Re: [RFC] Fix div/mul crash and more undefined behavior

Xi Wang <xi(dot)wang(at)gmail(dot)com> writes:
> The reality is that C compilers are not friendly to postcondition
> checking; they consider signed integer overflow as undefined behavior,
> so they do whatever they want to do. Even workaround options like
> -fwrapv are often broken, not to mention that they may not even have
> those options.

I think it's probably past time that we stopped guessing about this
sort of thing and added some regression test cases for it. I'm
planning to add cases like this:

-- check sane handling of INT_MIN overflow cases
SELECT (-2147483648)::int4 * (-1)::int4;
SELECT (-2147483648)::int4 / (-1)::int4;
SELECT (-2147483648)::int4 % (-1)::int4;

regards, tom lane