enum E
{
    A,
    B = A,
    C,
    D

}
class Stuff
{
    static void Foo(E e)
    {
        switch(e)
        {
            // Generate switch labels
        }
    }
}

class Stuff
{
    static void Foo(E e)
    {
        switch(e)
        {
            case E.A:
                break;
            case E.B: // Duplicate case label
                break;
            case E.C:
                break;
            case E.D:
                break;
            default:
                throw new ArgumentOutOfRangeException("e");
        }
    }
}