[Bug tree-optimization/112324] phiopt fail to recog if (b < 0) max = MAX(-b, max); else max = MAX (b, max) into max = MAX (ABS(b), max)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112324

--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Andrew Pinski <pins...@gcc.gnu.org>:

https://gcc.gnu.org/g:4d6c3f3b4fbf8c2774848fcb36705ea5f0d514d4

commit r16-2298-g4d6c3f3b4fbf8c2774848fcb36705ea5f0d514d4
Author: Andrew Pinski <quic_apin...@quicinc.com>
Date:   Mon Jul 7 20:01:04 2025 -0700

    ifconv: simple factor out operators while doing ifcvt [PR119920]

    For possible reductions, ifconv currently handles if the addition
    is on one side of the if. But in the case of PR 119920, the reduction
    addition is on both sides of the if.
    E.g.
    ```
      if (_27 == 0)
        goto <bb 14>; [50.00%]
      else
        goto <bb 13>; [50.00%]

      <bb 14>
      a_29 = b_14(D) + a_17;
      goto <bb 15>; [100.00%]

      <bb 13>
      a_28 = c_12(D) + a_17;

      <bb 15>
      # a_30 = PHI <a_28(13), a_29(14)>
    ```

    Which ifcvt converts into:
    ```
      _34 = _32 + _33;
      a_15 = (int) _34;
      _23 = _4 == 0;
      _37 = _33 + _35;
      a_13 = (int) _37;
      a_5 = _23 ? a_15 : a_13;
    ```

    But the vectorizer does not recognize this as a reduction.
    To fix this, we should factor out the addition from the `if`.
    This allows us to get:
    ```
      iftmp.0_7 = _22 ? b_13(D) : c_12(D);
      a_14 = iftmp.0_7 + a_18;
    ```

    Which then the vectorizer recognizes as a reduction.

    In the case of PR 112324 and PR 110015, it is similar but with MAX_EXPR
reduction
    instead of an addition.

    Note while this should be done in phiopt, there are regressions
    due to other passes not able to handle the factored out cases
    (see linked bug to PR 64700). I have not had time to fix all of the passes
    that could handle the addition being in the if/then/else rather than being
outside yet.
    So this is I thought it would be useful just to have a localized version in
ifconv which
    is then only used for the vectorizer.

    Bootstrapped and tested on x86_64-linux-gnu.

            PR tree-optimization/119920
            PR tree-optimization/112324
            PR tree-optimization/110015

    gcc/ChangeLog:

            * tree-if-conv.cc (find_different_opnum): New function.
            (factor_out_operators): New function.
            (predicate_scalar_phi): Call factor_out_operators when
            there is only 2 elements of a phi.

    gcc/testsuite/ChangeLog:

            * gcc.dg/vect/vect-reduc-cond-1.c: New test.
            * gcc.dg/vect/vect-reduc-cond-2.c: New test.
            * gcc.dg/vect/vect-reduc-cond-3.c: New test.

    Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>