Keep track of which maps are associated with prototype objects

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 
 #include <stdlib.h>
 
 #include "v8.h"
 
 #include "execution.h"
 #include "factory.h"
 #include "macro-assembler.h"
 #include "global-handles.h"
@@ skipping 1561 matching lines @@
       "  var prototype = {};"
       "  object.__proto__ = prototype;"
       "  if (i >= 3) live.push(object, prototype);"
       "}");
 
   Handle<JSObject> baseObject =
       v8::Utils::OpenHandle(
           *v8::Handle<v8::Object>::Cast(
               v8::Context::GetCurrent()->Global()->Get(v8_str("base"))));
 
-  // Verify that only dead prototype transitions are cleared.
-  CHECK_EQ(10, baseObject->map()->NumberOfProtoTransitions());
+  // Verify that only dead prototype transitions are cleared.  There is an
+  // extra, 11th, prototype transition on the Object map, which is the
+  // transition to a map with the used_for_prototype flag set (the key is
+  // the_hole).
+  CHECK_EQ(11, baseObject->map()->NumberOfProtoTransitions());
   HEAP->CollectAllGarbage(Heap::kNoGCFlags);
-  CHECK_EQ(10 - 3, baseObject->map()->NumberOfProtoTransitions());
+  CHECK_EQ(11 - 3, baseObject->map()->NumberOfProtoTransitions());
 
   // Verify that prototype transitions array was compacted.
   FixedArray* trans = baseObject->map()->prototype_transitions();
   for (int i = 0; i < 10 - 3; i++) {

[Michael Starzinger, 2012/05/30 14:08:03]

The loop should also go to (11 - 3) ... better put that in a constant.

[Erik Corry, 2012/05/30 15:24:13]

Done.

     int j = Map::kProtoTransitionHeaderSize +
         i * Map::kProtoTransitionElementsPerEntry;
     CHECK(trans->get(j + Map::kProtoTransitionMapOffset)->IsMap());
-    CHECK(trans->get(j + Map::kProtoTransitionPrototypeOffset)->IsJSObject());
+    Object* proto = trans->get(j + Map::kProtoTransitionPrototypeOffset);
+    CHECK(proto == trans->GetHeap()->the_hole_value() || proto->IsJSObject());

[Michael Starzinger, 2012/05/30 14:08:03]

Can we just use proto->IsTheHole() here, that's more readable?

[Erik Corry, 2012/05/30 15:24:13]

Done.

   }
 
   // Make sure next prototype is placed on an old-space evacuation candidate.
   Handle<JSObject> prototype;
   PagedSpace* space = HEAP->old_pointer_space();
   do {
     prototype = FACTORY->NewJSArray(32 * KB, FAST_HOLEY_ELEMENTS, TENURED);
   } while (space->FirstPage() == space->LastPage() ||
       !space->LastPage()->Contains(prototype->address()));
 
@@ skipping 183 matching lines @@
   CHECK(marking->IsComplete());
   HEAP->CollectAllGarbage(Heap::kNoGCFlags);
   CHECK(marking->IsStopped());
 
   // Count number of live transitions after marking.  Note that one transition
   // is left, because 'o' still holds an instance of one transition target.
   int transitions_after = CountMapTransitions(root->map());
   CompileRun("%DebugPrint(root);");
   CHECK_EQ(1, transitions_after);
 }