Re: [PATCH] Fix debug info for enumeration types with reverse Scalar_Storage_Order

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jan 10, 2024 at 12:53 PM Eric Botcazou <botcazou@adacore.com> wrote:
>
> > Can you elaborate on the DIE order constraint and why it was chosen?  That
> > is,
> >
> > +      /* The DIE with DW_AT_endianity is placed right after the naked DIE.
> > */ +      if (reverse)
> > +       {
> > +         gcc_assert (type_die);
> > ...
> >
> > and
> >
> > +      /* The DIE with DW_AT_endianity is placed right after the naked DIE.
> > */ +      if (reverse_type)
> > +       {
> > +         dw_die_ref after_die
> > +           = modified_type_die (type, cv_quals, false, context_die);
> > +         gen_type_die (type, context_die, true);
> > +         gcc_assert (after_die->die_sib
> > +                     && get_AT_unsigned (after_die->die_sib,
> > DW_AT_endianity)); +         return after_die->die_sib;
> >
> > ?
>
> That's preexisting though, see line 13730 where there is a small blurb.
>
> The crux of the matter is that there is no scalar *_TYPE node with a reverse
> SSO, so there is nothing to equate with for the DIE carrying DW_AT_endianity,
> unlike for type variants (the reverse SSO is on the enclosing aggregate type
> instead but this does not match the way DWARF describes it).
>
> Therefore, in order to avoid building a new DIE with DW_AT_endianity each
> time, the DIE with DW_AT_endianity is placed right after the naked DIE, so
> that the lookup done at line 13730 for reverse SSO is immediate.

Hmm, I see.  The patch is OK then.

Thanks,
Richard.

> > Likewise the extra argument to the functions is odd - is that not available
> > on the tree type?
>
> No, for the reason described above, so the extra parameter is preexisting for
> base_type_die, modified_type_die and add_type_attribute.
>
> --
> Eric Botcazou
>
>