[llvm] [DA] Test AddRecs are nsw before strong SIV test (PR #183421)

[Ehsan Amiri via llvm-commits]

amehsan wrote:

> > so this is mainly needed for the divisibility test, but putting the test early in the function covers both cases anyways.
> 
> Note: The Strong SIV test does more than divisibility checks. See the last else-statement.

Yes, I was referring to independence proofs.  I can mention distance/direction calculations too.

https://github.com/llvm/llvm-project/pull/183421