MLIR support for differentiating parallel loops

[etphipp]

We've noticed some support for differentiating parallel loops was recently added (e.g., 902bf1f for scf.parallel), but it seems incomplete. We were wondering if there is work to more fully support differentiating parallel loops (in particular, forward mode and scf.parallel.reduce), either planned or on-going? Differentiating parallel loops is central to our work, which is something we could contribute to, but don't want to duplicate efforts.

@brian-kelley

[wsmoses]

no one is working on that at the moment, so it would definitely be appreciated!