The other thing on my list are the removal of the ceildiv sorts of operators. These were added to arith as part of lowering from affine, and they are extremely expensive in terms of lowering and thus have completely different cost model from everything else in the arith dialect. IMO, these should be moved to the affine dialect or change affine lowering to generate more primitive arith ops.
I will say that there are theoretical reasons why it could make sense to have these operators somewhere in the system (e.g. range analysis could be used to lower them to cheaper operations) but none of that is implemented in tree AFAIK. Having these in arith is like adding einsum to HLO. I don’t think we would ever have accepted these into arith if they were proposed after arith was established.
Other random thing, why is arith in lib/Dialect/Arithmetic instead of lib/Dialect/Arith ?
-Chris