https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104386
--- Comment #2 from Artur Bać <gcc at ebasoft dot com.pl> --- I think it is connected with this case https://godbolt.org/z/cvfs1KqGW https://godbolt.org/z/vdzTzo7be //sizeof(foo) ==12 struct base { uint32_t x{}; std::byte v{}; base() noexcept = default; }; struct foo : public base { std::byte z; }; //sizeof(foo) == 8 struct base { uint32_t x; std::byte v; base() noexcept : x{}, v{} {} }; struct foo : public base { std::byte z; }; and https://www.reddit.com/r/cpp/comments/slfugx/comment/hvs4n7j/?utm_source=share&utm_medium=web2x&context=3 "Som1Lse · 5 hr. ago Interestingly GCC disagrees with itself: -std=c++17 it considers base to be a POD and doesn't reuse padding. -std=c++20 it considers base to not be a POD and agrees with Clang, reusing the padding bytes."
