[llvm] [DA] Add tests for nsw doesn't hold on entire iteration space (NFC) (PR #162281)

[Ehsan Amiri via llvm-commits]

================

----------------
amehsan wrote:

I posted an updated proof. https://github.com/llvm/llvm-project/issues/168823#issuecomment-3591966501

I will be happy to see a valid counter-example that refutes the proof to see what I might have missed. Thanks.

https://github.com/llvm/llvm-project/pull/162281