Improve performance of exception handling: quicker (and correcter) determination if the exception c…

runtime/vm/exceptions.cc

 // Copyright (c) 2011, 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/exceptions.h"
 
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/flags.h"
@@ skipping 360 matching lines @@
   }
   Isolate* isolate = Isolate::Current();
   Class& error_class = Class::Handle(isolate,
                                      isolate->object_store()->error_class());
   if (error_class.IsNull()) {
     const Library& core_lib = Library::Handle(isolate, Library::CoreLibrary());
     error_class = core_lib.LookupClass(Symbols::Error(), NULL);
     ASSERT(!error_class.IsNull());
     isolate->object_store()->set_error_class(error_class);
   }
-  const Class& instance_class = Class::Handle(isolate, instance.clazz());
-  Error& malformed_type_error = Error::Handle(isolate);
-  if (instance_class.IsSubtypeOf(Object::null_abstract_type_arguments(),
-                                 error_class,
-                                 Object::null_abstract_type_arguments(),
-                                 &malformed_type_error)) {
-    ASSERT(malformed_type_error.IsNull());
-    return error_class.LookupInstanceField(Symbols::_stackTrace());
-  }
+
+  Class& test_class = Class::Handle(isolate, instance.clazz());

[Ivan Posva, 2013/08/29 19:35:19]

// Comments please.

[srdjan, 2013/08/29 19:37:29]

Done.

+  AbstractType& type = AbstractType::Handle(isolate, AbstractType::null());
+  while (true) {
+    if (test_class.raw() == error_class.raw()) {
+      return error_class.LookupInstanceField(Symbols::_stackTrace());
+    }
+    type = test_class.super_type();
+    if (type.IsNull()) return Field::null();
+    test_class = type.type_class();
+  };
+  UNREACHABLE();
   return Field::null();
 }
 
 
 static void ThrowExceptionHelper(const Instance& incoming_exception,
                                  const Instance& existing_stacktrace) {
   bool use_preallocated_stacktrace = false;
   Isolate* isolate = Isolate::Current();
   Instance& exception = Instance::Handle(isolate, incoming_exception.raw());
   if (exception.IsNull()) {
@@ skipping 349 matching lines @@
       break;
   }
 
   return DartLibraryCalls::InstanceCreate(library,
                                           *class_name,
                                           *constructor_name,
                                           arguments);
 }
 
 }  // namespace dart