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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.
maximecb
approved these changes
Aug 30, 2021
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maximecb
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Nicely done 👍 and good job writing clear comments 👌
jhawthorn
approved these changes
Aug 30, 2021
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The code path for leave that returns to the interpreter
(gen_leave() -> yjit_gen_leave_exit()) used to have the logic:
The SP changes it made was unnecessary and this change removes it.
After this change,
leavedoesn't adjust thecfp->spof the callerand only writes
cfp->sp[0]. To accomodate this in the JIT-to-JITreturn case, return stubs have an
sp_offsetof 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
sendhas an
sp_offsetof 1 after the call, this change enables blockversion sharing.