[llvm] [ValueTracking] Ignore poison values in `computeKnownBits` (PR #72683)

[Nikita Popov via llvm-commits]

nikic wrote:

> > BTW, alive2 also reports some missed optimizations with `undef` elements in non-splat vectors. I have no idea how to handle it correctly. Just ignoring `undef` doesn't work.
> 
> Any thoughts?

There is nothing you can do inside computeKnownBits().

https://github.com/llvm/llvm-project/pull/72683