[Mlir-commits] [mlir] [mlir][ArmSME] Fold extracts from 3D create_masks of SME-like masks (PR #80148)

[Benjamin Maxwell]

MacDue wrote:

> Functionally the rewrite looks good to me, but I am wondering if it should be moved alongside Vector dialect transforms. I know this is only relevant for ArmSME right now but semantically these operations and types are expressible in the Vector dialect and if we pretended there were another target where 2-D scalable vector types were relevant then this would apply equally as well I think?

I don't want to muddy the vector dialect with rewrites like this, `-arm-sme-vector-legalization` was always intended to include rewrites like this (it purely works at the vector dialect level already). The reasons for this rewrite are tied to SME and how the current lowering decomposes masks, and I feel it's unlikely to become a generally useful. 

https://github.com/llvm/llvm-project/pull/80148