[llvm] [DAG] Improved ISD::SHL handling in isKnownToBeAPowerOfTwo (PR #181882)

[Aadarsh Keshri via llvm-commits]

Aadarsh-Keshri wrote:

For now, I will change the `auto`s to their respective explicit types.
After that, I'll start writing the lit tests.
Though, I have a doubt: should I write these tests in a new file or expand an existing one?

https://github.com/llvm/llvm-project/pull/181882