[Dsymutil][Debuginfo][NFC] #4 Refactor dsymutil to separate DWARF optimizing part.

[avl]

Summary

The primary goal of this refactoring is to separate DWARF optimizing part.
So that it could be reused by linker or by any other client.
There was a thread on llvm-dev discussing the necessity of such a refactoring:

http://lists.llvm.org/pipermail/llvm-dev/2019-September/135068.html.

This is a final part from series of patches for dsymutil.
Previous patches : D71068, D71839, D72476. This patch:

1. Creates lib/DWARFLinker interface :
   
   void addObjectFile(DwarfLinkerObjFile &ObjFile); bool link(); void setOptions;

1. Moves all linking logic from tools/dsymutil/DwarfLinkerForBinary into lib/DWARFLinker.
2. Renames RelocationManager into AddressesManager.
3. Remarks creation logic moved from separate parallel execution into object file loading routine.

Testing: it passes "check-all" lit testing. MD5 checksum for clang .dSYM bundle
matches for the dsymutil with/without that patch.

[merge_guards_bot]

Unit tests: pass. 61944 tests passed, 0 failed and 783 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[avl]

@JDevlieghere Jonas, Thank you for reviewing this set of patches for dsymutil!

llvm/include/llvm/CodeGen/DIE.h

 
 public:
   DIELoc() = default;
 
   /// ComputeSize - Calculate the size of the location expression.
   ///
   unsigned ComputeSize(const AsmPrinter *AP) const;
 
+  // TODO: move setSize() and Size to DIEValueList.
+  void setSize(unsigned size) { Size = size; }
+
   /// BestForm - Choose the best form for data.
   ///
   dwarf::Form BestForm(unsigned DwarfVersion) const {
     if (DwarfVersion > 3)
       return dwarf::DW_FORM_exprloc;
     // Pre-DWARF4 location expressions were blocks and not exprloc.
     if ((unsigned char)Size == Size)
       return dwarf::DW_FORM_block1;

 
 public:
   DIEBlock() = default;
 
   /// ComputeSize - Calculate the size of the location expression.
   ///
   unsigned ComputeSize(const AsmPrinter *AP) const;
 
+  // TODO: move setSize() and Size to DIEValueList.
+  void setSize(unsigned size) { Size = size; }
+
   /// BestForm - Choose the best form for data.
   ///
   dwarf::Form BestForm() const {
     if ((unsigned char)Size == Size)
       return dwarf::DW_FORM_block1;
     if ((unsigned short)Size == Size)
       return dwarf::DW_FORM_block2;
     if ((unsigned int)Size == Size)

llvm/include/llvm/DWARFLinker/DWARFLinker.h

 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
 #include "llvm/MC/MCDwarf.h"
 #include <map>
 
 namespace llvm {
 
 enum class DwarfLinkerClient { Dsymutil, LLD, General };
 
+/// The kind of accelerator tables we should emit.
+enum class AccelTableKind {
+  Apple,   ///< .apple_names, .apple_namespaces, .apple_types, .apple_objc.
+  Dwarf,   ///< DWARF v5 .debug_names.
+  Default, ///< Dwarf for DWARF5 or later, Apple otherwise.
+};
+
 /// Partial address range. Besides an offset, only the
 /// HighPC is stored. The structure is stored in a map where the LowPC is the
 /// key.
 struct ObjFileAddressRange {
   /// Function HighPC.
   uint64_t HighPC;
   /// Offset to apply to the linked address.
   /// should be 0 for not-linked object file.
public:
 
   /// Returns size of generated .debug_ranges section.
   virtual uint64_t getRangesSectionSize() const = 0;
 
   /// Returns size of generated .debug_info section.
   virtual uint64_t getDebugInfoSectionSize() const = 0;
 };
 
+using UnitListTy = std::vector<std::unique_ptr<CompileUnit>>;
+
+/// this class represents Object File and it`s additional info.
+class DwarfLinkerObjFile {
+public:
+  DwarfLinkerObjFile(StringRef Name, const object::ObjectFile *File,
+                     const std::vector<std::string> &Warnings)
+      : FileName(Name), ObjFile(File), Warnings(Warnings) {}
+
+  /// object file name.
+  StringRef FileName;
+  /// object file.
+  const object::ObjectFile *ObjFile;
+  /// helpful address information(list of valid address ranges, relocations).
+  std::unique_ptr<AddressesMap> Addresses;
+  /// warnings for object file.
+  const std::vector<std::string> &Warnings;
+};
+
+typedef std::function<void(const Twine &Warning, StringRef Context,
+                           const DWARFDie *DIE)>
+    messageHandler;
+typedef std::function<ErrorOr<DwarfLinkerObjFile &>(StringRef ContainerName,
+                                                    StringRef Path)>
+    objFileLoader;
+typedef std::map<std::string, std::string> swiftInterfacesMap;
+
+/// The core of the Dwarf linking logic.
+///
+/// The generation of the dwarf information from the object files will be
+/// driven by the selection of 'root DIEs', which are DIEs that
+/// describe variables or functions that resolves to the corresponding
+/// code section(and thus have entries in the Addresses map). All the debug
+/// information that will be generated(the DIEs, but also the line
+/// tables, ranges, ...) is derived from that set of root DIEs.
+///
+/// The root DIEs are identified because they contain relocations that
+/// points to code section(the low_pc for a function, the location for
+/// a variable). These relocations are called ValidRelocs in the
+/// AddressesInfo and are gathered as a very first step when we start
+/// processing a object file.
+class DWARFLinker {
+public:
+  DWARFLinker(const Triple &Triple, DwarfEmitter *Emitter,
+              DwarfLinkerClient ClientID = DwarfLinkerClient::General)
+      : Triple(Triple), DwarfEmitter(Emitter), DwarfLinkerClientID(ClientID) {}
+
+  /// Add object file to be linked.
+  void addObjectFile(DwarfLinkerObjFile &ObjFile);
+
+  /// Link debug info for added objFiles. Object
+  /// files are linked all together.
+  bool link();
+
+  /// A number of methods setting various linking options:
+
+  /// Allows to generate log of linking process to the standard output.
+  void setVerbosity(bool Verbose) { Options.Verbose = Verbose; }
+
+  /// Do not emit linked dwarf info.
+  void setNoOutput(bool NoOut) { Options.NoOutput = NoOut; }
+
+  /// Do not unique types according to ODR.
+  void setNoODR(bool NoODR) { Options.NoODR = NoODR; }
+
+  /// update existing DWARF info(for the linked binary).
+  void setUpdate(bool Update) { Options.Update = Update; }
+
+  /// Use specified number of threads for parallel files linking.
+  void setNumThreads(unsigned NumThreads) { Options.Threads = NumThreads; }
+
+  /// Set kind of accelerator tables to be generated.
+  void setAccelTableKind(AccelTableKind Kind) {
+    Options.TheAccelTableKind = Kind;
+  }
+
+  /// Set prepend path for clang modules.
+  void setPrependPath(const std::string &Ppath) { Options.PrependPath = Ppath; }
+
+  /// Set translator which would be used for strings.
+  void
+  setStringsTranslator(std::function<StringRef(StringRef)> StringsTranslator) {
+    this->StringsTranslator = StringsTranslator;
+  }
+
+  /// Set estimated objects files amount, for preliminary data allocation.
+  void setEstimatedObjfilesAmount(unsigned ObjFilesNum) {
+    ObjectContexts.reserve(ObjFilesNum);
+  }
+
+  /// Set warning handler which would be used to report warnings.
+  void setWarningHandler(messageHandler Handler) {
+    Options.WarningHandler = Handler;
+  }
+
+  /// Set error handler which would be used to report errors.
+  void setErrorHandler(messageHandler Handler) {
+    Options.ErrorHandler = Handler;
+  }
+
+  /// Set object files loader which would be used to load
+  /// additional objects for splitted dwarf.
+  void setObjFileLoader(objFileLoader Loader) {
+    Options.ObjFileLoader = Loader;
+  }
+
+  /// Set map for Swift interfaces.
+  void setSwiftInterfacesMap(swiftInterfacesMap *Map) {
+    Options.ParseableSwiftInterfaces = Map;
+  }
+
+private:
+  /// Flags passed to DwarfLinker::lookForDIEsToKeep
+  enum TraversalFlags {
+    TF_Keep = 1 << 0,            ///< Mark the traversed DIEs as kept.
+    TF_InFunctionScope = 1 << 1, ///< Current scope is a function scope.
+    TF_DependencyWalk = 1 << 2,  ///< Walking the dependencies of a kept DIE.
+    TF_ParentWalk = 1 << 3,      ///< Walking up the parents of a kept DIE.
+    TF_ODR = 1 << 4,             ///< Use the ODR while keeping dependents.
+    TF_SkipPC = 1 << 5,          ///< Skip all location attributes.
+  };
+
+  /// The  distinct types of work performed by the work loop.
+  enum class WorklistItemType {
+    /// Given a DIE, look for DIEs to be kept.
+    LookForDIEsToKeep,
+    /// Given a DIE, look for children of this DIE to be kept.
+    LookForChildDIEsToKeep,
+    /// Given a DIE, look for DIEs referencing this DIE to be kept.
+    LookForRefDIEsToKeep,
+    /// Given a DIE, look for parent DIEs to be kept.
+    LookForParentDIEsToKeep,
+    /// Given a DIE, update its incompleteness based on whether its children are
+    /// incomplete.
+    UpdateChildIncompleteness,
+    /// Given a DIE, update its incompleteness based on whether the DIEs it
+    /// references are incomplete.
+    UpdateRefIncompleteness,
+  };
+
+  /// This class represents an item in the work list. The type defines what kind
+  /// of work needs to be performed when processing the current item. The flags
+  /// and info fields are optional based on the type.
+  struct WorklistItem {
+    WorklistItemType Type;
+    DWARFDie Die;
+    CompileUnit &CU;
+    unsigned Flags;
+    unsigned AncestorIdx = 0;
+    CompileUnit::DIEInfo *OtherInfo = nullptr;
+
+    WorklistItem(DWARFDie Die, CompileUnit &CU, unsigned Flags,
+                 WorklistItemType T = WorklistItemType::LookForDIEsToKeep)
+        : Type(T), Die(Die), CU(CU), Flags(Flags) {}
+
+    WorklistItem(DWARFDie Die, CompileUnit &CU, WorklistItemType T,
+                 CompileUnit::DIEInfo *OtherInfo = nullptr)
+        : Type(T), Die(Die), CU(CU), OtherInfo(OtherInfo) {}
+
+    WorklistItem(unsigned AncestorIdx, CompileUnit &CU, unsigned Flags)
+        : Type(WorklistItemType::LookForParentDIEsToKeep), CU(CU), Flags(Flags),
+          AncestorIdx(AncestorIdx) {}
+  };
+
+  /// returns true if we need to translate strings.
+  bool needToTranslateStrings() { return StringsTranslator != nullptr; }
+
+  void reportWarning(const Twine &Warning, const DwarfLinkerObjFile &OF,
+                     const DWARFDie *DIE = nullptr) const {
+    if (Options.WarningHandler != nullptr)
+      Options.WarningHandler(Warning, OF.FileName, DIE);
+  }
+
+  void reportError(const Twine &Warning, const DwarfLinkerObjFile &OF,
+                   const DWARFDie *DIE = nullptr) const {
+    if (Options.ErrorHandler != nullptr)
+      Options.ErrorHandler(Warning, OF.FileName, DIE);
+  }
+
+  /// Remembers the oldest and newest DWARF version we've seen in a unit.
+  void updateDwarfVersion(unsigned Version) {
+    MaxDwarfVersion = std::max(MaxDwarfVersion, Version);
+    MinDwarfVersion = std::min(MinDwarfVersion, Version);
+  }
+
+  /// Remembers the kinds of accelerator tables we've seen in a unit.
+  void updateAccelKind(DWARFContext &Dwarf);
+
+  /// Emit warnings as Dwarf compile units to leave a trail after linking.
+  bool emitPaperTrailWarnings(const DwarfLinkerObjFile &OF,
+                              OffsetsStringPool &StringPool);
+
+  void copyInvariantDebugSection(const object::ObjectFile &Obj);
+
+  /// Keeps track of data associated with one object during linking.
+  struct LinkContext {
+    DwarfLinkerObjFile &ObjectFile;
+    std::unique_ptr<DWARFContext> DwarfContext;
+    UnitListTy CompileUnits;
+    bool Skip = false;
+
+    LinkContext(DwarfLinkerObjFile &objFile) : ObjectFile(objFile) {
+
+      if (ObjectFile.ObjFile)
+        DwarfContext = DWARFContext::create(*ObjectFile.ObjFile);
+    }
+
+    /// Clear part of the context that's no longer needed when we're done with
+    /// the debug object.
+    void clear() {
+      DwarfContext.reset(nullptr);
+      CompileUnits.clear();
+      ObjectFile.Addresses->clear();
+    }
+  };
+
+  /// Called before emitting object data
+  void cleanupAuxiliarryData(LinkContext &Context);
+
+  /// Look at the parent of the given DIE and decide whether they should be
+  /// kept.
+  void lookForParentDIEsToKeep(unsigned AncestorIdx, CompileUnit &CU,
+                               unsigned Flags,
+                               SmallVectorImpl<WorklistItem> &Worklist);
+
+  /// Look at the children of the given DIE and decide whether they should be
+  /// kept.
+  void lookForChildDIEsToKeep(const DWARFDie &Die, CompileUnit &CU,
+                              unsigned Flags,
+                              SmallVectorImpl<WorklistItem> &Worklist);
+
+  /// Look at DIEs referenced by the given DIE and decide whether they should be
+  /// kept. All DIEs referenced though attributes should be kept.
+  void lookForRefDIEsToKeep(const DWARFDie &Die, CompileUnit &CU,
+                            unsigned Flags, const UnitListTy &Units,
+                            const DwarfLinkerObjFile &OF,
+                            SmallVectorImpl<WorklistItem> &Worklist);
+
+  /// \defgroup FindRootDIEs Find DIEs corresponding to Address map entries.
+  ///
+  /// @{
+  /// Recursively walk the \p DIE tree and look for DIEs to
+  /// keep. Store that information in \p CU's DIEInfo.
+  ///
+  /// The return value indicates whether the DIE is incomplete.
+  void lookForDIEsToKeep(AddressesMap &RelocMgr, RangesTy &Ranges,
+                         const UnitListTy &Units, const DWARFDie &DIE,
+                         const DwarfLinkerObjFile &OF, CompileUnit &CU,
+                         unsigned Flags);
+
+  /// If this compile unit is really a skeleton CU that points to a
+  /// clang module, register it in ClangModules and return true.
+  ///
+  /// A skeleton CU is a CU without children, a DW_AT_gnu_dwo_name
+  /// pointing to the module, and a DW_AT_gnu_dwo_id with the module
+  /// hash.
+  bool registerModuleReference(DWARFDie CUDie, const DWARFUnit &Unit,
+                               const DwarfLinkerObjFile &OF,
+                               OffsetsStringPool &OffsetsStringPool,
+                               UniquingStringPool &UniquingStringPoolStringPool,
+                               DeclContextTree &ODRContexts,
+                               uint64_t ModulesEndOffset, unsigned &UnitID,
+                               bool IsLittleEndian, unsigned Indent = 0,
+                               bool Quiet = false);
+
+  /// Recursively add the debug info in this clang module .pcm
+  /// file (and all the modules imported by it in a bottom-up fashion)
+  /// to Units.
+  Error loadClangModule(DWARFDie CUDie, StringRef FilePath,
+                        StringRef ModuleName, uint64_t DwoId,
+                        const DwarfLinkerObjFile &OF,
+                        OffsetsStringPool &OffsetsStringPool,
+                        UniquingStringPool &UniquingStringPool,
+                        DeclContextTree &ODRContexts, uint64_t ModulesEndOffset,
+                        unsigned &UnitID, bool IsLittleEndian,
+                        unsigned Indent = 0, bool Quiet = false);
+
+  /// Mark the passed DIE as well as all the ones it depends on as kept.
+  void keepDIEAndDependencies(AddressesMap &RelocMgr, RangesTy &Ranges,
+                              const UnitListTy &Units, const DWARFDie &DIE,
+                              CompileUnit::DIEInfo &MyInfo,
+                              const DwarfLinkerObjFile &OF, CompileUnit &CU,
+                              bool UseODR);
+
+  unsigned shouldKeepDIE(AddressesMap &RelocMgr, RangesTy &Ranges,
+                         const DWARFDie &DIE, const DwarfLinkerObjFile &OF,
+                         CompileUnit &Unit, CompileUnit::DIEInfo &MyInfo,
+                         unsigned Flags);
+
+  /// Check if a variable describing DIE should be kept.
+  /// \returns updated TraversalFlags.
+  unsigned shouldKeepVariableDIE(AddressesMap &RelocMgr, const DWARFDie &DIE,
+                                 CompileUnit &Unit,
+                                 CompileUnit::DIEInfo &MyInfo, unsigned Flags);
+
+  unsigned shouldKeepSubprogramDIE(AddressesMap &RelocMgr, RangesTy &Ranges,
+                                   const DWARFDie &DIE,
+                                   const DwarfLinkerObjFile &OF,
+                                   CompileUnit &Unit,
+                                   CompileUnit::DIEInfo &MyInfo,
+                                   unsigned Flags);
+
+  /// Resolve the DIE attribute reference that has been extracted in \p
+  /// RefValue. The resulting DIE might be in another CompileUnit which is
+  /// stored into \p ReferencedCU. \returns null if resolving fails for any
+  /// reason.
+  DWARFDie resolveDIEReference(const DwarfLinkerObjFile &OF,
+                               const UnitListTy &Units,
+                               const DWARFFormValue &RefValue,
+                               const DWARFDie &DIE, CompileUnit *&RefCU);
+
+  /// @}
+
+  /// \defgroup Methods used to link the debug information
+  ///
+  /// @{
+
+  struct DWARFLinkerOptions;
+
+  class DIECloner {
+    DWARFLinker &Linker;
+    DwarfEmitter *Emitter;
+    DwarfLinkerObjFile &ObjFile;
+
+    /// Allocator used for all the DIEValue objects.
+    BumpPtrAllocator &DIEAlloc;
+
+    std::vector<std::unique_ptr<CompileUnit>> &CompileUnits;
+
+    bool Update;
+
+  public:
+    DIECloner(DWARFLinker &Linker, DwarfEmitter *Emitter,
+              DwarfLinkerObjFile &ObjFile, BumpPtrAllocator &DIEAlloc,
+              std::vector<std::unique_ptr<CompileUnit>> &CompileUnits,
+              bool Update)
+        : Linker(Linker), Emitter(Emitter), ObjFile(ObjFile),
+          DIEAlloc(DIEAlloc), CompileUnits(CompileUnits), Update(Update) {}
+
+    /// Recursively clone \p InputDIE into an tree of DIE objects
+    /// where useless (as decided by lookForDIEsToKeep()) bits have been
+    /// stripped out and addresses have been rewritten according to the
+    /// address map.
+    ///
+    /// \param OutOffset is the offset the cloned DIE in the output
+    /// compile unit.
+    /// \param PCOffset (while cloning a function scope) is the offset
+    /// applied to the entry point of the function to get the linked address.
+    /// \param Die the output DIE to use, pass NULL to create one.
+    /// \returns the root of the cloned tree or null if nothing was selected.
+    DIE *cloneDIE(const DWARFDie &InputDIE, const DwarfLinkerObjFile &OF,
+                  CompileUnit &U, OffsetsStringPool &StringPool,
+                  int64_t PCOffset, uint32_t OutOffset, unsigned Flags,
+                  bool IsLittleEndian, DIE *Die = nullptr);
+
+    /// Construct the output DIE tree by cloning the DIEs we
+    /// chose to keep above. If there are no valid relocs, then there's
+    /// nothing to clone/emit.
+    void cloneAllCompileUnits(DWARFContext &DwarfContext,
+                              const DwarfLinkerObjFile &OF,
+                              OffsetsStringPool &StringPool,
+                              bool IsLittleEndian);
+
+  private:
+    using AttributeSpec = DWARFAbbreviationDeclaration::AttributeSpec;
+
+    /// Information gathered and exchanged between the various
+    /// clone*Attributes helpers about the attributes of a particular DIE.
+    struct AttributesInfo {
+      /// Names.
+      DwarfStringPoolEntryRef Name, MangledName, NameWithoutTemplate;
+
+      /// Offsets in the string pool.
+      uint32_t NameOffset = 0;
+      uint32_t MangledNameOffset = 0;
+
+      /// Value of AT_low_pc in the input DIE
+      uint64_t OrigLowPc = std::numeric_limits<uint64_t>::max();
+
+      /// Value of AT_high_pc in the input DIE
+      uint64_t OrigHighPc = 0;
+
+      /// Offset to apply to PC addresses inside a function.
+      int64_t PCOffset = 0;
+
+      /// Does the DIE have a low_pc attribute?
+      bool HasLowPc = false;
+
+      /// Does the DIE have a ranges attribute?
+      bool HasRanges = false;
+
+      /// Is this DIE only a declaration?
+      bool IsDeclaration = false;
+
+      AttributesInfo() = default;
+    };
+
+    friend DIECloner;
+
+    /// Helper for cloneDIE.
+    unsigned cloneAttribute(DIE &Die, const DWARFDie &InputDIE,
+                            const DwarfLinkerObjFile &OF, CompileUnit &U,
+                            OffsetsStringPool &StringPool,
+                            const DWARFFormValue &Val,
+                            const AttributeSpec AttrSpec, unsigned AttrSize,
+                            AttributesInfo &AttrInfo, bool IsLittleEndian);
+
+    /// Clone a string attribute described by \p AttrSpec and add
+    /// it to \p Die.
+    /// \returns the size of the new attribute.
+    unsigned cloneStringAttribute(DIE &Die, AttributeSpec AttrSpec,
+                                  const DWARFFormValue &Val, const DWARFUnit &U,
+                                  OffsetsStringPool &StringPool,
+                                  AttributesInfo &Info);
+
+    /// Clone an attribute referencing another DIE and add
+    /// it to \p Die.
+    /// \returns the size of the new attribute.
+    unsigned cloneDieReferenceAttribute(DIE &Die, const DWARFDie &InputDIE,
+                                        AttributeSpec AttrSpec,
+                                        unsigned AttrSize,
+                                        const DWARFFormValue &Val,
+                                        const DwarfLinkerObjFile &OF,
+                                        CompileUnit &Unit);
+
+    /// Clone a DWARF expression that may be referencing another DIE.
+    void cloneExpression(DataExtractor &Data, DWARFExpression Expression,
+                         const DwarfLinkerObjFile &OF, CompileUnit &Unit,
+                         SmallVectorImpl<uint8_t> &OutputBuffer);
+
+    /// Clone an attribute referencing another DIE and add
+    /// it to \p Die.
+    /// \returns the size of the new attribute.
+    unsigned cloneBlockAttribute(DIE &Die, const DwarfLinkerObjFile &OF,
+                                 CompileUnit &Unit, AttributeSpec AttrSpec,
+                                 const DWARFFormValue &Val, unsigned AttrSize,
+                                 bool IsLittleEndian);
+
+    /// Clone an attribute referencing another DIE and add
+    /// it to \p Die.
+    /// \returns the size of the new attribute.
+    unsigned cloneAddressAttribute(DIE &Die, AttributeSpec AttrSpec,
+                                   const DWARFFormValue &Val,
+                                   const CompileUnit &Unit,
+                                   AttributesInfo &Info);
+
+    /// Clone a scalar attribute  and add it to \p Die.
+    /// \returns the size of the new attribute.
+    unsigned cloneScalarAttribute(DIE &Die, const DWARFDie &InputDIE,
+                                  const DwarfLinkerObjFile &OF, CompileUnit &U,
+                                  AttributeSpec AttrSpec,
+                                  const DWARFFormValue &Val, unsigned AttrSize,
+                                  AttributesInfo &Info);
+
+    /// Get the potential name and mangled name for the entity
+    /// described by \p Die and store them in \Info if they are not
+    /// already there.
+    /// \returns is a name was found.
+    bool getDIENames(const DWARFDie &Die, AttributesInfo &Info,
+                     OffsetsStringPool &StringPool, bool StripTemplate = false);
+
+    /// Create a copy of abbreviation Abbrev.
+    void copyAbbrev(const DWARFAbbreviationDeclaration &Abbrev, bool hasODR);
+
+    uint32_t hashFullyQualifiedName(DWARFDie DIE, CompileUnit &U,
+                                    const DwarfLinkerObjFile &OF,
+                                    int RecurseDepth = 0);
+
+    /// Helper for cloneDIE.
+    void addObjCAccelerator(CompileUnit &Unit, const DIE *Die,
+                            DwarfStringPoolEntryRef Name,
+                            OffsetsStringPool &StringPool, bool SkipPubSection);
+  };
+
+  /// Assign an abbreviation number to \p Abbrev
+  void assignAbbrev(DIEAbbrev &Abbrev);
+
+  /// Compute and emit debug_ranges section for \p Unit, and
+  /// patch the attributes referencing it.
+  void patchRangesForUnit(const CompileUnit &Unit, DWARFContext &Dwarf,
+                          const DwarfLinkerObjFile &OF) const;
+
+  /// Generate and emit the DW_AT_ranges attribute for a compile_unit if it had
+  /// one.
+  void generateUnitRanges(CompileUnit &Unit) const;
+
+  /// Extract the line tables from the original dwarf, extract the relevant
+  /// parts according to the linked function ranges and emit the result in the
+  /// debug_line section.
+  void patchLineTableForUnit(CompileUnit &Unit, DWARFContext &OrigDwarf,
+                             const DwarfLinkerObjFile &OF);
+
+  /// Emit the accelerator entries for \p Unit.
+  void emitAcceleratorEntriesForUnit(CompileUnit &Unit);
+  void emitDwarfAcceleratorEntriesForUnit(CompileUnit &Unit);
+  void emitAppleAcceleratorEntriesForUnit(CompileUnit &Unit);
+
+  /// Patch the frame info for an object file and emit it.
+  void patchFrameInfoForObject(const DwarfLinkerObjFile &, RangesTy &Ranges,
+                               DWARFContext &, unsigned AddressSize);
+
+  /// FoldingSet that uniques the abbreviations.
+  FoldingSet<DIEAbbrev> AbbreviationsSet;
+
+  /// Storage for the unique Abbreviations.
+  /// This is passed to AsmPrinter::emitDwarfAbbrevs(), thus it cannot be
+  /// changed to a vector of unique_ptrs.
+  std::vector<std::unique_ptr<DIEAbbrev>> Abbreviations;
+
+  /// DIELoc objects that need to be destructed (but not freed!).
+  std::vector<DIELoc *> DIELocs;
+
+  /// DIEBlock objects that need to be destructed (but not freed!).
+  std::vector<DIEBlock *> DIEBlocks;
+
+  /// Allocator used for all the DIEValue objects.
+  BumpPtrAllocator DIEAlloc;
+  /// @}
+
+  Triple Triple;
+
+  DwarfEmitter *DwarfEmitter;
+  std::vector<LinkContext> ObjectContexts;
+
+  unsigned MaxDwarfVersion = 0;
+  unsigned MinDwarfVersion = std::numeric_limits<unsigned>::max();
+
+  bool AtLeastOneAppleAccelTable = false;
+  bool AtLeastOneDwarfAccelTable = false;
+
+  /// The CIEs that have been emitted in the output section. The actual CIE
+  /// data serves a the key to this StringMap, this takes care of comparing the
+  /// semantics of CIEs defined in different object files.
+  StringMap<uint32_t> EmittedCIEs;
+
+  /// Offset of the last CIE that has been emitted in the output
+  /// debug_frame section.
+  uint32_t LastCIEOffset = 0;
+
+  /// Apple accelerator tables.
+  AccelTable<DWARF5AccelTableStaticData> DebugNames;
+  AccelTable<AppleAccelTableStaticOffsetData> AppleNames;
+  AccelTable<AppleAccelTableStaticOffsetData> AppleNamespaces;
+  AccelTable<AppleAccelTableStaticOffsetData> AppleObjc;
+  AccelTable<AppleAccelTableStaticTypeData> AppleTypes;
+
+  /// Mapping the PCM filename to the DwoId.
+  StringMap<uint64_t> ClangModules;
+
+  DwarfLinkerClient DwarfLinkerClientID;
+
+  std::function<StringRef(StringRef)> StringsTranslator = nullptr;
+
+  /// linking options
+  struct DWARFLinkerOptions {
+    /// Generate processing log to the standard output.
+    bool Verbose = false;
+
+    /// Skip emitting output
+    bool NoOutput = false;
+
+    /// Do not unique types according to ODR
+    bool NoODR = false;
+
+    /// Update
+    bool Update = false;
+
+    /// Number of threads.
+    unsigned Threads = 1;
+
+    /// The accelerator table kind
+    AccelTableKind TheAccelTableKind = AccelTableKind::Default;
+
+    /// Prepend path for the clang modules.
+    std::string PrependPath;
+
+    // warning handler
+    messageHandler WarningHandler = nullptr;
+
+    // error handler
+    messageHandler ErrorHandler = nullptr;
+
+    objFileLoader ObjFileLoader = nullptr;
+
+    /// A list of all .swiftinterface files referenced by the debug
+    /// info, mapping Module name to path on disk. The entries need to
+    /// be uniqued and sorted and there are only few entries expected
+    /// per compile unit, which is why this is a std::map.
+    /// this is dsymutil specific fag.
+    swiftInterfacesMap *ParseableSwiftInterfaces = nullptr;
+  } Options;
+};
+
 } // end namespace llvm
 
 #endif // LLVM_DWARFLINKER_DWARFLINKER_H

llvm/lib/DWARFLinker/DWARFLinker.cpp

 //=== DWARFLinker.cpp -----------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/DWARFLinker/DWARFLinker.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/CodeGen/NonRelocatableStringpool.h"
+#include "llvm/DWARFLinker/DWARFLinkerDeclContext.h"
+#include "llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
+#include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugRangeList.h"
+#include "llvm/DebugInfo/DWARF/DWARFDie.h"
+#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
+#include "llvm/DebugInfo/DWARF/DWARFSection.h"
+#include "llvm/DebugInfo/DWARF/DWARFUnit.h"
+#include "llvm/Object/ObjectFile.h"
+#include "llvm/Support/DataExtractor.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/ThreadPool.h"
+#include <vector>
 
 namespace llvm {
 
+/// Similar to DWARFUnitSection::getUnitForOffset(), but returning our
+/// CompileUnit object instead.
+static CompileUnit *getUnitForOffset(const UnitListTy &Units, uint64_t Offset) {
+  auto CU = std::upper_bound(
+      Units.begin(), Units.end(), Offset,
+      [](uint64_t LHS, const std::unique_ptr<CompileUnit> &RHS) {
+        return LHS < RHS->getOrigUnit().getNextUnitOffset();
+      });
+  return CU != Units.end() ? CU->get() : nullptr;
+}
+
+/// Resolve the DIE attribute reference that has been extracted in \p RefValue.
+/// The resulting DIE might be in another CompileUnit which is stored into \p
+/// ReferencedCU. \returns null if resolving fails for any reason.
+DWARFDie DWARFLinker::resolveDIEReference(const DwarfLinkerObjFile &OF,
+                                          const UnitListTy &Units,
+                                          const DWARFFormValue &RefValue,
+                                          const DWARFDie &DIE,
+                                          CompileUnit *&RefCU) {
+  assert(RefValue.isFormClass(DWARFFormValue::FC_Reference));
+  uint64_t RefOffset = *RefValue.getAsReference();
+  if ((RefCU = getUnitForOffset(Units, RefOffset)))
+    if (const auto RefDie = RefCU->getOrigUnit().getDIEForOffset(RefOffset)) {
+      // In a file with broken references, an attribute might point to a NULL
+      // DIE.
+      if (!RefDie.isNULL())
+        return RefDie;
+    }
+
+  reportWarning("could not find referenced DIE", OF, &DIE);
+  return DWARFDie();
+}
+
+/// \returns whether the passed \a Attr type might contain a DIE reference
+/// suitable for ODR uniquing.
+static bool isODRAttribute(uint16_t Attr) {
+  switch (Attr) {
+  default:
+    return false;
+  case dwarf::DW_AT_type:
+  case dwarf::DW_AT_containing_type:
+  case dwarf::DW_AT_specification:
+  case dwarf::DW_AT_abstract_origin:
+  case dwarf::DW_AT_import:
+    return true;
+  }
+  llvm_unreachable("Improper attribute.");
+}
+
+static bool isTypeTag(uint16_t Tag) {
+  switch (Tag) {
+  case dwarf::DW_TAG_array_type:
+  case dwarf::DW_TAG_class_type:
+  case dwarf::DW_TAG_enumeration_type:
+  case dwarf::DW_TAG_pointer_type:
+  case dwarf::DW_TAG_reference_type:
+  case dwarf::DW_TAG_string_type:
+  case dwarf::DW_TAG_structure_type:
+  case dwarf::DW_TAG_subroutine_type:
+  case dwarf::DW_TAG_typedef:
+  case dwarf::DW_TAG_union_type:
+  case dwarf::DW_TAG_ptr_to_member_type:
+  case dwarf::DW_TAG_set_type:
+  case dwarf::DW_TAG_subrange_type:
+  case dwarf::DW_TAG_base_type:
+  case dwarf::DW_TAG_const_type:
+  case dwarf::DW_TAG_constant:
+  case dwarf::DW_TAG_file_type:
+  case dwarf::DW_TAG_namelist:
+  case dwarf::DW_TAG_packed_type:
+  case dwarf::DW_TAG_volatile_type:
+  case dwarf::DW_TAG_restrict_type:
+  case dwarf::DW_TAG_atomic_type:
+  case dwarf::DW_TAG_interface_type:
+  case dwarf::DW_TAG_unspecified_type:
+  case dwarf::DW_TAG_shared_type:
+    return true;
+  default:
+    break;
+  }
+  return false;
+}
+
 AddressesMap::~AddressesMap() {}
 
 DwarfEmitter::~DwarfEmitter() {}
 
+bool DWARFLinker::DIECloner::getDIENames(const DWARFDie &Die,
+                                         AttributesInfo &Info,
+                                         OffsetsStringPool &StringPool,
+                                         bool StripTemplate) {
+  // This function will be called on DIEs having low_pcs and
+  // ranges. As getting the name might be more expansive, filter out
+  // blocks directly.
+  if (Die.getTag() == dwarf::DW_TAG_lexical_block)
+    return false;
+
+  // FIXME: a bit wasteful as the first getName might return the
+  // short name.
+  if (!Info.MangledName)
+    if (const char *MangledName = Die.getName(DINameKind::LinkageName))
+      Info.MangledName = StringPool.getEntry(MangledName);
+
+  if (!Info.Name)
+    if (const char *Name = Die.getName(DINameKind::ShortName))
+      Info.Name = StringPool.getEntry(Name);
+
+  if (StripTemplate && Info.Name && Info.MangledName != Info.Name) {
+    // FIXME: dsymutil compatibility. This is wrong for operator<
+    auto Split = Info.Name.getString().split('<');
+    if (!Split.second.empty())
+      Info.NameWithoutTemplate = StringPool.getEntry(Split.first);
+  }
+
+  return Info.Name || Info.MangledName;
+}
+
+/// Resolve the relative path to a build artifact referenced by DWARF by
+/// applying DW_AT_comp_dir.
+static void resolveRelativeObjectPath(SmallVectorImpl<char> &Buf, DWARFDie CU) {
+  sys::path::append(Buf, dwarf::toString(CU.find(dwarf::DW_AT_comp_dir), ""));
+}
+
+/// Collect references to parseable Swift interfaces in imported
+/// DW_TAG_module blocks.
+static void analyzeImportedModule(
+    const DWARFDie &DIE, CompileUnit &CU,
+    swiftInterfacesMap *ParseableSwiftInterfaces,
+    std::function<void(const Twine &, const DWARFDie &)> ReportWarning) {
+  if (CU.getLanguage() != dwarf::DW_LANG_Swift)
+    return;
+
+  if (!ParseableSwiftInterfaces)
+    return;
+
+  StringRef Path = dwarf::toStringRef(DIE.find(dwarf::DW_AT_LLVM_include_path));
+  if (!Path.endswith(".swiftinterface"))
+    return;
+  if (Optional<DWARFFormValue> Val = DIE.find(dwarf::DW_AT_name))
+    if (Optional<const char *> Name = Val->getAsCString()) {
+      auto &Entry = (*ParseableSwiftInterfaces)[*Name];
+      // The prepend path is applied later when copying.
+      DWARFDie CUDie = CU.getOrigUnit().getUnitDIE();
+      SmallString<128> ResolvedPath;
+      if (sys::path::is_relative(Path))
+        resolveRelativeObjectPath(ResolvedPath, CUDie);
+      sys::path::append(ResolvedPath, Path);
+      if (!Entry.empty() && Entry != ResolvedPath)
+        ReportWarning(
+            Twine("Conflicting parseable interfaces for Swift Module ") +
+                *Name + ": " + Entry + " and " + Path,
+            DIE);
+      Entry = ResolvedPath.str();
+    }
+}
+
+/// Recursive helper to build the global DeclContext information and
+/// gather the child->parent relationships in the original compile unit.
+///
+/// \return true when this DIE and all of its children are only
+/// forward declarations to types defined in external clang modules
+/// (i.e., forward declarations that are children of a DW_TAG_module).
+static bool analyzeContextInfo(
+    const DWARFDie &DIE, unsigned ParentIdx, CompileUnit &CU,
+    DeclContext *CurrentDeclContext, UniquingStringPool &StringPool,
+    DeclContextTree &Contexts, uint64_t ModulesEndOffset,
+    swiftInterfacesMap *ParseableSwiftInterfaces,
+    std::function<void(const Twine &, const DWARFDie &)> ReportWarning,
+    bool InImportedModule = false) {
+  unsigned MyIdx = CU.getOrigUnit().getDIEIndex(DIE);
+  CompileUnit::DIEInfo &Info = CU.getInfo(MyIdx);
+
+  // Clang imposes an ODR on modules(!) regardless of the language:
+  //  "The module-id should consist of only a single identifier,
+  //   which provides the name of the module being defined. Each
+  //   module shall have a single definition."
+  //
+  // This does not extend to the types inside the modules:
+  //  "[I]n C, this implies that if two structs are defined in
+  //   different submodules with the same name, those two types are
+  //   distinct types (but may be compatible types if their
+  //   definitions match)."
+  //
+  // We treat non-C++ modules like namespaces for this reason.
+  if (DIE.getTag() == dwarf::DW_TAG_module && ParentIdx == 0 &&
+      dwarf::toString(DIE.find(dwarf::DW_AT_name), "") !=
+          CU.getClangModuleName()) {
+    InImportedModule = true;
+    analyzeImportedModule(DIE, CU, ParseableSwiftInterfaces, ReportWarning);
+  }
+
+  Info.ParentIdx = ParentIdx;
+  bool InClangModule = CU.isClangModule() || InImportedModule;
+  if (CU.hasODR() || InClangModule) {
+    if (CurrentDeclContext) {
+      auto PtrInvalidPair = Contexts.getChildDeclContext(
+          *CurrentDeclContext, DIE, CU, StringPool, InClangModule);
+      CurrentDeclContext = PtrInvalidPair.getPointer();
+      Info.Ctxt =
+          PtrInvalidPair.getInt() ? nullptr : PtrInvalidPair.getPointer();
+      if (Info.Ctxt)
+        Info.Ctxt->setDefinedInClangModule(InClangModule);
+    } else
+      Info.Ctxt = CurrentDeclContext = nullptr;
+  }
+
+  Info.Prune = InImportedModule;
+  if (DIE.hasChildren())
+    for (auto Child : DIE.children())
+      Info.Prune &= analyzeContextInfo(Child, MyIdx, CU, CurrentDeclContext,
+                                       StringPool, Contexts, ModulesEndOffset,
+                                       ParseableSwiftInterfaces, ReportWarning,
+                                       InImportedModule);
+
+  // Prune this DIE if it is either a forward declaration inside a
+  // DW_TAG_module or a DW_TAG_module that contains nothing but
+  // forward declarations.
+  Info.Prune &= (DIE.getTag() == dwarf::DW_TAG_module) ||
+                (isTypeTag(DIE.getTag()) &&
+                 dwarf::toUnsigned(DIE.find(dwarf::DW_AT_declaration), 0));
+
+  // Only prune forward declarations inside a DW_TAG_module for which a
+  // definition exists elsewhere.
+  if (ModulesEndOffset == 0)
+    Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset();
+  else
+    Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() > 0 &&
+                  Info.Ctxt->getCanonicalDIEOffset() <= ModulesEndOffset;
+
+  return Info.Prune;
+}
+
+static bool dieNeedsChildrenToBeMeaningful(uint32_t Tag) {
+  switch (Tag) {
+  default:
+    return false;
+  case dwarf::DW_TAG_class_type:
+  case dwarf::DW_TAG_common_block:
+  case dwarf::DW_TAG_lexical_block:
+  case dwarf::DW_TAG_structure_type:
+  case dwarf::DW_TAG_subprogram:
+  case dwarf::DW_TAG_subroutine_type:
+  case dwarf::DW_TAG_union_type:
+    return true;
+  }
+  llvm_unreachable("Invalid Tag");
+}
+
+void DWARFLinker::cleanupAuxiliarryData(LinkContext &Context) {
+  Context.clear();
+
+  for (auto I = DIEBlocks.begin(), E = DIEBlocks.end(); I != E; ++I)
+    (*I)->~DIEBlock();
+  for (auto I = DIELocs.begin(), E = DIELocs.end(); I != E; ++I)
+    (*I)->~DIELoc();
+
+  DIEBlocks.clear();
+  DIELocs.clear();
+  DIEAlloc.Reset();
+}
+
+/// Get the starting and ending (exclusive) offset for the
+/// attribute with index \p Idx descibed by \p Abbrev. \p Offset is
+/// supposed to point to the position of the first attribute described
+/// by \p Abbrev.
+/// \return [StartOffset, EndOffset) as a pair.
+static std::pair<uint64_t, uint64_t>
+getAttributeOffsets(const DWARFAbbreviationDeclaration *Abbrev, unsigned Idx,
+                    uint64_t Offset, const DWARFUnit &Unit) {
+  DataExtractor Data = Unit.getDebugInfoExtractor();
+
+  for (unsigned I = 0; I < Idx; ++I)
+    DWARFFormValue::skipValue(Abbrev->getFormByIndex(I), Data, &Offset,
+                              Unit.getFormParams());
+
+  uint64_t End = Offset;
+  DWARFFormValue::skipValue(Abbrev->getFormByIndex(Idx), Data, &End,
+                            Unit.getFormParams());
+
+  return std::make_pair(Offset, End);
+}
+
+/// Check if a variable describing DIE should be kept.
+/// \returns updated TraversalFlags.
+unsigned DWARFLinker::shouldKeepVariableDIE(AddressesMap &RelocMgr,
+                                            const DWARFDie &DIE,
+                                            CompileUnit &Unit,
+                                            CompileUnit::DIEInfo &MyInfo,
+                                            unsigned Flags) {
+  const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
+
+  // Global variables with constant value can always be kept.
+  if (!(Flags & TF_InFunctionScope) &&
+      Abbrev->findAttributeIndex(dwarf::DW_AT_const_value)) {
+    MyInfo.InDebugMap = true;
+    return Flags | TF_Keep;
+  }
+
+  Optional<uint32_t> LocationIdx =
+      Abbrev->findAttributeIndex(dwarf::DW_AT_location);
+  if (!LocationIdx)
+    return Flags;
+
+  uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
+  const DWARFUnit &OrigUnit = Unit.getOrigUnit();
+  uint64_t LocationOffset, LocationEndOffset;
+  std::tie(LocationOffset, LocationEndOffset) =
+      getAttributeOffsets(Abbrev, *LocationIdx, Offset, OrigUnit);
+
+  // See if there is a relocation to a valid debug map entry inside
+  // this variable's location. The order is important here. We want to
+  // always check if the variable has a valid relocation, so that the
+  // DIEInfo is filled. However, we don't want a static variable in a
+  // function to force us to keep the enclosing function.
+  if (!RelocMgr.hasValidRelocationAt(LocationOffset, LocationEndOffset,
+                                     MyInfo) ||
+      (Flags & TF_InFunctionScope))
+    return Flags;
+
+  if (Options.Verbose) {
+    outs() << "Keeping variable DIE:";
+    DIDumpOptions DumpOpts;
+    DumpOpts.ChildRecurseDepth = 0;
+    DumpOpts.Verbose = Options.Verbose;
+    DIE.dump(outs(), 8 /* Indent */, DumpOpts);
+  }
+
+  return Flags | TF_Keep;
+}
+
+/// Check if a function describing DIE should be kept.
+/// \returns updated TraversalFlags.
+unsigned DWARFLinker::shouldKeepSubprogramDIE(
+    AddressesMap &RelocMgr, RangesTy &Ranges, const DWARFDie &DIE,
+    const DwarfLinkerObjFile &OF, CompileUnit &Unit,
+    CompileUnit::DIEInfo &MyInfo, unsigned Flags) {
+  const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
+
+  Flags |= TF_InFunctionScope;
+
+  Optional<uint32_t> LowPcIdx = Abbrev->findAttributeIndex(dwarf::DW_AT_low_pc);
+  if (!LowPcIdx)
+    return Flags;
+
+  uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
+  DWARFUnit &OrigUnit = Unit.getOrigUnit();
+  uint64_t LowPcOffset, LowPcEndOffset;
+  std::tie(LowPcOffset, LowPcEndOffset) =
+      getAttributeOffsets(Abbrev, *LowPcIdx, Offset, OrigUnit);
+
+  auto LowPc = dwarf::toAddress(DIE.find(dwarf::DW_AT_low_pc));
+  assert(LowPc.hasValue() && "low_pc attribute is not an address.");
+  if (!LowPc ||
+      !RelocMgr.hasValidRelocationAt(LowPcOffset, LowPcEndOffset, MyInfo))
+    return Flags;
+
+  if (Options.Verbose) {
+    outs() << "Keeping subprogram DIE:";
+    DIDumpOptions DumpOpts;
+    DumpOpts.ChildRecurseDepth = 0;
+    DumpOpts.Verbose = Options.Verbose;
+    DIE.dump(outs(), 8 /* Indent */, DumpOpts);
+  }
+
+  if (DIE.getTag() == dwarf::DW_TAG_label) {
+    if (Unit.hasLabelAt(*LowPc))
+      return Flags;
+    // FIXME: dsymutil-classic compat. dsymutil-classic doesn't consider labels
+    // that don't fall into the CU's aranges. This is wrong IMO. Debug info
+    // generation bugs aside, this is really wrong in the case of labels, where
+    // a label marking the end of a function will have a PC == CU's high_pc.
+    if (dwarf::toAddress(OrigUnit.getUnitDIE().find(dwarf::DW_AT_high_pc))
+            .getValueOr(UINT64_MAX) <= LowPc)
+      return Flags;
+    Unit.addLabelLowPc(*LowPc, MyInfo.AddrAdjust);
+    return Flags | TF_Keep;
+  }
+
+  Flags |= TF_Keep;
+
+  Optional<uint64_t> HighPc = DIE.getHighPC(*LowPc);
+  if (!HighPc) {
+    reportWarning("Function without high_pc. Range will be discarded.\n", OF,
+                  &DIE);
+    return Flags;
+  }
+
+  // Replace the debug map range with a more accurate one.
+  Ranges[*LowPc] = ObjFileAddressRange(*HighPc, MyInfo.AddrAdjust);
+  Unit.addFunctionRange(*LowPc, *HighPc, MyInfo.AddrAdjust);
+  return Flags;
+}
+
+/// Check if a DIE should be kept.
+/// \returns updated TraversalFlags.
+unsigned DWARFLinker::shouldKeepDIE(AddressesMap &RelocMgr, RangesTy &Ranges,
+                                    const DWARFDie &DIE,
+                                    const DwarfLinkerObjFile &OF,
+                                    CompileUnit &Unit,
+                                    CompileUnit::DIEInfo &MyInfo,
+                                    unsigned Flags) {
+  switch (DIE.getTag()) {
+  case dwarf::DW_TAG_constant:
+  case dwarf::DW_TAG_variable:
+    return shouldKeepVariableDIE(RelocMgr, DIE, Unit, MyInfo, Flags);
+  case dwarf::DW_TAG_subprogram:
+  case dwarf::DW_TAG_label:
+    return shouldKeepSubprogramDIE(RelocMgr, Ranges, DIE, OF, Unit, MyInfo,
+                                   Flags);
+  case dwarf::DW_TAG_base_type:
+    // DWARF Expressions may reference basic types, but scanning them
+    // is expensive. Basic types are tiny, so just keep all of them.
+  case dwarf::DW_TAG_imported_module:
+  case dwarf::DW_TAG_imported_declaration:
+  case dwarf::DW_TAG_imported_unit:
+    // We always want to keep these.
+    return Flags | TF_Keep;
+  default:
+    break;
+  }
+
+  return Flags;
+}
+
+/// Helper that updates the completeness of the current DIE based on the
+/// completeness of one of its children. It depends on the incompleteness of
+/// the children already being computed.
+static void updateChildIncompleteness(const DWARFDie &Die, CompileUnit &CU,
+                                      CompileUnit::DIEInfo &ChildInfo) {
+  switch (Die.getTag()) {
+  case dwarf::DW_TAG_structure_type:
+  case dwarf::DW_TAG_class_type:
+    break;
+  default:
+    return;
+  }
+
+  unsigned Idx = CU.getOrigUnit().getDIEIndex(Die);
+  CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
+
+  if (ChildInfo.Incomplete || ChildInfo.Prune)
+    MyInfo.Incomplete = true;
+}
+
+/// Helper that updates the completeness of the current DIE based on the
+/// completeness of the DIEs it references. It depends on the incompleteness of
+/// the referenced DIE already being computed.
+static void updateRefIncompleteness(const DWARFDie &Die, CompileUnit &CU,
+                                    CompileUnit::DIEInfo &RefInfo) {
+  switch (Die.getTag()) {
+  case dwarf::DW_TAG_typedef:
+  case dwarf::DW_TAG_member:
+  case dwarf::DW_TAG_reference_type:
+  case dwarf::DW_TAG_ptr_to_member_type:
+  case dwarf::DW_TAG_pointer_type:
+    break;
+  default:
+    return;
+  }
+
+  unsigned Idx = CU.getOrigUnit().getDIEIndex(Die);
+  CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
+
+  if (MyInfo.Incomplete)
+    return;
+
+  if (RefInfo.Incomplete)
+    MyInfo.Incomplete = true;
+}
+
+/// Look at the children of the given DIE and decide whether they should be
+/// kept.
+void DWARFLinker::lookForChildDIEsToKeep(
+    const DWARFDie &Die, CompileUnit &CU, unsigned Flags,
+    SmallVectorImpl<WorklistItem> &Worklist) {
+  // The TF_ParentWalk flag tells us that we are currently walking up the
+  // parent chain of a required DIE, and we don't want to mark all the children
+  // of the parents as kept (consider for example a DW_TAG_namespace node in
+  // the parent chain). There are however a set of DIE types for which we want
+  // to ignore that directive and still walk their children.
+  if (dieNeedsChildrenToBeMeaningful(Die.getTag()))
+    Flags &= ~DWARFLinker::TF_ParentWalk;
+
+  // We're finished if this DIE has no children or we're walking the parent
+  // chain.
+  if (!Die.hasChildren() || (Flags & DWARFLinker::TF_ParentWalk))
+    return;
+
+  // Add children in reverse order to the worklist to effectively process them
+  // in order.
+  for (auto Child : reverse(Die.children())) {
+    // Add a worklist item before every child to calculate incompleteness right
+    // after the current child is processed.
+    unsigned Idx = CU.getOrigUnit().getDIEIndex(Child);
+    CompileUnit::DIEInfo &ChildInfo = CU.getInfo(Idx);
+    Worklist.emplace_back(Die, CU, WorklistItemType::UpdateChildIncompleteness,
+                          &ChildInfo);
+    Worklist.emplace_back(Child, CU, Flags);
+  }
+}
+
+/// Look at DIEs referenced by the given DIE and decide whether they should be
+/// kept. All DIEs referenced though attributes should be kept.
+void DWARFLinker::lookForRefDIEsToKeep(
+    const DWARFDie &Die, CompileUnit &CU, unsigned Flags,
+    const UnitListTy &Units, const DwarfLinkerObjFile &OF,
+    SmallVectorImpl<WorklistItem> &Worklist) {
+  bool UseOdr = (Flags & DWARFLinker::TF_DependencyWalk)
+                    ? (Flags & DWARFLinker::TF_ODR)
+                    : CU.hasODR();
+  DWARFUnit &Unit = CU.getOrigUnit();
+  DWARFDataExtractor Data = Unit.getDebugInfoExtractor();
+  const auto *Abbrev = Die.getAbbreviationDeclarationPtr();
+  uint64_t Offset = Die.getOffset() + getULEB128Size(Abbrev->getCode());
+
+  SmallVector<std::pair<DWARFDie, CompileUnit &>, 4> ReferencedDIEs;
+  for (const auto &AttrSpec : Abbrev->attributes()) {
+    DWARFFormValue Val(AttrSpec.Form);
+    if (!Val.isFormClass(DWARFFormValue::FC_Reference) ||
+        AttrSpec.Attr == dwarf::DW_AT_sibling) {
+      DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
+                                Unit.getFormParams());
+      continue;
+    }
+
+    Val.extractValue(Data, &Offset, Unit.getFormParams(), &Unit);
+    CompileUnit *ReferencedCU;
+    if (auto RefDie = resolveDIEReference(OF, Units, Val, Die, ReferencedCU)) {
+      uint32_t RefIdx = ReferencedCU->getOrigUnit().getDIEIndex(RefDie);
+      CompileUnit::DIEInfo &Info = ReferencedCU->getInfo(RefIdx);
+      bool IsModuleRef = Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() &&
+                         Info.Ctxt->isDefinedInClangModule();
+      // If the referenced DIE has a DeclContext that has already been
+      // emitted, then do not keep the one in this CU. We'll link to
+      // the canonical DIE in cloneDieReferenceAttribute.
+      //
+      // FIXME: compatibility with dsymutil-classic. UseODR shouldn't
+      // be necessary and could be advantageously replaced by
+      // ReferencedCU->hasODR() && CU.hasODR().
+      //
+      // FIXME: compatibility with dsymutil-classic. There is no
+      // reason not to unique ref_addr references.
+      if (AttrSpec.Form != dwarf::DW_FORM_ref_addr && (UseOdr || IsModuleRef) &&
+          Info.Ctxt &&
+          Info.Ctxt != ReferencedCU->getInfo(Info.ParentIdx).Ctxt &&
+          Info.Ctxt->getCanonicalDIEOffset() && isODRAttribute(AttrSpec.Attr))
+        continue;
+
+      // Keep a module forward declaration if there is no definition.
+      if (!(isODRAttribute(AttrSpec.Attr) && Info.Ctxt &&
+            Info.Ctxt->getCanonicalDIEOffset()))
+        Info.Prune = false;
+      ReferencedDIEs.emplace_back(RefDie, *ReferencedCU);
+    }
+  }
+
+  unsigned ODRFlag = UseOdr ? DWARFLinker::TF_ODR : 0;
+
+  // Add referenced DIEs in reverse order to the worklist to effectively
+  // process them in order.
+  for (auto &P : reverse(ReferencedDIEs)) {
+    // Add a worklist item before every child to calculate incompleteness right
+    // after the current child is processed.
+    uint32_t RefIdx = P.second.getOrigUnit().getDIEIndex(P.first);
+    CompileUnit::DIEInfo &Info = P.second.getInfo(RefIdx);
+    Worklist.emplace_back(Die, CU, WorklistItemType::UpdateRefIncompleteness,
+                          &Info);
+    Worklist.emplace_back(P.first, P.second,
+                          DWARFLinker::TF_Keep |
+                              DWARFLinker::TF_DependencyWalk | ODRFlag);
+  }
+}
+
+/// Look at the parent of the given DIE and decide whether they should be kept.
+void DWARFLinker::lookForParentDIEsToKeep(
+    unsigned AncestorIdx, CompileUnit &CU, unsigned Flags,
+    SmallVectorImpl<WorklistItem> &Worklist) {
+  // Stop if we encounter an ancestor that's already marked as kept.
+  if (CU.getInfo(AncestorIdx).Keep)
+    return;
+
+  DWARFUnit &Unit = CU.getOrigUnit();
+  DWARFDie ParentDIE = Unit.getDIEAtIndex(AncestorIdx);
+  Worklist.emplace_back(CU.getInfo(AncestorIdx).ParentIdx, CU, Flags);
+  Worklist.emplace_back(ParentDIE, CU, Flags);
+}
+
+/// Recursively walk the \p DIE tree and look for DIEs to keep. Store that
+/// information in \p CU's DIEInfo.
+///
+/// This function is the entry point of the DIE selection algorithm. It is
+/// expected to walk the DIE tree in file order and (though the mediation of
+/// its helper) call hasValidRelocation() on each DIE that might be a 'root
+/// DIE' (See DwarfLinker class comment).
+///
+/// While walking the dependencies of root DIEs, this function is also called,
+/// but during these dependency walks the file order is not respected. The
+/// TF_DependencyWalk flag tells us which kind of traversal we are currently
+/// doing.
+///
+/// The recursive algorithm is implemented iteratively as a work list because
+/// very deep recursion could exhaust the stack for large projects. The work
+/// list acts as a scheduler for different types of work that need to be
+/// performed.
+///
+/// The recursive nature of the algorithm is simulated by running the "main"
+/// algorithm (LookForDIEsToKeep) followed by either looking at more DIEs
+/// (LookForChildDIEsToKeep, LookForRefDIEsToKeep, LookForParentDIEsToKeep) or
+/// fixing up a computed property (UpdateChildIncompleteness,
+/// UpdateRefIncompleteness).
+///
+/// The return value indicates whether the DIE is incomplete.
+void DWARFLinker::lookForDIEsToKeep(AddressesMap &AddressesMap,
+                                    RangesTy &Ranges, const UnitListTy &Units,
+                                    const DWARFDie &Die,
+                                    const DwarfLinkerObjFile &OF,
+                                    CompileUnit &Cu, unsigned Flags) {
+  // LIFO work list.
+  SmallVector<WorklistItem, 4> Worklist;
+  Worklist.emplace_back(Die, Cu, Flags);
+
+  while (!Worklist.empty()) {
+    WorklistItem Current = Worklist.back();
+    Worklist.pop_back();
+
+    // Look at the worklist type to decide what kind of work to perform.
+    switch (Current.Type) {
+    case WorklistItemType::UpdateChildIncompleteness:
+      updateChildIncompleteness(Current.Die, Current.CU, *Current.OtherInfo);
+      continue;
+    case WorklistItemType::UpdateRefIncompleteness:
+      updateRefIncompleteness(Current.Die, Current.CU, *Current.OtherInfo);
+      continue;
+    case WorklistItemType::LookForChildDIEsToKeep:
+      lookForChildDIEsToKeep(Current.Die, Current.CU, Current.Flags, Worklist);
+      continue;
+    case WorklistItemType::LookForRefDIEsToKeep:
+      lookForRefDIEsToKeep(Current.Die, Current.CU, Current.Flags, Units, OF,
+                           Worklist);
+      continue;
+    case WorklistItemType::LookForParentDIEsToKeep:
+      lookForParentDIEsToKeep(Current.AncestorIdx, Current.CU, Current.Flags,
+                              Worklist);
+      continue;
+    case WorklistItemType::LookForDIEsToKeep:
+      break;
+    }
+
+    unsigned Idx = Current.CU.getOrigUnit().getDIEIndex(Current.Die);
+    CompileUnit::DIEInfo &MyInfo = Current.CU.getInfo(Idx);
+
+    if (MyInfo.Prune)
+      continue;
+
+    // If the Keep flag is set, we are marking a required DIE's dependencies.
+    // If our target is already marked as kept, we're all set.
+    bool AlreadyKept = MyInfo.Keep;
+    if ((Current.Flags & TF_DependencyWalk) && AlreadyKept)
+      continue;
+
+    // We must not call shouldKeepDIE while called from keepDIEAndDependencies,
+    // because it would screw up the relocation finding logic.
+    if (!(Current.Flags & TF_DependencyWalk))
+      Current.Flags = shouldKeepDIE(AddressesMap, Ranges, Current.Die, OF,
+                                    Current.CU, MyInfo, Current.Flags);
+
+    // Finish by looking for child DIEs. Because of the LIFO worklist we need
+    // to schedule that work before any subsequent items are added to the
+    // worklist.
+    Worklist.emplace_back(Current.Die, Current.CU, Current.Flags,
+                          WorklistItemType::LookForChildDIEsToKeep);
+
+    if (AlreadyKept || !(Current.Flags & TF_Keep))
+      continue;
+
+    // If it is a newly kept DIE mark it as well as all its dependencies as
+    // kept.
+    MyInfo.Keep = true;
+
+    // We're looking for incomplete types.
+    MyInfo.Incomplete =
+        Current.Die.getTag() != dwarf::DW_TAG_subprogram &&
+        Current.Die.getTag() != dwarf::DW_TAG_member &&
+        dwarf::toUnsigned(Current.Die.find(dwarf::DW_AT_declaration), 0);
+
+    // After looking at the parent chain, look for referenced DIEs. Because of
+    // the LIFO worklist we need to schedule that work before any subsequent
+    // items are added to the worklist.
+    Worklist.emplace_back(Current.Die, Current.CU, Current.Flags,
+                          WorklistItemType::LookForRefDIEsToKeep);
+
+    bool UseOdr = (Current.Flags & TF_DependencyWalk) ? (Current.Flags & TF_ODR)
+                                                      : Current.CU.hasODR();
+    unsigned ODRFlag = UseOdr ? TF_ODR : 0;
+    unsigned ParFlags = TF_ParentWalk | TF_Keep | TF_DependencyWalk | ODRFlag;
+
+    // Now schedule the parent walk.
+    Worklist.emplace_back(MyInfo.ParentIdx, Current.CU, ParFlags);
+  }
+}
+
+/// Assign an abbreviation number to \p Abbrev.
+///
+/// Our DIEs get freed after every DebugMapObject has been processed,
+/// thus the FoldingSet we use to unique DIEAbbrevs cannot refer to
+/// the instances hold by the DIEs. When we encounter an abbreviation
+/// that we don't know, we create a permanent copy of it.
+void DWARFLinker::assignAbbrev(DIEAbbrev &Abbrev) {
+  // Check the set for priors.
+  FoldingSetNodeID ID;
+  Abbrev.Profile(ID);
+  void *InsertToken;
+  DIEAbbrev *InSet = AbbreviationsSet.FindNodeOrInsertPos(ID, InsertToken);
+
+  // If it's newly added.
+  if (InSet) {
+    // Assign existing abbreviation number.
+    Abbrev.setNumber(InSet->getNumber());
+  } else {
+    // Add to abbreviation list.
+    Abbreviations.push_back(
+        std::make_unique<DIEAbbrev>(Abbrev.getTag(), Abbrev.hasChildren()));
+    for (const auto &Attr : Abbrev.getData())
+      Abbreviations.back()->AddAttribute(Attr.getAttribute(), Attr.getForm());
+    AbbreviationsSet.InsertNode(Abbreviations.back().get(), InsertToken);
+    // Assign the unique abbreviation number.
+    Abbrev.setNumber(Abbreviations.size());
+    Abbreviations.back()->setNumber(Abbreviations.size());
+  }
+}
+
+unsigned DWARFLinker::DIECloner::cloneStringAttribute(
+    DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
+    const DWARFUnit &U, OffsetsStringPool &StringPool, AttributesInfo &Info) {
+  // Switch everything to out of line strings.
+  const char *String = *Val.getAsCString();
+  auto StringEntry = StringPool.getEntry(String);
+
+  // Update attributes info.
+  if (AttrSpec.Attr == dwarf::DW_AT_name)
+    Info.Name = StringEntry;
+  else if (AttrSpec.Attr == dwarf::DW_AT_MIPS_linkage_name ||
+           AttrSpec.Attr == dwarf::DW_AT_linkage_name)
+    Info.MangledName = StringEntry;
+
+  Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr), dwarf::DW_FORM_strp,
+               DIEInteger(StringEntry.getOffset()));
+
+  return 4;
+}
+
+unsigned DWARFLinker::DIECloner::cloneDieReferenceAttribute(
+    DIE &Die, const DWARFDie &InputDIE, AttributeSpec AttrSpec,
+    unsigned AttrSize, const DWARFFormValue &Val, const DwarfLinkerObjFile &OF,
+    CompileUnit &Unit) {
+  const DWARFUnit &U = Unit.getOrigUnit();
+  uint64_t Ref = *Val.getAsReference();
+
+  DIE *NewRefDie = nullptr;
+  CompileUnit *RefUnit = nullptr;
+  DeclContext *Ctxt = nullptr;
+
+  DWARFDie RefDie =
+      Linker.resolveDIEReference(OF, CompileUnits, Val, InputDIE, RefUnit);
+
+  // If the referenced DIE is not found,  drop the attribute.
+  if (!RefDie || AttrSpec.Attr == dwarf::DW_AT_sibling)
+    return 0;
+
+  unsigned Idx = RefUnit->getOrigUnit().getDIEIndex(RefDie);
+  CompileUnit::DIEInfo &RefInfo = RefUnit->getInfo(Idx);
+
+  // If we already have emitted an equivalent DeclContext, just point
+  // at it.
+  if (isODRAttribute(AttrSpec.Attr)) {
+    Ctxt = RefInfo.Ctxt;
+    if (Ctxt && Ctxt->getCanonicalDIEOffset()) {
+      DIEInteger Attr(Ctxt->getCanonicalDIEOffset());
+      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                   dwarf::DW_FORM_ref_addr, Attr);
+      return U.getRefAddrByteSize();
+    }
+  }
+
+  if (!RefInfo.Clone) {
+    assert(Ref > InputDIE.getOffset());
+    // We haven't cloned this DIE yet. Just create an empty one and
+    // store it. It'll get really cloned when we process it.
+    RefInfo.Clone = DIE::get(DIEAlloc, dwarf::Tag(RefDie.getTag()));
+  }
+  NewRefDie = RefInfo.Clone;
+
+  if (AttrSpec.Form == dwarf::DW_FORM_ref_addr ||
+      (Unit.hasODR() && isODRAttribute(AttrSpec.Attr))) {
+    // We cannot currently rely on a DIEEntry to emit ref_addr
+    // references, because the implementation calls back to DwarfDebug
+    // to find the unit offset. (We don't have a DwarfDebug)
+    // FIXME: we should be able to design DIEEntry reliance on
+    // DwarfDebug away.
+    uint64_t Attr;
+    if (Ref < InputDIE.getOffset()) {
+      // We must have already cloned that DIE.
+      uint32_t NewRefOffset =
+          RefUnit->getStartOffset() + NewRefDie->getOffset();
+      Attr = NewRefOffset;
+      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                   dwarf::DW_FORM_ref_addr, DIEInteger(Attr));
+    } else {
+      // A forward reference. Note and fixup later.
+      Attr = 0xBADDEF;
+      Unit.noteForwardReference(
+          NewRefDie, RefUnit, Ctxt,
+          Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                       dwarf::DW_FORM_ref_addr, DIEInteger(Attr)));
+    }
+    return U.getRefAddrByteSize();
+  }
+
+  Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+               dwarf::Form(AttrSpec.Form), DIEEntry(*NewRefDie));
+
+  return AttrSize;
+}
+
+void DWARFLinker::DIECloner::cloneExpression(
+    DataExtractor &Data, DWARFExpression Expression,
+    const DwarfLinkerObjFile &OF, CompileUnit &Unit,
+    SmallVectorImpl<uint8_t> &OutputBuffer) {
+  using Encoding = DWARFExpression::Operation::Encoding;
+
+  uint64_t OpOffset = 0;
+  for (auto &Op : Expression) {
+    auto Description = Op.getDescription();
+    // DW_OP_const_type is variable-length and has 3
+    // operands. DWARFExpression thus far only supports 2.
+    auto Op0 = Description.Op[0];
+    auto Op1 = Description.Op[1];
+    if ((Op0 == Encoding::BaseTypeRef && Op1 != Encoding::SizeNA) ||
+        (Op1 == Encoding::BaseTypeRef && Op0 != Encoding::Size1))
+      Linker.reportWarning("Unsupported DW_OP encoding.", OF);
+
+    if ((Op0 == Encoding::BaseTypeRef && Op1 == Encoding::SizeNA) ||
+        (Op1 == Encoding::BaseTypeRef && Op0 == Encoding::Size1)) {
+      // This code assumes that the other non-typeref operand fits into 1 byte.
+      assert(OpOffset < Op.getEndOffset());
+      uint32_t ULEBsize = Op.getEndOffset() - OpOffset - 1;
+      assert(ULEBsize <= 16);
+
+      // Copy over the operation.
+      OutputBuffer.push_back(Op.getCode());
+      uint64_t RefOffset;
+      if (Op1 == Encoding::SizeNA) {
+        RefOffset = Op.getRawOperand(0);
+      } else {
+        OutputBuffer.push_back(Op.getRawOperand(0));
+        RefOffset = Op.getRawOperand(1);
+      }
+      auto RefDie = Unit.getOrigUnit().getDIEForOffset(RefOffset);
+      uint32_t RefIdx = Unit.getOrigUnit().getDIEIndex(RefDie);
+      CompileUnit::DIEInfo &Info = Unit.getInfo(RefIdx);
+      uint32_t Offset = 0;
+      if (DIE *Clone = Info.Clone)
+        Offset = Clone->getOffset();
+      else
+        Linker.reportWarning("base type ref doesn't point to DW_TAG_base_type.",
+                             OF);
+      uint8_t ULEB[16];
+      unsigned RealSize = encodeULEB128(Offset, ULEB, ULEBsize);
+      if (RealSize > ULEBsize) {
+        // Emit the generic type as a fallback.
+        RealSize = encodeULEB128(0, ULEB, ULEBsize);
+        Linker.reportWarning("base type ref doesn't fit.", OF);
+      }
+      assert(RealSize == ULEBsize && "padding failed");
+      ArrayRef<uint8_t> ULEBbytes(ULEB, ULEBsize);
+      OutputBuffer.append(ULEBbytes.begin(), ULEBbytes.end());
+    } else {
+      // Copy over everything else unmodified.
+      StringRef Bytes = Data.getData().slice(OpOffset, Op.getEndOffset());
+      OutputBuffer.append(Bytes.begin(), Bytes.end());
+    }
+    OpOffset = Op.getEndOffset();
+  }
+}
+
+unsigned DWARFLinker::DIECloner::cloneBlockAttribute(
+    DIE &Die, const DwarfLinkerObjFile &OF, CompileUnit &Unit,
+    AttributeSpec AttrSpec, const DWARFFormValue &Val, unsigned AttrSize,
+    bool IsLittleEndian) {
+  DIEValueList *Attr;
+  DIEValue Value;
+  DIELoc *Loc = nullptr;
+  DIEBlock *Block = nullptr;
+  if (AttrSpec.Form == dwarf::DW_FORM_exprloc) {
+    Loc = new (DIEAlloc) DIELoc;
+    Linker.DIELocs.push_back(Loc);
+  } else {
+    Block = new (DIEAlloc) DIEBlock;
+    Linker.DIEBlocks.push_back(Block);
+  }
+  Attr = Loc ? static_cast<DIEValueList *>(Loc)
+             : static_cast<DIEValueList *>(Block);
+
+  if (Loc)
+    Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
+                     dwarf::Form(AttrSpec.Form), Loc);
+  else
+    Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
+                     dwarf::Form(AttrSpec.Form), Block);
+
+  // If the block is a DWARF Expression, clone it into the temporary
+  // buffer using cloneExpression(), otherwise copy the data directly.
+  SmallVector<uint8_t, 32> Buffer;
+  ArrayRef<uint8_t> Bytes = *Val.getAsBlock();
+  if (DWARFAttribute::mayHaveLocationDescription(AttrSpec.Attr) &&
+      (Val.isFormClass(DWARFFormValue::FC_Block) ||
+       Val.isFormClass(DWARFFormValue::FC_Exprloc))) {
+    DWARFUnit &OrigUnit = Unit.getOrigUnit();
+    DataExtractor Data(StringRef((const char *)Bytes.data(), Bytes.size()),
+                       IsLittleEndian, OrigUnit.getAddressByteSize());
+    DWARFExpression Expr(Data, OrigUnit.getVersion(),
+                         OrigUnit.getAddressByteSize());
+    cloneExpression(Data, Expr, OF, Unit, Buffer);
+    Bytes = Buffer;
+  }
+  for (auto Byte : Bytes)
+    Attr->addValue(DIEAlloc, static_cast<dwarf::Attribute>(0),
+                   dwarf::DW_FORM_data1, DIEInteger(Byte));
+
+  // FIXME: If DIEBlock and DIELoc just reuses the Size field of
+  // the DIE class, this "if" could be replaced by
+  // Attr->setSize(Bytes.size()).
+  if (Loc)
+    Loc->setSize(Bytes.size());
+  else
+    Block->setSize(Bytes.size());
+
+  Die.addValue(DIEAlloc, Value);
+  return AttrSize;
+}
+
+unsigned DWARFLinker::DIECloner::cloneAddressAttribute(
+    DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
+    const CompileUnit &Unit, AttributesInfo &Info) {
+  uint64_t Addr = *Val.getAsAddress();
+
+  if (LLVM_UNLIKELY(Linker.Options.Update)) {
+    if (AttrSpec.Attr == dwarf::DW_AT_low_pc)
+      Info.HasLowPc = true;
+    Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                 dwarf::Form(AttrSpec.Form), DIEInteger(Addr));
+    return Unit.getOrigUnit().getAddressByteSize();
+  }
+
+  if (AttrSpec.Attr == dwarf::DW_AT_low_pc) {
+    if (Die.getTag() == dwarf::DW_TAG_inlined_subroutine ||
+        Die.getTag() == dwarf::DW_TAG_lexical_block)
+      // The low_pc of a block or inline subroutine might get
+      // relocated because it happens to match the low_pc of the
+      // enclosing subprogram. To prevent issues with that, always use
+      // the low_pc from the input DIE if relocations have been applied.
+      Addr = (Info.OrigLowPc != std::numeric_limits<uint64_t>::max()
+                  ? Info.OrigLowPc
+                  : Addr) +
+             Info.PCOffset;
+    else if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
+      Addr = Unit.getLowPc();
+      if (Addr == std::numeric_limits<uint64_t>::max())
+        return 0;
+    }
+    Info.HasLowPc = true;
+  } else if (AttrSpec.Attr == dwarf::DW_AT_high_pc) {
+    if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
+      if (uint64_t HighPc = Unit.getHighPc())
+        Addr = HighPc;
+      else
+        return 0;
+    } else
+      // If we have a high_pc recorded for the input DIE, use
+      // it. Otherwise (when no relocations where applied) just use the
+      // one we just decoded.
+      Addr = (Info.OrigHighPc ? Info.OrigHighPc : Addr) + Info.PCOffset;
+  } else if (AttrSpec.Attr == dwarf::DW_AT_call_return_pc) {
+    // Relocate a return PC address within a call site entry.
+    if (Die.getTag() == dwarf::DW_TAG_call_site)
+      Addr += Info.PCOffset;
+  }
+
+  Die.addValue(DIEAlloc, static_cast<dwarf::Attribute>(AttrSpec.Attr),
+               static_cast<dwarf::Form>(AttrSpec.Form), DIEInteger(Addr));
+  return Unit.getOrigUnit().getAddressByteSize();
+}
+
+unsigned DWARFLinker::DIECloner::cloneScalarAttribute(
+    DIE &Die, const DWARFDie &InputDIE, const DwarfLinkerObjFile &OF,
+    CompileUnit &Unit, AttributeSpec AttrSpec, const DWARFFormValue &Val,
+    unsigned AttrSize, AttributesInfo &Info) {
+  uint64_t Value;
+
+  if (LLVM_UNLIKELY(Linker.Options.Update)) {
+    if (auto OptionalValue = Val.getAsUnsignedConstant())
+      Value = *OptionalValue;
+    else if (auto OptionalValue = Val.getAsSignedConstant())
+      Value = *OptionalValue;
+    else if (auto OptionalValue = Val.getAsSectionOffset())
+      Value = *OptionalValue;
+    else {
+      Linker.reportWarning(
+          "Unsupported scalar attribute form. Dropping attribute.", OF,
+          &InputDIE);
+      return 0;
+    }
+    if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
+      Info.IsDeclaration = true;
+    Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                 dwarf::Form(AttrSpec.Form), DIEInteger(Value));
+    return AttrSize;
+  }
+
+  if (AttrSpec.Attr == dwarf::DW_AT_high_pc &&
+      Die.getTag() == dwarf::DW_TAG_compile_unit) {
+    if (Unit.getLowPc() == -1ULL)
+      return 0;
+    // Dwarf >= 4 high_pc is an size, not an address.
+    Value = Unit.getHighPc() - Unit.getLowPc();
+  } else if (AttrSpec.Form == dwarf::DW_FORM_sec_offset)
+    Value = *Val.getAsSectionOffset();
+  else if (AttrSpec.Form == dwarf::DW_FORM_sdata)
+    Value = *Val.getAsSignedConstant();
+  else if (auto OptionalValue = Val.getAsUnsignedConstant())
+    Value = *OptionalValue;
+  else {
+    Linker.reportWarning(
+        "Unsupported scalar attribute form. Dropping attribute.", OF,
+        &InputDIE);
+    return 0;
+  }
+  PatchLocation Patch =
+      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
+                   dwarf::Form(AttrSpec.Form), DIEInteger(Value));
+  if (AttrSpec.Attr == dwarf::DW_AT_ranges) {
+    Unit.noteRangeAttribute(Die, Patch);
+    Info.HasRanges = true;
+  }
+
+  // A more generic way to check for location attributes would be
+  // nice, but it's very unlikely that any other attribute needs a
+  // location list.
+  // FIXME: use DWARFAttribute::mayHaveLocationDescription().
+  else if (AttrSpec.Attr == dwarf::DW_AT_location ||
+           AttrSpec.Attr == dwarf::DW_AT_frame_base) {
+    Unit.noteLocationAttribute(Patch, Info.PCOffset);
+  } else if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
+    Info.IsDeclaration = true;
+
+  return AttrSize;
+}
+
+/// Clone \p InputDIE's attribute described by \p AttrSpec with
+/// value \p Val, and add it to \p Die.
+/// \returns the size of the cloned attribute.
+unsigned DWARFLinker::DIECloner::cloneAttribute(
+    DIE &Die, const DWARFDie &InputDIE, const DwarfLinkerObjFile &OF,
+    CompileUnit &Unit, OffsetsStringPool &StringPool, const DWARFFormValue &Val,
+    const AttributeSpec AttrSpec, unsigned AttrSize, AttributesInfo &Info,
+    bool IsLittleEndian) {
+  const DWARFUnit &U = Unit.getOrigUnit();
+
+  switch (AttrSpec.Form) {
+  case dwarf::DW_FORM_strp:
+  case dwarf::DW_FORM_string:
+    return cloneStringAttribute(Die, AttrSpec, Val, U, StringPool, Info);
+  case dwarf::DW_FORM_ref_addr:
+  case dwarf::DW_FORM_ref1:
+  case dwarf::DW_FORM_ref2:
+  case dwarf::DW_FORM_ref4:
+  case dwarf::DW_FORM_ref8:
+    return cloneDieReferenceAttribute(Die, InputDIE, AttrSpec, AttrSize, Val,
+                                      OF, Unit);
+  case dwarf::DW_FORM_block:
+  case dwarf::DW_FORM_block1:
+  case dwarf::DW_FORM_block2:
+  case dwarf::DW_FORM_block4:
+  case dwarf::DW_FORM_exprloc:
+    return cloneBlockAttribute(Die, OF, Unit, AttrSpec, Val, AttrSize,
+                               IsLittleEndian);
+  case dwarf::DW_FORM_addr:
+    return cloneAddressAttribute(Die, AttrSpec, Val, Unit, Info);
+  case dwarf::DW_FORM_data1:
+  case dwarf::DW_FORM_data2:
+  case dwarf::DW_FORM_data4:
+  case dwarf::DW_FORM_data8:
+  case dwarf::DW_FORM_udata:
+  case dwarf::DW_FORM_sdata:
+  case dwarf::DW_FORM_sec_offset:
+  case dwarf::DW_FORM_flag:
+  case dwarf::DW_FORM_flag_present:
+    return cloneScalarAttribute(Die, InputDIE, OF, Unit, AttrSpec, Val,
+                                AttrSize, Info);
+  default:
+    Linker.reportWarning(
+        "Unsupported attribute form in cloneAttribute. Dropping.", OF,
+        &InputDIE);
+  }
+
+  return 0;
+}
+
+static bool isObjCSelector(StringRef Name) {
+  return Name.size() > 2 && (Name[0] == '-' || Name[0] == '+') &&
+         (Name[1] == '[');
+}
+
+void DWARFLinker::DIECloner::addObjCAccelerator(CompileUnit &Unit,
+                                                const DIE *Die,
+                                                DwarfStringPoolEntryRef Name,
+                                                OffsetsStringPool &StringPool,
+                                                bool SkipPubSection) {
+  assert(isObjCSelector(Name.getString()) && "not an objc selector");
+  // Objective C method or class function.
+  // "- [Class(Category) selector :withArg ...]"
+  StringRef ClassNameStart(Name.getString().drop_front(2));
+  size_t FirstSpace = ClassNameStart.find(' ');
+  if (FirstSpace == StringRef::npos)
+    return;
+
+  StringRef SelectorStart(ClassNameStart.data() + FirstSpace + 1);
+  if (!SelectorStart.size())
+    return;
+
+  StringRef Selector(SelectorStart.data(), SelectorStart.size() - 1);
+  Unit.addNameAccelerator(Die, StringPool.getEntry(Selector), SkipPubSection);
+
+  // Add an entry for the class name that points to this
+  // method/class function.
+  StringRef ClassName(ClassNameStart.data(), FirstSpace);
+  Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassName), SkipPubSection);
+
+  if (ClassName[ClassName.size() - 1] == ')') {
+    size_t OpenParens = ClassName.find('(');
+    if (OpenParens != StringRef::npos) {
+      StringRef ClassNameNoCategory(ClassName.data(), OpenParens);
+      Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassNameNoCategory),
+                              SkipPubSection);
+
+      std::string MethodNameNoCategory(Name.getString().data(), OpenParens + 2);
+      // FIXME: The missing space here may be a bug, but
+      //        dsymutil-classic also does it this way.
+      MethodNameNoCategory.append(SelectorStart);
+      Unit.addNameAccelerator(Die, StringPool.getEntry(MethodNameNoCategory),
+                              SkipPubSection);
+    }
+  }
+}
+
+static bool
+shouldSkipAttribute(DWARFAbbreviationDeclaration::AttributeSpec AttrSpec,
+                    uint16_t Tag, bool InDebugMap, bool SkipPC,
+                    bool InFunctionScope) {
+  switch (AttrSpec.Attr) {
+  default:
+    return false;
+  case dwarf::DW_AT_low_pc:
+  case dwarf::DW_AT_high_pc:
+  case dwarf::DW_AT_ranges:
+    return SkipPC;
+  case dwarf::DW_AT_location:
+  case dwarf::DW_AT_frame_base:
+    // FIXME: for some reason dsymutil-classic keeps the location attributes
+    // when they are of block type (i.e. not location lists). This is totally
+    // wrong for globals where we will keep a wrong address. It is mostly
+    // harmless for locals, but there is no point in keeping these anyway when
+    // the function wasn't linked.
+    return (SkipPC || (!InFunctionScope && Tag == dwarf::DW_TAG_variable &&
+                       !InDebugMap)) &&
+           !DWARFFormValue(AttrSpec.Form).isFormClass(DWARFFormValue::FC_Block);
+  }
+}
+
+DIE *DWARFLinker::DIECloner::cloneDIE(
+    const DWARFDie &InputDIE, const DwarfLinkerObjFile &OF, CompileUnit &Unit,
+    OffsetsStringPool &StringPool, int64_t PCOffset, uint32_t OutOffset,
+    unsigned Flags, bool IsLittleEndian, DIE *Die) {
+  DWARFUnit &U = Unit.getOrigUnit();
+  unsigned Idx = U.getDIEIndex(InputDIE);
+  CompileUnit::DIEInfo &Info = Unit.getInfo(Idx);
+
+  // Should the DIE appear in the output?
+  if (!Unit.getInfo(Idx).Keep)
+    return nullptr;
+
+  uint64_t Offset = InputDIE.getOffset();
+  assert(!(Die && Info.Clone) && "Can't supply a DIE and a cloned DIE");
+  if (!Die) {
+    // The DIE might have been already created by a forward reference
+    // (see cloneDieReferenceAttribute()).
+    if (!Info.Clone)
+      Info.Clone = DIE::get(DIEAlloc, dwarf::Tag(InputDIE.getTag()));
+    Die = Info.Clone;
+  }
+
+  assert(Die->getTag() == InputDIE.getTag());
+  Die->setOffset(OutOffset);
+  if ((Unit.hasODR() || Unit.isClangModule()) && !Info.Incomplete &&
+      Die->getTag() != dwarf::DW_TAG_namespace && Info.Ctxt &&
+      Info.Ctxt != Unit.getInfo(Info.ParentIdx).Ctxt &&
+      !Info.Ctxt->getCanonicalDIEOffset()) {
+    // We are about to emit a DIE that is the root of its own valid
+    // DeclContext tree. Make the current offset the canonical offset
+    // for this context.
+    Info.Ctxt->setCanonicalDIEOffset(OutOffset + Unit.getStartOffset());
+  }
+
+  // Extract and clone every attribute.
+  DWARFDataExtractor Data = U.getDebugInfoExtractor();
+  // Point to the next DIE (generally there is always at least a NULL
+  // entry after the current one). If this is a lone
+  // DW_TAG_compile_unit without any children, point to the next unit.
+  uint64_t NextOffset = (Idx + 1 < U.getNumDIEs())
+                            ? U.getDIEAtIndex(Idx + 1).getOffset()
+                            : U.getNextUnitOffset();
+  AttributesInfo AttrInfo;
+
+  // We could copy the data only if we need to apply a relocation to it. After
+  // testing, it seems there is no performance downside to doing the copy
+  // unconditionally, and it makes the code simpler.
+  SmallString<40> DIECopy(Data.getData().substr(Offset, NextOffset - Offset));
+  Data =
+      DWARFDataExtractor(DIECopy, Data.isLittleEndian(), Data.getAddressSize());
+
+  // Modify the copy with relocated addresses.
+  if (ObjFile.Addresses->areRelocationsResolved() &&
+      ObjFile.Addresses->applyValidRelocs(DIECopy, Offset,
+                                          Data.isLittleEndian())) {
+    // If we applied relocations, we store the value of high_pc that was
+    // potentially stored in the input DIE. If high_pc is an address
+    // (Dwarf version == 2), then it might have been relocated to a
+    // totally unrelated value (because the end address in the object
+    // file might be start address of another function which got moved
+    // independently by the linker). The computation of the actual
+    // high_pc value is done in cloneAddressAttribute().
+    AttrInfo.OrigHighPc =
+        dwarf::toAddress(InputDIE.find(dwarf::DW_AT_high_pc), 0);
+    // Also store the low_pc. It might get relocated in an
+    // inline_subprogram that happens at the beginning of its
+    // inlining function.
+    AttrInfo.OrigLowPc = dwarf::toAddress(InputDIE.find(dwarf::DW_AT_low_pc),
+                                          std::numeric_limits<uint64_t>::max());
+  }
+
+  // Reset the Offset to 0 as we will be working on the local copy of
+  // the data.
+  Offset = 0;
+
+  const auto *Abbrev = InputDIE.getAbbreviationDeclarationPtr();
+  Offset += getULEB128Size(Abbrev->getCode());
+
+  // We are entering a subprogram. Get and propagate the PCOffset.
+  if (Die->getTag() == dwarf::DW_TAG_subprogram)
+    PCOffset = Info.AddrAdjust;
+  AttrInfo.PCOffset = PCOffset;
+
+  if (Abbrev->getTag() == dwarf::DW_TAG_subprogram) {
+    Flags |= TF_InFunctionScope;
+    if (!Info.InDebugMap && LLVM_LIKELY(!Update))
+      Flags |= TF_SkipPC;
+  }
+
+  bool Copied = false;
+  for (const auto &AttrSpec : Abbrev->attributes()) {
+    if (LLVM_LIKELY(!Update) &&
+        shouldSkipAttribute(AttrSpec, Die->getTag(), Info.InDebugMap,
+                            Flags & TF_SkipPC, Flags & TF_InFunctionScope)) {
+      DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
+                                U.getFormParams());
+      // FIXME: dsymutil-classic keeps the old abbreviation around
+      // even if it's not used. We can remove this (and the copyAbbrev
+      // helper) as soon as bit-for-bit compatibility is not a goal anymore.
+      if (!Copied) {
+        copyAbbrev(*InputDIE.getAbbreviationDeclarationPtr(), Unit.hasODR());
+        Copied = true;
+      }
+      continue;
+    }
+
+    DWARFFormValue Val(AttrSpec.Form);
+    uint64_t AttrSize = Offset;
+    Val.extractValue(Data, &Offset, U.getFormParams(), &U);
+    AttrSize = Offset - AttrSize;
+
+    OutOffset += cloneAttribute(*Die, InputDIE, OF, Unit, StringPool, Val,
+                                AttrSpec, AttrSize, AttrInfo, IsLittleEndian);
+  }
+
+  // Look for accelerator entries.
+  uint16_t Tag = InputDIE.getTag();
+  // FIXME: This is slightly wrong. An inline_subroutine without a
+  // low_pc, but with AT_ranges might be interesting to get into the
+  // accelerator tables too. For now stick with dsymutil's behavior.
+  if ((Info.InDebugMap || AttrInfo.HasLowPc || AttrInfo.HasRanges) &&
+      Tag != dwarf::DW_TAG_compile_unit &&
+      getDIENames(InputDIE, AttrInfo, StringPool,
+                  Tag != dwarf::DW_TAG_inlined_subroutine)) {
+    if (AttrInfo.MangledName && AttrInfo.MangledName != AttrInfo.Name)
+      Unit.addNameAccelerator(Die, AttrInfo.MangledName,
+                              Tag == dwarf::DW_TAG_inlined_subroutine);
+    if (AttrInfo.Name) {
+      if (AttrInfo.NameWithoutTemplate)
+        Unit.addNameAccelerator(Die, AttrInfo.NameWithoutTemplate,
+                                /* SkipPubSection */ true);
+      Unit.addNameAccelerator(Die, AttrInfo.Name,
+                              Tag == dwarf::DW_TAG_inlined_subroutine);
+    }
+    if (AttrInfo.Name && isObjCSelector(AttrInfo.Name.getString()))
+      addObjCAccelerator(Unit, Die, AttrInfo.Name, StringPool,
+                         /* SkipPubSection =*/true);
+
+  } else if (Tag == dwarf::DW_TAG_namespace) {
+    if (!AttrInfo.Name)
+      AttrInfo.Name = StringPool.getEntry("(anonymous namespace)");
+    Unit.addNamespaceAccelerator(Die, AttrInfo.Name);
+  } else if (isTypeTag(Tag) && !AttrInfo.IsDeclaration &&
+             getDIENames(InputDIE, AttrInfo, StringPool) && AttrInfo.Name &&
+             AttrInfo.Name.getString()[0]) {
+    uint32_t Hash = hashFullyQualifiedName(InputDIE, Unit, OF);
+    uint64_t RuntimeLang =
+        dwarf::toUnsigned(InputDIE.find(dwarf::DW_AT_APPLE_runtime_class))
+            .getValueOr(0);
+    bool ObjCClassIsImplementation =
+        (RuntimeLang == dwarf::DW_LANG_ObjC ||
+         RuntimeLang == dwarf::DW_LANG_ObjC_plus_plus) &&
+        dwarf::toUnsigned(InputDIE.find(dwarf::DW_AT_APPLE_objc_complete_type))
+            .getValueOr(0);
+    Unit.addTypeAccelerator(Die, AttrInfo.Name, ObjCClassIsImplementation,
+                            Hash);
+  }
+
+  // Determine whether there are any children that we want to keep.
+  bool HasChildren = false;
+  for (auto Child : InputDIE.children()) {
+    unsigned Idx = U.getDIEIndex(Child);
+    if (Unit.getInfo(Idx).Keep) {
+      HasChildren = true;
+      break;
+    }
+  }
+
+  DIEAbbrev NewAbbrev = Die->generateAbbrev();
+  if (HasChildren)
+    NewAbbrev.setChildrenFlag(dwarf::DW_CHILDREN_yes);
+  // Assign a permanent abbrev number
+  Linker.assignAbbrev(NewAbbrev);
+  Die->setAbbrevNumber(NewAbbrev.getNumber());
+
+  // Add the size of the abbreviation number to the output offset.
+  OutOffset += getULEB128Size(Die->getAbbrevNumber());
+
+  if (!HasChildren) {
+    // Update our size.
+    Die->setSize(OutOffset - Die->getOffset());
+    return Die;
+  }
+
+  // Recursively clone children.
+  for (auto Child : InputDIE.children()) {
+    if (DIE *Clone = cloneDIE(Child, OF, Unit, StringPool, PCOffset, OutOffset,
+                              Flags, IsLittleEndian)) {
+      Die->addChild(Clone);
+      OutOffset = Clone->getOffset() + Clone->getSize();
+    }
+  }
+
+  // Account for the end of children marker.
+  OutOffset += sizeof(int8_t);
+  // Update our size.
+  Die->setSize(OutOffset - Die->getOffset());
+  return Die;
+}
+
+/// Patch the input object file relevant debug_ranges entries
+/// and emit them in the output file. Update the relevant attributes
+/// to point at the new entries.
+void DWARFLinker::patchRangesForUnit(const CompileUnit &Unit,
+                                     DWARFContext &OrigDwarf,
+                                     const DwarfLinkerObjFile &OF) const {
+  DWARFDebugRangeList RangeList;
+  const auto &FunctionRanges = Unit.getFunctionRanges();
+  unsigned AddressSize = Unit.getOrigUnit().getAddressByteSize();
+  DWARFDataExtractor RangeExtractor(OrigDwarf.getDWARFObj(),
+                                    OrigDwarf.getDWARFObj().getRangesSection(),
+                                    OrigDwarf.isLittleEndian(), AddressSize);
+  auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
+  DWARFUnit &OrigUnit = Unit.getOrigUnit();
+  auto OrigUnitDie = OrigUnit.getUnitDIE(false);
+  uint64_t OrigLowPc =
+      dwarf::toAddress(OrigUnitDie.find(dwarf::DW_AT_low_pc), -1ULL);
+  // Ranges addresses are based on the unit's low_pc. Compute the
+  // offset we need to apply to adapt to the new unit's low_pc.
+  int64_t UnitPcOffset = 0;
+  if (OrigLowPc != -1ULL)
+    UnitPcOffset = int64_t(OrigLowPc) - Unit.getLowPc();
+
+  for (const auto &RangeAttribute : Unit.getRangesAttributes()) {
+    uint64_t Offset = RangeAttribute.get();
+    RangeAttribute.set(DwarfEmitter->getRangesSectionSize());
+    if (Error E = RangeList.extract(RangeExtractor, &Offset)) {
+      llvm::consumeError(std::move(E));
+      reportWarning("invalid range list ignored.", OF);
+      RangeList.clear();
+    }
+    const auto &Entries = RangeList.getEntries();
+    if (!Entries.empty()) {
+      const DWARFDebugRangeList::RangeListEntry &First = Entries.front();
+
+      if (CurrRange == InvalidRange ||
+          First.StartAddress + OrigLowPc < CurrRange.start() ||
+          First.StartAddress + OrigLowPc >= CurrRange.stop()) {
+        CurrRange = FunctionRanges.find(First.StartAddress + OrigLowPc);
+        if (CurrRange == InvalidRange ||
+            CurrRange.start() > First.StartAddress + OrigLowPc) {
+          reportWarning("no mapping for range.", OF);
+          continue;
+        }
+      }
+    }
+
+    DwarfEmitter->emitRangesEntries(UnitPcOffset, OrigLowPc, CurrRange, Entries,
+                                    AddressSize);
+  }
+}
+
+/// Generate the debug_aranges entries for \p Unit and if the
+/// unit has a DW_AT_ranges attribute, also emit the debug_ranges
+/// contribution for this attribute.
+/// FIXME: this could actually be done right in patchRangesForUnit,
+/// but for the sake of initial bit-for-bit compatibility with legacy
+/// dsymutil, we have to do it in a delayed pass.
+void DWARFLinker::generateUnitRanges(CompileUnit &Unit) const {
+  auto Attr = Unit.getUnitRangesAttribute();
+  if (Attr)
+    Attr->set(DwarfEmitter->getRangesSectionSize());
+  DwarfEmitter->emitUnitRangesEntries(Unit, static_cast<bool>(Attr));
+}
+
+/// Insert the new line info sequence \p Seq into the current
+/// set of already linked line info \p Rows.
+static void insertLineSequence(std::vector<DWARFDebugLine::Row> &Seq,
+                               std::vector<DWARFDebugLine::Row> &Rows) {
+  if (Seq.empty())
+    return;
+
+  if (!Rows.empty() && Rows.back().Address < Seq.front().Address) {
+    Rows.insert(Rows.end(), Seq.begin(), Seq.end());
+    Seq.clear();
+    return;
+  }
+
+  object::SectionedAddress Front = Seq.front().Address;
+  auto InsertPoint = partition_point(
+      Rows, [=](const DWARFDebugLine::Row &O) { return O.Address < Front; });
+
+  // FIXME: this only removes the unneeded end_sequence if the
+  // sequences have been inserted in order. Using a global sort like
+  // described in patchLineTableForUnit() and delaying the end_sequene
+  // elimination to emitLineTableForUnit() we can get rid of all of them.
+  if (InsertPoint != Rows.end() && InsertPoint->Address == Front &&
+      InsertPoint->EndSequence) {
+    *InsertPoint = Seq.front();
+    Rows.insert(InsertPoint + 1, Seq.begin() + 1, Seq.end());
+  } else {
+    Rows.insert(InsertPoint, Seq.begin(), Seq.end());
+  }
+
+  Seq.clear();
+}
+
+static void patchStmtList(DIE &Die, DIEInteger Offset) {
+  for (auto &V : Die.values())
+    if (V.getAttribute() == dwarf::DW_AT_stmt_list) {
+      V = DIEValue(V.getAttribute(), V.getForm(), Offset);
+      return;
+    }
+
+  llvm_unreachable("Didn't find DW_AT_stmt_list in cloned DIE!");
+}
+
+/// Extract the line table for \p Unit from \p OrigDwarf, and
+/// recreate a relocated version of these for the address ranges that
+/// are present in the binary.
+void DWARFLinker::patchLineTableForUnit(CompileUnit &Unit,
+                                        DWARFContext &OrigDwarf,
+                                        const DwarfLinkerObjFile &OF) {
+  DWARFDie CUDie = Unit.getOrigUnit().getUnitDIE();
+  auto StmtList = dwarf::toSectionOffset(CUDie.find(dwarf::DW_AT_stmt_list));
+  if (!StmtList)
+    return;
+
+  // Update the cloned DW_AT_stmt_list with the correct debug_line offset.
+  if (auto *OutputDIE = Unit.getOutputUnitDIE())
+    patchStmtList(*OutputDIE, DIEInteger(DwarfEmitter->getLineSectionSize()));
+
+  RangesTy &Ranges = OF.Addresses->getValidAddressRanges();
+
+  // Parse the original line info for the unit.
+  DWARFDebugLine::LineTable LineTable;
+  uint64_t StmtOffset = *StmtList;
+  DWARFDataExtractor LineExtractor(
+      OrigDwarf.getDWARFObj(), OrigDwarf.getDWARFObj().getLineSection(),
+      OrigDwarf.isLittleEndian(), Unit.getOrigUnit().getAddressByteSize());
+  if (needToTranslateStrings())
+    return DwarfEmitter->translateLineTable(LineExtractor, StmtOffset);
+
+  Error Err = LineTable.parse(LineExtractor, &StmtOffset, OrigDwarf,
+                              &Unit.getOrigUnit(), DWARFContext::dumpWarning);
+  DWARFContext::dumpWarning(std::move(Err));
+
+  // This vector is the output line table.
+  std::vector<DWARFDebugLine::Row> NewRows;
+  NewRows.reserve(LineTable.Rows.size());
+
+  // Current sequence of rows being extracted, before being inserted
+  // in NewRows.
+  std::vector<DWARFDebugLine::Row> Seq;
+  const auto &FunctionRanges = Unit.getFunctionRanges();
+  auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
+
+  // FIXME: This logic is meant to generate exactly the same output as
+  // Darwin's classic dsymutil. There is a nicer way to implement this
+  // by simply putting all the relocated line info in NewRows and simply
+  // sorting NewRows before passing it to emitLineTableForUnit. This
+  // should be correct as sequences for a function should stay
+  // together in the sorted output. There are a few corner cases that
+  // look suspicious though, and that required to implement the logic
+  // this way. Revisit that once initial validation is finished.
+
+  // Iterate over the object file line info and extract the sequences
+  // that correspond to linked functions.
+  for (auto &Row : LineTable.Rows) {
+    // Check whether we stepped out of the range. The range is
+    // half-open, but consider accept the end address of the range if
+    // it is marked as end_sequence in the input (because in that
+    // case, the relocation offset is accurate and that entry won't
+    // serve as the start of another function).
+    if (CurrRange == InvalidRange || Row.Address.Address < CurrRange.start() ||
+        Row.Address.Address > CurrRange.stop() ||
+        (Row.Address.Address == CurrRange.stop() && !Row.EndSequence)) {
+      // We just stepped out of a known range. Insert a end_sequence
+      // corresponding to the end of the range.
+      uint64_t StopAddress = CurrRange != InvalidRange
+                                 ? CurrRange.stop() + CurrRange.value()
+                                 : -1ULL;
+      CurrRange = FunctionRanges.find(Row.Address.Address);
+      bool CurrRangeValid =
+          CurrRange != InvalidRange && CurrRange.start() <= Row.Address.Address;
+      if (!CurrRangeValid) {
+        CurrRange = InvalidRange;
+        if (StopAddress != -1ULL) {
+          // Try harder by looking in the Address ranges map.
+          // There are corner cases where this finds a
+          // valid entry. It's unclear if this is right or wrong, but
+          // for now do as dsymutil.
+          // FIXME: Understand exactly what cases this addresses and
+          // potentially remove it along with the Ranges map.
+          auto Range = Ranges.lower_bound(Row.Address.Address);
+          if (Range != Ranges.begin() && Range != Ranges.end())
+            --Range;
+
+          if (Range != Ranges.end() && Range->first <= Row.Address.Address &&
+              Range->second.HighPC >= Row.Address.Address) {
+            StopAddress = Row.Address.Address + Range->second.Offset;
+          }
+        }
+      }
+      if (StopAddress != -1ULL && !Seq.empty()) {
+        // Insert end sequence row with the computed end address, but
+        // the same line as the previous one.
+        auto NextLine = Seq.back();
+        NextLine.Address.Address = StopAddress;
+        NextLine.EndSequence = 1;
+        NextLine.PrologueEnd = 0;
+        NextLine.BasicBlock = 0;
+        NextLine.EpilogueBegin = 0;
+        Seq.push_back(NextLine);
+        insertLineSequence(Seq, NewRows);
+      }
+
+      if (!CurrRangeValid)
+        continue;
+    }
+
+    // Ignore empty sequences.
+    if (Row.EndSequence && Seq.empty())
+      continue;
+
+    // Relocate row address and add it to the current sequence.
+    Row.Address.Address += CurrRange.value();
+    Seq.emplace_back(Row);
+
+    if (Row.EndSequence)
+      insertLineSequence(Seq, NewRows);
+  }
+
+  // Finished extracting, now emit the line tables.
+  // FIXME: LLVM hard-codes its prologue values. We just copy the
+  // prologue over and that works because we act as both producer and
+  // consumer. It would be nicer to have a real configurable line
+  // table emitter.
+  if (LineTable.Prologue.getVersion() < 2 ||
+      LineTable.Prologue.getVersion() > 5 ||
+      LineTable.Prologue.DefaultIsStmt != DWARF2_LINE_DEFAULT_IS_STMT ||
+      LineTable.Prologue.OpcodeBase > 13)
+    reportWarning("line table parameters mismatch. Cannot emit.", OF);
+  else {
+    uint32_t PrologueEnd = *StmtList + 10 + LineTable.Prologue.PrologueLength;
+    // DWARF v5 has an extra 2 bytes of information before the header_length
+    // field.
+    if (LineTable.Prologue.getVersion() == 5)
+      PrologueEnd += 2;
+    StringRef LineData = OrigDwarf.getDWARFObj().getLineSection().Data;
+    MCDwarfLineTableParams Params;
+    Params.DWARF2LineOpcodeBase = LineTable.Prologue.OpcodeBase;
+    Params.DWARF2LineBase = LineTable.Prologue.LineBase;
+    Params.DWARF2LineRange = LineTable.Prologue.LineRange;
+    DwarfEmitter->emitLineTableForUnit(
+        Params, LineData.slice(*StmtList + 4, PrologueEnd),
+        LineTable.Prologue.MinInstLength, NewRows,
+        Unit.getOrigUnit().getAddressByteSize());
+  }
+}
+
+void DWARFLinker::emitAcceleratorEntriesForUnit(CompileUnit &Unit) {
+  switch (Options.TheAccelTableKind) {
+  case AccelTableKind::Apple:
+    emitAppleAcceleratorEntriesForUnit(Unit);
+    break;
+  case AccelTableKind::Dwarf:
+    emitDwarfAcceleratorEntriesForUnit(Unit);
+    break;
+  case AccelTableKind::Default:
+    llvm_unreachable("The default must be updated to a concrete value.");
+    break;
+  }
+}
+
+void DWARFLinker::emitAppleAcceleratorEntriesForUnit(CompileUnit &Unit) {
+  // Add namespaces.
+  for (const auto &Namespace : Unit.getNamespaces())
+    AppleNamespaces.addName(Namespace.Name,
+                            Namespace.Die->getOffset() + Unit.getStartOffset());
+
+  /// Add names.
+  DwarfEmitter->emitPubNamesForUnit(Unit);
+  for (const auto &Pubname : Unit.getPubnames())
+    AppleNames.addName(Pubname.Name,
+                       Pubname.Die->getOffset() + Unit.getStartOffset());
+
+  /// Add types.
+  DwarfEmitter->emitPubTypesForUnit(Unit);
+  for (const auto &Pubtype : Unit.getPubtypes())
+    AppleTypes.addName(
+        Pubtype.Name, Pubtype.Die->getOffset() + Unit.getStartOffset(),
+        Pubtype.Die->getTag(),
+        Pubtype.ObjcClassImplementation ? dwarf::DW_FLAG_type_implementation
+                                        : 0,
+        Pubtype.QualifiedNameHash);
+
+  /// Add ObjC names.
+  for (const auto &ObjC : Unit.getObjC())
+    AppleObjc.addName(ObjC.Name, ObjC.Die->getOffset() + Unit.getStartOffset());
+}
+
+void DWARFLinker::emitDwarfAcceleratorEntriesForUnit(CompileUnit &Unit) {
+  for (const auto &Namespace : Unit.getNamespaces())
+    DebugNames.addName(Namespace.Name, Namespace.Die->getOffset(),
+                       Namespace.Die->getTag(), Unit.getUniqueID());
+  for (const auto &Pubname : Unit.getPubnames())
+    DebugNames.addName(Pubname.Name, Pubname.Die->getOffset(),
+                       Pubname.Die->getTag(), Unit.getUniqueID());
+  for (const auto &Pubtype : Unit.getPubtypes())
+    DebugNames.addName(Pubtype.Name, Pubtype.Die->getOffset(),
+                       Pubtype.Die->getTag(), Unit.getUniqueID());
+}
+
+/// Read the frame info stored in the object, and emit the
+/// patched frame descriptions for the resulting file.
+///
+/// This is actually pretty easy as the data of the CIEs and FDEs can
+/// be considered as black boxes and moved as is. The only thing to do
+/// is to patch the addresses in the headers.
+void DWARFLinker::patchFrameInfoForObject(const DwarfLinkerObjFile &OF,
+                                          RangesTy &Ranges,
+                                          DWARFContext &OrigDwarf,
+                                          unsigned AddrSize) {
+  StringRef FrameData = OrigDwarf.getDWARFObj().getFrameSection().Data;
+  if (FrameData.empty())
+    return;
+
+  DataExtractor Data(FrameData, OrigDwarf.isLittleEndian(), 0);
+  uint64_t InputOffset = 0;
+
+  // Store the data of the CIEs defined in this object, keyed by their
+  // offsets.
+  DenseMap<uint64_t, StringRef> LocalCIES;
+
+  while (Data.isValidOffset(InputOffset)) {
+    uint64_t EntryOffset = InputOffset;
+    uint32_t InitialLength = Data.getU32(&InputOffset);
+    if (InitialLength == 0xFFFFFFFF)
+      return reportWarning("Dwarf64 bits no supported", OF);
+
+    uint32_t CIEId = Data.getU32(&InputOffset);
+    if (CIEId == 0xFFFFFFFF) {
+      // This is a CIE, store it.
+      StringRef CIEData = FrameData.substr(EntryOffset, InitialLength + 4);
+      LocalCIES[EntryOffset] = CIEData;
+      // The -4 is to account for the CIEId we just read.
+      InputOffset += InitialLength - 4;
+      continue;
+    }
+
+    uint32_t Loc = Data.getUnsigned(&InputOffset, AddrSize);
+
+    // Some compilers seem to emit frame info that doesn't start at
+    // the function entry point, thus we can't just lookup the address
+    // in the debug map. Use the AddressInfo's range map to see if the FDE
+    // describes something that we can relocate.
+    auto Range = Ranges.upper_bound(Loc);
+    if (Range != Ranges.begin())
+      --Range;
+    if (Range == Ranges.end() || Range->first > Loc ||
+        Range->second.HighPC <= Loc) {
+      // The +4 is to account for the size of the InitialLength field itself.
+      InputOffset = EntryOffset + InitialLength + 4;
+      continue;
+    }
+
+    // This is an FDE, and we have a mapping.
+    // Have we already emitted a corresponding CIE?
+    StringRef CIEData = LocalCIES[CIEId];
+    if (CIEData.empty())
+      return reportWarning("Inconsistent debug_frame content. Dropping.", OF);
+
+    // Look if we already emitted a CIE that corresponds to the
+    // referenced one (the CIE data is the key of that lookup).
+    auto IteratorInserted = EmittedCIEs.insert(
+        std::make_pair(CIEData, DwarfEmitter->getFrameSectionSize()));
+    // If there is no CIE yet for this ID, emit it.
+    if (IteratorInserted.second ||
+        // FIXME: dsymutil-classic only caches the last used CIE for
+        // reuse. Mimic that behavior for now. Just removing that
+        // second half of the condition and the LastCIEOffset variable
+        // makes the code DTRT.
+        LastCIEOffset != IteratorInserted.first->getValue()) {
+      LastCIEOffset = DwarfEmitter->getFrameSectionSize();
+      IteratorInserted.first->getValue() = LastCIEOffset;
+      DwarfEmitter->emitCIE(CIEData);
+    }
+
+    // Emit the FDE with updated address and CIE pointer.
+    // (4 + AddrSize) is the size of the CIEId + initial_location
+    // fields that will get reconstructed by emitFDE().
+    unsigned FDERemainingBytes = InitialLength - (4 + AddrSize);
+    DwarfEmitter->emitFDE(IteratorInserted.first->getValue(), AddrSize,
+                          Loc + Range->second.Offset,
+                          FrameData.substr(InputOffset, FDERemainingBytes));
+    InputOffset += FDERemainingBytes;
+  }
+}
+
+void DWARFLinker::DIECloner::copyAbbrev(
+    const DWARFAbbreviationDeclaration &Abbrev, bool HasODR) {
+  DIEAbbrev Copy(dwarf::Tag(Abbrev.getTag()),
+                 dwarf::Form(Abbrev.hasChildren()));
+
+  for (const auto &Attr : Abbrev.attributes()) {
+    uint16_t Form = Attr.Form;
+    if (HasODR && isODRAttribute(Attr.Attr))
+      Form = dwarf::DW_FORM_ref_addr;
+    Copy.AddAttribute(dwarf::Attribute(Attr.Attr), dwarf::Form(Form));
+  }
+
+  Linker.assignAbbrev(Copy);
+}
+
+uint32_t
+DWARFLinker::DIECloner::hashFullyQualifiedName(DWARFDie DIE, CompileUnit &U,
+                                               const DwarfLinkerObjFile &OF,
+                                               int ChildRecurseDepth) {
+  const char *Name = nullptr;
+  DWARFUnit *OrigUnit = &U.getOrigUnit();
+  CompileUnit *CU = &U;
+  Optional<DWARFFormValue> Ref;
+
+  while (1) {
+    if (const char *CurrentName = DIE.getName(DINameKind::ShortName))
+      Name = CurrentName;
+
+    if (!(Ref = DIE.find(dwarf::DW_AT_specification)) &&
+        !(Ref = DIE.find(dwarf::DW_AT_abstract_origin)))
+      break;
+
+    if (!Ref->isFormClass(DWARFFormValue::FC_Reference))
+      break;
+
+    CompileUnit *RefCU;
+    if (auto RefDIE =
+            Linker.resolveDIEReference(OF, CompileUnits, *Ref, DIE, RefCU)) {
+      CU = RefCU;
+      OrigUnit = &RefCU->getOrigUnit();
+      DIE = RefDIE;
+    }
+  }
+
+  unsigned Idx = OrigUnit->getDIEIndex(DIE);
+  if (!Name && DIE.getTag() == dwarf::DW_TAG_namespace)
+    Name = "(anonymous namespace)";
+
+  if (CU->getInfo(Idx).ParentIdx == 0 ||
+      // FIXME: dsymutil-classic compatibility. Ignore modules.
+      CU->getOrigUnit().getDIEAtIndex(CU->getInfo(Idx).ParentIdx).getTag() ==
+          dwarf::DW_TAG_module)
+    return djbHash(Name ? Name : "", djbHash(ChildRecurseDepth ? "" : "::"));
+
+  DWARFDie Die = OrigUnit->getDIEAtIndex(CU->getInfo(Idx).ParentIdx);
+  return djbHash(
+      (Name ? Name : ""),
+      djbHash((Name ? "::" : ""),
+              hashFullyQualifiedName(Die, *CU, OF, ++ChildRecurseDepth)));
+}
+
+static uint64_t getDwoId(const DWARFDie &CUDie, const DWARFUnit &Unit) {
+  auto DwoId = dwarf::toUnsigned(
+      CUDie.find({dwarf::DW_AT_dwo_id, dwarf::DW_AT_GNU_dwo_id}));
+  if (DwoId)
+    return *DwoId;
+  return 0;
+}
+
+bool DWARFLinker::registerModuleReference(
+    DWARFDie CUDie, const DWARFUnit &Unit, const DwarfLinkerObjFile &OF,
+    OffsetsStringPool &StringPool, UniquingStringPool &UniquingStringPool,
+    DeclContextTree &ODRContexts, uint64_t ModulesEndOffset, unsigned &UnitID,
+    bool IsLittleEndian, unsigned Indent, bool Quiet) {
+  std::string PCMfile = dwarf::toString(
+      CUDie.find({dwarf::DW_AT_dwo_name, dwarf::DW_AT_GNU_dwo_name}), "");
+  if (PCMfile.empty())
+    return false;
+
+  // Clang module DWARF skeleton CUs abuse this for the path to the module.
+  uint64_t DwoId = getDwoId(CUDie, Unit);
+
+  std::string Name = dwarf::toString(CUDie.find(dwarf::DW_AT_name), "");
+  if (Name.empty()) {
+    if (!Quiet)
+      reportWarning("Anonymous module skeleton CU for " + PCMfile, OF);
+    return true;
+  }
+
+  if (!Quiet && Options.Verbose) {
+    outs().indent(Indent);
+    outs() << "Found clang module reference " << PCMfile;
+  }
+
+  auto Cached = ClangModules.find(PCMfile);
+  if (Cached != ClangModules.end()) {
+    // FIXME: Until PR27449 (https://llvm.org/bugs/show_bug.cgi?id=27449) is
+    // fixed in clang, only warn about DWO_id mismatches in verbose mode.
+    // ASTFileSignatures will change randomly when a module is rebuilt.
+    if (!Quiet && Options.Verbose && (Cached->second != DwoId))
+      reportWarning(Twine("hash mismatch: this object file was built against a "
+                          "different version of the module ") +
+                        PCMfile,
+                    OF);
+    if (!Quiet && Options.Verbose)
+      outs() << " [cached].\n";
+    return true;
+  }
+  if (!Quiet && Options.Verbose)
+    outs() << " ...\n";
+
+  // Cyclic dependencies are disallowed by Clang, but we still
+  // shouldn't run into an infinite loop, so mark it as processed now.
+  ClangModules.insert({PCMfile, DwoId});
+
+  if (Error E =
+          loadClangModule(CUDie, PCMfile, Name, DwoId, OF, StringPool,
+                          UniquingStringPool, ODRContexts, ModulesEndOffset,
+                          UnitID, IsLittleEndian, Indent + 2, Quiet)) {
+    consumeError(std::move(E));
+    return false;
+  }
+  return true;
+}
+
+Error DWARFLinker::loadClangModule(
+    DWARFDie CUDie, StringRef Filename, StringRef ModuleName, uint64_t DwoId,
+    const DwarfLinkerObjFile &OF, OffsetsStringPool &StringPool,
+    UniquingStringPool &UniquingStringPool, DeclContextTree &ODRContexts,
+    uint64_t ModulesEndOffset, unsigned &UnitID, bool IsLittleEndian,
+    unsigned Indent, bool Quiet) {
+  /// Using a SmallString<0> because loadClangModule() is recursive.
+  SmallString<0> Path(Options.PrependPath);
+  if (sys::path::is_relative(Filename))
+    resolveRelativeObjectPath(Path, CUDie);
+  sys::path::append(Path, Filename);
+  // Don't use the cached binary holder because we have no thread-safety
+  // guarantee and the lifetime is limited.
+
+  if (Options.ObjFileLoader == nullptr)
+    return Error::success();
+
+  auto ErrOrObj = Options.ObjFileLoader(OF.FileName, Path);
+  if (!ErrOrObj)
+    return Error::success();
+
+  std::unique_ptr<CompileUnit> Unit;
+
+  // Setup access to the debug info.
+  auto DwarfContext = DWARFContext::create(*ErrOrObj->ObjFile);
+
+  for (const auto &CU : DwarfContext->compile_units()) {
+    updateDwarfVersion(CU->getVersion());
+    // Recursively get all modules imported by this one.
+    auto CUDie = CU->getUnitDIE(false);
+    if (!CUDie)
+      continue;
+    if (!registerModuleReference(CUDie, *CU, OF, StringPool, UniquingStringPool,
+                                 ODRContexts, ModulesEndOffset, UnitID,
+                                 IsLittleEndian, Indent, Quiet)) {
+      if (Unit) {
+        std::string Err =
+            (Filename +
+             ": Clang modules are expected to have exactly 1 compile unit.\n")
+                .str();
+        reportError(Err, OF);
+        return make_error<StringError>(Err, inconvertibleErrorCode());
+      }
+      // FIXME: Until PR27449 (https://llvm.org/bugs/show_bug.cgi?id=27449) is
+      // fixed in clang, only warn about DWO_id mismatches in verbose mode.
+      // ASTFileSignatures will change randomly when a module is rebuilt.
+      uint64_t PCMDwoId = getDwoId(CUDie, *CU);
+      if (PCMDwoId != DwoId) {
+        if (!Quiet && Options.Verbose)
+          reportWarning(
+              Twine("hash mismatch: this object file was built against a "
+                    "different version of the module ") +
+                  Filename,
+              OF);
+        // Update the cache entry with the DwoId of the module loaded from disk.
+        ClangModules[Filename] = PCMDwoId;
+      }
+
+      // Add this module.
+      Unit = std::make_unique<CompileUnit>(*CU, UnitID++, !Options.NoODR,
+                                           ModuleName);
+      Unit->setHasInterestingContent();
+      analyzeContextInfo(CUDie, 0, *Unit, &ODRContexts.getRoot(),
+                         UniquingStringPool, ODRContexts, ModulesEndOffset,
+                         Options.ParseableSwiftInterfaces,
+                         [&](const Twine &Warning, const DWARFDie &DIE) {
+                           reportWarning(Warning, OF, &DIE);
+                         });
+      // Keep everything.
+      Unit->markEverythingAsKept();
+    }
+  }
+  if (!Unit->getOrigUnit().getUnitDIE().hasChildren())
+    return Error::success();
+  if (!Quiet && Options.Verbose) {
+    outs().indent(Indent);
+    outs() << "cloning .debug_info from " << Filename << "\n";
+  }
+
+  UnitListTy CompileUnits;
+  CompileUnits.push_back(std::move(Unit));
+  assert(DwarfEmitter);
+  DIECloner(*this, DwarfEmitter, *ErrOrObj, DIEAlloc, CompileUnits,
+            Options.Update)
+      .cloneAllCompileUnits(*DwarfContext, OF, StringPool, IsLittleEndian);
+  return Error::success();
+}
+
+void DWARFLinker::DIECloner::cloneAllCompileUnits(DWARFContext &DwarfContext,
+                                                  const DwarfLinkerObjFile &OF,
+                                                  OffsetsStringPool &StringPool,
+                                                  bool IsLittleEndian) {
+  uint64_t OutputDebugInfoSize =
+      Linker.Options.NoOutput ? 0 : Emitter->getDebugInfoSectionSize();
+  for (auto &CurrentUnit : CompileUnits) {
+    auto InputDIE = CurrentUnit->getOrigUnit().getUnitDIE();
+    CurrentUnit->setStartOffset(OutputDebugInfoSize);
+    if (!InputDIE) {
+      OutputDebugInfoSize = CurrentUnit->computeNextUnitOffset();
+      continue;
+    }
+    if (CurrentUnit->getInfo(0).Keep) {
+      // Clone the InputDIE into your Unit DIE in our compile unit since it
+      // already has a DIE inside of it.
+      CurrentUnit->createOutputDIE();
+      cloneDIE(InputDIE, OF, *CurrentUnit, StringPool, 0 /* PC offset */,
+               11 /* Unit Header size */, 0, IsLittleEndian,
+               CurrentUnit->getOutputUnitDIE());
+    }
+
+    OutputDebugInfoSize = CurrentUnit->computeNextUnitOffset();
+
+    if (!Linker.Options.NoOutput) {
+      assert(Emitter);
+
+      if (LLVM_LIKELY(!Linker.Options.Update) ||
+          Linker.needToTranslateStrings())
+        Linker.patchLineTableForUnit(*CurrentUnit, DwarfContext, OF);
+
+      Linker.emitAcceleratorEntriesForUnit(*CurrentUnit);
+
+      if (LLVM_UNLIKELY(Linker.Options.Update))
+        continue;
+
+      Linker.patchRangesForUnit(*CurrentUnit, DwarfContext, OF);
+      auto ProcessExpr = [&](StringRef Bytes,
+                             SmallVectorImpl<uint8_t> &Buffer) {
+        DWARFUnit &OrigUnit = CurrentUnit->getOrigUnit();
+        DataExtractor Data(Bytes, IsLittleEndian,
+                           OrigUnit.getAddressByteSize());
+        cloneExpression(Data,
+                        DWARFExpression(Data, OrigUnit.getVersion(),
+                                        OrigUnit.getAddressByteSize()),
+                        OF, *CurrentUnit, Buffer);
+      };
+      Emitter->emitLocationsForUnit(*CurrentUnit, DwarfContext, ProcessExpr);
+    }
+  }
+
+  if (!Linker.Options.NoOutput) {
+    assert(Emitter);
+    // Emit all the compile unit's debug information.
+    for (auto &CurrentUnit : CompileUnits) {
+      if (LLVM_LIKELY(!Linker.Options.Update))
+        Linker.generateUnitRanges(*CurrentUnit);
+
+      CurrentUnit->fixupForwardReferences();
+
+      if (!CurrentUnit->getOutputUnitDIE())
+        continue;
+
+      assert(Emitter->getDebugInfoSectionSize() ==
+             CurrentUnit->getStartOffset());
+      Emitter->emitCompileUnitHeader(*CurrentUnit);
+      Emitter->emitDIE(*CurrentUnit->getOutputUnitDIE());
+      assert(Emitter->getDebugInfoSectionSize() ==
+             CurrentUnit->computeNextUnitOffset());
+    }
+  }
+}
+
+void DWARFLinker::updateAccelKind(DWARFContext &Dwarf) {
+  if (Options.TheAccelTableKind != AccelTableKind::Default)
+    return;
+
+  auto &DwarfObj = Dwarf.getDWARFObj();
+
+  if (!AtLeastOneDwarfAccelTable &&
+      (!DwarfObj.getAppleNamesSection().Data.empty() ||
+       !DwarfObj.getAppleTypesSection().Data.empty() ||
+       !DwarfObj.getAppleNamespacesSection().Data.empty() ||
+       !DwarfObj.getAppleObjCSection().Data.empty())) {
+    AtLeastOneAppleAccelTable = true;
+  }
+
+  if (!AtLeastOneDwarfAccelTable && !DwarfObj.getNamesSection().Data.empty()) {
+    AtLeastOneDwarfAccelTable = true;
+  }
+}
+
+bool DWARFLinker::emitPaperTrailWarnings(const DwarfLinkerObjFile &OF,
+                                         OffsetsStringPool &StringPool) {
+
+  if (OF.Warnings.empty() || (OF.ObjFile && (OF.ObjFile->symbols().begin() !=
+                                             OF.ObjFile->symbols().end())))
+    return false;
+
+  DIE *CUDie = DIE::get(DIEAlloc, dwarf::DW_TAG_compile_unit);
+  CUDie->setOffset(11);
+  StringRef Producer;
+  StringRef WarningHeader;
+
+  switch (DwarfLinkerClientID) {
+  case DwarfLinkerClient::Dsymutil:
+    Producer = StringPool.internString("dsymutil");
+    WarningHeader = "dsymutil_warning";
+    break;
+
+  default:
+    Producer = StringPool.internString("dwarfopt");
+    WarningHeader = "dwarfopt_warning";
+    break;
+  }
+
+  StringRef File = StringPool.internString(OF.FileName);
+  CUDie->addValue(DIEAlloc, dwarf::DW_AT_producer, dwarf::DW_FORM_strp,
+                  DIEInteger(StringPool.getStringOffset(Producer)));
+  DIEBlock *String = new (DIEAlloc) DIEBlock();
+  DIEBlocks.push_back(String);
+  for (auto &C : File)
+    String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
+                     DIEInteger(C));
+  String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
+                   DIEInteger(0));
+
+  CUDie->addValue(DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_string, String);
+  for (const auto &Warning : OF.Warnings) {
+    DIE &ConstDie = CUDie->addChild(DIE::get(DIEAlloc, dwarf::DW_TAG_constant));
+    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_strp,
+                      DIEInteger(StringPool.getStringOffset(WarningHeader)));
+    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_artificial, dwarf::DW_FORM_flag,
+                      DIEInteger(1));
+    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_const_value, dwarf::DW_FORM_strp,
+                      DIEInteger(StringPool.getStringOffset(Warning)));
+  }
+  unsigned Size = 4 /* FORM_strp */ + File.size() + 1 +
+                  OF.Warnings.size() * (4 + 1 + 4) + 1 /* End of children */;
+  DIEAbbrev Abbrev = CUDie->generateAbbrev();
+  assignAbbrev(Abbrev);
+  CUDie->setAbbrevNumber(Abbrev.getNumber());
+  Size += getULEB128Size(Abbrev.getNumber());
+  // Abbreviation ordering needed for classic compatibility.
+  for (auto &Child : CUDie->children()) {
+    Abbrev = Child.generateAbbrev();
+    assignAbbrev(Abbrev);
+    Child.setAbbrevNumber(Abbrev.getNumber());
+    Size += getULEB128Size(Abbrev.getNumber());
+  }
+  CUDie->setSize(Size);
+  DwarfEmitter->emitPaperTrailWarningsDie(Triple, *CUDie);
+
+  return true;
+}
+
+void DWARFLinker::copyInvariantDebugSection(const object::ObjectFile &Obj) {
+  if (!needToTranslateStrings())
+    DwarfEmitter->emitSectionContents(Obj, "debug_line");
+  DwarfEmitter->emitSectionContents(Obj, "debug_loc");
+  DwarfEmitter->emitSectionContents(Obj, "debug_ranges");
+  DwarfEmitter->emitSectionContents(Obj, "debug_frame");
+  DwarfEmitter->emitSectionContents(Obj, "debug_aranges");
+}
+
+void DWARFLinker::addObjectFile(DwarfLinkerObjFile &ObjFile) {
+  ObjectContexts.emplace_back(LinkContext(ObjFile));
+
+  if (ObjectContexts.back().DwarfContext)
+    updateAccelKind(*ObjectContexts.back().DwarfContext);
+}
+
+bool DWARFLinker::link() {
+  assert(Options.NoOutput || DwarfEmitter);
+
+  // A unique ID that identifies each compile unit.
+  unsigned UnitID = 0;
+
+  // First populate the data structure we need for each iteration of the
+  // parallel loop.
+  unsigned NumObjects = ObjectContexts.size();
+
+  // This Dwarf string pool which is only used for uniquing. This one should
+  // never be used for offsets as its not thread-safe or predictable.
+  UniquingStringPool UniquingStringPool(nullptr, true);
+
+  // This Dwarf string pool which is used for emission. It must be used
+  // serially as the order of calling getStringOffset matters for
+  // reproducibility.
+  OffsetsStringPool OffsetsStringPool(StringsTranslator, true);
+
+  // ODR Contexts for the optimize.
+  DeclContextTree ODRContexts;
+
+  // If we haven't decided on an accelerator table kind yet, we base ourselves
+  // on the DWARF we have seen so far. At this point we haven't pulled in debug
+  // information from modules yet, so it is technically possible that they
+  // would affect the decision. However, as they're built with the same
+  // compiler and flags, it is safe to assume that they will follow the
+  // decision made here.
+  if (Options.TheAccelTableKind == AccelTableKind::Default) {
+    if (AtLeastOneDwarfAccelTable && !AtLeastOneAppleAccelTable)
+      Options.TheAccelTableKind = AccelTableKind::Dwarf;
+    else
+      Options.TheAccelTableKind = AccelTableKind::Apple;
+  }
+
+  for (LinkContext &OptContext : ObjectContexts) {
+    if (Options.Verbose) {
+      if (DwarfLinkerClientID == DwarfLinkerClient::Dsymutil)
+        outs() << "DEBUG MAP OBJECT: " << OptContext.ObjectFile.FileName
+               << "\n";
+      else
+        outs() << "OBJECT FILE: " << OptContext.ObjectFile.FileName << "\n";
+    }
+
+    if (emitPaperTrailWarnings(OptContext.ObjectFile, OffsetsStringPool))
+      continue;
+
+    if (!OptContext.ObjectFile.ObjFile)
+      continue;
+    // Look for relocations that correspond to address map entries.
+
+    // there was findvalidrelocations previously ... probably we need to gather
+    // info here
+    if (LLVM_LIKELY(!Options.Update) &&
+        !OptContext.ObjectFile.Addresses->hasValidRelocs()) {
+      if (Options.Verbose)
+        outs() << "No valid relocations found. Skipping.\n";
+
+      // Set "Skip" flag as a signal to other loops that we should not
+      // process this iteration.
+      OptContext.Skip = true;
+      continue;
+    }
+
+    // Setup access to the debug info.
+    if (!OptContext.DwarfContext)
+      continue;
+
+    // In a first phase, just read in the debug info and load all clang modules.
+    OptContext.CompileUnits.reserve(
+        OptContext.DwarfContext->getNumCompileUnits());
+
+    for (const auto &CU : OptContext.DwarfContext->compile_units()) {
+      updateDwarfVersion(CU->getVersion());
+      auto CUDie = CU->getUnitDIE(false);
+      if (Options.Verbose) {
+        outs() << "Input compilation unit:";
+        DIDumpOptions DumpOpts;
+        DumpOpts.ChildRecurseDepth = 0;
+        DumpOpts.Verbose = Options.Verbose;
+        CUDie.dump(outs(), 0, DumpOpts);
+      }
+      if (CUDie && !LLVM_UNLIKELY(Options.Update))
+        registerModuleReference(CUDie, *CU, OptContext.ObjectFile,
+                                OffsetsStringPool, UniquingStringPool,
+                                ODRContexts, 0, UnitID,
+                                OptContext.DwarfContext->isLittleEndian());
+    }
+  }
+
+  // If we haven't seen any CUs, pick an arbitrary valid Dwarf version anyway.
+  if (MaxDwarfVersion == 0)
+    MaxDwarfVersion = 3;
+
+  // At this point we know how much data we have emitted. We use this value to
+  // compare canonical DIE offsets in analyzeContextInfo to see if a definition
+  // is already emitted, without being affected by canonical die offsets set
+  // later. This prevents undeterminism when analyze and clone execute
+  // concurrently, as clone set the canonical DIE offset and analyze reads it.
+  const uint64_t ModulesEndOffset =
+      Options.NoOutput ? 0 : DwarfEmitter->getDebugInfoSectionSize();
+
+  // These variables manage the list of processed object files.
+  // The mutex and condition variable are to ensure that this is thread safe.
+  std::mutex ProcessedFilesMutex;
+  std::condition_variable ProcessedFilesConditionVariable;
+  BitVector ProcessedFiles(NumObjects, false);
+
+  //  Analyzing the context info is particularly expensive so it is executed in
+  //  parallel with emitting the previous compile unit.
+  auto AnalyzeLambda = [&](size_t I) {
+    auto &Context = ObjectContexts[I];
+
+    if (Context.Skip || !Context.DwarfContext)
+      return;
+
+    for (const auto &CU : Context.DwarfContext->compile_units()) {
+      updateDwarfVersion(CU->getVersion());
+      // The !registerModuleReference() condition effectively skips
+      // over fully resolved skeleton units. This second pass of
+      // registerModuleReferences doesn't do any new work, but it
+      // will collect top-level errors, which are suppressed. Module
+      // warnings were already displayed in the first iteration.
+      bool Quiet = true;
+      auto CUDie = CU->getUnitDIE(false);
+      if (!CUDie || LLVM_UNLIKELY(Options.Update) ||
+          !registerModuleReference(CUDie, *CU, Context.ObjectFile,
+                                   OffsetsStringPool, UniquingStringPool,
+                                   ODRContexts, ModulesEndOffset, UnitID,
+                                   Quiet)) {
+        Context.CompileUnits.push_back(std::make_unique<CompileUnit>(
+            *CU, UnitID++, !Options.NoODR && !Options.Update, ""));
+      }
+    }
+
+    // Now build the DIE parent links that we will use during the next phase.
+    for (auto &CurrentUnit : Context.CompileUnits) {
+      auto CUDie = CurrentUnit->getOrigUnit().getUnitDIE();
+      if (!CUDie)
+        continue;
+      analyzeContextInfo(CurrentUnit->getOrigUnit().getUnitDIE(), 0,
+                         *CurrentUnit, &ODRContexts.getRoot(),
+                         UniquingStringPool, ODRContexts, ModulesEndOffset,
+                         Options.ParseableSwiftInterfaces,
+                         [&](const Twine &Warning, const DWARFDie &DIE) {
+                           reportWarning(Warning, Context.ObjectFile, &DIE);
+                         });
+    }
+  };
+
+  // And then the remaining work in serial again.
+  // Note, although this loop runs in serial, it can run in parallel with
+  // the analyzeContextInfo loop so long as we process files with indices >=
+  // than those processed by analyzeContextInfo.
+  auto CloneLambda = [&](size_t I) {
+    auto &OptContext = ObjectContexts[I];
+    if (OptContext.Skip || !OptContext.ObjectFile.ObjFile)
+      return;
+
+    // Then mark all the DIEs that need to be present in the generated output
+    // and collect some information about them.
+    // Note that this loop can not be merged with the previous one because
+    // cross-cu references require the ParentIdx to be setup for every CU in
+    // the object file before calling this.
+    if (LLVM_UNLIKELY(Options.Update)) {
+      for (auto &CurrentUnit : OptContext.CompileUnits)
+        CurrentUnit->markEverythingAsKept();
+      copyInvariantDebugSection(*OptContext.ObjectFile.ObjFile);
+    } else {
+      for (auto &CurrentUnit : OptContext.CompileUnits)
+        lookForDIEsToKeep(
+            *OptContext.ObjectFile.Addresses,
+            OptContext.ObjectFile.Addresses->getValidAddressRanges(),
+            OptContext.CompileUnits, CurrentUnit->getOrigUnit().getUnitDIE(),
+            OptContext.ObjectFile, *CurrentUnit, 0);
+    }
+
+    // The calls to applyValidRelocs inside cloneDIE will walk the reloc
+    // array again (in the same way findValidRelocsInDebugInfo() did). We
+    // need to reset the NextValidReloc index to the beginning.
+    if (OptContext.ObjectFile.Addresses->hasValidRelocs() ||
+        LLVM_UNLIKELY(Options.Update)) {
+      DIECloner(*this, DwarfEmitter, OptContext.ObjectFile, DIEAlloc,
+                OptContext.CompileUnits, Options.Update)
+          .cloneAllCompileUnits(*OptContext.DwarfContext, OptContext.ObjectFile,
+                                OffsetsStringPool,
+                                OptContext.DwarfContext->isLittleEndian());
+    }
+    if (!Options.NoOutput && !OptContext.CompileUnits.empty() &&
+        LLVM_LIKELY(!Options.Update))
+      patchFrameInfoForObject(
+          OptContext.ObjectFile,
+          OptContext.ObjectFile.Addresses->getValidAddressRanges(),
+          *OptContext.DwarfContext,
+          OptContext.CompileUnits[0]->getOrigUnit().getAddressByteSize());
+
+    // Clean-up before starting working on the next object.
+    cleanupAuxiliarryData(OptContext);
+  };
+
+  auto EmitLambda = [&]() {
+    // Emit everything that's global.
+    if (!Options.NoOutput) {
+      DwarfEmitter->emitAbbrevs(Abbreviations, MaxDwarfVersion);
+      DwarfEmitter->emitStrings(OffsetsStringPool);
+      switch (Options.TheAccelTableKind) {
+      case AccelTableKind::Apple:
+        DwarfEmitter->emitAppleNames(AppleNames);
+        DwarfEmitter->emitAppleNamespaces(AppleNamespaces);
+        DwarfEmitter->emitAppleTypes(AppleTypes);
+        DwarfEmitter->emitAppleObjc(AppleObjc);
+        break;
+      case AccelTableKind::Dwarf:
+        DwarfEmitter->emitDebugNames(DebugNames);
+        break;
+      case AccelTableKind::Default:
+        llvm_unreachable("Default should have already been resolved.");
+        break;
+      }
+    }
+  };
+
+  auto AnalyzeAll = [&]() {
+    for (unsigned I = 0, E = NumObjects; I != E; ++I) {
+      AnalyzeLambda(I);
+
+      std::unique_lock<std::mutex> LockGuard(ProcessedFilesMutex);
+      ProcessedFiles.set(I);
+      ProcessedFilesConditionVariable.notify_one();
+    }
+  };
+
+  auto CloneAll = [&]() {
+    for (unsigned I = 0, E = NumObjects; I != E; ++I) {
+      {
+        std::unique_lock<std::mutex> LockGuard(ProcessedFilesMutex);
+        if (!ProcessedFiles[I]) {
+          ProcessedFilesConditionVariable.wait(
+              LockGuard, [&]() { return ProcessedFiles[I]; });
+        }
+      }
+
+      CloneLambda(I);
+    }
+    EmitLambda();
+  };
+
+  // To limit memory usage in the single threaded case, analyze and clone are
+  // run sequentially so the OptContext is freed after processing each object
+  // in endDebugObject.
+  if (Options.Threads == 1) {
+    for (unsigned I = 0, E = NumObjects; I != E; ++I) {
+      AnalyzeLambda(I);
+      CloneLambda(I);
+    }
+    EmitLambda();
+  } else {
+    ThreadPool Pool(2);
+    Pool.async(AnalyzeAll);
+    Pool.async(CloneAll);
+    Pool.wait();
+  }
+
+  return true;
+}
+
 } // namespace llvm

llvm/tools/dsymutil/DwarfLinkerForBinary.h

 #include "BinaryHolder.h"
 #include "DebugMap.h"
 #include "DwarfStreamer.h"
 #include "LinkUtils.h"
 #include "llvm/DWARFLinker/DWARFLinker.h"
 #include "llvm/DWARFLinker/DWARFLinkerCompileUnit.h"
 #include "llvm/DWARFLinker/DWARFLinkerDeclContext.h"
 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
+#include "llvm/Remarks/RemarkFormat.h"
+#include "llvm/Remarks/RemarkLinker.h"
 
 namespace llvm {
 namespace dsymutil {
 
-using UnitListTy = std::vector<std::unique_ptr<CompileUnit>>;
-
-/// The core of the Dwarf linking logic.
+/// The core of the Dsymutil Dwarf linking logic.
 ///
 /// The link of the dwarf information from the object files will be
-/// driven by the selection of 'root DIEs', which are DIEs that
-/// describe variables or functions that are present in the linked
-/// binary (and thus have entries in the debug map). All the debug
-/// information that will be linked (the DIEs, but also the line
-/// tables, ranges, ...) is derived from that set of root DIEs.
-///
-/// The root DIEs are identified because they contain relocations that
-/// correspond to a debug map entry at specific places (the low_pc for
-/// a function, the location for a variable). These relocations are
-/// called ValidRelocs in the DwarfLinker and are gathered as a very
-/// first step when we start processing a DebugMapObject.
+/// driven by DWARFLinker. DwarfLinkerForBinary reads DebugMap objects
+/// and pass information to the DWARFLinker. DWARFLinker
+/// optimizes DWARF taking into account valid relocations.
+/// Finally, optimized DWARF is passed to DwarfLinkerForBinary through
+/// DWARFEmitter interface.
 class DwarfLinkerForBinary {
 public:
   DwarfLinkerForBinary(raw_fd_ostream &OutFile, BinaryHolder &BinHolder,
                        LinkOptions Options)
       : OutFile(OutFile), BinHolder(BinHolder), Options(std::move(Options)) {}
 
   /// Link the contents of the DebugMap.
   bool link(const DebugMap &);
 
-  void reportWarning(const Twine &Warning, const DebugMapObject &DMO,
+  void reportWarning(const Twine &Warning, StringRef Context,
                      const DWARFDie *DIE = nullptr) const;
 
   /// Flags passed to DwarfLinker::lookForDIEsToKeep
   enum TraversalFlags {
     TF_Keep = 1 << 0,            ///< Mark the traversed DIEs as kept.
     TF_InFunctionScope = 1 << 1, ///< Current scope is a function scope.
     TF_DependencyWalk = 1 << 2,  ///< Walking the dependencies of a kept DIE.
     TF_ParentWalk = 1 << 3,      ///< Walking up the parents of a kept DIE.
     TF_ODR = 1 << 4,             ///< Use the ODR while keeping dependents.
     TF_SkipPC = 1 << 5,          ///< Skip all location attributes.
   };
 
 private:
-  /// Remembers the oldest and newest DWARF version we've seen in a unit.
-  void updateDwarfVersion(unsigned Version) {
-    MaxDwarfVersion = std::max(MaxDwarfVersion, Version);
-    MinDwarfVersion = std::min(MinDwarfVersion, Version);
-  }
-
-  /// Remembers the kinds of accelerator tables we've seen in a unit.
-  void updateAccelKind(DWARFContext &Dwarf);
-
-  /// Emit warnings as Dwarf compile units to leave a trail after linking.
-  bool emitPaperTrailWarnings(const DebugMapObject &DMO, const DebugMap &Map,
-                              OffsetsStringPool &StringPool);
 
   /// Keeps track of relocations.
-  class RelocationManager : public AddressesMap {
+  class AddressManager : public AddressesMap {
     struct ValidReloc {
       uint64_t Offset;
       uint32_t Size;
       uint64_t Addend;
       const DebugMapObject::DebugMapEntry *Mapping;
 
       ValidReloc(uint64_t Offset, uint32_t Size, uint64_t Addend,
                  const DebugMapObject::DebugMapEntry *Mapping)
class AddressManager : public AddressesMap {
     /// the DIEs in acsending file offset and as ValidRelocs is sorted by file
     /// offset, keeping this index up to date is all we have to do to have a
     /// cheap lookup during the root DIE selection and during DIE cloning.
     unsigned NextValidReloc = 0;
 
     RangesTy AddressRanges;
 
   public:
-    RelocationManager(DwarfLinkerForBinary &Linker,
-                      const object::ObjectFile &Obj, const DebugMapObject &DMO)
+    AddressManager(DwarfLinkerForBinary &Linker, const object::ObjectFile &Obj,
+                   const DebugMapObject &DMO)
         : Linker(Linker) {
       findValidRelocsInDebugInfo(Obj, DMO);
 
       // Iterate over the debug map entries and put all the ones that are
       // functions (because they have a size) into the Ranges map. This map is
       // very similar to the FunctionRanges that are stored in each unit, with 2
       // notable differences:
       //
AddressManager(DwarfLinkerForBinary &Linker, const object::ObjectFile &Obj,
       for (const auto &Entry : DMO.symbols()) {
         const auto &Mapping = Entry.getValue();
         if (Mapping.Size && Mapping.ObjectAddress)
           AddressRanges[*Mapping.ObjectAddress] = ObjFileAddressRange(
               *Mapping.ObjectAddress + Mapping.Size,
               int64_t(Mapping.BinaryAddress) - *Mapping.ObjectAddress);
       }
     }
-    virtual ~RelocationManager() override { clear(); }
+    virtual ~AddressManager() override { clear(); }
 
     virtual bool areRelocationsResolved() const override { return true; }
 
     bool hasValidRelocs(bool ResetRelocsPtr = true) override {
       if (ResetRelocsPtr)
         NextValidReloc = 0;
       return !ValidRelocs.empty();
     }
public:
 
     void clear() override {
       AddressRanges.clear();
       ValidRelocs.clear();
       NextValidReloc = 0;
     }
   };
 
-  /// Keeps track of data associated with one object during linking.
-  struct LinkContext {
-    DwarfLinkerForBinary &Linker;
-    DebugMapObject &DMO;
-    const object::ObjectFile *ObjectFile = nullptr;
-    std::unique_ptr<RelocationManager> RelocMgr;
-    std::unique_ptr<DWARFContext> DwarfContext;
-    RangesTy Ranges;
-    UnitListTy CompileUnits;
-
-    LinkContext(const DebugMap &Map, DwarfLinkerForBinary &Linker,
-                DebugMapObject &DMO)
-        : Linker(Linker), DMO(DMO) {
-      // Swift ASTs are not object files.
-      if (DMO.getType() == MachO::N_AST) {
-        ObjectFile = nullptr;
-        return;
-      }
-      if (auto ErrOrObj = Linker.loadObject(DMO, Map)) {
-        ObjectFile = &*ErrOrObj;
-        DwarfContext = DWARFContext::create(*ObjectFile);
-        RelocMgr.reset(new RelocationManager(Linker, *ObjectFile, DMO));
-      }
-    }
-
-    /// Clear part of the context that's no longer needed when we're done with
-    /// the debug object.
-    void Clear() {
-      DwarfContext.reset(nullptr);
-      CompileUnits.clear();
-      Ranges.clear();
-      RelocMgr->clear();
-    }
-  };
-
-  /// Called at the start of a debug object link.
-  void startDebugObject(LinkContext &Context);
-
-  /// Called at the end of a debug object link.
-  void endDebugObject(LinkContext &Context);
-
-  /// \defgroup FindRootDIEs Find DIEs corresponding to debug map entries.
-  ///
-  /// @{
-  /// Recursively walk the \p DIE tree and look for DIEs to
-  /// keep. Store that information in \p CU's DIEInfo.
-  ///
-  /// The return value indicates whether the DIE is incomplete.
-  void lookForDIEsToKeep(RelocationManager &RelocMgr, RangesTy &Ranges,
-                         const UnitListTy &Units, const DWARFDie &DIE,
-                         const DebugMapObject &DMO, CompileUnit &CU,
-                         unsigned Flags);
-
-  /// If this compile unit is really a skeleton CU that points to a
-  /// clang module, register it in ClangModules and return true.
-  ///
-  /// A skeleton CU is a CU without children, a DW_AT_gnu_dwo_name
-  /// pointing to the module, and a DW_AT_gnu_dwo_id with the module
-  /// hash.
-  bool registerModuleReference(DWARFDie CUDie, const DWARFUnit &Unit,
-                               DebugMap &ModuleMap, const DebugMapObject &DMO,
-                               RangesTy &Ranges,
-                               OffsetsStringPool &OffsetsStringPool,
-                               UniquingStringPool &UniquingStringPoolStringPool,
-                               DeclContextTree &ODRContexts,
-                               uint64_t ModulesEndOffset, unsigned &UnitID,
-                               bool IsLittleEndian, unsigned Indent = 0,
-                               bool Quiet = false);
-
-  /// Recursively add the debug info in this clang module .pcm
-  /// file (and all the modules imported by it in a bottom-up fashion)
-  /// to Units.
-  Error loadClangModule(DWARFDie CUDie, StringRef FilePath,
-                        StringRef ModuleName, uint64_t DwoId,
-                        DebugMap &ModuleMap, const DebugMapObject &DMO,
-                        RangesTy &Ranges, OffsetsStringPool &OffsetsStringPool,
-                        UniquingStringPool &UniquingStringPool,
-                        DeclContextTree &ODRContexts, uint64_t ModulesEndOffset,
-                        unsigned &UnitID, bool IsLittleEndian,
-                        unsigned Indent = 0, bool Quiet = false);
-
-  /// Mark the passed DIE as well as all the ones it depends on as kept.
-  void keepDIEAndDependencies(RelocationManager &RelocMgr, RangesTy &Ranges,
-                              const UnitListTy &Units, const DWARFDie &DIE,
-                              CompileUnit::DIEInfo &MyInfo,
-                              const DebugMapObject &DMO, CompileUnit &CU,
-                              bool UseODR);
-
-  unsigned shouldKeepDIE(RelocationManager &RelocMgr, RangesTy &Ranges,
-                         const DWARFDie &DIE, const DebugMapObject &DMO,
-                         CompileUnit &Unit, CompileUnit::DIEInfo &MyInfo,
-                         unsigned Flags);
-
-  /// Check if a variable describing DIE should be kept.
-  /// \returns updated TraversalFlags.
-  unsigned shouldKeepVariableDIE(RelocationManager &RelocMgr,
-                                 const DWARFDie &DIE, CompileUnit &Unit,
-                                 CompileUnit::DIEInfo &MyInfo, unsigned Flags);
-
-  unsigned shouldKeepSubprogramDIE(RelocationManager &RelocMgr,
-                                   RangesTy &Ranges, const DWARFDie &DIE,
-                                   const DebugMapObject &DMO, CompileUnit &Unit,
-                                   CompileUnit::DIEInfo &MyInfo,
-                                   unsigned Flags);
-
-  bool hasValidRelocation(uint32_t StartOffset, uint32_t EndOffset,
-                          CompileUnit::DIEInfo &Info);
-  /// @}
-
-  /// \defgroup Linking Methods used to link the debug information
-  ///
-  /// @{
-
-  class DIECloner {
-    DwarfLinkerForBinary &Linker;
-    RelocationManager &RelocMgr;
-
-    /// Allocator used for all the DIEValue objects.
-    BumpPtrAllocator &DIEAlloc;
-
-    std::vector<std::unique_ptr<CompileUnit>> &CompileUnits;
-    LinkOptions Options;
-
-  public:
-    DIECloner(DwarfLinkerForBinary &Linker, RelocationManager &RelocMgr,
-              BumpPtrAllocator &DIEAlloc,
-              std::vector<std::unique_ptr<CompileUnit>> &CompileUnits,
-              LinkOptions &Options)
-        : Linker(Linker), RelocMgr(RelocMgr), DIEAlloc(DIEAlloc),
-          CompileUnits(CompileUnits), Options(Options) {}
-
-    /// Recursively clone \p InputDIE into an tree of DIE objects
-    /// where useless (as decided by lookForDIEsToKeep()) bits have been
-    /// stripped out and addresses have been rewritten according to the
-    /// debug map.
-    ///
-    /// \param OutOffset is the offset the cloned DIE in the output
-    /// compile unit.
-    /// \param PCOffset (while cloning a function scope) is the offset
-    /// applied to the entry point of the function to get the linked address.
-    /// \param Die the output DIE to use, pass NULL to create one.
-    /// \returns the root of the cloned tree or null if nothing was selected.
-    DIE *cloneDIE(const DWARFDie &InputDIE, const DebugMapObject &DMO,
-                  CompileUnit &U, OffsetsStringPool &StringPool,
-                  int64_t PCOffset, uint32_t OutOffset, unsigned Flags,
-                  bool IsLittleEndian, DIE *Die = nullptr);
-
-    /// Construct the output DIE tree by cloning the DIEs we
-    /// chose to keep above. If there are no valid relocs, then there's
-    /// nothing to clone/emit.
-    void cloneAllCompileUnits(DWARFContext &DwarfContext,
-                              const DebugMapObject &DMO, RangesTy &Ranges,
-                              OffsetsStringPool &StringPool,
-                              bool IsLittleEndian);
-
-  private:
-    using AttributeSpec = DWARFAbbreviationDeclaration::AttributeSpec;
-
-    /// Information gathered and exchanged between the various
-    /// clone*Attributes helpers about the attributes of a particular DIE.
-    struct AttributesInfo {
-      /// Names.
-      DwarfStringPoolEntryRef Name, MangledName, NameWithoutTemplate;
-
-      /// Offsets in the string pool.
-      uint32_t NameOffset = 0;
-      uint32_t MangledNameOffset = 0;
-
-      /// Value of AT_low_pc in the input DIE
-      uint64_t OrigLowPc = std::numeric_limits<uint64_t>::max();
-
-      /// Value of AT_high_pc in the input DIE
-      uint64_t OrigHighPc = 0;
-
-      /// Offset to apply to PC addresses inside a function.
-      int64_t PCOffset = 0;
-
-      /// Does the DIE have a low_pc attribute?
-      bool HasLowPc = false;
-
-      /// Does the DIE have a ranges attribute?
-      bool HasRanges = false;
-
-      /// Is this DIE only a declaration?
-      bool IsDeclaration = false;
-
-      AttributesInfo() = default;
-    };
-
-    /// Helper for cloneDIE.
-    unsigned cloneAttribute(DIE &Die, const DWARFDie &InputDIE,
-                            const DebugMapObject &DMO, CompileUnit &U,
-                            OffsetsStringPool &StringPool,
-                            const DWARFFormValue &Val,
-                            const AttributeSpec AttrSpec, unsigned AttrSize,
-                            AttributesInfo &AttrInfo, bool IsLittleEndian);
-
-    /// Clone a string attribute described by \p AttrSpec and add
-    /// it to \p Die.
-    /// \returns the size of the new attribute.
-    unsigned cloneStringAttribute(DIE &Die, AttributeSpec AttrSpec,
-                                  const DWARFFormValue &Val, const DWARFUnit &U,
-                                  OffsetsStringPool &StringPool,
-                                  AttributesInfo &Info);
-
-    /// Clone an attribute referencing another DIE and add
-    /// it to \p Die.
-    /// \returns the size of the new attribute.
-    unsigned cloneDieReferenceAttribute(DIE &Die, const DWARFDie &InputDIE,
-                                        AttributeSpec AttrSpec,
-                                        unsigned AttrSize,
-                                        const DWARFFormValue &Val,
-                                        const DebugMapObject &DMO,
-                                        CompileUnit &Unit);
-
-    /// Clone a DWARF expression that may be referencing another DIE.
-    void cloneExpression(DataExtractor &Data, DWARFExpression Expression,
-                         const DebugMapObject &DMO, CompileUnit &Unit,
-                         SmallVectorImpl<uint8_t> &OutputBuffer);
-
-    /// Clone an attribute referencing another DIE and add
-    /// it to \p Die.
-    /// \returns the size of the new attribute.
-    unsigned cloneBlockAttribute(DIE &Die, const DebugMapObject &DMO,
-                                 CompileUnit &Unit, AttributeSpec AttrSpec,
-                                 const DWARFFormValue &Val, unsigned AttrSize,
-                                 bool IsLittleEndian);
-
-    /// Clone an attribute referencing another DIE and add
-    /// it to \p Die.
-    /// \returns the size of the new attribute.
-    unsigned cloneAddressAttribute(DIE &Die, AttributeSpec AttrSpec,
-                                   const DWARFFormValue &Val,
-                                   const CompileUnit &Unit,
-                                   AttributesInfo &Info);
-
-    /// Clone a scalar attribute  and add it to \p Die.
-    /// \returns the size of the new attribute.
-    unsigned cloneScalarAttribute(DIE &Die, const DWARFDie &InputDIE,
-                                  const DebugMapObject &DMO, CompileUnit &U,
-                                  AttributeSpec AttrSpec,
-                                  const DWARFFormValue &Val, unsigned AttrSize,
-                                  AttributesInfo &Info);
-
-    /// Get the potential name and mangled name for the entity
-    /// described by \p Die and store them in \Info if they are not
-    /// already there.
-    /// \returns is a name was found.
-    bool getDIENames(const DWARFDie &Die, AttributesInfo &Info,
-                     OffsetsStringPool &StringPool, bool StripTemplate = false);
-
-    /// Create a copy of abbreviation Abbrev.
-    void copyAbbrev(const DWARFAbbreviationDeclaration &Abbrev, bool hasODR);
-
-    uint32_t hashFullyQualifiedName(DWARFDie DIE, CompileUnit &U,
-                                    const DebugMapObject &DMO,
-                                    int RecurseDepth = 0);
-
-    /// Helper for cloneDIE.
-    void addObjCAccelerator(CompileUnit &Unit, const DIE *Die,
-                            DwarfStringPoolEntryRef Name,
-                            OffsetsStringPool &StringPool, bool SkipPubSection);
-  };
-
-  /// Assign an abbreviation number to \p Abbrev
-  void assignAbbrev(DIEAbbrev &Abbrev);
-
-  /// Compute and emit debug_ranges section for \p Unit, and
-  /// patch the attributes referencing it.
-  void patchRangesForUnit(const CompileUnit &Unit, DWARFContext &Dwarf,
-                          const DebugMapObject &DMO) const;
-
-  /// Generate and emit the DW_AT_ranges attribute for a compile_unit if it had
-  /// one.
-  void generateUnitRanges(CompileUnit &Unit) const;
-
-  /// Extract the line tables from the original dwarf, extract the relevant
-  /// parts according to the linked function ranges and emit the result in the
-  /// debug_line section.
-  void patchLineTableForUnit(CompileUnit &Unit, DWARFContext &OrigDwarf,
-                             RangesTy &Ranges, const DebugMapObject &DMO);
-
-  /// Emit the accelerator entries for \p Unit.
-  void emitAcceleratorEntriesForUnit(CompileUnit &Unit);
-  void emitDwarfAcceleratorEntriesForUnit(CompileUnit &Unit);
-  void emitAppleAcceleratorEntriesForUnit(CompileUnit &Unit);
-
-  /// Patch the frame info for an object file and emit it.
-  void patchFrameInfoForObject(const DebugMapObject &, RangesTy &Ranges,
-                               DWARFContext &, unsigned AddressSize);
-
-  /// FoldingSet that uniques the abbreviations.
-  FoldingSet<DIEAbbrev> AbbreviationsSet;
-
-  /// Storage for the unique Abbreviations.
-  /// This is passed to AsmPrinter::emitDwarfAbbrevs(), thus it cannot be
-  /// changed to a vector of unique_ptrs.
-  std::vector<std::unique_ptr<DIEAbbrev>> Abbreviations;
-
-  /// DIELoc objects that need to be destructed (but not freed!).
-  std::vector<DIELoc *> DIELocs;
-
-  /// DIEBlock objects that need to be destructed (but not freed!).
-  std::vector<DIEBlock *> DIEBlocks;
-
-  /// Allocator used for all the DIEValue objects.
-  BumpPtrAllocator DIEAlloc;
-  /// @}
-
   /// \defgroup Helpers Various helper methods.
   ///
   /// @{
   bool createStreamer(const Triple &TheTriple, raw_fd_ostream &OutFile);
 
   /// Attempt to load a debug object from disk.
   ErrorOr<const object::ObjectFile &> loadObject(const DebugMapObject &Obj,
-                                                 const DebugMap &Map);
-  /// @}
+                                                 const Triple &triple);
+  ErrorOr<DwarfLinkerObjFile &> loadObject(const DebugMapObject &Obj,
+                                           const DebugMap &DebugMap,
+                                           remarks::RemarkLinker &RL);
 
   raw_fd_ostream &OutFile;
   BinaryHolder &BinHolder;
   LinkOptions Options;
   std::unique_ptr<DwarfStreamer> Streamer;
-
-  unsigned MaxDwarfVersion = 0;
-  unsigned MinDwarfVersion = std::numeric_limits<unsigned>::max();
-
-  bool AtLeastOneAppleAccelTable = false;
-  bool AtLeastOneDwarfAccelTable = false;
-
-  /// The CIEs that have been emitted in the output section. The actual CIE
-  /// data serves a the key to this StringMap, this takes care of comparing the
-  /// semantics of CIEs defined in different object files.
-  StringMap<uint32_t> EmittedCIEs;
-
-  /// Offset of the last CIE that has been emitted in the output
-  /// debug_frame section.
-  uint32_t LastCIEOffset = 0;
-
-  /// Apple accelerator tables.
-  AccelTable<DWARF5AccelTableStaticData> DebugNames;
-  AccelTable<AppleAccelTableStaticOffsetData> AppleNames;
-  AccelTable<AppleAccelTableStaticOffsetData> AppleNamespaces;
-  AccelTable<AppleAccelTableStaticOffsetData> AppleObjc;
-  AccelTable<AppleAccelTableStaticTypeData> AppleTypes;
-
-  /// Mapping the PCM filename to the DwoId.
-  StringMap<uint64_t> ClangModules;
+  std::vector<std::unique_ptr<DwarfLinkerObjFile>> ObjectsForLinking;
 
   /// A list of all .swiftinterface files referenced by the debug
   /// info, mapping Module name to path on disk. The entries need to
   /// be uniqued and sorted and there are only few entries expected
   /// per compile unit, which is why this is a std::map.
   std::map<std::string, std::string> ParseableSwiftInterfaces;
 
   bool ModuleCacheHintDisplayed = false;
   bool ArchiveHintDisplayed = false;
 };
 
 } // end namespace dsymutil
 } // end namespace llvm
 
 #endif // LLVM_TOOLS_DSYMUTIL_DWARFLINKER_H

llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCTargetOptions.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Object/SymbolicFile.h"
-#include "llvm/Remarks/RemarkFormat.h"
-#include "llvm/Remarks/RemarkLinker.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/DJB.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ErrorOr.h"

 #include <system_error>
 #include <tuple>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 namespace dsymutil {
 
-/// Similar to DWARFUnitSection::getUnitForOffset(), but returning our
-/// CompileUnit object instead.
-static CompileUnit *getUnitForOffset(const UnitListTy &Units, uint64_t Offset) {
-  auto CU = std::upper_bound(
-      Units.begin(), Units.end(), Offset,
-      [](uint64_t LHS, const std::unique_ptr<CompileUnit> &RHS) {
-        return LHS < RHS->getOrigUnit().getNextUnitOffset();
-      });
-  return CU != Units.end() ? CU->get() : nullptr;
+static Error copySwiftInterfaces(
+    const std::map<std::string, std::string> &ParseableSwiftInterfaces,
+    StringRef Architecture, const LinkOptions &Options) {
+  std::error_code EC;
+  SmallString<128> InputPath;
+  SmallString<128> Path;
+  sys::path::append(Path, *Options.ResourceDir, "Swift", Architecture);
+  if ((EC = sys::fs::create_directories(Path.str(), true,
+                                        sys::fs::perms::all_all)))
+    return make_error<StringError>(
+        "cannot create directory: " + toString(errorCodeToError(EC)), EC);
+  unsigned BaseLength = Path.size();
+
+  for (auto &I : ParseableSwiftInterfaces) {
+    StringRef ModuleName = I.first;
+    StringRef InterfaceFile = I.second;
+    if (!Options.PrependPath.empty()) {
+      InputPath.clear();
+      sys::path::append(InputPath, Options.PrependPath, InterfaceFile);
+      InterfaceFile = InputPath;
     }
+    sys::path::append(Path, ModuleName);
+    Path.append(".swiftinterface");
+    if (Options.Verbose)
+      outs() << "copy parseable Swift interface " << InterfaceFile << " -> "
+             << Path.str() << '\n';
 
-/// Resolve the DIE attribute reference that has been extracted in \p RefValue.
-/// The resulting DIE might be in another CompileUnit which is stored into \p
-/// ReferencedCU. \returns null if resolving fails for any reason.
-static DWARFDie resolveDIEReference(const DwarfLinkerForBinary &Linker,
-                                    const DebugMapObject &DMO,
-                                    const UnitListTy &Units,
-                                    const DWARFFormValue &RefValue,
-                                    const DWARFDie &DIE, CompileUnit *&RefCU) {
-  assert(RefValue.isFormClass(DWARFFormValue::FC_Reference));
-  uint64_t RefOffset = *RefValue.getAsReference();
-  if ((RefCU = getUnitForOffset(Units, RefOffset)))
-    if (const auto RefDie = RefCU->getOrigUnit().getDIEForOffset(RefOffset)) {
-      // In a file with broken references, an attribute might point to a NULL
-      // DIE.
-      if (!RefDie.isNULL())
-        return RefDie;
-    }
-
-  Linker.reportWarning("could not find referenced DIE", DMO, &DIE);
-  return DWARFDie();
-}
-
-/// \returns whether the passed \a Attr type might contain a DIE reference
-/// suitable for ODR uniquing.
-static bool isODRAttribute(uint16_t Attr) {
-  switch (Attr) {
-  default:
-    return false;
-  case dwarf::DW_AT_type:
-  case dwarf::DW_AT_containing_type:
-  case dwarf::DW_AT_specification:
-  case dwarf::DW_AT_abstract_origin:
-  case dwarf::DW_AT_import:
-    return true;
+    // copy_file attempts an APFS clone first, so this should be cheap.
+    if ((EC = sys::fs::copy_file(InterfaceFile, Path.str())))
+      warn(Twine("cannot copy parseable Swift interface ") + InterfaceFile +
+           ": " + toString(errorCodeToError(EC)));
+    Path.resize(BaseLength);
   }
-  llvm_unreachable("Improper attribute.");
+  return Error::success();
+}
+
+/// Report a warning to the user, optionally including information about a
+/// specific \p DIE related to the warning.
+void DwarfLinkerForBinary::reportWarning(const Twine &Warning,
+                                         StringRef Context,
+                                         const DWARFDie *DIE) const {
+
+  warn(Warning, Context);
+
+  if (!Options.Verbose || !DIE)
+    return;
+
+  DIDumpOptions DumpOpts;
+  DumpOpts.ChildRecurseDepth = 0;
+  DumpOpts.Verbose = Options.Verbose;
+
+  WithColor::note() << "    in DIE:\n";
+  DIE->dump(errs(), 6 /* Indent */, DumpOpts);
 }
 
-static bool isTypeTag(uint16_t Tag) {
-  switch (Tag) {
-  case dwarf::DW_TAG_array_type:
-  case dwarf::DW_TAG_class_type:
-  case dwarf::DW_TAG_enumeration_type:
-  case dwarf::DW_TAG_pointer_type:
-  case dwarf::DW_TAG_reference_type:
-  case dwarf::DW_TAG_string_type:
-  case dwarf::DW_TAG_structure_type:
-  case dwarf::DW_TAG_subroutine_type:
-  case dwarf::DW_TAG_typedef:
-  case dwarf::DW_TAG_union_type:
-  case dwarf::DW_TAG_ptr_to_member_type:
-  case dwarf::DW_TAG_set_type:
-  case dwarf::DW_TAG_subrange_type:
-  case dwarf::DW_TAG_base_type:
-  case dwarf::DW_TAG_const_type:
-  case dwarf::DW_TAG_constant:
-  case dwarf::DW_TAG_file_type:
-  case dwarf::DW_TAG_namelist:
-  case dwarf::DW_TAG_packed_type:
-  case dwarf::DW_TAG_volatile_type:
-  case dwarf::DW_TAG_restrict_type:
-  case dwarf::DW_TAG_atomic_type:
-  case dwarf::DW_TAG_interface_type:
-  case dwarf::DW_TAG_unspecified_type:
-  case dwarf::DW_TAG_shared_type:
+bool DwarfLinkerForBinary::createStreamer(const Triple &TheTriple,
+                                          raw_fd_ostream &OutFile) {
+  if (Options.NoOutput)
     return true;
-  default:
-    break;
-  }
-  return false;
+
+  Streamer = std::make_unique<DwarfStreamer>(OutFile, Options);
+  return Streamer->init(TheTriple);
+
+ErrorOr<const object::ObjectFile &>
+DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
+                                 const Triple &Triple) {
+  auto ObjectEntry =
+      BinHolder.getObjectEntry(Obj.getObjectFilename(), Obj.getTimestamp());
+  if (!ObjectEntry) {
+    auto Err = ObjectEntry.takeError();
+    reportWarning(Twine(Obj.getObjectFilename()) + ": " +
+                      toString(std::move(Err)),
+                  Obj.getObjectFilename());
+    return errorToErrorCode(std::move(Err));
+  }
+
+  auto Object = ObjectEntry->getObject(Triple);
+  if (!Object) {
+    auto Err = Object.takeError();
+    reportWarning(Twine(Obj.getObjectFilename()) + ": " +
+                      toString(std::move(Err)),
+                  Obj.getObjectFilename());
+    return errorToErrorCode(std::move(Err));
+  }
+
+  return *Object;
 }
 
 static Error remarksErrorHandler(const DebugMapObject &DMO,
                                  DwarfLinkerForBinary &Linker,
                                  std::unique_ptr<FileError> FE) {
   bool IsArchive = DMO.getObjectFilename().endswith(")");
   // Don't report errors for missing remark files from static
   // archives.
   if (!IsArchive)
     return Error(std::move(FE));
 
   std::string Message = FE->message();
   Error E = FE->takeError();
   Error NewE = handleErrors(std::move(E), [&](std::unique_ptr<ECError> EC) {
     if (EC->convertToErrorCode() != std::errc::no_such_file_or_directory)
       return Error(std::move(EC));
 
-    Linker.reportWarning(Message, DMO);
+    Linker.reportWarning(Message, DMO.getObjectFilename());
     return Error(Error::success());
   });
 
   if (!NewE)
     return Error::success();
 
   return createFileError(FE->getFileName(), std::move(NewE));
 }
 
-bool DwarfLinkerForBinary::DIECloner::getDIENames(const DWARFDie &Die,
-                                                  AttributesInfo &Info,
-                                                  OffsetsStringPool &StringPool,
-                                                  bool StripTemplate) {
-  // This function will be called on DIEs having low_pcs and
-  // ranges. As getting the name might be more expansive, filter out
-  // blocks directly.
-  if (Die.getTag() == dwarf::DW_TAG_lexical_block)
-    return false;
+static Error emitRemarks(const LinkOptions &Options, StringRef BinaryPath,
+                         StringRef ArchName, const remarks::RemarkLinker &RL) {
+  // Make sure we don't create the directories and the file if there is nothing
+  // to serialize.
+  if (RL.empty())
+    return Error::success();
+
+  SmallString<128> InputPath;
+  SmallString<128> Path;
+  // Create the "Remarks" directory in the "Resources" directory.
+  sys::path::append(Path, *Options.ResourceDir, "Remarks");
+  if (std::error_code EC = sys::fs::create_directories(Path.str(), true,
+                                                       sys::fs::perms::all_all))
+    return errorCodeToError(EC);
 
-  // FIXME: a bit wasteful as the first getName might return the
-  // short name.
-  if (!Info.MangledName)
-    if (const char *MangledName = Die.getName(DINameKind::LinkageName))
-      Info.MangledName = StringPool.getEntry(MangledName);
-
-  if (!Info.Name)
-    if (const char *Name = Die.getName(DINameKind::ShortName))
-      Info.Name = StringPool.getEntry(Name);
-
-  if (StripTemplate && Info.Name && Info.MangledName != Info.Name) {
-    // FIXME: dsymutil compatibility. This is wrong for operator<
-    auto Split = Info.Name.getString().split('<');
-    if (!Split.second.empty())
-      Info.NameWithoutTemplate = StringPool.getEntry(Split.first);
+  // Append the file name.
+  // For fat binaries, also append a dash and the architecture name.
+  sys::path::append(Path, sys::path::filename(BinaryPath));
+  if (Options.NumDebugMaps > 1) {
+    // More than one debug map means we have a fat binary.
+    Path += '-';
+    Path += ArchName;
   }
 
-  return Info.Name || Info.MangledName;
+  std::error_code EC;
+  raw_fd_ostream OS(Options.NoOutput ? "-" : Path.str(), EC, sys::fs::OF_None);
+  if (EC)
+    return errorCodeToError(EC);
+
+  if (Error E = RL.serialize(OS, Options.RemarksFormat))
+    return E;
+
+  return Error::success();
 }
 
-/// Report a warning to the user, optionally including information about a
-/// specific \p DIE related to the warning.
-void DwarfLinkerForBinary::reportWarning(const Twine &Warning,
-                                         const DebugMapObject &DMO,
-                                         const DWARFDie *DIE) const {
-  StringRef Context = DMO.getObjectFilename();
-  warn(Warning, Context);
+ErrorOr<DwarfLinkerObjFile &>
+DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
+                                 const DebugMap &DebugMap,
+                                 remarks::RemarkLinker &RL) {
+  auto ErrorOrObj = loadObject(Obj, DebugMap.getTriple());
+
+  if (ErrorOrObj) {
+    ObjectsForLinking.push_back(
+        std::unique_ptr<DwarfLinkerObjFile>(new DwarfLinkerObjFile(
+            Obj.getObjectFilename(), &*ErrorOrObj, Obj.getWarnings())));
 
-  if (!Options.Verbose || !DIE)
-    return;
+    ObjectsForLinking.back()->Addresses.reset(
+        new AddressManager(*this, *ErrorOrObj, Obj));
 
-  DIDumpOptions DumpOpts;
-  DumpOpts.ChildRecurseDepth = 0;
-  DumpOpts.Verbose = Options.Verbose;
+    Error E = RL.link(*ObjectsForLinking.back()->ObjFile);
+    if (Error NewE = handleErrors(
+            std::move(E), [&](std::unique_ptr<FileError> EC) -> Error {
+              return remarksErrorHandler(Obj, *this, std::move(EC));
+            }))
+      return errorToErrorCode(std::move(NewE));
 
-  WithColor::note() << "    in DIE:\n";
-  DIE->dump(errs(), 6 /* Indent */, DumpOpts);
+    return *ObjectsForLinking.back();
   }
 
-bool DwarfLinkerForBinary::createStreamer(const Triple &TheTriple,
-                                          raw_fd_ostream &OutFile) {
-  if (Options.NoOutput)
-    return true;
+  return ErrorOrObj.getError();
+}
 
-  Streamer = std::make_unique<DwarfStreamer>(OutFile, Options);
-  return Streamer->init(TheTriple);
+bool DwarfLinkerForBinary::link(const DebugMap &Map) {
+  if (!createStreamer(Map.getTriple(), OutFile))
+    return false;
+
+  ObjectsForLinking.clear();
+
+  DebugMap DebugMap(Map.getTriple(), Map.getBinaryPath());
+
+  DWARFLinker GeneralLinker(Map.getTriple(), Streamer.get(),
+                            DwarfLinkerClient::Dsymutil);
+
+  remarks::RemarkLinker RL;
+  if (!Options.RemarksPrependPath.empty())
+    RL.setExternalFilePrependPath(Options.RemarksPrependPath);
+
+  std::function<StringRef(StringRef)> TranslationLambda = [&](StringRef Input) {
+    assert(Options.Translator);
+    return Options.Translator(Input);
+  };
+
+  GeneralLinker.setVerbosity(Options.Verbose);
+  GeneralLinker.setNoOutput(Options.NoOutput);
+  GeneralLinker.setNoODR(Options.NoODR);
+  GeneralLinker.setUpdate(Options.Update);
+  GeneralLinker.setNumThreads(Options.Threads);
+  GeneralLinker.setAccelTableKind(Options.TheAccelTableKind);
+  GeneralLinker.setPrependPath(Options.PrependPath);
+  if (Options.Translator)
+    GeneralLinker.setStringsTranslator(TranslationLambda);
+  GeneralLinker.setWarningHandler(
+      [&](const Twine &Warning, StringRef Context, const DWARFDie *DIE) {
+        reportWarning(Warning, Context, DIE);
+      });
+  GeneralLinker.setErrorHandler(
+      [&](const Twine &Error, StringRef Context, const DWARFDie *DIE) {
+        error(Error, Context);
+      });
+  GeneralLinker.setObjFileLoader(
+      [&DebugMap, &RL, this](StringRef ContainerName,
+                             StringRef Path) -> ErrorOr<DwarfLinkerObjFile &> {
+        auto &Obj = DebugMap.addDebugMapObject(
+            Path, sys::TimePoint<std::chrono::seconds>(), MachO::N_OSO);
+
+        if (auto ErrorOrObj = loadObject(Obj, DebugMap, RL)) {
+          return *ErrorOrObj;
+        } else {
+          // Try and emit more helpful warnings by applying some heuristics.
+          StringRef ObjFile = ContainerName;
+          bool IsClangModule = sys::path::extension(Path).equals(".pcm");
+          bool IsArchive = ObjFile.endswith(")");
+
+          if (IsClangModule) {
+            StringRef ModuleCacheDir = sys::path::parent_path(Path);
+            if (sys::fs::exists(ModuleCacheDir)) {
+              // If the module's parent directory exists, we assume that the
+              // module cache has expired and was pruned by clang.  A more
+              // adventurous dsymutil would invoke clang to rebuild the module
+              // now.
+              if (!ModuleCacheHintDisplayed) {
+                WithColor::note()
+                    << "The clang module cache may have expired since "
+                       "this object file was built. Rebuilding the "
+                       "object file will rebuild the module cache.\n";
+                ModuleCacheHintDisplayed = true;
+              }
+            } else if (IsArchive) {
+              // If the module cache directory doesn't exist at all and the
+              // object file is inside a static library, we assume that the
+              // static library was built on a different machine. We don't want
+              // to discourage module debugging for convenience libraries within
+              // a project though.
+              if (!ArchiveHintDisplayed) {
+                WithColor::note()
+                    << "Linking a static library that was built with "
+                       "-gmodules, but the module cache was not found.  "
+                       "Redistributable static libraries should never be "
+                       "built with module debugging enabled.  The debug "
+                       "experience will be degraded due to incomplete "
+                       "debug information.\n";
+                ArchiveHintDisplayed = true;
+              }
+            }
           }
 
-/// Resolve the relative path to a build artifact referenced by DWARF by
-/// applying DW_AT_comp_dir.
-static void resolveRelativeObjectPath(SmallVectorImpl<char> &Buf, DWARFDie CU) {
-  sys::path::append(Buf, dwarf::toString(CU.find(dwarf::DW_AT_comp_dir), ""));
+          return ErrorOrObj.getError();
         }
 
-/// Collect references to parseable Swift interfaces in imported
-/// DW_TAG_module blocks.
-static void analyzeImportedModule(
-    const DWARFDie &DIE, CompileUnit &CU,
-    std::map<std::string, std::string> &ParseableSwiftInterfaces,
-    std::function<void(const Twine &, const DWARFDie &)> ReportWarning) {
-  if (CU.getLanguage() != dwarf::DW_LANG_Swift)
-    return;
+        llvm_unreachable("Unhandled DebugMap object");
+      });
+  GeneralLinker.setSwiftInterfacesMap(&ParseableSwiftInterfaces);
 
-  StringRef Path = dwarf::toStringRef(DIE.find(dwarf::DW_AT_LLVM_include_path));
-  if (!Path.endswith(".swiftinterface"))
-    return;
-  if (Optional<DWARFFormValue> Val = DIE.find(dwarf::DW_AT_name))
-    if (Optional<const char *> Name = Val->getAsCString()) {
-      auto &Entry = ParseableSwiftInterfaces[*Name];
-      // The prepend path is applied later when copying.
-      DWARFDie CUDie = CU.getOrigUnit().getUnitDIE();
-      SmallString<128> ResolvedPath;
-      if (sys::path::is_relative(Path))
-        resolveRelativeObjectPath(ResolvedPath, CUDie);
-      sys::path::append(ResolvedPath, Path);
-      if (!Entry.empty() && Entry != ResolvedPath)
-        ReportWarning(
-            Twine("Conflicting parseable interfaces for Swift Module ") +
-                *Name + ": " + Entry + " and " + Path,
-            DIE);
-      Entry = ResolvedPath.str();
+  for (const auto &Obj : Map.objects()) {
+    // N_AST objects (swiftmodule files) should get dumped directly into the
+    // appropriate DWARF section.
+    if (Obj->getType() == MachO::N_AST) {
+      if (Options.Verbose)
+        outs() << "DEBUG MAP OBJECT: " << Obj->getObjectFilename() << "\n";
+
+      StringRef File = Obj->getObjectFilename();
+      auto ErrorOrMem = MemoryBuffer::getFile(File);
+      if (!ErrorOrMem) {
+        warn("Could not open '" + File + "'\n");
+        continue;
+      }
+      sys::fs::file_status Stat;
+      if (auto Err = sys::fs::status(File, Stat)) {
+        warn(Err.message());
+        continue;
+      }
+      if (!Options.NoTimestamp) {
+        // The modification can have sub-second precision so we need to cast
+        // away the extra precision that's not present in the debug map.
+        auto ModificationTime =
+            std::chrono::time_point_cast<std::chrono::seconds>(
+                Stat.getLastModificationTime());
+        if (ModificationTime != Obj->getTimestamp()) {
+          // Not using the helper here as we can easily stream TimePoint<>.
+          WithColor::warning() << "Timestamp mismatch for " << File << ": "
+                               << Stat.getLastModificationTime() << " and "
+                               << sys::TimePoint<>(Obj->getTimestamp()) << "\n";
+          continue;
         }
       }
 
-/// Recursive helper to build the global DeclContext information and
-/// gather the child->parent relationships in the original compile unit.
-///
-/// \return true when this DIE and all of its children are only
-/// forward declarations to types defined in external clang modules
-/// (i.e., forward declarations that are children of a DW_TAG_module).
-static bool analyzeContextInfo(
-    const DWARFDie &DIE, unsigned ParentIdx, CompileUnit &CU,
-    DeclContext *CurrentDeclContext, UniquingStringPool &StringPool,
-    DeclContextTree &Contexts, uint64_t ModulesEndOffset,
-    std::map<std::string, std::string> &ParseableSwiftInterfaces,
-    std::function<void(const Twine &, const DWARFDie &)> ReportWarning,
-    bool InImportedModule = false) {
-  unsigned MyIdx = CU.getOrigUnit().getDIEIndex(DIE);
-  CompileUnit::DIEInfo &Info = CU.getInfo(MyIdx);
-
-  // Clang imposes an ODR on modules(!) regardless of the language:
-  //  "The module-id should consist of only a single identifier,
-  //   which provides the name of the module being defined. Each
-  //   module shall have a single definition."
-  //
-  // This does not extend to the types inside the modules:
-  //  "[I]n C, this implies that if two structs are defined in
-  //   different submodules with the same name, those two types are
-  //   distinct types (but may be compatible types if their
-  //   definitions match)."
-  //
-  // We treat non-C++ modules like namespaces for this reason.
-  if (DIE.getTag() == dwarf::DW_TAG_module && ParentIdx == 0 &&
-      dwarf::toString(DIE.find(dwarf::DW_AT_name), "") !=
-          CU.getClangModuleName()) {
-    InImportedModule = true;
-    analyzeImportedModule(DIE, CU, ParseableSwiftInterfaces, ReportWarning);
-  }
-
-  Info.ParentIdx = ParentIdx;
-  bool InClangModule = CU.isClangModule() || InImportedModule;
-  if (CU.hasODR() || InClangModule) {
-    if (CurrentDeclContext) {
-      auto PtrInvalidPair = Contexts.getChildDeclContext(
-          *CurrentDeclContext, DIE, CU, StringPool, InClangModule);
-      CurrentDeclContext = PtrInvalidPair.getPointer();
-      Info.Ctxt =
-          PtrInvalidPair.getInt() ? nullptr : PtrInvalidPair.getPointer();
-      if (Info.Ctxt)
-        Info.Ctxt->setDefinedInClangModule(InClangModule);
-    } else
-      Info.Ctxt = CurrentDeclContext = nullptr;
-  }
-
-  Info.Prune = InImportedModule;
-  if (DIE.hasChildren())
-    for (auto Child : DIE.children())
-      Info.Prune &= analyzeContextInfo(Child, MyIdx, CU, CurrentDeclContext,
-                                       StringPool, Contexts, ModulesEndOffset,
-                                       ParseableSwiftInterfaces, ReportWarning,
-                                       InImportedModule);
-
-  // Prune this DIE if it is either a forward declaration inside a
-  // DW_TAG_module or a DW_TAG_module that contains nothing but
-  // forward declarations.
-  Info.Prune &= (DIE.getTag() == dwarf::DW_TAG_module) ||
-                (isTypeTag(DIE.getTag()) &&
-                 dwarf::toUnsigned(DIE.find(dwarf::DW_AT_declaration), 0));
-
-  // Only prune forward declarations inside a DW_TAG_module for which a
-  // definition exists elsewhere.
-  if (ModulesEndOffset == 0)
-    Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset();
-  else
-    Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() > 0 &&
-                  Info.Ctxt->getCanonicalDIEOffset() <= ModulesEndOffset;
+      // Copy the module into the .swift_ast section.
+      if (!Options.NoOutput)
+        Streamer->emitSwiftAST((*ErrorOrMem)->getBuffer());
 
-  return Info.Prune;
-} // namespace dsymutil
+      continue;
+    }
 
-static bool dieNeedsChildrenToBeMeaningful(uint32_t Tag) {
-  switch (Tag) {
-  default:
-    return false;
-  case dwarf::DW_TAG_class_type:
-  case dwarf::DW_TAG_common_block:
-  case dwarf::DW_TAG_lexical_block:
-  case dwarf::DW_TAG_structure_type:
-  case dwarf::DW_TAG_subprogram:
-  case dwarf::DW_TAG_subroutine_type:
-  case dwarf::DW_TAG_union_type:
-    return true;
+    if (auto ErrorOrObj = loadObject(*Obj, Map, RL))
+      GeneralLinker.addObjectFile(*ErrorOrObj);
+    else {
+      ObjectsForLinking.push_back(
+          std::unique_ptr<DwarfLinkerObjFile>(new DwarfLinkerObjFile(
+              Obj->getObjectFilename(), nullptr, Obj->getWarnings())));
+      GeneralLinker.addObjectFile(*ObjectsForLinking.back());
     }
-  llvm_unreachable("Invalid Tag");
   }
 
-void DwarfLinkerForBinary::startDebugObject(LinkContext &Context) {}
+  // link debug info for loaded object files.
+  GeneralLinker.link();
+
+  StringRef ArchName = Map.getTriple().getArchName();
+  if (Error E = emitRemarks(Options, Map.getBinaryPath(), ArchName, RL))
+    return error(toString(std::move(E)));
 
-void DwarfLinkerForBinary::endDebugObject(LinkContext &Context) {
-  Context.Clear();
+  if (Options.NoOutput)
+    return true;
 
-  for (auto I = DIEBlocks.begin(), E = DIEBlocks.end(); I != E; ++I)
-    (*I)->~DIEBlock();
-  for (auto I = DIELocs.begin(), E = DIELocs.end(); I != E; ++I)
-    (*I)->~DIELoc();
+  if (Options.ResourceDir && !ParseableSwiftInterfaces.empty()) {
+    StringRef ArchName = Triple::getArchTypeName(Map.getTriple().getArch());
+    if (auto E =
+            copySwiftInterfaces(ParseableSwiftInterfaces, ArchName, Options))
+      return error(toString(std::move(E)));
+  }
 
-  DIEBlocks.clear();
-  DIELocs.clear();
-  DIEAlloc.Reset();
+  return Streamer->finish(Map, Options.Translator);
 }
 
 static bool isMachOPairedReloc(uint64_t RelocType, uint64_t Arch) {
   switch (Arch) {
   case Triple::x86:
     return RelocType == MachO::GENERIC_RELOC_SECTDIFF ||
            RelocType == MachO::GENERIC_RELOC_LOCAL_SECTDIFF;
   case Triple::x86_64:
static bool isMachOPairedReloc(uint64_t RelocType, uint64_t Arch) {
   default:
     return false;
   }
 }
 
 /// Iterate over the relocations of the given \p Section and
 /// store the ones that correspond to debug map entries into the
 /// ValidRelocs array.
-void DwarfLinkerForBinary::RelocationManager::findValidRelocsMachO(
+void DwarfLinkerForBinary::AddressManager::findValidRelocsMachO(
     const object::SectionRef &Section, const object::MachOObjectFile &Obj,
     const DebugMapObject &DMO) {
   Expected<StringRef> ContentsOrErr = Section.getContents();
   if (!ContentsOrErr) {
     consumeError(ContentsOrErr.takeError());
-    Linker.reportWarning("error reading section", DMO);
+    Linker.reportWarning("error reading section", DMO.getObjectFilename());
     return;
   }
   DataExtractor Data(*ContentsOrErr, Obj.isLittleEndian(), 0);
   bool SkipNext = false;
 
   for (const object::RelocationRef &Reloc : Section.relocations()) {
     if (SkipNext) {
       SkipNext = false;
       continue;
     }
 
     object::DataRefImpl RelocDataRef = Reloc.getRawDataRefImpl();
     MachO::any_relocation_info MachOReloc = Obj.getRelocation(RelocDataRef);
 
     if (isMachOPairedReloc(Obj.getAnyRelocationType(MachOReloc),
                            Obj.getArch())) {
       SkipNext = true;
       Linker.reportWarning("unsupported relocation in debug_info section.",
-                           DMO);
+                           DMO.getObjectFilename());
       continue;
     }
 
     unsigned RelocSize = 1 << Obj.getAnyRelocationLength(MachOReloc);
     uint64_t Offset64 = Reloc.getOffset();
     if ((RelocSize != 4 && RelocSize != 8)) {
       Linker.reportWarning("unsupported relocation in debug_info section.",
-                           DMO);
+                           DMO.getObjectFilename());
       continue;
     }
     uint64_t OffsetCopy = Offset64;
     // Mach-o uses REL relocations, the addend is at the relocation offset.
     uint64_t Addend = Data.getUnsigned(&OffsetCopy, RelocSize);
     uint64_t SymAddress;
     int64_t SymOffset;
 
     if (Obj.isRelocationScattered(MachOReloc)) {
       // The address of the base symbol for scattered relocations is
       // stored in the reloc itself. The actual addend will store the
       // base address plus the offset.
       SymAddress = Obj.getScatteredRelocationValue(MachOReloc);
       SymOffset = int64_t(Addend) - SymAddress;
     } else {
       SymAddress = Addend;
       SymOffset = 0;
     }
 
     auto Sym = Reloc.getSymbol();
     if (Sym != Obj.symbol_end()) {
       Expected<StringRef> SymbolName = Sym->getName();
       if (!SymbolName) {
         consumeError(SymbolName.takeError());
-        Linker.reportWarning("error getting relocation symbol name.", DMO);
+        Linker.reportWarning("error getting relocation symbol name.",
+                             DMO.getObjectFilename());
         continue;
       }
       if (const auto *Mapping = DMO.lookupSymbol(*SymbolName))
         ValidRelocs.emplace_back(Offset64, RelocSize, Addend, Mapping);
     } else if (const auto *Mapping = DMO.lookupObjectAddress(SymAddress)) {
       // Do not store the addend. The addend was the address of the symbol in
       // the object file, the address in the binary that is stored in the debug
       // map doesn't need to be offset.
       ValidRelocs.emplace_back(Offset64, RelocSize, SymOffset, Mapping);
     }
   }
 }
 
 /// Dispatch the valid relocation finding logic to the
 /// appropriate handler depending on the object file format.
-bool DwarfLinkerForBinary::RelocationManager::findValidRelocs(
+bool DwarfLinkerForBinary::AddressManager::findValidRelocs(
     const object::SectionRef &Section, const object::ObjectFile &Obj,
     const DebugMapObject &DMO) {
   // Dispatch to the right handler depending on the file type.
   if (auto *MachOObj = dyn_cast<object::MachOObjectFile>(&Obj))
     findValidRelocsMachO(Section, *MachOObj, DMO);
   else
-    Linker.reportWarning(
-        Twine("unsupported object file type: ") + Obj.getFileName(), DMO);
-
+    Linker.reportWarning(Twine("unsupported object file type: ") +
+                             Obj.getFileName(),
+                         DMO.getObjectFilename());
   if (ValidRelocs.empty())
     return false;
 
   // Sort the relocations by offset. We will walk the DIEs linearly in
   // the file, this allows us to just keep an index in the relocation
   // array that we advance during our walk, rather than resorting to
-  // some associative container. See DwarfLinker::NextValidReloc.
+  // some associative container. See DwarfLinkerForBinary::NextValidReloc.
   llvm::sort(ValidRelocs);
   return true;
 }
 
 /// Look for relocations in the debug_info section that match
 /// entries in the debug map. These relocations will drive the Dwarf
 /// link by indicating which DIEs refer to symbols present in the
 /// linked binary.
 /// \returns whether there are any valid relocations in the debug info.
-bool DwarfLinkerForBinary::RelocationManager::findValidRelocsInDebugInfo(
+bool DwarfLinkerForBinary::AddressManager::findValidRelocsInDebugInfo(
     const object::ObjectFile &Obj, const DebugMapObject &DMO) {
   // Find the debug_info section.
   for (const object::SectionRef &Section : Obj.sections()) {
     StringRef SectionName;
     if (Expected<StringRef> NameOrErr = Section.getName())
       SectionName = *NameOrErr;
     else
       consumeError(NameOrErr.takeError());
 
     SectionName = SectionName.substr(SectionName.find_first_not_of("._"));
     if (SectionName != "debug_info")
       continue;
     return findValidRelocs(Section, Obj, DMO);
   }
   return false;
 }
 
 /// Checks that there is a relocation against an actual debug
 /// map entry between \p StartOffset and \p NextOffset.
 ///
 /// This function must be called with offsets in strictly ascending
 /// order because it never looks back at relocations it already 'went past'.
 /// \returns true and sets Info.InDebugMap if it is the case.
-bool DwarfLinkerForBinary::RelocationManager::hasValidRelocationAt(
+bool DwarfLinkerForBinary::AddressManager::hasValidRelocationAt(
     uint64_t StartOffset, uint64_t EndOffset, CompileUnit::DIEInfo &Info) {
   assert(NextValidReloc == 0 ||
          StartOffset > ValidRelocs[NextValidReloc - 1].Offset);
   if (NextValidReloc >= ValidRelocs.size())
     return false;
 
   uint64_t RelocOffset = ValidRelocs[NextValidReloc].Offset;
 
bool DwarfLinkerForBinary::AddressManager::hasValidRelocationAt(
 
   Info.AddrAdjust = BinaryAddress + ValidReloc.Addend;
   if (Mapping.ObjectAddress)
     Info.AddrAdjust -= ObjectAddress;
   Info.InDebugMap = true;
   return true;
 }
 
-/// Get the starting and ending (exclusive) offset for the
-/// attribute with index \p Idx descibed by \p Abbrev. \p Offset is
-/// supposed to point to the position of the first attribute described
-/// by \p Abbrev.
-/// \return [StartOffset, EndOffset) as a pair.
-static std::pair<uint64_t, uint64_t>
-getAttributeOffsets(const DWARFAbbreviationDeclaration *Abbrev, unsigned Idx,
-                    uint64_t Offset, const DWARFUnit &Unit) {
-  DataExtractor Data = Unit.getDebugInfoExtractor();
-
-  for (unsigned i = 0; i < Idx; ++i)
-    DWARFFormValue::skipValue(Abbrev->getFormByIndex(i), Data, &Offset,
-                              Unit.getFormParams());
-
-  uint64_t End = Offset;
-  DWARFFormValue::skipValue(Abbrev->getFormByIndex(Idx), Data, &End,
-                            Unit.getFormParams());
-
-  return std::make_pair(Offset, End);
-}
-
-/// Check if a variable describing DIE should be kept.
-/// \returns updated TraversalFlags.
-unsigned DwarfLinkerForBinary::shouldKeepVariableDIE(
-    RelocationManager &RelocMgr, const DWARFDie &DIE, CompileUnit &Unit,
-    CompileUnit::DIEInfo &MyInfo, unsigned Flags) {
-  const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
-
-  // Global variables with constant value can always be kept.
-  if (!(Flags & TF_InFunctionScope) &&
-      Abbrev->findAttributeIndex(dwarf::DW_AT_const_value)) {
-    MyInfo.InDebugMap = true;
-    return Flags | TF_Keep;
-  }
-
-  Optional<uint32_t> LocationIdx =
-      Abbrev->findAttributeIndex(dwarf::DW_AT_location);
-  if (!LocationIdx)
-    return Flags;
-
-  uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
-  const DWARFUnit &OrigUnit = Unit.getOrigUnit();
-  uint64_t LocationOffset, LocationEndOffset;
-  std::tie(LocationOffset, LocationEndOffset) =
-      getAttributeOffsets(Abbrev, *LocationIdx, Offset, OrigUnit);
-
-  // See if there is a relocation to a valid debug map entry inside
-  // this variable's location. The order is important here. We want to
-  // always check if the variable has a valid relocation, so that the
-  // DIEInfo is filled. However, we don't want a static variable in a
-  // function to force us to keep the enclosing function.
-  if (!RelocMgr.hasValidRelocationAt(LocationOffset, LocationEndOffset,
-                                     MyInfo) ||
-      (Flags & TF_InFunctionScope))
-    return Flags;
-
-  if (Options.Verbose) {
-    outs() << "Keeping variable DIE:";
-    DIDumpOptions DumpOpts;
-    DumpOpts.ChildRecurseDepth = 0;
-    DumpOpts.Verbose = Options.Verbose;
-    DIE.dump(outs(), 8 /* Indent */, DumpOpts);
-  }
-
-  return Flags | TF_Keep;
-}
-
-/// Check if a function describing DIE should be kept.
-/// \returns updated TraversalFlags.
-unsigned DwarfLinkerForBinary::shouldKeepSubprogramDIE(
-    RelocationManager &RelocMgr, RangesTy &Ranges, const DWARFDie &DIE,
-    const DebugMapObject &DMO, CompileUnit &Unit, CompileUnit::DIEInfo &MyInfo,
-    unsigned Flags) {
-  const auto *Abbrev = DIE.getAbbreviationDeclarationPtr();
-
-  Flags |= TF_InFunctionScope;
-
-  Optional<uint32_t> LowPcIdx = Abbrev->findAttributeIndex(dwarf::DW_AT_low_pc);
-  if (!LowPcIdx)
-    return Flags;
-
-  uint64_t Offset = DIE.getOffset() + getULEB128Size(Abbrev->getCode());
-  DWARFUnit &OrigUnit = Unit.getOrigUnit();
-  uint64_t LowPcOffset, LowPcEndOffset;
-  std::tie(LowPcOffset, LowPcEndOffset) =
-      getAttributeOffsets(Abbrev, *LowPcIdx, Offset, OrigUnit);
-
-  auto LowPc = dwarf::toAddress(DIE.find(dwarf::DW_AT_low_pc));
-  assert(LowPc.hasValue() && "low_pc attribute is not an address.");
-  if (!LowPc ||
-      !RelocMgr.hasValidRelocationAt(LowPcOffset, LowPcEndOffset, MyInfo))
-    return Flags;
-
-  if (Options.Verbose) {
-    outs() << "Keeping subprogram DIE:";
-    DIDumpOptions DumpOpts;
-    DumpOpts.ChildRecurseDepth = 0;
-    DumpOpts.Verbose = Options.Verbose;
-    DIE.dump(outs(), 8 /* Indent */, DumpOpts);
-  }
-
-  if (DIE.getTag() == dwarf::DW_TAG_label) {
-    if (Unit.hasLabelAt(*LowPc))
-      return Flags;
-    // FIXME: dsymutil-classic compat. dsymutil-classic doesn't consider labels
-    // that don't fall into the CU's aranges. This is wrong IMO. Debug info
-    // generation bugs aside, this is really wrong in the case of labels, where
-    // a label marking the end of a function will have a PC == CU's high_pc.
-    if (dwarf::toAddress(OrigUnit.getUnitDIE().find(dwarf::DW_AT_high_pc))
-            .getValueOr(UINT64_MAX) <= LowPc)
-      return Flags;
-    Unit.addLabelLowPc(*LowPc, MyInfo.AddrAdjust);
-    return Flags | TF_Keep;
-  }
-
-  Flags |= TF_Keep;
-
-  Optional<uint64_t> HighPc = DIE.getHighPC(*LowPc);
-  if (!HighPc) {
-    reportWarning("Function without high_pc. Range will be discarded.\n", DMO,
-                  &DIE);
-    return Flags;
-  }
-
-  // Replace the debug map range with a more accurate one.
-  Ranges[*LowPc] = ObjFileAddressRange(*HighPc, MyInfo.AddrAdjust);
-  Unit.addFunctionRange(*LowPc, *HighPc, MyInfo.AddrAdjust);
-  return Flags;
-}
-
-/// Check if a DIE should be kept.
-/// \returns updated TraversalFlags.
-unsigned DwarfLinkerForBinary::shouldKeepDIE(
-    RelocationManager &RelocMgr, RangesTy &Ranges, const DWARFDie &DIE,
-    const DebugMapObject &DMO, CompileUnit &Unit, CompileUnit::DIEInfo &MyInfo,
-    unsigned Flags) {
-  switch (DIE.getTag()) {
-  case dwarf::DW_TAG_constant:
-  case dwarf::DW_TAG_variable:
-    return shouldKeepVariableDIE(RelocMgr, DIE, Unit, MyInfo, Flags);
-  case dwarf::DW_TAG_subprogram:
-  case dwarf::DW_TAG_label:
-    return shouldKeepSubprogramDIE(RelocMgr, Ranges, DIE, DMO, Unit, MyInfo,
-                                   Flags);
-  case dwarf::DW_TAG_base_type:
-    // DWARF Expressions may reference basic types, but scanning them
-    // is expensive. Basic types are tiny, so just keep all of them.
-  case dwarf::DW_TAG_imported_module:
-  case dwarf::DW_TAG_imported_declaration:
-  case dwarf::DW_TAG_imported_unit:
-    // We always want to keep these.
-    return Flags | TF_Keep;
-  default:
-    break;
-  }
-
-  return Flags;
-}
-
-namespace {
-/// The  distinct types of work performed by the work loop.
-enum class WorklistItemType {
-  /// Given a DIE, look for DIEs to be kept.
-  LookForDIEsToKeep,
-  /// Given a DIE, look for children of this DIE to be kept.
-  LookForChildDIEsToKeep,
-  /// Given a DIE, look for DIEs referencing this DIE to be kept.
-  LookForRefDIEsToKeep,
-  /// Given a DIE, look for parent DIEs to be kept.
-  LookForParentDIEsToKeep,
-  /// Given a DIE, update its incompleteness based on whether its children are
-  /// incomplete.
-  UpdateChildIncompleteness,
-  /// Given a DIE, update its incompleteness based on whether the DIEs it
-  /// references are incomplete.
-  UpdateRefIncompleteness,
-};
-
-/// This class represents an item in the work list. The type defines what kind
-/// of work needs to be performed when processing the current item. The flags
-/// and info fields are optional based on the type.
-struct WorklistItem {
-  WorklistItemType Type;
-  DWARFDie Die;
-  CompileUnit &CU;
-  unsigned Flags;
-  unsigned AncestorIdx = 0;
-  CompileUnit::DIEInfo *OtherInfo = nullptr;
-
-  WorklistItem(DWARFDie Die, CompileUnit &CU, unsigned Flags,
-               WorklistItemType T = WorklistItemType::LookForDIEsToKeep)
-      : Type(T), Die(Die), CU(CU), Flags(Flags){};
-
-  WorklistItem(DWARFDie Die, CompileUnit &CU, WorklistItemType T,
-               CompileUnit::DIEInfo *OtherInfo = nullptr)
-      : Type(T), Die(Die), CU(CU), OtherInfo(OtherInfo){};
-
-  WorklistItem(unsigned AncestorIdx, CompileUnit &CU, unsigned Flags)
-      : Type(WorklistItemType::LookForParentDIEsToKeep), CU(CU), Flags(Flags),
-        AncestorIdx(AncestorIdx){};
-};
-} // namespace
-
-/// Helper that updates the completeness of the current DIE based on the
-/// completeness of one of its children. It depends on the incompleteness of
-/// the children already being computed.
-static void updateChildIncompleteness(const DWARFDie &Die, CompileUnit &CU,
-                                      CompileUnit::DIEInfo &ChildInfo) {
-  switch (Die.getTag()) {
-  case dwarf::DW_TAG_structure_type:
-  case dwarf::DW_TAG_class_type:
-    break;
-  default:
-    return;
-  }
-
-  unsigned Idx = CU.getOrigUnit().getDIEIndex(Die);
-  CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
-
-  if (ChildInfo.Incomplete || ChildInfo.Prune)
-    MyInfo.Incomplete = true;
-}
-
-/// Helper that updates the completeness of the current DIE based on the
-/// completeness of the DIEs it references. It depends on the incompleteness of
-/// the referenced DIE already being computed.
-static void updateRefIncompleteness(const DWARFDie &Die, CompileUnit &CU,
-                                    CompileUnit::DIEInfo &RefInfo) {
-  switch (Die.getTag()) {
-  case dwarf::DW_TAG_typedef:
-  case dwarf::DW_TAG_member:
-  case dwarf::DW_TAG_reference_type:
-  case dwarf::DW_TAG_ptr_to_member_type:
-  case dwarf::DW_TAG_pointer_type:
-    break;
-  default:
-    return;
-  }
-
-  unsigned Idx = CU.getOrigUnit().getDIEIndex(Die);
-  CompileUnit::DIEInfo &MyInfo = CU.getInfo(Idx);
-
-  if (MyInfo.Incomplete)
-    return;
-
-  if (RefInfo.Incomplete)
-    MyInfo.Incomplete = true;
-}
-
-/// Look at the children of the given DIE and decide whether they should be
-/// kept.
-static void lookForChildDIEsToKeep(const DWARFDie &Die, CompileUnit &CU,
-                                   unsigned Flags,
-                                   SmallVectorImpl<WorklistItem> &Worklist) {
-  // The TF_ParentWalk flag tells us that we are currently walking up the
-  // parent chain of a required DIE, and we don't want to mark all the children
-  // of the parents as kept (consider for example a DW_TAG_namespace node in
-  // the parent chain). There are however a set of DIE types for which we want
-  // to ignore that directive and still walk their children.
-  if (dieNeedsChildrenToBeMeaningful(Die.getTag()))
-    Flags &= ~DwarfLinkerForBinary::TF_ParentWalk;
-
-  // We're finished if this DIE has no children or we're walking the parent
-  // chain.
-  if (!Die.hasChildren() || (Flags & DwarfLinkerForBinary::TF_ParentWalk))
-    return;
-
-  // Add children in reverse order to the worklist to effectively process them
-  // in order.
-  for (auto Child : reverse(Die.children())) {
-    // Add a worklist item before every child to calculate incompleteness right
-    // after the current child is processed.
-    unsigned Idx = CU.getOrigUnit().getDIEIndex(Child);
-    CompileUnit::DIEInfo &ChildInfo = CU.getInfo(Idx);
-    Worklist.emplace_back(Die, CU, WorklistItemType::UpdateChildIncompleteness,
-                          &ChildInfo);
-    Worklist.emplace_back(Child, CU, Flags);
-  }
-}
-
-/// Look at DIEs referenced by the given DIE and decide whether they should be
-/// kept. All DIEs referenced though attributes should be kept.
-static void lookForRefDIEsToKeep(const DWARFDie &Die, CompileUnit &CU,
-                                 unsigned Flags, DwarfLinkerForBinary &Linker,
-                                 const UnitListTy &Units,
-                                 const DebugMapObject &DMO,
-                                 SmallVectorImpl<WorklistItem> &Worklist) {
-  bool UseOdr = (Flags & DwarfLinkerForBinary::TF_DependencyWalk)
-                    ? (Flags & DwarfLinkerForBinary::TF_ODR)
-                    : CU.hasODR();
-  DWARFUnit &Unit = CU.getOrigUnit();
-  DWARFDataExtractor Data = Unit.getDebugInfoExtractor();
-  const auto *Abbrev = Die.getAbbreviationDeclarationPtr();
-  uint64_t Offset = Die.getOffset() + getULEB128Size(Abbrev->getCode());
-
-  SmallVector<std::pair<DWARFDie, CompileUnit &>, 4> ReferencedDIEs;
-  for (const auto &AttrSpec : Abbrev->attributes()) {
-    DWARFFormValue Val(AttrSpec.Form);
-    if (!Val.isFormClass(DWARFFormValue::FC_Reference) ||
-        AttrSpec.Attr == dwarf::DW_AT_sibling) {
-      DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
-                                Unit.getFormParams());
-      continue;
-    }
-
-    Val.extractValue(Data, &Offset, Unit.getFormParams(), &Unit);
-    CompileUnit *ReferencedCU;
-    if (auto RefDie =
-            resolveDIEReference(Linker, DMO, Units, Val, Die, ReferencedCU)) {
-      uint32_t RefIdx = ReferencedCU->getOrigUnit().getDIEIndex(RefDie);
-      CompileUnit::DIEInfo &Info = ReferencedCU->getInfo(RefIdx);
-      bool IsModuleRef = Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset() &&
-                         Info.Ctxt->isDefinedInClangModule();
-      // If the referenced DIE has a DeclContext that has already been
-      // emitted, then do not keep the one in this CU. We'll link to
-      // the canonical DIE in cloneDieReferenceAttribute.
-      //
-      // FIXME: compatibility with dsymutil-classic. UseODR shouldn't
-      // be necessary and could be advantageously replaced by
-      // ReferencedCU->hasODR() && CU.hasODR().
-      //
-      // FIXME: compatibility with dsymutil-classic. There is no
-      // reason not to unique ref_addr references.
-      if (AttrSpec.Form != dwarf::DW_FORM_ref_addr && (UseOdr || IsModuleRef) &&
-          Info.Ctxt &&
-          Info.Ctxt != ReferencedCU->getInfo(Info.ParentIdx).Ctxt &&
-          Info.Ctxt->getCanonicalDIEOffset() && isODRAttribute(AttrSpec.Attr))
-        continue;
-
-      // Keep a module forward declaration if there is no definition.
-      if (!(isODRAttribute(AttrSpec.Attr) && Info.Ctxt &&
-            Info.Ctxt->getCanonicalDIEOffset()))
-        Info.Prune = false;
-      ReferencedDIEs.emplace_back(RefDie, *ReferencedCU);
-    }
-  }
-
-  unsigned ODRFlag = UseOdr ? DwarfLinkerForBinary::TF_ODR : 0;
-
-  // Add referenced DIEs in reverse order to the worklist to effectively
-  // process them in order.
-  for (auto &P : reverse(ReferencedDIEs)) {
-    // Add a worklist item before every child to calculate incompleteness right
-    // after the current child is processed.
-    uint32_t RefIdx = P.second.getOrigUnit().getDIEIndex(P.first);
-    CompileUnit::DIEInfo &Info = P.second.getInfo(RefIdx);
-    Worklist.emplace_back(Die, CU, WorklistItemType::UpdateRefIncompleteness,
-                          &Info);
-    Worklist.emplace_back(P.first, P.second,
-                          DwarfLinkerForBinary::TF_Keep |
-                              DwarfLinkerForBinary::TF_DependencyWalk |
-                              ODRFlag);
-  }
-}
-
-/// Look at the parent of the given DIE and decide whether they should be kept.
-static void lookForParentDIEsToKeep(unsigned AncestorIdx, CompileUnit &CU,
-                                    unsigned Flags,
-                                    SmallVectorImpl<WorklistItem> &Worklist) {
-  // Stop if we encounter an ancestor that's already marked as kept.
-  if (CU.getInfo(AncestorIdx).Keep)
-    return;
-
-  DWARFUnit &Unit = CU.getOrigUnit();
-  DWARFDie ParentDIE = Unit.getDIEAtIndex(AncestorIdx);
-  Worklist.emplace_back(CU.getInfo(AncestorIdx).ParentIdx, CU, Flags);
-  Worklist.emplace_back(ParentDIE, CU, Flags);
-}
-
-/// Recursively walk the \p DIE tree and look for DIEs to keep. Store that
-/// information in \p CU's DIEInfo.
-///
-/// This function is the entry point of the DIE selection algorithm. It is
-/// expected to walk the DIE tree in file order and (though the mediation of
-/// its helper) call hasValidRelocation() on each DIE that might be a 'root
-/// DIE' (See DwarfLinker class comment).
-///
-/// While walking the dependencies of root DIEs, this function is also called,
-/// but during these dependency walks the file order is not respected. The
-/// TF_DependencyWalk flag tells us which kind of traversal we are currently
-/// doing.
-///
-/// The recursive algorithm is implemented iteratively as a work list because
-/// very deep recursion could exhaust the stack for large projects. The work
-/// list acts as a scheduler for different types of work that need to be
-/// performed.
-///
-/// The recursive nature of the algorithm is simulated by running the "main"
-/// algorithm (LookForDIEsToKeep) followed by either looking at more DIEs
-/// (LookForChildDIEsToKeep, LookForRefDIEsToKeep, LookForParentDIEsToKeep) or
-/// fixing up a computed property (UpdateChildIncompleteness,
-/// UpdateRefIncompleteness).
-///
-/// The return value indicates whether the DIE is incomplete.
-void DwarfLinkerForBinary::lookForDIEsToKeep(RelocationManager &RelocMgr,
-                                             RangesTy &Ranges,
-                                             const UnitListTy &Units,
-                                             const DWARFDie &Die,
-                                             const DebugMapObject &DMO,
-                                             CompileUnit &Cu, unsigned Flags) {
-  // LIFO work list.
-  SmallVector<WorklistItem, 4> Worklist;
-  Worklist.emplace_back(Die, Cu, Flags);
-
-  while (!Worklist.empty()) {
-    WorklistItem Current = Worklist.back();
-    Worklist.pop_back();
-
-    // Look at the worklist type to decide what kind of work to perform.
-    switch (Current.Type) {
-    case WorklistItemType::UpdateChildIncompleteness:
-      updateChildIncompleteness(Current.Die, Current.CU, *Current.OtherInfo);
-      continue;
-    case WorklistItemType::UpdateRefIncompleteness:
-      updateRefIncompleteness(Current.Die, Current.CU, *Current.OtherInfo);
-      continue;
-    case WorklistItemType::LookForChildDIEsToKeep:
-      lookForChildDIEsToKeep(Current.Die, Current.CU, Current.Flags, Worklist);
-      continue;
-    case WorklistItemType::LookForRefDIEsToKeep:
-      lookForRefDIEsToKeep(Current.Die, Current.CU, Current.Flags, *this, Units,
-                           DMO, Worklist);
-      continue;
-    case WorklistItemType::LookForParentDIEsToKeep:
-      lookForParentDIEsToKeep(Current.AncestorIdx, Current.CU, Current.Flags,
-                              Worklist);
-      continue;
-    case WorklistItemType::LookForDIEsToKeep:
-      break;
-    }
-
-    unsigned Idx = Current.CU.getOrigUnit().getDIEIndex(Current.Die);
-    CompileUnit::DIEInfo &MyInfo = Current.CU.getInfo(Idx);
-
-    if (MyInfo.Prune)
-      continue;
-
-    // If the Keep flag is set, we are marking a required DIE's dependencies.
-    // If our target is already marked as kept, we're all set.
-    bool AlreadyKept = MyInfo.Keep;
-    if ((Current.Flags & TF_DependencyWalk) && AlreadyKept)
-      continue;
-
-    // We must not call shouldKeepDIE while called from keepDIEAndDependencies,
-    // because it would screw up the relocation finding logic.
-    if (!(Current.Flags & TF_DependencyWalk))
-      Current.Flags = shouldKeepDIE(RelocMgr, Ranges, Current.Die, DMO,
-                                    Current.CU, MyInfo, Current.Flags);
-
-    // Finish by looking for child DIEs. Because of the LIFO worklist we need
-    // to schedule that work before any subsequent items are added to the
-    // worklist.
-    Worklist.emplace_back(Current.Die, Current.CU, Current.Flags,
-                          WorklistItemType::LookForChildDIEsToKeep);
-
-    if (AlreadyKept || !(Current.Flags & TF_Keep))
-      continue;
-
-    // If it is a newly kept DIE mark it as well as all its dependencies as
-    // kept.
-    MyInfo.Keep = true;
-
-    // We're looking for incomplete types.
-    MyInfo.Incomplete =
-        Current.Die.getTag() != dwarf::DW_TAG_subprogram &&
-        Current.Die.getTag() != dwarf::DW_TAG_member &&
-        dwarf::toUnsigned(Current.Die.find(dwarf::DW_AT_declaration), 0);
-
-    // After looking at the parent chain, look for referenced DIEs. Because of
-    // the LIFO worklist we need to schedule that work before any subsequent
-    // items are added to the worklist.
-    Worklist.emplace_back(Current.Die, Current.CU, Current.Flags,
-                          WorklistItemType::LookForRefDIEsToKeep);
-
-    bool UseOdr = (Current.Flags & TF_DependencyWalk) ? (Current.Flags & TF_ODR)
-                                                      : Current.CU.hasODR();
-    unsigned ODRFlag = UseOdr ? TF_ODR : 0;
-    unsigned ParFlags = TF_ParentWalk | TF_Keep | TF_DependencyWalk | ODRFlag;
-
-    // Now schedule the parent walk.
-    Worklist.emplace_back(MyInfo.ParentIdx, Current.CU, ParFlags);
-  }
-}
-
-/// Assign an abbreviation number to \p Abbrev.
-///
-/// Our DIEs get freed after every DebugMapObject has been processed,
-/// thus the FoldingSet we use to unique DIEAbbrevs cannot refer to
-/// the instances hold by the DIEs. When we encounter an abbreviation
-/// that we don't know, we create a permanent copy of it.
-void DwarfLinkerForBinary::assignAbbrev(DIEAbbrev &Abbrev) {
-  // Check the set for priors.
-  FoldingSetNodeID ID;
-  Abbrev.Profile(ID);
-  void *InsertToken;
-  DIEAbbrev *InSet = AbbreviationsSet.FindNodeOrInsertPos(ID, InsertToken);
-
-  // If it's newly added.
-  if (InSet) {
-    // Assign existing abbreviation number.
-    Abbrev.setNumber(InSet->getNumber());
-  } else {
-    // Add to abbreviation list.
-    Abbreviations.push_back(
-        std::make_unique<DIEAbbrev>(Abbrev.getTag(), Abbrev.hasChildren()));
-    for (const auto &Attr : Abbrev.getData())
-      Abbreviations.back()->AddAttribute(Attr.getAttribute(), Attr.getForm());
-    AbbreviationsSet.InsertNode(Abbreviations.back().get(), InsertToken);
-    // Assign the unique abbreviation number.
-    Abbrev.setNumber(Abbreviations.size());
-    Abbreviations.back()->setNumber(Abbreviations.size());
-  }
-}
-
-unsigned DwarfLinkerForBinary::DIECloner::cloneStringAttribute(
-    DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
-    const DWARFUnit &U, OffsetsStringPool &StringPool, AttributesInfo &Info) {
-  // Switch everything to out of line strings.
-  const char *String = *Val.getAsCString();
-  auto StringEntry = StringPool.getEntry(String);
-
-  // Update attributes info.
-  if (AttrSpec.Attr == dwarf::DW_AT_name)
-    Info.Name = StringEntry;
-  else if (AttrSpec.Attr == dwarf::DW_AT_MIPS_linkage_name ||
-           AttrSpec.Attr == dwarf::DW_AT_linkage_name)
-    Info.MangledName = StringEntry;
-
-  Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr), dwarf::DW_FORM_strp,
-               DIEInteger(StringEntry.getOffset()));
-
-  return 4;
-}
-
-unsigned DwarfLinkerForBinary::DIECloner::cloneDieReferenceAttribute(
-    DIE &Die, const DWARFDie &InputDIE, AttributeSpec AttrSpec,
-    unsigned AttrSize, const DWARFFormValue &Val, const DebugMapObject &DMO,
-    CompileUnit &Unit) {
-  const DWARFUnit &U = Unit.getOrigUnit();
-  uint64_t Ref = *Val.getAsReference();
-  DIE *NewRefDie = nullptr;
-  CompileUnit *RefUnit = nullptr;
-  DeclContext *Ctxt = nullptr;
-
-  DWARFDie RefDie =
-      resolveDIEReference(Linker, DMO, CompileUnits, Val, InputDIE, RefUnit);
-
-  // If the referenced DIE is not found,  drop the attribute.
-  if (!RefDie || AttrSpec.Attr == dwarf::DW_AT_sibling)
-    return 0;
-
-  unsigned Idx = RefUnit->getOrigUnit().getDIEIndex(RefDie);
-  CompileUnit::DIEInfo &RefInfo = RefUnit->getInfo(Idx);
-
-  // If we already have emitted an equivalent DeclContext, just point
-  // at it.
-  if (isODRAttribute(AttrSpec.Attr)) {
-    Ctxt = RefInfo.Ctxt;
-    if (Ctxt && Ctxt->getCanonicalDIEOffset()) {
-      DIEInteger Attr(Ctxt->getCanonicalDIEOffset());
-      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                   dwarf::DW_FORM_ref_addr, Attr);
-      return U.getRefAddrByteSize();
-    }
-  }
-
-  if (!RefInfo.Clone) {
-    assert(Ref > InputDIE.getOffset());
-    // We haven't cloned this DIE yet. Just create an empty one and
-    // store it. It'll get really cloned when we process it.
-    RefInfo.Clone = DIE::get(DIEAlloc, dwarf::Tag(RefDie.getTag()));
-  }
-  NewRefDie = RefInfo.Clone;
-
-  if (AttrSpec.Form == dwarf::DW_FORM_ref_addr ||
-      (Unit.hasODR() && isODRAttribute(AttrSpec.Attr))) {
-    // We cannot currently rely on a DIEEntry to emit ref_addr
-    // references, because the implementation calls back to DwarfDebug
-    // to find the unit offset. (We don't have a DwarfDebug)
-    // FIXME: we should be able to design DIEEntry reliance on
-    // DwarfDebug away.
-    uint64_t Attr;
-    if (Ref < InputDIE.getOffset()) {
-      // We must have already cloned that DIE.
-      uint32_t NewRefOffset =
-          RefUnit->getStartOffset() + NewRefDie->getOffset();
-      Attr = NewRefOffset;
-      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                   dwarf::DW_FORM_ref_addr, DIEInteger(Attr));
-    } else {
-      // A forward reference. Note and fixup later.
-      Attr = 0xBADDEF;
-      Unit.noteForwardReference(
-          NewRefDie, RefUnit, Ctxt,
-          Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                       dwarf::DW_FORM_ref_addr, DIEInteger(Attr)));
-    }
-    return U.getRefAddrByteSize();
-  }
-
-  Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-               dwarf::Form(AttrSpec.Form), DIEEntry(*NewRefDie));
-  return AttrSize;
-}
-
-void DwarfLinkerForBinary::DIECloner::cloneExpression(
-    DataExtractor &Data, DWARFExpression Expression, const DebugMapObject &DMO,
-    CompileUnit &Unit, SmallVectorImpl<uint8_t> &OutputBuffer) {
-  using Encoding = DWARFExpression::Operation::Encoding;
-
-  uint64_t OpOffset = 0;
-  for (auto &Op : Expression) {
-    auto Description = Op.getDescription();
-    // DW_OP_const_type is variable-length and has 3
-    // operands. DWARFExpression thus far only supports 2.
-    auto Op0 = Description.Op[0];
-    auto Op1 = Description.Op[1];
-    if ((Op0 == Encoding::BaseTypeRef && Op1 != Encoding::SizeNA) ||
-        (Op1 == Encoding::BaseTypeRef && Op0 != Encoding::Size1))
-      Linker.reportWarning("Unsupported DW_OP encoding.", DMO);
-
-    if ((Op0 == Encoding::BaseTypeRef && Op1 == Encoding::SizeNA) ||
-        (Op1 == Encoding::BaseTypeRef && Op0 == Encoding::Size1)) {
-      // This code assumes that the other non-typeref operand fits into 1 byte.
-      assert(OpOffset < Op.getEndOffset());
-      uint32_t ULEBsize = Op.getEndOffset() - OpOffset - 1;
-      assert(ULEBsize <= 16);
-
-      // Copy over the operation.
-      OutputBuffer.push_back(Op.getCode());
-      uint64_t RefOffset;
-      if (Op1 == Encoding::SizeNA) {
-        RefOffset = Op.getRawOperand(0);
-      } else {
-        OutputBuffer.push_back(Op.getRawOperand(0));
-        RefOffset = Op.getRawOperand(1);
-      }
-      auto RefDie = Unit.getOrigUnit().getDIEForOffset(RefOffset);
-      uint32_t RefIdx = Unit.getOrigUnit().getDIEIndex(RefDie);
-      CompileUnit::DIEInfo &Info = Unit.getInfo(RefIdx);
-      uint32_t Offset = 0;
-      if (DIE *Clone = Info.Clone)
-        Offset = Clone->getOffset();
-      else
-        Linker.reportWarning("base type ref doesn't point to DW_TAG_base_type.",
-                             DMO);
-      uint8_t ULEB[16];
-      unsigned RealSize = encodeULEB128(Offset, ULEB, ULEBsize);
-      if (RealSize > ULEBsize) {
-        // Emit the generic type as a fallback.
-        RealSize = encodeULEB128(0, ULEB, ULEBsize);
-        Linker.reportWarning("base type ref doesn't fit.", DMO);
-      }
-      assert(RealSize == ULEBsize && "padding failed");
-      ArrayRef<uint8_t> ULEBbytes(ULEB, ULEBsize);
-      OutputBuffer.append(ULEBbytes.begin(), ULEBbytes.end());
-    } else {
-      // Copy over everything else unmodified.
-      StringRef Bytes = Data.getData().slice(OpOffset, Op.getEndOffset());
-      OutputBuffer.append(Bytes.begin(), Bytes.end());
-    }
-    OpOffset = Op.getEndOffset();
-  }
-}
-
-unsigned DwarfLinkerForBinary::DIECloner::cloneBlockAttribute(
-    DIE &Die, const DebugMapObject &DMO, CompileUnit &Unit,
-    AttributeSpec AttrSpec, const DWARFFormValue &Val, unsigned AttrSize,
-    bool IsLittleEndian) {
-  DIEValueList *Attr;
-  DIEValue Value;
-  DIELoc *Loc = nullptr;
-  DIEBlock *Block = nullptr;
-  if (AttrSpec.Form == dwarf::DW_FORM_exprloc) {
-    Loc = new (DIEAlloc) DIELoc;
-    Linker.DIELocs.push_back(Loc);
-  } else {
-    Block = new (DIEAlloc) DIEBlock;
-    Linker.DIEBlocks.push_back(Block);
-  }
-  Attr = Loc ? static_cast<DIEValueList *>(Loc)
-             : static_cast<DIEValueList *>(Block);
-
-  if (Loc)
-    Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
-                     dwarf::Form(AttrSpec.Form), Loc);
-  else
-    Value = DIEValue(dwarf::Attribute(AttrSpec.Attr),
-                     dwarf::Form(AttrSpec.Form), Block);
-
-  // If the block is a DWARF Expression, clone it into the temporary
-  // buffer using cloneExpression(), otherwise copy the data directly.
-  SmallVector<uint8_t, 32> Buffer;
-  ArrayRef<uint8_t> Bytes = *Val.getAsBlock();
-  if (DWARFAttribute::mayHaveLocationDescription(AttrSpec.Attr) &&
-      (Val.isFormClass(DWARFFormValue::FC_Block) ||
-       Val.isFormClass(DWARFFormValue::FC_Exprloc))) {
-    DWARFUnit &OrigUnit = Unit.getOrigUnit();
-    DataExtractor Data(StringRef((const char *)Bytes.data(), Bytes.size()),
-                       IsLittleEndian, OrigUnit.getAddressByteSize());
-    DWARFExpression Expr(Data, OrigUnit.getVersion(),
-                         OrigUnit.getAddressByteSize());
-    cloneExpression(Data, Expr, DMO, Unit, Buffer);
-    Bytes = Buffer;
-  }
-  for (auto Byte : Bytes)
-    Attr->addValue(DIEAlloc, static_cast<dwarf::Attribute>(0),
-                   dwarf::DW_FORM_data1, DIEInteger(Byte));
-
-  // FIXME: If DIEBlock and DIELoc just reuses the Size field of
-  // the DIE class, this if could be replaced by
-  // Attr->setSize(Bytes.size()).
-  if (Linker.Streamer) {
-    auto *AsmPrinter = &Linker.Streamer->getAsmPrinter();
-    if (Loc)
-      Loc->ComputeSize(AsmPrinter);
-    else
-      Block->ComputeSize(AsmPrinter);
-  }
-  Die.addValue(DIEAlloc, Value);
-  return AttrSize;
-}
-
-unsigned DwarfLinkerForBinary::DIECloner::cloneAddressAttribute(
-    DIE &Die, AttributeSpec AttrSpec, const DWARFFormValue &Val,
-    const CompileUnit &Unit, AttributesInfo &Info) {
-  uint64_t Addr = *Val.getAsAddress();
-
-  if (LLVM_UNLIKELY(Linker.Options.Update)) {
-    if (AttrSpec.Attr == dwarf::DW_AT_low_pc)
-      Info.HasLowPc = true;
-    Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                 dwarf::Form(AttrSpec.Form), DIEInteger(Addr));
-    return Unit.getOrigUnit().getAddressByteSize();
-  }
-
-  if (AttrSpec.Attr == dwarf::DW_AT_low_pc) {
-    if (Die.getTag() == dwarf::DW_TAG_inlined_subroutine ||
-        Die.getTag() == dwarf::DW_TAG_lexical_block)
-      // The low_pc of a block or inline subroutine might get
-      // relocated because it happens to match the low_pc of the
-      // enclosing subprogram. To prevent issues with that, always use
-      // the low_pc from the input DIE if relocations have been applied.
-      Addr = (Info.OrigLowPc != std::numeric_limits<uint64_t>::max()
-                  ? Info.OrigLowPc
-                  : Addr) +
-             Info.PCOffset;
-    else if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
-      Addr = Unit.getLowPc();
-      if (Addr == std::numeric_limits<uint64_t>::max())
-        return 0;
-    }
-    Info.HasLowPc = true;
-  } else if (AttrSpec.Attr == dwarf::DW_AT_high_pc) {
-    if (Die.getTag() == dwarf::DW_TAG_compile_unit) {
-      if (uint64_t HighPc = Unit.getHighPc())
-        Addr = HighPc;
-      else
-        return 0;
-    } else
-      // If we have a high_pc recorded for the input DIE, use
-      // it. Otherwise (when no relocations where applied) just use the
-      // one we just decoded.
-      Addr = (Info.OrigHighPc ? Info.OrigHighPc : Addr) + Info.PCOffset;
-  } else if (AttrSpec.Attr == dwarf::DW_AT_call_return_pc) {
-    // Relocate a return PC address within a call site entry.
-    if (Die.getTag() == dwarf::DW_TAG_call_site)
-      Addr += Info.PCOffset;
-  }
-
-  Die.addValue(DIEAlloc, static_cast<dwarf::Attribute>(AttrSpec.Attr),
-               static_cast<dwarf::Form>(AttrSpec.Form), DIEInteger(Addr));
-  return Unit.getOrigUnit().getAddressByteSize();
-}
-
-unsigned DwarfLinkerForBinary::DIECloner::cloneScalarAttribute(
-    DIE &Die, const DWARFDie &InputDIE, const DebugMapObject &DMO,
-    CompileUnit &Unit, AttributeSpec AttrSpec, const DWARFFormValue &Val,
-    unsigned AttrSize, AttributesInfo &Info) {
-  uint64_t Value;
-
-  if (LLVM_UNLIKELY(Linker.Options.Update)) {
-    if (auto OptionalValue = Val.getAsUnsignedConstant())
-      Value = *OptionalValue;
-    else if (auto OptionalValue = Val.getAsSignedConstant())
-      Value = *OptionalValue;
-    else if (auto OptionalValue = Val.getAsSectionOffset())
-      Value = *OptionalValue;
-    else {
-      Linker.reportWarning(
-          "Unsupported scalar attribute form. Dropping attribute.", DMO,
-          &InputDIE);
-      return 0;
-    }
-    if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
-      Info.IsDeclaration = true;
-    Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                 dwarf::Form(AttrSpec.Form), DIEInteger(Value));
-    return AttrSize;
-  }
-
-  if (AttrSpec.Attr == dwarf::DW_AT_high_pc &&
-      Die.getTag() == dwarf::DW_TAG_compile_unit) {
-    if (Unit.getLowPc() == -1ULL)
-      return 0;
-    // Dwarf >= 4 high_pc is an size, not an address.
-    Value = Unit.getHighPc() - Unit.getLowPc();
-  } else if (AttrSpec.Form == dwarf::DW_FORM_sec_offset)
-    Value = *Val.getAsSectionOffset();
-  else if (AttrSpec.Form == dwarf::DW_FORM_sdata)
-    Value = *Val.getAsSignedConstant();
-  else if (auto OptionalValue = Val.getAsUnsignedConstant())
-    Value = *OptionalValue;
-  else {
-    Linker.reportWarning(
-        "Unsupported scalar attribute form. Dropping attribute.", DMO,
-        &InputDIE);
-    return 0;
-  }
-  PatchLocation Patch =
-      Die.addValue(DIEAlloc, dwarf::Attribute(AttrSpec.Attr),
-                   dwarf::Form(AttrSpec.Form), DIEInteger(Value));
-  if (AttrSpec.Attr == dwarf::DW_AT_ranges) {
-    Unit.noteRangeAttribute(Die, Patch);
-    Info.HasRanges = true;
-  }
-
-  // A more generic way to check for location attributes would be
-  // nice, but it's very unlikely that any other attribute needs a
-  // location list.
-  // FIXME: use DWARFAttribute::mayHaveLocationDescription().
-  else if (AttrSpec.Attr == dwarf::DW_AT_location ||
-           AttrSpec.Attr == dwarf::DW_AT_frame_base)
-    Unit.noteLocationAttribute(Patch, Info.PCOffset);
-  else if (AttrSpec.Attr == dwarf::DW_AT_declaration && Value)
-    Info.IsDeclaration = true;
-
-  return AttrSize;
-}
-
-/// Clone \p InputDIE's attribute described by \p AttrSpec with
-/// value \p Val, and add it to \p Die.
-/// \returns the size of the cloned attribute.
-unsigned DwarfLinkerForBinary::DIECloner::cloneAttribute(
-    DIE &Die, const DWARFDie &InputDIE, const DebugMapObject &DMO,
-    CompileUnit &Unit, OffsetsStringPool &StringPool, const DWARFFormValue &Val,
-    const AttributeSpec AttrSpec, unsigned AttrSize, AttributesInfo &Info,
-    bool IsLittleEndian) {
-  const DWARFUnit &U = Unit.getOrigUnit();
-
-  switch (AttrSpec.Form) {
-  case dwarf::DW_FORM_strp:
-  case dwarf::DW_FORM_string:
-    return cloneStringAttribute(Die, AttrSpec, Val, U, StringPool, Info);
-  case dwarf::DW_FORM_ref_addr:
-  case dwarf::DW_FORM_ref1:
-  case dwarf::DW_FORM_ref2:
-  case dwarf::DW_FORM_ref4:
-  case dwarf::DW_FORM_ref8:
-    return cloneDieReferenceAttribute(Die, InputDIE, AttrSpec, AttrSize, Val,
-                                      DMO, Unit);
-  case dwarf::DW_FORM_block:
-  case dwarf::DW_FORM_block1:
-  case dwarf::DW_FORM_block2:
-  case dwarf::DW_FORM_block4:
-  case dwarf::DW_FORM_exprloc:
-    return cloneBlockAttribute(Die, DMO, Unit, AttrSpec, Val, AttrSize,
-                               IsLittleEndian);
-  case dwarf::DW_FORM_addr:
-    return cloneAddressAttribute(Die, AttrSpec, Val, Unit, Info);
-  case dwarf::DW_FORM_data1:
-  case dwarf::DW_FORM_data2:
-  case dwarf::DW_FORM_data4:
-  case dwarf::DW_FORM_data8:
-  case dwarf::DW_FORM_udata:
-  case dwarf::DW_FORM_sdata:
-  case dwarf::DW_FORM_sec_offset:
-  case dwarf::DW_FORM_flag:
-  case dwarf::DW_FORM_flag_present:
-    return cloneScalarAttribute(Die, InputDIE, DMO, Unit, AttrSpec, Val,
-                                AttrSize, Info);
-  default:
-    Linker.reportWarning(
-        "Unsupported attribute form in cloneAttribute. Dropping.", DMO,
-        &InputDIE);
-  }
-
-  return 0;
-}
-
 /// Apply the valid relocations found by findValidRelocs() to
 /// the buffer \p Data, taking into account that Data is at \p BaseOffset
 /// in the debug_info section.
 ///
 /// Like for findValidRelocs(), this function must be called with
 /// monotonic \p BaseOffset values.
 ///
 /// \returns whether any reloc has been applied.
-bool DwarfLinkerForBinary::RelocationManager::applyValidRelocs(
+bool DwarfLinkerForBinary::AddressManager::applyValidRelocs(
     MutableArrayRef<char> Data, uint64_t BaseOffset, bool IsLittleEndian) {
+  assert(areRelocationsResolved());
   assert((NextValidReloc == 0 ||
           BaseOffset > ValidRelocs[NextValidReloc - 1].Offset) &&
          "BaseOffset should only be increasing.");
   if (NextValidReloc >= ValidRelocs.size())
     return false;
 
   // Skip relocs that haven't been applied.
   while (NextValidReloc < ValidRelocs.size() &&
          ValidRelocs[NextValidReloc].Offset < BaseOffset)
     ++NextValidReloc;
 
   bool Applied = false;
   uint64_t EndOffset = BaseOffset + Data.size();
   while (NextValidReloc < ValidRelocs.size() &&
          ValidRelocs[NextValidReloc].Offset >= BaseOffset &&
          ValidRelocs[NextValidReloc].Offset < EndOffset) {
     const auto &ValidReloc = ValidRelocs[NextValidReloc++];
     assert(ValidReloc.Offset - BaseOffset < Data.size());
     assert(ValidReloc.Offset - BaseOffset + ValidReloc.Size <= Data.size());
     char Buf[8];
     uint64_t Value = ValidReloc.Mapping->getValue().BinaryAddress;
     Value += ValidReloc.Addend;
-    for (unsigned i = 0; i != ValidReloc.Size; ++i) {
-      unsigned Index = IsLittleEndian ? i : (ValidReloc.Size - i - 1);
-      Buf[i] = uint8_t(Value >> (Index * 8));
+    for (unsigned I = 0; I != ValidReloc.Size; ++I) {
+      unsigned Index = IsLittleEndian ? I : (ValidReloc.Size - I - 1);
+      Buf[I] = uint8_t(Value >> (Index * 8));
     }
     assert(ValidReloc.Size <= sizeof(Buf));
     memcpy(&Data[ValidReloc.Offset - BaseOffset], Buf, ValidReloc.Size);
     Applied = true;
   }
 
   return Applied;
 }
 
-static bool isObjCSelector(StringRef Name) {
-  return Name.size() > 2 && (Name[0] == '-' || Name[0] == '+') &&
-         (Name[1] == '[');
-}
-
-void DwarfLinkerForBinary::DIECloner::addObjCAccelerator(
-    CompileUnit &Unit, const DIE *Die, DwarfStringPoolEntryRef Name,
-    OffsetsStringPool &StringPool, bool SkipPubSection) {
-  assert(isObjCSelector(Name.getString()) && "not an objc selector");
-  // Objective C method or class function.
-  // "- [Class(Category) selector :withArg ...]"
-  StringRef ClassNameStart(Name.getString().drop_front(2));
-  size_t FirstSpace = ClassNameStart.find(' ');
-  if (FirstSpace == StringRef::npos)
-    return;
-
-  StringRef SelectorStart(ClassNameStart.data() + FirstSpace + 1);
-  if (!SelectorStart.size())
-    return;
-
-  StringRef Selector(SelectorStart.data(), SelectorStart.size() - 1);
-  Unit.addNameAccelerator(Die, StringPool.getEntry(Selector), SkipPubSection);
-
-  // Add an entry for the class name that points to this
-  // method/class function.
-  StringRef ClassName(ClassNameStart.data(), FirstSpace);
-  Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassName), SkipPubSection);
-
-  if (ClassName[ClassName.size() - 1] == ')') {
-    size_t OpenParens = ClassName.find('(');
-    if (OpenParens != StringRef::npos) {
-      StringRef ClassNameNoCategory(ClassName.data(), OpenParens);
-      Unit.addObjCAccelerator(Die, StringPool.getEntry(ClassNameNoCategory),
-                              SkipPubSection);
-
-      std::string MethodNameNoCategory(Name.getString().data(), OpenParens + 2);
-      // FIXME: The missing space here may be a bug, but
-      //        dsymutil-classic also does it this way.
-      MethodNameNoCategory.append(SelectorStart);
-      Unit.addNameAccelerator(Die, StringPool.getEntry(MethodNameNoCategory),
-                              SkipPubSection);
-    }
-  }
-}
-
-static bool
-shouldSkipAttribute(DWARFAbbreviationDeclaration::AttributeSpec AttrSpec,
-                    uint16_t Tag, bool InDebugMap, bool SkipPC,
-                    bool InFunctionScope) {
-  switch (AttrSpec.Attr) {
-  default:
-    return false;
-  case dwarf::DW_AT_low_pc:
-  case dwarf::DW_AT_high_pc:
-  case dwarf::DW_AT_ranges:
-    return SkipPC;
-  case dwarf::DW_AT_location:
-  case dwarf::DW_AT_frame_base:
-    // FIXME: for some reason dsymutil-classic keeps the location attributes
-    // when they are of block type (i.e. not location lists). This is totally
-    // wrong for globals where we will keep a wrong address. It is mostly
-    // harmless for locals, but there is no point in keeping these anyway when
-    // the function wasn't linked.
-    return (SkipPC || (!InFunctionScope && Tag == dwarf::DW_TAG_variable &&
-                       !InDebugMap)) &&
-           !DWARFFormValue(AttrSpec.Form).isFormClass(DWARFFormValue::FC_Block);
-  }
-}
-
-DIE *DwarfLinkerForBinary::DIECloner::cloneDIE(
-    const DWARFDie &InputDIE, const DebugMapObject &DMO, CompileUnit &Unit,
-    OffsetsStringPool &StringPool, int64_t PCOffset, uint32_t OutOffset,
-    unsigned Flags, bool IsLittleEndian, DIE *Die) {
-  DWARFUnit &U = Unit.getOrigUnit();
-  unsigned Idx = U.getDIEIndex(InputDIE);
-  CompileUnit::DIEInfo &Info = Unit.getInfo(Idx);
-
-  // Should the DIE appear in the output?
-  if (!Unit.getInfo(Idx).Keep)
-    return nullptr;
-
-  uint64_t Offset = InputDIE.getOffset();
-  assert(!(Die && Info.Clone) && "Can't supply a DIE and a cloned DIE");
-  if (!Die) {
-    // The DIE might have been already created by a forward reference
-    // (see cloneDieReferenceAttribute()).
-    if (!Info.Clone)
-      Info.Clone = DIE::get(DIEAlloc, dwarf::Tag(InputDIE.getTag()));
-    Die = Info.Clone;
-  }
-
-  assert(Die->getTag() == InputDIE.getTag());
-  Die->setOffset(OutOffset);
-  if ((Unit.hasODR() || Unit.isClangModule()) && !Info.Incomplete &&
-      Die->getTag() != dwarf::DW_TAG_namespace && Info.Ctxt &&
-      Info.Ctxt != Unit.getInfo(Info.ParentIdx).Ctxt &&
-      !Info.Ctxt->getCanonicalDIEOffset()) {
-    // We are about to emit a DIE that is the root of its own valid
-    // DeclContext tree. Make the current offset the canonical offset
-    // for this context.
-    Info.Ctxt->setCanonicalDIEOffset(OutOffset + Unit.getStartOffset());
-  }
-
-  // Extract and clone every attribute.
-  DWARFDataExtractor Data = U.getDebugInfoExtractor();
-  // Point to the next DIE (generally there is always at least a NULL
-  // entry after the current one). If this is a lone
-  // DW_TAG_compile_unit without any children, point to the next unit.
-  uint64_t NextOffset = (Idx + 1 < U.getNumDIEs())
-                            ? U.getDIEAtIndex(Idx + 1).getOffset()
-                            : U.getNextUnitOffset();
-  AttributesInfo AttrInfo;
-
-  // We could copy the data only if we need to apply a relocation to it. After
-  // testing, it seems there is no performance downside to doing the copy
-  // unconditionally, and it makes the code simpler.
-  SmallString<40> DIECopy(Data.getData().substr(Offset, NextOffset - Offset));
-  Data =
-      DWARFDataExtractor(DIECopy, Data.isLittleEndian(), Data.getAddressSize());
-  // Modify the copy with relocated addresses.
-  if (RelocMgr.areRelocationsResolved() &&
-      RelocMgr.applyValidRelocs(DIECopy, Offset, Data.isLittleEndian())) {
-    // If we applied relocations, we store the value of high_pc that was
-    // potentially stored in the input DIE. If high_pc is an address
-    // (Dwarf version == 2), then it might have been relocated to a
-    // totally unrelated value (because the end address in the object
-    // file might be start address of another function which got moved
-    // independently by the linker). The computation of the actual
-    // high_pc value is done in cloneAddressAttribute().
-    AttrInfo.OrigHighPc =
-        dwarf::toAddress(InputDIE.find(dwarf::DW_AT_high_pc), 0);
-    // Also store the low_pc. It might get relocated in an
-    // inline_subprogram that happens at the beginning of its
-    // inlining function.
-    AttrInfo.OrigLowPc = dwarf::toAddress(InputDIE.find(dwarf::DW_AT_low_pc),
-                                          std::numeric_limits<uint64_t>::max());
-  }
-
-  // Reset the Offset to 0 as we will be working on the local copy of
-  // the data.
-  Offset = 0;
-
-  const auto *Abbrev = InputDIE.getAbbreviationDeclarationPtr();
-  Offset += getULEB128Size(Abbrev->getCode());
-
-  // We are entering a subprogram. Get and propagate the PCOffset.
-  if (Die->getTag() == dwarf::DW_TAG_subprogram)
-    PCOffset = Info.AddrAdjust;
-  AttrInfo.PCOffset = PCOffset;
-
-  if (Abbrev->getTag() == dwarf::DW_TAG_subprogram) {
-    Flags |= TF_InFunctionScope;
-    if (!Info.InDebugMap && LLVM_LIKELY(!Options.Update))
-      Flags |= TF_SkipPC;
-  }
-
-  bool Copied = false;
-  for (const auto &AttrSpec : Abbrev->attributes()) {
-    if (LLVM_LIKELY(!Options.Update) &&
-        shouldSkipAttribute(AttrSpec, Die->getTag(), Info.InDebugMap,
-                            Flags & TF_SkipPC, Flags & TF_InFunctionScope)) {
-      DWARFFormValue::skipValue(AttrSpec.Form, Data, &Offset,
-                                U.getFormParams());
-      // FIXME: dsymutil-classic keeps the old abbreviation around
-      // even if it's not used. We can remove this (and the copyAbbrev
-      // helper) as soon as bit-for-bit compatibility is not a goal anymore.
-      if (!Copied) {
-        copyAbbrev(*InputDIE.getAbbreviationDeclarationPtr(), Unit.hasODR());
-        Copied = true;
-      }
-      continue;
-    }
-
-    DWARFFormValue Val(AttrSpec.Form);
-    uint64_t AttrSize = Offset;
-    Val.extractValue(Data, &Offset, U.getFormParams(), &U);
-    AttrSize = Offset - AttrSize;
-
-    OutOffset += cloneAttribute(*Die, InputDIE, DMO, Unit, StringPool, Val,
-                                AttrSpec, AttrSize, AttrInfo, IsLittleEndian);
-  }
-
-  // Look for accelerator entries.
-  uint16_t Tag = InputDIE.getTag();
-  // FIXME: This is slightly wrong. An inline_subroutine without a
-  // low_pc, but with AT_ranges might be interesting to get into the
-  // accelerator tables too. For now stick with dsymutil's behavior.
-  if ((Info.InDebugMap || AttrInfo.HasLowPc || AttrInfo.HasRanges) &&
-      Tag != dwarf::DW_TAG_compile_unit &&
-      getDIENames(InputDIE, AttrInfo, StringPool,
-                  Tag != dwarf::DW_TAG_inlined_subroutine)) {
-    if (AttrInfo.MangledName && AttrInfo.MangledName != AttrInfo.Name)
-      Unit.addNameAccelerator(Die, AttrInfo.MangledName,
-                              Tag == dwarf::DW_TAG_inlined_subroutine);
-    if (AttrInfo.Name) {
-      if (AttrInfo.NameWithoutTemplate)
-        Unit.addNameAccelerator(Die, AttrInfo.NameWithoutTemplate,
-                                /* SkipPubSection */ true);
-      Unit.addNameAccelerator(Die, AttrInfo.Name,
-                              Tag == dwarf::DW_TAG_inlined_subroutine);
-    }
-    if (AttrInfo.Name && isObjCSelector(AttrInfo.Name.getString()))
-      addObjCAccelerator(Unit, Die, AttrInfo.Name, StringPool,
-                         /* SkipPubSection =*/true);
-
-  } else if (Tag == dwarf::DW_TAG_namespace) {
-    if (!AttrInfo.Name)
-      AttrInfo.Name = StringPool.getEntry("(anonymous namespace)");
-    Unit.addNamespaceAccelerator(Die, AttrInfo.Name);
-  } else if (isTypeTag(Tag) && !AttrInfo.IsDeclaration &&
-             getDIENames(InputDIE, AttrInfo, StringPool) && AttrInfo.Name &&
-             AttrInfo.Name.getString()[0]) {
-    uint32_t Hash = hashFullyQualifiedName(InputDIE, Unit, DMO);
-    uint64_t RuntimeLang =
-        dwarf::toUnsigned(InputDIE.find(dwarf::DW_AT_APPLE_runtime_class))
-            .getValueOr(0);
-    bool ObjCClassIsImplementation =
-        (RuntimeLang == dwarf::DW_LANG_ObjC ||
-         RuntimeLang == dwarf::DW_LANG_ObjC_plus_plus) &&
-        dwarf::toUnsigned(InputDIE.find(dwarf::DW_AT_APPLE_objc_complete_type))
-            .getValueOr(0);
-    Unit.addTypeAccelerator(Die, AttrInfo.Name, ObjCClassIsImplementation,
-                            Hash);
-  }
-
-  // Determine whether there are any children that we want to keep.
-  bool HasChildren = false;
-  for (auto Child : InputDIE.children()) {
-    unsigned Idx = U.getDIEIndex(Child);
-    if (Unit.getInfo(Idx).Keep) {
-      HasChildren = true;
-      break;
-    }
-  }
-
-  DIEAbbrev NewAbbrev = Die->generateAbbrev();
-  if (HasChildren)
-    NewAbbrev.setChildrenFlag(dwarf::DW_CHILDREN_yes);
-  // Assign a permanent abbrev number
-  Linker.assignAbbrev(NewAbbrev);
-  Die->setAbbrevNumber(NewAbbrev.getNumber());
-
-  // Add the size of the abbreviation number to the output offset.
-  OutOffset += getULEB128Size(Die->getAbbrevNumber());
-
-  if (!HasChildren) {
-    // Update our size.
-    Die->setSize(OutOffset - Die->getOffset());
-    return Die;
-  }
-
-  // Recursively clone children.
-  for (auto Child : InputDIE.children()) {
-    if (DIE *Clone = cloneDIE(Child, DMO, Unit, StringPool, PCOffset, OutOffset,
-                              Flags, IsLittleEndian)) {
-      Die->addChild(Clone);
-      OutOffset = Clone->getOffset() + Clone->getSize();
-    }
-  }
-
-  // Account for the end of children marker.
-  OutOffset += sizeof(int8_t);
-  // Update our size.
-  Die->setSize(OutOffset - Die->getOffset());
-  return Die;
-}
-
-/// Patch the input object file relevant debug_ranges entries
-/// and emit them in the output file. Update the relevant attributes
-/// to point at the new entries.
-void DwarfLinkerForBinary::patchRangesForUnit(const CompileUnit &Unit,
-                                              DWARFContext &OrigDwarf,
-                                              const DebugMapObject &DMO) const {
-  DWARFDebugRangeList RangeList;
-  const auto &FunctionRanges = Unit.getFunctionRanges();
-  unsigned AddressSize = Unit.getOrigUnit().getAddressByteSize();
-  DWARFDataExtractor RangeExtractor(OrigDwarf.getDWARFObj(),
-                                    OrigDwarf.getDWARFObj().getRangesSection(),
-                                    OrigDwarf.isLittleEndian(), AddressSize);
-  auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
-  DWARFUnit &OrigUnit = Unit.getOrigUnit();
-  auto OrigUnitDie = OrigUnit.getUnitDIE(false);
-  uint64_t OrigLowPc =
-      dwarf::toAddress(OrigUnitDie.find(dwarf::DW_AT_low_pc), -1ULL);
-  // Ranges addresses are based on the unit's low_pc. Compute the
-  // offset we need to apply to adapt to the new unit's low_pc.
-  int64_t UnitPcOffset = 0;
-  if (OrigLowPc != -1ULL)
-    UnitPcOffset = int64_t(OrigLowPc) - Unit.getLowPc();
-
-  for (const auto &RangeAttribute : Unit.getRangesAttributes()) {
-    uint64_t Offset = RangeAttribute.get();
-    RangeAttribute.set(Streamer->getRangesSectionSize());
-    if (Error E = RangeList.extract(RangeExtractor, &Offset)) {
-      llvm::consumeError(std::move(E));
-      reportWarning("invalid range list ignored.", DMO);
-      RangeList.clear();
-    }
-    const auto &Entries = RangeList.getEntries();
-    if (!Entries.empty()) {
-      const DWARFDebugRangeList::RangeListEntry &First = Entries.front();
-
-      if (CurrRange == InvalidRange ||
-          First.StartAddress + OrigLowPc < CurrRange.start() ||
-          First.StartAddress + OrigLowPc >= CurrRange.stop()) {
-        CurrRange = FunctionRanges.find(First.StartAddress + OrigLowPc);
-        if (CurrRange == InvalidRange ||
-            CurrRange.start() > First.StartAddress + OrigLowPc) {
-          reportWarning("no mapping for range.", DMO);
-          continue;
-        }
-      }
-    }
-
-    Streamer->emitRangesEntries(UnitPcOffset, OrigLowPc, CurrRange, Entries,
-                                AddressSize);
-  }
-}
-
-/// Generate the debug_aranges entries for \p Unit and if the
-/// unit has a DW_AT_ranges attribute, also emit the debug_ranges
-/// contribution for this attribute.
-/// FIXME: this could actually be done right in patchRangesForUnit,
-/// but for the sake of initial bit-for-bit compatibility with legacy
-/// dsymutil, we have to do it in a delayed pass.
-void DwarfLinkerForBinary::generateUnitRanges(CompileUnit &Unit) const {
-  auto Attr = Unit.getUnitRangesAttribute();
-  if (Attr)
-    Attr->set(Streamer->getRangesSectionSize());
-  Streamer->emitUnitRangesEntries(Unit, static_cast<bool>(Attr));
-}
-
-/// Insert the new line info sequence \p Seq into the current
-/// set of already linked line info \p Rows.
-static void insertLineSequence(std::vector<DWARFDebugLine::Row> &Seq,
-                               std::vector<DWARFDebugLine::Row> &Rows) {
-  if (Seq.empty())
-    return;
-
-  if (!Rows.empty() && Rows.back().Address < Seq.front().Address) {
-    Rows.insert(Rows.end(), Seq.begin(), Seq.end());
-    Seq.clear();
-    return;
-  }
-
-  object::SectionedAddress Front = Seq.front().Address;
-  auto InsertPoint = partition_point(
-      Rows, [=](const DWARFDebugLine::Row &O) { return O.Address < Front; });
-
-  // FIXME: this only removes the unneeded end_sequence if the
-  // sequences have been inserted in order. Using a global sort like
-  // described in patchLineTableForUnit() and delaying the end_sequene
-  // elimination to emitLineTableForUnit() we can get rid of all of them.
-  if (InsertPoint != Rows.end() && InsertPoint->Address == Front &&
-      InsertPoint->EndSequence) {
-    *InsertPoint = Seq.front();
-    Rows.insert(InsertPoint + 1, Seq.begin() + 1, Seq.end());
-  } else {
-    Rows.insert(InsertPoint, Seq.begin(), Seq.end());
-  }
-
-  Seq.clear();
-}
-
-static void patchStmtList(DIE &Die, DIEInteger Offset) {
-  for (auto &V : Die.values())
-    if (V.getAttribute() == dwarf::DW_AT_stmt_list) {
-      V = DIEValue(V.getAttribute(), V.getForm(), Offset);
-      return;
-    }
-
-  llvm_unreachable("Didn't find DW_AT_stmt_list in cloned DIE!");
-}
-
-/// Extract the line table for \p Unit from \p OrigDwarf, and
-/// recreate a relocated version of these for the address ranges that
-/// are present in the binary.
-void DwarfLinkerForBinary::patchLineTableForUnit(CompileUnit &Unit,
-                                                 DWARFContext &OrigDwarf,
-                                                 RangesTy &Ranges,
-                                                 const DebugMapObject &DMO) {
-  DWARFDie CUDie = Unit.getOrigUnit().getUnitDIE();
-  auto StmtList = dwarf::toSectionOffset(CUDie.find(dwarf::DW_AT_stmt_list));
-  if (!StmtList)
-    return;
-
-  // Update the cloned DW_AT_stmt_list with the correct debug_line offset.
-  if (auto *OutputDIE = Unit.getOutputUnitDIE())
-    patchStmtList(*OutputDIE, DIEInteger(Streamer->getLineSectionSize()));
-
-  // Parse the original line info for the unit.
-  DWARFDebugLine::LineTable LineTable;
-  uint64_t StmtOffset = *StmtList;
-  DWARFDataExtractor LineExtractor(
-      OrigDwarf.getDWARFObj(), OrigDwarf.getDWARFObj().getLineSection(),
-      OrigDwarf.isLittleEndian(), Unit.getOrigUnit().getAddressByteSize());
-  if (Options.Translator)
-    return Streamer->translateLineTable(LineExtractor, StmtOffset);
-
-  Error Err = LineTable.parse(LineExtractor, &StmtOffset, OrigDwarf,
-                              &Unit.getOrigUnit(), DWARFContext::dumpWarning);
-  DWARFContext::dumpWarning(std::move(Err));
-
-  // This vector is the output line table.
-  std::vector<DWARFDebugLine::Row> NewRows;
-  NewRows.reserve(LineTable.Rows.size());
-
-  // Current sequence of rows being extracted, before being inserted
-  // in NewRows.
-  std::vector<DWARFDebugLine::Row> Seq;
-  const auto &FunctionRanges = Unit.getFunctionRanges();
-  auto InvalidRange = FunctionRanges.end(), CurrRange = InvalidRange;
-
-  // FIXME: This logic is meant to generate exactly the same output as
-  // Darwin's classic dsymutil. There is a nicer way to implement this
-  // by simply putting all the relocated line info in NewRows and simply
-  // sorting NewRows before passing it to emitLineTableForUnit. This
-  // should be correct as sequences for a function should stay
-  // together in the sorted output. There are a few corner cases that
-  // look suspicious though, and that required to implement the logic
-  // this way. Revisit that once initial validation is finished.
-
-  // Iterate over the object file line info and extract the sequences
-  // that correspond to linked functions.
-  for (auto &Row : LineTable.Rows) {
-    // Check whether we stepped out of the range. The range is
-    // half-open, but consider accept the end address of the range if
-    // it is marked as end_sequence in the input (because in that
-    // case, the relocation offset is accurate and that entry won't
-    // serve as the start of another function).
-    if (CurrRange == InvalidRange || Row.Address.Address < CurrRange.start() ||
-        Row.Address.Address > CurrRange.stop() ||
-        (Row.Address.Address == CurrRange.stop() && !Row.EndSequence)) {
-      // We just stepped out of a known range. Insert a end_sequence
-      // corresponding to the end of the range.
-      uint64_t StopAddress = CurrRange != InvalidRange
-                                 ? CurrRange.stop() + CurrRange.value()
-                                 : -1ULL;
-      CurrRange = FunctionRanges.find(Row.Address.Address);
-      bool CurrRangeValid =
-          CurrRange != InvalidRange && CurrRange.start() <= Row.Address.Address;
-      if (!CurrRangeValid) {
-        CurrRange = InvalidRange;
-        if (StopAddress != -1ULL) {
-          // Try harder by looking in the DebugMapObject function
-          // ranges map. There are corner cases where this finds a
-          // valid entry. It's unclear if this is right or wrong, but
-          // for now do as dsymutil.
-          // FIXME: Understand exactly what cases this addresses and
-          // potentially remove it along with the Ranges map.
-          auto Range = Ranges.lower_bound(Row.Address.Address);
-          if (Range != Ranges.begin() && Range != Ranges.end())
-            --Range;
-
-          if (Range != Ranges.end() && Range->first <= Row.Address.Address &&
-              Range->second.HighPC >= Row.Address.Address) {
-            StopAddress = Row.Address.Address + Range->second.Offset;
-          }
-        }
-      }
-      if (StopAddress != -1ULL && !Seq.empty()) {
-        // Insert end sequence row with the computed end address, but
-        // the same line as the previous one.
-        auto NextLine = Seq.back();
-        NextLine.Address.Address = StopAddress;
-        NextLine.EndSequence = 1;
-        NextLine.PrologueEnd = 0;
-        NextLine.BasicBlock = 0;
-        NextLine.EpilogueBegin = 0;
-        Seq.push_back(NextLine);
-        insertLineSequence(Seq, NewRows);
-      }
-
-      if (!CurrRangeValid)
-        continue;
-    }
-
-    // Ignore empty sequences.
-    if (Row.EndSequence && Seq.empty())
-      continue;
-
-    // Relocate row address and add it to the current sequence.
-    Row.Address.Address += CurrRange.value();
-    Seq.emplace_back(Row);
-
-    if (Row.EndSequence)
-      insertLineSequence(Seq, NewRows);
-  }
-
-  // Finished extracting, now emit the line tables.
-  // FIXME: LLVM hard-codes its prologue values. We just copy the
-  // prologue over and that works because we act as both producer and
-  // consumer. It would be nicer to have a real configurable line
-  // table emitter.
-  if (LineTable.Prologue.getVersion() < 2 ||
-      LineTable.Prologue.getVersion() > 5 ||
-      LineTable.Prologue.DefaultIsStmt != DWARF2_LINE_DEFAULT_IS_STMT ||
-      LineTable.Prologue.OpcodeBase > 13)
-    reportWarning("line table parameters mismatch. Cannot emit.", DMO);
-  else {
-    uint32_t PrologueEnd = *StmtList + 10 + LineTable.Prologue.PrologueLength;
-    // DWARF v5 has an extra 2 bytes of information before the header_length
-    // field.
-    if (LineTable.Prologue.getVersion() == 5)
-      PrologueEnd += 2;
-    StringRef LineData = OrigDwarf.getDWARFObj().getLineSection().Data;
-    MCDwarfLineTableParams Params;
-    Params.DWARF2LineOpcodeBase = LineTable.Prologue.OpcodeBase;
-    Params.DWARF2LineBase = LineTable.Prologue.LineBase;
-    Params.DWARF2LineRange = LineTable.Prologue.LineRange;
-    Streamer->emitLineTableForUnit(Params,
-                                   LineData.slice(*StmtList + 4, PrologueEnd),
-                                   LineTable.Prologue.MinInstLength, NewRows,
-                                   Unit.getOrigUnit().getAddressByteSize());
-  }
-}
-
-void DwarfLinkerForBinary::emitAcceleratorEntriesForUnit(CompileUnit &Unit) {
-  switch (Options.TheAccelTableKind) {
-  case AccelTableKind::Apple:
-    emitAppleAcceleratorEntriesForUnit(Unit);
-    break;
-  case AccelTableKind::Dwarf:
-    emitDwarfAcceleratorEntriesForUnit(Unit);
-    break;
-  case AccelTableKind::Default:
-    llvm_unreachable("The default must be updated to a concrete value.");
-    break;
-  }
-}
-
-void DwarfLinkerForBinary::emitAppleAcceleratorEntriesForUnit(
-    CompileUnit &Unit) {
-  // Add namespaces.
-  for (const auto &Namespace : Unit.getNamespaces())
-    AppleNamespaces.addName(Namespace.Name,
-                            Namespace.Die->getOffset() + Unit.getStartOffset());
-
-  /// Add names.
-  if (!Options.Minimize)
-    Streamer->emitPubNamesForUnit(Unit);
-  for (const auto &Pubname : Unit.getPubnames())
-    AppleNames.addName(Pubname.Name,
-                       Pubname.Die->getOffset() + Unit.getStartOffset());
-
-  /// Add types.
-  if (!Options.Minimize)
-    Streamer->emitPubTypesForUnit(Unit);
-  for (const auto &Pubtype : Unit.getPubtypes())
-    AppleTypes.addName(
-        Pubtype.Name, Pubtype.Die->getOffset() + Unit.getStartOffset(),
-        Pubtype.Die->getTag(),
-        Pubtype.ObjcClassImplementation ? dwarf::DW_FLAG_type_implementation
-                                        : 0,
-        Pubtype.QualifiedNameHash);
-
-  /// Add ObjC names.
-  for (const auto &ObjC : Unit.getObjC())
-    AppleObjc.addName(ObjC.Name, ObjC.Die->getOffset() + Unit.getStartOffset());
-}
-
-void DwarfLinkerForBinary::emitDwarfAcceleratorEntriesForUnit(
-    CompileUnit &Unit) {
-  for (const auto &Namespace : Unit.getNamespaces())
-    DebugNames.addName(Namespace.Name, Namespace.Die->getOffset(),
-                       Namespace.Die->getTag(), Unit.getUniqueID());
-  for (const auto &Pubname : Unit.getPubnames())
-    DebugNames.addName(Pubname.Name, Pubname.Die->getOffset(),
-                       Pubname.Die->getTag(), Unit.getUniqueID());
-  for (const auto &Pubtype : Unit.getPubtypes())
-    DebugNames.addName(Pubtype.Name, Pubtype.Die->getOffset(),
-                       Pubtype.Die->getTag(), Unit.getUniqueID());
-}
-
-/// Read the frame info stored in the object, and emit the
-/// patched frame descriptions for the linked binary.
-///
-/// This is actually pretty easy as the data of the CIEs and FDEs can
-/// be considered as black boxes and moved as is. The only thing to do
-/// is to patch the addresses in the headers.
-void DwarfLinkerForBinary::patchFrameInfoForObject(const DebugMapObject &DMO,
-                                                   RangesTy &Ranges,
-                                                   DWARFContext &OrigDwarf,
-                                                   unsigned AddrSize) {
-  StringRef FrameData = OrigDwarf.getDWARFObj().getFrameSection().Data;
-  if (FrameData.empty())
-    return;
-
-  DataExtractor Data(FrameData, OrigDwarf.isLittleEndian(), 0);
-  uint64_t InputOffset = 0;
-
-  // Store the data of the CIEs defined in this object, keyed by their
-  // offsets.
-  DenseMap<uint64_t, StringRef> LocalCIES;
-
-  while (Data.isValidOffset(InputOffset)) {
-    uint64_t EntryOffset = InputOffset;
-    uint32_t InitialLength = Data.getU32(&InputOffset);
-    if (InitialLength == 0xFFFFFFFF)
-      return reportWarning("Dwarf64 bits no supported", DMO);
-
-    uint32_t CIEId = Data.getU32(&InputOffset);
-    if (CIEId == 0xFFFFFFFF) {
-      // This is a CIE, store it.
-      StringRef CIEData = FrameData.substr(EntryOffset, InitialLength + 4);
-      LocalCIES[EntryOffset] = CIEData;
-      // The -4 is to account for the CIEId we just read.
-      InputOffset += InitialLength - 4;
-      continue;
-    }
-
-    uint32_t Loc = Data.getUnsigned(&InputOffset, AddrSize);
-
-    // Some compilers seem to emit frame info that doesn't start at
-    // the function entry point, thus we can't just lookup the address
-    // in the debug map. Use the linker's range map to see if the FDE
-    // describes something that we can relocate.
-    auto Range = Ranges.upper_bound(Loc);
-    if (Range != Ranges.begin())
-      --Range;
-    if (Range == Ranges.end() || Range->first > Loc ||
-        Range->second.HighPC <= Loc) {
-      // The +4 is to account for the size of the InitialLength field itself.
-      InputOffset = EntryOffset + InitialLength + 4;
-      continue;
-    }
-
-    // This is an FDE, and we have a mapping.
-    // Have we already emitted a corresponding CIE?
-    StringRef CIEData = LocalCIES[CIEId];
-    if (CIEData.empty())
-      return reportWarning("Inconsistent debug_frame content. Dropping.", DMO);
-
-    // Look if we already emitted a CIE that corresponds to the
-    // referenced one (the CIE data is the key of that lookup).
-    auto IteratorInserted = EmittedCIEs.insert(
-        std::make_pair(CIEData, Streamer->getFrameSectionSize()));
-    // If there is no CIE yet for this ID, emit it.
-    if (IteratorInserted.second ||
-        // FIXME: dsymutil-classic only caches the last used CIE for
-        // reuse. Mimic that behavior for now. Just removing that
-        // second half of the condition and the LastCIEOffset variable
-        // makes the code DTRT.
-        LastCIEOffset != IteratorInserted.first->getValue()) {
-      LastCIEOffset = Streamer->getFrameSectionSize();
-      IteratorInserted.first->getValue() = LastCIEOffset;
-      Streamer->emitCIE(CIEData);
-    }
-
-    // Emit the FDE with updated address and CIE pointer.
-    // (4 + AddrSize) is the size of the CIEId + initial_location
-    // fields that will get reconstructed by emitFDE().
-    unsigned FDERemainingBytes = InitialLength - (4 + AddrSize);
-    Streamer->emitFDE(IteratorInserted.first->getValue(), AddrSize,
-                      Loc + Range->second.Offset,
-                      FrameData.substr(InputOffset, FDERemainingBytes));
-    InputOffset += FDERemainingBytes;
-  }
-}
-
-void DwarfLinkerForBinary::DIECloner::copyAbbrev(
-    const DWARFAbbreviationDeclaration &Abbrev, bool HasODR) {
-  DIEAbbrev Copy(dwarf::Tag(Abbrev.getTag()),
-                 dwarf::Form(Abbrev.hasChildren()));
-
-  for (const auto &Attr : Abbrev.attributes()) {
-    uint16_t Form = Attr.Form;
-    if (HasODR && isODRAttribute(Attr.Attr))
-      Form = dwarf::DW_FORM_ref_addr;
-    Copy.AddAttribute(dwarf::Attribute(Attr.Attr), dwarf::Form(Form));
-  }
-
-  Linker.assignAbbrev(Copy);
-}
-
-uint32_t DwarfLinkerForBinary::DIECloner::hashFullyQualifiedName(
-    DWARFDie DIE, CompileUnit &U, const DebugMapObject &DMO,
-    int ChildRecurseDepth) {
-  const char *Name = nullptr;
-  DWARFUnit *OrigUnit = &U.getOrigUnit();
-  CompileUnit *CU = &U;
-  Optional<DWARFFormValue> Ref;
-
-  while (1) {
-    if (const char *CurrentName = DIE.getName(DINameKind::ShortName))
-      Name = CurrentName;
-
-    if (!(Ref = DIE.find(dwarf::DW_AT_specification)) &&
-        !(Ref = DIE.find(dwarf::DW_AT_abstract_origin)))
-      break;
-
-    if (!Ref->isFormClass(DWARFFormValue::FC_Reference))
-      break;
-
-    CompileUnit *RefCU;
-    if (auto RefDIE =
-            resolveDIEReference(Linker, DMO, CompileUnits, *Ref, DIE, RefCU)) {
-      CU = RefCU;
-      OrigUnit = &RefCU->getOrigUnit();
-      DIE = RefDIE;
-    }
-  }
-
-  unsigned Idx = OrigUnit->getDIEIndex(DIE);
-  if (!Name && DIE.getTag() == dwarf::DW_TAG_namespace)
-    Name = "(anonymous namespace)";
-
-  if (CU->getInfo(Idx).ParentIdx == 0 ||
-      // FIXME: dsymutil-classic compatibility. Ignore modules.
-      CU->getOrigUnit().getDIEAtIndex(CU->getInfo(Idx).ParentIdx).getTag() ==
-          dwarf::DW_TAG_module)
-    return djbHash(Name ? Name : "", djbHash(ChildRecurseDepth ? "" : "::"));
-
-  DWARFDie Die = OrigUnit->getDIEAtIndex(CU->getInfo(Idx).ParentIdx);
-  return djbHash(
-      (Name ? Name : ""),
-      djbHash((Name ? "::" : ""),
-              hashFullyQualifiedName(Die, *CU, DMO, ++ChildRecurseDepth)));
-}
-
-static uint64_t getDwoId(const DWARFDie &CUDie, const DWARFUnit &Unit) {
-  auto DwoId = dwarf::toUnsigned(
-      CUDie.find({dwarf::DW_AT_dwo_id, dwarf::DW_AT_GNU_dwo_id}));
-  if (DwoId)
-    return *DwoId;
-  return 0;
-}
-
-bool DwarfLinkerForBinary::registerModuleReference(
-    DWARFDie CUDie, const DWARFUnit &Unit, DebugMap &ModuleMap,
-    const DebugMapObject &DMO, RangesTy &Ranges, OffsetsStringPool &StringPool,
-    UniquingStringPool &UniquingStringPool, DeclContextTree &ODRContexts,
-    uint64_t ModulesEndOffset, unsigned &UnitID, bool IsLittleEndian,
-    unsigned Indent, bool Quiet) {
-  std::string PCMfile = dwarf::toString(
-      CUDie.find({dwarf::DW_AT_dwo_name, dwarf::DW_AT_GNU_dwo_name}), "");
-  if (PCMfile.empty())
-    return false;
-
-  // Clang module DWARF skeleton CUs abuse this for the path to the module.
-  uint64_t DwoId = getDwoId(CUDie, Unit);
-
-  std::string Name = dwarf::toString(CUDie.find(dwarf::DW_AT_name), "");
-  if (Name.empty()) {
-    if (!Quiet)
-      reportWarning("Anonymous module skeleton CU for " + PCMfile, DMO);
-    return true;
-  }
-
-  if (!Quiet && Options.Verbose) {
-    outs().indent(Indent);
-    outs() << "Found clang module reference " << PCMfile;
-  }
-
-  auto Cached = ClangModules.find(PCMfile);
-  if (Cached != ClangModules.end()) {
-    // FIXME: Until PR27449 (https://llvm.org/bugs/show_bug.cgi?id=27449) is
-    // fixed in clang, only warn about DWO_id mismatches in verbose mode.
-    // ASTFileSignatures will change randomly when a module is rebuilt.
-    if (!Quiet && Options.Verbose && (Cached->second != DwoId))
-      reportWarning(Twine("hash mismatch: this object file was built against a "
-                          "different version of the module ") +
-                        PCMfile,
-                    DMO);
-    if (!Quiet && Options.Verbose)
-      outs() << " [cached].\n";
-    return true;
-  }
-  if (!Quiet && Options.Verbose)
-    outs() << " ...\n";
-
-  // Cyclic dependencies are disallowed by Clang, but we still
-  // shouldn't run into an infinite loop, so mark it as processed now.
-  ClangModules.insert({PCMfile, DwoId});
-
-  if (Error E = loadClangModule(CUDie, PCMfile, Name, DwoId, ModuleMap, DMO,
-                                Ranges, StringPool, UniquingStringPool,
-                                ODRContexts, ModulesEndOffset, UnitID,
-                                IsLittleEndian, Indent + 2, Quiet)) {
-    consumeError(std::move(E));
-    return false;
-  }
-  return true;
-}
-
-ErrorOr<const object::ObjectFile &>
-DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
-                                 const DebugMap &Map) {
-  auto ObjectEntry =
-      BinHolder.getObjectEntry(Obj.getObjectFilename(), Obj.getTimestamp());
-  if (!ObjectEntry) {
-    auto Err = ObjectEntry.takeError();
-    reportWarning(
-        Twine(Obj.getObjectFilename()) + ": " + toString(std::move(Err)), Obj);
-    return errorToErrorCode(std::move(Err));
-  }
-
-  auto Object = ObjectEntry->getObject(Map.getTriple());
-  if (!Object) {
-    auto Err = Object.takeError();
-    reportWarning(
-        Twine(Obj.getObjectFilename()) + ": " + toString(std::move(Err)), Obj);
-    return errorToErrorCode(std::move(Err));
-  }
-
-  return *Object;
-}
-
-Error DwarfLinkerForBinary::loadClangModule(
-    DWARFDie CUDie, StringRef Filename, StringRef ModuleName, uint64_t DwoId,
-    DebugMap &ModuleMap, const DebugMapObject &DMO, RangesTy &Ranges,
-    OffsetsStringPool &StringPool, UniquingStringPool &UniquingStringPool,
-    DeclContextTree &ODRContexts, uint64_t ModulesEndOffset, unsigned &UnitID,
-    bool IsLittleEndian, unsigned Indent, bool Quiet) {
-  /// Using a SmallString<0> because loadClangModule() is recursive.
-  SmallString<0> Path(Options.PrependPath);
-  if (sys::path::is_relative(Filename))
-    resolveRelativeObjectPath(Path, CUDie);
-  sys::path::append(Path, Filename);
-  // Don't use the cached binary holder because we have no thread-safety
-  // guarantee and the lifetime is limited.
-  auto &Obj = ModuleMap.addDebugMapObject(
-      Path, sys::TimePoint<std::chrono::seconds>(), MachO::N_OSO);
-  auto ErrOrObj = loadObject(Obj, ModuleMap);
-  if (!ErrOrObj) {
-    // Try and emit more helpful warnings by applying some heuristics.
-    StringRef ObjFile = DMO.getObjectFilename();
-    bool isClangModule = sys::path::extension(Filename).equals(".pcm");
-    bool isArchive = ObjFile.endswith(")");
-    if (isClangModule) {
-      StringRef ModuleCacheDir = sys::path::parent_path(Path);
-      if (sys::fs::exists(ModuleCacheDir)) {
-        // If the module's parent directory exists, we assume that the module
-        // cache has expired and was pruned by clang.  A more adventurous
-        // dsymutil would invoke clang to rebuild the module now.
-        if (!ModuleCacheHintDisplayed) {
-          WithColor::note() << "The clang module cache may have expired since "
-                               "this object file was built. Rebuilding the "
-                               "object file will rebuild the module cache.\n";
-          ModuleCacheHintDisplayed = true;
-        }
-      } else if (isArchive) {
-        // If the module cache directory doesn't exist at all and the object
-        // file is inside a static library, we assume that the static library
-        // was built on a different machine. We don't want to discourage module
-        // debugging for convenience libraries within a project though.
-        if (!ArchiveHintDisplayed) {
-          WithColor::note()
-              << "Linking a static library that was built with "
-                 "-gmodules, but the module cache was not found.  "
-                 "Redistributable static libraries should never be "
-                 "built with module debugging enabled.  The debug "
-                 "experience will be degraded due to incomplete "
-                 "debug information.\n";
-          ArchiveHintDisplayed = true;
-        }
-      }
-    }
-    return Error::success();
-  }
-
-  std::unique_ptr<CompileUnit> Unit;
-
-  // Setup access to the debug info.
-  auto DwarfContext = DWARFContext::create(*ErrOrObj);
-  RelocationManager RelocMgr(*this, *ErrOrObj, DMO);
-
-  for (const auto &CU : DwarfContext->compile_units()) {
-    updateDwarfVersion(CU->getVersion());
-    // Recursively get all modules imported by this one.
-    auto CUDie = CU->getUnitDIE(false);
-    if (!CUDie)
-      continue;
-    if (!registerModuleReference(CUDie, *CU, ModuleMap, DMO, Ranges, StringPool,
-                                 UniquingStringPool, ODRContexts,
-                                 ModulesEndOffset, UnitID, IsLittleEndian,
-                                 Indent, Quiet)) {
-      if (Unit) {
-        std::string Err =
-            (Filename +
-             ": Clang modules are expected to have exactly 1 compile unit.\n")
-                .str();
-        error(Err);
-        return make_error<StringError>(Err, inconvertibleErrorCode());
-      }
-      // FIXME: Until PR27449 (https://llvm.org/bugs/show_bug.cgi?id=27449) is
-      // fixed in clang, only warn about DWO_id mismatches in verbose mode.
-      // ASTFileSignatures will change randomly when a module is rebuilt.
-      uint64_t PCMDwoId = getDwoId(CUDie, *CU);
-      if (PCMDwoId != DwoId) {
-        if (!Quiet && Options.Verbose)
-          reportWarning(
-              Twine("hash mismatch: this object file was built against a "
-                    "different version of the module ") +
-                  Filename,
-              DMO);
-        // Update the cache entry with the DwoId of the module loaded from disk.
-        ClangModules[Filename] = PCMDwoId;
-      }
-
-      // Add this module.
-      Unit = std::make_unique<CompileUnit>(*CU, UnitID++, !Options.NoODR,
-                                           ModuleName);
-      Unit->setHasInterestingContent();
-      analyzeContextInfo(CUDie, 0, *Unit, &ODRContexts.getRoot(),
-                         UniquingStringPool, ODRContexts, ModulesEndOffset,
-                         ParseableSwiftInterfaces,
-                         [&](const Twine &Warning, const DWARFDie &DIE) {
-                           reportWarning(Warning, DMO, &DIE);
-                         });
-      // Keep everything.
-      Unit->markEverythingAsKept();
-    }
-  }
-  if (!Unit->getOrigUnit().getUnitDIE().hasChildren())
-    return Error::success();
-  if (!Quiet && Options.Verbose) {
-    outs().indent(Indent);
-    outs() << "cloning .debug_info from " << Filename << "\n";
-  }
-
-  UnitListTy CompileUnits;
-  CompileUnits.push_back(std::move(Unit));
-  DIECloner(*this, RelocMgr, DIEAlloc, CompileUnits, Options)
-      .cloneAllCompileUnits(*DwarfContext, DMO, Ranges, StringPool,
-                            IsLittleEndian);
-  return Error::success();
-}
-
-void DwarfLinkerForBinary::DIECloner::cloneAllCompileUnits(
-    DWARFContext &DwarfContext, const DebugMapObject &DMO, RangesTy &Ranges,
-    OffsetsStringPool &StringPool, bool IsLittleEndian) {
-  if (!Linker.Streamer)
-    return;
-
-  uint64_t OutputDebugInfoSize = Linker.Streamer->getDebugInfoSectionSize();
-  for (auto &CurrentUnit : CompileUnits) {
-    auto InputDIE = CurrentUnit->getOrigUnit().getUnitDIE();
-    CurrentUnit->setStartOffset(OutputDebugInfoSize);
-    if (!InputDIE) {
-      OutputDebugInfoSize = CurrentUnit->computeNextUnitOffset();
-      continue;
-    }
-    if (CurrentUnit->getInfo(0).Keep) {
-      // Clone the InputDIE into your Unit DIE in our compile unit since it
-      // already has a DIE inside of it.
-      CurrentUnit->createOutputDIE();
-      cloneDIE(InputDIE, DMO, *CurrentUnit, StringPool, 0 /* PC offset */,
-               11 /* Unit Header size */, 0, IsLittleEndian,
-               CurrentUnit->getOutputUnitDIE());
-    }
-
-    OutputDebugInfoSize = CurrentUnit->computeNextUnitOffset();
-
-    if (Linker.Options.NoOutput)
-      continue;
-
-    // FIXME: for compatibility with the classic dsymutil, we emit
-    // an empty line table for the unit, even if the unit doesn't
-    // actually exist in the DIE tree.
-    if (LLVM_LIKELY(!Linker.Options.Update) || Linker.Options.Translator)
-      Linker.patchLineTableForUnit(*CurrentUnit, DwarfContext, Ranges, DMO);
-
-    Linker.emitAcceleratorEntriesForUnit(*CurrentUnit);
-
-    if (LLVM_UNLIKELY(Linker.Options.Update))
-      continue;
-
-    Linker.patchRangesForUnit(*CurrentUnit, DwarfContext, DMO);
-    auto ProcessExpr = [&](StringRef Bytes, SmallVectorImpl<uint8_t> &Buffer) {
-      DWARFUnit &OrigUnit = CurrentUnit->getOrigUnit();
-      DataExtractor Data(Bytes, IsLittleEndian, OrigUnit.getAddressByteSize());
-      cloneExpression(Data,
-                      DWARFExpression(Data, OrigUnit.getVersion(),
-                                      OrigUnit.getAddressByteSize()),
-                      DMO, *CurrentUnit, Buffer);
-    };
-    Linker.Streamer->emitLocationsForUnit(*CurrentUnit, DwarfContext,
-                                          ProcessExpr);
-  }
-
-  if (Linker.Options.NoOutput)
-    return;
-
-  // Emit all the compile unit's debug information.
-  for (auto &CurrentUnit : CompileUnits) {
-    if (LLVM_LIKELY(!Linker.Options.Update))
-      Linker.generateUnitRanges(*CurrentUnit);
-
-    CurrentUnit->fixupForwardReferences();
-
-    if (!CurrentUnit->getOutputUnitDIE())
-      continue;
-
-    assert(Linker.Streamer->getDebugInfoSectionSize() ==
-           CurrentUnit->getStartOffset());
-    Linker.Streamer->emitCompileUnitHeader(*CurrentUnit);
-    Linker.Streamer->emitDIE(*CurrentUnit->getOutputUnitDIE());
-    assert(Linker.Streamer->getDebugInfoSectionSize() ==
-           CurrentUnit->computeNextUnitOffset());
-  }
-}
-
-void DwarfLinkerForBinary::updateAccelKind(DWARFContext &Dwarf) {
-  if (Options.TheAccelTableKind != AccelTableKind::Default)
-    return;
-
-  auto &DwarfObj = Dwarf.getDWARFObj();
-
-  if (!AtLeastOneDwarfAccelTable &&
-      (!DwarfObj.getAppleNamesSection().Data.empty() ||
-       !DwarfObj.getAppleTypesSection().Data.empty() ||
-       !DwarfObj.getAppleNamespacesSection().Data.empty() ||
-       !DwarfObj.getAppleObjCSection().Data.empty())) {
-    AtLeastOneAppleAccelTable = true;
-  }
-
-  if (!AtLeastOneDwarfAccelTable && !DwarfObj.getNamesSection().Data.empty()) {
-    AtLeastOneDwarfAccelTable = true;
-  }
-}
-
-bool DwarfLinkerForBinary::emitPaperTrailWarnings(
-    const DebugMapObject &DMO, const DebugMap &Map,
-    OffsetsStringPool &StringPool) {
-  if (DMO.getWarnings().empty() || !DMO.empty())
-    return false;
-
-  Streamer->switchToDebugInfoSection(/* Version */ 2);
-  DIE *CUDie = DIE::get(DIEAlloc, dwarf::DW_TAG_compile_unit);
-  CUDie->setOffset(11);
-  StringRef Producer = StringPool.internString("dsymutil");
-  StringRef File = StringPool.internString(DMO.getObjectFilename());
-  CUDie->addValue(DIEAlloc, dwarf::DW_AT_producer, dwarf::DW_FORM_strp,
-                  DIEInteger(StringPool.getStringOffset(Producer)));
-  DIEBlock *String = new (DIEAlloc) DIEBlock();
-  DIEBlocks.push_back(String);
-  for (auto &C : File)
-    String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
-                     DIEInteger(C));
-  String->addValue(DIEAlloc, dwarf::Attribute(0), dwarf::DW_FORM_data1,
-                   DIEInteger(0));
-
-  CUDie->addValue(DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_string, String);
-  for (const auto &Warning : DMO.getWarnings()) {
-    DIE &ConstDie = CUDie->addChild(DIE::get(DIEAlloc, dwarf::DW_TAG_constant));
-    ConstDie.addValue(
-        DIEAlloc, dwarf::DW_AT_name, dwarf::DW_FORM_strp,
-        DIEInteger(StringPool.getStringOffset("dsymutil_warning")));
-    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_artificial, dwarf::DW_FORM_flag,
-                      DIEInteger(1));
-    ConstDie.addValue(DIEAlloc, dwarf::DW_AT_const_value, dwarf::DW_FORM_strp,
-                      DIEInteger(StringPool.getStringOffset(Warning)));
-  }
-  unsigned Size = 4 /* FORM_strp */ + File.size() + 1 +
-                  DMO.getWarnings().size() * (4 + 1 + 4) +
-                  1 /* End of children */;
-  DIEAbbrev Abbrev = CUDie->generateAbbrev();
-  assignAbbrev(Abbrev);
-  CUDie->setAbbrevNumber(Abbrev.getNumber());
-  Size += getULEB128Size(Abbrev.getNumber());
-  // Abbreviation ordering needed for classic compatibility.
-  for (auto &Child : CUDie->children()) {
-    Abbrev = Child.generateAbbrev();
-    assignAbbrev(Abbrev);
-    Child.setAbbrevNumber(Abbrev.getNumber());
-    Size += getULEB128Size(Abbrev.getNumber());
-  }
-  CUDie->setSize(Size);
-  Streamer->emitPaperTrailWarningsDie(Map.getTriple(), *CUDie);
-
-  return true;
-}
-
-static Error copySwiftInterfaces(
-    const std::map<std::string, std::string> &ParseableSwiftInterfaces,
-    StringRef Architecture, const LinkOptions &Options) {
-  std::error_code EC;
-  SmallString<128> InputPath;
-  SmallString<128> Path;
-  sys::path::append(Path, *Options.ResourceDir, "Swift", Architecture);
-  if ((EC = sys::fs::create_directories(Path.str(), true,
-                                        sys::fs::perms::all_all)))
-    return make_error<StringError>(
-        "cannot create directory: " + toString(errorCodeToError(EC)), EC);
-  unsigned BaseLength = Path.size();
-
-  for (auto &I : ParseableSwiftInterfaces) {
-    StringRef ModuleName = I.first;
-    StringRef InterfaceFile = I.second;
-    if (!Options.PrependPath.empty()) {
-      InputPath.clear();
-      sys::path::append(InputPath, Options.PrependPath, InterfaceFile);
-      InterfaceFile = InputPath;
-    }
-    sys::path::append(Path, ModuleName);
-    Path.append(".swiftinterface");
-    if (Options.Verbose)
-      outs() << "copy parseable Swift interface " << InterfaceFile << " -> "
-             << Path.str() << '\n';
-
-    // copy_file attempts an APFS clone first, so this should be cheap.
-    if ((EC = sys::fs::copy_file(InterfaceFile, Path.str())))
-      warn(Twine("cannot copy parseable Swift interface ") + InterfaceFile +
-           ": " + toString(errorCodeToError(EC)));
-    Path.resize(BaseLength);
-  }
-  return Error::success();
-}
-
-static Error emitRemarks(const LinkOptions &Options, StringRef BinaryPath,
-                         StringRef ArchName, const remarks::RemarkLinker &RL) {
-  // Make sure we don't create the directories and the file if there is nothing
-  // to serialize.
-  if (RL.empty())
-    return Error::success();
-
-  SmallString<128> InputPath;
-  SmallString<128> Path;
-  // Create the "Remarks" directory in the "Resources" directory.
-  sys::path::append(Path, *Options.ResourceDir, "Remarks");
-  if (std::error_code EC = sys::fs::create_directories(Path.str(), true,
-                                                       sys::fs::perms::all_all))
-    return errorCodeToError(EC);
-
-  // Append the file name.
-  // For fat binaries, also append a dash and the architecture name.
-  sys::path::append(Path, sys::path::filename(BinaryPath));
-  if (Options.NumDebugMaps > 1) {
-    // More than one debug map means we have a fat binary.
-    Path += '-';
-    Path += ArchName;
-  }
-
-  std::error_code EC;
-  raw_fd_ostream OS(Options.NoOutput ? "-" : Path.str(), EC, sys::fs::OF_None);
-  if (EC)
-    return errorCodeToError(EC);
-
-  if (Error E = RL.serialize(OS, Options.RemarksFormat))
-    return E;
-
-  return Error::success();
-}
-
-bool DwarfLinkerForBinary::link(const DebugMap &Map) {
-  if (!createStreamer(Map.getTriple(), OutFile))
-    return false;
-
-  // Size of the DIEs (and headers) generated for the linked output.
-  // A unique ID that identifies each compile unit.
-  unsigned UnitID = 0;
-  DebugMap ModuleMap(Map.getTriple(), Map.getBinaryPath());
-
-  // First populate the data structure we need for each iteration of the
-  // parallel loop.
-  unsigned NumObjects = Map.getNumberOfObjects();
-  std::vector<LinkContext> ObjectContexts;
-  ObjectContexts.reserve(NumObjects);
-  for (const auto &Obj : Map.objects()) {
-    ObjectContexts.emplace_back(Map, *this, *Obj.get());
-    LinkContext &LC = ObjectContexts.back();
-    if (LC.ObjectFile)
-      updateAccelKind(*LC.DwarfContext);
-  }
-
-  // This Dwarf string pool which is only used for uniquing. This one should
-  // never be used for offsets as its not thread-safe or predictable.
-  UniquingStringPool UniquingStringPool(nullptr, true);
-
-  // This Dwarf string pool which is used for emission. It must be used
-  // serially as the order of calling getStringOffset matters for
-  // reproducibility.
-  OffsetsStringPool OffsetsStringPool(Options.Translator, true);
-
-  // ODR Contexts for the link.
-  DeclContextTree ODRContexts;
-
-  // If we haven't decided on an accelerator table kind yet, we base ourselves
-  // on the DWARF we have seen so far. At this point we haven't pulled in debug
-  // information from modules yet, so it is technically possible that they
-  // would affect the decision. However, as they're built with the same
-  // compiler and flags, it is safe to assume that they will follow the
-  // decision made here.
-  if (Options.TheAccelTableKind == AccelTableKind::Default) {
-    if (AtLeastOneDwarfAccelTable && !AtLeastOneAppleAccelTable)
-      Options.TheAccelTableKind = AccelTableKind::Dwarf;
-    else
-      Options.TheAccelTableKind = AccelTableKind::Apple;
-  }
-
-  for (LinkContext &LinkContext : ObjectContexts) {
-    if (Options.Verbose)
-      outs() << "DEBUG MAP OBJECT: " << LinkContext.DMO.getObjectFilename()
-             << "\n";
-
-    // N_AST objects (swiftmodule files) should get dumped directly into the
-    // appropriate DWARF section.
-    if (LinkContext.DMO.getType() == MachO::N_AST) {
-      StringRef File = LinkContext.DMO.getObjectFilename();
-      auto ErrorOrMem = MemoryBuffer::getFile(File);
-      if (!ErrorOrMem) {
-        warn("Could not open '" + File + "'\n");
-        continue;
-      }
-      sys::fs::file_status Stat;
-      if (auto Err = sys::fs::status(File, Stat)) {
-        warn(Err.message());
-        continue;
-      }
-      if (!Options.NoTimestamp) {
-        // The modification can have sub-second precision so we need to cast
-        // away the extra precision that's not present in the debug map.
-        auto ModificationTime =
-            std::chrono::time_point_cast<std::chrono::seconds>(
-                Stat.getLastModificationTime());
-        if (ModificationTime != LinkContext.DMO.getTimestamp()) {
-          // Not using the helper here as we can easily stream TimePoint<>.
-          WithColor::warning()
-              << "Timestamp mismatch for " << File << ": "
-              << Stat.getLastModificationTime() << " and "
-              << sys::TimePoint<>(LinkContext.DMO.getTimestamp()) << "\n";
-          continue;
-        }
-      }
-
-      // Copy the module into the .swift_ast section.
-      if (!Options.NoOutput)
-        Streamer->emitSwiftAST((*ErrorOrMem)->getBuffer());
-      continue;
-    }
-
-    if (emitPaperTrailWarnings(LinkContext.DMO, Map, OffsetsStringPool))
-      continue;
-
-    if (!LinkContext.ObjectFile)
-      continue;
-
-    // Look for relocations that correspond to debug map entries.
-
-    if (LLVM_LIKELY(!Options.Update) &&
-        !LinkContext.RelocMgr->hasValidRelocs()) {
-      if (Options.Verbose)
-        outs() << "No valid relocations found. Skipping.\n";
-
-      // Clear this ObjFile entry as a signal to other loops that we should not
-      // process this iteration.
-      LinkContext.ObjectFile = nullptr;
-      continue;
-    }
-
-    // Setup access to the debug info.
-    if (!LinkContext.DwarfContext)
-      continue;
-
-    startDebugObject(LinkContext);
-
-    // In a first phase, just read in the debug info and load all clang modules.
-    LinkContext.CompileUnits.reserve(
-        LinkContext.DwarfContext->getNumCompileUnits());
-
-    for (const auto &CU : LinkContext.DwarfContext->compile_units()) {
-      updateDwarfVersion(CU->getVersion());
-      auto CUDie = CU->getUnitDIE(false);
-      if (Options.Verbose) {
-        outs() << "Input compilation unit:";
-        DIDumpOptions DumpOpts;
-        DumpOpts.ChildRecurseDepth = 0;
-        DumpOpts.Verbose = Options.Verbose;
-        CUDie.dump(outs(), 0, DumpOpts);
-      }
-      if (CUDie && !LLVM_UNLIKELY(Options.Update))
-        registerModuleReference(CUDie, *CU, ModuleMap, LinkContext.DMO,
-                                LinkContext.Ranges, OffsetsStringPool,
-                                UniquingStringPool, ODRContexts, 0, UnitID,
-                                LinkContext.DwarfContext->isLittleEndian());
-    }
-  }
-
-  // If we haven't seen any CUs, pick an arbitrary valid Dwarf version anyway.
-  if (MaxDwarfVersion == 0)
-    MaxDwarfVersion = 3;
-
-  // At this point we know how much data we have emitted. We use this value to
-  // compare canonical DIE offsets in analyzeContextInfo to see if a definition
-  // is already emitted, without being affected by canonical die offsets set
-  // later. This prevents undeterminism when analyze and clone execute
-  // concurrently, as clone set the canonical DIE offset and analyze reads it.
-  const uint64_t ModulesEndOffset =
-      Options.NoOutput ? 0 : Streamer->getDebugInfoSectionSize();
-
-  // These variables manage the list of processed object files.
-  // The mutex and condition variable are to ensure that this is thread safe.
-  std::mutex ProcessedFilesMutex;
-  std::condition_variable ProcessedFilesConditionVariable;
-  BitVector ProcessedFiles(NumObjects, false);
-
-  //  Analyzing the context info is particularly expensive so it is executed in
-  //  parallel with emitting the previous compile unit.
-  auto AnalyzeLambda = [&](size_t i) {
-    auto &LinkContext = ObjectContexts[i];
-
-    if (!LinkContext.ObjectFile || !LinkContext.DwarfContext)
-      return;
-
-    for (const auto &CU : LinkContext.DwarfContext->compile_units()) {
-      updateDwarfVersion(CU->getVersion());
-      // The !registerModuleReference() condition effectively skips
-      // over fully resolved skeleton units. This second pass of
-      // registerModuleReferences doesn't do any new work, but it
-      // will collect top-level errors, which are suppressed. Module
-      // warnings were already displayed in the first iteration.
-      bool Quiet = true;
-      auto CUDie = CU->getUnitDIE(false);
-      if (!CUDie || LLVM_UNLIKELY(Options.Update) ||
-          !registerModuleReference(CUDie, *CU, ModuleMap, LinkContext.DMO,
-                                   LinkContext.Ranges, OffsetsStringPool,
-                                   UniquingStringPool, ODRContexts,
-                                   ModulesEndOffset, UnitID, Quiet)) {
-        LinkContext.CompileUnits.push_back(std::make_unique<CompileUnit>(
-            *CU, UnitID++, !Options.NoODR && !Options.Update, ""));
-      }
-    }
-
-    // Now build the DIE parent links that we will use during the next phase.
-    for (auto &CurrentUnit : LinkContext.CompileUnits) {
-      auto CUDie = CurrentUnit->getOrigUnit().getUnitDIE();
-      if (!CUDie)
-        continue;
-      analyzeContextInfo(CurrentUnit->getOrigUnit().getUnitDIE(), 0,
-                         *CurrentUnit, &ODRContexts.getRoot(),
-                         UniquingStringPool, ODRContexts, ModulesEndOffset,
-                         ParseableSwiftInterfaces,
-                         [&](const Twine &Warning, const DWARFDie &DIE) {
-                           reportWarning(Warning, LinkContext.DMO, &DIE);
-                         });
-    }
-  };
-
-  // And then the remaining work in serial again.
-  // Note, although this loop runs in serial, it can run in parallel with
-  // the analyzeContextInfo loop so long as we process files with indices >=
-  // than those processed by analyzeContextInfo.
-  auto CloneLambda = [&](size_t i) {
-    auto &LinkContext = ObjectContexts[i];
-    if (!LinkContext.ObjectFile)
-      return;
-
-    // Then mark all the DIEs that need to be present in the linked output
-    // and collect some information about them.
-    // Note that this loop can not be merged with the previous one because
-    // cross-cu references require the ParentIdx to be setup for every CU in
-    // the object file before calling this.
-    if (LLVM_UNLIKELY(Options.Update)) {
-      for (auto &CurrentUnit : LinkContext.CompileUnits)
-        CurrentUnit->markEverythingAsKept();
-      Streamer->copyInvariantDebugSection(*LinkContext.ObjectFile);
-    } else {
-      for (auto &CurrentUnit : LinkContext.CompileUnits)
-        lookForDIEsToKeep(*LinkContext.RelocMgr, LinkContext.Ranges,
-                          LinkContext.CompileUnits,
-                          CurrentUnit->getOrigUnit().getUnitDIE(),
-                          LinkContext.DMO, *CurrentUnit, 0);
-    }
-
-    // The calls to applyValidRelocs inside cloneDIE will walk the reloc
-    // array again (in the same way findValidRelocsInDebugInfo() did). We
-    // need to reset the NextValidReloc index to the beginning.
-    if (LinkContext.RelocMgr->hasValidRelocs() || LLVM_UNLIKELY(Options.Update))
-      DIECloner(*this, *LinkContext.RelocMgr, DIEAlloc,
-                LinkContext.CompileUnits, Options)
-          .cloneAllCompileUnits(*LinkContext.DwarfContext, LinkContext.DMO,
-                                LinkContext.Ranges, OffsetsStringPool,
-                                LinkContext.DwarfContext->isLittleEndian());
-    if (!Options.NoOutput && !LinkContext.CompileUnits.empty() &&
-        LLVM_LIKELY(!Options.Update))
-      patchFrameInfoForObject(
-          LinkContext.DMO, LinkContext.Ranges, *LinkContext.DwarfContext,
-          LinkContext.CompileUnits[0]->getOrigUnit().getAddressByteSize());
-
-    // Clean-up before starting working on the next object.
-    endDebugObject(LinkContext);
-  };
-
-  auto EmitLambda = [&]() {
-    // Emit everything that's global.
-    if (!Options.NoOutput) {
-      Streamer->emitAbbrevs(Abbreviations, MaxDwarfVersion);
-      Streamer->emitStrings(OffsetsStringPool);
-      switch (Options.TheAccelTableKind) {
-      case AccelTableKind::Apple:
-        Streamer->emitAppleNames(AppleNames);
-        Streamer->emitAppleNamespaces(AppleNamespaces);
-        Streamer->emitAppleTypes(AppleTypes);
-        Streamer->emitAppleObjc(AppleObjc);
-        break;
-      case AccelTableKind::Dwarf:
-        Streamer->emitDebugNames(DebugNames);
-        break;
-      case AccelTableKind::Default:
-        llvm_unreachable("Default should have already been resolved.");
-        break;
-      }
-    }
-  };
-
-  remarks::RemarkLinker RL;
-  if (!Options.RemarksPrependPath.empty())
-    RL.setExternalFilePrependPath(Options.RemarksPrependPath);
-  auto RemarkLinkLambda = [&](size_t i) {
-    // Link remarks from one object file.
-    auto &LinkContext = ObjectContexts[i];
-    if (const object::ObjectFile *Obj = LinkContext.ObjectFile) {
-      Error E = RL.link(*Obj);
-      if (Error NewE = handleErrors(
-              std::move(E), [&](std::unique_ptr<FileError> EC) -> Error {
-                return remarksErrorHandler(LinkContext.DMO, *this,
-                                           std::move(EC));
-              }))
-        return NewE;
-    }
-    return Error(Error::success());
-  };
-
-  auto AnalyzeAll = [&]() {
-    for (unsigned i = 0, e = NumObjects; i != e; ++i) {
-      AnalyzeLambda(i);
-
-      std::unique_lock<std::mutex> LockGuard(ProcessedFilesMutex);
-      ProcessedFiles.set(i);
-      ProcessedFilesConditionVariable.notify_one();
-    }
-  };
-
-  auto CloneAll = [&]() {
-    for (unsigned i = 0, e = NumObjects; i != e; ++i) {
-      {
-        std::unique_lock<std::mutex> LockGuard(ProcessedFilesMutex);
-        if (!ProcessedFiles[i]) {
-          ProcessedFilesConditionVariable.wait(
-              LockGuard, [&]() { return ProcessedFiles[i]; });
-        }
-      }
-
-      CloneLambda(i);
-    }
-    EmitLambda();
-  };
-
-  auto EmitRemarksLambda = [&]() {
-    StringRef ArchName = Map.getTriple().getArchName();
-    return emitRemarks(Options, Map.getBinaryPath(), ArchName, RL);
-  };
-
-  // Instead of making error handling a lot more complicated using futures,
-  // write to one llvm::Error instance if something went wrong.
-  // We're assuming RemarkLinkAllError is alive longer than the thread
-  // executing RemarkLinkAll.
-  auto RemarkLinkAll = [&](Error &RemarkLinkAllError) {
-    // Allow assigning to the error only within the lambda.
-    ErrorAsOutParameter EAO(&RemarkLinkAllError);
-    for (unsigned i = 0, e = NumObjects; i != e; ++i)
-      if ((RemarkLinkAllError = RemarkLinkLambda(i)))
-        return;
-
-    if ((RemarkLinkAllError = EmitRemarksLambda()))
-      return;
-  };
-
-  // To limit memory usage in the single threaded case, analyze and clone are
-  // run sequentially so the LinkContext is freed after processing each object
-  // in endDebugObject.
-  if (Options.Threads == 1) {
-    for (unsigned i = 0, e = NumObjects; i != e; ++i) {
-      AnalyzeLambda(i);
-      CloneLambda(i);
-
-      if (Error E = RemarkLinkLambda(i))
-        return error(toString(std::move(E)));
-    }
-    EmitLambda();
-
-    if (Error E = EmitRemarksLambda())
-      return error(toString(std::move(E)));
-
-  } else {
-    // This should not be constructed on the single-threaded path to avoid fatal
-    // errors from unchecked llvm::Error objects.
-    Error RemarkLinkAllError = Error::success();
-
-    ThreadPool pool(3);
-    pool.async(AnalyzeAll);
-    pool.async(CloneAll);
-    pool.async(RemarkLinkAll, std::ref(RemarkLinkAllError));
-    pool.wait();
-
-    // Report errors from RemarkLinkAll, if any.
-    if (Error E = std::move(RemarkLinkAllError))
-      return error(toString(std::move(E)));
-  }
-
-  if (Options.NoOutput)
-    return true;
-
-  if (Options.ResourceDir && !ParseableSwiftInterfaces.empty()) {
-    StringRef ArchName = Triple::getArchTypeName(Map.getTriple().getArch());
-    if (auto E =
-            copySwiftInterfaces(ParseableSwiftInterfaces, ArchName, Options))
-      return error(toString(std::move(E)));
-  }
-
-  return Streamer->finish(Map, Options.Translator);
-} // namespace dsymutil
-
 bool linkDwarf(raw_fd_ostream &OutFile, BinaryHolder &BinHolder,
                const DebugMap &DM, LinkOptions Options) {
   DwarfLinkerForBinary Linker(OutFile, BinHolder, std::move(Options));
   return Linker.link(DM);
 }
 
 } // namespace dsymutil
 } // namespace llvm

llvm/tools/dsymutil/DwarfStreamer.cpp

void DwarfStreamer::emitPubSectionForUnit(
   if (!HeaderEmitted)
     return;
   Asm->emitInt32(0); // End marker.
   Asm->OutStreamer->EmitLabel(EndLabel);
 }
 
 /// Emit .debug_pubnames for \p Unit.
 void DwarfStreamer::emitPubNamesForUnit(const CompileUnit &Unit) {
+  if (Options.Minimize)
+    return;
   emitPubSectionForUnit(MC->getObjectFileInfo()->getDwarfPubNamesSection(),
                         "names", Unit, Unit.getPubnames());
 }
 
 /// Emit .debug_pubtypes for \p Unit.
 void DwarfStreamer::emitPubTypesForUnit(const CompileUnit &Unit) {
+  if (Options.Minimize)
+    return;
   emitPubSectionForUnit(MC->getObjectFileInfo()->getDwarfPubTypesSection(),
                         "types", Unit, Unit.getPubtypes());
 }
 
 /// Emit a CIE into the debug_frame section.
 void DwarfStreamer::emitCIE(StringRef CIEBytes) {
   MS->SwitchSection(MC->getObjectFileInfo()->getDwarfFrameSection());
 

llvm/tools/dsymutil/LinkUtils.h

 #define LLVM_TOOLS_DSYMUTIL_LINKOPTIONS_H
 
 #include "SymbolMap.h"
 
 #include "llvm/ADT/Twine.h"
 #include "llvm/Remarks/RemarkFormat.h"
 #include "llvm/Support/WithColor.h"
 
+#include "llvm/DWARFLinker/DWARFLinker.h"
 #include <string>
 
 namespace llvm {
 namespace dsymutil {
 
 enum class OutputFileType {
   Object,
   Assembly,
 };
 
-/// The kind of accelerator tables we should emit.
-enum class AccelTableKind {
-  Apple,   ///< .apple_names, .apple_namespaces, .apple_types, .apple_objc.
-  Dwarf,   ///< DWARF v5 .debug_names.
-  Default, ///< Dwarf for DWARF5 or later, Apple otherwise.
-};
-
 struct LinkOptions {
   /// Verbosity
   bool Verbose = false;
 
   /// Skip emitting output
   bool NoOutput = false;
 
   /// Do not unique types according to ODR