Tail call optimization in last CLR

I've discovered (by accident) that the last CLR does the tail call optimization. I have tested it with a piece of code, but frankly it doesn't behave the way I expected. I thought the tail call optimization may happen when the last thing in the function is a function call.

I'm trying to "break" this code to prevent form tail call op.

class Program
{
    static void Foo(int counter, int limit)
    {
        try
        {
            if (counter == limit)
            {
                ret开发者_StackOverflow中文版urn;
            }
            Foo(++counter, limit);

            int d = 1;
            d = Bar(d);
            //Console.Write(d);
            //Thread.Sleep(1);
            int baz = 0;
            var z = baz + d;
            StringBuilder b = new StringBuilder();
            b.Append("D");
        }
        catch (Exception)
        {
            throw;
        }
    }

    static int Sum(int s)
    {
        if (s == 1)
        {
            return s;
        }
        return s + Sum(s - 1);
    }

    static int Bar(int d)
    {
      return  d = 10 + d;
    }

    static void Main(string[] args)
    {
        int i = 0;

        Foo(i, 10000); // jitter 
        Sum(10000);

        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        Foo(i, 10000);
        stopwatch.Stop();
        Console.WriteLine(string.Format("time of execution = {0}ms",stopwatch.ElapsedMilliseconds));

        stopwatch = new Stopwatch();
        stopwatch.Start();
        Sum(10000);
        stopwatch.Stop();
        Console.WriteLine(string.Format("time of execution = {0}ms", stopwatch.ElapsedMilliseconds));

        Console.ReadKey();
    }
}

Yet still Foo is optimized. How come?

You haven't done anything with side-effects after the recursive call to Foo. I assume you tried the commented out code and it DID prevent optimization. So what's the problem?

You could also write to a class member, that would be a side-effect that couldn't be discarded.

private static int dummy;
static void Foo(int counter, int limit)
{
    if (counter == limit) return;
    Foo(++counter, limit);
    dummy++;
}

and then read dummy at the end of Main.