[llvm] [X86] Remove redundant TEST after shifts when count is non-zero (PR #169069)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

For minsize/optsize cases only - as the isKnownNeverZero cases would still be dependent on the shift eflags microcoding. If you can do this as an isel td pattern that'd be best - but if you have to do it in the DAG with new X86ISD::SHL type opcodes then so be it.

https://github.com/llvm/llvm-project/pull/169069