[Bug tree-optimization/109002] -O1 -ftree-pre -ftree-partial-pre results in stall value

[akihiko.odaki at daynix dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109002

--- Comment #2 from Akihiko Odaki <akihiko.odaki at daynix dot com> ---
Oops. Replacing i++ with i = !i removes the undefined behavior while the bug
still remains.