visitCount++;
  public final void markGrey(VM_Address object)    throws VM_PragmaInline {    if (VM.VerifyAssertions) VM._assert(workQueue.pop().isZero());    while (!object.isZero()) {      if (!SimpleRCBaseHeader.isGrey(object)) {	SimpleRCBaseHeader.makeGrey(object);	ScanObject.scan(object);      }      object = workQueue.pop();    }  }