Index: include/llvm/Bitcode/LLVMBitCodes.h
===================================================================
--- include/llvm/Bitcode/LLVMBitCodes.h
+++ include/llvm/Bitcode/LLVMBitCodes.h
@@ -167,6 +167,7 @@
     METADATA_EXPRESSION    = 29,  // [distinct, n x element]
     METADATA_OBJC_PROPERTY = 30,  // [distinct, name, file, line, ...]
     METADATA_IMPORTED_ENTITY=31,  // [distinct, tag, scope, entity, line, name]
+    METADATA_EXTERNAL_TYPE_REF=32,// [distinct, tag, file, uid]
   };
 
   // The constants block (CONSTANTS_BLOCK_ID) describes emission for each
Index: include/llvm/IR/DIBuilder.h
===================================================================
--- include/llvm/IR/DIBuilder.h
+++ include/llvm/IR/DIBuilder.h
@@ -386,6 +386,13 @@
                                            DITypeRefArray ParameterTypes,
                                            unsigned Flags = 0);
 
+    /// createExternalTypeRef - Create external type ref.
+    /// @param Tag              Dwarf TAG.
+    /// @param File             Module in which this type is defined.
+    /// @param UniqueIdentifire Mangled name or unique identifier for the type.
+    DIExternalTypeRef *createExternalTypeRef(unsigned Tag, DIFile *File,
+                                             StringRef UniqueIdentifier);
+
     /// createArtificialType - Create a new DIType* with "artificial" flag set.
     DIType *createArtificialType(DIType *Ty);
 
Index: include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- include/llvm/IR/DebugInfoMetadata.h
+++ include/llvm/IR/DebugInfoMetadata.h
@@ -206,6 +206,7 @@
     case DIDerivedTypeKind:
     case DICompositeTypeKind:
     case DISubroutineTypeKind:
+    case DIExternalTypeRefKind:
     case DIFileKind:
     case DICompileUnitKind:
     case DISubprogramKind:
@@ -437,6 +438,7 @@
     case DIDerivedTypeKind:
     case DICompositeTypeKind:
     case DISubroutineTypeKind:
+    case DIExternalTypeRefKind:
     case DIFileKind:
     case DICompileUnitKind:
     case DISubprogramKind:
@@ -583,6 +585,7 @@
     case DIDerivedTypeKind:
     case DICompositeTypeKind:
     case DISubroutineTypeKind:
+    case DIExternalTypeRefKind:
       return true;
     }
   }
@@ -664,7 +667,8 @@
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == DIDerivedTypeKind ||
            MD->getMetadataID() == DICompositeTypeKind ||
-           MD->getMetadataID() == DISubroutineTypeKind;
+           MD->getMetadataID() == DISubroutineTypeKind ||
+           MD->getMetadataID() == DIExternalTypeRefKind;
   }
 };
 
@@ -762,7 +766,8 @@
   }
 };
 
-/// \brief Base class for DICompositeType and DISubroutineType.
+/// \brief Base class for DICompositeType, DISubroutineType
+///        and DIExternalTypeRef.
 ///
 /// TODO: Delete; they're not really related.
 class DICompositeTypeBase : public DIDerivedTypeBase {
@@ -825,7 +830,8 @@
 
   static bool classof(const Metadata *MD) {
     return MD->getMetadataID() == DICompositeTypeKind ||
-           MD->getMetadataID() == DISubroutineTypeKind;
+           MD->getMetadataID() == DISubroutineTypeKind ||
+           MD->getMetadataID() == DIExternalTypeRefKind;
   }
 };
 
@@ -962,6 +968,46 @@
   }
 };
 
+/// \brief External (module) type references.
+///
+/// TODO: Detach from CompositeType.
+class DIExternalTypeRef : public DICompositeTypeBase {
+  friend class LLVMContextImpl;
+  friend class MDNode;
+
+  DIExternalTypeRef(LLVMContext &C, StorageType Storage, unsigned Tag,
+                    ArrayRef<Metadata *> Ops)
+      : DICompositeTypeBase(C, DIExternalTypeRefKind, Storage, Tag, 0, 0, 0, 0,
+                            0, 0, Ops) {}
+  ~DIExternalTypeRef() {}
+
+  static DIExternalTypeRef *
+  getImpl(LLVMContext &Context, unsigned Tag, Metadata *File, StringRef Identifier,
+          StorageType Storage, bool ShouldCreate = true) {
+    return getImpl(Context, Tag, File, getCanonicalMDString(Context, Identifier),
+                   Storage, ShouldCreate);
+  }
+  static DIExternalTypeRef *
+  getImpl(LLVMContext &Context, unsigned Tag, Metadata *File, MDString *Identifier,
+          StorageType Storage, bool ShouldCreate = true);
+
+  TempDIExternalTypeRef cloneImpl() const {
+    return getTemporary(getContext(), getTag(), getFile(), getIdentifier());
+  }
+
+public:
+  DEFINE_MDNODE_GET(DIExternalTypeRef, (unsigned Tag, Metadata *File,
+                    StringRef Identifier), (Tag, File, Identifier))
+  DEFINE_MDNODE_GET(DIExternalTypeRef, (unsigned Tag, Metadata *File,
+                    MDString *Identifier), (Tag, File, Identifier))
+
+  TempDIExternalTypeRef clone() const { return cloneImpl(); }
+
+  static bool classof(const Metadata *MD) {
+    return MD->getMetadataID() == DIExternalTypeRefKind;
+  }
+};
+
 /// \brief Compile unit.
 class DICompileUnit : public DIScope {
   friend class LLVMContextImpl;
Index: include/llvm/IR/Metadata.h
===================================================================
--- include/llvm/IR/Metadata.h
+++ include/llvm/IR/Metadata.h
@@ -67,6 +67,7 @@
     DIDerivedTypeKind,
     DICompositeTypeKind,
     DISubroutineTypeKind,
+    DIExternalTypeRefKind,
     DIFileKind,
     DICompileUnitKind,
     DISubprogramKind,
Index: include/llvm/IR/Metadata.def
===================================================================
--- include/llvm/IR/Metadata.def
+++ include/llvm/IR/Metadata.def
@@ -74,6 +74,7 @@
 HANDLE_SPECIALIZED_MDNODE_BRANCH(DICompositeTypeBase)
 HANDLE_SPECIALIZED_MDNODE_LEAF(DICompositeType)
 HANDLE_SPECIALIZED_MDNODE_LEAF(DISubroutineType)
+HANDLE_SPECIALIZED_MDNODE_LEAF(DIExternalTypeRef)
 HANDLE_SPECIALIZED_MDNODE_LEAF(DIFile)
 HANDLE_SPECIALIZED_MDNODE_LEAF(DICompileUnit)
 HANDLE_SPECIALIZED_MDNODE_BRANCH(DILocalScope)
Index: lib/AsmParser/LLParser.cpp
===================================================================
--- lib/AsmParser/LLParser.cpp
+++ lib/AsmParser/LLParser.cpp
@@ -3529,6 +3529,21 @@
   return false;
 }
 
+/// ParseDIExternalTypeRef:
+///   ::= !DIExternalTypeRef(tag: DW_TAG_class_type, module: !1, identifier: "UUID")
+bool LLParser::ParseDIExternalTypeRef(MDNode *&Result, bool IsDistinct) {
+#define VISIT_MD_FIELDS(OPTIONAL, REQUIRED)                                    \
+  REQUIRED(tag, DwarfTagField, );                                              \
+  REQUIRED(file, MDField, );                                                   \
+  REQUIRED(identifier, MDStringField, );
+  PARSE_MD_FIELDS();
+#undef VISIT_MD_FIELDS
+
+  Result = GET_OR_DISTINCT(DIExternalTypeRef,
+                           (Context, tag.Val, file.Val, identifier.Val));
+  return false;
+}
+
 /// ParseDIFileType:
 ///   ::= !DIFileType(filename: "path/to/file", directory: "/path/to/dir")
 bool LLParser::ParseDIFile(MDNode *&Result, bool IsDistinct) {
Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1824,6 +1824,17 @@
           NextMDValueNo++);
       break;
     }
+    case bitc::METADATA_EXTERNAL_TYPE_REF: {
+      if (Record.size() != 4)
+        return Error("Invalid record");
+
+      MDValueList.AssignValue(
+          GET_OR_DISTINCT(DIExternalTypeRef, Record[0],
+                          (Context, Record[1], getMDOrNull(Record[2]),
+                                    getMDString(Record[3]))),
+          NextMDValueNo++);
+      break;
+    }
     case bitc::METADATA_FILE: {
       if (Record.size() != 3)
         return Error("Invalid record");
Index: lib/Bitcode/Writer/BitcodeWriter.cpp
===================================================================
--- lib/Bitcode/Writer/BitcodeWriter.cpp
+++ lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -919,6 +919,20 @@
   Record.clear();
 }
 
+static void WriteDIExternalTypeRef(const DIExternalTypeRef *N,
+                                   const ValueEnumerator &VE,
+                                   BitstreamWriter &Stream,
+                                   SmallVectorImpl<uint64_t> &Record,
+                                   unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawIdentifier()));
+
+  Stream.EmitRecord(bitc::METADATA_EXTERNAL_TYPE_REF, Record, Abbrev);
+  Record.clear();
+}
+
 static void WriteDIFile(const DIFile *N, const ValueEnumerator &VE,
                         BitstreamWriter &Stream,
                         SmallVectorImpl<uint64_t> &Record, unsigned Abbrev) {
Index: lib/IR/AsmWriter.cpp
===================================================================
--- lib/IR/AsmWriter.cpp
+++ lib/IR/AsmWriter.cpp
@@ -1591,6 +1591,18 @@
   Out << ")";
 }
 
+static void writeDIExternalTypeRef(raw_ostream &Out,
+                                   const DIExternalTypeRef *N,
+                                   TypePrinting *TypePrinter,
+                                   SlotTracker *Machine, const Module *Context) {
+  Out << "!DIExternalTypeRef(";
+  MDFieldPrinter Printer(Out, TypePrinter, Machine, Context);
+  Printer.printTag(N);
+  Printer.printMetadata("file", N->getFile());
+  Printer.printString("identifier", N->getIdentifier());
+  Out << ")";
+}
+
 static void writeDIFile(raw_ostream &Out, const DIFile *N, TypePrinting *,
                         SlotTracker *, const Module *) {
   Out << "!DIFile(";
Index: lib/IR/DIBuilder.cpp
===================================================================
--- lib/IR/DIBuilder.cpp
+++ lib/IR/DIBuilder.cpp
@@ -425,6 +425,11 @@
   return DISubroutineType::get(VMContext, Flags, ParameterTypes);
 }
 
+DIExternalTypeRef *DIBuilder::createExternalTypeRef(unsigned Tag, DIFile *File,
+                                                    StringRef Identifier) {
+ return DIExternalTypeRef::get(VMContext, Tag, File, Identifier);
+}
+
 DICompositeType *DIBuilder::createEnumerationType(
     DIScope *Scope, StringRef Name, DIFile *File, unsigned LineNumber,
     uint64_t SizeInBits, uint64_t AlignInBits, DINodeArray Elements,
Index: lib/IR/DebugInfoMetadata.cpp
===================================================================
--- lib/IR/DebugInfoMetadata.cpp
+++ lib/IR/DebugInfoMetadata.cpp
@@ -295,6 +295,18 @@
   DEFINE_GETIMPL_STORE(DISubroutineType, (Flags), Ops);
 }
 
+DIExternalTypeRef *DIExternalTypeRef::getImpl(LLVMContext &Context,
+                                              unsigned Tag,
+                                              Metadata *File,
+                                              MDString *Identifier,
+                                              StorageType Storage,
+                                              bool ShouldCreate) {
+  DEFINE_GETIMPL_LOOKUP(DIExternalTypeRef, (Tag, File, getString(Identifier)));
+  Metadata *Ops[] = {File,    nullptr, nullptr, nullptr,
+                     nullptr, nullptr, nullptr, Identifier};
+  DEFINE_GETIMPL_STORE(DIExternalTypeRef, (Tag), Ops);
+}
+
 DIFile *DIFile::getImpl(LLVMContext &Context, MDString *Filename,
                         MDString *Directory, StorageType Storage,
                         bool ShouldCreate) {
Index: lib/IR/LLVMContextImpl.h
===================================================================
--- lib/IR/LLVMContextImpl.h
+++ lib/IR/LLVMContextImpl.h
@@ -443,6 +443,24 @@
   unsigned getHashValue() const { return hash_combine(Flags, TypeArray); }
 };
 
+template <> struct MDNodeKeyImpl<DIExternalTypeRef> {
+  unsigned Tag;
+  Metadata *File;
+  StringRef Identifier;
+
+  MDNodeKeyImpl(unsigned Tag, Metadata *File, StringRef Identifier)
+      : Tag(Tag), File(File), Identifier(Identifier) {}
+  MDNodeKeyImpl(const DIExternalTypeRef *N)
+      : Tag(N->getTag()), File(N->getRawFile()),
+        Identifier(N->getIdentifier()) {}
+
+  bool isKeyOf(const DIExternalTypeRef *RHS) const {
+    return Tag == RHS->getTag() && File == RHS->getRawFile() &&
+           Identifier == RHS->getIdentifier();
+  }
+  unsigned getHashValue() const { return hash_combine(Tag, File, Identifier); }
+};
+
 template <> struct MDNodeKeyImpl<DIFile> {
   StringRef Filename;
   StringRef Directory;
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -880,6 +880,10 @@
          &N);
 }
 
+void Verifier::visitDIExternalTypeRef(const DIExternalTypeRef &N) {
+  Assert(!N.getIdentifier().empty(), "invalid identifier", &N);
+}
+
 void Verifier::visitDIFile(const DIFile &N) {
   Assert(N.getTag() == dwarf::DW_TAG_file_type, "invalid tag", &N);
 }
Index: test/Assembler/DIExternalTypeRef.ll
===================================================================
--- /dev/null
+++ test/Assembler/DIExternalTypeRef.ll
@@ -0,0 +1,11 @@
+; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
+; RUN: verify-uselistorder %s
+
+; CHECK: !named = !{!0, !1}
+!named = !{!0, !1}
+
+!0 = !DIFile(filename: "foo", directory: "/dir")
+
+; CHECK: !1 = !DIExternalTypeRef(tag: DW_TAG_structure_type, file: !0, identifier: "c:objc(cs)Foo")
+!1 = !DIExternalTypeRef(tag: DW_TAG_structure_type, file: !0, identifier: "c:objc(cs)Foo")
+