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GET /api/1.1/patches/2233376/?format=api
{ "id": 2233376, "url": "http://patchwork.ozlabs.org/api/1.1/patches/2233376/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/20260506085339.325517-1-jwakely@redhat.com/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/1.1/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null }, "msgid": "<20260506085339.325517-1-jwakely@redhat.com>", "date": "2026-05-06T08:48:04", "name": "[v2,1/3] libstdc++: Replace uses of EBO with [[no_unique_address]]", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "9fe0b6561f7212b446ce1504fdf213473570c9be", "submitter": { "id": 48004, "url": "http://patchwork.ozlabs.org/api/1.1/people/48004/?format=api", "name": "Jonathan Wakely", "email": "jwakely@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/20260506085339.325517-1-jwakely@redhat.com/mbox/", "series": [ { "id": 502950, "url": "http://patchwork.ozlabs.org/api/1.1/series/502950/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=502950", "date": "2026-05-06T08:48:05", "name": "[v2,1/3] libstdc++: Replace uses of EBO with [[no_unique_address]]", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/502950/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2233376/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2233376/checks/", "tags": {}, "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=Xzjmk6qS;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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sourceware.org;\n dkim=pass (1024-bit key, unprotected)\n header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=Xzjmk6qS", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1778057626;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding;\n bh=/gLvmsU0C5sSPNYR4NT1HbrD/Fz+TQVbORtEDShrjVU=;\n b=Xzjmk6qSG7dQqhVcMTPxPw8uv5U1+LaowORajT9OMvo9DowoUbWKkI4YfOYd0og+a/k6Gc\n Rv2WhaRdZbwbVBArrE9fHPfSZbD0K9FxrI2/Sq6SNO1BRQM5hpQMxcHCPFoTJG3SvjpALv\n jDmIxn5ZgrhugCTaWwUj3yYXTSn48Vw=", "X-MC-Unique": "yyYHEzrUMdqpa33Qp0BpyQ-1", "X-Mimecast-MFC-AGG-ID": "yyYHEzrUMdqpa33Qp0BpyQ_1778057622", "From": "Jonathan Wakely <jwakely@redhat.com>", "To": "gcc-patches@gcc.gnu.org,\n\tlibstdc++@gcc.gnu.org", "Subject": "[PATCH v2 1/3] libstdc++: Replace uses of EBO with\n [[no_unique_address]]", "Date": "Wed, 6 May 2026 09:48:04 +0100", "Message-ID": "<20260506085339.325517-1-jwakely@redhat.com>", "MIME-Version": "1.0", "X-Scanned-By": "MIMEDefang 3.4.1 on 10.30.177.111", "X-Mimecast-Spam-Score": "0", "X-Mimecast-MFC-PROC-ID": "WNozS6X0qXxEdT-DpK5j1oR533F0x_1ylY8JgemkDVk_1778057622", "X-Mimecast-Originator": "redhat.com", "Content-Type": "text/plain", "Content-Transfer-Encoding": "8bit", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "Clang 9 added support for [[__no_unique_address__]] and we don't support\nIntel icc any longer, so we can remove the code in <tuple> that works\naround the absence of that attribute. We can also address a FIXME in\n<bits/shared_ptr_base.h> and replace uses of EBO with the attribute.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/shared_ptr_base.h (_Sp_ebo_helper): Simplify by\n\tusing [[__no_unique_address__]] instead of EBO. Use the\n\tattribute unconditionally for the unstable ABI.\n\t(_Sp_counted_deleter::_Impl): Adjust uses of _Sp_ebo_helper.\n\t(_Sp_counted_ptr_inplace::_Impl): Likewise.\n\t* include/std/tuple (_Head_base): Remove implementation for\n\tcompilers that don't support [[__no_unique_address__]]. Use the\n\tattribute unconditionally for the unstable ABI.\n---\n\nv2: Add the attribute to the data members of _Impl as well as to the\n_M_obj data member of _Sp_ebo_helper. Otherwise the _M_obj subobject is\npotentially overlapping, but the _M_ and _M_d ones are not. We need both\nto be marked with the attribute.\n\nWhat we *really* want is [[no_unique_address(expr)]] so that we can get\nrid of _Sp_ebo_helper entirely, and just do:\n\n #if ! _GLIBCXX_INLINE_VERSION // Stable ABI\n template<typename T> __can_overlap = !__is_final(T) && __is_empty(T);\n #else // Unstable ABI\n template<typename T> __can_overlap = true;\n #endif\n [[no_unique_address(__can_overlap<_Del>)]] _M_del;\n\nI should propose that to WG21, and if rejected just get it added to GCC\nand Clang.\n\nTested x86_64-linux.\n\n libstdc++-v3/include/bits/shared_ptr_base.h | 65 +++++++++----------\n libstdc++-v3/include/std/tuple | 69 ++++-----------------\n 2 files changed, 43 insertions(+), 91 deletions(-)", "diff": "diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h\nindex b92e3a4c90e4..3ab73f6e4a0d 100644\n--- a/libstdc++-v3/include/bits/shared_ptr_base.h\n+++ b/libstdc++-v3/include/bits/shared_ptr_base.h\n@@ -513,57 +513,52 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n inline void\n _Sp_counted_ptr<nullptr_t, _S_atomic>::_M_dispose() noexcept { }\n \n- // FIXME: once __has_cpp_attribute(__no_unique_address__)) is true for\n- // all supported compilers we can greatly simplify _Sp_ebo_helper.\n+#if ! __has_cpp_attribute(__no_unique_address__)\n+#error \"support for [[__no_unique_address__]] attribute is required\"\n+#endif\n+\n+#if ! _GLIBCXX_INLINE_VERSION\n // N.B. unconditionally applying the attribute could change layout for\n // final types, which currently cannot use EBO so have a unique address.\n-\n- template<int _Nm, typename _Tp,\n-\t bool __use_ebo = !__is_final(_Tp) && __is_empty(_Tp)>\n+ template<typename _Tp, bool = !__is_final(_Tp) && __is_empty(_Tp)>\n struct _Sp_ebo_helper;\n+#else\n+ template<typename _Tp, bool = true>\n+ struct _Sp_ebo_helper;\n+#endif\n \n- /// Specialization using EBO.\n- template<int _Nm, typename _Tp>\n- struct _Sp_ebo_helper<_Nm, _Tp, true> : private _Tp\n+ /// Specialization using [[no_unique_address]].\n+ template<typename _Tp>\n+ struct _Sp_ebo_helper<_Tp, true>\n {\n- explicit _Sp_ebo_helper(const _Tp& __tp) : _Tp(__tp) { }\n- explicit _Sp_ebo_helper(_Tp&& __tp) : _Tp(std::move(__tp)) { }\n-\n- static _Tp&\n- _S_get(_Sp_ebo_helper& __eboh) { return static_cast<_Tp&>(__eboh); }\n+ [[__no_unique_address__]] _Tp _M_obj;\n };\n \n- /// Specialization not using EBO.\n- template<int _Nm, typename _Tp>\n- struct _Sp_ebo_helper<_Nm, _Tp, false>\n+#if ! _GLIBCXX_INLINE_VERSION\n+ /// Specialization not using [[no_unique_address]].\n+ template<typename _Tp>\n+ struct _Sp_ebo_helper<_Tp, false>\n {\n- explicit _Sp_ebo_helper(const _Tp& __tp) : _M_tp(__tp) { }\n- explicit _Sp_ebo_helper(_Tp&& __tp) : _M_tp(std::move(__tp)) { }\n-\n- static _Tp&\n- _S_get(_Sp_ebo_helper& __eboh)\n- { return __eboh._M_tp; }\n-\n- private:\n- _Tp _M_tp;\n+ _Tp _M_obj;\n };\n+#endif\n \n // Support for custom deleter and/or allocator\n template<typename _Ptr, typename _Deleter, typename _Alloc, _Lock_policy _Lp>\n class _Sp_counted_deleter final : public _Sp_counted_base<_Lp>\n {\n- class _Impl : _Sp_ebo_helper<0, _Deleter>, _Sp_ebo_helper<1, _Alloc>\n+ class _Impl\n {\n-\ttypedef _Sp_ebo_helper<0, _Deleter>\t_Del_base;\n-\ttypedef _Sp_ebo_helper<1, _Alloc>\t_Alloc_base;\n+\t[[__no_unique_address__]] _Sp_ebo_helper<_Deleter> _M_d;\n+\t[[__no_unique_address__]] _Sp_ebo_helper<_Alloc> _M_a;\n \n public:\n \t_Impl(_Ptr __p, _Deleter __d, const _Alloc& __a) noexcept\n-\t: _Del_base(std::move(__d)), _Alloc_base(__a), _M_ptr(__p)\n+\t: _M_d{std::move(__d)}, _M_a{__a}, _M_ptr(__p)\n \t{ }\n \n-\t_Deleter& _M_del() noexcept { return _Del_base::_S_get(*this); }\n-\t_Alloc& _M_alloc() noexcept { return _Alloc_base::_S_get(*this); }\n+\t_Deleter& _M_del() noexcept { return _M_d._M_obj; }\n+\t_Alloc& _M_alloc() noexcept { return _M_a._M_obj; }\n \n \t_Ptr _M_ptr;\n };\n@@ -645,14 +640,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n template<typename _Tp, typename _Alloc, _Lock_policy _Lp>\n class _Sp_counted_ptr_inplace final : public _Sp_counted_base<_Lp>\n {\n- class _Impl : _Sp_ebo_helper<0, _Alloc>\n+ class _Impl\n {\n-\ttypedef _Sp_ebo_helper<0, _Alloc>\t_A_base;\n+\t[[__no_unique_address__]] _Sp_ebo_helper<_Alloc> _M_a;\n \n public:\n-\texplicit _Impl(_Alloc __a) noexcept : _A_base(__a) { }\n+\texplicit _Impl(_Alloc __a) noexcept : _M_a{std::move(__a)} { }\n \n-\t_Alloc& _M_alloc() noexcept { return _A_base::_S_get(*this); }\n+\t_Alloc& _M_alloc() noexcept { return _M_a._M_obj; }\n \n \t__gnu_cxx::__aligned_buffer<__remove_cv_t<_Tp>> _M_storage;\n };\ndiff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple\nindex f7caa79cda04..32800d8d7752 100644\n--- a/libstdc++-v3/include/std/tuple\n+++ b/libstdc++-v3/include/std/tuple\n@@ -68,7 +68,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n template<typename... _Elements>\n class tuple;\n \n+#if ! __has_cpp_attribute(__no_unique_address__)\n+#error \"support for [[__no_unique_address__]] attribute is required\"\n+#endif\n+\n /// @cond undocumented\n+#if ! _GLIBCXX_INLINE_VERSION\n template<typename _Tp>\n struct __is_empty_non_tuple : is_empty<_Tp> { };\n \n@@ -76,17 +81,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n template<typename _El0, typename... _El>\n struct __is_empty_non_tuple<tuple<_El0, _El...>> : false_type { };\n \n- // Use the Empty Base-class Optimization for empty, non-final types.\n+ // Use [[no_unique_address]] for empty, non-final types.\n template<typename _Tp>\n using __empty_not_final\n = __conditional_t<__is_final(_Tp), false_type,\n \t\t __is_empty_non_tuple<_Tp>>;\n+#else\n+ // For the unstable ABI we always use [[no_unique_address]].\n+ template<typename>\n+ using __empty_not_final = true_type;\n+#endif\n \n template<size_t _Idx, typename _Head,\n \t bool = __empty_not_final<_Head>::value>\n struct _Head_base;\n \n-#if __has_cpp_attribute(__no_unique_address__)\n template<size_t _Idx, typename _Head>\n struct _Head_base<_Idx, _Head, true>\n {\n@@ -141,61 +150,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \n [[__no_unique_address__]] _Head _M_head_impl;\n };\n-#else\n- template<size_t _Idx, typename _Head>\n- struct _Head_base<_Idx, _Head, true>\n- : public _Head\n- {\n- constexpr _Head_base()\n- : _Head() { }\n-\n- constexpr _Head_base(const _Head& __h)\n- : _Head(__h) { }\n-\n- constexpr _Head_base(const _Head_base&) = default;\n- constexpr _Head_base(_Head_base&&) = default;\n-\n- template<typename _UHead>\n- constexpr _Head_base(_UHead&& __h)\n-\t: _Head(std::forward<_UHead>(__h)) { }\n-\n- _GLIBCXX20_CONSTEXPR\n- _Head_base(allocator_arg_t, __uses_alloc0)\n- : _Head() { }\n-\n- template<typename _Alloc>\n-\t_GLIBCXX20_CONSTEXPR\n-\t_Head_base(allocator_arg_t, __uses_alloc1<_Alloc> __a)\n-\t: _Head(allocator_arg, *__a._M_a) { }\n-\n- template<typename _Alloc>\n-\t_GLIBCXX20_CONSTEXPR\n-\t_Head_base(allocator_arg_t, __uses_alloc2<_Alloc> __a)\n-\t: _Head(*__a._M_a) { }\n-\n- template<typename _UHead>\n-\t_GLIBCXX20_CONSTEXPR\n-\t_Head_base(__uses_alloc0, _UHead&& __uhead)\n-\t: _Head(std::forward<_UHead>(__uhead)) { }\n-\n- template<typename _Alloc, typename _UHead>\n-\t_GLIBCXX20_CONSTEXPR\n-\t_Head_base(__uses_alloc1<_Alloc> __a, _UHead&& __uhead)\n-\t: _Head(allocator_arg, *__a._M_a, std::forward<_UHead>(__uhead)) { }\n-\n- template<typename _Alloc, typename _UHead>\n-\t_GLIBCXX20_CONSTEXPR\n-\t_Head_base(__uses_alloc2<_Alloc> __a, _UHead&& __uhead)\n-\t: _Head(std::forward<_UHead>(__uhead), *__a._M_a) { }\n-\n- static constexpr _Head&\n- _M_head(_Head_base& __b) noexcept { return __b; }\n-\n- static constexpr const _Head&\n- _M_head(const _Head_base& __b) noexcept { return __b; }\n- };\n-#endif\n \n+#if ! _GLIBCXX_INLINE_VERSION\n template<size_t _Idx, typename _Head>\n struct _Head_base<_Idx, _Head, false>\n {\n@@ -250,6 +206,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \n _Head _M_head_impl;\n };\n+#endif\n \n #if __cpp_lib_tuple_like // >= C++23\n struct __tuple_like_tag_t { explicit __tuple_like_tag_t() = default; };\n", "prefixes": [ "v2", "1/3" ] }