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 CE59D3858D3C; Thu,  7 Dec 2023 21:51:58 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org CE59D3858D3C
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1701985918;
	bh=i0MdMOF8aLtk3KLUUSGSQj2tdzCdtzPt0BOsF1+KGFQ=;
	h=From:To:Subject:Date:From;
	b=DRWH0+6ccvROYp5u5a0rOFK50IZano3416D9qSDIFTg4iLUY9VfirU4et31kN8RWF
	 eomOQD2V7VpXClyu/ESl8sXWLZwV5Klcgnm6+eYAOoN0SSmdDr6KnNU7WFr5CPfid9
	 18tqYLWgQ8rSRJcxA7BYNz3DObQ0eIMHzcE7qYAE=
From: "mital at mitalashok dot co.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/112908] New:
 __reference_{converts,constructs}_from_temporary checks for move constructor
 when binding prvalue to reference of the same type
Date: Thu, 07 Dec 2023 21:51:58 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: mital at mitalashok dot co.uk
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-112908-4@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=3D112908

            Bug ID: 112908
           Summary: __reference_{converts,constructs}_from_temporary
                    checks for move constructor when binding prvalue to
                    reference of the same type
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mital at mitalashok dot co.uk
  Target Milestone: ---

The following compiles on trunk:

    struct NonMovable {
      NonMovable() =3D default;
      NonMovable(NonMovable&&) =3D delete;
    };

    static_assert( __reference_converts_from_temporary(int&&, int));
    static_assert(!__reference_converts_from_temporary(NonMovable&&,
NonMovable));
    static_assert( __reference_constructs_from_temporary(int&&, int));
    static_assert(!__reference_constructs_from_temporary(NonMovable&&,
NonMovable));

When the NonMovable assertions should fail because there *is* a temporary b=
eing
bound to a reference (in exactly the same way as the int case).

We can observe it instantiating constructors that shouldn't be too:

    template<typename T>
    struct S {
      template<typename U =3D T>
      S(const S&&) noexcept(U()) {}
    };

    static_assert(__reference_converts_from_temporary(const S<bool>&&, const
S<bool>));
    static_assert(__reference_converts_from_temporary(const S<void*>&&, con=
st
S<void*>));

Which complains about a conversion from void* to bool even though construct=
ors
shouldn't be looked at.=