          E = SD.fixit_end();
         I != E; ++I) {
      FixIts.push_back(FixItHint());
      FixItHint &FH = FixIts.back();
      FH.CodeToInsert = I->CodeToInsert;
      SourceLocation BL = I->RemoveRange.getBegin();
      TranslateSLoc(BL, Remap);
      SourceLocation EL = I->RemoveRange.getEnd();
      TranslateSLoc(EL, Remap);
      FH.RemoveRange = CharSourceRange(SourceRange(BL, EL),
                                       I->RemoveRange.isTokenRange());
    }

    Result.push_back(StoredDiagnostic(SD.getLevel(), SD.getID(),
                                      SD.getMessage(), Loc, Ranges, FixIts));
  }
  Result.swap(Out);
}

SourceLocation ASTUnit::getLocation(const FileEntry *File,
                                    unsigned Line, unsigned Col) const {
  const SourceManager &SM = getSourceManager();
  SourceLocation Loc = SM.translateFileLineCol(File, Line, Col);
  return SM.getMacroArgExpandedLocation(Loc);
}

SourceLocation ASTUnit::getLocation(const FileEntry *File,
                                    unsigned Offset) const {
  const SourceManager &SM = getSourceManager();
  SourceLocation FileLoc = SM.translateFileLineCol(File, 1, 1);
  return SM.getMacroArgExpandedLocation(FileLoc.getLocWithOffset(Offset));
}

/// \brief If \arg Loc is a loaded location from the preamble, returns
/// the corresponding local location of the main file, otherwise it returns
/// \arg Loc.
SourceLocation ASTUnit::mapLocationFromPreamble(SourceLocation Loc) {
  FileID PreambleID;
  if (SourceMgr)
    PreambleID = SourceMgr->getPreambleFileID();

  if (Loc.isInvalid() || Preamble.empty() || PreambleID.isInvalid())
    return Loc;

  unsigned Offs;
  if (SourceMgr->isInFileID(Loc, PreambleID, &Offs) && Offs < Preamble.size()) {
    SourceLocation FileLoc
        = SourceMgr->getLocForStartOfFile(SourceMgr->getMainFileID());
    return FileLoc.getLocWithOffset(Offs);
  }

  return Loc;
}

/// \brief If \arg Loc is a local location of the main file but inside the
/// preamble chunk, returns the corresponding loaded location from the
/// preamble, otherwise it returns \arg Loc.
SourceLocation ASTUnit::mapLocationToPreamble(SourceLocation Loc) {
  FileID PreambleID;
  if (SourceMgr)
    PreambleID = SourceMgr->getPreambleFileID();

  if (Loc.isInvalid() || Preamble.empty() || PreambleID.isInvalid())
    return Loc;

  unsigned Offs;
  if (SourceMgr->isInFileID(Loc, SourceMgr->getMainFileID(), &Offs) &&
      Offs < Preamble.size()) {
    SourceLocation FileLoc = SourceMgr->getLocForStartOfFile(PreambleID);
    return FileLoc.getLocWithOffset(Offs);
  }

  return Loc;
}

void ASTUnit::PreambleData::countLines() const {
  NumLines = 0;
  if (empty())
    return;

  for (std::vector<char>::const_iterator
         I = Buffer.begin(), E = Buffer.end(); I != E; ++I) {
    if (*I == '\n')
      ++NumLines;
  }
  if (Buffer.back() != '\n')
    ++NumLines;
}