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 469363858CD1; Thu,  2 Nov 2023 07:30:58 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 469363858CD1
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1698910258;
	bh=mComSloKI8OPpoJmPiO0e3CBPblAhlV3ACXNnRNAXHQ=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=U2pcBlukrPHDAsNuNPdAt1e8ojP9YNbxyaM20l50tW+LANGmHEqSXILca46hexZ8F
	 F1AqR10bStVTziiyPFQv0D+5q9mRk/ekQwCMjJkKcyUo0jtBB6Zgld7wjbr8EazFPx
	 EtA1fj7gOs0chbNS7beV8L9jOMgEZ5bNPR4Et+KY=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/112335] missed optimization on reset and assign unique_ptr
Date: Thu, 02 Nov 2023 07:30:57 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 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-112335-4-ofPmEdODGo@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-112335-4@http.gcc.gnu.org/bugzilla/>
References: <bug-112335-4@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=3D112335

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Federico Kircheis from comment #2)
> > Well s::~s could touch the reference std::unique_ptr<s> (ps1).
>=20
> In both cases, s::~s is called only once.
>=20
> Also during the move-assignment no user-provided-code is involved (except
> the destruction of ps1, and even case of a user-provided deleter, it is o=
nly
> called if the pointer is not nullptr.

NO. NO.


std::unique_ptr<s> t;

__thread bool tt;
inline s::~s()
{
  if (tt)
    return;
  tt =3D true;
  t.reset(new s);
  tt =3D false;
}

Is still a valid ~s as far as I can tell.
Yes it is odd but so what it is still valid.

Now will anyone write code like this, doubt it.

Also note clang does not optimize this with either libstdc++ or libc++.=