[llvm] [LV] Don't simplify wide binops to constants if non-uniform (PR #121898)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Would it be possible to add the test case first? I've been thinking about some potential alternatives, but it seems like none of the options are really great :(

I committed the test case in e83e0c300d6f2cc41c9c74ed4fce90272acef16a. This isn't an area of code that I'm super familiar with so I'd be happy to close this PR and let you take over if needed!

https://github.com/llvm/llvm-project/pull/121898