[llvm] [DAG] visitCTPOP - if only the upper half of the ctpop operand is zero then see if its profitable to only count the lower half. (PR #80473)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

Do we still need https://github.com/llvm/llvm-project/commit/275729ae06d568e9589392c142a416fb8c2bb1a8 with this change?

https://github.com/llvm/llvm-project/pull/80473