[llvm-dev] Function with multi return path?

[TONGARI J via llvm-dev]

2017-06-07 23:42 GMT+08:00 David Chisnall <David.Chisnall at cl.cam.ac.uk>:
>
> No, but you can take the address of the block, pass it to the function,
> have the function return to the alternate return address and then (in the
> caller) jump immediately to the address in the return register.


Yeah, that's the closest way we can get in LLVM at this moment.


> Note that this (along with your original suggestion) will have really poor
> interaction with any modern branch predictor.
>

In my idea the caller and callee have full knowledge about the branch
destinations, so if the optimizer inlines the callee, it can jump to the
alternate destinations w/o indirection.
In case it's not inlined, the normal return path should incur no overhead
as well, and for alternate return paths it's just a matter of setting the
return register.
But as I said, I'm not an expert so I don't really know whether what I
described is implementable in LLVM on all architectures.
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