[Patch, fortran] PR69834 - Collision in derived type hashes

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

Dear All,

The first attempts at fixing this bug were posted to the PR in
February of this year. Since then, real life has intervened and I have
not been able to get back to it until now.

The first patch used the address of the vtable to perform the
switching in SELECT_TYPE. Unfortunately, it failed in submodule_6.f90
and I have not been able to find a way to fix this without breaking
the ABI and having to bump up the module version number.

The second patch uses a string for the switching, which comprises a
concatenation of the type name and the module or procedure name.
Clearly, there is a performance penalty associated with this. My
recent efforts have been focussed on making this version detect
incoming selectors and associates that are use associated with
libraries that were compiled before this patch was applied and the
result is this submission. By the way, I was unable to find a way of
testing this feature as part of the testsuite but have done so 'by
hand'.

If the performance penalty is considered to be a show stopper, I could
develop further the version based on the vtable addresses but will
have to postpone any further work on this for a few weeks.

Otherwise, this patch does bootstrap and regtest on FC21/x86_64 - OK for trunk?

Cheers

Paul

2016-09-27  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/69834
    * class.c (get_unique_type_string): Add an extra argument
    'icase' that defaults to false but, when true, switches the
    order of type name and module or procedure name.
    (get_unique_hashed_string): New argument 'icase' switches
    bewteen the old form and a new one in which the string length
    is limited to GFC_MAX_SYMBOL_LEN and, in case of this limit
    being exceeded, the hash string is followed by as much of the
    composite name as possible.
    (gfc_case_name): New function.
    (gfc_find_derived_vtab): Add '_name' field to vtable. This is
    initialized by 'get_unique_type_string' with 'icase' true.
    (find_intrinsic_vtab): Ditto with initialization performed by a
    call to 'gfc_case_name'.
    * gfortran.h : Add macro 'gfc_add_name_component' and prototype
    for 'gfc_case_name'.
    * resolve.c (vtable_old_style): New function to determine if a
    use associated vtable is missing the '_name' field.
    (resolve_select_type): Call 'vtable_old_style' to determine if
    any of the derived types or vtables come from a library that
    was compiled before this patch. If this is the case, the old
    form of SELECT TYPE is activated, in which the cases are set by
    the hash value. Otherwise, the 'unique_type_string' is used.

2016-09-27  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/69834
    * gfortran.dg/finalize_21.f90: Remove semi colon from the tree
    scan.
    * gfortran.dg/select_type_36.f03: New test.
    * gfortran.dg/select_type_37.f03: New test.

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