private void AddTryStart(Handler handler)
{
Label tryStart = CodeProvider.TryStart(handler);
Stack <Handler> stack;
this.try_start_list.TryGetValue(tryStart, out stack);
if (stack == null)
{
stack = new Stack <Handler> ();
this.try_start_list [tryStart] = stack;
}
stack.Push(handler);
AddTargetLabel(tryStart);
}