Splits the cleanup block lowered from AsyncToAsyncRuntime.
The incentive of this change is to clarify the CFG branched by
`async.coro.suspend`.
The `async.coro.suspend` op branches into 3 blocks, depending on the
state of the coroutine:
1) suspend
2) resume
3) cleanup
The behavior before this change is that after the coroutine is resumed
and completed, it will jump to a shared cleanup block for destroying the
states of coroutines. The CFG looks like the following,
Entry block
| \
resume |
| |
Cleanup
|
End
This CFG can potentially be problematic, because the `Cleanup` block is
a shared block and it is not dominated by `resume`. For instance, if
some pass wants to add some specific cleanup mechanism to resume, it can
be confused and add them to the shared `Cleanup`, which leads to the
"operand not dominate its use" error because of the existence of the
other "Entry->cleanup" path.
After this change, the CFG will look like the following,
The overall structure of the lowered CFG can be the following,
Entry (calling async.coro.suspend)
| \
Resume Destroy (duplicate of Cleanup)
| |
Cleanup |
| /
End (ends the corontine)
In this case, the Cleanup block tied to the Resume block will be
isolated from the other path and it is strictly dominated by "Resume".
af562fd27f