https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101186
--- Comment #2 from Di Zhao <dizhao at os dot amperecomputing.com> ---
(In reply to Richard Biener from comment #1)
> The complication is that the a == b equivalence has to be taken into account
> to relate the c < a and c >= b relations.
>
> Maybe the new relation code can do sth here, but confirmed on trunk.
>
> void g (int a, int b, int x, int y)
> {
> int c = y;
> if (a != 0)
> c = x;
> while (b < 1000)
> // without this loop, jump thread & VRP can remove dead code
> {
> if (a != 0)
> {
> if (c > x)
> printf ("Unreachable!");
> }
>
> that's also a classical example for predicated value-numbering (which we
> don't implement).
I've implemented a patch on FRE regarding this and will send it to patches
mailing list soon.
Thanks
