From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 74E0839730E4; Wed, 10 Mar 2021 16:12:18 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 74E0839730E4 From: "pilarlatiesa at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/99522] New: Using the unseq execution policy in min_element requires the sequence value type to be copy assignable Date: Wed, 10 Mar 2021 16:12:18 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Version: 10.2.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: pilarlatiesa at gmail dot com 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: 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Mar 2021 16:12:18 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99522 Bug ID: 99522 Summary: Using the unseq execution policy in min_element requires the sequence value type to be copy assignable Product: gcc Version: 10.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: pilarlatiesa at gmail dot com Target Milestone: --- Many algorithms have the precondition that *first meets the Cpp17MoveAssign= able requirements. However, I don=E2=80=99t see such a requirement for min_eleme= nt, max_element, or minmax_element. In spite of that, the following snippet is rejected: $ cat test.cpp #include #include #include struct T { int const ID; // Not Cpp17CopyAssignable }; int f(std::vector const &v) { if (v.empty()) return -1; return std::min_element(std::execution::par_unseq, v.begin(), v.end(), [](T const &lhs, T const &rhs) { return lhs.ID < rhs.ID; })->ID; } The error message is: $ g++-10 -std=3Dc++17 -c test.cpp [=E2=80=A6] error: use of deleted function 'T& T::operator=3D(const T&)' 643 | __min_val =3D __obj.__min_val; | ~~~~~~~~~~^~~~~~~~~~~~~~~~~ [=E2=80=A6] There=E2=80=99s also [algorithms.parallel.exec]/3 Unless otherwise stated, implementations may m= ake arbitrary copies of elements (with type T) from sequences where is_trivially_copy_constructible_v and is_trivially_destructible_v are true. but I=E2=80=99ve been told that it grants copy construction, but not copy a= ssignment. $ g++-10 -v Using built-in specs. COLLECT_GCC=3Dg++-10 COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa:hsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu 10.2.0-5ubuntu1~20.04' --with-bugurl=3Dfile:///usr/share/doc/gcc-10/README.= Bugs --enable-languages=3Dc,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix= =3D/usr --with-gcc-major-version-only --program-suffix=3D-10 --program-prefix=3Dx86_64-linux-gnu- --enable-shared --enable-linker-build-= id --libexecdir=3D/usr/lib --without-included-gettext --enable-threads=3Dposix --libdir=3D/usr/lib --enable-nls --enable-clocale=3Dgnu --enable-libstdcxx-= debug --enable-libstdcxx-time=3Dyes --with-default-libstdcxx-abi=3Dnew --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=3Drelea= se --with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch --disable-werror --with-arch-32=3Di686 --with-abi=3Dm64 --with-multilib-list=3Dm32,m64,mx32 --enable-multilib --with-tune=3Dgeneric --enable-offload-targets=3Dnvptx-none=3D/build/gcc-10-WJNXnb/gcc-10-10.2.0/= debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-10-WJNXnb/gcc-10-10.2.0/deb= ian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=3Drelease --build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.2.0 (Ubuntu 10.2.0-5ubuntu1~20.04)=