On Wed, Jan 10, 2024 at 12:53 PM Eric Botcazou <botca...@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
>
>
