Sure, but they're already paying that cost for every non-static function anyway. Any DSO, or executable that allows function interposition, already pays.

Ideally you should just multiversion the topmost exported symbol, everything below that should either directly inlined, or, as the architecture variant is known statically by the compiler, variants and a direct call generated. I know at least GCC can do this variant generation for things like constant propagation over static function boundaries, so /assume/ it can do the same for other optimization variants like this, but admittedly haven't checked.