Improve the performance of bit set searches with a compiler intrinsic.

runtime/vm/freelist.h

 // 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.
 
 #ifndef VM_FREELIST_H_
 #define VM_FREELIST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bit_set.h"
@@ skipping 75 matching lines @@
  private:
   static const int kNumLists = 128;
 
   static intptr_t IndexForSize(intptr_t size);
 
   void EnqueueElement(FreeListElement* element, intptr_t index);
   FreeListElement* DequeueElement(intptr_t index);
 
   void SplitElementAfterAndEnqueue(FreeListElement* element, intptr_t size);
 
-  BitSet<kNumLists + 1> free_map_;
+  BitSet<kNumLists> free_map_;
 
   FreeListElement* free_lists_[kNumLists + 1];
 
   DISALLOW_COPY_AND_ASSIGN(FreeList);
 };
 
 }  // namespace dart
 
 #endif  // VM_FREELIST_H_