Re: [PATCH] DW_TAG_ptr_to_member_type for PMF and DW_AT_{,rvalue_}reference for those

[Jason Merrill <jason at redhat dot com>]

On Wed, Nov 2, 2016 at 10:31 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> It uses Alex' LANG_HOOKS_GET_PTRMEMFN_TYPE langhook.  I've tried
> to think about https://gcc.gnu.org/ml/gcc-patches/2011-05/msg00227.html
> and we even have such a langhook now, modified_type_die
> uses lang_hooks.types.get_debug_type, but
> 1) it is just called in modified_type_die and not in
>    gen_type_die_with_usage, that looks weird

How much of a problem is that?  modified_type_die calls gen_type_die,
does that not cover the cases needed here?

> 2) it is used for something Ada-ish I really don't know how to test etc.
>    to be able to find out if it is safe to call it in
>    gen_type_die_with_usage too

You could find an Ada test that uses the code and verify that the
output stays the same?

> 3) most importantly, if the C++ version of this langhook would create
>    OFFSET_TYPE on the fly, I don't know how to ensure effective sharing
>    of DW_TAG_ptr_to_member_type nodes with the same DW_AT_type
>    and DW_AT_containing_type; unless the C++ langhook adds some extra
>    hash table that caches already created OFFSET_TYPEs or something similar,
>    it would create a new OFFSET_TYPE each time it is called

build_offset_type already uses a hash table.

> Also, I really don't know how well does GDB (especially older releases)
> handle DW_TAG_ptr_to_member_type for PMF, so the patch wraps that currently
> with if (dwarf_version >= 5).  Quick grep revealed that GDB has code to
> handle the __pfn/__delta fields.  So, can I ask somebody from the GDB
> team to test this patch with that if (dwarf_version >= 5) replaced
> with if (1) and see if it works properly with current GDB as well as say
> 4-5 years old one (e.g. with -gdwarf-2 or -gdwarf-3)?  If yes, we
> should emit it unconditionally.

This all makes sense to me.

> +      if (dwarf_version >= 5)
> +       {
> +         tree class_type = lang_hooks.types.get_ptrmemfn_type (type, 0);
> +         if (class_type != NULL_TREE)

This can be

if (dwarf_version >= 5)
  if (tree class_type = lang_hooks.types.get_ptrmemfn_type (type, 0))

Jason