Re: [COMMITTED] Convert nonzero mask in irange to wide_int.

[Aldy Hernandez <aldyh@redhat.com>]

On Tue, Oct 4, 2022 at 9:55 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
>
> Am 04.10.2022 um 09:36 schrieb Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org>:
> >
> > The reason the nonzero mask was kept in a tree was basically inertia,
> > as everything in irange is a tree.  However, there's no need to keep
> > it in a tree, as the conversions to and from wide ints are very
> > annoying.  That, plus special casing NULL masks to be -1 is prone
> > to error.
> >
> > I have not only rewritten all the uses to assume a wide int, but
> > have corrected a few places where we weren't propagating the masks, or
> > rather pessimizing them to -1.  This will become more important in
> > upcoming patches where we make better use of the masks.
> >
> > Performance testing shows a trivial improvement in VRP, as things like
> > irange::contains_p() are tied to a tree.  Ughh, can't wait for trees in
> > iranges to go away.
>
> You want trailing wide int storage though.  A wide_int is quite large.

Absolutely, this is only for short term storage.  Any time we need
long term storage, say global ranges in SSA_NAME_RANGE_INFO, we go
through vrange_storage which will stream things in a more memory
efficient manner.  For irange, vrange_storage will stream all the
sub-ranges, including the nonzero bitmask which is the first entry in
such storage, as trailing_wide_ints.

See irange_storage_slot to see how it lives in GC memory.

Aldy