Re: [PATCH] Fix regressions caused by early debug (DW_OP_GNU_variable_value extension 161109.2; PR debug/77589)

[Jason Merrill <jason at redhat dot com>]

On Fri, Feb 24, 2017 at 3:58 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> +      copy = ggc_alloc<dw_loc_descr_node> ();
> +      memcpy (copy, ref, sizeof (dw_loc_descr_node));
> +      list->expr = copy;
> +      while (copy->dw_loc_next != ref_end)
> +       {
> +         dw_loc_descr_ref new_copy = ggc_alloc<dw_loc_descr_node> ();
> +         memcpy (new_copy, copy->dw_loc_next, sizeof (dw_loc_descr_node));
> +         copy->dw_loc_next = new_copy;
> +         copy = new_copy;
> +       }

This seems like it could use a copy_loc_descr function, shared with
add_loc_descr_to_each.

> +               && (GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (loc)))
> +                   <= DWARF2_ADDR_SIZE))

Is this condition necessary, given that DWARF 5 supports typed
expressions that are not restricted to the size of the generic type?

> @@ -27532,6 +27538,18 @@ prune_unused_types_walk_loc_descr (dw_lo
>         if (loc->dw_loc_oprnd1.val_class == dw_val_class_die_ref)
>           prune_unused_types_mark (loc->dw_loc_oprnd1.v.val_die_ref.die, 1);
>         break;
> +      case DW_OP_GNU_variable_value:
> +       if (loc->dw_loc_oprnd1.val_class == dw_val_class_decl_ref)
> +         {
> +           dw_die_ref ref
> +             = lookup_decl_die (loc->dw_loc_oprnd1.v.val_decl_ref);
> +           if (ref == NULL)
> +             break;
> +           loc->dw_loc_oprnd1.val_class = dw_val_class_die_ref;
> +           loc->dw_loc_oprnd1.v.val_die_ref.die = ref;
> +           loc->dw_loc_oprnd1.v.val_die_ref.external = 0;
> +         }

Doing this adjustment in prune_unused_types is surprising.  Why is it
needed here as well as in the other places you do it?  What if the
user specifies -fno-eliminate-unused-debug-types?

Jason