v8:3539 - hold constructor feedback in weak cells

test/cctest/test-feedback-vector.cc

 // Copyright 2014 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/v8.h"
 #include "test/cctest/cctest.h"
 
 #include "src/api.h"
 #include "src/debug.h"
 #include "src/execution.h"
@@ skipping 122 matching lines @@
   Factory* factory = isolate->factory();
 
   // We only test clearing FeedbackVectorSlots, not FeedbackVectorICSlots.
   // The reason is that FeedbackVectorICSlots need a full code environment
   // to fully test (See VectorICProfilerStatistics test below).
   FeedbackVectorSpec spec(5);
   Handle<TypeFeedbackVector> vector = factory->NewTypeFeedbackVector(&spec);
 
   // Fill with information
   vector->Set(FeedbackVectorSlot(0), Smi::FromInt(1));
-  vector->Set(FeedbackVectorSlot(1), *factory->fixed_array_map());
+  Handle<WeakCell> cell = factory->NewWeakCell(factory->fixed_array_map());
+  vector->Set(FeedbackVectorSlot(1), *cell);
   Handle<AllocationSite> site = factory->NewAllocationSite();
   vector->Set(FeedbackVectorSlot(2), *site);
 
+  // GC time clearing leaves slots alone.
+  vector->ClearSlotsAtGCTime(NULL);
+  Object* obj = vector->Get(FeedbackVectorSlot(1));
+  CHECK(obj->IsWeakCell() && !WeakCell::cast(obj)->cleared());
+
   vector->ClearSlots(NULL);
 
-  // The feedback vector slots are cleared. AllocationSites are granted
+  // The feedback vector slots are cleared. AllocationSites are still granted
   // an exemption from clearing, as are smis.
   CHECK_EQ(Smi::FromInt(1), vector->Get(FeedbackVectorSlot(0)));
   CHECK_EQ(*TypeFeedbackVector::UninitializedSentinel(isolate),
            vector->Get(FeedbackVectorSlot(1)));
   CHECK(vector->Get(FeedbackVectorSlot(2))->IsAllocationSite());
 }
 
 
 TEST(VectorICProfilerStatistics) {
   if (i::FLAG_always_opt) return;
@@ skipping 224 matching lines @@
   CHECK(number_map_found && o_map_found);
 
   // The degree of polymorphism doesn't change.
   CompileRun("f(100)");
   CHECK_EQ(POLYMORPHIC, nexus.StateFromFeedback());
   MapHandleList maps2;
   nexus.FindAllMaps(&maps2);
   CHECK_EQ(2, maps2.length());
 }
 }