This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: Prune TYPE_NEXT_VARIANT lists in free_lang_data
> On September 8, 2018 10:49:02 AM GMT+01:00, Jan Hubicka <hubicka@ucw.cz> wrote:
> >Hi
> >while working on path to replace type variant by first compatible one I
> >run
> >into issue that the first vairant was not seen by free_lang_data. I
> >think this
> >is a bug becuase nothing prevents middle-end from looking up a variant
> >there
> >and using it when it needs to do so.
> >
> >I tried to walk the variant lists and free lang data on them but that
> >crahses
> >because not all types in variant list passes verify_type (C++ puts
> >there
> >incomplete type variants whose canonical type is complete and thus they
> >are
> >considered bogus). So pruning those lists seems to be better variant.
> >
> >Bootstrapped/regtested x86_64-linux, OK?
>
> But if they are still reachable by GC they are now bogously unlinked. We already do not stream unused variants, so what does this achieve? Maybe we should make the variant list GCable somehow?
Main goal is to prevent middle end to walk the TYPE_NEXT_VARIANT list (for example by get_qualified_variant)
and pick up a variant that was not seen by free_lang_data and put it into the IL.
I know that if we end up referring to some type variant in a way not seen
by free lang data then the type won't be reachable from the list, but why that
would be a problem?
Honza
>
> >Honza
> >
> > * tree.c (free_lang_data_in_cgraph): Prune TYPE_NEXT_VARIANT lists.
> >Index: tree.c
> >===================================================================
> >--- tree.c (revision 263989)
> >+++ tree.c (working copy)
> >@@ -5845,7 +5845,12 @@ free_lang_data_in_cgraph (void)
> >
> > /* Traverse every type found freeing its language data. */
> > FOR_EACH_VEC_ELT (fld.types, i, t)
> >- free_lang_data_in_type (t);
> >+ {
> >+ free_lang_data_in_type (t);
> >+ while (TYPE_NEXT_VARIANT (t)
> >+ && !fld.pset.contains (TYPE_NEXT_VARIANT (t)))
> >+ TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (TYPE_NEXT_VARIANT (t));
> >+ }
> > if (flag_checking)
> > {
> > FOR_EACH_VEC_ELT (fld.types, i, t)
>