slicing passmanagers

[ajavadia]

following #3004, implement methods to slice PassManagers to only get a subset of passes:

pm = PassManager(...)

pm[1]
pm[1:3]

pm1[1:3] + pm2[4:6]  # be able to concatenate several passmanagers
pm_level1[:8] + pm_3rdparty[0] + pm_level1[9:]

[faisaldebouni]

I'm trying to implement this. However I need some guidance:
pm[..] should return a PassManager with subset of passes (rather than the subset of passes it self) correct?
because this way it would allow to carry conditions, options .. etc
also it will allow something like
pm[0:3].draw()
it will also allow
pm[..] + pm[..]
and
pm + pm[..]
to act in similar way.

the only downside would be that this won't work:
pm1[3] = pm2[1]

[1ucian0]

pm[..] should return a PassManager with subset of passes (rather than the subset of passes it self) correct?

Yes. It should. Currently, a PassManager does not fully emulate a container type. And I think it should though. A PassManager is a collection of pass sets (FlowController instances) that are saved in working_list list. That's the list that is important here.

"Wrap" the working_list. Let me know if that makes sense. We can discuss it with code.

[faisaldebouni]

That makes perfect sense. Thanks. Will report once I finish.

[1ucian0]

pending PR in #3209

[1ucian0]

closed via #3209