Avoid map transitions and multiple backing arrays for builtin prototypes...

src/v8natives.js

 // Copyright 2006-2008 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 28 matching lines @@
 // const $floor = MathFloor
 
 const $isNaN = GlobalIsNaN;
 const $isFinite = GlobalIsFinite;
 
 // ----------------------------------------------------------------------------
 
 
 // Helper function used to install functions on objects.
 function InstallFunctions(object, attributes, functions) {
+  if (functions.length >= 8) {
+    %OptimizeObjectForAddingMultipleProperties(object, functions.length >> 1);
+  }
   for (var i = 0; i < functions.length; i += 2) {
     var key = functions[i];
     var f = functions[i + 1];
     %FunctionSetName(f, key);
     %SetProperty(object, key, f, attributes);
   }
+  %TransformToFastProperties(object);
 }
 
 // Emulates JSC by installing functions on a hidden prototype that
 // lies above the current object/prototype.  This lets you override
 // functions on String.prototype etc. and then restore the old function
 // with delete.  See http://code.google.com/p/chromium/issues/detail?id=1717
 function InstallFunctionsOnHiddenPrototype(object, attributes, functions) {
   var hidden_prototype = new $Object();
   %SetHiddenPrototype(object, hidden_prototype);
   InstallFunctions(hidden_prototype, attributes, functions);
@@ skipping 382 matching lines @@
 
 function NumberToJSON(key) {
   return CheckJSONPrimitive(this.valueOf());
 }
 
 
 // ----------------------------------------------------------------------------
 
 function SetupNumber() {
   // Setup the constructor property on the Number prototype object.
+  %OptimizeObjectForAddingMultipleProperties($Number.prototype, 8);
   %SetProperty($Number.prototype, "constructor", $Number, DONT_ENUM);
 
+  %OptimizeObjectForAddingMultipleProperties($Number, 5);
   // ECMA-262 section 15.7.3.1.
   %SetProperty($Number,
                "MAX_VALUE",
                1.7976931348623157e+308,
                DONT_ENUM | DONT_DELETE | READ_ONLY);
 
   // ECMA-262 section 15.7.3.2.
   %SetProperty($Number, "MIN_VALUE", 5e-324, DONT_ENUM | DONT_DELETE | READ_ONLY);
 
   // ECMA-262 section 15.7.3.3.
@@ skipping 93 matching lines @@
 
 // ----------------------------------------------------------------------------
 
 function SetupFunction() {
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "toString", FunctionToString
   ));
 }
 
 SetupFunction();