On Tue, Nov 06, 2018 at 01:27:58PM -0700, Jeff Law wrote:
> So the one worry I have/had in this code is nested subregs. My
> recollection is they do happen in rare cases. But I can also find a
> reference where Jim W. has indicated they're invalid (and I absolutely
> trust Jim on this kind of historical RTL stuff).
>
> https://gcc.gnu.org/ml/gcc/2005-04/msg01173.html
rtl.texi says
@code{subreg}s of @code{subreg}s are not supported. Using
@code{simplify_gen_subreg} is the recommended way to avoid this problem.
(since r133982, from 2008).
> So, after all that, I think we're OK. It might make sense to verify we
> don't have nested subregs in the IL verifiers. Bonus points if you add
> that checking.
Or more general, that what is inside the subreg is a reg, because the
code does rely on that.
Segher
