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Qiskit / qiskit

Qiskit is an open-source SDK for working with quantum computers at the level of extended quantum circuits, operators, and primitives.
https://www.ibm.com/quantum/qiskit
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Support control flow in `CommutationAnalysis` and `CommutativeCancellation` #9423

Closed jakelishman closed 1 year ago

jakelishman commented 1 year ago

What should we add?

Part of #9417.

These two passes likely come as a pair, but this issue can be split in two if the discovery phase finds that that is preferable.

Details

The commutation analysis and cancellation is the main addition to the optimisation loop at transpiler optimisation level 2. This currently doesn't support control-flow, mostly because the CommutationAnalysis pass doesn't have a way of passing the information about nested blocks through to CommutativeCancellation in the property set. To solve this, we need to:

This shouldn't be too difficult, beyond finding a data format; commutation relations can't span control-flow blocks, so a fairly simple recursive structure and visitor should be fine. When designing the data format, we may want to consider related work on DAGCircuit.collect_runs, since the collection and exchange of information is largely the same. See #9425.

It is possible that a control-flow block could commute blockwise with another, or with non-controlled operations. For the purposes of this initial support, we do not need to support recognising these cases, but it will be a goal in the future. Please note on closure of this issue whether this was achieved or not.

mtreinish commented 1 year ago

The first step for this is being implemented by https://github.com/Qiskit/qiskit-terra/pull/9143

jlapeyre commented 1 year ago

It looks like modifying CommutationAnalysis might not be useful at the moment. Even if we modified it to support control flow ops in some sense, we have no use for it. See https://github.com/Qiskit/qiskit-terra/pull/9143#issuecomment-1610260665

In fact, I think @ewinston 's approach might also work well for #9426 as well.

EDIT: It does work. See

mtreinish commented 1 year ago

This was implemented by: https://github.com/Qiskit/qiskit-terra/pull/9143 it superseded the need for the commutation analysis pass to be updated