https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91555
--- Comment #4 from Daniel Richard G. <skunk at iskunk dot org> --- Yes, that is the case: $ gcc -O2 gcc9-opt-bug.c -o bug $ ./bug WRONG 13 result: t = 18446744073709551615 (wrong) $ gcc -O2 -fwrapv gcc9-opt-bug.c -o bug $ ./bug result: t = 1009489458 (correct)