[Bug fortran/57871] gfortran -freal-4-real-16 gives wrong result for selected_real_kind(1)

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57871

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
   Last reconfirmed|                            |2013-07-10
                 CC|                            |kargl at gcc dot gnu.org
         Resolution|INVALID                     |---
     Ever confirmed|0                           |1

--- Comment #2 from kargl at gcc dot gnu.org ---
(In reply to Dominique d'Humieres from comment #1)
> > gfortran 4.8.1 -freal-4-real-16 gives real(16) kind with 
> > selected_real_kind(1) but it ought to give real(8) because that is 
> > the smallest decimal precision available with that compiler option. 
> 
> and your example does exactly that: Closing as INVALID.

I think that you may have been a little too hasty in closing
this PR.  The issue lies in the code for selected_real_kind.

  implicit none
  integer,parameter:: p1 = selected_real_kind(1)

This initialization expression is requesting the type with
smallest precision that exceeds 1.  With -freal-4-real-16,
that type is double precision (ie kind=8).  The problem
lies in gfc_simplify_selected_real_kind.  It has no knowledge
of the -freal-*-real-* options.  The loop (lines 5447-5457)

  for (i = 0; gfc_real_kinds[i].kind != 0; i++)
    {
      if (gfc_real_kinds[i].precision >= precision)
        found_precision = 1;

      if (gfc_real_kinds[i].range >= range)
        found_range = 1;

      if (gfc_real_kinds[i].radix >= radix)
        found_radix = 1;

      if (gfc_real_kinds[i].precision >= precision
      && gfc_real_kinds[i].range >= range
      && gfc_real_kinds[i].radix >= radix && gfc_real_kinds[i].kind < kind)
    kind = gfc_real_kinds[i].kind;
    }

searchs the ordered set [24, 53, 53, 113] (on FreeBSD-i386) or
[24, 53, 64, 113] (on FreeBSD-amd64).  In either case, the
initialization expression returns REAL(4).  However, with
-freal-4-real-16,  one might expect the ordered set to be
searched is [113, 53, 64, 113] as REAL(4) has been promoted
to REAL(16).