Ensure newly allocated empty Arrays are transitioned to FAST_ELEMENT

test/mjsunit/elements-kind.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 21 matching lines @@
 // time sticks if built with snapshot.  If --smi-only-arrays is deactivated
 // by default, only a no-snapshot build actually has smi-only arrays enabled
 // in this test case.  Depending on whether smi-only arrays are actually
 // enabled, this test takes the appropriate code path to check smi-only arrays.
 
 support_smi_only_arrays = %HasFastSmiOnlyElements([1,2,3,4,5,6,7,8,9,10]);
 
 if (support_smi_only_arrays) {
   print("Tests include smi-only arrays.");
 } else {
-  print("Tests do NOT include smi-only arrays.");

[Jakob Kummerow, 2012/01/04 20:55:17]

intentional removal?

+  print("Tests do NOT include smi-only.");
 }
 
+// Ensure that there is a global bais for not aggressively transitioning Arrays

[Jakob Kummerow, 2012/01/04 20:55:17]

suggestion: "Ensure that Arrays default to SMI_ONLY elements."

+// to FAST_ELEMENTs.
+// TODO(danno): Remove this code when bias for early ElementsKind transition is
+// tracked per allocation site and not globally.
+[1,2,3][0] = 1.5;
+[1,2,3][0] = 1.5;
+[1,2,3][0] = 1.5;
+[1,2,3][0] = 1.5;
+[1,2,3][0] = 1.5;
+
 var elements_kind = {
   fast_smi_only            :  'fast smi only elements',
   fast                     :  'fast elements',
   fast_double              :  'fast double elements',
   dictionary               :  'dictionary elements',
   external_byte            :  'external byte elements',
   external_unsigned_byte   :  'external unsigned byte elements',
   external_short           :  'external short elements',
   external_unsigned_short  :  'external unsigned short elements',
   external_int             :  'external int elements',
@@ skipping 53 matching lines @@
 me.drink = 0xC0C0A;
 assertKind(elements_kind.fast, me);
 
 var too = [1,2,3];
 assertKind(elements_kind.fast_smi_only, too);
 too.dance = 0xD15C0;
 too.drink = 0xC0C0A;
 assertKind(elements_kind.fast_smi_only, too);
 
 // Make sure the element kind transitions from smionly when a non-smi is stored.
-var you = new Array();
+var you = new Array(1);
 assertKind(elements_kind.fast_smi_only, you);
 for (var i = 0; i < 1337; i++) {
   var val = i;
   if (i == 1336) {
     assertKind(elements_kind.fast_smi_only, you);
     val = new Object();
   }
   you[i] = val;
 }
 assertKind(elements_kind.fast, you);
@@ skipping 202 matching lines @@
   var a = ["foo", "bar"];
   assertKind(elements_kind.fast, a);
   var b = a.splice(0, 1);
   assertKind(elements_kind.fast, b);
   var c = a.slice(0, 1);
   assertKind(elements_kind.fast, c);
 }
 
 // Throw away type information in the ICs for next stress run.
 gc();