Again, forgot to save before uploading/comitting (just added a comment)

runtime/vm/code_generator_ia32.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/code_generator.h"
 
 #include "lib/error.h"
@@ skipping 1527 matching lines @@
       }
       // Compare if the classes are equal.
       __ Bind(&compare_classes);
       // If dst_type is an interface, we can skip the class equality check,
       // because instances cannot be of an interface type.
       if (!dst_type_class.is_interface()) {
         __ movl(ECX, FieldAddress(EAX, Object::class_offset()));
         TestClassAndJump(dst_type_class, &done);  // Uses ECX.
         // Check superclass
         __ movl(ECX, FieldAddress(ECX, Class::super_type_offset()));
+        // Note that supertypes can't be NULL as every Dart instance has
+        // as supertype class Object.

[regis, 2012/03/27 20:18:02]

Does that include a Dart instance of type Object?

[srdjan, 2012/03/27 20:43:40]

Good point, I thought that we cannot allocate instances of class object, but it
seems we can. Will add check. Thanks!

[srdjan, 2012/03/27 20:47:09]

Object.super_type is null, i.e., null object which has null class, so it should
be working fine. No checks needed (discussed offline).

         __ movl(ECX, FieldAddress(ECX, Type::type_class_offset()));
         TestClassAndJump(dst_type_class, &done);  // Uses ECX.
       } else {
         // However, for specific core library interfaces, we can check for
         // specific core library classes.
         Error& malformed_error = Error::Handle();
         if (dst_type.IsBoolInterface()) {
           __ movl(ECX, FieldAddress(EAX, Object::class_offset()));
           const Class& bool_class = Class::ZoneHandle(
               Isolate::Current()->object_store()->bool_class());
@@ skipping 1171 matching lines @@
   const Error& error = Error::Handle(
       Parser::FormatError(script, token_index, "Error", format, args));
   va_end(args);
   Isolate::Current()->long_jump_base()->Jump(1, error);
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32