From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 6F9953858C30; Wed, 31 May 2023 23:38:52 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 6F9953858C30
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1685576332;
	bh=rMCjrGyudgoQ8xbtGJWeRbXCr6JgmZKEhx/WmJZbToQ=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=rYyEvtKb/rgBEjjYdRn2ArSHMI0MbGZcc5XQ/+uDJc4yIWnpzPnz2piYutK1ertBQ
	 dqfB92Cm6AgiNfvXAaZdXZ1zUIRyw5bZ+AXgbwoH21qAWPh0WkOEL66Vu2ByFzfKV1
	 JtOV0R4ZtiGGjSJpIfRaebFBlw01p3lUqyhD2s3M=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110060] Adding optimizer hints to std::vector
 causes a new -Wstringop-overread false positive
Date: Wed, 31 May 2023 23:38:52 +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: 14.0
X-Bugzilla-Keywords: diagnostic, missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-110060-4-3zWXPcAbbg@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-110060-4@http.gcc.gnu.org/bugzilla/>
References: <bug-110060-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110060

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note you can reduce main to just:
```
int main()
{
  std::vector<int> v(5);
  const std::vector<int> w(1);

  v.resize(1);
//  v.insert(v.begin(), 0);
  //v.insert(v.begin(), 1, 0);
//  v.insert(v.begin(), w.begin(), w.end());
  v =3D w;

  return 0;
}
```
And get the warning still at -O2.

With the above main in .optimized we get:
```
  MEM[(struct _Vector_base *)&w]._M_impl.D.25239._M_start =3D _53;
  _46 =3D _53 + 4;
  MEM[(struct _Vector_base *)&w]._M_impl.D.25239._M_end_of_storage =3D _46;
  *_53 =3D 0;
  w.D.25935._M_impl.D.25239._M_finish =3D _46;
  v.D.25935._M_impl.D.25239._M_finish =3D __first_33;
  __xlen_82 =3D std::vector<int>::size (&w);
  if (__xlen_82 > 5)
    goto <bb 4>; [33.00%]
  else
    goto <bb 10>; [67.00%]
```

std::vector<int>::size is literally just:
```
        movq    8(%rdi), %rax
        subq    (%rdi), %rax
        sarq    $2, %rax
        ret
```

So that is definitely an issue there.=