RFA: PATCH to gimple_canonical_types_compatible_p for middle-end/66214

[Jan Hubicka]

> The problem here is that we're trying to compare the TYPE_FIELDS of
> two variants of an incomplete type, which doesn't make sense; we
> shouldn't expect TYPE_FIELDS of an incomplete type to be meaningful.
> 
> Tested x86_64-pc-linux-gnu.  OK for trunk?

> commit c6f5cd55d0bbebc2fa46628ebb8fdec2a44abf3a
> Author: Jason Merrill <jason@redhat.com>
> Date:   Wed Nov 25 10:47:03 2015 -0500
> 
>     	PR middle-end/66214
>     
>     	* tree.c (gimple_canonical_types_compatible_p) [RECORD_TYPE]:
>     	Don't try to compare the fields of incomplete types.

This makes sense to me.  I would still add a check that incomplete types have to
TYPE_FIELDS during LTO so we are sure that all types are either completed or
have no fields at all once the frontends are done.

Honza