[llvm] [DAG] isKnownNeverZero - add ISD::SHL DemandedElts handling and tests (PR #183772)

[via llvm-commits]

Joeljm1 wrote:

> This looks more promising but I'll let CI confirm. Did you identify the problem?

my llvm build was a few days old and i had forgotten to build after merging. My bad :)

https://github.com/llvm/llvm-project/pull/183772