[Runtime] Use CF superclass metadata in runtime lookups.

When searching the superclasses at runtime, e.g., to find a suitable
protocol conformance record, also consider the superclasses of CF
types, which were recorded in the metadata but otherwise unused.

Author: DougGregor

stdlib/public/runtime/Casting.cpp

@@ -3085,9 +3085,17 @@ bool _swift_isClassOrObjCExistentialType(const Metadata *value,
 
 SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_INTERNAL
 const Metadata *swift::_swift_class_getSuperclass(const Metadata *theClass) {
-  if (const ClassMetadata *classType = theClass->getClassObject())
+  if (const ClassMetadata *classType = theClass->getClassObject()) {
     if (classHasSuperclass(classType))
       return getMetadataForClass(classType->Superclass);
+  }
+
+  if (const ForeignClassMetadata *foreignClassType
+        = dyn_cast<ForeignClassMetadata>(theClass)) {
+    if (const Metadata *superclass = foreignClassType->Superclass)
+      return superclass;
+  }
+
   return nullptr;
 }
 

stdlib/public/runtime/ProtocolConformance.cpp

@@ -463,12 +463,10 @@ searchInConformanceCache(const Metadata *type,
     }
   }
 
-  // If the type is a class, try its superclass.
-  if (const ClassMetadata *classType = type->getClassObject()) {
-    if (classHasSuperclass(classType)) {
-      type = getMetadataForClass(classType->Superclass);
-      goto recur;
-    }
+  // If there is a superclass, look there.
+  if (auto superclass = _swift_class_getSuperclass(type)) {
+    type = superclass;
+    goto recur;
   }
 
   // We did not find an up-to-date cache entry.
@@ -506,12 +504,10 @@ bool isRelatedType(const Metadata *type, const void *candidate,
         return true;
     }
 
-    // If the type is a class, try its superclass.
-    if (const ClassMetadata *classType = type->getClassObject()) {
-      if (classHasSuperclass(classType)) {
-        type = getMetadataForClass(classType->Superclass);
-        continue;
-      }
+    // If there is a superclass, look there.
+    if (auto superclass = _swift_class_getSuperclass(type)) {
+      type = superclass;
+      continue;
     }
 
     break;

test/Runtime/demangleToMetadataObjC.swift

@@ -91,5 +91,10 @@ DemangleToMetadataTests.test("members of runtime-only Objective-C classes") {
     _typeByMangledName("So17OS_dispatch_queueC8DispatchE10AttributesV")!)
 }
 
+DemangleToMetadataTests.test("runtime conformance lookup via foreign superclasses") {
+  expectEqual(Set<CFMutableString>.self,
+    _typeByMangledName("ShySo18CFMutableStringRefaG")!)
+}
+
 runAllTests()