https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80683
--- Comment #5 from Xi Ruoyao <ryxi at stu dot xidian.edu.cn> ---
The issue is in cp/method.c:
/* If that user-written default constructor would satisfy the
requirements of a constexpr constructor (7.1.5), the
implicitly-defined default constructor is constexpr.
The implicitly-defined copy/move assignment operator is constexpr if
- X is a literal type, and
- the assignment operator selected to copy/move each direct base class
subobject is a constexpr function, and
- for each non-static data member of X that is of class type (or array
thereof), the assignment operator selected to copy/move that
member is a constexpr function. */
if (constexpr_p)
*constexpr_p = ctor_p || (assign_p && cxx_dialect >= cxx14);
But if we have default member initializers, the implicitly-defined default
constructor can not be constexpr. We have to check it.
