Move hash code from hidden string to a private symbol

src/collection.js

Index: src/collection.js
diff --git a/src/collection.js b/src/collection.js
index db30546165119e53f0c4e03a1b5e856259927f10..a4d5204ce3e3dd0ff025103d4c4ad3ab65401842 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+var $gethash;

[adamk, 2015/05/21 19:11:32]

Rename to $getHash

[Erik Corry, 2015/05/22 06:20:24]

Done.

+var $getexistinghash;

[adamk, 2015/05/21 19:11:32]

and $getExistingHash

[Erik Corry, 2015/05/22 06:20:24]

Done.

+
 (function(global, shared, exports) {
 
 "use strict";
@@ -22,17 +25,19 @@ function HashToEntry(table, hash, numBuckets) {
 
 
 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);

[adamk, 2015/05/21 19:11:32]

Why did this get rewritten as a while loop? From my inspection the only
difference I see is extra calls to KEY_AT and extra comparisons.

[Erik Corry, 2015/05/21 20:19:01]

The idea is to avoid testing the key for Nan-ness in the case where the first
probe fails or hits.

-       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;
 }
@@ -40,17 +45,19 @@ function SetFindEntry(table, numBuckets, key, hash) {
 
 
 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);

[adamk, 2015/05/21 19:11:32]

Same question down here.

[Erik Corry, 2015/05/21 20:19:01]

Same answer :-)

-       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;
 }
@@ -66,12 +73,13 @@ function ComputeIntegerHash(key, seed) {
   hash = hash ^ (hash >>> 4);
   hash = (hash * 2057) | 0;  // hash = (hash + (hash << 3)) + (hash << 11);
   hash = hash ^ (hash >>> 16);
-  return hash;
+  return hash & 0x3fffffff;

[adamk, 2015/05/21 19:11:32]

Why the extra &? This used to be equivalent to ComputeIntegerHash() in utils.h.

[Erik Corry, 2015/05/22 06:20:24]

To make sure it's always a Smi.  I changed ComputeIntegerHash to match.

 }
 %SetInlineBuiltinFlag(ComputeIntegerHash);
 
+var hash_code_symbol = GLOBAL_PRIVATE("hash_code_symbol");

[adamk, 2015/05/21 19:11:32]

Please use JS style here ("hashCodeSymbol").

[Erik Corry, 2015/05/22 06:20:24]

Done.

 
-function GetHash(key) {
+function GetExistingHash(key) {
   if (%_IsSmi(key)) {
     return ComputeIntegerHash(key, 0);
   }
@@ -80,9 +88,27 @@ function GetHash(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, hash_code_symbol);
+    return hash;
   }
   return %GenericHash(key);

[adamk, 2015/05/21 19:11:32]

%GenericHash calls GetOrCreateHash, which seems wrong for this case. Maybe add a
new runtime function that calls GetHash() instead (though maybe we don't care
much about this case).

[Erik Corry, 2015/05/21 20:19:02]

I think we don't care much about this case, it's only proxies.  And symbols, but
they should be born with a hash code (and it would be nice to handle them above
in the string clause, which would then be a name clause).

 }
+%SetInlineBuiltinFlag(GetExistingHash);
+
+
+function GetHash(key) {
+  var hash = GetExistingHash(key);
+  if (IS_UNDEFINED(hash)) {
+    if (IS_GLOBAL(key)) {

[adamk, 2015/05/21 19:11:32]

I think this branch is currently unreachable due to the above.

[Erik Corry, 2015/05/21 20:19:02]

Good point.

I think a better solution would be for global objects to be born with a hash
code, and it should always be 1 (or 42).  That way we don't have to keep track
of them specially, and that would give us back our 5% on the weak maps.

+      return %GenericHash(key);
+    }
+    hash = $intrandom() | 0;
+    if (hash === 0) hash = 1;
+    SET_PRIVATE(key, hash_code_symbol, hash);
+  }
+  return hash;
+}
 %SetInlineBuiltinFlag(GetHash);
 
 
@@ -155,7 +181,8 @@ function SetHas(key) {
   }
   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;
 }
 
@@ -167,7 +194,8 @@ function SetDelete(key) {
   }
   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;
 
@@ -282,7 +310,8 @@ function MapGet(key) {
   }
   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);
@@ -437,4 +466,8 @@ $installFunctions(GlobalMap.prototype, DONT_ENUM, [
   "forEach", MapForEach
 ]);
 
+// Expose to the global scope.
+$gethash = GetHash;
+$getexistinghash = GetExistingHash;
+
 })