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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-3901] libstdc++: Remove std::bind_front specialization for no bound args Date: Tue, 12 Sep 2023 15:27:58 +0000 (GMT) [thread overview] Message-ID: <20230912152758.186583896C3C@sourceware.org> (raw) https://gcc.gnu.org/g:f1e87aee5b7023fb4f5791c6869db705e18c2705 commit r14-3901-gf1e87aee5b7023fb4f5791c6869db705e18c2705 Author: Patrick Palka <ppalka@redhat.com> Date: Tue Sep 12 11:23:08 2023 -0400 libstdc++: Remove std::bind_front specialization for no bound args The specialization used by std::bind_front when there are no bound args (added by r13-4214-gcbd05ca5ab1231) seems to be mostly obsoleted by r13-5033-ge2eab3c4edb6aa which added [[no_unique_address]] to the main template's data members. What's left to consider is the compile time advantage of the specialization, which doesn't seem huge since it just avoids using tuple<> (which is an explicit specialization anyway) and expanding some pack expansions with an empty argument pack. So this patch removes this specialization; this means we have one less spot to fix the PR libstdc++/111327 perfect forwarding bug. libstdc++-v3/ChangeLog: * include/std/functional (_Bind_front0): Remove. (_Bind_front_t): Adjust. Diff: --- libstdc++-v3/include/std/functional | 63 +------------------------------------ 1 file changed, 1 insertion(+), 62 deletions(-) diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional index 60d4d1f3dd22..7d1b890bb4e9 100644 --- a/libstdc++-v3/include/std/functional +++ b/libstdc++-v3/include/std/functional @@ -996,69 +996,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION [[no_unique_address]] std::tuple<_BoundArgs...> _M_bound_args; }; - // Avoid the overhead of an empty tuple<> if there are no bound args. - template<typename _Fd> - struct _Bind_front0 - { - static_assert(is_move_constructible_v<_Fd>); - - // First parameter is to ensure this constructor is never used - // instead of the copy/move constructor. - template<typename _Fn> - explicit constexpr - _Bind_front0(int, _Fn&& __fn) - noexcept(is_nothrow_constructible_v<_Fd, _Fn>) - : _M_fd(std::forward<_Fn>(__fn)) - { } - - _Bind_front0(const _Bind_front0&) = default; - _Bind_front0(_Bind_front0&&) = default; - _Bind_front0& operator=(const _Bind_front0&) = default; - _Bind_front0& operator=(_Bind_front0&&) = default; - ~_Bind_front0() = default; - - template<typename... _CallArgs> - constexpr - invoke_result_t<_Fd&, _CallArgs...> - operator()(_CallArgs&&... __call_args) & - noexcept(is_nothrow_invocable_v<_Fd&, _CallArgs...>) - { return std::invoke(_M_fd, std::forward<_CallArgs>(__call_args)...); } - - template<typename... _CallArgs> - constexpr - invoke_result_t<const _Fd&, _CallArgs...> - operator()(_CallArgs&&... __call_args) const & - noexcept(is_nothrow_invocable_v<const _Fd&, _CallArgs...>) - { return std::invoke(_M_fd, std::forward<_CallArgs>(__call_args)...); } - - template<typename... _CallArgs> - constexpr - invoke_result_t<_Fd, _CallArgs...> - operator()(_CallArgs&&... __call_args) && - noexcept(is_nothrow_invocable_v<_Fd, _CallArgs...>) - { - return std::invoke(std::move(_M_fd), - std::forward<_CallArgs>(__call_args)...); - } - - template<typename... _CallArgs> - constexpr - invoke_result_t<const _Fd, _CallArgs...> - operator()(_CallArgs&&... __call_args) const && - noexcept(is_nothrow_invocable_v<const _Fd, _CallArgs...>) - { - return std::invoke(std::move(_M_fd), - std::forward<_CallArgs>(__call_args)...); - } - - private: - [[no_unique_address]] _Fd _M_fd; - }; - template<typename _Fn, typename... _Args> - using _Bind_front_t - = __conditional_t<sizeof...(_Args) == 0, _Bind_front0<decay_t<_Fn>>, - _Bind_front<decay_t<_Fn>, decay_t<_Args>...>>; + using _Bind_front_t = _Bind_front<decay_t<_Fn>, decay_t<_Args>...>; /** Create call wrapper by partial application of arguments to function. *
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