https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91067
--- Comment #15 from Viktor Ostashevskyi <ostash at ostash dot kiev.ua> --- (In reply to Jonathan Wakely from comment #14) > I can reproduce the link failure. For some reason Clang requires that > constructor at -O1, but not at any other optimization level. It will require it at any -O level with fno-inline.