[Bug fortran/107819] ICE in gfc_check_argument_var_dependency, at fortran/dependency.cc:978

["anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107819

--- Comment #5 from anlauf at gcc dot gnu.org ---
(In reply to Mikael Morin from comment #4)
> But is it required to generate a temporary?
> As I understand it, the code is invalid, and (correctly) diagnosed, so there
> is nothing else to do.
> It's invalid because of 15.5.2.13 Restrictions on entities associated with
> dummy arguments:
> (4) If the value of the entity or any subobject of it is affected through
> the dummy argument, then at any time during the invocation and execution of
> the procedure, either before or after the definition, it shall be referenced
> only through that dummy argument unless (...)

Right.

I was confused by two observations.  First, NAG & Cray seem to generate
temporaries, while Intel and NVidia don't and would agree with gfortran
after the patch.

Second, I stumbled over:

! 15.5.2.3 Argument association
! (4) A present dummy argument with the VALUE attribute becomes argument
! associated with a definable anonymous data object whose initial value is
! the value of the actual argument.

So it boils down to what ELEMENTAL actually means in that context.  F2018:

15.8.3 Elemental subroutine actual arguments

! In a reference to an elemental subroutine, if the actual arguments
! corresponding to INTENT(OUT) and INTENT(INOUT) dummy arguments are
! arrays, the values of the elements, if any, of the results are the same
! as would be obtained if the subroutine had been applied separately, in
! array element order, to corresponding elements of each array actual
! argument.

So I read this that

   call s (a(n), a)

is to be interpreted as

  do i = 1, size (a)
     call s (a(n(i)), a(i))
  end do

and this would actually be well-defined behavior... ;-)