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* [Bug c++/110245] New: constant evaluation fails with uninitialized union and default constructor @ 2023-06-14 3:47 danakj at orodu dot net 2023-06-14 3:52 ` [Bug c++/110245] " danakj at orodu dot net 2023-06-14 4:04 ` pinskia at gcc dot gnu.org 0 siblings, 2 replies; 3+ messages in thread From: danakj at orodu dot net @ 2023-06-14 3:47 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110245 Bug ID: 110245 Summary: constant evaluation fails with uninitialized union and default constructor Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: danakj at orodu dot net Target Milestone: --- ``` struct Store { constexpr Store() {} union { int i; }; bool b = false; }; struct C { constexpr C() = default; Store s; }; int main() { constexpr auto c = C(); // } ``` This should compile but does not, GCC complains that it refers to an incompletely initialized variable. Union members are not required to be active. https://godbolt.org/z/G9vcosTG1 Reproduced on GCC trunk and GCC 11. ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/110245] constant evaluation fails with uninitialized union and default constructor 2023-06-14 3:47 [Bug c++/110245] New: constant evaluation fails with uninitialized union and default constructor danakj at orodu dot net @ 2023-06-14 3:52 ` danakj at orodu dot net 2023-06-14 4:04 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: danakj at orodu dot net @ 2023-06-14 3:52 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110245 --- Comment #1 from danakj at orodu dot net --- Note that GCC has no problem with doing this constexpr construction if the object is not stored as an lvalue. ``` struct Store { constexpr Store() {} union { int i; }; bool b = false; }; struct C { constexpr C() = default; Store s; }; int main() { constexpr auto c = C(); // Fails. constexpr auto b = C().s.b; // OK } ``` https://godbolt.org/z/31MTenKoo ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/110245] constant evaluation fails with uninitialized union and default constructor 2023-06-14 3:47 [Bug c++/110245] New: constant evaluation fails with uninitialized union and default constructor danakj at orodu dot net 2023-06-14 3:52 ` [Bug c++/110245] " danakj at orodu dot net @ 2023-06-14 4:04 ` pinskia at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-06-14 4:04 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110245 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- So if I read: https://cplusplus.github.io/CWG/issues/2558.html there is still an open question about "Union types shall be initialized such that they have an active member in the result of a constant expression" but I am not 100% sure here. ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2023-06-14 4:04 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-06-14 3:47 [Bug c++/110245] New: constant evaluation fails with uninitialized union and default constructor danakj at orodu dot net 2023-06-14 3:52 ` [Bug c++/110245] " danakj at orodu dot net 2023-06-14 4:04 ` pinskia at gcc dot gnu.org
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