[Bug fortran/101635] New: FAIL: gfortran.dg/PR93963.f90 – alias-handling issue with BIND(C)'s _gfortran_cfi_desc_to_gfc_desc

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101635

            Bug ID: 101635
           Summary: FAIL: gfortran.dg/PR93963.f90 – alias-handling issue
                    with BIND(C)'s _gfortran_cfi_desc_to_gfc_desc
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
                CC: jrfsousa at gcc dot gnu.org, sandra at gcc dot gnu.org
  Target Milestone: ---

This is kind of a regression as the testcase is new with the
commit r12-2511-g0cbf03689e3e7d9d6002b8e5d159ef3716d0404c
for PR 93308, PR 93963, PR 94327, PR 94331, and PR 97046.

The testcase  gfortran.dg/PR93963.f90  has the following;
the → lines are from the -fdump-tree-original:

  integer(kind=c_int),     pointer :: intp(:)
  nullify(intp)
  irnk = rank_p(intp)   ! this is BIND(C) with an assumed-rank argument

and the dump

   intp.dtype = {.elem_len=4, .rank=1, .type=1};
   intp.data = 0B;

and for the rank_p call:
      void * cfi.6;

      if ((integer(kind=4)[0:] *) intp.data == 0B)
        {
          intp.dtype = {.elem_len=4, .rank=1, .type=1};
        }
      _gfortran_gfc_desc_to_cfi_desc (&cfi.6, &intp);
      irnk = rank_p (cfi.6);
      __builtin_free (cfi.6);


With -m32  + optimizations, there seems to be an alias analysis issue which
causes that in rank_p, the argument's rank is <0 or >15 – such that rank_p
returns -1000. Unsurprisingly,
  -1000 != 1
and, hence, the program runs into:
  if (irnk /= rnk)        stop 1

 * * *

Solution:  I think the proper fix is to remove both 
_gfortran_gfc_desc_to_cfi_desc  and  _gfortran_cfi_desc_to_gfc_desc from
libgfortran/runtime/ISO_Fortran_binding.c and create inline code in the
compiler itself, i.e. in gcc/fortran/trans-expr.c's
gfc_conv_gfc_desc_to_cfi_desc and in gcc/fortran/trans-decl.c's
convert_CFI_desc.

The code in libgfortran is rather simple - and in the compiler itself,
knowledge about the type can be used, avoiding both type alias issues and
generating proper code – it also improves the performance.