VM: Fix _CompactLinkedHashSet performance regression.

runtime/lib/compact_hash.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:typed_data';
 import 'dart:_internal' as internal;
 
 // Hash table with open addressing that separates the index from keys/values.
 
 abstract class _HashFieldBase {
   // Each occupied entry in _index is a fixed-size integer that encodes a pair:
   //   [ hash pattern for key | index of entry in _data ]
   // The hash pattern is based on hashCode, but is guaranteed to be non-zero.
   // The length of _index is always a power of two, and there is always at
   // least one unoccupied entry.
   // NOTE: When maps are deserialized, their _index and _hashMask is regenerated
   // lazily by _regenerateIndex.
   // TODO(koda): Consider also using null _index for tiny, linear-search tables.
-  Uint32List _index;
+  Uint32List _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
 
   // Cached in-place mask for the hash pattern component. 
-  int _hashMask;
+  int _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
 
   // Fixed-length list of keys (set) or key/value at even/odd indices (map).
   List _data;
 
   // Length of _data that is used (i.e., keys + values for a map).
   int _usedData = 0;
 
   // Number of deleted keys.
   int _deletedKeys = 0;
+
+  // Note: All fields are initialized in a single constructor so that the VM
+  // recognizes they cannot hold null values. This makes a big (20%) performance
+  // difference on some operations.
+  _HashFieldBase(int dataSize) : this._data = new List(dataSize);
 }
 
 // Base class for VM-internal classes; keep in sync with _HashFieldBase.
 abstract class _HashVMBase {
   Uint32List get _index native "LinkedHashMap_getIndex";
   void set _index(Uint32List value) native "LinkedHashMap_setIndex";
 
   int get _hashMask native "LinkedHashMap_getHashMask";
   void set _hashMask(int value) native "LinkedHashMap_setHashMask";
 
@@ skipping 303 matching lines @@
       new _CompactIterable<K>(this, _data, _usedData, -2, 2);
   Iterable<V> get values =>
       new _CompactIterable<V>(this, _data, _usedData, -1, 2);
 }
 
 class _CompactLinkedIdentityHashMap<K, V> extends _HashFieldBase
     with MapMixin<K, V>, _LinkedHashMapMixin<K, V>, _HashBase,
          _IdenticalAndIdentityHashCode
     implements LinkedHashMap<K, V> {
 
-  _CompactLinkedIdentityHashMap() {
-    _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
-    _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
-    _data = new List(_HashBase._INITIAL_INDEX_SIZE);
-  }
+  _CompactLinkedIdentityHashMap() : super(_HashBase._INITIAL_INDEX_SIZE);
 }
 
 class _CompactLinkedCustomHashMap<K, V> extends _HashFieldBase
     with MapMixin<K, V>, _LinkedHashMapMixin<K, V>, _HashBase
     implements LinkedHashMap<K, V> {
   final _equality;
   final _hasher;
   final _validKey;
 
   // TODO(koda): Ask gbracha why I cannot have fields _equals/_hashCode.
   int _hashCode(e) => _hasher(e);
   bool _equals(e1, e2) => _equality(e1, e2);
 
   bool containsKey(Object o) => _validKey(o) ? super.containsKey(o) : false;
   V operator[](Object o) => _validKey(o) ? super[o] : null;
   V remove(Object o) => _validKey(o) ? super.remove(o) : null;
 
   _CompactLinkedCustomHashMap(this._equality, this._hasher, validKey)
-      : _validKey = (validKey != null) ? validKey : new _TypeTest<K>().test {
-    _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
-    _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
-    _data = new List(_HashBase._INITIAL_INDEX_SIZE);
-  }
+      : _validKey = (validKey != null) ? validKey : new _TypeTest<K>().test,
+        super(_HashBase._INITIAL_INDEX_SIZE);
 }
 
 // Iterates through _data[_offset + _step], _data[_offset + 2*_step], ...
 // and checks for concurrent modification.
 class _CompactIterable<E> extends IterableBase<E> {
   final _table;
   final List _data;
   final int _len;
   final int _offset;
   final int _step;
@@ skipping 36 matching lines @@
       return false;
     }
   }
 }
 
 // Set implementation, analogous to _CompactLinkedHashMap.
 class _CompactLinkedHashSet<E> extends _HashFieldBase
     with _HashBase, _OperatorEqualsAndHashCode, SetMixin<E>
     implements LinkedHashSet<E> {
 
-  _CompactLinkedHashSet() {
+  _CompactLinkedHashSet() : super(_HashBase._INITIAL_INDEX_SIZE >> 1) {
     assert(_HashBase._UNUSED_PAIR == 0);
-    _index = new Uint32List(_HashBase._INITIAL_INDEX_SIZE);
-    _hashMask = _HashBase._indexSizeToHashMask(_HashBase._INITIAL_INDEX_SIZE);
-    _data = new List(_HashBase._INITIAL_INDEX_SIZE >> 1);
   }
 
   int get length => _usedData - _deletedKeys;
 
   void _rehash() {
     if ((_deletedKeys << 1) > _usedData) {
       _init(_index.length, _hashMask, _data, _usedData);
     } else {
       _init(_index.length << 1, _hashMask >> 1, _data, _usedData);
     }
@@ skipping 137 matching lines @@
   E lookup(Object o) => _validKey(o) ? super.lookup(o) : null;
   bool remove(Object o) => _validKey(o) ? super.remove(o) : false;
 
   _CompactLinkedCustomHashSet(this._equality, this._hasher, validKey)
       : _validKey = (validKey != null) ? validKey : new _TypeTest<E>().test;
 
   Set<E> toSet() =>
       new _CompactLinkedCustomHashSet<E>(_equality, _hasher, _validKey)
           ..addAll(this);
 }