Index: llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
+++ llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -801,15 +801,35 @@
   }
 }
 
+// Determines if the specified tag declaration requires a unique identifier.
+static bool needsUniqueTagTypeName(const TagDecl *TD,
+                                   CodeGenModule& CGM,
+                                   llvm::DICompileUnit *TheCU) {
+  // We are only adding unique names if they have C++ mangling.
+  if (!hasCXXMangling(TD, TheCU))
+    return false;
+
+  // CodeView types with C++ mangling need unique identifiers.
+  if (CGM.getCodeGenOpts().EmitCodeView)
+    return true;
+
+  // Externally visible types with C++ mangling need unique identifiers.
+  if (TD->isExternallyVisible())
+    return true;
+
+  return false;
+}
+
 /// In C++ mode, types have linkage, so we can rely on the ODR and
-/// on their mangled names, if they're external.
+/// on their mangled names, if they're external or when emitting a C++
+/// record using CodeView.
 static SmallString<256> getUniqueTagTypeName(const TagType *Ty,
                                              CodeGenModule &CGM,
                                              llvm::DICompileUnit *TheCU) {
   SmallString<256> FullName;
   const TagDecl *TD = Ty->getDecl();
 
-  if (!hasCXXMangling(TD, TheCU) || !TD->isExternallyVisible())
+  if (!needsUniqueTagTypeName(TD, CGM, TheCU))
     return FullName;
 
   // TODO: This is using the RTTI name. Is there a better way to get
Index: llvm/tools/clang/test/CodeGen/debug-info-codeview-unnamed.c
===================================================================
--- llvm/tools/clang/test/CodeGen/debug-info-codeview-unnamed.c
+++ llvm/tools/clang/test/CodeGen/debug-info-codeview-unnamed.c
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -debug-info-kind=limited -S -emit-llvm -o - %s | FileCheck --check-prefix LINUX %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -debug-info-kind=limited -gcodeview -S -emit-llvm -o - %s | FileCheck --check-prefix MSVC %s
+
+int main(int argc, char* argv[], char* arge[]) {
+
+  // In both DWARF and CodeView, an unnamed C structure type will generate a
+  // DICompositeType without a name or identifier attribute;
+  //
+  struct { int bar; } one = {42};
+  //
+  // LINUX:      !{{[0-9]+}} = !DILocalVariable(name: "one"
+  // LINUX-SAME:     type: [[TYPE_OF_ONE:![0-9]+]]
+  // LINUX-SAME:     )
+  // LINUX:      [[TYPE_OF_ONE]] = distinct !DICompositeType(
+  // LINUX-SAME:     tag: DW_TAG_structure_type
+  // LINUX-NOT:      name:
+  // LINUX-NOT:      identifier:
+  // LINUX-SAME:     )
+  //
+  // MSVC:       !{{[0-9]+}} = !DILocalVariable(name: "one"
+  // MSVC-SAME:      type: [[TYPE_OF_ONE:![0-9]+]]
+  // MSVC-SAME:      )
+  // MSVC:       [[TYPE_OF_ONE]] = distinct !DICompositeType
+  // MSVC-SAME:      tag: DW_TAG_structure_type
+  // MSVC-NOT:       name:
+  // MSVC-NOT:       identifier:
+  // MSVC-SAME:      )
+
+  return 0;
+}
Index: llvm/tools/clang/test/CodeGenCXX/debug-info-codeview-unnamed.cpp
===================================================================
--- llvm/tools/clang/test/CodeGenCXX/debug-info-codeview-unnamed.cpp
+++ llvm/tools/clang/test/CodeGenCXX/debug-info-codeview-unnamed.cpp
@@ -0,0 +1,108 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -debug-info-kind=limited -S -emit-llvm -std=c++11 -o - %s | FileCheck --check-prefix LINUX %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -debug-info-kind=limited -gcodeview -S -emit-llvm -std=c++11 -o - %s | FileCheck --check-prefix MSVC %s
+
+int main(int argc, char* argv[], char* arge[]) {
+  //
+  // In CodeView, the LF_MFUNCTION entry for "bar()" refers to the forward
+  // reference of the unnamed struct. Visual Studio requires a unique
+  // identifier to match the LF_STRUCTURE forward reference to the definition.
+  //
+  struct { void bar() {} } one;
+  //
+  // LINUX:      !{{[0-9]+}} = !DILocalVariable(name: "one"
+  // LINUX-SAME:     type: [[TYPE_OF_ONE:![0-9]+]]
+  // LINUX-SAME:     )
+  // LINUX:      [[TYPE_OF_ONE]] = distinct !DICompositeType(
+  // LINUX-SAME:     tag: DW_TAG_structure_type
+  // LINUX-NOT:      name:
+  // LINUX-NOT:      identifier:
+  // LINUX-SAME:     )
+  //
+  // MSVC:       !{{[0-9]+}} = !DILocalVariable(name: "one"
+  // MSVC-SAME:      type: [[TYPE_OF_ONE:![0-9]+]]
+  // MSVC-SAME:      )
+  // MSVC:       [[TYPE_OF_ONE]] = distinct !DICompositeType
+  // MSVC-SAME:      tag: DW_TAG_structure_type
+  // MSVC-SAME:      name: "<unnamed-type-one>"
+  // MSVC-SAME:      identifier: ".?AU<unnamed-type-one>@?1??main@@9@"
+  // MSVC-SAME:      )
+
+
+  // In CodeView, the LF_POINTER entry for "ptr2unnamed" refers to the forward
+  // reference of the unnamed struct. Visual Studio requires a unique
+  // identifier to match the LF_STRUCTURE forward reference to the definition.
+  //
+  struct { int bar; } two = { 42 };
+  int decltype(two)::*ptr2unnamed = &decltype(two)::bar;
+  //
+  // LINUX:      !{{[0-9]+}} = !DILocalVariable(name: "two"
+  // LINUX-SAME:     type: [[TYPE_OF_TWO:![0-9]+]]
+  // LINUX-SAME:     )
+  // LINUX:      [[TYPE_OF_TWO]] = distinct !DICompositeType(
+  // LINUX-SAME:     tag: DW_TAG_structure_type
+  // LINUX-NOT:      name:
+  // LINUX-NOT:      identifier:
+  // LINUX-SAME:     )
+  //
+  // MSVC:       !{{[0-9]+}} = !DILocalVariable(name: "two"
+  // MSVC-SAME:      type: [[TYPE_OF_TWO:![0-9]+]]
+  // MSVC-SAME:      )
+  // MSVC:       [[TYPE_OF_TWO]] = distinct !DICompositeType
+  // MSVC-SAME:      tag: DW_TAG_structure_type
+  // MSVC-SAME:      name: "<unnamed-type-two>"
+  // MSVC-SAME:      identifier: ".?AU<unnamed-type-two>@?2??main@@9@"
+  // MSVC-SAME:      )
+
+
+  // In DWARF, named structures which are not externally visibile do not
+  // require an identifier.  In CodeView, named structures are given an
+  // identifier.
+  //
+  struct named { int bar; int named::* p2mem; } three = { 42, &named::bar };
+  //
+  // LINUX:      !{{[0-9]+}} = !DILocalVariable(name: "three"
+  // LINUX-SAME:     type: [[TYPE_OF_THREE:![0-9]+]]
+  // LINUX-SAME:     )
+  // LINUX:      [[TYPE_OF_THREE]] = distinct !DICompositeType(
+  // LINUX-SAME:     tag: DW_TAG_structure_type
+  // LINUX-SAME:     name: "named"
+  // LINUX-NOT:      identifier:
+  // LINUX-SAME:     )
+  //
+  // MSVC:       !{{[0-9]+}} = !DILocalVariable(name: "three"
+  // MSVC-SAME:      type: [[TYPE_OF_THREE:![0-9]+]]
+  // MSVC-SAME:      )
+  // MSVC:       [[TYPE_OF_THREE]] = distinct !DICompositeType
+  // MSVC-SAME:      tag: DW_TAG_structure_type
+  // MSVC-SAME:      name: "named"
+  // MSVC-SAME:      identifier: ".?AUnamed@?1??main@@9@"
+  // MSVC-SAME:      )
+
+
+  // In CodeView, the LF_MFUNCTION entry for the lambda "operator()" routine
+  // refers to the forward reference of the unnamed LF_CLASS for the lambda.
+  // Visual Studio requires a unique identifier to match the forward reference
+  // of the LF_CLASS to its definition.
+  //
+  auto four = [argc](int i) -> int { return argc == i ? 1 : 0; };
+  //
+  // LINUX:      !{{[0-9]+}} = !DILocalVariable(name: "four"
+  // LINUX-SAME:     type: [[TYPE_OF_FOUR:![0-9]+]]
+  // LINUX-SAME:     )
+  // LINUX:      [[TYPE_OF_FOUR]] = distinct !DICompositeType(
+  // LINUX-SAME:     tag: DW_TAG_class_type
+  // LINUX-NOT:      name:
+  // LINUX-NOT:      identifier:
+  // LINUX-SAME:     )
+  //
+  // MSVC:       !{{[0-9]+}} = !DILocalVariable(name: "four"
+  // MSVC-SAME:      type: [[TYPE_OF_FOUR:![0-9]+]]
+  // MSVC-SAME:      )
+  // MSVC:       [[TYPE_OF_FOUR]] = distinct !DICompositeType
+  // MSVC-SAME:      tag: DW_TAG_class_type
+  // MSVC-NOT:       name:
+  // MSVC-SAME:      identifier: ".?AV<lambda_0>@?0??main@@9@"
+  // MSVC-SAME:      )
+
+  return 0;
+}