https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64099
--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> --- > My guess is that -fstack-arrays makes the difference. Confirmed: [Book15] lin/test% gfc -Ofast -fwhole-program fatigue.f90 -fno-stack-arrays [Book15] lin/test% time a.out > /dev/null 2.982u 0.001s 0:02.98 100.0% 0+0k 0+1io 0pf+0w