mlir: run mincut for scf.if ops

[pengmai]

No description provided.

[wsmoses]

lgtm, but can we also do this for affineif as well?

[Pangoraw]

lgtm! we could potentially run mincut for every pairs of forward / reverse blocks as present in gutils->mapReverseModeBlocks (though nested ops don't populate the map rn)

[wsmoses]

@pengmai we have a conflict here rn if you can take a quick look [then we can merge, and address affine.if in follow ups]

[pengmai]

@pengmai we have a conflict here rn if you can take a quick look [then we can merge, and address affine.if in follow ups]

Done. FYI it looks like we don't currently support differentiation of affine.if at all, but these changes are templated in an IfLike remover that should work with affine.if without modification when support for affine.if is added.

we could potentially run mincut for every pairs of forward / reverse blocks as present in gutils->mapReverseModeBlocks (though nested ops don't populate the map rn)

This would be interesting. We'd need to make sure it respects the preserve_cache attributes.