Subject: bug#2790: emacs 22.1.1 cannot open 5GB file on
64GB 64-bit GNU/Linux box

> The compiler can (and does) optimize on the fact that overflow does not
> occur, thus the operation x*4/4 becomes a no-op.

No way!? Hmm... yes, I guess it's within the allowed semantics, indeed.
We could prevent optimization by going through a volatile var,
of course.

So in the end, I still prefer the current solution of removing the
check altogether.