VM: Optimize RegExp.matchAsPrefix(...) by generating a sticky RegExp specialization.

runtime/lib/regexp_patch.dart

 // Copyright (c) 2012, 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.
 
 @patch class RegExp {
   @patch factory RegExp(String source,
                               {bool multiLine: false,
                                bool caseSensitive: true}) {
     _RegExpHashKey key = new _RegExpHashKey(
         source, multiLine, caseSensitive);
@@ skipping 142 matching lines @@
     }
     return new _AllMatchesIterable(this, string, start);
   }
 
   Match matchAsPrefix(String string, [int start = 0]) {
     if (string is! String) throw new ArgumentError(string);
     if (start is! int) throw new ArgumentError(start);
     if (start < 0 || start > string.length) {
       throw new RangeError.range(start, 0, string.length);
     }
-    // Inefficient check that searches for a later match too.
-    // Change this when possible.
-    List<int> list = _ExecuteMatch(string, start);
+    List<int> list = _ExecuteMatchSticky(string, start);
     if (list == null) return null;
-    if (list[0] != start) return null;
     return new _RegExpMatch(this, string, list);
   }
 
   bool hasMatch(String str) {
     if (str is! String) throw new ArgumentError(str);
     List match = _ExecuteMatch(str, 0);
     return (match == null) ? false : true;
   }
 
   String stringMatch(String str) {
@@ skipping 53 matching lines @@
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
 
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   ];
 
   List _ExecuteMatch(String str, int start_index)
       native "RegExp_ExecuteMatch";
+
+  List _ExecuteMatchSticky(String str, int start_index)
+      native "RegExp_ExecuteMatchSticky";
 }
 
 class _AllMatchesIterable extends IterableBase<Match> {
   final _RegExp _re;
   final String _str;
   final int _start;
 
   _AllMatchesIterable(this._re, this._str, this._start);
 
   Iterator<Match> get iterator => new _AllMatchesIterator(_re, _str, _start);
@@ skipping 21 matching lines @@
           _nextIndex++;
         }
         return true;
       }
     }
     _current = null;
     _re = null;
     return false;
   }
 }