[Bug c/65467] [libgomp] sorry, unimplemented: '_Atomic' with OpenMP

["jeff.science at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65467

--- Comment #10 from Jeff Hammond <jeff.science at gmail dot com> ---
(In reply to Andrew Pinski from comment #9)
> (In reply to Jeff Hammond from comment #8)
> > So GCC refuses to compile any code that potentially includes undefined
> > behavior?
> 
> Semantics not being defined is different than undefined behavior.

GCC happily compiles a C++11 OpenMP program that is equivalent to the C11
OpenMP program that it will not compile.

GCC happily compiles the following Fortran 2008 OpenMP program that actually
does something that could be considered undefined.

$ gfortran-6 -fopenmp -std=f2008 -fcoarray=single caf-openmp.f 
$ cat caf-openmp.f 
      program atomic
      use iso_fortran_env
      use omp_lib
      implicit none
      integer :: i
      integer(atomic_int_kind) :: atom[*]
      call atomic_define (atom[1], this_image())
      !$OMP ATOMIC
      atom[1] = -this_image()
      end program atomic

If you want to break user experience for OpenMP programmers, please do it
systematically.