[llvm] [SDAG] Simplify is-power-of-2 codegen (PR #72275)

[Tavian Barnes via llvm-commits]

tavianator wrote:

Thanks for the reviews!  It seems like most people merge their own PRs here, but I don't have write access so I'll need someone to do that for me.

https://github.com/llvm/llvm-project/pull/72275