Well, they've special cased this anyways, as these will often be caught in the rename stage and not even occupy an execution slot

They still need to be fetched and decoded, and take up space in caches and RAM that could be used for more purposeful instructions.

Which is also why the 'inline' heuristic exists.

Inlining has its own problems too.

I mean, things like ELF dynamic symbol tables, and linux thread local storage annoy me far more than calling conventions ever have.

Don't get me started on the whole ELF and dynamic linking situation...