Use a WeakCell in the CallIC type vector.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3302 matching lines @@
     // Check size.
     FieldIndex index = FieldIndex::ForDescriptor(internal_obj->map(), 0);
     ObjectHashTable* hashtable = ObjectHashTable::cast(
         internal_obj->RawFastPropertyAt(index));
     // HashTable header (5) and 4 initial entries (8).
     CHECK_LE(hashtable->SizeFor(hashtable->length()), 13 * kPointerSize);
   }
 }
 
 
-TEST(IncrementalMarkingClearsTypeFeedbackInfo) {
+TEST(IncrementalMarkingPreservesMonomorphicCallIC) {
   if (i::FLAG_always_opt) return;
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
   v8::Local<v8::Value> fun1, fun2;
 
   {
     LocalContext env;
     CompileRun("function fun() {};");
     fun1 = env->Global()->Get(v8_str("fun"));
   }
@@ skipping 14 matching lines @@
       v8::Utils::OpenHandle(
           *v8::Handle<v8::Function>::Cast(
               CcTest::global()->Get(v8_str("f"))));
 
   Handle<TypeFeedbackVector> feedback_vector(f->shared()->feedback_vector());
 
   int expected_slots = 2;
   CHECK_EQ(expected_slots, feedback_vector->ICSlots());
   int slot1 = 0;
   int slot2 = 1;
-  CHECK(feedback_vector->Get(FeedbackVectorICSlot(slot1))->IsJSFunction());
-  CHECK(feedback_vector->Get(FeedbackVectorICSlot(slot2))->IsJSFunction());
+  CHECK(feedback_vector->Get(FeedbackVectorICSlot(slot1))->IsWeakCell());
+  CHECK(feedback_vector->Get(FeedbackVectorICSlot(slot2))->IsWeakCell());
 
   SimulateIncrementalMarking(CcTest::heap());
   CcTest::heap()->CollectAllGarbage(Heap::kNoGCFlags);
 
-  CHECK_EQ(feedback_vector->Get(FeedbackVectorICSlot(slot1)),
-           *TypeFeedbackVector::UninitializedSentinel(CcTest::i_isolate()));
-  CHECK_EQ(feedback_vector->Get(FeedbackVectorICSlot(slot2)),
-           *TypeFeedbackVector::UninitializedSentinel(CcTest::i_isolate()));
+  CHECK(!WeakCell::cast(feedback_vector->Get(FeedbackVectorICSlot(slot1)))
+             ->cleared());
+  CHECK(!WeakCell::cast(feedback_vector->Get(FeedbackVectorICSlot(slot2)))
+             ->cleared());
 }
 
 
 static Code* FindFirstIC(Code* code, Code::Kind kind) {
   int mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET) |
              RelocInfo::ModeMask(RelocInfo::CONSTRUCT_CALL) |
              RelocInfo::ModeMask(RelocInfo::CODE_TARGET_WITH_ID);
   for (RelocIterator it(code, mask); !it.done(); it.next()) {
     RelocInfo* info = it.rinfo();
     Code* target = Code::GetCodeFromTargetAddress(info->target_address());
@@ skipping 1710 matching lines @@
 #ifdef DEBUG
 TEST(PathTracer) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
 
   v8::Local<v8::Value> result = CompileRun("'abc'");
   Handle<Object> o = v8::Utils::OpenHandle(*result);
   CcTest::i_isolate()->heap()->TracePathToObject(*o);
 }
 #endif  // DEBUG