[llvm] [ValueTracking] Add support for `vector_reduce_{s, u}{min, max}` in `isKnownNonZero`/`computeKnownBits`. (PR #88169)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

I think some basic support here could be reasonable, but this implementation looks too precise. In particular, I think the approach of doing a per-element evaluation of the vector is unprecedented -- we generally only look at all (demanded) elements as a unit.

So the implementation I'd expect would be more something along the lines of taking the known bits of the input vector and using those as the result known bits as well.

https://github.com/llvm/llvm-project/pull/88169