[Bug c/66348] Simple loop never exits with -O1, exits with -O0

[sebastiano.vigna at unimi dot it]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66348

--- Comment #13 from Sebastiano Vigna <sebastiano.vigna at unimi dot it> ---
I can confirm that compiling/running with ubsan and asan no problem is
reported. The bug does not show up.