On Fri, Aug 26, 2022 at 12:16 PM Aldy Hernandez <al...@redhat.com> wrote:
>
> On Fri, Aug 26, 2022 at 7:40 PM Andrew Pinski <pins...@gmail.com> wrote:
> >
> > On Fri, Aug 26, 2022 at 8:55 AM Aldy Hernandez <al...@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
>
