diff --git a/lib/IRGen/IRGenDebugInfo.cpp b/lib/IRGen/IRGenDebugInfo.cpp
index e8b4f279d1cd7..31a76cd6d4f14 100644
--- a/lib/IRGen/IRGenDebugInfo.cpp
+++ b/lib/IRGen/IRGenDebugInfo.cpp
@@ -729,6 +729,16 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
     if (!DC)
       return TheCU;
 
+    auto createContext = [&](NominalTypeDecl &NTD) {
+      GenericContextScope scope(
+          IGM, NTD.getGenericSignature().getCanonicalSignature());
+
+      auto Ty = NTD.getDeclaredInterfaceType();
+      // Create a Forward-declared type.
+      auto DbgTy = DebugTypeInfo::getForwardDecl(Ty);
+      return getOrCreateType(DbgTy);
+    };
+
     if (isa<FuncDecl>(DC))
       if (auto *Decl = IGM.getSILModule().lookUpFunction(SILDeclRef(
               cast<AbstractFunctionDecl>(DC), SILDeclRef::Kind::Func)))
@@ -742,7 +752,6 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
 
     // We don't model these in DWARF.
     case DeclContextKind::Initializer:
-    case DeclContextKind::ExtensionDecl:
     case DeclContextKind::SubscriptDecl:
     case DeclContextKind::EnumElementDecl:
     case DeclContextKind::TopLevelCodeDecl:
@@ -761,16 +770,17 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
       return getOrCreateContext(DC->getParent());
     case DeclContextKind::MacroDecl:
       return getOrCreateContext(DC->getParent());
+    case DeclContextKind::ExtensionDecl: {
+      auto *ED = cast<ExtensionDecl>(DC);
+      if (auto *NTD = ED->getExtendedNominal())
+        return createContext(*NTD);
+      return getOrCreateContext(DC->getParent());
+    }
     case DeclContextKind::GenericTypeDecl: {
-      // The generic signature of this nominal type has no relation to the current
-      // function's generic signature.
+      // The generic signature of this nominal type has no relation to the
+      // current function's generic signature.
       auto *NTD = cast<NominalTypeDecl>(DC);
-      GenericContextScope scope(IGM, NTD->getGenericSignature().getCanonicalSignature());
-
-      auto Ty = NTD->getDeclaredInterfaceType();
-      // Create a Forward-declared type.
-      auto DbgTy = DebugTypeInfo::getForwardDecl(Ty);
-      return getOrCreateType(DbgTy);
+      return createContext(*NTD);
     }
     }
     return TheCU;
@@ -2684,8 +2694,9 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
       // declarations may not have a unique ID to avoid a forward declaration
       // winning over a full definition.
       auto *FwdDecl = DBuilder.createReplaceableCompositeType(
-          llvm::dwarf::DW_TAG_structure_type, MangledName, Scope, 0, 0,
-          llvm::dwarf::DW_LANG_Swift);
+          llvm::dwarf::DW_TAG_structure_type, Name, Scope, 0, 0,
+          llvm::dwarf::DW_LANG_Swift, 0, 0, llvm::DINode::FlagFwdDecl,
+          MangledName);
       FwdDeclTypes.emplace_back(
           std::piecewise_construct, std::make_tuple(MangledName),
           std::make_tuple(static_cast<llvm::Metadata *>(FwdDecl)));
diff --git a/test/DebugInfo/BoundGenericStruct.swift b/test/DebugInfo/BoundGenericStruct.swift
index a8aa816e80c86..f324cdc003c4f 100644
--- a/test/DebugInfo/BoundGenericStruct.swift
+++ b/test/DebugInfo/BoundGenericStruct.swift
@@ -31,12 +31,11 @@ public let inner = S2<Double>.Inner(t:4.2)
 
 // CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "Inner", 
 // CHECK-SAME: size: 64, {{.*}}identifier: "$s18BoundGenericStruct2S2V5InnerVySd_GD")
-// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "$s18BoundGenericStruct2S2VyxGD", 
-// CHECK-SAME: flags: DIFlagFwdDecl, runtimeLang: DW_LANG_Swift)
+// CHECK: !DICompositeType(tag: DW_TAG_structure_type, {{.*}}flags: DIFlagFwdDecl, runtimeLang: DW_LANG_Swift, {{.*}}identifier: "$s18BoundGenericStruct2S2VyxGD"
 
 // DWARF-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "$s18BoundGenericStruct2S2V5InnerVySd_GD", scope: ![[SCOPE1:[0-9]+]], {{.*}}flags: DIFlagFwdDecl, runtimeLang: DW_LANG_Swift, templateParams: ![[PARAMS2:[0-9]+]])
 
-// DWARF-DAG: ![[SCOPE1]] = !DICompositeType(tag: DW_TAG_structure_type, name: "$s18BoundGenericStruct2S2VyxGD", 
+// DWARF-DAG: ![[SCOPE1]] = !DICompositeType(tag: DW_TAG_structure_type, {{.*}}identifier: "$s18BoundGenericStruct2S2VyxGD"
 
 // DWARF-DAG: ![[PARAMS2]] = !{![[PARAMS3:[0-9]+]]}
 // DWARF-DAG: ![[PARAMS3]] = !DITemplateTypeParameter(type: ![[PARAMS4:[0-9]+]])
diff --git a/test/DebugInfo/Errors.swift b/test/DebugInfo/Errors.swift
index 41f5b31e732ac..9dc1f3b715d67 100644
--- a/test/DebugInfo/Errors.swift
+++ b/test/DebugInfo/Errors.swift
@@ -3,7 +3,7 @@ public enum E : Error { case Err }
 
 // Function throws.
 public func throwError() throws { throw E.Err }
-// CHECK: !DISubprogram(name: "throwError", {{.*}}thrownTypes: ![[THROWN:.*]])
+// CHECK-DAG: !DISubprogram(name: "throwError", {{.*}}thrownTypes: ![[THROWN:.*]])
 // CHECK-DAG: ![[THROWN]] = !{![[ERROR:[0-9]+]]}
 // CHECK-DAG: ![[ERROR]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Error"
 
diff --git a/test/DebugInfo/NestedTypes.swift b/test/DebugInfo/NestedTypes.swift
index eb4c82a85394e..b2b7857aa9169 100644
--- a/test/DebugInfo/NestedTypes.swift
+++ b/test/DebugInfo/NestedTypes.swift
@@ -16,3 +16,27 @@ public let e : Enum = .WithClass(C())
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "WithStruct",
 // CHECK-SAME:           size: 128)
 
+public struct D<U> {
+  var v : V
+  let u: U
+}
+
+extension D {
+  struct V {
+    internal var obj: Int
+  }
+}
+
+public let d = D<Int>(v: D.V(obj: 1), u: 2)
+
+// CHECK: ![[D:.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "D"
+// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "V", scope: ![[D]],
+
+public struct Unused {
+  public struct W {}
+}
+
+public let w = Unused.W()
+
+// CHECK-DAG: ![[Unused:.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Unused"
+// CHECK-DAG: !DICompositeType(tag: DW_TAG_structure_type, name: "W", scope: ![[Unused]],
diff --git a/test/DebugInfo/generic_arg4.swift b/test/DebugInfo/generic_arg4.swift
index fb3dcefd16e69..36acf634362b9 100644
--- a/test/DebugInfo/generic_arg4.swift
+++ b/test/DebugInfo/generic_arg4.swift
@@ -9,7 +9,7 @@ public struct Q<T> {
 // CHECK-SAME:       ![[ARG:.*]], !DIExpression()
 // CHECK: store ptr %0, ptr %[[ALLOCA]], align
 // No deref here: the array argument is passed by value.
-// CHECK: ![[DITY:.*]] = !DICompositeType({{.*}}name: "$sSay12generic_arg41QVyxGGD"
+// CHECK: ![[DITY:.*]] = !DICompositeType({{.*}}identifier: "$sSay12generic_arg41QVyxGGD"
 public func foo<T>(_ arg: [Q<T>]) {
 // CHECK: ![[ARG]] = !DILocalVariable(name: "arg", arg: 1,
 // CHECK-SAME:                        line: [[@LINE-2]], type: ![[DITY:.*]])
diff --git a/test/DebugInfo/generic_arg5.swift b/test/DebugInfo/generic_arg5.swift
index ded6a3c3ae7bb..7f9a5efb194d0 100644
--- a/test/DebugInfo/generic_arg5.swift
+++ b/test/DebugInfo/generic_arg5.swift
@@ -12,7 +12,7 @@ public func foo<Type>(_ values : [S<Type>])
   // CHECK-SAME:       ![[ARG:[0-9]+]],
   // CHECK-SAME:       !DIExpression(DW_OP_deref)
   // CHECK: store ptr %1, ptr %[[ALLOCA]], align
-  // CHECK-DAG: ![[TYP:[0-9]+]] = !DICompositeType({{.*}}, name: "$s12generic_arg51SVyxGD"
+  // CHECK-DAG: ![[TYP:[0-9]+]] = !DICompositeType({{.*}}, identifier: "$s12generic_arg51SVyxGD"
   // The argument is a by-ref struct and thus needs to be dereferenced.
   // CHECK-DAG: ![[ARG]] = !DILocalVariable(name: "arg", arg: 1,{{.*}}line: [[@LINE+6]],{{.*}} type: ![[LET_TYP:[0-9]+]])
   // CHECK-DAG: ![[LET_TYP]] = !DIDerivedType(tag: DW_TAG_const_type,{{.*}} baseType: ![[TYP_CONTAINER:[0-9]+]])
diff --git a/test/DebugInfo/struct_resilience.swift b/test/DebugInfo/struct_resilience.swift
index cb61989359983..34a28a4c11e51 100644
--- a/test/DebugInfo/struct_resilience.swift
+++ b/test/DebugInfo/struct_resilience.swift
@@ -29,7 +29,7 @@ public func f() {
   // CHECK: store ptr %[[S1]], ptr %[[ADDR]]
 }
 
-// CHECK: ![[TY:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "$s16resilient_struct4SizeVD",
+// CHECK: ![[TY:[0-9]+]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Size",
 // CHECK: ![[LET_TY:[0-9]+]] = !DIDerivedType(tag: DW_TAG_const_type,
 // CHECK-SAME:                                baseType: ![[TY:[0-9]+]])
 // CHECK: ![[V1]] = !DILocalVariable(name: "s1", {{.*}}type: ![[LET_TY]])
diff --git a/test/DebugInfo/typealias.swift b/test/DebugInfo/typealias.swift
index 993cf2fa14e76..7942c96cbd20f 100644
--- a/test/DebugInfo/typealias.swift
+++ b/test/DebugInfo/typealias.swift
@@ -120,10 +120,11 @@ public protocol Down {
 }
 
 public typealias DependentAlias<T : Up> = T.A.A
+// CHECK-DAG: ![[DEPENDENTALIAS:.*]] = !DIDerivedType(tag: DW_TAG_typedef, name: "DependentAlias", {{.*}} baseType: ![[INTTYPE]])
 
 extension Up where A.A == Int {
   public func foo() {
-    // CHECK-DAG: !DILocalVariable(name: "gg",{{.*}} type: ![[INTTYPE]]
+    // CHECK-DAG: !DILocalVariable(name: "gg",{{.*}} type: ![[DEPENDENTALIAS]]
     var gg: DependentAlias<Self> = 123
   }
 }