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 514DD38515CD; Wed, 18 May 2022 12:42:27 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 514DD38515CD
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/96710] __int128 vs <type_traits>
Date: Wed, 18 May 2022 12:42:27 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
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-96710-4-dWQHtTpRoJ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-96710-4@http.gcc.gnu.org/bugzilla/>
References: <bug-96710-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 18 May 2022 12:42:27 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96710

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> Our definitions of is_scalar depends on is_arithmetic, so
> is_scalar<__int128> is false, and therefore is_object<__int128> is false.
> This is clearly nonsense.

Hmm, what I wrote is nonsense. Our is_object does not depend on is_scalar:

  /// is_object
  template<typename _Tp>
    struct is_object
    : public __not_<__or_<is_function<_Tp>, is_reference<_Tp>,
                          is_void<_Tp>>>::type
    { };

So is_object<__int128> is always true.

But is_scalar<__int128> still depends on __STRICT_ANSI__ which seems wrong.
It's not a compound type, so it's scalar.


Currently we define is_scalar as:

  template<typename _Tp>
    struct is_scalar
    : public __or_<is_arithmetic<_Tp>, is_enum<_Tp>, is_pointer<_Tp>,
                   is_member_pointer<_Tp>, is_null_pointer<_Tp>>::type
    { };

I think a better definition would be:

  template<typename _Tp>
    struct is_scalar
    : public __and_<is_object<_Tp>, __not_<is_array<_Tp>>,
                                    __not_<is_class<_Tp>>,
                                    __not_<is_union<_Tp>>>
    { };

Which could be optimized using partial specializations for the array cases:

  template<typename _Tp>
    struct is_scalar
    : public __and_<is_object<_Tp>, __not_<is_class<_Tp>>,
                                    __not_<is_union<_Tp>>>
    { };

  template<typename _Tp>
    struct is_scalar<_Tp[]>
    : public false_type
    { };

  template<typename _Tp, size_t _Num>
    struct is_scalar<_Tp[_Num]>
    : public false_type
    { };=