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* [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" @ 2022-10-24 15:36 johelegp at gmail dot com 2022-10-24 15:59 ` [Bug c++/107378] " pinskia at gcc dot gnu.org ` (6 more replies) 0 siblings, 7 replies; 8+ messages in thread From: johelegp at gmail dot com @ 2022-10-24 15:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 Bug ID: 107378 Summary: `get_if` implementation "is not a constant expression" Product: gcc Version: 13.0 Status: UNCONFIRMED Keywords: rejects-valid Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: johelegp at gmail dot com CC: johelegp at gmail dot com Target Milestone: --- See https://godbolt.org/z/cf1T7q6Tj. ```C++ #include <variant> static_assert([v = std::variant<int*>{}] { return get_if<0>(&v); }()); ``` ``` <source>:2:67: error: non-constant condition for static assertion 2 | static_assert([v = std::variant<int*>{}] { return get_if<0>(&v); }()); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ In file included from <source>:1: <source>:2:67: in 'constexpr' expansion of '<lambda closure object><lambda()>{std::variant<int*>{std::__detail::__variant::_Variant_base<int*>{std::__detail::__variant::_Move_assign_base<true, int*>{std::__detail::__variant::_Copy_assign_base<true, int*>{std::__detail::__variant::_Move_ctor_base<true, int*>{std::__detail::__variant::_Copy_ctor_base<true, int*>{std::__detail::__variant::_Variant_storage<true, int*>{std::__detail::__variant::_Variadic_union<int*>{std::__detail::__variant::_Uninitialized<int*, true>{0}}, 0}}}}}}}}.<lambda()>()' <source>:2:60: in 'constexpr' expansion of 'std::get_if<0, int*>((& v))' /opt/compiler-explorer/gcc-trunk-20221024/include/c++/13.0.0/variant:1183:11: error: '((&<anonymous>.<lambda()>::__v) != 0)' is not a constant expression 1183 | if (__ptr && __ptr->index() == _Np) | ^~~~~ Compiler returned: 1 ``` ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com @ 2022-10-24 15:59 ` pinskia at gcc dot gnu.org 2022-10-24 16:20 ` mpolacek at gcc dot gnu.org ` (5 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-10-24 15:59 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Component|libstdc++ |c++ --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- I suspect this is a front-end issue and not a library issue. ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com 2022-10-24 15:59 ` [Bug c++/107378] " pinskia at gcc dot gnu.org @ 2022-10-24 16:20 ` mpolacek at gcc dot gnu.org 2022-10-24 16:55 ` pinskia at gcc dot gnu.org ` (4 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: mpolacek at gcc dot gnu.org @ 2022-10-24 16:20 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 Marek Polacek <mpolacek at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 CC| |mpolacek at gcc dot gnu.org Last reconfirmed| |2022-10-24 Status|UNCONFIRMED |NEW ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com 2022-10-24 15:59 ` [Bug c++/107378] " pinskia at gcc dot gnu.org 2022-10-24 16:20 ` mpolacek at gcc dot gnu.org @ 2022-10-24 16:55 ` pinskia at gcc dot gnu.org 2022-10-24 18:59 ` johelegp at gmail dot com ` (3 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: pinskia at gcc dot gnu.org @ 2022-10-24 16:55 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Reduced testcase without any headers: ``` struct g { char a; }; constexpr bool f(const char *a) { return a != nullptr; } static_assert([v = g{}] { return f(&v.a); }()); ``` This works with clang. But MSVC rejects it ... ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com ` (2 preceding siblings ...) 2022-10-24 16:55 ` pinskia at gcc dot gnu.org @ 2022-10-24 18:59 ` johelegp at gmail dot com 2022-10-24 20:43 ` ppalka at gcc dot gnu.org ` (2 subsequent siblings) 6 siblings, 0 replies; 8+ messages in thread From: johelegp at gmail dot com @ 2022-10-24 18:59 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 --- Comment #3 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> --- MSVC accepts https://godbolt.org/z/nheYz9aez. ```C++ static_assert([i = 0] { return &i != nullptr; }()); ``` ``` <source>: In lambda function: <source>:1:35: warning: the address of 'i' will never be NULL [-Waddress] 1 | static_assert([i = 0] { return &i != nullptr; }()); | ~~~^~~~~~~~~~ <source>:1:21: note: 'i' declared here 1 | static_assert([i = 0] { return &i != nullptr; }()); | ^ <source>: At global scope: <source>:1:48: error: non-constant condition for static assertion 1 | static_assert([i = 0] { return &i != nullptr; }()); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~ <source>:1:35: error: '((&<anonymous>.<lambda()>::__i) != 0)' is not a constant expression 1 | static_assert([i = 0] { return &i != nullptr; }()); | ~~~^~~~~~~~~~ Compiler returned: 1 ``` ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com ` (3 preceding siblings ...) 2022-10-24 18:59 ` johelegp at gmail dot com @ 2022-10-24 20:43 ` ppalka at gcc dot gnu.org 2022-10-24 22:00 ` johelegp at gmail dot com 2022-10-25 6:57 ` rguenth at gcc dot gnu.org 6 siblings, 0 replies; 8+ messages in thread From: ppalka at gcc dot gnu.org @ 2022-10-24 20:43 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 Patrick Palka <ppalka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ppalka at gcc dot gnu.org --- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> --- dup of PR85944? ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com ` (4 preceding siblings ...) 2022-10-24 20:43 ` ppalka at gcc dot gnu.org @ 2022-10-24 22:00 ` johelegp at gmail dot com 2022-10-25 6:57 ` rguenth at gcc dot gnu.org 6 siblings, 0 replies; 8+ messages in thread From: johelegp at gmail dot com @ 2022-10-24 22:00 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 --- Comment #5 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> --- I think so. My actual use case looks like `constexpr auto v = E;` at global scope, where `E` creates a temporary with a subobject of `std::variant`. Wrapping `E` in an IILE is a workaround for this Bug. ^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107378] `get_if` implementation "is not a constant expression" 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com ` (5 preceding siblings ...) 2022-10-24 22:00 ` johelegp at gmail dot com @ 2022-10-25 6:57 ` rguenth at gcc dot gnu.org 6 siblings, 0 replies; 8+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-10-25 6:57 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107378 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |DUPLICATE --- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- dup then *** This bug has been marked as a duplicate of bug 85944 *** ^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2022-10-25 6:57 UTC | newest] Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-10-24 15:36 [Bug libstdc++/107378] New: `get_if` implementation "is not a constant expression" johelegp at gmail dot com 2022-10-24 15:59 ` [Bug c++/107378] " pinskia at gcc dot gnu.org 2022-10-24 16:20 ` mpolacek at gcc dot gnu.org 2022-10-24 16:55 ` pinskia at gcc dot gnu.org 2022-10-24 18:59 ` johelegp at gmail dot com 2022-10-24 20:43 ` ppalka at gcc dot gnu.org 2022-10-24 22:00 ` johelegp at gmail dot com 2022-10-25 6:57 ` rguenth at gcc dot gnu.org
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