[heap] Filter out non-heap values when tracing wrappers

src/heap/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/assembler-inl.h"
 #include "src/ast/context-slot-cache.h"
@@ skipping 5653 matching lines @@
       js_object->GetEmbedderField(0) != undefined_value() &&
       js_object->GetEmbedderField(1) != undefined_value()) {
     DCHECK(reinterpret_cast<intptr_t>(js_object->GetEmbedderField(0)) % 2 == 0);
     local_embedder_heap_tracer()->AddWrapperToTrace(std::pair<void*, void*>(
         reinterpret_cast<void*>(js_object->GetEmbedderField(0)),
         reinterpret_cast<void*>(js_object->GetEmbedderField(1))));
   }
 }
 
 void Heap::RegisterExternallyReferencedObject(Object** object) {
+  // The embedder is not aware of whether numbers are materialized as heap
+  // objects are just passed around as Smis.
+  if (!(*object)->IsHeapObject()) return;

[Hannes Payer (out of office), 2017/04/27 14:46:18]

Do you still want to keep the nullptr check? Or can it never be null?

[Michael Lippautz, 2017/04/27 14:47:50]

If it is a heap object it cannot be null, as this would be represented as an
empty handle on the embedder side.

If we get a tagged null pointer we will crash in the DCHECK, which is what we
want to see.

   HeapObject* heap_object = HeapObject::cast(*object);
-  if (heap_object == nullptr) {
-    // We might encounter non-empty handles that point to nullptr.
-    return;
-  }
   DCHECK(Contains(heap_object));
   if (FLAG_incremental_marking_wrappers && incremental_marking()->IsMarking()) {
     IncrementalMarking::MarkGrey(this, heap_object);
   } else {
     DCHECK(mark_compact_collector()->in_use());
     mark_compact_collector()->MarkObject(heap_object);
   }
 }
 
 void Heap::TearDown() {
@@ skipping 750 matching lines @@
     case LO_SPACE:
       return "LO_SPACE";
     default:
       UNREACHABLE();
   }
   return NULL;
 }
 
 }  // namespace internal
 }  // namespace v8