[llvm] [InstCombine] Factorise add/sub and max/min using distributivity (PR #101507)

[via llvm-commits]

goldsteinn wrote:

> > The alive proof sometimes times out. I have to add `noundef` to certain variables to make it not time out more consistently. Given how min/max/add preserve undef, I believe these optimisations to be correct when undef values are passed through.
> 
> Try replacing all the i32s with i8. That usually helps with timeouts.

In this case even `i4` times out: https://alive2.llvm.org/ce/z/UPjvkJ

https://github.com/llvm/llvm-project/pull/101507