[llvm] [RISCV][WIP] Fold (sh3add Z, (add X, (slli Y, 6))) -> (sh3add (sh3add Y, Z), X). (PR #85734)

[Philip Reames via llvm-commits]

preames wrote:

One possible approach: https://github.com/llvm/llvm-project/pull/86883

Thanks @mgudim for the reduced test case and the discussion which got me thinking about this.

https://github.com/llvm/llvm-project/pull/85734