Re: [PATCH] Replace VRP threader with a hybrid forward threader.

[Aldy Hernandez <aldyh@redhat.com>]

On Mon, Sep 27, 2021 at 7:29 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On September 27, 2021 6:07:40 PM GMT+02:00, Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> >
> >
> >On 9/27/21 5:27 PM, Aldy Hernandez wrote:
> >>
> >>
> >> On 9/27/21 5:01 PM, Jeff Law wrote:
> >>>
> >>>
> >>> On 9/24/2021 9:46 AM, Aldy Hernandez wrote:
> >
> >>> And the big question, is the pass running after VRP2 doing anything
> >>> particularly useful?  Do we want to try and kill it now, or later?
> >>
> >> Interesting question.  Perhaps if we convert DOM threading to a hybrid
> >> model, it will render the post-VRP threader completely useless.  Huhh...
> >> That could kill 2 birds with one stone... we get rid of a threading
> >> pass, and we don't need to worry about as much about the super-fast ranger.
> >
> >These are just a few of the threading passes at -O2:
> >
> >a.c.192t.thread3   <-- bck threader
> >a.c.193t.dom3      <-- fwd threader
> >a.c.194t.strlen1
> >a.c.195t.thread4   <-- bck threader
> >a.c.196t.vrp2
> >a.c.197t.vrp-thread2 <-- fwd threader
> >
> >That's almost 4 back to back threaders!
> >
> >*pause for effect*
>
> We've always known we have too many of these once Jeff triplicated all the backwards threading ones. I do hope we manage to reduce the number for GCC 12. Esp. If the new ones are slower because they no longer use simple lattices.

By the way, what is the blessed way of knowing which of the N passes
we are in?  For instance, there are 4 back threading passes (well 5
with ethread).  I'd like to know how to know if I'm in the 4th one,
which is the one that runs before VRP2 threading.  I know there's
gimple_opt_pass::set_pass_param, but that seems to only take a bool.

Thanks.
Aldy