[Bug c++/124431] [16 Regression] Possibly incorrect 'error: accessing uninitialised array element' in C++20 module

[nshead at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124431

--- Comment #3 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
Actually, e.cpp is not needed, and d.cpp can be

// d.cpp
import C;
import B;
constexpr auto rotn_y = mat<4>()[0];

Using `mat<4>{}` also fixes the error.