Avoid allocating an exception object in the snapshot reader.

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 12675 matching lines @@
                                       space);
     NoGCScope no_gc;
     result ^= raw;
   }
   result.set_exception(exception);
   result.set_stacktrace(stacktrace);
   return result.raw();
 }
 
 
+RawUnhandledException* UnhandledException::New(Heap::Space space) {
+  ASSERT(Object::unhandled_exception_class() != Class::null());
+  UnhandledException& result = UnhandledException::Handle();
+  {
+    RawObject* raw = Object::Allocate(UnhandledException::kClassId,
+                                      UnhandledException::InstanceSize(),
+                                      space);
+    NoGCScope no_gc;
+    result ^= raw;
+  }
+  const Instance& null_object = Instance::Handle();
+  result.set_exception(null_object);
+  result.set_stacktrace(null_object);

[siva, 2014/07/16 01:00:13]

Can we use Object::null_instance() here instead of creating a new
handle or are we too early in the initialization code that
Object::null_instance() is not set up yet?

[Florian Schneider, 2014/07/16 11:15:42]

Done.

+  return result.raw();
+}
+
+
 void UnhandledException::set_exception(const Instance& exception) const {
   StorePointer(&raw_ptr()->exception_, exception.raw());
 }
 
 
 void UnhandledException::set_stacktrace(const Instance& stacktrace) const {
   StorePointer(&raw_ptr()->stacktrace_, stacktrace.raw());
 }
 
 
@@ skipping 6375 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart