[Bug c/84121] optimizer breaks code without -frwapv, but -Wall -Wextra show no warnings

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84121

--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> ---
What I don't understand is why -fsanitize=undefined does not say anything when
running this program, whether I use gcc or clang...