ObjFW runtime: Add objc_msg_lookup(_super)_{fp,st}ret

[Eli Friedman]

On Mon, Jul 8, 2013 at 12:00 PM, Jonathan Schleifer <js at webkeks.org> wrote:
> Am 08.07.2013 um 19:22 schrieb Eli Friedman:
>
>> If you are going to call a function for nil receivers, you have to have a specialized fpret form for x86-32: otherwise, the program will misbehave due to mismatched push/pop on the FP stack.
>
> Yes, but this won't be a problem for forwarding, I guess. And for handling nil correctly, it sounds like letting the compiler do the magic is a much more robust way, even though it might bloat the code a little. But it has the advantage of even working on platforms where the dispatch is not done in assembly, but in pure C.
>
> It would be possible to have a method return_fpnil or something that just returns nil and could be returned by objc_msg_lookup_fpret, though. But then again, it's highly platform-dependant what type(s) exactly need(s) fpret.
>
>> That said, it wouldn't be unreasonable to just nil-check before any call that doesn't have an integer/pointer return; on the Mac side, we actually do such a check anyway for structs because we zero-initialize them.
>
> Great, so there is already code for that :).
>
> Do you agree that if not taking nil-messaging into account and letting the compiler handle that there is no need for objc_msg_lookup_fpret? I could not think of a reason why it would be required for forwarding.

If you ignore nil-messaging, you don't need any of these specialized
versions: objc_msg_lookup can always return a pointer to a function of
an appropriate type without any special knowledge of what that type
is.

-Eli