[llvm] [InstCombine] Reduce multiplicands of even numbers when a shift is involved (PR #92475)

[via llvm-commits]

AtariDreams wrote:

I do want to expand this to do things like splat vectors though the code for that will be a bit more involved. I want to at least get something working and then do baby steps.

https://github.com/llvm/llvm-project/pull/92475