Move hash code from hidden string to a private symbol

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();
 
 var GlobalMap = global.Map;
 var GlobalObject = global.Object;
 var GlobalSet = global.Set;
+var IntRandom;
+
+utils.Import(function(from) {
+  IntRandom = from.IntRandom;
+});
 
 // -------------------------------------------------------------------
 
 function HashToEntry(table, hash, numBuckets) {
   var bucket = ORDERED_HASH_TABLE_HASH_TO_BUCKET(hash, numBuckets);
   return ORDERED_HASH_TABLE_BUCKET_AT(table, bucket);
 }
 %SetForceInlineFlag(HashToEntry);
 
 
 function SetFindEntry(table, numBuckets, key, hash) {
+  var entry = HashToEntry(table, hash, numBuckets);
+  if (entry === NOT_FOUND) return entry;
+  var candidate = ORDERED_HASH_SET_KEY_AT(table, entry, numBuckets);
+  if (key === candidate) return entry;
   var keyIsNaN = $numberIsNaN(key);
-  for (var entry = HashToEntry(table, hash, numBuckets);
-       entry !== NOT_FOUND;
-       entry = ORDERED_HASH_SET_CHAIN_AT(table, entry, numBuckets)) {
-    var candidate = ORDERED_HASH_SET_KEY_AT(table, entry, numBuckets);
-    if (key === candidate) {
-      return entry;
-    }
+  while (true) {
     if (keyIsNaN && $numberIsNaN(candidate)) {
       return entry;
     }
+    entry = ORDERED_HASH_SET_CHAIN_AT(table, entry, numBuckets);
+    if (entry === NOT_FOUND) return entry;
+    candidate = ORDERED_HASH_SET_KEY_AT(table, entry, numBuckets);
+    if (key === candidate) return entry;
   }
   return NOT_FOUND;
 }
 %SetForceInlineFlag(SetFindEntry);
 
 
 function MapFindEntry(table, numBuckets, key, hash) {
+  var entry = HashToEntry(table, hash, numBuckets);
+  if (entry === NOT_FOUND) return entry;
+  var candidate = ORDERED_HASH_MAP_KEY_AT(table, entry, numBuckets);
+  if (key === candidate) return entry;
   var keyIsNaN = $numberIsNaN(key);
-  for (var entry = HashToEntry(table, hash, numBuckets);
-       entry !== NOT_FOUND;
-       entry = ORDERED_HASH_MAP_CHAIN_AT(table, entry, numBuckets)) {
-    var candidate = ORDERED_HASH_MAP_KEY_AT(table, entry, numBuckets);
-    if (key === candidate) {
-      return entry;
-    }
+  while (true) {
     if (keyIsNaN && $numberIsNaN(candidate)) {
       return entry;
     }
+    entry = ORDERED_HASH_MAP_CHAIN_AT(table, entry, numBuckets);
+    if (entry === NOT_FOUND) return entry;
+    candidate = ORDERED_HASH_MAP_KEY_AT(table, entry, numBuckets);
+    if (key === candidate) return entry;
   }
   return NOT_FOUND;
 }
 %SetForceInlineFlag(MapFindEntry);
 
 
 function ComputeIntegerHash(key, seed) {
   var hash = key;
   hash = hash ^ seed;
   hash = ~hash + (hash << 15);  // hash = (hash << 15) - hash - 1;
   hash = hash ^ (hash >>> 12);
   hash = hash + (hash << 2);
   hash = hash ^ (hash >>> 4);
   hash = (hash * 2057) | 0;  // hash = (hash + (hash << 3)) + (hash << 11);
   hash = hash ^ (hash >>> 16);
-  return hash;
+  return hash & 0x3fffffff;
 }
 %SetForceInlineFlag(ComputeIntegerHash);
 
+var hashCodeSymbol = GLOBAL_PRIVATE("hash_code_symbol");
 
-function GetHash(key) {
+function GetExistingHash(key) {

[Toon Verwaest, 2015/05/26 09:06:26]

That's a pretty deceiving name since it does compute a new hash for
non-jsobjects (and global proxies)

[Erik Corry Chromium.org, 2015/05/26 09:51:32]

Left as is after offline discussion.

   if (%_IsSmi(key)) {
     return ComputeIntegerHash(key, 0);
   }
   if (IS_STRING(key)) {
     var field = %_StringGetRawHashField(key);
     if ((field & 1 /* Name::kHashNotComputedMask */) === 0) {
       return field >>> 2 /* Name::kHashShift */;
     }
+  } else if (IS_SPEC_OBJECT(key) && !%_IsJSProxy(key) && !IS_GLOBAL(key)) {
+    var hash = GET_PRIVATE(key, hashCodeSymbol);
+    return hash;
   }
   return %GenericHash(key);
 }
+%SetForceInlineFlag(GetExistingHash);
+
+
+function GetHash(key) {
+  var hash = GetExistingHash(key);
+  if (IS_UNDEFINED(hash)) {
+    hash = IntRandom() | 0;
+    if (hash === 0) hash = 1;
+    SET_PRIVATE(key, hashCodeSymbol, hash);
+  }
+  return hash;
+}
 %SetForceInlineFlag(GetHash);
 
 
 // -------------------------------------------------------------------
 // Harmony Set
 
 function SetConstructor(iterable) {
   if (!%_IsConstructCall()) {
     throw MakeTypeError(kConstructorNotFunction, "Set");
   }
@@ skipping 52 matching lines @@
   return this;
 }
 
 
 function SetHas(key) {
   if (!IS_SET(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver, 'Set.prototype.has', this);
   }
   var table = %_JSCollectionGetTable(this);
   var numBuckets = ORDERED_HASH_TABLE_BUCKET_COUNT(table);
-  var hash = GetHash(key);
+  var hash = GetExistingHash(key);
+  if (IS_UNDEFINED(hash)) return false;
   return SetFindEntry(table, numBuckets, key, hash) !== NOT_FOUND;
 }
 
 
 function SetDelete(key) {
   if (!IS_SET(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver,
                         'Set.prototype.delete', this);
   }
   var table = %_JSCollectionGetTable(this);
   var numBuckets = ORDERED_HASH_TABLE_BUCKET_COUNT(table);
-  var hash = GetHash(key);
+  var hash = GetExistingHash(key);
+  if (IS_UNDEFINED(hash)) return false;
   var entry = SetFindEntry(table, numBuckets, key, hash);
   if (entry === NOT_FOUND) return false;
 
   var nof = ORDERED_HASH_TABLE_ELEMENT_COUNT(table) - 1;
   var nod = ORDERED_HASH_TABLE_DELETED_COUNT(table) + 1;
   var index = ORDERED_HASH_SET_ENTRY_TO_INDEX(entry, numBuckets);
   FIXED_ARRAY_SET(table, index, %_TheHole());
   ORDERED_HASH_TABLE_SET_ELEMENT_COUNT(table, nof);
   ORDERED_HASH_TABLE_SET_DELETED_COUNT(table, nod);
   if (nof < (numBuckets >>> 1)) %SetShrink(this);
@@ skipping 94 matching lines @@
 }
 
 
 function MapGet(key) {
   if (!IS_MAP(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver,
                         'Map.prototype.get', this);
   }
   var table = %_JSCollectionGetTable(this);
   var numBuckets = ORDERED_HASH_TABLE_BUCKET_COUNT(table);
-  var hash = GetHash(key);
+  var hash = GetExistingHash(key);
+  if (IS_UNDEFINED(hash)) return UNDEFINED;
   var entry = MapFindEntry(table, numBuckets, key, hash);
   if (entry === NOT_FOUND) return UNDEFINED;
   return ORDERED_HASH_MAP_VALUE_AT(table, entry, numBuckets);
 }
 
 
 function MapSet(key, value) {
   if (!IS_MAP(this)) {
     throw MakeTypeError(kIncompatibleMethodReceiver,
                         'Map.prototype.set', this);
@@ skipping 134 matching lines @@
 $installGetter(GlobalMap.prototype, "size", MapGetSize);
 $installFunctions(GlobalMap.prototype, DONT_ENUM, [
   "get", MapGet,
   "set", MapSet,
   "has", MapHas,
   "delete", MapDelete,
   "clear", MapClearJS,
   "forEach", MapForEach
 ]);
 
+// Expose to the global scope.
+$getHash = GetHash;
+$getExistingHash = GetExistingHash;
+
 })