[llvm] [RISCV] Introduce new AND combine to expose additional load narrowing opportunities (PR #170483)

[Philip Reames via llvm-commits]

https://github.com/preames commented:

I see a bunch of related load narrowing heuristics in DAGCombine, but nothing which immediately seems like to cover this case.  Both reduceLoadWidth and BackwardsPropagateMask appear related.  I think there's some room for generalization/refactoring here, but I'm specifically not asking you to do it.  :)

https://github.com/llvm/llvm-project/pull/170483