[llvm] [SelectOpt] Add handling for Select-like operations. (PR #77284)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

> I might be wrong, but I suspect we could do with some more test-cases, especially negative tests when this shouldn't trigger. From a quick look, things like when the pattern doesn't exactly matches, one use, dbg instructions, if it is not a terminator, etc.

There should be tests for one uses select groups and the positions in selectopt.ll. See 365fbbfbcfefb8766f7716109b9c3767b58e6058. Debug info tests we would not usually add unless we had good reason, they can be quite bulky, but I've added a run line. Anything else specific you think needs adding?

https://github.com/llvm/llvm-project/pull/77284