[llvm] [SCEV] Prove no-self-wrap from negative power of two step (PR #101416)

[Philip Reames via llvm-commits]

preames wrote:

> > Not really a fan of the conditional negate logic here, but it seemed like a bit of overkill to have isKnownToBeAPossibleNegativePowerOfTwo. Any better ideas on how to structure this?
> 
> I think it would be okay to add an OrNegative parameter to the function. Computing getNegativeSCEV() may be expensive if it's not just negating a constant.

Will do.  Update pending later today.

https://github.com/llvm/llvm-project/pull/101416