[llvm] [ARM] Record store with pre/post-indexed addressing as `mayStore` (PR #121565)

[David Green via llvm-commits]

https://github.com/davemgreen approved this pull request.

This seems like an obvious improvement on it's own. I was expecting UnmodeledSideEffects to act as a load barrier, as in MachineInstr::isLoadFoldBarrier. You could argue there is another problem in MachineSink, but providing we reliably mark store as MayStore it should be OK. I'll look to see if there are other instructions in Arm that could do with the same.

LGTM, thanks.

https://github.com/llvm/llvm-project/pull/121565