MetadataReader: Fix caching of Objective C class metadata

If resolving the type of an instance produces a class metadata for
which we cannot build a type (for example, a special class like
__NSCFNumber, which the ClangImporter does not produce a ClassDecl
for), we try the superclass.

The caching logic was broken in this case, so subsequent calls
would return an empty type.

Author: slavapestov

include/swift/Remote/MetadataReader.h

@@ -502,14 +502,14 @@ class MetadataReader {
         if (!readObjCClassName(MetadataAddress, className))
           return BuiltType();
 
-        auto BuiltObjCClass = Builder.createObjCClassType(std::move(className));
+        BuiltType BuiltObjCClass = Builder.createObjCClassType(std::move(className));
         if (!BuiltObjCClass) {
           // Try the superclass.
           if (!classMeta->Superclass)
             return BuiltType();
 
-          return readTypeFromMetadata(classMeta->Superclass,
-                                      skipArtificialSubclasses);
+          BuiltObjCClass = readTypeFromMetadata(classMeta->Superclass,
+                                                skipArtificialSubclasses);
         }
 
         TypeCache[MetadataAddress] = BuiltObjCClass;

test/RemoteAST/existentials_objc.swift

@@ -12,5 +12,22 @@ func printDynamicTypeAndAddressForExistential<T>(_: T)
 // CHECK: NSObject
 printDynamicTypeAndAddressForExistential(NSObject() as AnyObject)
 
+// Print tagged pointer types three times to ensure the caching works.
+
+// CHECK: NSNumber
+printDynamicTypeAndAddressForExistential(NSNumber(123) as AnyObject)
+
+// CHECK: NSNumber
+printDynamicTypeAndAddressForExistential(NSNumber(123) as AnyObject)
+
 // CHECK: NSNumber
 printDynamicTypeAndAddressForExistential(NSNumber(123) as AnyObject)
+
+// CHECK: NSString
+printDynamicTypeAndAddressForExistential(NSString("hello") as AnyObject)
+
+// CHECK: NSString
+printDynamicTypeAndAddressForExistential(NSString("hello") as AnyObject)
+
+// CHECK: NSString
+printDynamicTypeAndAddressForExistential(NSString("hello") as AnyObject)