Re: [PATCH] Add support for floating point endpoints to frange.

[Aldy Hernandez <aldyh@redhat.com>]

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?

Aldy