[Bug tree-optimization/96480] [8/9/10/11 Regression] missed optimisation: unnecessary compare in standard algorithms

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96480

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:b3aa137212b1af0c824a9890eba2ca27a7271d56

commit r11-2593-gb3aa137212b1af0c824a9890eba2ca27a7271d56
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Aug 6 15:47:25 2020 +0200

    reassoc: Improve maybe_optimize_range_tests [PR96480]

    On the following testcase, if the IL before reassoc would be:
    ...
      <bb 4> [local count: 354334800]:
      if (x_3(D) == 2)
        goto <bb 7>; [34.00%]
      else
        goto <bb 5>; [66.00%]

      <bb 5> [local count: 233860967]:
      if (x_3(D) == 3)
        goto <bb 7>; [34.00%]
      else
        goto <bb 6>; [66.00%]

      <bb 6> [local count: 79512730]:

      <bb 7> [local count: 1073741824]:
      # prephitmp_7 = PHI <1(3), 1(4), 1(5), 1(2), 0(6)>
    then we'd optimize it properly, but as bb 5-7 is instead:
      <bb 5> [local count: 233860967]:
      if (x_3(D) == 3)
        goto <bb 6>; [34.00%]
      else
        goto <bb 7>; [66.00%]

      <bb 6> [local count: 79512730]:

      <bb 7> [local count: 1073741824]:
      # prephitmp_7 = PHI <1(3), 1(4), 0(5), 1(2), 1(6)>
    (i.e. the true/false edges on the last bb with condition swapped
    and ditto for the phi args), we don't recognize it.  If bb 6
    is empty, there should be no functional difference between the two IL
    representations.

    This patch handles those special cases.

    2020-08-06  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/96480
            * tree-ssa-reassoc.c (suitable_cond_bb): Add TEST_SWAPPED_P
argument.
            If TEST_BB ends in cond and has one edge to *OTHER_BB and another
            through an empty bb to that block too, if PHI args don't match,
retry
            them through the other path from TEST_BB.
            (maybe_optimize_range_tests): Adjust callers.  Handle such LAST_BB
            through inversion of the condition.

            * gcc.dg/tree-ssa/pr96480.c: New test.