[runtime] Avoid @@isConcatSpreadable lookup for fast path Array.prototype.concat

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index aca86484bd01b8a1dc372ac0fac8a175dd2b266c..1cbe59d8b0d34cee0df91e38955030e8ee82297f 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2907,6 +2907,11 @@ void Heap::CreateInitialObjects() {
   set_array_protector(*cell);
 
   cell = factory->NewPropertyCell();
+  cell->set_value(
+      Smi::FromInt(Isolate::kArrayIsConcatSpreadableProtectorValid));
+  set_array_is_concat_spreadable_protector(*cell);

[Toon Verwaest, 2016/03/31 08:09:46]

Unless you want to be able to add dependencies to the cell in optimized code,
there's no need to use a PropertyCell rather than a Cell. The same is probably
true for species_cell below.

[Camillo Bruni, 2016/04/06 13:14:32]

ok.

+
+  cell = factory->NewPropertyCell();
   cell->set_value(the_hole_value());
   set_empty_property_cell(*cell);