https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80988
--- Comment #5 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Simple test case:
$ cat swim.f90
program main
implicit none
integer :: i,j
integer, dimension(3,3) :: a
a = reshape([(((i*10+j),i=1,3),j=1,3)], shape(a))
print *,(a(i,i),i=1,3)
end program main
$ gfortran swim.f90 && ./a.out
11 22 33
$ gfortran -O swim.f90 && ./a.out
0 -188758720 32767
$
