https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128218
--- Comment #4 from Harald Anlauf <anlauf at gcc dot gnu.org> --- IIRC there used to be an issue with the built-in memmove in early 16.x when the size of the area was exactly 64 bytes. This was fixed later. Don't remember the PR. Can you try a different size (like double or half the size)? If that helps, then this is a known & resolved issue.
