[llvm] [X86][PartialReduction] Lower zext-byte add reductions to vpsadbw (PR #201076)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@mbhade-amd I'll be finishing #198893 soon which will make ISD::VECREDUCE_ADD nodes legal and prevent reduction expansion - its likely that this can be handled much easier after that

https://github.com/llvm/llvm-project/pull/201076