[Runtime] Add nominal type descriptor field to foreign class metadata.

Like other nominal type metadata, include a nominal type descriptor in
foreign class metadata.

Author: DougGregor

docs/ABI/TypeMetadata.rst

@@ -273,6 +273,19 @@ parameter vector contains witness tables for those protocols, as if laid out::
     AnsibleWitnessTable *U_Ansible;
   };
 
+Foreign Class Metadata
+~~~~~~~~~~~~~~~~~~~~~~
+
+Foreign class metadata describes "foreign" class types, which support Swift
+reference counting but are otherwise opaque to the Swift runtime.
+
+- The `nominal type descriptor`_ for the most-derived class type is stored at
+  **offset 0**.
+- The **super pointer** pointing to the metadata record for the superclass is
+  stored at **offset 1**. If the class is a root class, it is null.
+- Three **pointer-sized fields**, starting at **offset 2**, are reserved for
+  future use.
+
 Nominal Type Descriptor
 ~~~~~~~~~~~~~~~~~~~~~~~
 

include/swift/Runtime/Metadata.h

@@ -729,6 +729,7 @@ template <typename Runtime> struct TargetClassMetadata;
 template <typename Runtime> struct TargetStructMetadata;
 template <typename Runtime> struct TargetOpaqueMetadata;
 template <typename Runtime> struct TargetValueMetadata;
+template <typename Runtime> struct TargetForeignClassMetadata;
 
 // FIXME: https://bugs.swift.org/browse/SR-1155
 #pragma clang diagnostic push
@@ -907,6 +908,8 @@ struct TargetMetadata {
       return static_cast<const TargetValueMetadata<Runtime> *>(this)
           ->Description;
     case MetadataKind::ForeignClass:
+      return static_cast<const TargetForeignClassMetadata<Runtime> *>(this)
+          ->Description;
     case MetadataKind::Opaque:
     case MetadataKind::Tuple:
     case MetadataKind::Function:
@@ -1812,9 +1815,12 @@ struct TargetForeignClassMetadata
   : public TargetForeignTypeMetadata<Runtime> {
   using StoredPointer = typename Runtime::StoredPointer;
 
+  /// An out-of-line description of the type.
+  const TargetNominalTypeDescriptor<Runtime> *Description;
+
   /// The superclass of the foreign class, if any.
   ConstTargetMetadataPointer<Runtime, swift::TargetForeignClassMetadata>
-  SuperClass;
+    SuperClass;
 
   /// Reserved space.  For now, these should be zero-initialized.
   StoredPointer Reserved[3];

lib/IRGen/GenMeta.cpp

@@ -4901,6 +4901,7 @@ namespace {
 
     void layout() {
       super::layout();
+      asImpl().addNominalTypeDescriptor();
       asImpl().addSuperClass();
       asImpl().addReservedWord();
       asImpl().addReservedWord();
@@ -5053,6 +5054,11 @@ namespace {
       B.addInt(IGM.MetadataKindTy, (unsigned) MetadataKind::ForeignClass);
     }
 
+    void addNominalTypeDescriptor() {
+      auto descriptor = ClassNominalTypeDescriptorBuilder(this->IGM, Target).emit();
+      B.add(descriptor);
+    }
+
     void addSuperClass() {
       // TODO: superclasses
       B.addNullPointer(IGM.TypeMetadataPtrTy);

test/IRGen/cf.sil

@@ -12,13 +12,13 @@
 // CHECK-32: @_T0So14CCRefrigeratorCN = linkonce_odr hidden global <{ {{.*}} }> <{
 // CHECK-32-SAME: [[REFRIGERATOR_NAME]] to i32
 // CHECK-32-SAME: i32 0,
-// CHECK-32-SAME: i8** @_T0BOWV, i32 16, [[TYPE]]* null, i8* null, i8* null, i8* null }>
+// CHECK-32-SAME: i8** @_T0BOWV, i32 16, {{.*}}_T0So14CCRefrigeratorCMn, [[TYPE]]* null, i8* null, i8* null, i8* null }>
 
 // CHECK-64: @_T0So14CCRefrigeratorCN = linkonce_odr hidden global <{ {{.*}} }> <{
 // CHECK-64-SAME: i32 0,
 // CHECK-64-SAME: i32 trunc {{.*}} [[REFRIGERATOR_NAME]] to i64
 // CHECK-64-SAME: i64 0,
-// CHECK-64-SAME: i8** @_T0BOWV, i64 16, [[TYPE]]* null, i8* null, i8* null, i8* null }>
+// CHECK-64-SAME: i8** @_T0BOWV, i64 16, {{.*}}_T0So14CCRefrigeratorCMn, [[TYPE]]* null, i8* null, i8* null, i8* null }>
 
 sil_stage canonical