Only allow allocation site lifetime transitions from undicided to tenure or don't tenure.

src/objects-inl.h

 // 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.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 1569 matching lines @@
 inline bool AllocationSite::DigestPretenuringFeedback() {
   bool decision_changed = false;
   int create_count = memento_create_count();
   int found_count = memento_found_count();
   bool minimum_mementos_created = create_count >= kPretenureMinimumCreated;
   double ratio =
       minimum_mementos_created || FLAG_trace_pretenuring_statistics ?
           static_cast<double>(found_count) / create_count : 0.0;
   PretenureFlag current_mode = GetPretenureMode();
 
-  if (minimum_mementos_created) {
+  // TODO(hpayer): Add an intermediate state MAYBE_TENURE which collects
+  // more lifetime feedback for tenuring candidates. In the meantime, we
+  // just allow transitions from undecided to tenured or not tenured.
+  if (minimum_mementos_created && pretenure_decision() == kUndecided) {
     PretenureDecision result = ratio >= kPretenureRatio
         ? kTenure
         : kDontTenure;
     set_pretenure_decision(result);
     if (current_mode != GetPretenureMode()) {
       decision_changed = true;
       set_deopt_dependent_code(true);
     }
   }
 
@@ skipping 5254 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_