[llvm-dev] Function with multi return path?

[TONGARI J via llvm-dev]

Hi folks,

I'm new to LLVM and non-expert in hardware architecture, so my question
might be dumb.

I'm looking for the possibility to define/call a function with multi return
path, it might look like this:

```
; Define a function with 1 alternate return path
define i32 @f(i1 %i) fork 1 {
  br i1 %i, label %noraml, label %alternate
noraml:
  ...
  setpath ret i32 42 ; take normal return path
  br %cleanup
alternate:
  ...
  setpath fork 0 ; take the alternate return path
  br %cleanup
cleanup: ; preds = %noraml, %alternate
  ...
  unwind ; return to the caller
}
```

And at the call side:
```
  %ret = call @f(i1 %i) fork [%otherwise]
  ...
otherwise:
  ...
```

Ideally, the callee sets the return address so it returns directly to the
desired location in the caller w/o the caller taking extra switch.

The idea is to implement some non-local control flow w/o extra overhead at
each call side.

I know LLVM doesn't have something like this currently, but is it possible
to implement?
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