[Draft] Stackless map transition tree traversal.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index ef5185145a1ae55148e816a9c486600c6ab2ec15..369df4c96c58a2187592d83adc0a44e7b4476e67 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -5123,6 +5123,47 @@ void Map::ClearNonLiveTransitions(Object* real_prototype) {
 }
 
 
+void Map::TraverseTransitionTree() {
+  Map* current = this;
+  while (current != Heap::meta_map()) {
+    DescriptorArray* d = reinterpret_cast<DescriptorArray*>(
+        *RawField(current, Map::kInstanceDescriptorsOffset));
+    if (d == Heap::empty_descriptor_array()) {
+      Map* prev = current->map();
+      current->set_map(Heap::meta_map());
+      current->Print();
+      current = prev;
+      continue;
+    }
+    FixedArray* contents = reinterpret_cast<FixedArray*>(
+        d->get(DescriptorArray::kContentArrayIndex));
+    Object** map_or_index_field = RawField(contents, HeapObject::kMapOffset);
+    Object* map_or_index = *map_or_index_field;
+    ASSERT(map_or_index->IsSmi() || map_or_index == Heap::fixed_array_map());
+    bool map_done = true;
+    for (int i = map_or_index->IsSmi() ? Smi::cast(map_or_index)->value() : 0;
+         i < contents->length();
+         i += 2) {
+      PropertyDetails details(Smi::cast(contents->get(i + 1)));
+      if (details.IsTransition()) {
+        Map* next = Map::cast(contents->get(i));
+        next->set_map(current);
+        *map_or_index_field = Smi::FromInt(i + 2);
+        current = next;
+        map_done = false;
+        break;
+      }
+    }
+    if (!map_done) continue;
+    *map_or_index_field = Heap::fixed_array_map();
+    Map* prev = current->map();
+    current->set_map(Heap::meta_map());
+    current->Print();
+    current = prev;
+  }
+}
+
+
 void JSFunction::JSFunctionIterateBody(int object_size, ObjectVisitor* v) {
   // Iterate over all fields in the body but take care in dealing with
   // the code entry.