[Bug tree-optimization/103061] [12 Regression] 527.cam4_r miscompiled with -O2 -march=znver1 since r12-4790-g4b3a325f07acebf4

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103061

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Aldy Hernandez <aldyh@gcc.gnu.org>:

https://gcc.gnu.org/g:4856699eeb2809c50930bafe341a96470877195d

commit r12-4971-g4856699eeb2809c50930bafe341a96470877195d
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Fri Nov 5 22:25:19 2021 +0100

    path oracle: Do not look at root oracle for killed defs.

    The problem here is that we are incorrectly threading 41->20->21 here:

      <bb 35> [local count: 56063504182]:
      _134 = M.10_120 + 1;
      if (_71 <= _134)
        goto <bb 19>; [11.00%]
      else
        goto <bb 41>; [89.00%]
    ...
    ...
    ...
      <bb 41> [local count: 49896518755]:

      <bb 20> [local count: 56063503181]:
      # lb_75 = PHI <_134(41), 1(18)>
      _117 = mstep_49 + lb_75;
      _118 = _117 + -1;
      _119 = mstep_49 + _118;
      M.10_120 = MIN_EXPR <_119, _71>;
      if (lb_75 > M.10_120)
        goto <bb 21>; [11.00%]
      else
        goto <bb 22>; [89.00%]

    First, lb_17 == _134 because of the PHI.
    Second, _134 > M.10_120 because of _134 = M.10_120 + 1.

    We then assume that lb_75 > M.10_120, but this is incorrect because
    M.10_120 was killed along the path.

    This incorrect thread causes the miscompilation in 527.cam4_r.

    Tested on x86-64 and ppc64le Linux.

    gcc/ChangeLog:

            PR tree-optimization/103061
            * value-relation.cc (path_oracle::path_oracle): Initialize
            m_killed_defs.
            (path_oracle::killing_def): Set m_killed_defs.
            (path_oracle::query_relation): Do not look at the root oracle for
            killed defs.
            * value-relation.h (class path_oracle): Add m_killed_defs.