[Bug c/68120] can't easily deal with integer overflow at compile time

[eggert at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68120

--- Comment #6 from Paul Eggert <eggert at gnu dot org> ---
(In reply to Martin Sebor from comment #5)
> Patch posted for review:
> https://gcc.gnu.org/ml/gcc-patches/2016-05/msg00013.html

Thanks. This patch appears to address almost all the request, and it is
definitely a step forward.

Even with the change, I see no easy way in a constant expression to compute the
bottom-order bits (ignoring overflow) of a signed integer value, but I can
raise this issue as a separate enhancement request if it turns into a problem
in practice.