alt Hacker NewsYyyyes... But like I said, TCO cannot make use of the calling convention, because it doesn't involve calling. That means you can't have TCO loops crossing module boundaries (or function pointers for that matter). So we're back to my original question: what does it matter what the calling convention is if the compiler has the liberty to compile both functions however it pleases?
With the right calling convention, tail calls could conform to the convention.
A tail call certainly can't use a CALL instruction, because it would set the wrong return address. But that doesn't mean it's not a call; architectures without CALL/RETURN instructions exist, but you can still call into functions and return from them, the compiler just has to do different work.
In a callee cleanup convention, a tail caller could adjust the stack and jump to an unaware tail callee. The original caller and the tail callee would be none the wiser. I don't know enough to really evaluate calling conventions against each other, but it's pretty clear that caller cleanup makes tail call optimization more intrusive.