[Bug fortran/109500] SIGABRT when calling a function that returns an unallocated value

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109500

--- Comment #17 from anlauf at gcc dot gnu.org ---
(In reply to Steve Kargl from comment #16)
> First, note, 'allocated(f())' throws an error.

Agree.

> Now, with the original code,
> 
>       is_allocated(f())
> 
> The function reference is evaluated, and then the function result
> (aka it's value) is argument associated with an allocatable dummy
> argument.  This is technically wrong as the actual argument (aka
> value returned by the function reference) should not have the
> allocatable attribute.

Agree.  See also the discussion on the J3 mailing list.

> I'll repeat.  The actual argument is the value resulting from
> the function reference.  The "shall" in "shall be allocatable"
> applies to something the programmer must ensure.

Agree.

> If we go back to the original code and modify to allocate
> f by say doing 'f = 42' in f(), gfortran produces 
> 
> % gfcx -o z -Wall a.f90 && ./z
>  T
> 
> This is the problem.  Yes, f is allocated and assigned 
> 42.  The printed 'T' is bogus because 42 is value of
> the function.  42 is no allocatable.

Agree again.

The point is that there is a bug in gfortran which currently effectively
generates code which resembles

  integer, allocatable :: p
  p = f()
  print *, is_allocated(p)
  deallocate (p)

(of course with a temporary for the function result).
The technical reason for the crash is the copying of the function (non)result.

The patch in comment#9 rejects all related misuses.

Given the lengthy thread on the J3 mailing list, I am wondering whether there
ever was an explicit IR on the issue, or was it considered so obvious that
the clarification was deferred to the F2018 document.



> One place to possibly check for an error is when 
> gfortran resolves argument association.  If a dummy
> argument is allocatable, the actual argument needs 
> to be allocatable and cannot not also be a function
> result variable.