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* [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member @ 2023-12-14 14:25 miro.palmu at helsinki dot fi 2023-12-14 17:35 ` [Bug c++/113021] " pinskia at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: miro.palmu at helsinki dot fi @ 2023-12-14 14:25 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113021 Bug ID: 113021 Summary: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: miro.palmu at helsinki dot fi Target Milestone: --- Following code fails to compile on gcc (GCC) 13.2.1 20230801 but on clang (16.0.6 or 17.0.1). ``` #include <vector> struct A { std::vector<int> vec; int a; }; consteval auto foo() { const A tmp1{{1, 2}, 42}; } int main() { foo(); return 0; } ``` With following error message: ``` > g++ -Wall -Wextra -std=c++20 main.cpp In file included from /usr/include/c++/13.2.1/vector:66, from main2.cpp:1: /usr/include/c++/13.2.1/bits/stl_vector.h: In function ‘int main()’: main2.cpp:11:6: in ‘constexpr’ expansion of ‘foo()’ main2.cpp:8:49: in ‘constexpr’ expansion of ‘std::vector<int>(std::initializer_list<int>{((const int*)(& const int [2]{1, 2})), 2}, ((const std::vector<int>::allocator_type&)(& std::allocator<int>())))’ /usr/include/c++/13.2.1/bits/stl_vector.h:679:21: in ‘constexpr’ expansion of ‘((std::vector<int>*)this)->std::vector<int>::_M_range_initialize<const int*>(__l.std::initializer_list<int>::begin(), __l.std::initializer_list<int>::end(), (std::random_access_iterator_tag{std::bidirectional_iterator_tag()}, std::forward_iterator_tag()))’ /usr/include/c++/13.2.1/bits/stl_vector.h:1689:13: error: modifying a const object ‘((std::vector<int>*)this)->std::vector<int>::<anonymous>.std::_Vector_base<int, std::allocator<int> >::_M_impl.std::_Vector_base<int, std::allocator<int> >::_Vector_impl::<anonymous>.std::_Vector_base<int, std::allocator<int> >::_Vector_impl_data::_M_start’ is not allowed in a constant expression 1688 | this->_M_impl._M_start | ~~~~~~~~~~~~~~~~~~~~~~ 1689 | = this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator())); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main2.cpp:8:32: note: originally declared ‘const’ here 8 | consteval auto foo() { const A tmp1{ {1, 2}, 42 }; } | ^~~~ ``` If member variable `a` is removed it compiles: ``` #include <vector> struct A { std::vector<int> vec; }; consteval auto foo() { const A tmp1{ {1, 2} }; } int main() { foo(); return 0; } ``` ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113021] [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member 2023-12-14 14:25 [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member miro.palmu at helsinki dot fi @ 2023-12-14 17:35 ` pinskia at gcc dot gnu.org 2023-12-15 10:44 ` miro.palmu at helsinki dot fi ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-12-14 17:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113021 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Last reconfirmed| |2023-12-14 Status|UNCONFIRMED |NEW Keywords| |needs-reduction --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Confirmed. We should reduce this to remove the include file too ... ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113021] [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member 2023-12-14 14:25 [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member miro.palmu at helsinki dot fi 2023-12-14 17:35 ` [Bug c++/113021] " pinskia at gcc dot gnu.org @ 2023-12-15 10:44 ` miro.palmu at helsinki dot fi 2023-12-15 10:55 ` miro.palmu at helsinki dot fi 2023-12-15 19:40 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: miro.palmu at helsinki dot fi @ 2023-12-15 10:44 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113021 --- Comment #2 from Miro Palmu <miro.palmu at helsinki dot fi> --- (In reply to Andrew Pinski from comment #1) > Confirmed. We should reduce this to remove the include file too ... Here is somewhat reduced: ``` #include <memory> auto alloc = std::allocator<int>{}; constexpr auto n = 3; struct vec { int* data; constexpr vec() { this->data = alloc.allocate(n); } constexpr ~vec() { alloc.deallocate(this->data, n); } }; struct A { vec v; int a; }; consteval auto foo() { A temp1{{}, 42}; // This compiles fine const A tmp2{{}, 42}; // This does not } int main() { foo(); } ``` ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113021] [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member 2023-12-14 14:25 [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member miro.palmu at helsinki dot fi 2023-12-14 17:35 ` [Bug c++/113021] " pinskia at gcc dot gnu.org 2023-12-15 10:44 ` miro.palmu at helsinki dot fi @ 2023-12-15 10:55 ` miro.palmu at helsinki dot fi 2023-12-15 19:40 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: miro.palmu at helsinki dot fi @ 2023-12-15 10:55 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113021 --- Comment #3 from Miro Palmu <miro.palmu at helsinki dot fi> --- Here is even more reduced. Notice that if the unused data member `pointer` is removed from `vec` the problem goes away. Same with data member `a` in struct `A`. ``` struct vec { int data; int* pointer; // This is required for compilation to fail constexpr vec() { data = 42; } }; struct A { vec v; int a; // This is required for compilation to fail }; consteval auto foo() { A temp1{{}, 42}; // This compiles fine const A tmp2{{}, 42}; // This does not } int main() { foo(); } ``` ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/113021] [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member 2023-12-14 14:25 [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member miro.palmu at helsinki dot fi ` (2 preceding siblings ...) 2023-12-15 10:55 ` miro.palmu at helsinki dot fi @ 2023-12-15 19:40 ` pinskia at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-12-15 19:40 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113021 --- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Looks like it is the uninitialized field pointer which is causing the issues. Looks like GCC does not currently fully support that for const variables inside a constexpr/consteval . The linked PRs are about string but I think the same issue shows up. ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-12-15 19:40 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-12-14 14:25 [Bug c++/113021] New: [constexpr] gcc rejects initializing struct containing vector during constant evaluation depending if the struct also contains other member miro.palmu at helsinki dot fi 2023-12-14 17:35 ` [Bug c++/113021] " pinskia at gcc dot gnu.org 2023-12-15 10:44 ` miro.palmu at helsinki dot fi 2023-12-15 10:55 ` miro.palmu at helsinki dot fi 2023-12-15 19:40 ` pinskia at gcc dot gnu.org
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