Basic array capacity feedback via allocation sites.

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 1686 matching lines @@
       }
       set_pretenure_decision(kMaybeTenure);
     } else {
       set_pretenure_decision(kDontTenure);
     }
   }
   return false;
 }
 
 
+int AllocationSite::GetInitialElementsCapacity() {
+  if (FLAG_initial_capacity_mode != 2) {
+    return JSArray::PreallocatedArrayElements();
+  }
+
+  if (SitePointsToLiteral()) return 0;
+  int value = Smi::cast(transition_info())->value();
+  return InitialElementsCapacity::decode(value);
+}
+
+
+void AllocationSite::DigestInitialElementsCapacityFeedback(int new_length) {
+  if (FLAG_initial_capacity_mode != 2) return;
+
+  if (new_length > 0 && !SitePointsToLiteral()) {
+    int to_store = (new_length + (new_length >> 1) + 16) / 4;
+    int old_capacity = GetInitialElementsCapacity();
+    if (to_store > old_capacity &&
+        InitialElementsCapacity::is_valid(to_store)) {
+      int value = Smi::cast(transition_info())->value();
+      set_transition_info(
+          Smi::FromInt(InitialElementsCapacity::update(value, to_store)),
+          SKIP_WRITE_BARRIER);
+      if (FLAG_trace_track_allocation_sites) {
+        PrintF("Initial elements capacity for site %p, updated to %d.\n",
+               static_cast<void*>(this), to_store);
+      }
+    }
+  }
+}
+
+
 inline bool AllocationSite::DigestPretenuringFeedback(
     bool maximum_size_scavenge) {
   bool deopt = 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;
   PretenureDecision current_decision = pretenure_decision();
@@ skipping 5540 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_