https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60608
--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
I'm going to save some debugging notes, mostly about non-variadic vs variadic.
First one: the tsubst in fn_type_unification:
fntype = tsubst (TREE_TYPE (fn), explicit_targs,
complain | tf_partial, NULL_TREE);
working on TREE_TYPE (fn) which has uses_template_parms true, returns a fntype
which has uses_template_parms false in the non-variadic case, still true in the
variadic case. Note that later uses_template_parms matters at the beginning of
unify_one_argument.
