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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/98753] -Wfree-nonheap-object on unreachable code
 with -O0
Date: Wed, 20 Jan 2021 17:34:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98753

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|-Wfree-nonheap-object on    |-Wfree-nonheap-object on
                   |Bison generated code        |unreachable code with -O0
      Known to fail|                            |11.0
             Status|WAITING                     |NEW
          Component|c++                         |middle-end

--- Comment #7 from Martin Sebor <msebor at gcc dot gnu.org> ---
I can reproduce the warning with no optimization, thanks.  At -O0, there are
three calls to free in the IL when the warning runs.  The second one that
triggers it

  # .MEM_218 =3D VDEF <.MEM_216>
  free (yymsg.17_83);

is eliminated by copy propagation at -O1.  It's not eliminated at -O0 becau=
se
the optimization isn't done then.  So the ultimate root cause of the proble=
m is
the same as in pr54202, except at -O0 (the test case there depends on
inlining).

It would be possible to disable the warning at -O0 to avoid this false posi=
tive
at the expense of some false negatives.  I'm not sure that would be a good
solution based on a single report.  If more bugs like this are reported we
might reconsider.  Let me keep this bug open until then.=