ASTReader.cpp

Go to the documentation of this file.

//===- ASTReader.cpp - AST File Reader ------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defines the ASTReader class, which reads AST files.
//
//===----------------------------------------------------------------------===//
 
#include "ASTCommon.h"
#include "ASTReaderInternals.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTMutationListener.h"
#include "clang/AST/ASTStructuralEquivalence.h"
#include "clang/AST/ASTUnresolvedSet.h"
#include "clang/AST/AbstractTypeReader.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclFriend.h"
#include "clang/AST/DeclGroup.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/ExternalASTSource.h"
#include "clang/AST/NestedNameSpecifier.h"
#include "clang/AST/ODRDiagsEmitter.h"
#include "clang/AST/OpenACCClause.h"
#include "clang/AST/OpenMPClause.h"
#include "clang/AST/RawCommentList.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/TemplateName.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/AST/TypeLocVisitor.h"
#include "clang/AST/UnresolvedSet.h"
#include "clang/Basic/ASTSourceDescriptor.h"
#include "clang/Basic/CommentOptions.h"
#include "clang/Basic/Diagnostic.h"
#include "clang/Basic/DiagnosticError.h"
#include "clang/Basic/DiagnosticIDs.h"
#include "clang/Basic/DiagnosticOptions.h"
#include "clang/Basic/DiagnosticSema.h"
#include "clang/Basic/ExceptionSpecificationType.h"
#include "clang/Basic/FileManager.h"
#include "clang/Basic/FileSystemOptions.h"
#include "clang/Basic/IdentifierTable.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/LangOptions.h"
#include "clang/Basic/Module.h"
#include "clang/Basic/ObjCRuntime.h"
#include "clang/Basic/OpenACCKinds.h"
#include "clang/Basic/OpenMPKinds.h"
#include "clang/Basic/OperatorKinds.h"
#include "clang/Basic/PragmaKinds.h"
#include "clang/Basic/Sanitizers.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Basic/SourceManagerInternals.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Basic/TargetOptions.h"
#include "clang/Basic/TokenKinds.h"
#include "clang/Basic/Version.h"
#include "clang/Lex/HeaderSearch.h"
#include "clang/Lex/HeaderSearchOptions.h"
#include "clang/Lex/MacroInfo.h"
#include "clang/Lex/ModuleMap.h"
#include "clang/Lex/PreprocessingRecord.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "clang/Lex/Token.h"
#include "clang/Sema/ObjCMethodList.h"
#include "clang/Sema/Scope.h"
#include "clang/Sema/Sema.h"
#include "clang/Sema/SemaCUDA.h"
#include "clang/Sema/SemaObjC.h"
#include "clang/Sema/Weak.h"
#include "clang/Serialization/ASTBitCodes.h"
#include "clang/Serialization/ASTDeserializationListener.h"
#include "clang/Serialization/ASTRecordReader.h"
#include "clang/Serialization/ContinuousRangeMap.h"
#include "clang/Serialization/GlobalModuleIndex.h"
#include "clang/Serialization/InMemoryModuleCache.h"
#include "clang/Serialization/ModuleFile.h"
#include "clang/Serialization/ModuleFileExtension.h"
#include "clang/Serialization/ModuleManager.h"
#include "clang/Serialization/PCHContainerOperations.h"
#include "clang/Serialization/SerializationDiagnostic.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/APSInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/FloatingPointMode.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Bitstream/BitstreamReader.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SaveAndRestore.h"
#include "llvm/Support/TimeProfiler.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/VersionTuple.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/Triple.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <ctime>
#include <iterator>
#include <limits>
#include <map>
#include <memory>
#include <optional>
#include <string>
#include <system_error>
#include <tuple>
#include <utility>
#include <vector>
 
using namespace clang;
using namespace clang::serialization;
using namespace clang::serialization::reader;
using llvm::BitstreamCursor;
 
//===----------------------------------------------------------------------===//
// ChainedASTReaderListener implementation
//===----------------------------------------------------------------------===//
 
bool
ChainedASTReaderListener::ReadFullVersionInformation(StringRef FullVersion) {
  return First->ReadFullVersionInformation(FullVersion) ||
         Second->ReadFullVersionInformation(FullVersion);
}
 
void ChainedASTReaderListener::ReadModuleName(StringRef ModuleName) {
  First->ReadModuleName(ModuleName);
  Second->ReadModuleName(ModuleName);
}
 
void ChainedASTReaderListener::ReadModuleMapFile(StringRef ModuleMapPath) {
  First->ReadModuleMapFile(ModuleMapPath);
  Second->ReadModuleMapFile(ModuleMapPath);
}
 
bool ChainedASTReaderListener::ReadLanguageOptions(
    const LangOptions &LangOpts, StringRef ModuleFilename, bool Complain,
    bool AllowCompatibleDifferences) {
  return First->ReadLanguageOptions(LangOpts, ModuleFilename, Complain,
                                    AllowCompatibleDifferences) ||
         Second->ReadLanguageOptions(LangOpts, ModuleFilename, Complain,
                                     AllowCompatibleDifferences);
}
 
bool ChainedASTReaderListener::ReadTargetOptions(
    const TargetOptions &TargetOpts, StringRef ModuleFilename, bool Complain,
    bool AllowCompatibleDifferences) {
  return First->ReadTargetOptions(TargetOpts, ModuleFilename, Complain,
                                  AllowCompatibleDifferences) ||
         Second->ReadTargetOptions(TargetOpts, ModuleFilename, Complain,
                                   AllowCompatibleDifferences);
}
 
bool ChainedASTReaderListener::ReadDiagnosticOptions(
    IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts, StringRef ModuleFilename,
    bool Complain) {
  return First->ReadDiagnosticOptions(DiagOpts, ModuleFilename, Complain) ||
         Second->ReadDiagnosticOptions(DiagOpts, ModuleFilename, Complain);
}
 
bool
ChainedASTReaderListener::ReadFileSystemOptions(const FileSystemOptions &FSOpts,
                                                bool Complain) {
  return First->ReadFileSystemOptions(FSOpts, Complain) ||
         Second->ReadFileSystemOptions(FSOpts, Complain);
}
 
bool ChainedASTReaderListener::ReadHeaderSearchOptions(
    const HeaderSearchOptions &HSOpts, StringRef ModuleFilename,
    StringRef SpecificModuleCachePath, bool Complain) {
  return First->ReadHeaderSearchOptions(HSOpts, ModuleFilename,
                                        SpecificModuleCachePath, Complain) ||
         Second->ReadHeaderSearchOptions(HSOpts, ModuleFilename,
                                         SpecificModuleCachePath, Complain);
}
 
bool ChainedASTReaderListener::ReadPreprocessorOptions(
    const PreprocessorOptions &PPOpts, StringRef ModuleFilename,
    bool ReadMacros, bool Complain, std::string &SuggestedPredefines) {
  return First->ReadPreprocessorOptions(PPOpts, ModuleFilename, ReadMacros,
                                        Complain, SuggestedPredefines) ||
         Second->ReadPreprocessorOptions(PPOpts, ModuleFilename, ReadMacros,
                                         Complain, SuggestedPredefines);
}
 
void ChainedASTReaderListener::ReadCounter(const serialization::ModuleFile &M,
                                           unsigned Value) {
  First->ReadCounter(M, Value);
  Second->ReadCounter(M, Value);
}
 
bool ChainedASTReaderListener::needsInputFileVisitation() {
  return First->needsInputFileVisitation() ||
         Second->needsInputFileVisitation();
}
 
bool ChainedASTReaderListener::needsSystemInputFileVisitation() {
  return First->needsSystemInputFileVisitation() ||
  Second->needsSystemInputFileVisitation();
}
 
void ChainedASTReaderListener::visitModuleFile(StringRef Filename,
                                               ModuleKind Kind) {
  First->visitModuleFile(Filename, Kind);
  Second->visitModuleFile(Filename, Kind);
}
 
bool ChainedASTReaderListener::visitInputFile(StringRef Filename,
                                              bool isSystem,
                                              bool isOverridden,
                                              bool isExplicitModule) {
  bool Continue = false;
  if (First->needsInputFileVisitation() &&
      (!isSystem || First->needsSystemInputFileVisitation()))
    Continue |= First->visitInputFile(Filename, isSystem, isOverridden,
                                      isExplicitModule);
  if (Second->needsInputFileVisitation() &&
      (!isSystem || Second->needsSystemInputFileVisitation()))
    Continue |= Second->visitInputFile(Filename, isSystem, isOverridden,
                                       isExplicitModule);
  return Continue;
}
 
void ChainedASTReaderListener::readModuleFileExtension(
       const ModuleFileExtensionMetadata &Metadata) {
  First->readModuleFileExtension(Metadata);
  Second->readModuleFileExtension(Metadata);
}
 
//===----------------------------------------------------------------------===//
// PCH validator implementation
//===----------------------------------------------------------------------===//
 
ASTReaderListener::~ASTReaderListener() = default;
 
/// Compare the given set of language options against an existing set of
/// language options.
///
/// \param Diags If non-NULL, diagnostics will be emitted via this engine.
/// \param AllowCompatibleDifferences If true, differences between compatible
///        language options will be permitted.
///
/// \returns true if the languagae options mis-match, false otherwise.
static bool checkLanguageOptions(const LangOptions &LangOpts,
                                 const LangOptions &ExistingLangOpts,
                                 StringRef ModuleFilename,
                                 DiagnosticsEngine *Diags,
                                 bool AllowCompatibleDifferences = true) {
#define LANGOPT(Name, Bits, Default, Description)                              \
  if (ExistingLangOpts.Name != LangOpts.Name) {                                \
    if (Diags) {                                                               \
      if (Bits == 1)                                                           \
        Diags->Report(diag::err_ast_file_langopt_mismatch)                     \
            << Description << LangOpts.Name << ExistingLangOpts.Name           \
            << ModuleFilename;                                                 \
      else                                                                     \
        Diags->Report(diag::err_ast_file_langopt_value_mismatch)               \
            << Description << ModuleFilename;                                  \
    }                                                                          \
    return true;                                                               \
  }
 
#define VALUE_LANGOPT(Name, Bits, Default, Description)                        \
  if (ExistingLangOpts.Name != LangOpts.Name) {                                \
    if (Diags)                                                                 \
      Diags->Report(diag::err_ast_file_langopt_value_mismatch)                 \
          << Description << ModuleFilename;                                    \
    return true;                                                               \
  }
 
#define ENUM_LANGOPT(Name, Type, Bits, Default, Description)                   \
  if (ExistingLangOpts.get##Name() != LangOpts.get##Name()) {                  \
    if (Diags)                                                                 \
      Diags->Report(diag::err_ast_file_langopt_value_mismatch)                 \
          << Description << ModuleFilename;                                    \
    return true;                                                               \
  }
 
#define COMPATIBLE_LANGOPT(Name, Bits, Default, Description)  \
  if (!AllowCompatibleDifferences)                            \
    LANGOPT(Name, Bits, Default, Description)
 
#define COMPATIBLE_ENUM_LANGOPT(Name, Bits, Default, Description)  \
  if (!AllowCompatibleDifferences)                                 \
    ENUM_LANGOPT(Name, Bits, Default, Description)
 
#define COMPATIBLE_VALUE_LANGOPT(Name, Bits, Default, Description) \
  if (!AllowCompatibleDifferences)                                 \
    VALUE_LANGOPT(Name, Bits, Default, Description)
 
#define BENIGN_LANGOPT(Name, Bits, Default, Description)
#define BENIGN_ENUM_LANGOPT(Name, Type, Bits, Default, Description)
#define BENIGN_VALUE_LANGOPT(Name, Bits, Default, Description)
#include "clang/Basic/LangOptions.def"
 
  if (ExistingLangOpts.ModuleFeatures != LangOpts.ModuleFeatures) {
    if (Diags)
      Diags->Report(diag::err_ast_file_langopt_value_mismatch)
          << "module features" << ModuleFilename;
    return true;
  }
 
  if (ExistingLangOpts.ObjCRuntime != LangOpts.ObjCRuntime) {
    if (Diags)
      Diags->Report(diag::err_ast_file_langopt_value_mismatch)
          << "target Objective-C runtime" << ModuleFilename;
    return true;
  }
 
  if (ExistingLangOpts.CommentOpts.BlockCommandNames !=
      LangOpts.CommentOpts.BlockCommandNames) {
    if (Diags)
      Diags->Report(diag::err_ast_file_langopt_value_mismatch)
          << "block command names" << ModuleFilename;
    return true;
  }
 
  // Sanitizer feature mismatches are treated as compatible differences. If
  // compatible differences aren't allowed, we still only want to check for
  // mismatches of non-modular sanitizers (the only ones which can affect AST
  // generation).
  if (!AllowCompatibleDifferences) {
    SanitizerMask ModularSanitizers = getPPTransparentSanitizers();
    SanitizerSet ExistingSanitizers = ExistingLangOpts.Sanitize;
    SanitizerSet ImportedSanitizers = LangOpts.Sanitize;
    ExistingSanitizers.clear(ModularSanitizers);
    ImportedSanitizers.clear(ModularSanitizers);
    if (ExistingSanitizers.Mask != ImportedSanitizers.Mask) {
      const std::string Flag = "-fsanitize=";
      if (Diags) {
#define SANITIZER(NAME, ID)                                                    \
  {                                                                            \
    bool InExistingModule = ExistingSanitizers.has(SanitizerKind::ID);         \
    bool InImportedModule = ImportedSanitizers.has(SanitizerKind::ID);         \
    if (InExistingModule != InImportedModule)                                  \
      Diags->Report(diag::err_ast_file_targetopt_feature_mismatch)             \
          << InExistingModule << ModuleFilename << (Flag + NAME);              \
  }
#include "clang/Basic/Sanitizers.def"
      }
      return true;
    }
  }
 
  return false;
}
 
/// Compare the given set of target options against an existing set of
/// target options.
///
/// \param Diags If non-NULL, diagnostics will be emitted via this engine.
///
/// \returns true if the target options mis-match, false otherwise.
static bool checkTargetOptions(const TargetOptions &TargetOpts,
                               const TargetOptions &ExistingTargetOpts,
                               StringRef ModuleFilename,
                               DiagnosticsEngine *Diags,
                               bool AllowCompatibleDifferences = true) {
#define CHECK_TARGET_OPT(Field, Name)                                          \
  if (TargetOpts.Field != ExistingTargetOpts.Field) {                          \
    if (Diags)                                                                 \
      Diags->Report(diag::err_ast_file_targetopt_mismatch)                     \
          << ModuleFilename << Name << TargetOpts.Field                        \
          << ExistingTargetOpts.Field;                                         \
    return true;                                                               \
  }
 
  // The triple and ABI must match exactly.
  CHECK_TARGET_OPT(Triple, "target");
  CHECK_TARGET_OPT(ABI, "target ABI");
 
  // We can tolerate different CPUs in many cases, notably when one CPU
  // supports a strict superset of another. When allowing compatible
  // differences skip this check.
  if (!AllowCompatibleDifferences) {
    CHECK_TARGET_OPT(CPU, "target CPU");
    CHECK_TARGET_OPT(TuneCPU, "tune CPU");
  }
 
#undef CHECK_TARGET_OPT
 
  // Compare feature sets.
  SmallVector<StringRef, 4> ExistingFeatures(
                                             ExistingTargetOpts.FeaturesAsWritten.begin(),
                                             ExistingTargetOpts.FeaturesAsWritten.end());
  SmallVector<StringRef, 4> ReadFeatures(TargetOpts.FeaturesAsWritten.begin(),
                                         TargetOpts.FeaturesAsWritten.end());
  llvm::sort(ExistingFeatures);
  llvm::sort(ReadFeatures);
 
  // We compute the set difference in both directions explicitly so that we can
  // diagnose the differences differently.
  SmallVector<StringRef, 4> UnmatchedExistingFeatures, UnmatchedReadFeatures;
  std::set_difference(
      ExistingFeatures.begin(), ExistingFeatures.end(), ReadFeatures.begin(),
      ReadFeatures.end(), std::back_inserter(UnmatchedExistingFeatures));
  std::set_difference(ReadFeatures.begin(), ReadFeatures.end(),
                      ExistingFeatures.begin(), ExistingFeatures.end(),
                      std::back_inserter(UnmatchedReadFeatures));
 
  // If we are allowing compatible differences and the read feature set is
  // a strict subset of the existing feature set, there is nothing to diagnose.
  if (AllowCompatibleDifferences && UnmatchedReadFeatures.empty())
    return false;
 
  if (Diags) {
    for (StringRef Feature : UnmatchedReadFeatures)
      Diags->Report(diag::err_ast_file_targetopt_feature_mismatch)
          << /* is-existing-feature */ false << ModuleFilename << Feature;
    for (StringRef Feature : UnmatchedExistingFeatures)
      Diags->Report(diag::err_ast_file_targetopt_feature_mismatch)
          << /* is-existing-feature */ true << ModuleFilename << Feature;
  }
 
  return !UnmatchedReadFeatures.empty() || !UnmatchedExistingFeatures.empty();
}
 
bool PCHValidator::ReadLanguageOptions(const LangOptions &LangOpts,
                                       StringRef ModuleFilename, bool Complain,
                                       bool AllowCompatibleDifferences) {
  const LangOptions &ExistingLangOpts = PP.getLangOpts();
  return checkLanguageOptions(LangOpts, ExistingLangOpts, ModuleFilename,
                              Complain ? &Reader.Diags : nullptr,
                              AllowCompatibleDifferences);
}
 
bool PCHValidator::ReadTargetOptions(const TargetOptions &TargetOpts,
                                     StringRef ModuleFilename, bool Complain,
                                     bool AllowCompatibleDifferences) {
  const TargetOptions &ExistingTargetOpts = PP.getTargetInfo().getTargetOpts();
  return checkTargetOptions(TargetOpts, ExistingTargetOpts, ModuleFilename,
                            Complain ? &Reader.Diags : nullptr,
                            AllowCompatibleDifferences);
}
 
namespace {
 
using MacroDefinitionsMap =
    llvm::StringMap<std::pair<StringRef, bool /*IsUndef*/>>;
using DeclsMap = llvm::DenseMap<DeclarationName, SmallVector<NamedDecl *, 8>>;
 
} // namespace
 
static bool checkDiagnosticGroupMappings(DiagnosticsEngine &StoredDiags,
                                         DiagnosticsEngine &Diags,
                                         StringRef ModuleFilename,
                                         bool Complain) {
  using Level = DiagnosticsEngine::Level;
 
  // Check current mappings for new -Werror mappings, and the stored mappings
  // for cases that were explicitly mapped to *not* be errors that are now
  // errors because of options like -Werror.
  DiagnosticsEngine *MappingSources[] = { &Diags, &StoredDiags };
 
  for (DiagnosticsEngine *MappingSource : MappingSources) {
    for (auto DiagIDMappingPair : MappingSource->getDiagnosticMappings()) {
      diag::kind DiagID = DiagIDMappingPair.first;
      Level CurLevel = Diags.getDiagnosticLevel(DiagID, SourceLocation());
      if (CurLevel < DiagnosticsEngine::Error)
        continue; // not significant
      Level StoredLevel =
          StoredDiags.getDiagnosticLevel(DiagID, SourceLocation());
      if (StoredLevel < DiagnosticsEngine::Error) {
        if (Complain)
          Diags.Report(diag::err_ast_file_diagopt_mismatch)
              << "-Werror=" + Diags.getDiagnosticIDs()
                                  ->getWarningOptionForDiag(DiagID)
                                  .str()
              << ModuleFilename;
        return true;
      }
    }
  }
 
  return false;
}
 
static bool isExtHandlingFromDiagsError(DiagnosticsEngine &Diags) {
  diag::Severity Ext = Diags.getExtensionHandlingBehavior();
  if (Ext == diag::Severity::Warning && Diags.getWarningsAsErrors())
    return true;
  return Ext >= diag::Severity::Error;
}
 
static bool checkDiagnosticMappings(DiagnosticsEngine &StoredDiags,
                                    DiagnosticsEngine &Diags,
                                    StringRef ModuleFilename, bool IsSystem,
                                    bool SystemHeaderWarningsInModule,
                                    bool Complain) {
  // Top-level options
  if (IsSystem) {
    if (Diags.getSuppressSystemWarnings())
      return false;
    // If -Wsystem-headers was not enabled before, and it was not explicit,
    // be conservative
    if (StoredDiags.getSuppressSystemWarnings() &&
        !SystemHeaderWarningsInModule) {
      if (Complain)
        Diags.Report(diag::err_ast_file_diagopt_mismatch)
            << "-Wsystem-headers" << ModuleFilename;
      return true;
    }
  }
 
  if (Diags.getWarningsAsErrors() && !StoredDiags.getWarningsAsErrors()) {
    if (Complain)
      Diags.Report(diag::err_ast_file_diagopt_mismatch)
          << "-Werror" << ModuleFilename;
    return true;
  }
 
  if (Diags.getWarningsAsErrors() && Diags.getEnableAllWarnings() &&
      !StoredDiags.getEnableAllWarnings()) {
    if (Complain)
      Diags.Report(diag::err_ast_file_diagopt_mismatch)
          << "-Weverything -Werror" << ModuleFilename;
    return true;
  }
 
  if (isExtHandlingFromDiagsError(Diags) &&
      !isExtHandlingFromDiagsError(StoredDiags)) {
    if (Complain)
      Diags.Report(diag::err_ast_file_diagopt_mismatch)
          << "-pedantic-errors" << ModuleFilename;
    return true;
  }
 
  return checkDiagnosticGroupMappings(StoredDiags, Diags, ModuleFilename,
                                      Complain);
}
 
/// Return the top import module if it is implicit, nullptr otherwise.
static Module *getTopImportImplicitModule(ModuleManager &ModuleMgr,
                                          Preprocessor &PP) {
  // If the original import came from a file explicitly generated by the user,
  // don't check the diagnostic mappings.
  // FIXME: currently this is approximated by checking whether this is not a
  // module import of an implicitly-loaded module file.
  // Note: ModuleMgr.rbegin() may not be the current module, but it must be in
  // the transitive closure of its imports, since unrelated modules cannot be
  // imported until after this module finishes validation.
  ModuleFile *TopImport = &*ModuleMgr.rbegin();
  while (!TopImport->ImportedBy.empty())
    TopImport = TopImport->ImportedBy[0];
  if (TopImport->Kind != MK_ImplicitModule)
    return nullptr;
 
  StringRef ModuleName = TopImport->ModuleName;
  assert(!ModuleName.empty() && "diagnostic options read before module name");
 
  Module *M =
      PP.getHeaderSearchInfo().lookupModule(ModuleName, TopImport->ImportLoc);
  assert(M && "missing module");
  return M;
}
 
bool PCHValidator::ReadDiagnosticOptions(
    IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts, StringRef ModuleFilename,
    bool Complain) {
  DiagnosticsEngine &ExistingDiags = PP.getDiagnostics();
  IntrusiveRefCntPtr<DiagnosticIDs> DiagIDs(ExistingDiags.getDiagnosticIDs());
  IntrusiveRefCntPtr<DiagnosticsEngine> Diags(
      new DiagnosticsEngine(DiagIDs, DiagOpts.get()));
  // This should never fail, because we would have processed these options
  // before writing them to an ASTFile.
  ProcessWarningOptions(*Diags, *DiagOpts, /*Report*/false);
 
  ModuleManager &ModuleMgr = Reader.getModuleManager();
  assert(ModuleMgr.size() >= 1 && "what ASTFile is this then");
 
  Module *TopM = getTopImportImplicitModule(ModuleMgr, PP);
  if (!TopM)
    return false;
 
  Module *Importer = PP.getCurrentModule();
 
  DiagnosticOptions &ExistingOpts = ExistingDiags.getDiagnosticOptions();
  bool SystemHeaderWarningsInModule =
      Importer && llvm::is_contained(ExistingOpts.SystemHeaderWarningsModules,
                                     Importer->Name);
 
  // FIXME: if the diagnostics are incompatible, save a DiagnosticOptions that
  // contains the union of their flags.
  return checkDiagnosticMappings(*Diags, ExistingDiags, ModuleFilename,
                                 TopM->IsSystem, SystemHeaderWarningsInModule,
                                 Complain);
}
 
/// Collect the macro definitions provided by the given preprocessor
/// options.
static void
collectMacroDefinitions(const PreprocessorOptions &PPOpts,
                        MacroDefinitionsMap &Macros,
                        SmallVectorImpl<StringRef> *MacroNames = nullptr) {
  for (unsigned I = 0, N = PPOpts.Macros.size(); I != N; ++I) {
    StringRef Macro = PPOpts.Macros[I].first;
    bool IsUndef = PPOpts.Macros[I].second;
 
    std::pair<StringRef, StringRef> MacroPair = Macro.split('=');
    StringRef MacroName = MacroPair.first;
    StringRef MacroBody = MacroPair.second;
 
    // For an #undef'd macro, we only care about the name.
    if (IsUndef) {
      if (MacroNames && !Macros.count(MacroName))
        MacroNames->push_back(MacroName);
 
      Macros[MacroName] = std::make_pair("", true);
      continue;
    }
 
    // For a #define'd macro, figure out the actual definition.
    if (MacroName.size() == Macro.size())
      MacroBody = "1";
    else {
      // Note: GCC drops anything following an end-of-line character.
      StringRef::size_type End = MacroBody.find_first_of("\n\r");
      MacroBody = MacroBody.substr(0, End);
    }
 
    if (MacroNames && !Macros.count(MacroName))
      MacroNames->push_back(MacroName);
    Macros[MacroName] = std::make_pair(MacroBody, false);
  }
}
 
enum OptionValidation {
  OptionValidateNone,
  OptionValidateContradictions,
  OptionValidateStrictMatches,
};
 
/// Check the preprocessor options deserialized from the control block
/// against the preprocessor options in an existing preprocessor.
///
/// \param Diags If non-null, produce diagnostics for any mismatches incurred.
/// \param Validation If set to OptionValidateNone, ignore differences in
///        preprocessor options. If set to OptionValidateContradictions,
///        require that options passed both in the AST file and on the command
///        line (-D or -U) match, but tolerate options missing in one or the
///        other. If set to OptionValidateContradictions, require that there
///        are no differences in the options between the two.
static bool checkPreprocessorOptions(
    const PreprocessorOptions &PPOpts,
    const PreprocessorOptions &ExistingPPOpts, StringRef ModuleFilename,
    bool ReadMacros, DiagnosticsEngine *Diags, FileManager &FileMgr,
    std::string &SuggestedPredefines, const LangOptions &LangOpts,
    OptionValidation Validation = OptionValidateContradictions) {
  if (ReadMacros) {
    // Check macro definitions.
    MacroDefinitionsMap ASTFileMacros;
    collectMacroDefinitions(PPOpts, ASTFileMacros);
    MacroDefinitionsMap ExistingMacros;
    SmallVector<StringRef, 4> ExistingMacroNames;
    collectMacroDefinitions(ExistingPPOpts, ExistingMacros,
                            &ExistingMacroNames);
 
    // Use a line marker to enter the <command line> file, as the defines and
    // undefines here will have come from the command line.
    SuggestedPredefines += "# 1 \"<command line>\" 1\n";
 
    for (unsigned I = 0, N = ExistingMacroNames.size(); I != N; ++I) {
      // Dig out the macro definition in the existing preprocessor options.
      StringRef MacroName = ExistingMacroNames[I];
      std::pair<StringRef, bool> Existing = ExistingMacros[MacroName];
 
      // Check whether we know anything about this macro name or not.
      llvm::StringMap<std::pair<StringRef, bool /*IsUndef*/>>::iterator Known =
          ASTFileMacros.find(MacroName);
      if (Validation == OptionValidateNone || Known == ASTFileMacros.end()) {
        if (Validation == OptionValidateStrictMatches) {
          // If strict matches are requested, don't tolerate any extra defines
          // on the command line that are missing in the AST file.
          if (Diags) {
            Diags->Report(diag::err_ast_file_macro_def_undef)
                << MacroName << true << ModuleFilename;
          }
          return true;
        }
        // FIXME: Check whether this identifier was referenced anywhere in the
        // AST file. If so, we should reject the AST file. Unfortunately, this
        // information isn't in the control block. What shall we do about it?
 
        if (Existing.second) {
          SuggestedPredefines += "#undef ";
          SuggestedPredefines += MacroName.str();
          SuggestedPredefines += '\n';
        } else {
          SuggestedPredefines += "#define ";
          SuggestedPredefines += MacroName.str();
          SuggestedPredefines += ' ';
          SuggestedPredefines += Existing.first.str();
          SuggestedPredefines += '\n';
        }
        continue;
      }
 
      // If the macro was defined in one but undef'd in the other, we have a
      // conflict.
      if (Existing.second != Known->second.second) {
        if (Diags) {
          Diags->Report(diag::err_ast_file_macro_def_undef)
              << MacroName << Known->second.second << ModuleFilename;
        }
        return true;
      }
 
      // If the macro was #undef'd in both, or if the macro bodies are
      // identical, it's fine.
      if (Existing.second || Existing.first == Known->second.first) {
        ASTFileMacros.erase(Known);
        continue;
      }
 
      // The macro bodies differ; complain.
      if (Diags) {
        Diags->Report(diag::err_ast_file_macro_def_conflict)
            << MacroName << Known->second.first << Existing.first
            << ModuleFilename;
      }
      return true;
    }
 
    // Leave the <command line> file and return to <built-in>.
    SuggestedPredefines += "# 1 \"<built-in>\" 2\n";
 
    if (Validation == OptionValidateStrictMatches) {
      // If strict matches are requested, don't tolerate any extra defines in
      // the AST file that are missing on the command line.
      for (const auto &MacroName : ASTFileMacros.keys()) {
        if (Diags) {
          Diags->Report(diag::err_ast_file_macro_def_undef)
              << MacroName << false << ModuleFilename;
        }
        return true;
      }
    }
  }
 
  // Check whether we're using predefines.
  if (PPOpts.UsePredefines != ExistingPPOpts.UsePredefines &&
      Validation != OptionValidateNone) {
    if (Diags) {
      Diags->Report(diag::err_ast_file_undef)
          << ExistingPPOpts.UsePredefines << ModuleFilename;
    }
    return true;
  }
 
  // Detailed record is important since it is used for the module cache hash.
  if (LangOpts.Modules &&
      PPOpts.DetailedRecord != ExistingPPOpts.DetailedRecord &&
      Validation != OptionValidateNone) {
    if (Diags) {
      Diags->Report(diag::err_ast_file_pp_detailed_record)
          << PPOpts.DetailedRecord << ModuleFilename;
    }
    return true;
  }
 
  // Compute the #include and #include_macros lines we need.
  for (unsigned I = 0, N = ExistingPPOpts.Includes.size(); I != N; ++I) {
    StringRef File = ExistingPPOpts.Includes[I];
 
    if (!ExistingPPOpts.ImplicitPCHInclude.empty() &&
        !ExistingPPOpts.PCHThroughHeader.empty()) {
      // In case the through header is an include, we must add all the includes
      // to the predefines so the start point can be determined.
      SuggestedPredefines += "#include \"";
      SuggestedPredefines += File;
      SuggestedPredefines += "\"\n";
      continue;
    }
 
    if (File == ExistingPPOpts.ImplicitPCHInclude)
      continue;
 
    if (llvm::is_contained(PPOpts.Includes, File))
      continue;
 
    SuggestedPredefines += "#include \"";
    SuggestedPredefines += File;
    SuggestedPredefines += "\"\n";
  }
 
  for (unsigned I = 0, N = ExistingPPOpts.MacroIncludes.size(); I != N; ++I) {
    StringRef File = ExistingPPOpts.MacroIncludes[I];
    if (llvm::is_contained(PPOpts.MacroIncludes, File))
      continue;
 
    SuggestedPredefines += "#__include_macros \"";
    SuggestedPredefines += File;
    SuggestedPredefines += "\"\n##\n";
  }
 
  return false;
}
 
bool PCHValidator::ReadPreprocessorOptions(const PreprocessorOptions &PPOpts,
                                           StringRef ModuleFilename,
                                           bool ReadMacros, bool Complain,
                                           std::string &SuggestedPredefines) {
  const PreprocessorOptions &ExistingPPOpts = PP.getPreprocessorOpts();
 
  return checkPreprocessorOptions(
      PPOpts, ExistingPPOpts, ModuleFilename, ReadMacros,
      Complain ? &Reader.Diags : nullptr, PP.getFileManager(),
      SuggestedPredefines, PP.getLangOpts());
}
 
bool SimpleASTReaderListener::ReadPreprocessorOptions(
    const PreprocessorOptions &PPOpts, StringRef ModuleFilename,
    bool ReadMacros, bool Complain, std::string &SuggestedPredefines) {
  return checkPreprocessorOptions(PPOpts, PP.getPreprocessorOpts(),
                                  ModuleFilename, ReadMacros, nullptr,
                                  PP.getFileManager(), SuggestedPredefines,
                                  PP.getLangOpts(), OptionValidateNone);
}
 
/// Check that the specified and the existing module cache paths are equivalent.
///
/// \param Diags If non-null, produce diagnostics for any mismatches incurred.
/// \returns true when the module cache paths differ.
static bool checkModuleCachePath(llvm::vfs::FileSystem &VFS,
                                 StringRef SpecificModuleCachePath,
                                 StringRef ExistingModuleCachePath,
                                 StringRef ModuleFilename,
                                 DiagnosticsEngine *Diags,
                                 const LangOptions &LangOpts,
                                 const PreprocessorOptions &PPOpts) {
  if (!LangOpts.Modules || PPOpts.AllowPCHWithDifferentModulesCachePath ||
      SpecificModuleCachePath == ExistingModuleCachePath)
    return false;
  auto EqualOrErr =
      VFS.equivalent(SpecificModuleCachePath, ExistingModuleCachePath);
  if (EqualOrErr && *EqualOrErr)
    return false;
  if (Diags)
    Diags->Report(diag::err_ast_file_modulecache_mismatch)
        << SpecificModuleCachePath << ExistingModuleCachePath << ModuleFilename;
  return true;
}
 
bool PCHValidator::ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                           StringRef ModuleFilename,
                                           StringRef SpecificModuleCachePath,
                                           bool Complain) {
  return checkModuleCachePath(
      Reader.getFileManager().getVirtualFileSystem(), SpecificModuleCachePath,
      PP.getHeaderSearchInfo().getModuleCachePath(), ModuleFilename,
      Complain ? &Reader.Diags : nullptr, PP.getLangOpts(),
      PP.getPreprocessorOpts());
}
 
void PCHValidator::ReadCounter(const ModuleFile &M, unsigned Value) {
  PP.setCounterValue(Value);
}
 
//===----------------------------------------------------------------------===//
// AST reader implementation
//===----------------------------------------------------------------------===//
 
static uint64_t readULEB(const unsigned char *&P) {
  unsigned Length = 0;
  const char *Error = nullptr;
 
  uint64_t Val = llvm::decodeULEB128(P, &Length, nullptr, &Error);
  if (Error)
    llvm::report_fatal_error(Error);
  P += Length;
  return Val;
}
 
/// Read ULEB-encoded key length and data length.
static std::pair<unsigned, unsigned>
readULEBKeyDataLength(const unsigned char *&P) {
  unsigned KeyLen = readULEB(P);
  if ((unsigned)KeyLen != KeyLen)
    llvm::report_fatal_error("key too large");
 
  unsigned DataLen = readULEB(P);
  if ((unsigned)DataLen != DataLen)
    llvm::report_fatal_error("data too large");
 
  return std::make_pair(KeyLen, DataLen);
}
 
void ASTReader::setDeserializationListener(ASTDeserializationListener *Listener,
                                           bool TakeOwnership) {
  DeserializationListener = Listener;
  OwnsDeserializationListener = TakeOwnership;
}
 
unsigned ASTSelectorLookupTrait::ComputeHash(Selector Sel) {
  return serialization::ComputeHash(Sel);
}
 
LocalDeclID LocalDeclID::get(ASTReader &Reader, ModuleFile &MF, DeclID Value) {
  LocalDeclID ID(Value);
#ifndef NDEBUG
  if (!MF.ModuleOffsetMap.empty())
    Reader.ReadModuleOffsetMap(MF);
 
  unsigned ModuleFileIndex = ID.getModuleFileIndex();
  unsigned LocalDeclID = ID.getLocalDeclIndex();
 
  assert(ModuleFileIndex <= MF.TransitiveImports.size());
 
  ModuleFile *OwningModuleFile =
      ModuleFileIndex == 0 ? &MF : MF.TransitiveImports[ModuleFileIndex - 1];
  assert(OwningModuleFile);
 
  unsigned LocalNumDecls = OwningModuleFile->LocalNumDecls;
 
  if (!ModuleFileIndex)
    LocalNumDecls += NUM_PREDEF_DECL_IDS;
 
  assert(LocalDeclID < LocalNumDecls);
#endif
  (void)Reader;
  (void)MF;
  return ID;
}
 
LocalDeclID LocalDeclID::get(ASTReader &Reader, ModuleFile &MF,
                             unsigned ModuleFileIndex, unsigned LocalDeclID) {
  DeclID Value = (DeclID)ModuleFileIndex << 32 | (DeclID)LocalDeclID;
  return LocalDeclID::get(Reader, MF, Value);
}
 
std::pair<unsigned, unsigned>
ASTSelectorLookupTrait::ReadKeyDataLength(const unsigned char*& d) {
  return readULEBKeyDataLength(d);
}
 
ASTSelectorLookupTrait::internal_key_type
ASTSelectorLookupTrait::ReadKey(const unsigned char* d, unsigned) {
  using namespace llvm::support;
 
  SelectorTable &SelTable = Reader.getContext().Selectors;
  unsigned N = endian::readNext<uint16_t, llvm::endianness::little>(d);
  const IdentifierInfo *FirstII = Reader.getLocalIdentifier(
      F, endian::readNext<IdentifierID, llvm::endianness::little>(d));
  if (N == 0)
    return SelTable.getNullarySelector(FirstII);
  else if (N == 1)
    return SelTable.getUnarySelector(FirstII);
 
  SmallVector<const IdentifierInfo *, 16> Args;
  Args.push_back(FirstII);
  for (unsigned I = 1; I != N; ++I)
    Args.push_back(Reader.getLocalIdentifier(
        F, endian::readNext<IdentifierID, llvm::endianness::little>(d)));
 
  return SelTable.getSelector(N, Args.data());
}
 
ASTSelectorLookupTrait::data_type
ASTSelectorLookupTrait::ReadData(Selector, const unsigned char* d,
                                 unsigned DataLen) {
  using namespace llvm::support;
 
  data_type Result;
 
  Result.ID = Reader.getGlobalSelectorID(
      F, endian::readNext<uint32_t, llvm::endianness::little>(d));
  unsigned FullInstanceBits =
      endian::readNext<uint16_t, llvm::endianness::little>(d);
  unsigned FullFactoryBits =
      endian::readNext<uint16_t, llvm::endianness::little>(d);
  Result.InstanceBits = FullInstanceBits & 0x3;
  Result.InstanceHasMoreThanOneDecl = (FullInstanceBits >> 2) & 0x1;
  Result.FactoryBits = FullFactoryBits & 0x3;
  Result.FactoryHasMoreThanOneDecl = (FullFactoryBits >> 2) & 0x1;
  unsigned NumInstanceMethods = FullInstanceBits >> 3;
  unsigned NumFactoryMethods = FullFactoryBits >> 3;
 
  // Load instance methods
  for (unsigned I = 0; I != NumInstanceMethods; ++I) {
    if (ObjCMethodDecl *Method = Reader.GetLocalDeclAs<ObjCMethodDecl>(
            F, LocalDeclID::get(
                   Reader, F,
                   endian::readNext<DeclID, llvm::endianness::little>(d))))
      Result.Instance.push_back(Method);
  }
 
  // Load factory methods
  for (unsigned I = 0; I != NumFactoryMethods; ++I) {
    if (ObjCMethodDecl *Method = Reader.GetLocalDeclAs<ObjCMethodDecl>(
            F, LocalDeclID::get(
                   Reader, F,
                   endian::readNext<DeclID, llvm::endianness::little>(d))))
      Result.Factory.push_back(Method);
  }
 
  return Result;
}
 
unsigned ASTIdentifierLookupTraitBase::ComputeHash(const internal_key_type& a) {
  return llvm::djbHash(a);
}
 
std::pair<unsigned, unsigned>
ASTIdentifierLookupTraitBase::ReadKeyDataLength(const unsigned char*& d) {
  return readULEBKeyDataLength(d);
}
 
ASTIdentifierLookupTraitBase::internal_key_type
ASTIdentifierLookupTraitBase::ReadKey(const unsigned char* d, unsigned n) {
  assert(n >= 2 && d[n-1] == '\0');
  return StringRef((const char*) d, n-1);
}
 
/// Whether the given identifier is "interesting".
static bool isInterestingIdentifier(ASTReader &Reader, const IdentifierInfo &II,
                                    bool IsModule) {
  bool IsInteresting =
      II.getNotableIdentifierID() != tok::NotableIdentifierKind::not_notable ||
      II.getBuiltinID() != Builtin::ID::NotBuiltin ||
      II.getObjCKeywordID() != tok::ObjCKeywordKind::objc_not_keyword;
  return II.hadMacroDefinition() || II.isPoisoned() ||
         (!IsModule && IsInteresting) || II.hasRevertedTokenIDToIdentifier() ||
         (!(IsModule && Reader.getPreprocessor().getLangOpts().CPlusPlus) &&
          II.getFETokenInfo());
}
 
static bool readBit(unsigned &Bits) {
  bool Value = Bits & 0x1;
  Bits >>= 1;
  return Value;
}
 
IdentifierID ASTIdentifierLookupTrait::ReadIdentifierID(const unsigned char *d) {
  using namespace llvm::support;
 
  IdentifierID RawID =
      endian::readNext<IdentifierID, llvm::endianness::little>(d);
  return Reader.getGlobalIdentifierID(F, RawID >> 1);
}
 
static void markIdentifierFromAST(ASTReader &Reader, IdentifierInfo &II,
                                  bool IsModule) {
  if (!II.isFromAST()) {
    II.setIsFromAST();
    if (isInterestingIdentifier(Reader, II, IsModule))
      II.setChangedSinceDeserialization();
  }
}
 
IdentifierInfo *ASTIdentifierLookupTrait::ReadData(const internal_key_type& k,
                                                   const unsigned char* d,
                                                   unsigned DataLen) {
  using namespace llvm::support;
 
  IdentifierID RawID =
      endian::readNext<IdentifierID, llvm::endianness::little>(d);
  bool IsInteresting = RawID & 0x01;
 
  DataLen -= sizeof(IdentifierID);
 
  // Wipe out the "is interesting" bit.
  RawID = RawID >> 1;
 
  // Build the IdentifierInfo and link the identifier ID with it.
  IdentifierInfo *II = KnownII;
  if (!II) {
    II = &Reader.getIdentifierTable().getOwn(k);
    KnownII = II;
  }
  bool IsModule = Reader.getPreprocessor().getCurrentModule() != nullptr;
  markIdentifierFromAST(Reader, *II, IsModule);
  Reader.markIdentifierUpToDate(II);
 
  IdentifierID ID = Reader.getGlobalIdentifierID(F, RawID);
  if (!IsInteresting) {
    // For uninteresting identifiers, there's nothing else to do. Just notify
    // the reader that we've finished loading this identifier.
    Reader.SetIdentifierInfo(ID, II);
    return II;
  }
 
  unsigned ObjCOrBuiltinID =
      endian::readNext<uint16_t, llvm::endianness::little>(d);
  unsigned Bits = endian::readNext<uint16_t, llvm::endianness::little>(d);
  bool CPlusPlusOperatorKeyword = readBit(Bits);
  bool HasRevertedTokenIDToIdentifier = readBit(Bits);
  bool Poisoned = readBit(Bits);
  bool ExtensionToken = readBit(Bits);
  bool HadMacroDefinition = readBit(Bits);
 
  assert(Bits == 0 && "Extra bits in the identifier?");
  DataLen -= sizeof(uint16_t) * 2;
 
  // Set or check the various bits in the IdentifierInfo structure.
  // Token IDs are read-only.
  if (HasRevertedTokenIDToIdentifier && II->getTokenID() != tok::identifier)
    II->revertTokenIDToIdentifier();
  if (!F.isModule())
    II->setObjCOrBuiltinID(ObjCOrBuiltinID);
  assert(II->isExtensionToken() == ExtensionToken &&
         "Incorrect extension token flag");
  (void)ExtensionToken;
  if (Poisoned)
    II->setIsPoisoned(true);
  assert(II->isCPlusPlusOperatorKeyword() == CPlusPlusOperatorKeyword &&
         "Incorrect C++ operator keyword flag");
  (void)CPlusPlusOperatorKeyword;
 
  // If this identifier is a macro, deserialize the macro
  // definition.
  if (HadMacroDefinition) {
    uint32_t MacroDirectivesOffset =
        endian::readNext<uint32_t, llvm::endianness::little>(d);
    DataLen -= 4;
 
    Reader.addPendingMacro(II, &F, MacroDirectivesOffset);
  }
 
  Reader.SetIdentifierInfo(ID, II);
 
  // Read all of the declarations visible at global scope with this
  // name.
  if (DataLen > 0) {
    SmallVector<GlobalDeclID, 4> DeclIDs;
    for (; DataLen > 0; DataLen -= sizeof(DeclID))
      DeclIDs.push_back(Reader.getGlobalDeclID(
          F, LocalDeclID::get(
                 Reader, F,
                 endian::readNext<DeclID, llvm::endianness::little>(d))));
    Reader.SetGloballyVisibleDecls(II, DeclIDs);
  }
 
  return II;
}
 
DeclarationNameKey::DeclarationNameKey(DeclarationName Name)
    : Kind(Name.getNameKind()) {
  switch (Kind) {
  case DeclarationName::Identifier:
    Data = (uint64_t)Name.getAsIdentifierInfo();
    break;
  case DeclarationName::ObjCZeroArgSelector:
  case DeclarationName::ObjCOneArgSelector:
  case DeclarationName::ObjCMultiArgSelector:
    Data = (uint64_t)Name.getObjCSelector().getAsOpaquePtr();
    break;
  case DeclarationName::CXXOperatorName:
    Data = Name.getCXXOverloadedOperator();
    break;
  case DeclarationName::CXXLiteralOperatorName:
    Data = (uint64_t)Name.getCXXLiteralIdentifier();
    break;
  case DeclarationName::CXXDeductionGuideName:
    Data = (uint64_t)Name.getCXXDeductionGuideTemplate()
               ->getDeclName().getAsIdentifierInfo();
    break;
  case DeclarationName::CXXConstructorName:
  case DeclarationName::CXXDestructorName:
  case DeclarationName::CXXConversionFunctionName:
  case DeclarationName::CXXUsingDirective:
    Data = 0;
    break;
  }
}
 
unsigned DeclarationNameKey::getHash() const {
  llvm::FoldingSetNodeID ID;
  ID.AddInteger(Kind);
 
  switch (Kind) {
  case DeclarationName::Identifier:
  case DeclarationName::CXXLiteralOperatorName:
  case DeclarationName::CXXDeductionGuideName:
    ID.AddString(((IdentifierInfo*)Data)->getName());
    break;
  case DeclarationName::ObjCZeroArgSelector:
  case DeclarationName::ObjCOneArgSelector:
  case DeclarationName::ObjCMultiArgSelector:
    ID.AddInteger(serialization::ComputeHash(Selector(Data)));
    break;
  case DeclarationName::CXXOperatorName:
    ID.AddInteger((OverloadedOperatorKind)Data);
    break;
  case DeclarationName::CXXConstructorName:
  case DeclarationName::CXXDestructorName:
  case DeclarationName::CXXConversionFunctionName:
  case DeclarationName::CXXUsingDirective:
    break;
  }
 
  return ID.computeStableHash();
}
 
ModuleFile *
ASTDeclContextNameLookupTrait::ReadFileRef(const unsigned char *&d) {
  using namespace llvm::support;
 
  uint32_t ModuleFileID =
      endian::readNext<uint32_t, llvm::endianness::little>(d);
  return Reader.getLocalModuleFile(F, ModuleFileID);
}
 
std::pair<unsigned, unsigned>
ASTDeclContextNameLookupTrait::ReadKeyDataLength(const unsigned char *&d) {
  return readULEBKeyDataLength(d);
}
 
ASTDeclContextNameLookupTrait::internal_key_type
ASTDeclContextNameLookupTrait::ReadKey(const unsigned char *d, unsigned) {
  using namespace llvm::support;
 
  auto Kind = (DeclarationName::NameKind)*d++;
  uint64_t Data;
  switch (Kind) {
  case DeclarationName::Identifier:
  case DeclarationName::CXXLiteralOperatorName:
  case DeclarationName::CXXDeductionGuideName:
    Data = (uint64_t)Reader.getLocalIdentifier(
        F, endian::readNext<IdentifierID, llvm::endianness::little>(d));
    break;
  case DeclarationName::ObjCZeroArgSelector:
  case DeclarationName::ObjCOneArgSelector:
  case DeclarationName::ObjCMultiArgSelector:
    Data = (uint64_t)Reader
               .getLocalSelector(
                   F, endian::readNext<uint32_t, llvm::endianness::little>(d))
               .getAsOpaquePtr();
    break;
  case DeclarationName::CXXOperatorName:
    Data = *d++; // OverloadedOperatorKind
    break;
  case DeclarationName::CXXConstructorName:
  case DeclarationName::CXXDestructorName:
  case DeclarationName::CXXConversionFunctionName:
  case DeclarationName::CXXUsingDirective:
    Data = 0;
    break;
  }
 
  return DeclarationNameKey(Kind, Data);
}
 
void ASTDeclContextNameLookupTrait::ReadDataInto(internal_key_type,
                                                 const unsigned char *d,
                                                 unsigned DataLen,
                                                 data_type_builder &Val) {
  using namespace llvm::support;
 
  for (unsigned NumDecls = DataLen / sizeof(DeclID); NumDecls; --NumDecls) {
    LocalDeclID ID = LocalDeclID::get(
        Reader, F, endian::readNext<DeclID, llvm::endianness::little>(d));
    Val.insert(Reader.getGlobalDeclID(F, ID));
  }
}
 
bool ASTReader::ReadLexicalDeclContextStorage(ModuleFile &M,
                                              BitstreamCursor &Cursor,
                                              uint64_t Offset,
                                              DeclContext *DC) {
  assert(Offset != 0);
 
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err = Cursor.JumpToBit(Offset)) {
    Error(std::move(Err));
    return true;
  }
 
  RecordData Record;
  StringRef Blob;
  Expected<unsigned> MaybeCode = Cursor.ReadCode();
  if (!MaybeCode) {
    Error(MaybeCode.takeError());
    return true;
  }
  unsigned Code = MaybeCode.get();
 
  Expected<unsigned> MaybeRecCode = Cursor.readRecord(Code, Record, &Blob);
  if (!MaybeRecCode) {
    Error(MaybeRecCode.takeError());
    return true;
  }
  unsigned RecCode = MaybeRecCode.get();
  if (RecCode != DECL_CONTEXT_LEXICAL) {
    Error("Expected lexical block");
    return true;
  }
 
  assert(!isa<TranslationUnitDecl>(DC) &&
         "expected a TU_UPDATE_LEXICAL record for TU");
  // If we are handling a C++ class template instantiation, we can see multiple
  // lexical updates for the same record. It's important that we select only one
  // of them, so that field numbering works properly. Just pick the first one we
  // see.
  auto &Lex = LexicalDecls[DC];
  if (!Lex.first) {
    Lex = std::make_pair(
        &M, llvm::ArrayRef(
                reinterpret_cast<const unaligned_decl_id_t *>(Blob.data()),
                Blob.size() / sizeof(DeclID)));
  }
  DC->setHasExternalLexicalStorage(true);
  return false;
}
 
bool ASTReader::ReadVisibleDeclContextStorage(ModuleFile &M,
                                              BitstreamCursor &Cursor,
                                              uint64_t Offset,
                                              GlobalDeclID ID) {
  assert(Offset != 0);
 
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err = Cursor.JumpToBit(Offset)) {
    Error(std::move(Err));
    return true;
  }
 
  RecordData Record;
  StringRef Blob;
  Expected<unsigned> MaybeCode = Cursor.ReadCode();
  if (!MaybeCode) {
    Error(MaybeCode.takeError());
    return true;
  }
  unsigned Code = MaybeCode.get();
 
  Expected<unsigned> MaybeRecCode = Cursor.readRecord(Code, Record, &Blob);
  if (!MaybeRecCode) {
    Error(MaybeRecCode.takeError());
    return true;
  }
  unsigned RecCode = MaybeRecCode.get();
  if (RecCode != DECL_CONTEXT_VISIBLE) {
    Error("Expected visible lookup table block");
    return true;
  }
 
  // We can't safely determine the primary context yet, so delay attaching the
  // lookup table until we're done with recursive deserialization.
  auto *Data = (const unsigned char*)Blob.data();
  PendingVisibleUpdates[ID].push_back(PendingVisibleUpdate{&M, Data});
  return false;
}
 
void ASTReader::Error(StringRef Msg) const {
  Error(diag::err_fe_pch_malformed, Msg);
  if (PP.getLangOpts().Modules && !Diags.isDiagnosticInFlight() &&
      !PP.getHeaderSearchInfo().getModuleCachePath().empty()) {
    Diag(diag::note_module_cache_path)
      << PP.getHeaderSearchInfo().getModuleCachePath();
  }
}
 
void ASTReader::Error(unsigned DiagID, StringRef Arg1, StringRef Arg2,
                      StringRef Arg3) const {
  if (Diags.isDiagnosticInFlight())
    Diags.SetDelayedDiagnostic(DiagID, Arg1, Arg2, Arg3);
  else
    Diag(DiagID) << Arg1 << Arg2 << Arg3;
}
 
void ASTReader::Error(llvm::Error &&Err) const {
  llvm::Error RemainingErr =
      handleErrors(std::move(Err), [this](const DiagnosticError &E) {
        auto Diag = E.getDiagnostic().second;
 
        // Ideally we'd just emit it, but have to handle a possible in-flight
        // diagnostic. Note that the location is currently ignored as well.
        auto NumArgs = Diag.getStorage()->NumDiagArgs;
        assert(NumArgs <= 3 && "Can only have up to 3 arguments");
        StringRef Arg1, Arg2, Arg3;
        switch (NumArgs) {
        case 3:
          Arg3 = Diag.getStringArg(2);
          [[fallthrough]];
        case 2:
          Arg2 = Diag.getStringArg(1);
          [[fallthrough]];
        case 1:
          Arg1 = Diag.getStringArg(0);
        }
        Error(Diag.getDiagID(), Arg1, Arg2, Arg3);
      });
  if (RemainingErr)
    Error(toString(std::move(RemainingErr)));
}
 
//===----------------------------------------------------------------------===//
// Source Manager Deserialization
//===----------------------------------------------------------------------===//
 
/// Read the line table in the source manager block.
void ASTReader::ParseLineTable(ModuleFile &F, const RecordData &Record) {
  unsigned Idx = 0;
  LineTableInfo &LineTable = SourceMgr.getLineTable();
 
  // Parse the file names
  std::map<int, int> FileIDs;
  FileIDs[-1] = -1; // For unspecified filenames.
  for (unsigned I = 0; Record[Idx]; ++I) {
    // Extract the file name
    auto Filename = ReadPath(F, Record, Idx);
    FileIDs[I] = LineTable.getLineTableFilenameID(Filename);
  }
  ++Idx;
 
  // Parse the line entries
  std::vector<LineEntry> Entries;
  while (Idx < Record.size()) {
    FileID FID = ReadFileID(F, Record, Idx);
 
    // Extract the line entries
    unsigned NumEntries = Record[Idx++];
    assert(NumEntries && "no line entries for file ID");
    Entries.clear();
    Entries.reserve(NumEntries);
    for (unsigned I = 0; I != NumEntries; ++I) {
      unsigned FileOffset = Record[Idx++];
      unsigned LineNo = Record[Idx++];
      int FilenameID = FileIDs[Record[Idx++]];
      SrcMgr::CharacteristicKind FileKind
        = (SrcMgr::CharacteristicKind)Record[Idx++];
      unsigned IncludeOffset = Record[Idx++];
      Entries.push_back(LineEntry::get(FileOffset, LineNo, FilenameID,
                                       FileKind, IncludeOffset));
    }
    LineTable.AddEntry(FID, Entries);
  }
}
 
/// Read a source manager block
llvm::Error ASTReader::ReadSourceManagerBlock(ModuleFile &F) {
  using namespace SrcMgr;
 
  BitstreamCursor &SLocEntryCursor = F.SLocEntryCursor;
 
  // Set the source-location entry cursor to the current position in
  // the stream. This cursor will be used to read the contents of the
  // source manager block initially, and then lazily read
  // source-location entries as needed.
  SLocEntryCursor = F.Stream;
 
  // The stream itself is going to skip over the source manager block.
  if (llvm::Error Err = F.Stream.SkipBlock())
    return Err;
 
  // Enter the source manager block.
  if (llvm::Error Err = SLocEntryCursor.EnterSubBlock(SOURCE_MANAGER_BLOCK_ID))
    return Err;
  F.SourceManagerBlockStartOffset = SLocEntryCursor.GetCurrentBitNo();
 
  RecordData Record;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeE =
        SLocEntryCursor.advanceSkippingSubblocks();
    if (!MaybeE)
      return MaybeE.takeError();
    llvm::BitstreamEntry E = MaybeE.get();
 
    switch (E.Kind) {
    case llvm::BitstreamEntry::SubBlock: // Handled for us already.
    case llvm::BitstreamEntry::Error:
      return llvm::createStringError(std::errc::illegal_byte_sequence,
                                     "malformed block record in AST file");
    case llvm::BitstreamEntry::EndBlock:
      return llvm::Error::success();
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read a record.
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecord =
        SLocEntryCursor.readRecord(E.ID, Record, &Blob);
    if (!MaybeRecord)
      return MaybeRecord.takeError();
    switch (MaybeRecord.get()) {
    default:  // Default behavior: ignore.
      break;
 
    case SM_SLOC_FILE_ENTRY:
    case SM_SLOC_BUFFER_ENTRY:
    case SM_SLOC_EXPANSION_ENTRY:
      // Once we hit one of the source location entries, we're done.
      return llvm::Error::success();
    }
  }
}
 
llvm::Expected<SourceLocation::UIntTy>
ASTReader::readSLocOffset(ModuleFile *F, unsigned Index) {
  BitstreamCursor &Cursor = F->SLocEntryCursor;
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err = Cursor.JumpToBit(F->SLocEntryOffsetsBase +
                                         F->SLocEntryOffsets[Index]))
    return std::move(Err);
 
  Expected<llvm::BitstreamEntry> MaybeEntry = Cursor.advance();
  if (!MaybeEntry)
    return MaybeEntry.takeError();
 
  llvm::BitstreamEntry Entry = MaybeEntry.get();
  if (Entry.Kind != llvm::BitstreamEntry::Record)
    return llvm::createStringError(
        std::errc::illegal_byte_sequence,
        "incorrectly-formatted source location entry in AST file");
 
  RecordData Record;
  StringRef Blob;
  Expected<unsigned> MaybeSLOC = Cursor.readRecord(Entry.ID, Record, &Blob);
  if (!MaybeSLOC)
    return MaybeSLOC.takeError();
 
  switch (MaybeSLOC.get()) {
  default:
    return llvm::createStringError(
        std::errc::illegal_byte_sequence,
        "incorrectly-formatted source location entry in AST file");
  case SM_SLOC_FILE_ENTRY:
  case SM_SLOC_BUFFER_ENTRY:
  case SM_SLOC_EXPANSION_ENTRY:
    return F->SLocEntryBaseOffset + Record[0];
  }
}
 
int ASTReader::getSLocEntryID(SourceLocation::UIntTy SLocOffset) {
  auto SLocMapI =
      GlobalSLocOffsetMap.find(SourceManager::MaxLoadedOffset - SLocOffset - 1);
  assert(SLocMapI != GlobalSLocOffsetMap.end() &&
         "Corrupted global sloc offset map");
  ModuleFile *F = SLocMapI->second;
 
  bool Invalid = false;
 
  auto It = llvm::upper_bound(
      llvm::index_range(0, F->LocalNumSLocEntries), SLocOffset,
      [&](SourceLocation::UIntTy Offset, std::size_t LocalIndex) {
        int ID = F->SLocEntryBaseID + LocalIndex;
        std::size_t Index = -ID - 2;
        if (!SourceMgr.SLocEntryOffsetLoaded[Index]) {
          assert(!SourceMgr.SLocEntryLoaded[Index]);
          auto MaybeEntryOffset = readSLocOffset(F, LocalIndex);
          if (!MaybeEntryOffset) {
            Error(MaybeEntryOffset.takeError());
            Invalid = true;
            return true;
          }
          SourceMgr.LoadedSLocEntryTable[Index] =
              SrcMgr::SLocEntry::getOffsetOnly(*MaybeEntryOffset);
          SourceMgr.SLocEntryOffsetLoaded[Index] = true;
        }
        return Offset < SourceMgr.LoadedSLocEntryTable[Index].getOffset();
      });
 
  if (Invalid)
    return 0;
 
  // The iterator points to the first entry with start offset greater than the
  // offset of interest. The previous entry must contain the offset of interest.
  return F->SLocEntryBaseID + *std::prev(It);
}
 
bool ASTReader::ReadSLocEntry(int ID) {
  if (ID == 0)
    return false;
 
  if (unsigned(-ID) - 2 >= getTotalNumSLocs() || ID > 0) {
    Error("source location entry ID out-of-range for AST file");
    return true;
  }
 
  // Local helper to read the (possibly-compressed) buffer data following the
  // entry record.
  auto ReadBuffer = [this](
      BitstreamCursor &SLocEntryCursor,
      StringRef Name) -> std::unique_ptr<llvm::MemoryBuffer> {
    RecordData Record;
    StringRef Blob;
    Expected<unsigned> MaybeCode = SLocEntryCursor.ReadCode();
    if (!MaybeCode) {
      Error(MaybeCode.takeError());
      return nullptr;
    }
    unsigned Code = MaybeCode.get();
 
    Expected<unsigned> MaybeRecCode =
        SLocEntryCursor.readRecord(Code, Record, &Blob);
    if (!MaybeRecCode) {
      Error(MaybeRecCode.takeError());
      return nullptr;
    }
    unsigned RecCode = MaybeRecCode.get();
 
    if (RecCode == SM_SLOC_BUFFER_BLOB_COMPRESSED) {
      // Inspect the first byte to differentiate zlib (\x78) and zstd
      // (little-endian 0xFD2FB528).
      const llvm::compression::Format F =
          Blob.size() > 0 && Blob.data()[0] == 0x78
              ? llvm::compression::Format::Zlib
              : llvm::compression::Format::Zstd;
      if (const char *Reason = llvm::compression::getReasonIfUnsupported(F)) {
        Error(Reason);
        return nullptr;
      }
      SmallVector<uint8_t, 0> Decompressed;
      if (llvm::Error E = llvm::compression::decompress(
              F, llvm::arrayRefFromStringRef(Blob), Decompressed, Record[0])) {
        Error("could not decompress embedded file contents: " +
              llvm::toString(std::move(E)));
        return nullptr;
      }
      return llvm::MemoryBuffer::getMemBufferCopy(
          llvm::toStringRef(Decompressed), Name);
    } else if (RecCode == SM_SLOC_BUFFER_BLOB) {
      return llvm::MemoryBuffer::getMemBuffer(Blob.drop_back(1), Name, true);
    } else {
      Error("AST record has invalid code");
      return nullptr;
    }
  };
 
  ModuleFile *F = GlobalSLocEntryMap.find(-ID)->second;
  if (llvm::Error Err = F->SLocEntryCursor.JumpToBit(
          F->SLocEntryOffsetsBase +
          F->SLocEntryOffsets[ID - F->SLocEntryBaseID])) {
    Error(std::move(Err));
    return true;
  }
 
  BitstreamCursor &SLocEntryCursor = F->SLocEntryCursor;
  SourceLocation::UIntTy BaseOffset = F->SLocEntryBaseOffset;
 
  ++NumSLocEntriesRead;
  Expected<llvm::BitstreamEntry> MaybeEntry = SLocEntryCursor.advance();
  if (!MaybeEntry) {
    Error(MaybeEntry.takeError());
    return true;
  }
  llvm::BitstreamEntry Entry = MaybeEntry.get();
 
  if (Entry.Kind != llvm::BitstreamEntry::Record) {
    Error("incorrectly-formatted source location entry in AST file");
    return true;
  }
 
  RecordData Record;
  StringRef Blob;
  Expected<unsigned> MaybeSLOC =
      SLocEntryCursor.readRecord(Entry.ID, Record, &Blob);
  if (!MaybeSLOC) {
    Error(MaybeSLOC.takeError());
    return true;
  }
  switch (MaybeSLOC.get()) {
  default:
    Error("incorrectly-formatted source location entry in AST file");
    return true;
 
  case SM_SLOC_FILE_ENTRY: {
    // We will detect whether a file changed and return 'Failure' for it, but
    // we will also try to fail gracefully by setting up the SLocEntry.
    unsigned InputID = Record[4];
    InputFile IF = getInputFile(*F, InputID);
    OptionalFileEntryRef File = IF.getFile();
    bool OverriddenBuffer = IF.isOverridden();
 
    // Note that we only check if a File was returned. If it was out-of-date
    // we have complained but we will continue creating a FileID to recover
    // gracefully.
    if (!File)
      return true;
 
    SourceLocation IncludeLoc = ReadSourceLocation(*F, Record[1]);
    if (IncludeLoc.isInvalid() && F->Kind != MK_MainFile) {
      // This is the module's main file.
      IncludeLoc = getImportLocation(F);
    }
    SrcMgr::CharacteristicKind
      FileCharacter = (SrcMgr::CharacteristicKind)Record[2];
    FileID FID = SourceMgr.createFileID(*File, IncludeLoc, FileCharacter, ID,
                                        BaseOffset + Record[0]);
    SrcMgr::FileInfo &FileInfo = SourceMgr.getSLocEntry(FID).getFile();
    FileInfo.NumCreatedFIDs = Record[5];
    if (Record[3])
      FileInfo.setHasLineDirectives();
 
    unsigned NumFileDecls = Record[7];
    if (NumFileDecls && ContextObj) {
      const unaligned_decl_id_t *FirstDecl = F->FileSortedDecls + Record[6];
      assert(F->FileSortedDecls && "FILE_SORTED_DECLS not encountered yet ?");
      FileDeclIDs[FID] =
          FileDeclsInfo(F, llvm::ArrayRef(FirstDecl, NumFileDecls));
    }
 
    const SrcMgr::ContentCache &ContentCache =
        SourceMgr.getOrCreateContentCache(*File, isSystem(FileCharacter));
    if (OverriddenBuffer && !ContentCache.BufferOverridden &&
        ContentCache.ContentsEntry == ContentCache.OrigEntry &&
        !ContentCache.getBufferIfLoaded()) {
      auto Buffer = ReadBuffer(SLocEntryCursor, File->getName());
      if (!Buffer)
        return true;
      SourceMgr.overrideFileContents(*File, std::move(Buffer));
    }
 
    break;
  }
 
  case SM_SLOC_BUFFER_ENTRY: {
    const char *Name = Blob.data();
    unsigned Offset = Record[0];
    SrcMgr::CharacteristicKind
      FileCharacter = (SrcMgr::CharacteristicKind)Record[2];
    SourceLocation IncludeLoc = ReadSourceLocation(*F, Record[1]);
    if (IncludeLoc.isInvalid() && F->isModule()) {
      IncludeLoc = getImportLocation(F);
    }
 
    auto Buffer = ReadBuffer(SLocEntryCursor, Name);
    if (!Buffer)
      return true;
    FileID FID = SourceMgr.createFileID(std::move(Buffer), FileCharacter, ID,
                                        BaseOffset + Offset, IncludeLoc);
    if (Record[3]) {
      auto &FileInfo = SourceMgr.getSLocEntry(FID).getFile();
      FileInfo.setHasLineDirectives();
    }
    break;
  }
 
  case SM_SLOC_EXPANSION_ENTRY: {
    LocSeq::State Seq;
    SourceLocation SpellingLoc = ReadSourceLocation(*F, Record[1], Seq);
    SourceLocation ExpansionBegin = ReadSourceLocation(*F, Record[2], Seq);
    SourceLocation ExpansionEnd = ReadSourceLocation(*F, Record[3], Seq);
    SourceMgr.createExpansionLoc(SpellingLoc, ExpansionBegin, ExpansionEnd,
                                 Record[5], Record[4], ID,
                                 BaseOffset + Record[0]);
    break;
  }
  }
 
  return false;
}
 
std::pair<SourceLocation, StringRef> ASTReader::getModuleImportLoc(int ID) {
  if (ID == 0)
    return std::make_pair(SourceLocation(), "");
 
  if (unsigned(-ID) - 2 >= getTotalNumSLocs() || ID > 0) {
    Error("source location entry ID out-of-range for AST file");
    return std::make_pair(SourceLocation(), "");
  }
 
  // Find which module file this entry lands in.
  ModuleFile *M = GlobalSLocEntryMap.find(-ID)->second;
  if (!M->isModule())
    return std::make_pair(SourceLocation(), "");
 
  // FIXME: Can we map this down to a particular submodule? That would be
  // ideal.
  return std::make_pair(M->ImportLoc, StringRef(M->ModuleName));
}
 
/// Find the location where the module F is imported.
SourceLocation ASTReader::getImportLocation(ModuleFile *F) {
  if (F->ImportLoc.isValid())
    return F->ImportLoc;
 
  // Otherwise we have a PCH. It's considered to be "imported" at the first
  // location of its includer.
  if (F->ImportedBy.empty() || !F->ImportedBy[0]) {
    // Main file is the importer.
    assert(SourceMgr.getMainFileID().isValid() && "missing main file");
    return SourceMgr.getLocForStartOfFile(SourceMgr.getMainFileID());
  }
  return F->ImportedBy[0]->FirstLoc;
}
 
/// Enter a subblock of the specified BlockID with the specified cursor. Read
/// the abbreviations that are at the top of the block and then leave the cursor
/// pointing into the block.
llvm::Error ASTReader::ReadBlockAbbrevs(BitstreamCursor &Cursor,
                                        unsigned BlockID,
                                        uint64_t *StartOfBlockOffset) {
  if (llvm::Error Err = Cursor.EnterSubBlock(BlockID))
    return Err;
 
  if (StartOfBlockOffset)
    *StartOfBlockOffset = Cursor.GetCurrentBitNo();
 
  while (true) {
    uint64_t Offset = Cursor.GetCurrentBitNo();
    Expected<unsigned> MaybeCode = Cursor.ReadCode();
    if (!MaybeCode)
      return MaybeCode.takeError();
    unsigned Code = MaybeCode.get();
 
    // We expect all abbrevs to be at the start of the block.
    if (Code != llvm::bitc::DEFINE_ABBREV) {
      if (llvm::Error Err = Cursor.JumpToBit(Offset))
        return Err;
      return llvm::Error::success();
    }
    if (llvm::Error Err = Cursor.ReadAbbrevRecord())
      return Err;
  }
}
 
Token ASTReader::ReadToken(ModuleFile &M, const RecordDataImpl &Record,
                           unsigned &Idx) {
  Token Tok;
  Tok.startToken();
  Tok.setLocation(ReadSourceLocation(M, Record, Idx));
  Tok.setKind((tok::TokenKind)Record[Idx++]);
  Tok.setFlag((Token::TokenFlags)Record[Idx++]);
 
  if (Tok.isAnnotation()) {
    Tok.setAnnotationEndLoc(ReadSourceLocation(M, Record, Idx));
    switch (Tok.getKind()) {
    case tok::annot_pragma_loop_hint: {
      auto *Info = new (PP.getPreprocessorAllocator()) PragmaLoopHintInfo;
      Info->PragmaName = ReadToken(M, Record, Idx);
      Info->Option = ReadToken(M, Record, Idx);
      unsigned NumTokens = Record[Idx++];
      SmallVector<Token, 4> Toks;
      Toks.reserve(NumTokens);
      for (unsigned I = 0; I < NumTokens; ++I)
        Toks.push_back(ReadToken(M, Record, Idx));
      Info->Toks = llvm::ArrayRef(Toks).copy(PP.getPreprocessorAllocator());
      Tok.setAnnotationValue(static_cast<void *>(Info));
      break;
    }
    case tok::annot_pragma_pack: {
      auto *Info = new (PP.getPreprocessorAllocator()) Sema::PragmaPackInfo;
      Info->Action = static_cast<Sema::PragmaMsStackAction>(Record[Idx++]);
      auto SlotLabel = ReadString(Record, Idx);
      Info->SlotLabel =
          llvm::StringRef(SlotLabel).copy(PP.getPreprocessorAllocator());
      Info->Alignment = ReadToken(M, Record, Idx);
      Tok.setAnnotationValue(static_cast<void *>(Info));
      break;
    }
    // Some annotation tokens do not use the PtrData field.
    case tok::annot_pragma_openmp:
    case tok::annot_pragma_openmp_end:
    case tok::annot_pragma_unused:
    case tok::annot_pragma_openacc:
    case tok::annot_pragma_openacc_end:
    case tok::annot_repl_input_end:
      break;
    default:
      llvm_unreachable("missing deserialization code for annotation token");
    }
  } else {
    Tok.setLength(Record[Idx++]);
    if (IdentifierInfo *II = getLocalIdentifier(M, Record[Idx++]))
      Tok.setIdentifierInfo(II);
  }
  return Tok;
}
 
MacroInfo *ASTReader::ReadMacroRecord(ModuleFile &F, uint64_t Offset) {
  BitstreamCursor &Stream = F.MacroCursor;
 
  // Keep track of where we are in the stream, then jump back there
  // after reading this macro.
  SavedStreamPosition SavedPosition(Stream);
 
  if (llvm::Error Err = Stream.JumpToBit(Offset)) {
    // FIXME this drops errors on the floor.
    consumeError(std::move(Err));
    return nullptr;
  }
  RecordData Record;
  SmallVector<IdentifierInfo*, 16> MacroParams;
  MacroInfo *Macro = nullptr;
  llvm::MutableArrayRef<Token> MacroTokens;
 
  while (true) {
    // Advance to the next record, but if we get to the end of the block, don't
    // pop it (removing all the abbreviations from the cursor) since we want to
    // be able to reseek within the block and read entries.
    unsigned Flags = BitstreamCursor::AF_DontPopBlockAtEnd;
    Expected<llvm::BitstreamEntry> MaybeEntry =
        Stream.advanceSkippingSubblocks(Flags);
    if (!MaybeEntry) {
      Error(MaybeEntry.takeError());
      return Macro;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::SubBlock: // Handled for us already.
    case llvm::BitstreamEntry::Error:
      Error("malformed block record in AST file");
      return Macro;
    case llvm::BitstreamEntry::EndBlock:
      return Macro;
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read a record.
    Record.clear();
    PreprocessorRecordTypes RecType;
    if (Expected<unsigned> MaybeRecType = Stream.readRecord(Entry.ID, Record))
      RecType = (PreprocessorRecordTypes)MaybeRecType.get();
    else {
      Error(MaybeRecType.takeError());
      return Macro;
    }
    switch (RecType) {
    case PP_MODULE_MACRO:
    case PP_MACRO_DIRECTIVE_HISTORY:
      return Macro;
 
    case PP_MACRO_OBJECT_LIKE:
    case PP_MACRO_FUNCTION_LIKE: {
      // If we already have a macro, that means that we've hit the end
      // of the definition of the macro we were looking for. We're
      // done.
      if (Macro)
        return Macro;
 
      unsigned NextIndex = 1; // Skip identifier ID.
      SourceLocation Loc = ReadSourceLocation(F, Record, NextIndex);
      MacroInfo *MI = PP.AllocateMacroInfo(Loc);
      MI->setDefinitionEndLoc(ReadSourceLocation(F, Record, NextIndex));
      MI->setIsUsed(Record[NextIndex++]);
      MI->setUsedForHeaderGuard(Record[NextIndex++]);
      MacroTokens = MI->allocateTokens(Record[NextIndex++],
                                       PP.getPreprocessorAllocator());
      if (RecType == PP_MACRO_FUNCTION_LIKE) {
        // Decode function-like macro info.
        bool isC99VarArgs = Record[NextIndex++];
        bool isGNUVarArgs = Record[NextIndex++];
        bool hasCommaPasting = Record[NextIndex++];
        MacroParams.clear();
        unsigned NumArgs = Record[NextIndex++];
        for (unsigned i = 0; i != NumArgs; ++i)
          MacroParams.push_back(getLocalIdentifier(F, Record[NextIndex++]));
 
        // Install function-like macro info.
        MI->setIsFunctionLike();
        if (isC99VarArgs) MI->setIsC99Varargs();
        if (isGNUVarArgs) MI->setIsGNUVarargs();
        if (hasCommaPasting) MI->setHasCommaPasting();
        MI->setParameterList(MacroParams, PP.getPreprocessorAllocator());
      }
 
      // Remember that we saw this macro last so that we add the tokens that
      // form its body to it.
      Macro = MI;
 
      if (NextIndex + 1 == Record.size() && PP.getPreprocessingRecord() &&
          Record[NextIndex]) {
        // We have a macro definition. Register the association
        PreprocessedEntityID
            GlobalID = getGlobalPreprocessedEntityID(F, Record[NextIndex]);
        PreprocessingRecord &PPRec = *PP.getPreprocessingRecord();
        PreprocessingRecord::PPEntityID PPID =
            PPRec.getPPEntityID(GlobalID - 1, /*isLoaded=*/true);
        MacroDefinitionRecord *PPDef = cast_or_null<MacroDefinitionRecord>(
            PPRec.getPreprocessedEntity(PPID));
        if (PPDef)
          PPRec.RegisterMacroDefinition(Macro, PPDef);
      }
 
      ++NumMacrosRead;
      break;
    }
 
    case PP_TOKEN: {
      // If we see a TOKEN before a PP_MACRO_*, then the file is
      // erroneous, just pretend we didn't see this.
      if (!Macro) break;
      if (MacroTokens.empty()) {
        Error("unexpected number of macro tokens for a macro in AST file");
        return Macro;
      }
 
      unsigned Idx = 0;
      MacroTokens[0] = ReadToken(F, Record, Idx);
      MacroTokens = MacroTokens.drop_front();
      break;
    }
    }
  }
}
 
PreprocessedEntityID
ASTReader::getGlobalPreprocessedEntityID(ModuleFile &M,
                                         unsigned LocalID) const {
  if (!M.ModuleOffsetMap.empty())
    ReadModuleOffsetMap(M);
 
  ContinuousRangeMap<uint32_t, int, 2>::const_iterator
    I = M.PreprocessedEntityRemap.find(LocalID - NUM_PREDEF_PP_ENTITY_IDS);
  assert(I != M.PreprocessedEntityRemap.end()
         && "Invalid index into preprocessed entity index remap");
 
  return LocalID + I->second;
}
 
const FileEntry *HeaderFileInfoTrait::getFile(const internal_key_type &Key) {
  FileManager &FileMgr = Reader.getFileManager();
  if (!Key.Imported) {
    if (auto File = FileMgr.getFile(Key.Filename))
      return *File;
    return nullptr;
  }
 
  std::string Resolved = std::string(Key.Filename);
  Reader.ResolveImportedPath(M, Resolved);
  if (auto File = FileMgr.getFile(Resolved))
    return *File;
  return nullptr;
}
 
unsigned HeaderFileInfoTrait::ComputeHash(internal_key_ref ikey) {
  uint8_t buf[sizeof(ikey.Size) + sizeof(ikey.ModTime)];
  memcpy(buf, &ikey.Size, sizeof(ikey.Size));
  memcpy(buf + sizeof(ikey.Size), &ikey.ModTime, sizeof(ikey.ModTime));
  return llvm::xxh3_64bits(buf);
}
 
HeaderFileInfoTrait::internal_key_type
HeaderFileInfoTrait::GetInternalKey(external_key_type ekey) {
  internal_key_type ikey = {ekey.getSize(),
                            M.HasTimestamps ? ekey.getModificationTime() : 0,
                            ekey.getName(), /*Imported*/ false};
  return ikey;
}
 
bool HeaderFileInfoTrait::EqualKey(internal_key_ref a, internal_key_ref b) {
  if (a.Size != b.Size || (a.ModTime && b.ModTime && a.ModTime != b.ModTime))
    return false;
 
  if (llvm::sys::path::is_absolute(a.Filename) && a.Filename == b.Filename)
    return true;
 
  // Determine whether the actual files are equivalent.
  const FileEntry *FEA = getFile(a);
  const FileEntry *FEB = getFile(b);
  return FEA && FEA == FEB;
}
 
std::pair<unsigned, unsigned>
HeaderFileInfoTrait::ReadKeyDataLength(const unsigned char*& d) {
  return readULEBKeyDataLength(d);
}
 
HeaderFileInfoTrait::internal_key_type
HeaderFileInfoTrait::ReadKey(const unsigned char *d, unsigned) {
  using namespace llvm::support;
 
  internal_key_type ikey;
  ikey.Size = off_t(endian::readNext<uint64_t, llvm::endianness::little>(d));
  ikey.ModTime =
      time_t(endian::readNext<uint64_t, llvm::endianness::little>(d));
  ikey.Filename = (const char *)d;
  ikey.Imported = true;
  return ikey;
}
 
HeaderFileInfoTrait::data_type
HeaderFileInfoTrait::ReadData(internal_key_ref key, const unsigned char *d,
                              unsigned DataLen) {
  using namespace llvm::support;
 
  const unsigned char *End = d + DataLen;
  HeaderFileInfo HFI;
  unsigned Flags = *d++;
 
  bool Included = (Flags >> 6) & 0x01;
  if (Included)
    if (const FileEntry *FE = getFile(key))
      // Not using \c Preprocessor::markIncluded(), since that would attempt to
      // deserialize this header file info again.
      Reader.getPreprocessor().getIncludedFiles().insert(FE);
 
  // FIXME: Refactor with mergeHeaderFileInfo in HeaderSearch.cpp.
  HFI.isImport |= (Flags >> 5) & 0x01;
  HFI.isPragmaOnce |= (Flags >> 4) & 0x01;
  HFI.DirInfo = (Flags >> 1) & 0x07;
  HFI.IndexHeaderMapHeader = Flags & 0x01;
  HFI.LazyControllingMacro = Reader.getGlobalIdentifierID(
      M, endian::readNext<IdentifierID, llvm::endianness::little>(d));
  if (unsigned FrameworkOffset =
          endian::readNext<uint32_t, llvm::endianness::little>(d)) {
    // The framework offset is 1 greater than the actual offset,
    // since 0 is used as an indicator for "no framework name".
    StringRef FrameworkName(FrameworkStrings + FrameworkOffset - 1);
    HFI.Framework = HS->getUniqueFrameworkName(FrameworkName);
  }
 
  assert((End - d) % 4 == 0 &&
         "Wrong data length in HeaderFileInfo deserialization");
  while (d != End) {
    uint32_t LocalSMID =
        endian::readNext<uint32_t, llvm::endianness::little>(d);
    auto HeaderRole = static_cast<ModuleMap::ModuleHeaderRole>(LocalSMID & 7);
    LocalSMID >>= 3;
 
    // This header is part of a module. Associate it with the module to enable
    // implicit module import.
    SubmoduleID GlobalSMID = Reader.getGlobalSubmoduleID(M, LocalSMID);
    Module *Mod = Reader.getSubmodule(GlobalSMID);
    FileManager &FileMgr = Reader.getFileManager();
    ModuleMap &ModMap =
        Reader.getPreprocessor().getHeaderSearchInfo().getModuleMap();
 
    std::string Filename = std::string(key.Filename);
    if (key.Imported)
      Reader.ResolveImportedPath(M, Filename);
    if (auto FE = FileMgr.getOptionalFileRef(Filename)) {
      // FIXME: NameAsWritten
      Module::Header H = {std::string(key.Filename), "", *FE};
      ModMap.addHeader(Mod, H, HeaderRole, /*Imported=*/true);
    }
    HFI.mergeModuleMembership(HeaderRole);
  }
 
  // This HeaderFileInfo was externally loaded.
  HFI.External = true;
  HFI.IsValid = true;
  return HFI;
}
 
void ASTReader::addPendingMacro(IdentifierInfo *II, ModuleFile *M,
                                uint32_t MacroDirectivesOffset) {
  assert(NumCurrentElementsDeserializing > 0 &&"Missing deserialization guard");
  PendingMacroIDs[II].push_back(PendingMacroInfo(M, MacroDirectivesOffset));
}
 
void ASTReader::ReadDefinedMacros() {
  // Note that we are loading defined macros.
  Deserializing Macros(this);
 
  for (ModuleFile &I : llvm::reverse(ModuleMgr)) {
    BitstreamCursor &MacroCursor = I.MacroCursor;
 
    // If there was no preprocessor block, skip this file.
    if (MacroCursor.getBitcodeBytes().empty())
      continue;
 
    BitstreamCursor Cursor = MacroCursor;
    if (llvm::Error Err = Cursor.JumpToBit(I.MacroStartOffset)) {
      Error(std::move(Err));
      return;
    }
 
    RecordData Record;
    while (true) {
      Expected<llvm::BitstreamEntry> MaybeE = Cursor.advanceSkippingSubblocks();
      if (!MaybeE) {
        Error(MaybeE.takeError());
        return;
      }
      llvm::BitstreamEntry E = MaybeE.get();
 
      switch (E.Kind) {
      case llvm::BitstreamEntry::SubBlock: // Handled for us already.
      case llvm::BitstreamEntry::Error:
        Error("malformed block record in AST file");
        return;
      case llvm::BitstreamEntry::EndBlock:
        goto NextCursor;
 
      case llvm::BitstreamEntry::Record: {
        Record.clear();
        Expected<unsigned> MaybeRecord = Cursor.readRecord(E.ID, Record);
        if (!MaybeRecord) {
          Error(MaybeRecord.takeError());
          return;
        }
        switch (MaybeRecord.get()) {
        default:  // Default behavior: ignore.
          break;
 
        case PP_MACRO_OBJECT_LIKE:
        case PP_MACRO_FUNCTION_LIKE: {
          IdentifierInfo *II = getLocalIdentifier(I, Record[0]);
          if (II->isOutOfDate())
            updateOutOfDateIdentifier(*II);
          break;
        }
 
        case PP_TOKEN:
          // Ignore tokens.
          break;
        }
        break;
      }
      }
    }
    NextCursor:  ;
  }
}
 
namespace {
 
  /// Visitor class used to look up identifirs in an AST file.
  class IdentifierLookupVisitor {
    StringRef Name;
    unsigned NameHash;
    unsigned PriorGeneration;
    unsigned &NumIdentifierLookups;
    unsigned &NumIdentifierLookupHits;
    IdentifierInfo *Found = nullptr;
 
  public:
    IdentifierLookupVisitor(StringRef Name, unsigned PriorGeneration,
                            unsigned &NumIdentifierLookups,
                            unsigned &NumIdentifierLookupHits)
      : Name(Name), NameHash(ASTIdentifierLookupTrait::ComputeHash(Name)),
        PriorGeneration(PriorGeneration),
        NumIdentifierLookups(NumIdentifierLookups),
        NumIdentifierLookupHits(NumIdentifierLookupHits) {}
 
    bool operator()(ModuleFile &M) {
      // If we've already searched this module file, skip it now.
      if (M.Generation <= PriorGeneration)
        return true;
 
      ASTIdentifierLookupTable *IdTable
        = (ASTIdentifierLookupTable *)M.IdentifierLookupTable;
      if (!IdTable)
        return false;
 
      ASTIdentifierLookupTrait Trait(IdTable->getInfoObj().getReader(), M,
                                     Found);
      ++NumIdentifierLookups;
      ASTIdentifierLookupTable::iterator Pos =
          IdTable->find_hashed(Name, NameHash, &Trait);
      if (Pos == IdTable->end())
        return false;
 
      // Dereferencing the iterator has the effect of building the
      // IdentifierInfo node and populating it with the various
      // declarations it needs.
      ++NumIdentifierLookupHits;
      Found = *Pos;
      return true;
    }
 
    // Retrieve the identifier info found within the module
    // files.
    IdentifierInfo *getIdentifierInfo() const { return Found; }
  };
 
} // namespace
 
void ASTReader::updateOutOfDateIdentifier(const IdentifierInfo &II) {
  // Note that we are loading an identifier.
  Deserializing AnIdentifier(this);
 
  unsigned PriorGeneration = 0;
  if (getContext().getLangOpts().Modules)
    PriorGeneration = IdentifierGeneration[&II];
 
  // If there is a global index, look there first to determine which modules
  // provably do not have any results for this identifier.
  GlobalModuleIndex::HitSet Hits;
  GlobalModuleIndex::HitSet *HitsPtr = nullptr;
  if (!loadGlobalIndex()) {
    if (GlobalIndex->lookupIdentifier(II.getName(), Hits)) {
      HitsPtr = &Hits;
    }
  }
 
  IdentifierLookupVisitor Visitor(II.getName(), PriorGeneration,
                                  NumIdentifierLookups,
                                  NumIdentifierLookupHits);
  ModuleMgr.visit(Visitor, HitsPtr);
  markIdentifierUpToDate(&II);
}
 
void ASTReader::markIdentifierUpToDate(const IdentifierInfo *II) {
  if (!II)
    return;
 
  const_cast<IdentifierInfo *>(II)->setOutOfDate(false);
 
  // Update the generation for this identifier.
  if (getContext().getLangOpts().Modules)
    IdentifierGeneration[II] = getGeneration();
}
 
void ASTReader::resolvePendingMacro(IdentifierInfo *II,
                                    const PendingMacroInfo &PMInfo) {
  ModuleFile &M = *PMInfo.M;
 
  BitstreamCursor &Cursor = M.MacroCursor;
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err =
          Cursor.JumpToBit(M.MacroOffsetsBase + PMInfo.MacroDirectivesOffset)) {
    Error(std::move(Err));
    return;
  }
 
  struct ModuleMacroRecord {
    SubmoduleID SubModID;
    MacroInfo *MI;
    SmallVector<SubmoduleID, 8> Overrides;
  };
  llvm::SmallVector<ModuleMacroRecord, 8> ModuleMacros;
 
  // We expect to see a sequence of PP_MODULE_MACRO records listing exported
  // macros, followed by a PP_MACRO_DIRECTIVE_HISTORY record with the complete
  // macro histroy.
  RecordData Record;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry =
        Cursor.advance(BitstreamCursor::AF_DontPopBlockAtEnd);
    if (!MaybeEntry) {
      Error(MaybeEntry.takeError());
      return;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    if (Entry.Kind != llvm::BitstreamEntry::Record) {
      Error("malformed block record in AST file");
      return;
    }
 
    Record.clear();
    Expected<unsigned> MaybePP = Cursor.readRecord(Entry.ID, Record);
    if (!MaybePP) {
      Error(MaybePP.takeError());
      return;
    }
    switch ((PreprocessorRecordTypes)MaybePP.get()) {
    case PP_MACRO_DIRECTIVE_HISTORY:
      break;
 
    case PP_MODULE_MACRO: {
      ModuleMacros.push_back(ModuleMacroRecord());
      auto &Info = ModuleMacros.back();
      Info.SubModID = getGlobalSubmoduleID(M, Record[0]);
      Info.MI = getMacro(getGlobalMacroID(M, Record[1]));
      for (int I = 2, N = Record.size(); I != N; ++I)
        Info.Overrides.push_back(getGlobalSubmoduleID(M, Record[I]));
      continue;
    }
 
    default:
      Error("malformed block record in AST file");
      return;
    }
 
    // We found the macro directive history; that's the last record
    // for this macro.
    break;
  }
 
  // Module macros are listed in reverse dependency order.
  {
    std::reverse(ModuleMacros.begin(), ModuleMacros.end());
    llvm::SmallVector<ModuleMacro*, 8> Overrides;
    for (auto &MMR : ModuleMacros) {
      Overrides.clear();
      for (unsigned ModID : MMR.Overrides) {
        Module *Mod = getSubmodule(ModID);
        auto *Macro = PP.getModuleMacro(Mod, II);
        assert(Macro && "missing definition for overridden macro");
        Overrides.push_back(Macro);
      }
 
      bool Inserted = false;
      Module *Owner = getSubmodule(MMR.SubModID);
      PP.addModuleMacro(Owner, II, MMR.MI, Overrides, Inserted);
    }
  }
 
  // Don't read the directive history for a module; we don't have anywhere
  // to put it.
  if (M.isModule())
    return;
 
  // Deserialize the macro directives history in reverse source-order.
  MacroDirective *Latest = nullptr, *Earliest = nullptr;
  unsigned Idx = 0, N = Record.size();
  while (Idx < N) {
    MacroDirective *MD = nullptr;
    SourceLocation Loc = ReadSourceLocation(M, Record, Idx);
    MacroDirective::Kind K = (MacroDirective::Kind)Record[Idx++];
    switch (K) {
    case MacroDirective::MD_Define: {
      MacroInfo *MI = getMacro(getGlobalMacroID(M, Record[Idx++]));
      MD = PP.AllocateDefMacroDirective(MI, Loc);
      break;
    }
    case MacroDirective::MD_Undefine:
      MD = PP.AllocateUndefMacroDirective(Loc);
      break;
    case MacroDirective::MD_Visibility:
      bool isPublic = Record[Idx++];
      MD = PP.AllocateVisibilityMacroDirective(Loc, isPublic);
      break;
    }
 
    if (!Latest)
      Latest = MD;
    if (Earliest)
      Earliest->setPrevious(MD);
    Earliest = MD;
  }
 
  if (Latest)
    PP.setLoadedMacroDirective(II, Earliest, Latest);
}
 
bool ASTReader::shouldDisableValidationForFile(
    const serialization::ModuleFile &M) const {
  if (DisableValidationKind == DisableValidationForModuleKind::None)
    return false;
 
  // If a PCH is loaded and validation is disabled for PCH then disable
  // validation for the PCH and the modules it loads.
  ModuleKind K = CurrentDeserializingModuleKind.value_or(M.Kind);
 
  switch (K) {
  case MK_MainFile:
  case MK_Preamble:
  case MK_PCH:
    return bool(DisableValidationKind & DisableValidationForModuleKind::PCH);
  case MK_ImplicitModule:
  case MK_ExplicitModule:
  case MK_PrebuiltModule:
    return bool(DisableValidationKind & DisableValidationForModuleKind::Module);
  }
 
  return false;
}
 
InputFileInfo ASTReader::getInputFileInfo(ModuleFile &F, unsigned ID) {
  // If this ID is bogus, just return an empty input file.
  if (ID == 0 || ID > F.InputFileInfosLoaded.size())
    return InputFileInfo();
 
  // If we've already loaded this input file, return it.
  if (!F.InputFileInfosLoaded[ID - 1].Filename.empty())
    return F.InputFileInfosLoaded[ID - 1];
 
  // Go find this input file.
  BitstreamCursor &Cursor = F.InputFilesCursor;
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err = Cursor.JumpToBit(F.InputFilesOffsetBase +
                                         F.InputFileOffsets[ID - 1])) {
    // FIXME this drops errors on the floor.
    consumeError(std::move(Err));
  }
 
  Expected<unsigned> MaybeCode = Cursor.ReadCode();
  if (!MaybeCode) {
    // FIXME this drops errors on the floor.
    consumeError(MaybeCode.takeError());
  }
  unsigned Code = MaybeCode.get();
  RecordData Record;
  StringRef Blob;
 
  if (Expected<unsigned> Maybe = Cursor.readRecord(Code, Record, &Blob))
    assert(static_cast<InputFileRecordTypes>(Maybe.get()) == INPUT_FILE &&
           "invalid record type for input file");
  else {
    // FIXME this drops errors on the floor.
    consumeError(Maybe.takeError());
  }
 
  assert(Record[0] == ID && "Bogus stored ID or offset");
  InputFileInfo R;
  R.StoredSize = static_cast<off_t>(Record[1]);
  R.StoredTime = static_cast<time_t>(Record[2]);
  R.Overridden = static_cast<bool>(Record[3]);
  R.Transient = static_cast<bool>(Record[4]);
  R.TopLevel = static_cast<bool>(Record[5]);
  R.ModuleMap = static_cast<bool>(Record[6]);
  std::tie(R.FilenameAsRequested, R.Filename) = [&]() {
    uint16_t AsRequestedLength = Record[7];
 
    std::string NameAsRequested = Blob.substr(0, AsRequestedLength).str();
    std::string Name = Blob.substr(AsRequestedLength).str();
 
    ResolveImportedPath(F, NameAsRequested);
    ResolveImportedPath(F, Name);
 
    if (Name.empty())
      Name = NameAsRequested;
 
    return std::make_pair(std::move(NameAsRequested), std::move(Name));
  }();
 
  Expected<llvm::BitstreamEntry> MaybeEntry = Cursor.advance();
  if (!MaybeEntry) // FIXME this drops errors on the floor.
    consumeError(MaybeEntry.takeError());
  llvm::BitstreamEntry Entry = MaybeEntry.get();
  assert(Entry.Kind == llvm::BitstreamEntry::Record &&
         "expected record type for input file hash");
 
  Record.clear();
  if (Expected<unsigned> Maybe = Cursor.readRecord(Entry.ID, Record))
    assert(static_cast<InputFileRecordTypes>(Maybe.get()) == INPUT_FILE_HASH &&
           "invalid record type for input file hash");
  else {
    // FIXME this drops errors on the floor.
    consumeError(Maybe.takeError());
  }
  R.ContentHash = (static_cast<uint64_t>(Record[1]) << 32) |
                  static_cast<uint64_t>(Record[0]);
 
  // Note that we've loaded this input file info.
  F.InputFileInfosLoaded[ID - 1] = R;
  return R;
}
 
static unsigned moduleKindForDiagnostic(ModuleKind Kind);
InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
  // If this ID is bogus, just return an empty input file.
  if (ID == 0 || ID > F.InputFilesLoaded.size())
    return InputFile();
 
  // If we've already loaded this input file, return it.
  if (F.InputFilesLoaded[ID-1].getFile())
    return F.InputFilesLoaded[ID-1];
 
  if (F.InputFilesLoaded[ID-1].isNotFound())
    return InputFile();
 
  // Go find this input file.
  BitstreamCursor &Cursor = F.InputFilesCursor;
  SavedStreamPosition SavedPosition(Cursor);
  if (llvm::Error Err = Cursor.JumpToBit(F.InputFilesOffsetBase +
                                         F.InputFileOffsets[ID - 1])) {
    // FIXME this drops errors on the floor.
    consumeError(std::move(Err));
  }
 
  InputFileInfo FI = getInputFileInfo(F, ID);
  off_t StoredSize = FI.StoredSize;
  time_t StoredTime = FI.StoredTime;
  bool Overridden = FI.Overridden;
  bool Transient = FI.Transient;
  StringRef Filename = FI.FilenameAsRequested;
  uint64_t StoredContentHash = FI.ContentHash;
 
  // For standard C++ modules, we don't need to check the inputs.
  bool SkipChecks = F.StandardCXXModule;
 
  const HeaderSearchOptions &HSOpts =
      PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
  // The option ForceCheckCXX20ModulesInputFiles is only meaningful for C++20
  // modules.
  if (F.StandardCXXModule && HSOpts.ForceCheckCXX20ModulesInputFiles) {
    SkipChecks = false;
    Overridden = false;
  }
 
  auto File = FileMgr.getOptionalFileRef(Filename, /*OpenFile=*/false);
 
  // For an overridden file, create a virtual file with the stored
  // size/timestamp.
  if ((Overridden || Transient || SkipChecks) && !File)
    File = FileMgr.getVirtualFileRef(Filename, StoredSize, StoredTime);
 
  if (!File) {
    if (Complain) {
      std::string ErrorStr = "could not find file '";
      ErrorStr += Filename;
      ErrorStr += "' referenced by AST file '";
      ErrorStr += F.FileName;
      ErrorStr += "'";
      Error(ErrorStr);
    }
    // Record that we didn't find the file.
    F.InputFilesLoaded[ID-1] = InputFile::getNotFound();
    return InputFile();
  }
 
  // Check if there was a request to override the contents of the file
  // that was part of the precompiled header. Overriding such a file
  // can lead to problems when lexing using the source locations from the
  // PCH.
  SourceManager &SM = getSourceManager();
  // FIXME: Reject if the overrides are different.
  if ((!Overridden && !Transient) && !SkipChecks &&
      SM.isFileOverridden(*File)) {
    if (Complain)
      Error(diag::err_fe_pch_file_overridden, Filename);
 
    // After emitting the diagnostic, bypass the overriding file to recover
    // (this creates a separate FileEntry).
    File = SM.bypassFileContentsOverride(*File);
    if (!File) {
      F.InputFilesLoaded[ID - 1] = InputFile::getNotFound();
      return InputFile();
    }
  }
 
  struct Change {
    enum ModificationKind {
      Size,
      ModTime,
      Content,
      None,
    } Kind;
    std::optional<int64_t> Old = std::nullopt;
    std::optional<int64_t> New = std::nullopt;
  };
  auto HasInputContentChanged = [&](Change OriginalChange) {
    assert(ValidateASTInputFilesContent &&
           "We should only check the content of the inputs with "
           "ValidateASTInputFilesContent enabled.");
 
    if (StoredContentHash == 0)
      return OriginalChange;
 
    auto MemBuffOrError = FileMgr.getBufferForFile(*File);
    if (!MemBuffOrError) {
      if (!Complain)
        return OriginalChange;
      std::string ErrorStr = "could not get buffer for file '";
      ErrorStr += File->getName();
      ErrorStr += "'";
      Error(ErrorStr);
      return OriginalChange;
    }
 
    auto ContentHash = xxh3_64bits(MemBuffOrError.get()->getBuffer());
    if (StoredContentHash == static_cast<uint64_t>(ContentHash))
      return Change{Change::None};
 
    return Change{Change::Content};
  };
  auto HasInputFileChanged = [&]() {
    if (StoredSize != File->getSize())
      return Change{Change::Size, StoredSize, File->getSize()};
    if (!shouldDisableValidationForFile(F) && StoredTime &&
        StoredTime != File->getModificationTime()) {
      Change MTimeChange = {Change::ModTime, StoredTime,
                            File->getModificationTime()};
 
      // In case the modification time changes but not the content,
      // accept the cached file as legit.
      if (ValidateASTInputFilesContent)
        return HasInputContentChanged(MTimeChange);
 
      return MTimeChange;
    }
    return Change{Change::None};
  };
 
  bool IsOutOfDate = false;
  auto FileChange = SkipChecks ? Change{Change::None} : HasInputFileChanged();
  // When ForceCheckCXX20ModulesInputFiles and ValidateASTInputFilesContent
  // enabled, it is better to check the contents of the inputs. Since we can't
  // get correct modified time information for inputs from overriden inputs.
  if (HSOpts.ForceCheckCXX20ModulesInputFiles && ValidateASTInputFilesContent &&
      F.StandardCXXModule && FileChange.Kind == Change::None)
    FileChange = HasInputContentChanged(FileChange);
 
  // When we have StoredTime equal to zero and ValidateASTInputFilesContent,
  // it is better to check the content of the input files because we cannot rely
  // on the file modification time, which will be the same (zero) for these
  // files.
  if (!StoredTime && ValidateASTInputFilesContent &&
      FileChange.Kind == Change::None)
    FileChange = HasInputContentChanged(FileChange);
 
  // For an overridden file, there is nothing to validate.
  if (!Overridden && FileChange.Kind != Change::None) {
    if (Complain && !Diags.isDiagnosticInFlight()) {
      // Build a list of the PCH imports that got us here (in reverse).
      SmallVector<ModuleFile *, 4> ImportStack(1, &F);
      while (!ImportStack.back()->ImportedBy.empty())
        ImportStack.push_back(ImportStack.back()->ImportedBy[0]);
 
      // The top-level PCH is stale.
      StringRef TopLevelPCHName(ImportStack.back()->FileName);
      Diag(diag::err_fe_ast_file_modified)
          << Filename << moduleKindForDiagnostic(ImportStack.back()->Kind)
          << TopLevelPCHName << FileChange.Kind
          << (FileChange.Old && FileChange.New)
          << llvm::itostr(FileChange.Old.value_or(0))
          << llvm::itostr(FileChange.New.value_or(0));
 
      // Print the import stack.
      if (ImportStack.size() > 1) {
        Diag(diag::note_pch_required_by)
          << Filename << ImportStack[0]->FileName;
        for (unsigned I = 1; I < ImportStack.size(); ++I)
          Diag(diag::note_pch_required_by)
            << ImportStack[I-1]->FileName << ImportStack[I]->FileName;
      }
 
      Diag(diag::note_pch_rebuild_required) << TopLevelPCHName;
    }
 
    IsOutOfDate = true;
  }
  // FIXME: If the file is overridden and we've already opened it,
  // issue an error (or split it into a separate FileEntry).
 
  InputFile IF = InputFile(*File, Overridden || Transient, IsOutOfDate);
 
  // Note that we've loaded this input file.
  F.InputFilesLoaded[ID-1] = IF;
  return IF;
}
 
/// If we are loading a relocatable PCH or module file, and the filename
/// is not an absolute path, add the system or module root to the beginning of
/// the file name.
void ASTReader::ResolveImportedPath(ModuleFile &M, std::string &Filename) {
  // Resolve relative to the base directory, if we have one.
  if (!M.BaseDirectory.empty())
    return ResolveImportedPath(Filename, M.BaseDirectory);
}
 
void ASTReader::ResolveImportedPath(std::string &Filename, StringRef Prefix) {
  if (Filename.empty() || llvm::sys::path::is_absolute(Filename) ||
      Filename == "<built-in>" || Filename == "<command line>")
    return;
 
  SmallString<128> Buffer;
  llvm::sys::path::append(Buffer, Prefix, Filename);
  Filename.assign(Buffer.begin(), Buffer.end());
}
 
static bool isDiagnosedResult(ASTReader::ASTReadResult ARR, unsigned Caps) {
  switch (ARR) {
  case ASTReader::Failure: return true;
  case ASTReader::Missing: return !(Caps & ASTReader::ARR_Missing);
  case ASTReader::OutOfDate: return !(Caps & ASTReader::ARR_OutOfDate);
  case ASTReader::VersionMismatch: return !(Caps & ASTReader::ARR_VersionMismatch);
  case ASTReader::ConfigurationMismatch:
    return !(Caps & ASTReader::ARR_ConfigurationMismatch);
  case ASTReader::HadErrors: return true;
  case ASTReader::Success: return false;
  }
 
  llvm_unreachable("unknown ASTReadResult");
}
 
ASTReader::ASTReadResult ASTReader::ReadOptionsBlock(
    BitstreamCursor &Stream, StringRef Filename,
    unsigned ClientLoadCapabilities, bool AllowCompatibleConfigurationMismatch,
    ASTReaderListener &Listener, std::string &SuggestedPredefines) {
  if (llvm::Error Err = Stream.EnterSubBlock(OPTIONS_BLOCK_ID)) {
    // FIXME this drops errors on the floor.
    consumeError(std::move(Err));
    return Failure;
  }
 
  // Read all of the records in the options block.
  RecordData Record;
  ASTReadResult Result = Success;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry) {
      // FIXME this drops errors on the floor.
      consumeError(MaybeEntry.takeError());
      return Failure;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
    case llvm::BitstreamEntry::SubBlock:
      return Failure;
 
    case llvm::BitstreamEntry::EndBlock:
      return Result;
 
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read and process a record.
    Record.clear();
    Expected<unsigned> MaybeRecordType = Stream.readRecord(Entry.ID, Record);
    if (!MaybeRecordType) {
      // FIXME this drops errors on the floor.
      consumeError(MaybeRecordType.takeError());
      return Failure;
    }
    switch ((OptionsRecordTypes)MaybeRecordType.get()) {
    case LANGUAGE_OPTIONS: {
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (ParseLanguageOptions(Record, Filename, Complain, Listener,
                               AllowCompatibleConfigurationMismatch))
        Result = ConfigurationMismatch;
      break;
    }
 
    case TARGET_OPTIONS: {
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (ParseTargetOptions(Record, Filename, Complain, Listener,
                             AllowCompatibleConfigurationMismatch))
        Result = ConfigurationMismatch;
      break;
    }
 
    case FILE_SYSTEM_OPTIONS: {
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (!AllowCompatibleConfigurationMismatch &&
          ParseFileSystemOptions(Record, Complain, Listener))
        Result = ConfigurationMismatch;
      break;
    }
 
    case HEADER_SEARCH_OPTIONS: {
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (!AllowCompatibleConfigurationMismatch &&
          ParseHeaderSearchOptions(Record, Filename, Complain, Listener))
        Result = ConfigurationMismatch;
      break;
    }
 
    case PREPROCESSOR_OPTIONS:
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (!AllowCompatibleConfigurationMismatch &&
          ParsePreprocessorOptions(Record, Filename, Complain, Listener,
                                   SuggestedPredefines))
        Result = ConfigurationMismatch;
      break;
    }
  }
}
 
ASTReader::ASTReadResult
ASTReader::ReadControlBlock(ModuleFile &F,
                            SmallVectorImpl<ImportedModule> &Loaded,
                            const ModuleFile *ImportedBy,
                            unsigned ClientLoadCapabilities) {
  BitstreamCursor &Stream = F.Stream;
 
  if (llvm::Error Err = Stream.EnterSubBlock(CONTROL_BLOCK_ID)) {
    Error(std::move(Err));
    return Failure;
  }
 
  // Lambda to read the unhashed control block the first time it's called.
  //
  // For PCM files, the unhashed control block cannot be read until after the
  // MODULE_NAME record.  However, PCH files have no MODULE_NAME, and yet still
  // need to look ahead before reading the IMPORTS record.  For consistency,
  // this block is always read somehow (see BitstreamEntry::EndBlock).
  bool HasReadUnhashedControlBlock = false;
  auto readUnhashedControlBlockOnce = [&]() {
    if (!HasReadUnhashedControlBlock) {
      HasReadUnhashedControlBlock = true;
      if (ASTReadResult Result =
              readUnhashedControlBlock(F, ImportedBy, ClientLoadCapabilities))
        return Result;
    }
    return Success;
  };
 
  bool DisableValidation = shouldDisableValidationForFile(F);
 
  // Read all of the records and blocks in the control block.
  RecordData Record;
  unsigned NumInputs = 0;
  unsigned NumUserInputs = 0;
  StringRef BaseDirectoryAsWritten;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry) {
      Error(MaybeEntry.takeError());
      return Failure;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
      Error("malformed block record in AST file");
      return Failure;
    case llvm::BitstreamEntry::EndBlock: {
      // Validate the module before returning.  This call catches an AST with
      // no module name and no imports.
      if (ASTReadResult Result = readUnhashedControlBlockOnce())
        return Result;
 
      // Validate input files.
      const HeaderSearchOptions &HSOpts =
          PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
      // All user input files reside at the index range [0, NumUserInputs), and
      // system input files reside at [NumUserInputs, NumInputs). For explicitly
      // loaded module files, ignore missing inputs.
      if (!DisableValidation && F.Kind != MK_ExplicitModule &&
          F.Kind != MK_PrebuiltModule) {
        bool Complain = (ClientLoadCapabilities & ARR_OutOfDate) == 0;
 
        // If we are reading a module, we will create a verification timestamp,
        // so we verify all input files.  Otherwise, verify only user input
        // files.
 
        unsigned N = ValidateSystemInputs ? NumInputs : NumUserInputs;
        if (HSOpts.ModulesValidateOncePerBuildSession &&
            F.InputFilesValidationTimestamp > HSOpts.BuildSessionTimestamp &&
            F.Kind == MK_ImplicitModule)
          N = NumUserInputs;
 
        for (unsigned I = 0; I < N; ++I) {
          InputFile IF = getInputFile(F, I+1, Complain);
          if (!IF.getFile() || IF.isOutOfDate())
            return OutOfDate;
        }
      }
 
      if (Listener)
        Listener->visitModuleFile(F.FileName, F.Kind);
 
      if (Listener && Listener->needsInputFileVisitation()) {
        unsigned N = Listener->needsSystemInputFileVisitation() ? NumInputs
                                                                : NumUserInputs;
        for (unsigned I = 0; I < N; ++I) {
          bool IsSystem = I >= NumUserInputs;
          InputFileInfo FI = getInputFileInfo(F, I + 1);
          Listener->visitInputFile(
              FI.FilenameAsRequested, IsSystem, FI.Overridden,
              F.Kind == MK_ExplicitModule || F.Kind == MK_PrebuiltModule);
        }
      }
 
      return Success;
    }
 
    case llvm::BitstreamEntry::SubBlock:
      switch (Entry.ID) {
      case INPUT_FILES_BLOCK_ID:
        F.InputFilesCursor = Stream;
        if (llvm::Error Err = Stream.SkipBlock()) {
          Error(std::move(Err));
          return Failure;
        }
        if (ReadBlockAbbrevs(F.InputFilesCursor, INPUT_FILES_BLOCK_ID)) {
          Error("malformed block record in AST file");
          return Failure;
        }
        F.InputFilesOffsetBase = F.InputFilesCursor.GetCurrentBitNo();
        continue;
 
      case OPTIONS_BLOCK_ID:
        // If we're reading the first module for this group, check its options
        // are compatible with ours. For modules it imports, no further checking
        // is required, because we checked them when we built it.
        if (Listener && !ImportedBy) {
          // Should we allow the configuration of the module file to differ from
          // the configuration of the current translation unit in a compatible
          // way?
          //
          // FIXME: Allow this for files explicitly specified with -include-pch.
          bool AllowCompatibleConfigurationMismatch =
              F.Kind == MK_ExplicitModule || F.Kind == MK_PrebuiltModule;
 
          ASTReadResult Result =
              ReadOptionsBlock(Stream, F.FileName, ClientLoadCapabilities,
                               AllowCompatibleConfigurationMismatch, *Listener,
                               SuggestedPredefines);
          if (Result == Failure) {
            Error("malformed block record in AST file");
            return Result;
          }
 
          if (DisableValidation ||
              (AllowConfigurationMismatch && Result == ConfigurationMismatch))
            Result = Success;
 
          // If we can't load the module, exit early since we likely
          // will rebuild the module anyway. The stream may be in the
          // middle of a block.
          if (Result != Success)
            return Result;
        } else if (llvm::Error Err = Stream.SkipBlock()) {
          Error(std::move(Err));
          return Failure;
        }
        continue;
 
      default:
        if (llvm::Error Err = Stream.SkipBlock()) {
          Error(std::move(Err));
          return Failure;
        }
        continue;
      }
 
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read and process a record.
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecordType =
        Stream.readRecord(Entry.ID, Record, &Blob);
    if (!MaybeRecordType) {
      Error(MaybeRecordType.takeError());
      return Failure;
    }
    switch ((ControlRecordTypes)MaybeRecordType.get()) {
    case METADATA: {
      if (Record[0] != VERSION_MAJOR && !DisableValidation) {
        if ((ClientLoadCapabilities & ARR_VersionMismatch) == 0)
          Diag(Record[0] < VERSION_MAJOR ? diag::err_ast_file_version_too_old
                                         : diag::err_ast_file_version_too_new)
              << moduleKindForDiagnostic(F.Kind) << F.FileName;
        return VersionMismatch;
      }
 
      bool hasErrors = Record[7];
      if (hasErrors && !DisableValidation) {
        // If requested by the caller and the module hasn't already been read
        // or compiled, mark modules on error as out-of-date.
        if ((ClientLoadCapabilities & ARR_TreatModuleWithErrorsAsOutOfDate) &&
            canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
          return OutOfDate;
 
        if (!AllowASTWithCompilerErrors) {
          Diag(diag::err_ast_file_with_compiler_errors)
              << moduleKindForDiagnostic(F.Kind) << F.FileName;
          return HadErrors;
        }
      }
      if (hasErrors) {
        Diags.ErrorOccurred = true;
        Diags.UncompilableErrorOccurred = true;
        Diags.UnrecoverableErrorOccurred = true;
      }
 
      F.RelocatablePCH = Record[4];
      // Relative paths in a relocatable PCH are relative to our sysroot.
      if (F.RelocatablePCH)
        F.BaseDirectory = isysroot.empty() ? "/" : isysroot;
 
      F.StandardCXXModule = Record[5];
 
      F.HasTimestamps = Record[6];
 
      const std::string &CurBranch = getClangFullRepositoryVersion();
      StringRef ASTBranch = Blob;
      if (StringRef(CurBranch) != ASTBranch && !DisableValidation) {
        if ((ClientLoadCapabilities & ARR_VersionMismatch) == 0)
          Diag(diag::err_ast_file_different_branch)
              << moduleKindForDiagnostic(F.Kind) << F.FileName << ASTBranch
              << CurBranch;
        return VersionMismatch;
      }
      break;
    }
 
    case IMPORTS: {
      // Validate the AST before processing any imports (otherwise, untangling
      // them can be error-prone and expensive).  A module will have a name and
      // will already have been validated, but this catches the PCH case.
      if (ASTReadResult Result = readUnhashedControlBlockOnce())
        return Result;
 
      // Load each of the imported PCH files.
      unsigned Idx = 0, N = Record.size();
      while (Idx < N) {
        // Read information about the AST file.
        ModuleKind ImportedKind = (ModuleKind)Record[Idx++];
        // Whether we're importing a standard c++ module.
        bool IsImportingStdCXXModule = Record[Idx++];
        // The import location will be the local one for now; we will adjust
        // all import locations of module imports after the global source
        // location info are setup, in ReadAST.
        auto [ImportLoc, ImportModuleFileIndex] =
            ReadUntranslatedSourceLocation(Record[Idx++]);
        // The import location must belong to the current module file itself.
        assert(ImportModuleFileIndex == 0);
        off_t StoredSize = !IsImportingStdCXXModule ? (off_t)Record[Idx++] : 0;
        time_t StoredModTime =
            !IsImportingStdCXXModule ? (time_t)Record[Idx++] : 0;
 
        ASTFileSignature StoredSignature;
        if (!IsImportingStdCXXModule) {
          auto FirstSignatureByte = Record.begin() + Idx;
          StoredSignature = ASTFileSignature::create(
              FirstSignatureByte, FirstSignatureByte + ASTFileSignature::size);
          Idx += ASTFileSignature::size;
        }
 
        std::string ImportedName = ReadString(Record, Idx);
        std::string ImportedFile;
 
        // For prebuilt and explicit modules first consult the file map for
        // an override. Note that here we don't search prebuilt module
        // directories if we're not importing standard c++ module, only the
        // explicit name to file mappings. Also, we will still verify the
        // size/signature making sure it is essentially the same file but
        // perhaps in a different location.
        if (ImportedKind == MK_PrebuiltModule || ImportedKind == MK_ExplicitModule)
          ImportedFile = PP.getHeaderSearchInfo().getPrebuiltModuleFileName(
              ImportedName, /*FileMapOnly*/ !IsImportingStdCXXModule);
 
        // For C++20 Modules, we won't record the path to the imported modules
        // in the BMI
        if (!IsImportingStdCXXModule) {
          if (ImportedFile.empty()) {
            // Use BaseDirectoryAsWritten to ensure we use the same path in the
            // ModuleCache as when writing.
            ImportedFile = ReadPath(BaseDirectoryAsWritten, Record, Idx);
          } else
            SkipPath(Record, Idx);
        } else if (ImportedFile.empty()) {
          Diag(clang::diag::err_failed_to_find_module_file) << ImportedName;
          return Missing;
        }
 
        // If our client can't cope with us being out of date, we can't cope with
        // our dependency being missing.
        unsigned Capabilities = ClientLoadCapabilities;
        if ((ClientLoadCapabilities & ARR_OutOfDate) == 0)
          Capabilities &= ~ARR_Missing;
 
        // Load the AST file.
        auto Result = ReadASTCore(ImportedFile, ImportedKind, ImportLoc, &F,
                                  Loaded, StoredSize, StoredModTime,
                                  StoredSignature, Capabilities);
 
        // If we diagnosed a problem, produce a backtrace.
        bool recompilingFinalized =
            Result == OutOfDate && (Capabilities & ARR_OutOfDate) &&
            getModuleManager().getModuleCache().isPCMFinal(F.FileName);
        if (isDiagnosedResult(Result, Capabilities) || recompilingFinalized)
          Diag(diag::note_module_file_imported_by)
              << F.FileName << !F.ModuleName.empty() << F.ModuleName;
        if (recompilingFinalized)
          Diag(diag::note_module_file_conflict);
 
        switch (Result) {
        case Failure: return Failure;
          // If we have to ignore the dependency, we'll have to ignore this too.
        case Missing:
        case OutOfDate: return OutOfDate;
        case VersionMismatch: return VersionMismatch;
        case ConfigurationMismatch: return ConfigurationMismatch;
        case HadErrors: return HadErrors;
        case Success: break;
        }
      }
      break;
    }
 
    case ORIGINAL_FILE:
      F.OriginalSourceFileID = FileID::get(Record[0]);
      F.ActualOriginalSourceFileName = std::string(Blob);
      F.OriginalSourceFileName = F.ActualOriginalSourceFileName;
      ResolveImportedPath(F, F.OriginalSourceFileName);
      break;
 
    case ORIGINAL_FILE_ID:
      F.OriginalSourceFileID = FileID::get(Record[0]);
      break;
 
    case MODULE_NAME:
      F.ModuleName = std::string(Blob);
      Diag(diag::remark_module_import)
          << F.ModuleName << F.FileName << (ImportedBy ? true : false)
          << (ImportedBy ? StringRef(ImportedBy->ModuleName) : StringRef());
      if (Listener)
        Listener->ReadModuleName(F.ModuleName);
 
      // Validate the AST as soon as we have a name so we can exit early on
      // failure.
      if (ASTReadResult Result = readUnhashedControlBlockOnce())
        return Result;
 
      break;
 
    case MODULE_DIRECTORY: {
      // Save the BaseDirectory as written in the PCM for computing the module
      // filename for the ModuleCache.
      BaseDirectoryAsWritten = Blob;
      assert(!F.ModuleName.empty() &&
             "MODULE_DIRECTORY found before MODULE_NAME");
      F.BaseDirectory = std::string(Blob);
      if (!PP.getPreprocessorOpts().ModulesCheckRelocated)
        break;
      // If we've already loaded a module map file covering this module, we may
      // have a better path for it (relative to the current build).
      Module *M = PP.getHeaderSearchInfo().lookupModule(
          F.ModuleName, SourceLocation(), /*AllowSearch*/ true,
          /*AllowExtraModuleMapSearch*/ true);
      if (M && M->Directory) {
        // If we're implicitly loading a module, the base directory can't
        // change between the build and use.
        // Don't emit module relocation error if we have -fno-validate-pch
        if (!bool(PP.getPreprocessorOpts().DisablePCHOrModuleValidation &
                  DisableValidationForModuleKind::Module) &&
            F.Kind != MK_ExplicitModule && F.Kind != MK_PrebuiltModule) {
          auto BuildDir = PP.getFileManager().getOptionalDirectoryRef(Blob);
          if (!BuildDir || *BuildDir != M->Directory) {
            if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
              Diag(diag::err_imported_module_relocated)
                  << F.ModuleName << Blob << M->Directory->getName();
            return OutOfDate;
          }
        }
        F.BaseDirectory = std::string(M->Directory->getName());
      }
      break;
    }
 
    case MODULE_MAP_FILE:
      if (ASTReadResult Result =
              ReadModuleMapFileBlock(Record, F, ImportedBy, ClientLoadCapabilities))
        return Result;
      break;
 
    case INPUT_FILE_OFFSETS:
      NumInputs = Record[0];
      NumUserInputs = Record[1];
      F.InputFileOffsets =
          (const llvm::support::unaligned_uint64_t *)Blob.data();
      F.InputFilesLoaded.resize(NumInputs);
      F.InputFileInfosLoaded.resize(NumInputs);
      F.NumUserInputFiles = NumUserInputs;
      break;
    }
  }
}
 
llvm::Error ASTReader::ReadASTBlock(ModuleFile &F,
                                    unsigned ClientLoadCapabilities) {
  BitstreamCursor &Stream = F.Stream;
 
  if (llvm::Error Err = Stream.EnterSubBlock(AST_BLOCK_ID))
    return Err;
  F.ASTBlockStartOffset = Stream.GetCurrentBitNo();
 
  // Read all of the records and blocks for the AST file.
  RecordData Record;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry)
      return MaybeEntry.takeError();
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
      return llvm::createStringError(
          std::errc::illegal_byte_sequence,
          "error at end of module block in AST file");
    case llvm::BitstreamEntry::EndBlock:
      // Outside of C++, we do not store a lookup map for the translation unit.
      // Instead, mark it as needing a lookup map to be built if this module
      // contains any declarations lexically within it (which it always does!).
      // This usually has no cost, since we very rarely need the lookup map for
      // the translation unit outside C++.
      if (ASTContext *Ctx = ContextObj) {
        DeclContext *DC = Ctx->getTranslationUnitDecl();
        if (DC->hasExternalLexicalStorage() && !Ctx->getLangOpts().CPlusPlus)
          DC->setMustBuildLookupTable();
      }
 
      return llvm::Error::success();
    case llvm::BitstreamEntry::SubBlock:
      switch (Entry.ID) {
      case DECLTYPES_BLOCK_ID:
        // We lazily load the decls block, but we want to set up the
        // DeclsCursor cursor to point into it.  Clone our current bitcode
        // cursor to it, enter the block and read the abbrevs in that block.
        // With the main cursor, we just skip over it.
        F.DeclsCursor = Stream;
        if (llvm::Error Err = Stream.SkipBlock())
          return Err;
        if (llvm::Error Err = ReadBlockAbbrevs(
                F.DeclsCursor, DECLTYPES_BLOCK_ID, &F.DeclsBlockStartOffset))
          return Err;
        break;
 
      case PREPROCESSOR_BLOCK_ID:
        F.MacroCursor = Stream;
        if (!PP.getExternalSource())
          PP.setExternalSource(this);
 
        if (llvm::Error Err = Stream.SkipBlock())
          return Err;
        if (llvm::Error Err =
                ReadBlockAbbrevs(F.MacroCursor, PREPROCESSOR_BLOCK_ID))
          return Err;
        F.MacroStartOffset = F.MacroCursor.GetCurrentBitNo();
        break;
 
      case PREPROCESSOR_DETAIL_BLOCK_ID:
        F.PreprocessorDetailCursor = Stream;
 
        if (llvm::Error Err = Stream.SkipBlock()) {
          return Err;
        }
        if (llvm::Error Err = ReadBlockAbbrevs(F.PreprocessorDetailCursor,
                                               PREPROCESSOR_DETAIL_BLOCK_ID))
          return Err;
        F.PreprocessorDetailStartOffset
        = F.PreprocessorDetailCursor.GetCurrentBitNo();
 
        if (!PP.getPreprocessingRecord())
          PP.createPreprocessingRecord();
        if (!PP.getPreprocessingRecord()->getExternalSource())
          PP.getPreprocessingRecord()->SetExternalSource(*this);
        break;
 
      case SOURCE_MANAGER_BLOCK_ID:
        if (llvm::Error Err = ReadSourceManagerBlock(F))
          return Err;
        break;
 
      case SUBMODULE_BLOCK_ID:
        if (llvm::Error Err = ReadSubmoduleBlock(F, ClientLoadCapabilities))
          return Err;
        break;
 
      case COMMENTS_BLOCK_ID: {
        BitstreamCursor C = Stream;
 
        if (llvm::Error Err = Stream.SkipBlock())
          return Err;
        if (llvm::Error Err = ReadBlockAbbrevs(C, COMMENTS_BLOCK_ID))
          return Err;
        CommentsCursors.push_back(std::make_pair(C, &F));
        break;
      }
 
      default:
        if (llvm::Error Err = Stream.SkipBlock())
          return Err;
        break;
      }
      continue;
 
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read and process a record.
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecordType =
        Stream.readRecord(Entry.ID, Record, &Blob);
    if (!MaybeRecordType)
      return MaybeRecordType.takeError();
    ASTRecordTypes RecordType = (ASTRecordTypes)MaybeRecordType.get();
 
    // If we're not loading an AST context, we don't care about most records.
    if (!ContextObj) {
      switch (RecordType) {
      case IDENTIFIER_TABLE:
      case IDENTIFIER_OFFSET:
      case INTERESTING_IDENTIFIERS:
      case STATISTICS:
      case PP_ASSUME_NONNULL_LOC:
      case PP_CONDITIONAL_STACK:
      case PP_COUNTER_VALUE:
      case SOURCE_LOCATION_OFFSETS:
      case MODULE_OFFSET_MAP:
      case SOURCE_MANAGER_LINE_TABLE:
      case PPD_ENTITIES_OFFSETS:
      case HEADER_SEARCH_TABLE:
      case IMPORTED_MODULES:
      case MACRO_OFFSET:
        break;
      default:
        continue;
      }
    }
 
    switch (RecordType) {
    default:  // Default behavior: ignore.
      break;
 
    case TYPE_OFFSET: {
      if (F.LocalNumTypes != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "duplicate TYPE_OFFSET record in AST file");
      F.TypeOffsets = reinterpret_cast<const UnalignedUInt64 *>(Blob.data());
      F.LocalNumTypes = Record[0];
      F.BaseTypeIndex = getTotalNumTypes();
 
      if (F.LocalNumTypes > 0)
        TypesLoaded.resize(TypesLoaded.size() + F.LocalNumTypes);
 
      break;
    }
 
    case DECL_OFFSET: {
      if (F.LocalNumDecls != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "duplicate DECL_OFFSET record in AST file");
      F.DeclOffsets = (const DeclOffset *)Blob.data();
      F.LocalNumDecls = Record[0];
      F.BaseDeclIndex = getTotalNumDecls();
 
      if (F.LocalNumDecls > 0)
        DeclsLoaded.resize(DeclsLoaded.size() + F.LocalNumDecls);
 
      break;
    }
 
    case TU_UPDATE_LEXICAL: {
      DeclContext *TU = ContextObj->getTranslationUnitDecl();
      LexicalContents Contents(
          reinterpret_cast<const unaligned_decl_id_t *>(Blob.data()),
          static_cast<unsigned int>(Blob.size() / sizeof(DeclID)));
      TULexicalDecls.push_back(std::make_pair(&F, Contents));
      TU->setHasExternalLexicalStorage(true);
      break;
    }
 
    case UPDATE_VISIBLE: {
      unsigned Idx = 0;
      GlobalDeclID ID = ReadDeclID(F, Record, Idx);
      auto *Data = (const unsigned char*)Blob.data();
      PendingVisibleUpdates[ID].push_back(PendingVisibleUpdate{&F, Data});
      // If we've already loaded the decl, perform the updates when we finish
      // loading this block.
      if (Decl *D = GetExistingDecl(ID))
        PendingUpdateRecords.push_back(
            PendingUpdateRecord(ID, D, /*JustLoaded=*/false));
      break;
    }
 
    case IDENTIFIER_TABLE:
      F.IdentifierTableData =
          reinterpret_cast<const unsigned char *>(Blob.data());
      if (Record[0]) {
        F.IdentifierLookupTable = ASTIdentifierLookupTable::Create(
            F.IdentifierTableData + Record[0],
            F.IdentifierTableData + sizeof(uint32_t),
            F.IdentifierTableData,
            ASTIdentifierLookupTrait(*this, F));
 
        PP.getIdentifierTable().setExternalIdentifierLookup(this);
      }
      break;
 
    case IDENTIFIER_OFFSET: {
      if (F.LocalNumIdentifiers != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "duplicate IDENTIFIER_OFFSET record in AST file");
      F.IdentifierOffsets = (const uint32_t *)Blob.data();
      F.LocalNumIdentifiers = Record[0];
      F.BaseIdentifierID = getTotalNumIdentifiers();
 
      if (F.LocalNumIdentifiers > 0)
        IdentifiersLoaded.resize(IdentifiersLoaded.size()
                                 + F.LocalNumIdentifiers);
      break;
    }
 
    case INTERESTING_IDENTIFIERS:
      F.PreloadIdentifierOffsets.assign(Record.begin(), Record.end());
      break;
 
    case EAGERLY_DESERIALIZED_DECLS:
      // FIXME: Skip reading this record if our ASTConsumer doesn't care
      // about "interesting" decls (for instance, if we're building a module).
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        EagerlyDeserializedDecls.push_back(ReadDeclID(F, Record, I));
      break;
 
    case MODULAR_CODEGEN_DECLS:
      // FIXME: Skip reading this record if our ASTConsumer doesn't care about
      // them (ie: if we're not codegenerating this module).
      if (F.Kind == MK_MainFile ||
          getContext().getLangOpts().BuildingPCHWithObjectFile)
        for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
          EagerlyDeserializedDecls.push_back(ReadDeclID(F, Record, I));
      break;
 
    case SPECIAL_TYPES:
      if (SpecialTypes.empty()) {
        for (unsigned I = 0, N = Record.size(); I != N; ++I)
          SpecialTypes.push_back(getGlobalTypeID(F, Record[I]));
        break;
      }
 
      if (SpecialTypes.size() != Record.size())
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid special-types record");
 
      for (unsigned I = 0, N = Record.size(); I != N; ++I) {
        serialization::TypeID ID = getGlobalTypeID(F, Record[I]);
        if (!SpecialTypes[I])
          SpecialTypes[I] = ID;
        // FIXME: If ID && SpecialTypes[I] != ID, do we need a separate
        // merge step?
      }
      break;
 
    case STATISTICS:
      TotalNumStatements += Record[0];
      TotalNumMacros += Record[1];
      TotalLexicalDeclContexts += Record[2];
      TotalVisibleDeclContexts += Record[3];
      break;
 
    case UNUSED_FILESCOPED_DECLS:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        UnusedFileScopedDecls.push_back(ReadDeclID(F, Record, I));
      break;
 
    case DELEGATING_CTORS:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        DelegatingCtorDecls.push_back(ReadDeclID(F, Record, I));
      break;
 
    case WEAK_UNDECLARED_IDENTIFIERS:
      if (Record.size() % 3 != 0)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid weak identifiers record");
 
      // FIXME: Ignore weak undeclared identifiers from non-original PCH
      // files. This isn't the way to do it :)
      WeakUndeclaredIdentifiers.clear();
 
      // Translate the weak, undeclared identifiers into global IDs.
      for (unsigned I = 0, N = Record.size(); I < N; /* in loop */) {
        WeakUndeclaredIdentifiers.push_back(
          getGlobalIdentifierID(F, Record[I++]));
        WeakUndeclaredIdentifiers.push_back(
          getGlobalIdentifierID(F, Record[I++]));
        WeakUndeclaredIdentifiers.push_back(
            ReadSourceLocation(F, Record, I).getRawEncoding());
      }
      break;
 
    case SELECTOR_OFFSETS: {
      F.SelectorOffsets = (const uint32_t *)Blob.data();
      F.LocalNumSelectors = Record[0];
      unsigned LocalBaseSelectorID = Record[1];
      F.BaseSelectorID = getTotalNumSelectors();
 
      if (F.LocalNumSelectors > 0) {
        // Introduce the global -> local mapping for selectors within this
        // module.
        GlobalSelectorMap.insert(std::make_pair(getTotalNumSelectors()+1, &F));
 
        // Introduce the local -> global mapping for selectors within this
        // module.
        F.SelectorRemap.insertOrReplace(
          std::make_pair(LocalBaseSelectorID,
                         F.BaseSelectorID - LocalBaseSelectorID));
 
        SelectorsLoaded.resize(SelectorsLoaded.size() + F.LocalNumSelectors);
      }
      break;
    }
 
    case METHOD_POOL:
      F.SelectorLookupTableData = (const unsigned char *)Blob.data();
      if (Record[0])
        F.SelectorLookupTable
          = ASTSelectorLookupTable::Create(
                        F.SelectorLookupTableData + Record[0],
                        F.SelectorLookupTableData,
                        ASTSelectorLookupTrait(*this, F));
      TotalNumMethodPoolEntries += Record[1];
      break;
 
    case REFERENCED_SELECTOR_POOL:
      if (!Record.empty()) {
        for (unsigned Idx = 0, N = Record.size() - 1; Idx < N; /* in loop */) {
          ReferencedSelectorsData.push_back(getGlobalSelectorID(F,
                                                                Record[Idx++]));
          ReferencedSelectorsData.push_back(ReadSourceLocation(F, Record, Idx).
                                              getRawEncoding());
        }
      }
      break;
 
    case PP_ASSUME_NONNULL_LOC: {
      unsigned Idx = 0;
      if (!Record.empty())
        PP.setPreambleRecordedPragmaAssumeNonNullLoc(
            ReadSourceLocation(F, Record, Idx));
      break;
    }
 
    case PP_UNSAFE_BUFFER_USAGE: {
      if (!Record.empty()) {
        SmallVector<SourceLocation, 64> SrcLocs;
        unsigned Idx = 0;
        while (Idx < Record.size())
          SrcLocs.push_back(ReadSourceLocation(F, Record, Idx));
        PP.setDeserializedSafeBufferOptOutMap(SrcLocs);
      }
      break;
    }
 
    case PP_CONDITIONAL_STACK:
      if (!Record.empty()) {
        unsigned Idx = 0, End = Record.size() - 1;
        bool ReachedEOFWhileSkipping = Record[Idx++];
        std::optional<Preprocessor::PreambleSkipInfo> SkipInfo;
        if (ReachedEOFWhileSkipping) {
          SourceLocation HashToken = ReadSourceLocation(F, Record, Idx);
          SourceLocation IfTokenLoc = ReadSourceLocation(F, Record, Idx);
          bool FoundNonSkipPortion = Record[Idx++];
          bool FoundElse = Record[Idx++];
          SourceLocation ElseLoc = ReadSourceLocation(F, Record, Idx);
          SkipInfo.emplace(HashToken, IfTokenLoc, FoundNonSkipPortion,
                           FoundElse, ElseLoc);
        }
        SmallVector<PPConditionalInfo, 4> ConditionalStack;
        while (Idx < End) {
          auto Loc = ReadSourceLocation(F, Record, Idx);
          bool WasSkipping = Record[Idx++];
          bool FoundNonSkip = Record[Idx++];
          bool FoundElse = Record[Idx++];
          ConditionalStack.push_back(
              {Loc, WasSkipping, FoundNonSkip, FoundElse});
        }
        PP.setReplayablePreambleConditionalStack(ConditionalStack, SkipInfo);
      }
      break;
 
    case PP_COUNTER_VALUE:
      if (!Record.empty() && Listener)
        Listener->ReadCounter(F, Record[0]);
      break;
 
    case FILE_SORTED_DECLS:
      F.FileSortedDecls = (const unaligned_decl_id_t *)Blob.data();
      F.NumFileSortedDecls = Record[0];
      break;
 
    case SOURCE_LOCATION_OFFSETS: {
      F.SLocEntryOffsets = (const uint32_t *)Blob.data();
      F.LocalNumSLocEntries = Record[0];
      SourceLocation::UIntTy SLocSpaceSize = Record[1];
      F.SLocEntryOffsetsBase = Record[2] + F.SourceManagerBlockStartOffset;
      std::tie(F.SLocEntryBaseID, F.SLocEntryBaseOffset) =
          SourceMgr.AllocateLoadedSLocEntries(F.LocalNumSLocEntries,
                                              SLocSpaceSize);
      if (!F.SLocEntryBaseID) {
        if (!Diags.isDiagnosticInFlight()) {
          Diags.Report(SourceLocation(), diag::remark_sloc_usage);
          SourceMgr.noteSLocAddressSpaceUsage(Diags);
        }
        return llvm::createStringError(std::errc::invalid_argument,
                                       "ran out of source locations");
      }
      // Make our entry in the range map. BaseID is negative and growing, so
      // we invert it. Because we invert it, though, we need the other end of
      // the range.
      unsigned RangeStart =
          unsigned(-F.SLocEntryBaseID) - F.LocalNumSLocEntries + 1;
      GlobalSLocEntryMap.insert(std::make_pair(RangeStart, &F));
      F.FirstLoc = SourceLocation::getFromRawEncoding(F.SLocEntryBaseOffset);
 
      // SLocEntryBaseOffset is lower than MaxLoadedOffset and decreasing.
      assert((F.SLocEntryBaseOffset & SourceLocation::MacroIDBit) == 0);
      GlobalSLocOffsetMap.insert(
          std::make_pair(SourceManager::MaxLoadedOffset - F.SLocEntryBaseOffset
                           - SLocSpaceSize,&F));
 
      TotalNumSLocEntries += F.LocalNumSLocEntries;
      break;
    }
 
    case MODULE_OFFSET_MAP:
      F.ModuleOffsetMap = Blob;
      break;
 
    case SOURCE_MANAGER_LINE_TABLE:
      ParseLineTable(F, Record);
      break;
 
    case EXT_VECTOR_DECLS:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        ExtVectorDecls.push_back(ReadDeclID(F, Record, I));
      break;
 
    case VTABLE_USES:
      if (Record.size() % 3 != 0)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "Invalid VTABLE_USES record");
 
      // Later tables overwrite earlier ones.
      // FIXME: Modules will have some trouble with this. This is clearly not
      // the right way to do this.
      VTableUses.clear();
 
      for (unsigned Idx = 0, N = Record.size(); Idx != N; /* In loop */) {
        VTableUses.push_back(
            {ReadDeclID(F, Record, Idx),
             ReadSourceLocation(F, Record, Idx).getRawEncoding(),
             (bool)Record[Idx++]});
      }
      break;
 
    case PENDING_IMPLICIT_INSTANTIATIONS:
 
      if (Record.size() % 2 != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "Invalid PENDING_IMPLICIT_INSTANTIATIONS block");
 
      for (unsigned I = 0, N = Record.size(); I != N; /* in loop */) {
        PendingInstantiations.push_back(
            {ReadDeclID(F, Record, I),
             ReadSourceLocation(F, Record, I).getRawEncoding()});
      }
      break;
 
    case SEMA_DECL_REFS:
      if (Record.size() != 3)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "Invalid SEMA_DECL_REFS block");
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        SemaDeclRefs.push_back(ReadDeclID(F, Record, I));
      break;
 
    case PPD_ENTITIES_OFFSETS: {
      F.PreprocessedEntityOffsets = (const PPEntityOffset *)Blob.data();
      assert(Blob.size() % sizeof(PPEntityOffset) == 0);
      F.NumPreprocessedEntities = Blob.size() / sizeof(PPEntityOffset);
 
      unsigned LocalBasePreprocessedEntityID = Record[0];
 
      unsigned StartingID;
      if (!PP.getPreprocessingRecord())
        PP.createPreprocessingRecord();
      if (!PP.getPreprocessingRecord()->getExternalSource())
        PP.getPreprocessingRecord()->SetExternalSource(*this);
      StartingID
        = PP.getPreprocessingRecord()
            ->allocateLoadedEntities(F.NumPreprocessedEntities);
      F.BasePreprocessedEntityID = StartingID;
 
      if (F.NumPreprocessedEntities > 0) {
        // Introduce the global -> local mapping for preprocessed entities in
        // this module.
        GlobalPreprocessedEntityMap.insert(std::make_pair(StartingID, &F));
 
        // Introduce the local -> global mapping for preprocessed entities in
        // this module.
        F.PreprocessedEntityRemap.insertOrReplace(
          std::make_pair(LocalBasePreprocessedEntityID,
            F.BasePreprocessedEntityID - LocalBasePreprocessedEntityID));
      }
 
      break;
    }
 
    case PPD_SKIPPED_RANGES: {
      F.PreprocessedSkippedRangeOffsets = (const PPSkippedRange*)Blob.data();
      assert(Blob.size() % sizeof(PPSkippedRange) == 0);
      F.NumPreprocessedSkippedRanges = Blob.size() / sizeof(PPSkippedRange);
 
      if (!PP.getPreprocessingRecord())
        PP.createPreprocessingRecord();
      if (!PP.getPreprocessingRecord()->getExternalSource())
        PP.getPreprocessingRecord()->SetExternalSource(*this);
      F.BasePreprocessedSkippedRangeID = PP.getPreprocessingRecord()
          ->allocateSkippedRanges(F.NumPreprocessedSkippedRanges);
 
      if (F.NumPreprocessedSkippedRanges > 0)
        GlobalSkippedRangeMap.insert(
            std::make_pair(F.BasePreprocessedSkippedRangeID, &F));
      break;
    }
 
    case DECL_UPDATE_OFFSETS:
      if (Record.size() % 2 != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "invalid DECL_UPDATE_OFFSETS block in AST file");
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/) {
        GlobalDeclID ID = ReadDeclID(F, Record, I);
        DeclUpdateOffsets[ID].push_back(std::make_pair(&F, Record[I++]));
 
        // If we've already loaded the decl, perform the updates when we finish
        // loading this block.
        if (Decl *D = GetExistingDecl(ID))
          PendingUpdateRecords.push_back(
              PendingUpdateRecord(ID, D, /*JustLoaded=*/false));
      }
      break;
 
    case DELAYED_NAMESPACE_LEXICAL_VISIBLE_RECORD: {
      if (Record.size() % 3 != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "invalid DELAYED_NAMESPACE_LEXICAL_VISIBLE_RECORD block in AST "
            "file");
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/) {
        GlobalDeclID ID = ReadDeclID(F, Record, I);
 
        uint64_t BaseOffset = F.DeclsBlockStartOffset;
        assert(BaseOffset && "Invalid DeclsBlockStartOffset for module file!");
        uint64_t LocalLexicalOffset = Record[I++];
        uint64_t LexicalOffset =
            LocalLexicalOffset ? BaseOffset + LocalLexicalOffset : 0;
        uint64_t LocalVisibleOffset = Record[I++];
        uint64_t VisibleOffset =
            LocalVisibleOffset ? BaseOffset + LocalVisibleOffset : 0;
 
        DelayedNamespaceOffsetMap[ID] = {LexicalOffset, VisibleOffset};
 
        assert(!GetExistingDecl(ID) &&
               "We shouldn't load the namespace in the front of delayed "
               "namespace lexical and visible block");
      }
      break;
    }
 
    case OBJC_CATEGORIES_MAP:
      if (F.LocalNumObjCCategoriesInMap != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "duplicate OBJC_CATEGORIES_MAP record in AST file");
 
      F.LocalNumObjCCategoriesInMap = Record[0];
      F.ObjCCategoriesMap = (const ObjCCategoriesInfo *)Blob.data();
      break;
 
    case OBJC_CATEGORIES:
      F.ObjCCategories.swap(Record);
      break;
 
    case CUDA_SPECIAL_DECL_REFS:
      // Later tables overwrite earlier ones.
      // FIXME: Modules will have trouble with this.
      CUDASpecialDeclRefs.clear();
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        CUDASpecialDeclRefs.push_back(ReadDeclID(F, Record, I));
      break;
 
    case HEADER_SEARCH_TABLE:
      F.HeaderFileInfoTableData = Blob.data();
      F.LocalNumHeaderFileInfos = Record[1];
      if (Record[0]) {
        F.HeaderFileInfoTable
          = HeaderFileInfoLookupTable::Create(
                   (const unsigned char *)F.HeaderFileInfoTableData + Record[0],
                   (const unsigned char *)F.HeaderFileInfoTableData,
                   HeaderFileInfoTrait(*this, F,
                                       &PP.getHeaderSearchInfo(),
                                       Blob.data() + Record[2]));
 
        PP.getHeaderSearchInfo().SetExternalSource(this);
        if (!PP.getHeaderSearchInfo().getExternalLookup())
          PP.getHeaderSearchInfo().SetExternalLookup(this);
      }
      break;
 
    case FP_PRAGMA_OPTIONS:
      // Later tables overwrite earlier ones.
      FPPragmaOptions.swap(Record);
      break;
 
    case OPENCL_EXTENSIONS:
      for (unsigned I = 0, E = Record.size(); I != E; ) {
        auto Name = ReadString(Record, I);
        auto &OptInfo = OpenCLExtensions.OptMap[Name];
        OptInfo.Supported = Record[I++] != 0;
        OptInfo.Enabled = Record[I++] != 0;
        OptInfo.WithPragma = Record[I++] != 0;
        OptInfo.Avail = Record[I++];
        OptInfo.Core = Record[I++];
        OptInfo.Opt = Record[I++];
      }
      break;
 
    case TENTATIVE_DEFINITIONS:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        TentativeDefinitions.push_back(ReadDeclID(F, Record, I));
      break;
 
    case KNOWN_NAMESPACES:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        KnownNamespaces.push_back(ReadDeclID(F, Record, I));
      break;
 
    case UNDEFINED_BUT_USED:
      if (Record.size() % 2 != 0)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid undefined-but-used record");
      for (unsigned I = 0, N = Record.size(); I != N; /* in loop */) {
        UndefinedButUsed.push_back(
            {ReadDeclID(F, Record, I),
             ReadSourceLocation(F, Record, I).getRawEncoding()});
      }
      break;
 
    case DELETE_EXPRS_TO_ANALYZE:
      for (unsigned I = 0, N = Record.size(); I != N;) {
        DelayedDeleteExprs.push_back(ReadDeclID(F, Record, I).getRawValue());
        const uint64_t Count = Record[I++];
        DelayedDeleteExprs.push_back(Count);
        for (uint64_t C = 0; C < Count; ++C) {
          DelayedDeleteExprs.push_back(ReadSourceLocation(F, Record, I).getRawEncoding());
          bool IsArrayForm = Record[I++] == 1;
          DelayedDeleteExprs.push_back(IsArrayForm);
        }
      }
      break;
 
    case VTABLES_TO_EMIT:
      if (F.Kind == MK_MainFile ||
          getContext().getLangOpts().BuildingPCHWithObjectFile)
        for (unsigned I = 0, N = Record.size(); I != N;)
          VTablesToEmit.push_back(ReadDeclID(F, Record, I));
      break;
 
    case IMPORTED_MODULES:
      if (!F.isModule()) {
        // If we aren't loading a module (which has its own exports), make
        // all of the imported modules visible.
        // FIXME: Deal with macros-only imports.
        for (unsigned I = 0, N = Record.size(); I != N; /**/) {
          unsigned GlobalID = getGlobalSubmoduleID(F, Record[I++]);
          SourceLocation Loc = ReadSourceLocation(F, Record, I);
          if (GlobalID) {
            PendingImportedModules.push_back(ImportedSubmodule(GlobalID, Loc));
            if (DeserializationListener)
              DeserializationListener->ModuleImportRead(GlobalID, Loc);
          }
        }
      }
      break;
 
    case MACRO_OFFSET: {
      if (F.LocalNumMacros != 0)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "duplicate MACRO_OFFSET record in AST file");
      F.MacroOffsets = (const uint32_t *)Blob.data();
      F.LocalNumMacros = Record[0];
      unsigned LocalBaseMacroID = Record[1];
      F.MacroOffsetsBase = Record[2] + F.ASTBlockStartOffset;
      F.BaseMacroID = getTotalNumMacros();
 
      if (F.LocalNumMacros > 0) {
        // Introduce the global -> local mapping for macros within this module.
        GlobalMacroMap.insert(std::make_pair(getTotalNumMacros() + 1, &F));
 
        // Introduce the local -> global mapping for macros within this module.
        F.MacroRemap.insertOrReplace(
          std::make_pair(LocalBaseMacroID,
                         F.BaseMacroID - LocalBaseMacroID));
 
        MacrosLoaded.resize(MacrosLoaded.size() + F.LocalNumMacros);
      }
      break;
    }
 
    case LATE_PARSED_TEMPLATE:
      LateParsedTemplates.emplace_back(
          std::piecewise_construct, std::forward_as_tuple(&F),
          std::forward_as_tuple(Record.begin(), Record.end()));
      break;
 
    case OPTIMIZE_PRAGMA_OPTIONS:
      if (Record.size() != 1)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid pragma optimize record");
      OptimizeOffPragmaLocation = ReadSourceLocation(F, Record[0]);
      break;
 
    case MSSTRUCT_PRAGMA_OPTIONS:
      if (Record.size() != 1)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid pragma ms_struct record");
      PragmaMSStructState = Record[0];
      break;
 
    case POINTERS_TO_MEMBERS_PRAGMA_OPTIONS:
      if (Record.size() != 2)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "invalid pragma pointers to members record");
      PragmaMSPointersToMembersState = Record[0];
      PointersToMembersPragmaLocation = ReadSourceLocation(F, Record[1]);
      break;
 
    case UNUSED_LOCAL_TYPEDEF_NAME_CANDIDATES:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        UnusedLocalTypedefNameCandidates.push_back(ReadDeclID(F, Record, I));
      break;
 
    case CUDA_PRAGMA_FORCE_HOST_DEVICE_DEPTH:
      if (Record.size() != 1)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid cuda pragma options record");
      ForceHostDeviceDepth = Record[0];
      break;
 
    case ALIGN_PACK_PRAGMA_OPTIONS: {
      if (Record.size() < 3)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid pragma pack record");
      PragmaAlignPackCurrentValue = ReadAlignPackInfo(Record[0]);
      PragmaAlignPackCurrentLocation = ReadSourceLocation(F, Record[1]);
      unsigned NumStackEntries = Record[2];
      unsigned Idx = 3;
      // Reset the stack when importing a new module.
      PragmaAlignPackStack.clear();
      for (unsigned I = 0; I < NumStackEntries; ++I) {
        PragmaAlignPackStackEntry Entry;
        Entry.Value = ReadAlignPackInfo(Record[Idx++]);
        Entry.Location = ReadSourceLocation(F, Record[Idx++]);
        Entry.PushLocation = ReadSourceLocation(F, Record[Idx++]);
        PragmaAlignPackStrings.push_back(ReadString(Record, Idx));
        Entry.SlotLabel = PragmaAlignPackStrings.back();
        PragmaAlignPackStack.push_back(Entry);
      }
      break;
    }
 
    case FLOAT_CONTROL_PRAGMA_OPTIONS: {
      if (Record.size() < 3)
        return llvm::createStringError(std::errc::illegal_byte_sequence,
                                       "invalid pragma float control record");
      FpPragmaCurrentValue = FPOptionsOverride::getFromOpaqueInt(Record[0]);
      FpPragmaCurrentLocation = ReadSourceLocation(F, Record[1]);
      unsigned NumStackEntries = Record[2];
      unsigned Idx = 3;
      // Reset the stack when importing a new module.
      FpPragmaStack.clear();
      for (unsigned I = 0; I < NumStackEntries; ++I) {
        FpPragmaStackEntry Entry;
        Entry.Value = FPOptionsOverride::getFromOpaqueInt(Record[Idx++]);
        Entry.Location = ReadSourceLocation(F, Record[Idx++]);
        Entry.PushLocation = ReadSourceLocation(F, Record[Idx++]);
        FpPragmaStrings.push_back(ReadString(Record, Idx));
        Entry.SlotLabel = FpPragmaStrings.back();
        FpPragmaStack.push_back(Entry);
      }
      break;
    }
 
    case DECLS_TO_CHECK_FOR_DEFERRED_DIAGS:
      for (unsigned I = 0, N = Record.size(); I != N; /*in loop*/)
        DeclsToCheckForDeferredDiags.insert(ReadDeclID(F, Record, I));
      break;
    }
  }
}
 
void ASTReader::ReadModuleOffsetMap(ModuleFile &F) const {
  assert(!F.ModuleOffsetMap.empty() && "no module offset map to read");
 
  // Additional remapping information.
  const unsigned char *Data = (const unsigned char*)F.ModuleOffsetMap.data();
  const unsigned char *DataEnd = Data + F.ModuleOffsetMap.size();
  F.ModuleOffsetMap = StringRef();
 
  using RemapBuilder = ContinuousRangeMap<uint32_t, int, 2>::Builder;
  RemapBuilder MacroRemap(F.MacroRemap);
  RemapBuilder PreprocessedEntityRemap(F.PreprocessedEntityRemap);
  RemapBuilder SubmoduleRemap(F.SubmoduleRemap);
  RemapBuilder SelectorRemap(F.SelectorRemap);
 
  auto &ImportedModuleVector = F.TransitiveImports;
  assert(ImportedModuleVector.empty());
 
  while (Data < DataEnd) {
    // FIXME: Looking up dependency modules by filename is horrible. Let's
    // start fixing this with prebuilt, explicit and implicit modules and see
    // how it goes...
    using namespace llvm::support;
    ModuleKind Kind = static_cast<ModuleKind>(
        endian::readNext<uint8_t, llvm::endianness::little>(Data));
    uint16_t Len = endian::readNext<uint16_t, llvm::endianness::little>(Data);
    StringRef Name = StringRef((const char*)Data, Len);
    Data += Len;
    ModuleFile *OM = (Kind == MK_PrebuiltModule || Kind == MK_ExplicitModule ||
                              Kind == MK_ImplicitModule
                          ? ModuleMgr.lookupByModuleName(Name)
                          : ModuleMgr.lookupByFileName(Name));
    if (!OM) {
      std::string Msg = "refers to unknown module, cannot find ";
      Msg.append(std::string(Name));
      Error(Msg);
      return;
    }
 
    ImportedModuleVector.push_back(OM);
 
    uint32_t MacroIDOffset =
        endian::readNext<uint32_t, llvm::endianness::little>(Data);
    uint32_t PreprocessedEntityIDOffset =
        endian::readNext<uint32_t, llvm::endianness::little>(Data);
    uint32_t SubmoduleIDOffset =
        endian::readNext<uint32_t, llvm::endianness::little>(Data);
    uint32_t SelectorIDOffset =
        endian::readNext<uint32_t, llvm::endianness::little>(Data);
 
    auto mapOffset = [&](uint32_t Offset, uint32_t BaseOffset,
                         RemapBuilder &Remap) {
      constexpr uint32_t None = std::numeric_limits<uint32_t>::max();
      if (Offset != None)
        Remap.insert(std::make_pair(Offset,
                                    static_cast<int>(BaseOffset - Offset)));
    };
 
    mapOffset(MacroIDOffset, OM->BaseMacroID, MacroRemap);
    mapOffset(PreprocessedEntityIDOffset, OM->BasePreprocessedEntityID,
              PreprocessedEntityRemap);
    mapOffset(SubmoduleIDOffset, OM->BaseSubmoduleID, SubmoduleRemap);
    mapOffset(SelectorIDOffset, OM->BaseSelectorID, SelectorRemap);
  }
}
 
ASTReader::ASTReadResult
ASTReader::ReadModuleMapFileBlock(RecordData &Record, ModuleFile &F,
                                  const ModuleFile *ImportedBy,
                                  unsigned ClientLoadCapabilities) {
  unsigned Idx = 0;
  F.ModuleMapPath = ReadPath(F, Record, Idx);
 
  // Try to resolve ModuleName in the current header search context and
  // verify that it is found in the same module map file as we saved. If the
  // top-level AST file is a main file, skip this check because there is no
  // usable header search context.
  assert(!F.ModuleName.empty() &&
         "MODULE_NAME should come before MODULE_MAP_FILE");
  if (PP.getPreprocessorOpts().ModulesCheckRelocated &&
      F.Kind == MK_ImplicitModule && ModuleMgr.begin()->Kind != MK_MainFile) {
    // An implicitly-loaded module file should have its module listed in some
    // module map file that we've already loaded.
    Module *M =
        PP.getHeaderSearchInfo().lookupModule(F.ModuleName, F.ImportLoc);
    auto &Map = PP.getHeaderSearchInfo().getModuleMap();
    OptionalFileEntryRef ModMap =
        M ? Map.getModuleMapFileForUniquing(M) : std::nullopt;
    // Don't emit module relocation error if we have -fno-validate-pch
    if (!bool(PP.getPreprocessorOpts().DisablePCHOrModuleValidation &
              DisableValidationForModuleKind::Module) &&
        !ModMap) {
      if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities)) {
        if (auto ASTFE = M ? M->getASTFile() : std::nullopt) {
          // This module was defined by an imported (explicit) module.
          Diag(diag::err_module_file_conflict) << F.ModuleName << F.FileName
                                               << ASTFE->getName();
        } else {
          // This module was built with a different module map.
          Diag(diag::err_imported_module_not_found)
              << F.ModuleName << F.FileName
              << (ImportedBy ? ImportedBy->FileName : "") << F.ModuleMapPath
              << !ImportedBy;
          // In case it was imported by a PCH, there's a chance the user is
          // just missing to include the search path to the directory containing
          // the modulemap.
          if (ImportedBy && ImportedBy->Kind == MK_PCH)
            Diag(diag::note_imported_by_pch_module_not_found)
                << llvm::sys::path::parent_path(F.ModuleMapPath);
        }
      }
      return OutOfDate;
    }
 
    assert(M && M->Name == F.ModuleName && "found module with different name");
 
    // Check the primary module map file.
    auto StoredModMap = FileMgr.getFile(F.ModuleMapPath);
    if (!StoredModMap || *StoredModMap != ModMap) {
      assert(ModMap && "found module is missing module map file");
      assert((ImportedBy || F.Kind == MK_ImplicitModule) &&
             "top-level import should be verified");
      bool NotImported = F.Kind == MK_ImplicitModule && !ImportedBy;
      if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
        Diag(diag::err_imported_module_modmap_changed)
            << F.ModuleName << (NotImported ? F.FileName : ImportedBy->FileName)
            << ModMap->getName() << F.ModuleMapPath << NotImported;
      return OutOfDate;
    }
 
    ModuleMap::AdditionalModMapsSet AdditionalStoredMaps;
    for (unsigned I = 0, N = Record[Idx++]; I < N; ++I) {
      // FIXME: we should use input files rather than storing names.
      std::string Filename = ReadPath(F, Record, Idx);
      auto SF = FileMgr.getOptionalFileRef(Filename, false, false);
      if (!SF) {
        if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
          Error("could not find file '" + Filename +"' referenced by AST file");
        return OutOfDate;
      }
      AdditionalStoredMaps.insert(*SF);
    }
 
    // Check any additional module map files (e.g. module.private.modulemap)
    // that are not in the pcm.
    if (auto *AdditionalModuleMaps = Map.getAdditionalModuleMapFiles(M)) {
      for (FileEntryRef ModMap : *AdditionalModuleMaps) {
        // Remove files that match
        // Note: SmallPtrSet::erase is really remove
        if (!AdditionalStoredMaps.erase(ModMap)) {
          if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
            Diag(diag::err_module_different_modmap)
              << F.ModuleName << /*new*/0 << ModMap.getName();
          return OutOfDate;
        }
      }
    }
 
    // Check any additional module map files that are in the pcm, but not
    // found in header search. Cases that match are already removed.
    for (FileEntryRef ModMap : AdditionalStoredMaps) {
      if (!canRecoverFromOutOfDate(F.FileName, ClientLoadCapabilities))
        Diag(diag::err_module_different_modmap)
          << F.ModuleName << /*not new*/1 << ModMap.getName();
      return OutOfDate;
    }
  }
 
  if (Listener)
    Listener->ReadModuleMapFile(F.ModuleMapPath);
  return Success;
}
 
/// Move the given method to the back of the global list of methods.
static void moveMethodToBackOfGlobalList(Sema &S, ObjCMethodDecl *Method) {
  // Find the entry for this selector in the method pool.
  SemaObjC::GlobalMethodPool::iterator Known =
      S.ObjC().MethodPool.find(Method->getSelector());
  if (Known == S.ObjC().MethodPool.end())
    return;
 
  // Retrieve the appropriate method list.
  ObjCMethodList &Start = Method->isInstanceMethod()? Known->second.first
                                                    : Known->second.second;
  bool Found = false;
  for (ObjCMethodList *List = &Start; List; List = List->getNext()) {
    if (!Found) {
      if (List->getMethod() == Method) {
        Found = true;
      } else {
        // Keep searching.
        continue;
      }
    }
 
    if (List->getNext())
      List->setMethod(List->getNext()->getMethod());
    else
      List->setMethod(Method);
  }
}
 
void ASTReader::makeNamesVisible(const HiddenNames &Names, Module *Owner) {
  assert(Owner->NameVisibility != Module::Hidden && "nothing to make visible?");
  for (Decl *D : Names) {
    bool wasHidden = !D->isUnconditionallyVisible();
    D->setVisibleDespiteOwningModule();
 
    if (wasHidden && SemaObj) {
      if (ObjCMethodDecl *Method = dyn_cast<ObjCMethodDecl>(D)) {
        moveMethodToBackOfGlobalList(*SemaObj, Method);
      }
    }
  }
}
 
void ASTReader::makeModuleVisible(Module *Mod,
                                  Module::NameVisibilityKind NameVisibility,
                                  SourceLocation ImportLoc) {
  llvm::SmallPtrSet<Module *, 4> Visited;
  SmallVector<Module *, 4> Stack;
  Stack.push_back(Mod);
  while (!Stack.empty()) {
    Mod = Stack.pop_back_val();
 
    if (NameVisibility <= Mod->NameVisibility) {
      // This module already has this level of visibility (or greater), so
      // there is nothing more to do.
      continue;
    }
 
    if (Mod->isUnimportable()) {
      // Modules that aren't importable cannot be made visible.
      continue;
    }
 
    // Update the module's name visibility.
    Mod->NameVisibility = NameVisibility;
 
    // If we've already deserialized any names from this module,
    // mark them as visible.
    HiddenNamesMapType::iterator Hidden = HiddenNamesMap.find(Mod);
    if (Hidden != HiddenNamesMap.end()) {
      auto HiddenNames = std::move(*Hidden);
      HiddenNamesMap.erase(Hidden);
      makeNamesVisible(HiddenNames.second, HiddenNames.first);
      assert(!HiddenNamesMap.contains(Mod) &&
             "making names visible added hidden names");
    }
 
    // Push any exported modules onto the stack to be marked as visible.
    SmallVector<Module *, 16> Exports;
    Mod->getExportedModules(Exports);
    for (SmallVectorImpl<Module *>::iterator
           I = Exports.begin(), E = Exports.end(); I != E; ++I) {
      Module *Exported = *I;
      if (Visited.insert(Exported).second)
        Stack.push_back(Exported);
    }
  }
}
 
/// We've merged the definition \p MergedDef into the existing definition
/// \p Def. Ensure that \p Def is made visible whenever \p MergedDef is made
/// visible.
void ASTReader::mergeDefinitionVisibility(NamedDecl *Def,
                                          NamedDecl *MergedDef) {
  if (!Def->isUnconditionallyVisible()) {
    // If MergedDef is visible or becomes visible, make the definition visible.
    if (MergedDef->isUnconditionallyVisible())
      Def->setVisibleDespiteOwningModule();
    else {
      getContext().mergeDefinitionIntoModule(
          Def, MergedDef->getImportedOwningModule(),
          /*NotifyListeners*/ false);
      PendingMergedDefinitionsToDeduplicate.insert(Def);
    }
  }
}
 
bool ASTReader::loadGlobalIndex() {
  if (GlobalIndex)
    return false;
 
  if (TriedLoadingGlobalIndex || !UseGlobalIndex ||
      !PP.getLangOpts().Modules)
    return true;
 
  // Try to load the global index.
  TriedLoadingGlobalIndex = true;
  StringRef ModuleCachePath
    = getPreprocessor().getHeaderSearchInfo().getModuleCachePath();
  std::pair<GlobalModuleIndex *, llvm::Error> Result =
      GlobalModuleIndex::readIndex(ModuleCachePath);
  if (llvm::Error Err = std::move(Result.second)) {
    assert(!Result.first);
    consumeError(std::move(Err)); // FIXME this drops errors on the floor.
    return true;
  }
 
  GlobalIndex.reset(Result.first);
  ModuleMgr.setGlobalIndex(GlobalIndex.get());
  return false;
}
 
bool ASTReader::isGlobalIndexUnavailable() const {
  return PP.getLangOpts().Modules && UseGlobalIndex &&
         !hasGlobalIndex() && TriedLoadingGlobalIndex;
}
 
static void updateModuleTimestamp(ModuleFile &MF) {
  // Overwrite the timestamp file contents so that file's mtime changes.
  std::string TimestampFilename = MF.getTimestampFilename();
  std::error_code EC;
  llvm::raw_fd_ostream OS(TimestampFilename, EC,
                          llvm::sys::fs::OF_TextWithCRLF);
  if (EC)
    return;
  OS << "Timestamp file\n";
  OS.close();
  OS.clear_error(); // Avoid triggering a fatal error.
}
 
/// Given a cursor at the start of an AST file, scan ahead and drop the
/// cursor into the start of the given block ID, returning false on success and
/// true on failure.
static bool SkipCursorToBlock(BitstreamCursor &Cursor, unsigned BlockID) {
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Cursor.advance();
    if (!MaybeEntry) {
      // FIXME this drops errors on the floor.
      consumeError(MaybeEntry.takeError());
      return true;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
    case llvm::BitstreamEntry::EndBlock:
      return true;
 
    case llvm::BitstreamEntry::Record:
      // Ignore top-level records.
      if (Expected<unsigned> Skipped = Cursor.skipRecord(Entry.ID))
        break;
      else {
        // FIXME this drops errors on the floor.
        consumeError(Skipped.takeError());
        return true;
      }
 
    case llvm::BitstreamEntry::SubBlock:
      if (Entry.ID == BlockID) {
        if (llvm::Error Err = Cursor.EnterSubBlock(BlockID)) {
          // FIXME this drops the error on the floor.
          consumeError(std::move(Err));
          return true;
        }
        // Found it!
        return false;
      }
 
      if (llvm::Error Err = Cursor.SkipBlock()) {
        // FIXME this drops the error on the floor.
        consumeError(std::move(Err));
        return true;
      }
    }
  }
}
 
ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName, ModuleKind Type,
                                            SourceLocation ImportLoc,
                                            unsigned ClientLoadCapabilities,
                                            ModuleFile **NewLoadedModuleFile) {
  llvm::TimeTraceScope scope("ReadAST", FileName);
 
  llvm::SaveAndRestore SetCurImportLocRAII(CurrentImportLoc, ImportLoc);
  llvm::SaveAndRestore<std::optional<ModuleKind>> SetCurModuleKindRAII(
      CurrentDeserializingModuleKind, Type);
 
  // Defer any pending actions until we get to the end of reading the AST file.
  Deserializing AnASTFile(this);
 
  // Bump the generation number.
  unsigned PreviousGeneration = 0;
  if (ContextObj)
    PreviousGeneration = incrementGeneration(*ContextObj);
 
  unsigned NumModules = ModuleMgr.size();
  SmallVector<ImportedModule, 4> Loaded;
  if (ASTReadResult ReadResult =
          ReadASTCore(FileName, Type, ImportLoc,
                      /*ImportedBy=*/nullptr, Loaded, 0, 0, ASTFileSignature(),
                      ClientLoadCapabilities)) {
    ModuleMgr.removeModules(ModuleMgr.begin() + NumModules);
 
    // If we find that any modules are unusable, the global index is going
    // to be out-of-date. Just remove it.
    GlobalIndex.reset();
    ModuleMgr.setGlobalIndex(nullptr);
    return ReadResult;
  }
 
  if (NewLoadedModuleFile && !Loaded.empty())
    *NewLoadedModuleFile = Loaded.back().Mod;
 
  // Here comes stuff that we only do once the entire chain is loaded. Do *not*
  // remove modules from this point. Various fields are updated during reading
  // the AST block and removing the modules would result in dangling pointers.
  // They are generally only incidentally dereferenced, ie. a binary search
  // runs over `GlobalSLocEntryMap`, which could cause an invalid module to
  // be dereferenced but it wouldn't actually be used.
 
  // Load the AST blocks of all of the modules that we loaded. We can still
  // hit errors parsing the ASTs at this point.
  for (ImportedModule &M : Loaded) {
    ModuleFile &F = *M.Mod;
    llvm::TimeTraceScope Scope2("Read Loaded AST", F.ModuleName);
 
    // Read the AST block.
    if (llvm::Error Err = ReadASTBlock(F, ClientLoadCapabilities)) {
      Error(std::move(Err));
      return Failure;
    }
 
    // The AST block should always have a definition for the main module.
    if (F.isModule() && !F.DidReadTopLevelSubmodule) {
      Error(diag::err_module_file_missing_top_level_submodule, F.FileName);
      return Failure;
    }
 
    // Read the extension blocks.
    while (!SkipCursorToBlock(F.Stream, EXTENSION_BLOCK_ID)) {
      if (llvm::Error Err = ReadExtensionBlock(F)) {
        Error(std::move(Err));
        return Failure;
      }
    }
 
    // Once read, set the ModuleFile bit base offset and update the size in
    // bits of all files we've seen.
    F.GlobalBitOffset = TotalModulesSizeInBits;
    TotalModulesSizeInBits += F.SizeInBits;
    GlobalBitOffsetsMap.insert(std::make_pair(F.GlobalBitOffset, &F));
  }
 
  // Preload source locations and interesting indentifiers.
  for (ImportedModule &M : Loaded) {
    ModuleFile &F = *M.Mod;
 
    // Map the original source file ID into the ID space of the current
    // compilation.
    if (F.OriginalSourceFileID.isValid())
      F.OriginalSourceFileID = TranslateFileID(F, F.OriginalSourceFileID);
 
    for (auto Offset : F.PreloadIdentifierOffsets) {
      const unsigned char *Data = F.IdentifierTableData + Offset;
 
      ASTIdentifierLookupTrait Trait(*this, F);
      auto KeyDataLen = Trait.ReadKeyDataLength(Data);
      auto Key = Trait.ReadKey(Data, KeyDataLen.first);
 
      IdentifierInfo *II;
      if (!PP.getLangOpts().CPlusPlus) {
        // Identifiers present in both the module file and the importing
        // instance are marked out-of-date so that they can be deserialized
        // on next use via ASTReader::updateOutOfDateIdentifier().
        // Identifiers present in the module file but not in the importing
        // instance are ignored for now, preventing growth of the identifier
        // table. They will be deserialized on first use via ASTReader::get().
        auto It = PP.getIdentifierTable().find(Key);
        if (It == PP.getIdentifierTable().end())
          continue;
        II = It->second;
      } else {
        // With C++ modules, not many identifiers are considered interesting.
        // All identifiers in the module file can be placed into the identifier
        // table of the importing instance and marked as out-of-date. This makes
        // ASTReader::get() a no-op, and deserialization will take place on
        // first/next use via ASTReader::updateOutOfDateIdentifier().
        II = &PP.getIdentifierTable().getOwn(Key);
      }
 
      II->setOutOfDate(true);
 
      // Mark this identifier as being from an AST file so that we can track
      // whether we need to serialize it.
      markIdentifierFromAST(*this, *II, /*IsModule=*/true);
 
      // Associate the ID with the identifier so that the writer can reuse it.
      auto ID = Trait.ReadIdentifierID(Data + KeyDataLen.first);
      SetIdentifierInfo(ID, II);
    }
  }
 
  // Builtins and library builtins have already been initialized. Mark all
  // identifiers as out-of-date, so that they are deserialized on first use.
  if (Type == MK_PCH || Type == MK_Preamble || Type == MK_MainFile)
    for (auto &Id : PP.getIdentifierTable())
      Id.second->setOutOfDate(true);
 
  // Mark selectors as out of date.
  for (const auto &Sel : SelectorGeneration)
    SelectorOutOfDate[Sel.first] = true;
 
  // Setup the import locations and notify the module manager that we've
  // committed to these module files.
  for (ImportedModule &M : Loaded) {
    ModuleFile &F = *M.Mod;
 
    ModuleMgr.moduleFileAccepted(&F);
 
    // Set the import location.
    F.DirectImportLoc = ImportLoc;
    // FIXME: We assume that locations from PCH / preamble do not need
    // any translation.
    if (!M.ImportedBy)
      F.ImportLoc = M.ImportLoc;
    else
      F.ImportLoc = TranslateSourceLocation(*M.ImportedBy, M.ImportLoc);
  }
 
  // Resolve any unresolved module exports.
  for (unsigned I = 0, N = UnresolvedModuleRefs.size(); I != N; ++I) {
    UnresolvedModuleRef &Unresolved = UnresolvedModuleRefs[I];
    SubmoduleID GlobalID = getGlobalSubmoduleID(*Unresolved.File,Unresolved.ID);
    Module *ResolvedMod = getSubmodule(GlobalID);
 
    switch (Unresolved.Kind) {
    case UnresolvedModuleRef::Conflict:
      if (ResolvedMod) {
        Module::Conflict Conflict;
        Conflict.Other = ResolvedMod;
        Conflict.Message = Unresolved.String.str();
        Unresolved.Mod->Conflicts.push_back(Conflict);
      }
      continue;
 
    case UnresolvedModuleRef::Import:
      if (ResolvedMod)
        Unresolved.Mod->Imports.insert(ResolvedMod);
      continue;
 
    case UnresolvedModuleRef::Affecting:
      if (ResolvedMod)
        Unresolved.Mod->AffectingClangModules.insert(ResolvedMod);
      continue;
 
    case UnresolvedModuleRef::Export:
      if (ResolvedMod || Unresolved.IsWildcard)
        Unresolved.Mod->Exports.push_back(
          Module::ExportDecl(ResolvedMod, Unresolved.IsWildcard));
      continue;
    }
  }
  UnresolvedModuleRefs.clear();
 
  // FIXME: How do we load the 'use'd modules? They may not be submodules.
  // Might be unnecessary as use declarations are only used to build the
  // module itself.
 
  if (ContextObj)
    InitializeContext();
 
  if (SemaObj)
    UpdateSema();
 
  if (DeserializationListener)
    DeserializationListener->ReaderInitialized(this);
 
  ModuleFile &PrimaryModule = ModuleMgr.getPrimaryModule();
  if (PrimaryModule.OriginalSourceFileID.isValid()) {
    // If this AST file is a precompiled preamble, then set the
    // preamble file ID of the source manager to the file source file
    // from which the preamble was built.
    if (Type == MK_Preamble) {
      SourceMgr.setPreambleFileID(PrimaryModule.OriginalSourceFileID);
    } else if (Type == MK_MainFile) {
      SourceMgr.setMainFileID(PrimaryModule.OriginalSourceFileID);
    }
  }
 
  // For any Objective-C class definitions we have already loaded, make sure
  // that we load any additional categories.
  if (ContextObj) {
    for (unsigned I = 0, N = ObjCClassesLoaded.size(); I != N; ++I) {
      loadObjCCategories(ObjCClassesLoaded[I]->getGlobalID(),
                         ObjCClassesLoaded[I], PreviousGeneration);
    }
  }
 
  HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
  if (HSOpts.ModulesValidateOncePerBuildSession) {
    // Now we are certain that the module and all modules it depends on are
    // up-to-date. For implicitly-built module files, ensure the corresponding
    // timestamp files are up-to-date in this build session.
    for (unsigned I = 0, N = Loaded.size(); I != N; ++I) {
      ImportedModule &M = Loaded[I];
      if (M.Mod->Kind == MK_ImplicitModule &&
          M.Mod->InputFilesValidationTimestamp < HSOpts.BuildSessionTimestamp)
        updateModuleTimestamp(*M.Mod);
    }
  }
 
  return Success;
}
 
static ASTFileSignature readASTFileSignature(StringRef PCH);
 
/// Whether \p Stream doesn't start with the AST/PCH file magic number 'CPCH'.
static llvm::Error doesntStartWithASTFileMagic(BitstreamCursor &Stream) {
  // FIXME checking magic headers is done in other places such as
  // SerializedDiagnosticReader and GlobalModuleIndex, but error handling isn't
  // always done the same. Unify it all with a helper.
  if (!Stream.canSkipToPos(4))
    return llvm::createStringError(std::errc::illegal_byte_sequence,
                                   "file too small to contain AST file magic");
  for (unsigned C : {'C', 'P', 'C', 'H'})
    if (Expected<llvm::SimpleBitstreamCursor::word_t> Res = Stream.Read(8)) {
      if (Res.get() != C)
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "file doesn't start with AST file magic");
    } else
      return Res.takeError();
  return llvm::Error::success();
}
 
static unsigned moduleKindForDiagnostic(ModuleKind Kind) {
  switch (Kind) {
  case MK_PCH:
    return 0; // PCH
  case MK_ImplicitModule:
  case MK_ExplicitModule:
  case MK_PrebuiltModule:
    return 1; // module
  case MK_MainFile:
  case MK_Preamble:
    return 2; // main source file
  }
  llvm_unreachable("unknown module kind");
}
 
ASTReader::ASTReadResult
ASTReader::ReadASTCore(StringRef FileName,
                       ModuleKind Type,
                       SourceLocation ImportLoc,
                       ModuleFile *ImportedBy,
                       SmallVectorImpl<ImportedModule> &Loaded,
                       off_t ExpectedSize, time_t ExpectedModTime,
                       ASTFileSignature ExpectedSignature,
                       unsigned ClientLoadCapabilities) {
  ModuleFile *M;
  std::string ErrorStr;
  ModuleManager::AddModuleResult AddResult
    = ModuleMgr.addModule(FileName, Type, ImportLoc, ImportedBy,
                          getGeneration(), ExpectedSize, ExpectedModTime,
                          ExpectedSignature, readASTFileSignature,
                          M, ErrorStr);
 
  switch (AddResult) {
  case ModuleManager::AlreadyLoaded:
    Diag(diag::remark_module_import)
        << M->ModuleName << M->FileName << (ImportedBy ? true : false)
        << (ImportedBy ? StringRef(ImportedBy->ModuleName) : StringRef());
    return Success;
 
  case ModuleManager::NewlyLoaded:
    // Load module file below.
    break;
 
  case ModuleManager::Missing:
    // The module file was missing; if the client can handle that, return
    // it.
    if (ClientLoadCapabilities & ARR_Missing)
      return Missing;
 
    // Otherwise, return an error.
    Diag(diag::err_ast_file_not_found)
        << moduleKindForDiagnostic(Type) << FileName << !ErrorStr.empty()
        << ErrorStr;
    return Failure;
 
  case ModuleManager::OutOfDate:
    // We couldn't load the module file because it is out-of-date. If the
    // client can handle out-of-date, return it.
    if (ClientLoadCapabilities & ARR_OutOfDate)
      return OutOfDate;
 
    // Otherwise, return an error.
    Diag(diag::err_ast_file_out_of_date)
        << moduleKindForDiagnostic(Type) << FileName << !ErrorStr.empty()
        << ErrorStr;
    return Failure;
  }
 
  assert(M && "Missing module file");
 
  bool ShouldFinalizePCM = false;
  auto FinalizeOrDropPCM = llvm::make_scope_exit([&]() {
    auto &MC = getModuleManager().getModuleCache();
    if (ShouldFinalizePCM)
      MC.finalizePCM(FileName);
    else
      MC.tryToDropPCM(FileName);
  });
  ModuleFile &F = *M;
  BitstreamCursor &Stream = F.Stream;
  Stream = BitstreamCursor(PCHContainerRdr.ExtractPCH(*F.Buffer));
  F.SizeInBits = F.Buffer->getBufferSize() * 8;
 
  // Sniff for the signature.
  if (llvm::Error Err = doesntStartWithASTFileMagic(Stream)) {
    Diag(diag::err_ast_file_invalid)
        << moduleKindForDiagnostic(Type) << FileName << std::move(Err);
    return Failure;
  }
 
  // This is used for compatibility with older PCH formats.
  bool HaveReadControlBlock = false;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry) {
      Error(MaybeEntry.takeError());
      return Failure;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
    case llvm::BitstreamEntry::Record:
    case llvm::BitstreamEntry::EndBlock:
      Error("invalid record at top-level of AST file");
      return Failure;
 
    case llvm::BitstreamEntry::SubBlock:
      break;
    }
 
    switch (Entry.ID) {
    case CONTROL_BLOCK_ID:
      HaveReadControlBlock = true;
      switch (ReadControlBlock(F, Loaded, ImportedBy, ClientLoadCapabilities)) {
      case Success:
        // Check that we didn't try to load a non-module AST file as a module.
        //
        // FIXME: Should we also perform the converse check? Loading a module as
        // a PCH file sort of works, but it's a bit wonky.
        if ((Type == MK_ImplicitModule || Type == MK_ExplicitModule ||
             Type == MK_PrebuiltModule) &&
            F.ModuleName.empty()) {
          auto Result = (Type == MK_ImplicitModule) ? OutOfDate : Failure;
          if (Result != OutOfDate ||
              (ClientLoadCapabilities & ARR_OutOfDate) == 0)
            Diag(diag::err_module_file_not_module) << FileName;
          return Result;
        }
        break;
 
      case Failure: return Failure;
      case Missing: return Missing;
      case OutOfDate: return OutOfDate;
      case VersionMismatch: return VersionMismatch;
      case ConfigurationMismatch: return ConfigurationMismatch;
      case HadErrors: return HadErrors;
      }
      break;
 
    case AST_BLOCK_ID:
      if (!HaveReadControlBlock) {
        if ((ClientLoadCapabilities & ARR_VersionMismatch) == 0)
          Diag(diag::err_ast_file_version_too_old)
              << moduleKindForDiagnostic(Type) << FileName;
        return VersionMismatch;
      }
 
      // Record that we've loaded this module.
      Loaded.push_back(ImportedModule(M, ImportedBy, ImportLoc));
      ShouldFinalizePCM = true;
      return Success;
 
    default:
      if (llvm::Error Err = Stream.SkipBlock()) {
        Error(std::move(Err));
        return Failure;
      }
      break;
    }
  }
 
  llvm_unreachable("unexpected break; expected return");
}
 
ASTReader::ASTReadResult
ASTReader::readUnhashedControlBlock(ModuleFile &F, bool WasImportedBy,
                                    unsigned ClientLoadCapabilities) {
  const HeaderSearchOptions &HSOpts =
      PP.getHeaderSearchInfo().getHeaderSearchOpts();
  bool AllowCompatibleConfigurationMismatch =
      F.Kind == MK_ExplicitModule || F.Kind == MK_PrebuiltModule;
  bool DisableValidation = shouldDisableValidationForFile(F);
 
  ASTReadResult Result = readUnhashedControlBlockImpl(
      &F, F.Data, F.FileName, ClientLoadCapabilities,
      AllowCompatibleConfigurationMismatch, Listener.get(),
      WasImportedBy ? false : HSOpts.ModulesValidateDiagnosticOptions);
 
  // If F was directly imported by another module, it's implicitly validated by
  // the importing module.
  if (DisableValidation || WasImportedBy ||
      (AllowConfigurationMismatch && Result == ConfigurationMismatch))
    return Success;
 
  if (Result == Failure) {
    Error("malformed block record in AST file");
    return Failure;
  }
 
  if (Result == OutOfDate && F.Kind == MK_ImplicitModule) {
    // If this module has already been finalized in the ModuleCache, we're stuck
    // with it; we can only load a single version of each module.
    //
    // This can happen when a module is imported in two contexts: in one, as a
    // user module; in another, as a system module (due to an import from
    // another module marked with the [system] flag).  It usually indicates a
    // bug in the module map: this module should also be marked with [system].
    //
    // If -Wno-system-headers (the default), and the first import is as a
    // system module, then validation will fail during the as-user import,
    // since -Werror flags won't have been validated.  However, it's reasonable
    // to treat this consistently as a system module.
    //
    // If -Wsystem-headers, the PCM on disk was built with
    // -Wno-system-headers, and the first import is as a user module, then
    // validation will fail during the as-system import since the PCM on disk
    // doesn't guarantee that -Werror was respected.  However, the -Werror
    // flags were checked during the initial as-user import.
    if (getModuleManager().getModuleCache().isPCMFinal(F.FileName)) {
      Diag(diag::warn_module_system_bit_conflict) << F.FileName;
      return Success;
    }
  }
 
  return Result;
}
 
ASTReader::ASTReadResult ASTReader::readUnhashedControlBlockImpl(
    ModuleFile *F, llvm::StringRef StreamData, StringRef Filename,
    unsigned ClientLoadCapabilities, bool AllowCompatibleConfigurationMismatch,
    ASTReaderListener *Listener, bool ValidateDiagnosticOptions) {
  // Initialize a stream.
  BitstreamCursor Stream(StreamData);
 
  // Sniff for the signature.
  if (llvm::Error Err = doesntStartWithASTFileMagic(Stream)) {
    // FIXME this drops the error on the floor.
    consumeError(std::move(Err));
    return Failure;
  }
 
  // Scan for the UNHASHED_CONTROL_BLOCK_ID block.
  if (SkipCursorToBlock(Stream, UNHASHED_CONTROL_BLOCK_ID))
    return Failure;
 
  // Read all of the records in the options block.
  RecordData Record;
  ASTReadResult Result = Success;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry) {
      // FIXME this drops the error on the floor.
      consumeError(MaybeEntry.takeError());
      return Failure;
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::Error:
    case llvm::BitstreamEntry::SubBlock:
      return Failure;
 
    case llvm::BitstreamEntry::EndBlock:
      return Result;
 
    case llvm::BitstreamEntry::Record:
      // The interesting case.
      break;
    }
 
    // Read and process a record.
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecordType =
        Stream.readRecord(Entry.ID, Record, &Blob);
    if (!MaybeRecordType) {
      // FIXME this drops the error.
      return Failure;
    }
    switch ((UnhashedControlBlockRecordTypes)MaybeRecordType.get()) {
    case SIGNATURE:
      if (F) {
        F->Signature = ASTFileSignature::create(Blob.begin(), Blob.end());
        assert(F->Signature != ASTFileSignature::createDummy() &&
               "Dummy AST file signature not backpatched in ASTWriter.");
      }
      break;
    case AST_BLOCK_HASH:
      if (F) {
        F->ASTBlockHash = ASTFileSignature::create(Blob.begin(), Blob.end());
        assert(F->ASTBlockHash != ASTFileSignature::createDummy() &&
               "Dummy AST block hash not backpatched in ASTWriter.");
      }
      break;
    case DIAGNOSTIC_OPTIONS: {
      bool Complain = (ClientLoadCapabilities & ARR_OutOfDate) == 0;
      if (Listener && ValidateDiagnosticOptions &&
          !AllowCompatibleConfigurationMismatch &&
          ParseDiagnosticOptions(Record, Filename, Complain, *Listener))
        Result = OutOfDate; // Don't return early.  Read the signature.
      break;
    }
    case HEADER_SEARCH_PATHS: {
      bool Complain = (ClientLoadCapabilities & ARR_ConfigurationMismatch) == 0;
      if (Listener && !AllowCompatibleConfigurationMismatch &&
          ParseHeaderSearchPaths(Record, Complain, *Listener))
        Result = ConfigurationMismatch;
      break;
    }
    case DIAG_PRAGMA_MAPPINGS:
      if (!F)
        break;
      if (F->PragmaDiagMappings.empty())
        F->PragmaDiagMappings.swap(Record);
      else
        F->PragmaDiagMappings.insert(F->PragmaDiagMappings.end(),
                                     Record.begin(), Record.end());
      break;
    case HEADER_SEARCH_ENTRY_USAGE:
      if (F)
        F->SearchPathUsage = ReadBitVector(Record, Blob);
      break;
    case VFS_USAGE:
      if (F)
        F->VFSUsage = ReadBitVector(Record, Blob);
      break;
    }
  }
}
 
/// Parse a record and blob containing module file extension metadata.
static bool parseModuleFileExtensionMetadata(
              const SmallVectorImpl<uint64_t> &Record,
              StringRef Blob,
              ModuleFileExtensionMetadata &Metadata) {
  if (Record.size() < 4) return true;
 
  Metadata.MajorVersion = Record[0];
  Metadata.MinorVersion = Record[1];
 
  unsigned BlockNameLen = Record[2];
  unsigned UserInfoLen = Record[3];
 
  if (BlockNameLen + UserInfoLen > Blob.size()) return true;
 
  Metadata.BlockName = std::string(Blob.data(), Blob.data() + BlockNameLen);
  Metadata.UserInfo = std::string(Blob.data() + BlockNameLen,
                                  Blob.data() + BlockNameLen + UserInfoLen);
  return false;
}
 
llvm::Error ASTReader::ReadExtensionBlock(ModuleFile &F) {
  BitstreamCursor &Stream = F.Stream;
 
  RecordData Record;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry = Stream.advance();
    if (!MaybeEntry)
      return MaybeEntry.takeError();
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    switch (Entry.Kind) {
    case llvm::BitstreamEntry::SubBlock:
      if (llvm::Error Err = Stream.SkipBlock())
        return Err;
      continue;
    case llvm::BitstreamEntry::EndBlock:
      return llvm::Error::success();
    case llvm::BitstreamEntry::Error:
      return llvm::createStringError(std::errc::illegal_byte_sequence,
                                     "malformed block record in AST file");
    case llvm::BitstreamEntry::Record:
      break;
    }
 
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecCode =
        Stream.readRecord(Entry.ID, Record, &Blob);
    if (!MaybeRecCode)
      return MaybeRecCode.takeError();
    switch (MaybeRecCode.get()) {
    case EXTENSION_METADATA: {
      ModuleFileExtensionMetadata Metadata;
      if (parseModuleFileExtensionMetadata(Record, Blob, Metadata))
        return llvm::createStringError(
            std::errc::illegal_byte_sequence,
            "malformed EXTENSION_METADATA in AST file");
 
      // Find a module file extension with this block name.
      auto Known = ModuleFileExtensions.find(Metadata.BlockName);
      if (Known == ModuleFileExtensions.end()) break;
 
      // Form a reader.
      if (auto Reader = Known->second->createExtensionReader(Metadata, *this,
                                                             F, Stream)) {
        F.ExtensionReaders.push_back(std::move(Reader));
      }
 
      break;
    }
    }
  }
 
  return llvm::Error::success();
}
 
void ASTReader::InitializeContext() {
  assert(ContextObj && "no context to initialize");
  ASTContext &Context = *ContextObj;
 
  // If there's a listener, notify them that we "read" the translation unit.
  if (DeserializationListener)
    DeserializationListener->DeclRead(
        GlobalDeclID(PREDEF_DECL_TRANSLATION_UNIT_ID),
        Context.getTranslationUnitDecl());
 
  // FIXME: Find a better way to deal with collisions between these
  // built-in types. Right now, we just ignore the problem.
 
  // Load the special types.
  if (SpecialTypes.size() >= NumSpecialTypeIDs) {
    if (TypeID String = SpecialTypes[SPECIAL_TYPE_CF_CONSTANT_STRING]) {
      if (!Context.CFConstantStringTypeDecl)
        Context.setCFConstantStringType(GetType(String));
    }
 
    if (TypeID File = SpecialTypes[SPECIAL_TYPE_FILE]) {
      QualType FileType = GetType(File);
      if (FileType.isNull()) {
        Error("FILE type is NULL");
        return;
      }
 
      if (!Context.FILEDecl) {
        if (const TypedefType *Typedef = FileType->getAs<TypedefType>())
          Context.setFILEDecl(Typedef->getDecl());
        else {
          const TagType *Tag = FileType->getAs<TagType>();
          if (!Tag) {
            Error("Invalid FILE type in AST file");
            return;
          }
          Context.setFILEDecl(Tag->getDecl());
        }
      }
    }
 
    if (TypeID Jmp_buf = SpecialTypes[SPECIAL_TYPE_JMP_BUF]) {
      QualType Jmp_bufType = GetType(Jmp_buf);
      if (Jmp_bufType.isNull()) {
        Error("jmp_buf type is NULL");
        return;
      }
 
      if (!Context.jmp_bufDecl) {
        if (const TypedefType *Typedef = Jmp_bufType->getAs<TypedefType>())
          Context.setjmp_bufDecl(Typedef->getDecl());
        else {
          const TagType *Tag = Jmp_bufType->getAs<TagType>();
          if (!Tag) {
            Error("Invalid jmp_buf type in AST file");
            return;
          }
          Context.setjmp_bufDecl(Tag->getDecl());
        }
      }
    }
 
    if (TypeID Sigjmp_buf = SpecialTypes[SPECIAL_TYPE_SIGJMP_BUF]) {
      QualType Sigjmp_bufType = GetType(Sigjmp_buf);
      if (Sigjmp_bufType.isNull()) {
        Error("sigjmp_buf type is NULL");
        return;
      }
 
      if (!Context.sigjmp_bufDecl) {
        if (const TypedefType *Typedef = Sigjmp_bufType->getAs<TypedefType>())
          Context.setsigjmp_bufDecl(Typedef->getDecl());
        else {
          const TagType *Tag = Sigjmp_bufType->getAs<TagType>();
          assert(Tag && "Invalid sigjmp_buf type in AST file");
          Context.setsigjmp_bufDecl(Tag->getDecl());
        }
      }
    }
 
    if (TypeID ObjCIdRedef = SpecialTypes[SPECIAL_TYPE_OBJC_ID_REDEFINITION]) {
      if (Context.ObjCIdRedefinitionType.isNull())
        Context.ObjCIdRedefinitionType = GetType(ObjCIdRedef);
    }
 
    if (TypeID ObjCClassRedef =
            SpecialTypes[SPECIAL_TYPE_OBJC_CLASS_REDEFINITION]) {
      if (Context.ObjCClassRedefinitionType.isNull())
        Context.ObjCClassRedefinitionType = GetType(ObjCClassRedef);
    }
 
    if (TypeID ObjCSelRedef =
            SpecialTypes[SPECIAL_TYPE_OBJC_SEL_REDEFINITION]) {
      if (Context.ObjCSelRedefinitionType.isNull())
        Context.ObjCSelRedefinitionType = GetType(ObjCSelRedef);
    }
 
    if (TypeID Ucontext_t = SpecialTypes[SPECIAL_TYPE_UCONTEXT_T]) {
      QualType Ucontext_tType = GetType(Ucontext_t);
      if (Ucontext_tType.isNull()) {
        Error("ucontext_t type is NULL");
        return;
      }
 
      if (!Context.ucontext_tDecl) {
        if (const TypedefType *Typedef = Ucontext_tType->getAs<TypedefType>())
          Context.setucontext_tDecl(Typedef->getDecl());
        else {
          const TagType *Tag = Ucontext_tType->getAs<TagType>();
          assert(Tag && "Invalid ucontext_t type in AST file");
          Context.setucontext_tDecl(Tag->getDecl());
        }
      }
    }
  }
 
  ReadPragmaDiagnosticMappings(Context.getDiagnostics());
 
  // If there were any CUDA special declarations, deserialize them.
  if (!CUDASpecialDeclRefs.empty()) {
    assert(CUDASpecialDeclRefs.size() == 1 && "More decl refs than expected!");
    Context.setcudaConfigureCallDecl(
                           cast<FunctionDecl>(GetDecl(CUDASpecialDeclRefs[0])));
  }
 
  // Re-export any modules that were imported by a non-module AST file.
  // FIXME: This does not make macro-only imports visible again.
  for (auto &Import : PendingImportedModules) {
    if (Module *Imported = getSubmodule(Import.ID)) {
      makeModuleVisible(Imported, Module::AllVisible,
                        /*ImportLoc=*/Import.ImportLoc);
      if (Import.ImportLoc.isValid())
        PP.makeModuleVisible(Imported, Import.ImportLoc);
      // This updates visibility for Preprocessor only. For Sema, which can be
      // nullptr here, we do the same later, in UpdateSema().
    }
  }
 
  // Hand off these modules to Sema.
  PendingImportedModulesSema.append(PendingImportedModules);
  PendingImportedModules.clear();
}
 
void ASTReader::finalizeForWriting() {
  // Nothing to do for now.
}
 
/// Reads and return the signature record from \p PCH's control block, or
/// else returns 0.
static ASTFileSignature readASTFileSignature(StringRef PCH) {
  BitstreamCursor Stream(PCH);
  if (llvm::Error Err = doesntStartWithASTFileMagic(Stream)) {
    // FIXME this drops the error on the floor.
    consumeError(std::move(Err));
    return ASTFileSignature();
  }
 
  // Scan for the UNHASHED_CONTROL_BLOCK_ID block.
  if (SkipCursorToBlock(Stream, UNHASHED_CONTROL_BLOCK_ID))
    return ASTFileSignature();
 
  // Scan for SIGNATURE inside the diagnostic options block.
  ASTReader::RecordData Record;
  while (true) {
    Expected<llvm::BitstreamEntry> MaybeEntry =
        Stream.advanceSkippingSubblocks();
    if (!MaybeEntry) {
      // FIXME this drops the error on the floor.
      consumeError(MaybeEntry.takeError());
      return ASTFileSignature();
    }
    llvm::BitstreamEntry Entry = MaybeEntry.get();
 
    if (Entry.Kind != llvm::BitstreamEntry::Record)
      return ASTFileSignature();
 
    Record.clear();
    StringRef Blob;
    Expected<unsigned> MaybeRecord = Stream.readRecord(Entry.ID, Record, &Blob);
    if (!MaybeRecord) {
      // FIXME this drops the error on the floor.
      consumeError(MaybeRecord.takeError());
      return ASTFileSignature();
    }
    if (SIGNATURE == MaybeRecord.get()) {
      auto Signature = ASTFileSignature::create(Blob.begin(), Blob.end());
      assert(Signature != ASTFileSignature::createDummy() &&
             "Dummy AST file signature not backpatched in ASTWriter.");
      return Signature;
    }
  }
}
 
/// Retrieve the name of the original source file name
/// directly from the AST file, without actually loading the AST
/// file.
std::string ASTReader::getOriginalSourceFile(
    const std::string &ASTFileName, FileManager &FileMgr,
    const PCHContainerReader &PCHContainerRdr, DiagnosticsEngine &Diags) {
  // Open the AST file.
  auto Buffer = FileMgr.getBufferForFile(ASTFileName, /*IsVolatile=*/false,
                                         /*RequiresNullTerminator=*/false);
  if (!Buffer) {
    Diags.Report(diag::err_fe_unable_to_read_pch_file)