Debug garbage collector does not correctly remove cross-gen garbage

runtime/vm/heap.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/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 426 matching lines @@
     CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kOldSpace);
   } else {
     ASSERT(space == kNew);
     CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kNewSpace);
   }
 }
 
 
 void Heap::CollectAllGarbage() {
   Thread* thread = Thread::Current();
-  CollectNewSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
+  new_space_.Evacuate();

[rmacnak, 2017/06/22 21:59:33]

Add a comment here that we evacuate new space to deal with dead objects that
have a cross-generational incoming pointer.

[danunez, 2017/06/22 22:07:47]

Done.

   CollectOldSpaceGarbage(thread, kInvokeApiCallbacks, kFull);
 }
 
 
 void Heap::WaitForSweeperTasks(Thread* thread) {
   MonitorLocker ml(old_space_.tasks_lock());
   while (old_space_.tasks() > 0) {
     ml.WaitWithSafepointCheck(thread);
   }
 }
@@ skipping 407 matching lines @@
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart