Warn about do nothing expressions?

[Timon Gehr]

On 03/28/2014 10:56 PM, Ali Çehreli wrote:
>
>  >
>  > Both gcc and clang agree that in C, assigning a post-increment to itself
>  > results in the original value.
>
> The result of a test program cannot be proof of that. In fact, changing
> the value of a variable more than once between two sequence points is
> undefined behavior.
>
>  > At least Clang warns, which is good,
>
> It is unfortunate that Clang does not use the word "undefined" there.
>
>  > but D is consistent with C's behavior on this point.
>
> It is undefined behavior in both languages.

How do you reach that conclusion in the case of D?