v8:3539 - hold constructor feedback in weak cells

src/type-info.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/v8.h"
 
 #include "src/ast.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
 #include "src/ic/ic.h"
@@ skipping 33 matching lines @@
     } else {
       return Handle<Object>(value, isolate());
     }
   }
   return Handle<Object>::cast(isolate()->factory()->undefined_value());
 }
 
 
 Handle<Object> TypeFeedbackOracle::GetInfo(FeedbackVectorSlot slot) {
   DCHECK(slot.ToInt() >= 0 && slot.ToInt() < feedback_vector_->length());
+  Handle<Object> undefined =
+      Handle<Object>::cast(isolate()->factory()->undefined_value());
   Object* obj = feedback_vector_->Get(slot);
+
+  // Slots do not embed direct pointers to functions. Instead a WeakCell is
+  // always used.
+  if (obj->IsWeakCell()) {
+    WeakCell* cell = WeakCell::cast(obj);
+    if (cell->cleared()) return undefined;
+    obj = cell->value();
+  }
+
   if (!obj->IsJSFunction() ||
       !CanRetainOtherContext(JSFunction::cast(obj), *native_context_)) {
     DCHECK(!obj->IsMap());
     return Handle<Object>(obj, isolate());
   }
-  return Handle<Object>::cast(isolate()->factory()->undefined_value());
+
+  return undefined;
 }
 
 
 Handle<Object> TypeFeedbackOracle::GetInfo(FeedbackVectorICSlot slot) {
   DCHECK(slot.ToInt() >= 0 && slot.ToInt() < feedback_vector_->length());
   Handle<Object> undefined =
       Handle<Object>::cast(isolate()->factory()->undefined_value());
   Object* obj = feedback_vector_->Get(slot);
 
   // Vector-based ICs do not embed direct pointers to maps, functions.
@@ skipping 498 matching lines @@
          UnseededNumberDictionary::kNotFound);
   // Dictionary has been allocated with sufficient size for all elements.
   DisallowHeapAllocation no_need_to_resize_dictionary;
   HandleScope scope(isolate());
   USE(UnseededNumberDictionary::AtNumberPut(
       dictionary_, IdToKey(ast_id), handle(target, isolate())));
 }
 
 
 } }  // namespace v8::internal