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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101150] [11/12/13 Regression] null pointer
 dereference false positive disappears when compiling an additional function
Date: Thu, 23 Mar 2023 18:05:12 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.1.0
X-Bugzilla-Keywords: diagnostic, missed-optimization, needs-bisection
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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X-Bugzilla-Target-Milestone: 11.4
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101150

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection
      Known to work|                            |13.0

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
On the trunk, the warning is gone so is the missed optimization mentioned in
comment #1.

We do have another missed optimization though:
  _12 =3D _9 - _15;
  _7 =3D _12 /[ex] 4;
  _18 =3D (long unsigned int) _7;
  _120 =3D _18 !=3D 0;
  _54 =3D _12 !=3D 0;
  _127 =3D _54 & _120;
  if (_127 !=3D 0)
    goto <bb 3>; [16.50%]
  else
    goto <bb 9>; [83.50%]
...
  <bb 9> [local count: 98623186]:
  if (_9 !=3D _15)
    goto <bb 10>; [89.00%]
  else
    goto <bb 23>; [11.00%]

Only one of those comparisons is actually needed. and then another missing =
jump
threading because _9 be equal _15 on the goto <bb 9> branch.=