[Bug tree-optimization/91200] ICE on valid code at -O1: verify_ssa failed

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91200

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So we're applying cselim to

  if (a.0_1 != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 766958447]:
  # i_20 = PHI <i_22(D)(2)>
  h[i_20] = &c;

  <bb 4> [local count: 168730858]:
  # i_21 = PHI <i_22(D)(2), i_20(3)>

where bb3 has only a single stmt but the PHI node precludes simply inserting
the stmt elsewhere.

The PHI node is left from non-iterating FRE which isn't able to do all
simplification in one go.