https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110311
--- Comment #24 from Jürgen Reuter <juergen.reuter at desy dot de> --- Here is a first reproducer without the need for OCaml, unfortunately a bit too big to be uploaded, here is the link: https://www.desy.de/~reuter/downloads/repro001.tar.xz the tarball contains Fortran files that compile to two binaries, ./whizard and ./whizard_check. After compilation, perform ./whizard r1.sin to run the program. There will be NaNs generated in our RNG stream random number generator. They originate from an erroneous optimization by the gcc/gfortran tree-optimizer. This code resides in rng_stream_sub.f90, in the function mult_mod. Eliminating the intrinsic function mod and explicitly doing the calculation makes the problem go away. function mult_mod (a, b, c, m) result (v) real(default), intent(in) :: a real(default), intent(in) :: b real(default), intent(in) :: c real(default), intent(in) :: m real(default) :: v integer :: a1 real(default) :: a2 v = a * b + c if (v >= two53 .or. v <= -two53) then a1 = int (a / two17) a2 = a - a1 * two17 v = mmm_mod (a1 * b, m) v = v * two17 + a2 * b + c end if v = mmm_mod (v, m) if (v < 0.0_default) v = v + m contains elemental function mmm_mod (x1, x2) result (res) real(default), intent(in) :: x1, x2 real(default) :: res res = x1 - int(x1/x2) * x2 end function mmm_mod end function mult_mod
