From: Andrew Pinski <pinskia@gmail.com>
To: Aldy Hernandez <aldyh@redhat.com>
Cc: GCC patches <gcc-patches@gcc.gnu.org>,
Andrew MacLeod <amacleod@redhat.com>,
Jakub Jelinek <jakub@redhat.com>
Subject: Re: [PATCH] Add support for floating point endpoints to frange.
Date: Fri, 26 Aug 2022 12:44:25 -0700 [thread overview]
Message-ID: <CA+=Sn1mf79m8SbQuTrNDhSR6Ad5MxJ9GcadVM=OLi98W7+0YVQ@mail.gmail.com> (raw)
In-Reply-To: <CAGm3qMW=00SwDqO-7T5Q5aA=CAbtHbkit6sW2j3dY+PAtjVHUA@mail.gmail.com>
On Fri, Aug 26, 2022 at 12:16 PM Aldy Hernandez <aldyh@redhat.com> wrote:
>
> On Fri, Aug 26, 2022 at 7:40 PM Andrew Pinski <pinskia@gmail.com> wrote:
> >
> > On Fri, Aug 26, 2022 at 8:55 AM Aldy Hernandez <aldyh@redhat.com> wrote:
> > >
> > > [pinskia: I'm CCing you as the author of the match.pd pattern.]
> > >
> > > So, as I wrap up the work here (latest patch attached), I see there's
> > > another phiopt regression (not spaceship related). I was hoping
> > > someone could either give me a hand, or offer some guidance.
> > >
> > > The failure is in gcc.dg/tree-ssa/phi-opt-24.c.
> > >
> > > We fail to transform the following into -A:
> > >
> > > /* { dg-options "-O2 -fno-signed-zeros -fdump-tree-phiopt" } */
> > >
> > > float f0(float A)
> > > {
> > > // A == 0? A : -A same as -A
> > > if (A == 0) return A;
> > > return -A;
> > > }
> > >
> > > This is because the abs/negative match.pd pattern here:
> > >
> > > /* abs/negative simplifications moved from fold_cond_expr_with_comparison,
> > > Need to handle (A - B) case as fold_cond_expr_with_comparison does.
> > > Need to handle UN* comparisons.
> > > ...
> > > ...
> > >
> > > Sees IL that has the 0.0 propagated.
> > >
> > > Instead of:
> > >
> > > <bb 2> [local count: 1073741824]:
> > > if (A_2(D) == 0.0)
> > > goto <bb 4>; [34.00%]
> > > else
> > > goto <bb 3>; [66.00%]
> > >
> > > <bb 3> [local count: 708669601]:
> > > _3 = -A_2(D);
> > >
> > > <bb 4> [local count: 1073741824]:
> > > # _1 = PHI <A_2(D)(2), _3(3)>
> > >
> > > It now sees:
> > >
> > > <bb 4> [local count: 1073741824]:
> > > # _1 = PHI <0.0(2), _3(3)>
> > >
> > > which it leaves untouched, causing the if conditional to survive.
> > >
> > > Is this something that can be done by improving the match.pd pattern,
> > > or should be done elsewhere?
> >
> > Oh the pattern which is supposed to catch this does:
> > (simplify
> > (cnd (cmp @0 zerop) integer_zerop (negate@1 @0))
> > (if (!HONOR_SIGNED_ZEROS (type))
> > @1))
>
> On trunk without any patches, for the following snippet with -O2
> -fno-signed-zeros -fdump-tree-phiopt-folding...
>
> float f0(float A)
> {
> // A == 0? A : -A same as -A
> if (A == 0) return A;
> return -A;
> }
>
> ...the phiopt2 dump file has:
>
> Applying pattern match.pd:4805, gimple-match.cc:69291, which
> corresponds to the aforementioned pattern. So it looks like that was
> the pattern that was matching that isn't any more?
>
> Are you saying this pattern should only work with integers?
I am saying the pattern which is right after the one that matches
(without your patch) currrently works for integer only.
You could change integer_zerop to zerop in that pattern but I am not
100% sure that is valid thing to do.
Note there are a few other patterns in that for loop that does
integer_zerop which might need to be zerop too.
Thanks,
Andrew Pinski
>
> Aldy
>
next prev parent reply other threads:[~2022-08-26 19:44 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-23 11:42 Aldy Hernandez
2022-08-26 15:55 ` Aldy Hernandez
2022-08-26 17:40 ` Andrew Pinski
2022-08-26 18:11 ` Aldy Hernandez
2022-08-26 18:11 ` Aldy Hernandez
2022-08-26 19:16 ` Aldy Hernandez
2022-08-26 19:44 ` Andrew Pinski [this message]
2022-08-29 13:45 ` Aldy Hernandez
2022-08-29 13:54 ` Jakub Jelinek
2022-08-29 14:07 ` Toon Moene
2022-08-29 14:15 ` Aldy Hernandez
2022-08-29 14:30 ` Toon Moene
2022-08-29 14:36 ` Aldy Hernandez
2022-08-29 14:42 ` Toon Moene
2022-08-30 9:27 ` Aldy Hernandez
2022-08-31 15:22 ` Jeff Law
2022-08-31 15:19 ` Jeff Law
2022-08-29 14:08 ` Aldy Hernandez
2022-08-29 14:17 ` Jakub Jelinek
2022-08-29 14:20 ` Aldy Hernandez
2022-08-29 14:27 ` Jakub Jelinek
2022-08-29 14:30 ` Aldy Hernandez
2022-08-31 15:24 ` Jeff Law
2022-08-30 22:32 ` Joseph Myers
2022-08-31 15:16 ` Jeff Law
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