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

[Ryotaro Kasuga via llvm-commits]

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kasuga-fj wrote:

Could you please first answer the following question?
- Is your objections based on the fact that you can prove its correctness?
- You seem confident in your proof. Is this right?
- I'm strongly opposed to humans writing such proofs by hand in the first place. Is that coming across? 

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