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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109561] -Wmaybe-uninitialized false positive with std::optional
Date: Thu, 20 Apr 2023 07:09:05 +0000	[thread overview]
Message-ID: <bug-109561-4-HSTERAm3Xi@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109561-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109561

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We diagnose

<bb7>
pretmp_108 = MEM[(const struct basic_string *)&D.58534 + 8B]._M_string_length;

which is guarded by


<bb 5> [local count: 955630225]:
# ivtmp.123_51 = PHI <ivtmp.123_74(34), ivtmp.123_42(4)>
MEM[(struct optional *)&D.58534] ={v} {CLOBBER};
MEM[(union _Storage *)&D.58534] ={v} {CLOBBER};
MEM[(struct _Optional_payload_base *)&D.58534]._M_engaged = 0;
MEM[(struct optional *)&D.58534 + 8B] ={v} {CLOBBER};
MEM[(union _Storage *)&D.58534 + 8B] ={v} {CLOBBER};
MEM[(struct _Optional_payload_base *)&D.58534 + 8B]._M_engaged = 0;
_1 = (void *) ivtmp.123_51;
MEM[(struct optional *)_1 + -24B] = D.58534.i;
_23 = MEM[(bool *)_1 + 16B];
if (_23 != 0)
  goto <bb 6>; [50.00%]
else
  goto <bb 22>; [50.00%]

<bb 6> [local count: 477815112]:
_24 = MEM[(struct _Optional_payload_base &)&D.58534 + 8]._M_engaged;
pretmp_110 = MEM[(char * *)_1 + -16B];
if (_24 != 0)
  goto <bb 7>; [33.00%]
else
  goto <bb 21>; [67.00%]

clearly there's missed CSE of .M_engaged here, but

  MEM[(struct optional *)_1 + -24B] = D.58534.i;

must aliases the location.

  parent reply	other threads:[~2023-04-20  7:09 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-20  1:34 [Bug c++/109561] New: -Wmaybe-uninitialized false positive false positive false positive false positive false positive f.heckenbach@fh-soft.de
2023-04-20  6:55 ` [Bug tree-optimization/109561] -Wmaybe-uninitialized false positive with std::optional rguenth at gcc dot gnu.org
2023-04-20  7:09 ` rguenth at gcc dot gnu.org [this message]
2024-05-24  1:44 ` sjames at gcc dot gnu.org

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