[Bug fortran/56907] New: C_LOC shall not call internal-PACK when an array argument is used

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56907

             Bug #: 56907
           Summary: C_LOC shall not call internal-PACK when an array
                    argument is used
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


Found when looking at gfortran.dg/assumed_type_2.f90.

For an array argument, C_LOC should simply take the first element of the array
(section). Currently, it invokes internal packing.

As Fortran 2008 demands that the argument is contiguous, internal_packing
should simply return the original array (section) - hence, there is no
wrong-code issue - just a missed optimization.

>From the dump:
    D.1901 = _gfortran_internal_pack (&parm.4);
    D.1903 = D.1901;

Test case:

! { dg-do compile }
! { dg-options "-fdump-tree-original" }
!
! PR fortran/ <<<<<<<<<<<
!

subroutine sub(xxx)
  use iso_c_binding
  implicit none
  integer, target :: xxx(:)
  type(c_ptr) :: ptr
  ptr = c_loc (xxx)
end
! { dg-final { scan-tree-dump-not " _gfortran_internal_pack" "original" } }
! { dg-final { cleanup-tree-dump "optimized" } }