Re: RFC - VRP1 default mode

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Oct 28, 2022 at 3:43 PM Andrew MacLeod <amacleod@redhat.com> wrote:
>
>
> On 10/28/22 03:17, Richard Biener wrote:
> > On Wed, Oct 26, 2022 at 4:24 PM Andrew MacLeod <amacleod@redhat.com> wrote:
> >> Figured I would ask what you guys think of making ranger the default for
> >> the VRP1 pass now.
> >>
> >> With partial equivalences and the other bits I checked in the past few
> >> weeks I'm not aware of much that the legacy VRP pass gets that ranger
> >> doesn't.  The only exception to that which I am aware of is the trick
> >> played with the unreachable edges to set global ranges, but that is done
> >> in the DOM passes now anyway... so it just happens slightly later in the
> >> optimization cycle.
> > Note DOM should go away at some point.  Why can this not happen during
> > ranger driven VRP?
>
> I have been working on that for the last 2 days.  Turns out VRP1 can
> remove builtin_unreachable from the
>    if (X)
>      __builtin_unreachable ()
>
> idiom and set the appropriate global ranges, but it has to leave those
> with 2 ssa-names:
>
>    if (a_1 != b_2)
>      __builtin_unreachable()
>
> until the second pass of VRP or we lose the relationship between a_1 and
> b_2.  That triggers some failures.  Specifically a vectorizor fail
> because it cant be sure that the start and end point are not the same
> without the condition in the IL. Trying to store global relations over
> multiple passes would be problematic at this stage of development, so I
> don't see a problem with leaving it that way.

Hmm, I don't remember VRP1 doing anything special with the above though?
Did it somehow propagate the (un!)conditional equivalence?

> bultin_unreachables() from switches get removed during the second pass
> of switch-conversion... which I presume remains OK.
>
> Anyway, thats pretty much under control.  Patch probably coming later today.
>
>
>
> >> There is one test case that needs adjustment for
> >> that which was just checking for a mask in DOM2
> >> (gcc.dg/tree-ssa/pr107009.c).   At this point I have not aware of
> >> anything that Id be concerned about, and the testsuite seems to run
> >> cleanly.
> > Did you enable Ada?  The only feature I don't see implemented is
> > symbolic range handling which boils down to general base + constant offset
> > range endpoints (that's what symbolic ranges allow).  That area was
> > specifically improved to optimize range checks emitted by the Ada frontend
> > but IIRC also applies to fortran -frange-check (not sure about test coverage
> > of that).
> I get a clean testsuite run configured and bootstrapped with
>
>     --enable-languages=c,c++,go,fortran,ada,obj-c++,jit --enable-host-shared
>
> Is there a PR or specific tests in either fortran or ada for those
> improvements? ie, something specific I should check for? Part of rangers
> point is to be able to do symbolic relationships without storing the
> symbolic in the range, just picking it up from the IL as needed.

I'm defering to Eric here.

Richard.

> Andrew
>
>