spaceship_replacement cannot see through simplified set of FP conditionals

spaceship_replacement cannot see through simplified set of FP conditionals

[Aldy Hernandez]

Hi.

With my upcoming patch enabling floating point VRP,
g++.dg/opt/pr94589-2.C is failing:

https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598788.html

The problem is that phiopt no longer sees the following snippet,
because we have folded away the final conditional as true:

bool f5 (double i, double j)
{
  signed char __v$_M_value;
  signed char c$_M_value;
  bool D.8519;
  struct partial_ordering __v;
  struct partial_ordering c;
  unsigned int _11;
  bool _16;

  <bb 2> :
  if (i_2(D) != j_4(D))
    goto <bb 3>; [INV]
  else
    goto <bb 6>; [INV]

  <bb 3> :
  if (i_2(D) >= j_4(D))
    goto <bb 4>; [INV]
  else
    goto <bb 6>; [INV]

  <bb 4> :
  if (i_2(D) > j_4(D))
    goto <bb 6>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 5> :

  <bb 6> :
  # c$_M_value_3 = PHI <-1(3), 0(2), 2(5), 1(4)>
  _11 = (unsigned int) c$_M_value_3;
  _16 = _11 <= 1;
  return _16;
}

This means that spaceship_replacement()  now sees one less argument to the PHI:

  <bb 2> :
  if (i_2(D) != j_4(D))
    goto <bb 3>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 3> :
  if (i_2(D) >= j_4(D))
    goto <bb 4>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 4> :

  <bb 5> :
  # c$_M_value_3 = PHI <-1(3), 0(2), 1(4)>

...and we bail because we are expecting 4 arguments:

      if (EDGE_COUNT (phi_bb->preds) != 4)
    return false;

Could someone give me a hand here? Can spaceship_replacement easily be
adapted to handle this case, or should we be simplifying this
elsewhere?

Thanks.
Aldy

Re: spaceship_replacement cannot see through simplified set of FP conditionals

[Jakub Jelinek]

On Fri, Jul 29, 2022 at 01:40:12PM +0200, Aldy Hernandez wrote:
> With my upcoming patch enabling floating point VRP,
> g++.dg/opt/pr94589-2.C is failing:
> 
> https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598788.html
> 
> The problem is that phiopt no longer sees the following snippet,
> because we have folded away the final conditional as true:

> Could someone give me a hand here? Can spaceship_replacement easily be
> adapted to handle this case, or should we be simplifying this
> elsewhere?

Leave it to me, once you commit, file a PR and I'll work on it.

	Jakub

Re: spaceship_replacement cannot see through simplified set of FP conditionals

[Aldy Hernandez]

Sweeeet!

Would you like me to XFAIL the test or leave it as a failure?

Thanks.
Aldy

On Fri, Jul 29, 2022 at 1:50 PM Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Fri, Jul 29, 2022 at 01:40:12PM +0200, Aldy Hernandez wrote:
> > With my upcoming patch enabling floating point VRP,
> > g++.dg/opt/pr94589-2.C is failing:
> >
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598788.html
> >
> > The problem is that phiopt no longer sees the following snippet,
> > because we have folded away the final conditional as true:
>
> > Could someone give me a hand here? Can spaceship_replacement easily be
> > adapted to handle this case, or should we be simplifying this
> > elsewhere?
>
> Leave it to me, once you commit, file a PR and I'll work on it.
>
>         Jakub
>

Re: spaceship_replacement cannot see through simplified set of FP conditionals

[Jakub Jelinek]

On Fri, Jul 29, 2022 at 01:51:00PM +0200, Aldy Hernandez wrote:
> Sweeeet!
> 
> Would you like me to XFAIL the test or leave it as a failure?

Either is fine.

	Jakub