Shave a few instructions off of leave

The code path for leave that returns to the interpreter
(gen_leave() -> yjit_gen_leave_exit()) used to have the logic:

```
    cfp->sp++;
    cfp->sp[-1] = return_val;
    cfp->sp--;
    return return_val;
```

The SP changes it made was unnecessary and this change removes it.

After this change, `leave` doesn't adjust the `cfp->sp` of the caller
and only writes `cfp->sp[0]`. To accomodate this in the JIT-to-JIT
return case, return stubs have an `sp_offset` of 1.

The change removes sp adjustment from the JIT-to-JIT return case, too,
making it more efficient. Also, since the C method case of `send`
has an `sp_offset` of 1 after the call, this change enables block
version sharing.

0 files changed, 0 insertions, 0 deletions