new DIP38: Safe references and rvalue references without runtime checks.

[Timothee Cour]

> It requires interprocedural analysis. This is possible for the same
> functions (such as template functions) that can infer pure/nothrow/@safe,
> but it cannot be done for ordinary functions.

Can you please provide me a simple example for which the algorithm
proposed in the DIP38 will fail, and that does not involve cycles (as
described in the DIP) ?