https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103202
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Sergei Trofimovich from comment #3)
> Created attachment 51776 [details]
> main_loop_simpler.c
>
> Attaching seemingly simpler example. I applied most inlines and simplified
> loops as much as I could. It looks like VRP does something funny with:
>
> while (n > 0)
> {
> while (n-- > 0)
> {
>
> Looking at 039t.mergephi1
>
> with -fno-tree-vrp:
>
> --- no-vrp/ed-main_loop.c.039t.mergephi1 2021-11-12 09:07:55.120821967
> +0000
> +++ yes-vrp/ed-main_loop.c.039t.mergephi1 2021-11-12 09:07:55.186822973
> +0000
> @@ -93,7 +93,7 @@
> # np_6 = PHI <np_7(10), np_40(6)>
> # n_8 = PHI <n_9(10), n_23(6)>
> n_23 = n_8 + -1;
> - if (n_8 > 0)
> + if (n_8 != 0)
> goto <bb 4>; [INV]
> else
> goto <bb 8>; [INV]
>
> I think our loop is executed with n == -1 on real data and vrp provided
> incorrect range.
But how would the inner loop be reachable with n == -1?
