VM: Remove too strict assertion in rethrow.

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 "platform/address_sanitizer.h"
 
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 391 matching lines @@
   } else {
     // Get stacktrace field of class Error. This is needed to determine whether
     // we have a subclass of Error which carries around its stack trace.
     const Field& stacktrace_field =
         Field::Handle(zone, LookupStacktraceField(exception));
 
     // Find the exception handler and determine if the handler needs a
     // stacktrace.
     handler_exists =
         FindExceptionHandler(thread, &handler_pc, &handler_sp, &handler_fp,
                              &handler_needs_stacktrace);

[kustermann, 2016/11/17 11:07:48]

Can this FindExceptionHandler() be hoisted out of the if/else branches?

[Florian Schneider, 2016/11/17 18:59:07]

Done.

     if (!existing_stacktrace.IsNull()) {
       // If we have an existing stack trace then this better be a rethrow. The
       // reverse is not necessarily true (e.g. Dart_PropagateError can cause
       // a rethrow being called without an existing stacktrace.)
       ASSERT(is_rethrow);
-      ASSERT(stacktrace_field.IsNull() ||
-             (exception.GetField(stacktrace_field) != Object::null()));
       stacktrace = existing_stacktrace.raw();

[kustermann, 2016/11/17 11:07:48]

This branch doesn't need [stacktrace_field] anymore. Maybe only do the
Field::Handle(zone, LookupStacktraceField(exception) in the else-case?

[Florian Schneider, 2016/11/17 18:59:07]

Done.

     } else if (!stacktrace_field.IsNull() || handler_needs_stacktrace) {
       // Collect the stacktrace if needed.
       ASSERT(existing_stacktrace.IsNull());
       stacktrace = Exceptions::CurrentStacktrace();
       // If we have an Error object, then set its stackTrace field only if it
       // not yet initialized.
       if (!stacktrace_field.IsNull() &&
           (exception.GetField(stacktrace_field) == Object::null())) {
         exception.SetField(stacktrace_field, stacktrace);
       }
@@ skipping 357 matching lines @@
       class_name = &Symbols::_CompileTimeError();
       break;
   }
 
   return DartLibraryCalls::InstanceCreate(library, *class_name,
                                           *constructor_name, arguments);
 }
 
 
 }  // namespace dart