Count closures using the feedback vector cell map, specialize if count==1.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 24f3a0ada74d549b4e368fd8328bb63366cc41c1..1c38193a5634f7fcbb3af1b405540b87649d5d66 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1173,6 +1173,24 @@ Handle<Cell> Factory::NewCell(Handle<Object> value) {
       Cell);
 }
 
+Handle<Cell> Factory::NewNoClosuresCell(Handle<Object> value) {
+  Handle<Cell> cell = NewCell(value);
+  cell->set_map_no_write_barrier(*no_closures_cell_map());
+  return cell;
+}
+
+Handle<Cell> Factory::NewOneClosureCell(Handle<Object> value) {
+  Handle<Cell> cell = NewCell(value);
+  cell->set_map_no_write_barrier(*one_closure_cell_map());
+  return cell;
+}
+
+Handle<Cell> Factory::NewManyClosuresCell(Handle<Object> value) {
+  Handle<Cell> cell = NewCell(value);
+  cell->set_map_no_write_barrier(*many_closures_cell_map());
+  return cell;
+}
+
 Handle<PropertyCell> Factory::NewPropertyCell() {
   CALL_HEAP_FUNCTION(
       isolate(),
@@ -1590,6 +1608,15 @@ Handle<JSFunction> Factory::NewFunctionFromSharedFunctionInfo(
   Handle<JSFunction> result =
       NewFunction(initial_map, info, context_or_undefined, pretenure);
 
+  // Bump the closure count that is encoded in the vector cell's map.
+  if (vector->map() == *no_closures_cell_map()) {
+    vector->set_map(*one_closure_cell_map());
+  } else if (vector->map() == *one_closure_cell_map()) {
+    vector->set_map(*many_closures_cell_map());
+  } else {
+    DCHECK_EQ(vector->map(), *many_closures_cell_map());
+  }
+
   result->set_feedback_vector_cell(*vector);
   if (info->ic_age() != isolate()->heap()->global_ic_age()) {
     info->ResetForNewContext(isolate()->heap()->global_ic_age());