[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?

Thanks.
Aldy