[patch, fortran] PR45516 - [F08] allocatable components of recursive type

[Paul Richard Thomas <paul dot richard dot thomas at gmail dot com>]

Dear All,

Please find attached the patch for allocatable components of recursive
type. The patch is pretty straightforward in that for the main part
they are treated exactly as their pointer equivalents. The exception
to this is the automatic deallocation of allocatable components. I
tried to use the vtable finalization wrapper to do this but found it
impossible to prevent the compilation going into an infinite loop on
trying to build the automatic deallocation code. I therefore added a
new field to the vtable that points to a component that does nothing
more than deallocate the component. This function takes a rank 1
array, which can be done safely for automatic deallocation of an
allocatable component.

The testcases indicate some of the possibilities for these components,
which provide the benefit of automatic garbage collection. As the
comment in the fourth testcase says, array components are fiendishly
difficult to use and, I suspect, will find very little application.

Bootstraps and regtests on FC21/x86_64 - OK for trunk?

Paul

2016-10-24  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/45516
    * class.c (gfc_find_derived_vtab): Detect recursive allocatable
    derived type components. If present, add '_deallocate' field to
    the vtable and build the '__deallocate' function.
    * decl.c (build_struct): Allow recursive allocatable derived
    type components for -std=f2008 or more.
    (gfc_match_data_decl): Accept these derived types.
    * expr.c (gfc_has_default_initializer): Ditto.
    * resolve.c (resolve_component): Make sure that the vtable is
    built for these derived types.
    * trans-array.c(structure_alloc_comps) : Use the '__deallocate'
    function for the automatic deallocation of these types.
    * trans-expr.c : Generate the deallocate accessor.
    * trans.h : Add its prototype.
    * trans-types.c (gfc_get_derived_type): Treat the recursive
    allocatable components in the same way as the corresponding
    pointer components.

2016-10-24  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/45516
    * gfortran.dg/class_2.f03: Set -std=f2003.
    * gfortran.dg/finalize_21.f90: Modify tree-dump.
    * gfortran.dg/recursive_alloc_comp_1.f08: New test.
    * gfortran.dg/recursive_alloc_comp_2.f08: New test.
    * gfortran.dg/recursive_alloc_comp_3.f08: New test.
    * gfortran.dg/recursive_alloc_comp_4.f08: New test.

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