Speed up object-keyed Map and Set by giving out sequential hash codes

src/collection.js

 // 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.
 
 var $getHash;
 var $getExistingHash;
 
 (function(global, utils) {
 "use strict";
 
 %CheckIsBootstrapping();
 
 // -------------------------------------------------------------------
 // Imports
 
 var GlobalMap = global.Map;
 var GlobalObject = global.Object;
 var GlobalSet = global.Set;
-var IntRandom;
-
-utils.Import(function(from) {
-  IntRandom = from.IntRandom;
-});
 
 var NumberIsNaN;
 
 utils.Import(function(from) {
   NumberIsNaN = from.NumberIsNaN;
 });
 
 // -------------------------------------------------------------------
 
 function HashToEntry(table, hash, numBuckets) {
@@ skipping 69 matching lines @@
     }
   } else if (IS_SPEC_OBJECT(key) && !%_IsJSProxy(key) && !IS_GLOBAL(key)) {
     var hash = GET_PRIVATE(key, hashCodeSymbol);
     return hash;
   }
   return %GenericHash(key);
 }
 %SetForceInlineFlag(GetExistingHash);
 
 
+var hashCounter = 1;
+
+
 function GetHash(key) {
   var hash = GetExistingHash(key);
   if (IS_UNDEFINED(hash)) {
-    hash = IntRandom() | 0;
-    if (hash === 0) hash = 1;
+    hash = hashCounter;
+    // Avoid a hash of zero, reserved for the hidden string. Also avoid
+    // non-Smi hashes.
+    hashCounter = hash == 0x3fffffff ? 1 : hash + 1;
     SET_PRIVATE(key, hashCodeSymbol, hash);
   }
   return hash;
 }
 %SetForceInlineFlag(GetHash);
 
 
 // -------------------------------------------------------------------
 // Harmony Set
 
@@ skipping 346 matching lines @@
   "delete", MapDelete,
   "clear", MapClearJS,
   "forEach", MapForEach
 ]);
 
 // Expose to the global scope.
 $getHash = GetHash;
 $getExistingHash = GetExistingHash;
 
 })