https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83334
--- Comment #5 from zenith432 at users dot sourceforge.net --- I looked at the source a bit, and I see what's going on. __builtin_ms_va_copy and __builtin_sysv_va_copy are treated both the same as __builtin_va_copy, which is implemented in gcc/builtins.s by expand_builtin_va_copy This function then calls targetm.fn_abi_va_list (cfun->decl) to get the type of va_list associated to the containing function. this leads to ix86_fn_abi_va_list which identifies it as either an ms_va_list_type_node or sysv_va_list_type_node based on the abi of the containing function.
