[llvm] [DAG]SimplifyDemandedVectorElts-add ISD::AVGCEILS/AVGCEILU/AVGFLOORS/AVGFLOORU nodes (PR #86284)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> Also, the ISD:: opcode passed to SimplifyDemandedVectorElts is `INTRINSIC_WO_CHAIN`(45) rather than one of AVGCEIL(S/U)/AVGFLOOR(S/U)?

That's prior to lowering - after legalization the intrinsic call will lower to a ISD::AVG* node, but by that point the shuffles have become AArch64ISD::DUPLANE* nodes.

https://github.com/llvm/llvm-project/pull/86284