diff --git a/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 51a5d06b954..52165773012 100644
--- a/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -994,20 +994,25 @@ TypeIndex CodeViewDebug::lowerTypeArray(const DICompositeType *Ty) {
 
   uint64_t ElementSize = getBaseTypeSize(ElementTypeRef) / 8;
 
-  bool UndefinedSubrange = false;
 
-  // FIXME:
-  // There is a bug in the front-end where an array of a structure, which was
-  // declared as incomplete structure first, ends up not getting a size assigned
-  // to it. (PR28303)
+  // We want to assert that the element type multiplied by the array lengths
+  // match the size of the overall array. However, if we don't have complete
+  // type information for the base type, we can't make this assertion. This
+  // happens if limited debug info is enabled in this case:
+  //   struct VTableOptzn { VTableOptzn(); virtual ~VTableOptzn(); };
+  //   VTableOptzn array[3];
+  // The DICompositeType of VTableOptzn will have size zero, and the array will
+  // have size 3 * sizeof(void*), and we should avoid asserting.
+  //
+  // There is a related bug in the front-end where an array of a structure,
+  // which was declared as incomplete structure first, ends up not getting a
+  // size assigned to it. (PR28303)
   // Example:
   //   struct A(*p)[3];
   //   struct A { int f; } a[3];
-  //
-  // This needs to be fixed in the front-end, but in the meantime we don't want
-  // to trigger an assertion because of this.
-  if (Ty->getSizeInBits() == 0) {
-    UndefinedSubrange = true;
+  bool PartiallyIncomplete = false;
+  if (Ty->getSizeInBits() == 0 || ElementSize == 0) {
+    PartiallyIncomplete = true;
   }
 
   // Add subranges to array type.
@@ -1026,18 +1031,24 @@ TypeIndex CodeViewDebug::lowerTypeArray(const DICompositeType *Ty) {
     // FIXME: Make front-end support VLA subrange and emit LF_DIMVARLU.
     if (Count == -1) {
       Count = 1;
-      UndefinedSubrange = true;
+      PartiallyIncomplete = true;
     }
 
-    StringRef Name = (i == 0) ? Ty->getName() : "";
     // Update the element size and element type index for subsequent subranges.
     ElementSize *= Count;
+
+    // If this is the outermost array, use the size from the array. It will be
+    // more accurate if PartiallyIncomplete is true.
+    uint64_t ArraySize =
+        (i == 0 && ElementSize == 0) ? Ty->getSizeInBits() / 8 : ElementSize;
+
+    StringRef Name = (i == 0) ? Ty->getName() : "";
     ElementTypeIndex = TypeTable.writeKnownType(
-        ArrayRecord(ElementTypeIndex, IndexType, ElementSize, Name));
+        ArrayRecord(ElementTypeIndex, IndexType, ArraySize, Name));
   }
 
-  (void)UndefinedSubrange;
-  assert(UndefinedSubrange || ElementSize == (Ty->getSizeInBits() / 8));
+  (void)PartiallyIncomplete;
+  assert(PartiallyIncomplete || ElementSize == (Ty->getSizeInBits() / 8));
 
   return ElementTypeIndex;
 }
diff --git a/test/DebugInfo/COFF/vtable-optzn-array.ll b/test/DebugInfo/COFF/vtable-optzn-array.ll
new file mode 100644
index 00000000000..7503e7294b9
--- /dev/null
+++ b/test/DebugInfo/COFF/vtable-optzn-array.ll
@@ -0,0 +1,140 @@
+; RUN: llc < %s -filetype=obj -o - | llvm-readobj - -codeview | FileCheck %s
+
+; We used to crash on this input because UnicodeString is a forward declaration
+; with no size. Our array type logic wanted to assert the size of the elements
+; times the length matched the overall size.
+
+; C++ source to regenerate:
+; struct UnicodeString;
+; struct GetFwdDecl {
+;   static UnicodeString format;
+; };
+; GetFwdDecl force_fwd_decl;
+; struct UnicodeString {
+; private:
+;   virtual ~UnicodeString();
+; };
+; struct UseCompleteType {
+;   UseCompleteType();
+;   ~UseCompleteType();
+;   UnicodeString currencySpcAfterSym[1];
+; };
+; UseCompleteType require_complete;
+
+; CHECK:      Array ({{.*}}) {
+; CHECK-NEXT:   TypeLeafKind: LF_ARRAY (0x1503)
+; CHECK-NEXT:   ElementType: UnicodeString
+; CHECK-NEXT:   IndexType: unsigned __int64 (0x23)
+; CHECK-NEXT:   SizeOf: 8
+; CHECK-NEXT:   Name:
+; CHECK-NEXT: }
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+%struct.GetFwdDecl = type { i8 }
+%struct.UseCompleteType = type { [1 x %struct.UnicodeString] }
+%struct.UnicodeString = type { i32 (...)** }
+
+$"\01??_DUseCompleteType@@QEAA@XZ" = comdat any
+
+@"\01?force_fwd_decl@@3UGetFwdDecl@@A" = global %struct.GetFwdDecl zeroinitializer, align 1
+@"\01?require_complete@@3UUseCompleteType@@A" = global %struct.UseCompleteType zeroinitializer, align 8
+@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_t.cpp, i8* null }]
+
+; Function Attrs: nounwind
+define internal void @"\01??__Erequire_complete@@YAXXZ"() #0 !dbg !25 {
+entry:
+  %call = call %struct.UseCompleteType* @"\01??0UseCompleteType@@QEAA@XZ"(%struct.UseCompleteType* @"\01?require_complete@@3UUseCompleteType@@A"), !dbg !28
+  %0 = call i32 @atexit(void ()* @"\01??__Frequire_complete@@YAXXZ") #2, !dbg !28
+  ret void, !dbg !28
+}
+
+declare %struct.UseCompleteType* @"\01??0UseCompleteType@@QEAA@XZ"(%struct.UseCompleteType* returned) unnamed_addr #1
+
+; Function Attrs: nounwind
+define linkonce_odr void @"\01??_DUseCompleteType@@QEAA@XZ"(%struct.UseCompleteType* %this) unnamed_addr #0 comdat align 2 !dbg !29 {
+entry:
+  %this.addr = alloca %struct.UseCompleteType*, align 8
+  store %struct.UseCompleteType* %this, %struct.UseCompleteType** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %struct.UseCompleteType** %this.addr, metadata !30, metadata !32), !dbg !33
+  %this1 = load %struct.UseCompleteType*, %struct.UseCompleteType** %this.addr, align 8
+  call void @"\01??1UseCompleteType@@QEAA@XZ"(%struct.UseCompleteType* %this1), !dbg !34
+  ret void, !dbg !34
+}
+
+; Function Attrs: nounwind
+define internal void @"\01??__Frequire_complete@@YAXXZ"() #0 !dbg !35 {
+entry:
+  call void @"\01??_DUseCompleteType@@QEAA@XZ"(%struct.UseCompleteType* @"\01?require_complete@@3UUseCompleteType@@A"), !dbg !36
+  ret void, !dbg !37
+}
+
+; Function Attrs: nounwind
+declare i32 @atexit(void ()*) #2
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #3
+
+declare void @"\01??1UseCompleteType@@QEAA@XZ"(%struct.UseCompleteType*) unnamed_addr #1
+
+; Function Attrs: nounwind
+define internal void @_GLOBAL__sub_I_t.cpp() #0 !dbg !39 {
+entry:
+  call void @"\01??__Erequire_complete@@YAXXZ"(), !dbg !41
+  ret void
+}
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-features"="+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!22, !23}
+!llvm.ident = !{!24}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 4.0.0 (trunk 281056) (llvm/trunk 281051)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3)
+!1 = !DIFile(filename: "<stdin>", directory: "C:\5Csrc\5Cllvm\5Cbuild")
+!2 = !{}
+!3 = !{!4, !10}
+!4 = distinct !DIGlobalVariable(name: "force_fwd_decl", linkageName: "\01?force_fwd_decl@@3UGetFwdDecl@@A", scope: !0, file: !5, line: 5, type: !6, isLocal: false, isDefinition: true, variable: %struct.GetFwdDecl* @"\01?force_fwd_decl@@3UGetFwdDecl@@A")
+!5 = !DIFile(filename: "t.cpp", directory: "C:\5Csrc\5Cllvm\5Cbuild")
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "GetFwdDecl", file: !5, line: 2, size: 8, align: 8, elements: !7, identifier: ".?AUGetFwdDecl@@")
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "format", scope: !6, file: !5, line: 3, baseType: !9, flags: DIFlagStaticMember)
+!9 = !DICompositeType(tag: DW_TAG_structure_type, name: "UnicodeString", file: !5, line: 1, flags: DIFlagFwdDecl, identifier: ".?AUUnicodeString@@")
+!10 = distinct !DIGlobalVariable(name: "require_complete", linkageName: "\01?require_complete@@3UUseCompleteType@@A", scope: !0, file: !5, line: 15, type: !11, isLocal: false, isDefinition: true, variable: %struct.UseCompleteType* @"\01?require_complete@@3UUseCompleteType@@A")
+!11 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "UseCompleteType", file: !5, line: 10, size: 64, align: 64, elements: !12, identifier: ".?AUUseCompleteType@@")
+!12 = !{!13, !17, !21}
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "currencySpcAfterSym", scope: !11, file: !5, line: 13, baseType: !14, size: 64, align: 64)
+!14 = !DICompositeType(tag: DW_TAG_array_type, baseType: !9, size: 64, align: 64, elements: !15)
+!15 = !{!16}
+!16 = !DISubrange(count: 1)
+!17 = !DISubprogram(name: "UseCompleteType", scope: !11, file: !5, line: 11, type: !18, isLocal: false, isDefinition: false, scopeLine: 11, flags: DIFlagPrototyped, isOptimized: false)
+!18 = !DISubroutineType(types: !19)
+!19 = !{null, !20}
+!20 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64, align: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!21 = !DISubprogram(name: "~UseCompleteType", scope: !11, file: !5, line: 12, type: !18, isLocal: false, isDefinition: false, scopeLine: 12, flags: DIFlagPrototyped, isOptimized: false)
+!22 = !{i32 2, !"CodeView", i32 1}
+!23 = !{i32 2, !"Debug Info Version", i32 3}
+!24 = !{!"clang version 4.0.0 (trunk 281056) (llvm/trunk 281051)"}
+!25 = distinct !DISubprogram(name: "??__Erequire_complete@@YAXXZ", scope: !5, file: !5, line: 15, type: !26, isLocal: true, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!26 = !DISubroutineType(types: !27)
+!27 = !{null}
+!28 = !DILocation(line: 15, scope: !25)
+!29 = distinct !DISubprogram(name: "~UseCompleteType", linkageName: "\01??_DUseCompleteType@@QEAA@XZ", scope: !11, file: !5, line: 12, type: !18, isLocal: false, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !21, variables: !2)
+!30 = !DILocalVariable(name: "this", arg: 1, scope: !29, type: !31, flags: DIFlagArtificial | DIFlagObjectPointer)
+!31 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64, align: 64)
+!32 = !DIExpression()
+!33 = !DILocation(line: 0, scope: !29)
+!34 = !DILocation(line: 15, scope: !29)
+!35 = distinct !DISubprogram(name: "??__Frequire_complete@@YAXXZ", scope: !1, file: !1, line: 15, type: !26, isLocal: true, isDefinition: true, scopeLine: 15, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!36 = !DILocation(line: 15, scope: !35)
+!37 = !DILocation(line: 15, scope: !38)
+!38 = !DILexicalBlockFile(scope: !35, file: !5, discriminator: 0)
+!39 = distinct !DISubprogram(linkageName: "_GLOBAL__sub_I_t.cpp", scope: !1, file: !1, type: !40, isLocal: true, isDefinition: true, flags: DIFlagArtificial, isOptimized: false, unit: !0, variables: !2)
+!40 = !DISubroutineType(types: !2)
+!41 = !DILocation(line: 0, scope: !39)