https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108165
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- So at the warning is not flow sensitive at all and does not take into account the definition of f; only the call location of f is taken into account. In this case, the call site of f has a temporary and the warning is saying possibly because a temporary is made in the call arguments of f.
