From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 7BC253857B99 for ; Thu, 7 Jul 2022 16:54:50 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 7BC253857B99 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-628-bukXeleoP9eHzNQMuS4PkA-1; Thu, 07 Jul 2022 12:54:49 -0400 X-MC-Unique: bukXeleoP9eHzNQMuS4PkA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1393F2919EDB; Thu, 7 Jul 2022 16:54:43 +0000 (UTC) Received: from localhost (unknown [10.33.36.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id CC7A22026D64; Thu, 7 Jul 2022 16:54:42 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [PATCH] libstdc++: Prefer const T to std::add_const_t Date: Thu, 7 Jul 2022 17:54:42 +0100 Message-Id: <20220707165442.1418451-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.9 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 07 Jul 2022 16:54:51 -0000 Does anybody see a problem with this change? The point is to avoid unnecessary class template instantiations. Tested aarch64-linux. -- >8 -- For any typedef-name or template parameter, T, add_const_t is equivalent to T const, so we can avoid instantiating the std::add_const class template and just say T const (or const T). This isn't true for a non-typedef like int&, where int& const would be ill-formed, but we shouldn't be using add_const_t anyway, because we know what that type is. The only place we need to continue using std::add_const is in the std::bind implementation where it's used as a template template parameter to be applied as a metafunction elsewhere. libstdc++-v3/ChangeLog: * include/bits/stl_iterator.h (__iter_to_alloc_t): Replace add_const_t with const-qualifier. * include/bits/utility.h (tuple_element): Likewise for all cv-qualifiers. * include/std/type_traits (add_const, add_volatile): Replace typedef-declaration with using-declaration. (add_cv): Replace add_const and add_volatile with cv-qualifiers. * include/std/variant (variant_alternative): Replace add_const_t, add_volatile_t and add_cv_t etc. with cv-qualifiers. --- libstdc++-v3/include/bits/stl_iterator.h | 11 +++++------ libstdc++-v3/include/bits/utility.h | 6 +++--- libstdc++-v3/include/std/type_traits | 9 +++------ libstdc++-v3/include/std/variant | 6 +++--- 4 files changed, 14 insertions(+), 18 deletions(-) diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index 12a89ab229f..049cb02a4c4 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -2536,19 +2536,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // of associative containers. template using __iter_key_t = remove_const_t< - typename iterator_traits<_InputIterator>::value_type::first_type>; + typename iterator_traits<_InputIterator>::value_type::first_type>; template - using __iter_val_t = - typename iterator_traits<_InputIterator>::value_type::second_type; + using __iter_val_t + = typename iterator_traits<_InputIterator>::value_type::second_type; template struct pair; template - using __iter_to_alloc_t = - pair>, - __iter_val_t<_InputIterator>>; + using __iter_to_alloc_t + = pair, __iter_val_t<_InputIterator>>; #endif // __cpp_deduction_guides _GLIBCXX_END_NAMESPACE_VERSION diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h index e0e40309a6d..6a192e27836 100644 --- a/libstdc++-v3/include/bits/utility.h +++ b/libstdc++-v3/include/bits/utility.h @@ -86,19 +86,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template struct tuple_element<__i, const _Tp> { - typedef typename add_const<__tuple_element_t<__i, _Tp>>::type type; + using type = const __tuple_element_t<__i, _Tp>; }; template struct tuple_element<__i, volatile _Tp> { - typedef typename add_volatile<__tuple_element_t<__i, _Tp>>::type type; + using type = volatile __tuple_element_t<__i, _Tp>; }; template struct tuple_element<__i, const volatile _Tp> { - typedef typename add_cv<__tuple_element_t<__i, _Tp>>::type type; + using type = const volatile __tuple_element_t<__i, _Tp>; }; #if __cplusplus >= 201402L diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index 2572d8edd69..e5f58bc2e3f 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -1577,20 +1577,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// add_const template struct add_const - { typedef _Tp const type; }; + { using type = _Tp const; }; /// add_volatile template struct add_volatile - { typedef _Tp volatile type; }; + { using type = _Tp volatile; }; /// add_cv template struct add_cv - { - typedef typename - add_const::type>::type type; - }; + { using type = _Tp const volatile; }; #if __cplusplus > 201103L diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 5ff1e3edcdf..f8f15665433 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -107,15 +107,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template struct variant_alternative<_Np, const _Variant> - { using type = add_const_t>; }; + { using type = const variant_alternative_t<_Np, _Variant>; }; template struct variant_alternative<_Np, volatile _Variant> - { using type = add_volatile_t>; }; + { using type = volatile variant_alternative_t<_Np, _Variant>; }; template struct variant_alternative<_Np, const volatile _Variant> - { using type = add_cv_t>; }; + { using type = const volatile variant_alternative_t<_Np, _Variant>; }; inline constexpr size_t variant_npos = -1; -- 2.36.1