[Bug tree-optimization/25290] PHI-OPT could be rewritten so that is uses match

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25290

--- Comment #29 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #28)
> Created attachment 54821 [details]
> New set of patches including some other improvements

Note this series does not bootstrap, the last patch found that I had a latent
bug in the patch that started to handle diamond shaped PHIs.

For:
  if (_16 == 34)
    goto <bb 10>; [INV]
  else
    goto <bb 12>; [INV]

  <bb 10> :
  ...
  _27 = csets__identifier_char[_26];
  if (_27 != 0)
    goto <bb 11>; [INV]
  else
    goto <bb 12>; [INV]

  <bb 11> :
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 13>; [INV]

  <bb 12> :
  // predicted unlikely by early return (on trees) predictor.

  <bb 13> :
  # _28 = PHI <1(7), 0(12), 1(4), 1(11)>

I would transform it to use _27 even from bb 12 which is wrong.

I had missed that minmax_replacement did:

      if (!single_pred_p (middle_bb)
          || !single_pred_p (alt_middle_bb)
          || !single_succ_p (middle_bb)
          || !single_succ_p (alt_middle_bb))
        return false;

I will add that check tomorrow.