[llvm] [DA] Refine identical SameSD addrec dependences (PR #206425)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj requested changes to this pull request.

In the test case you added, neither addrec has `nsw`, so we can't classify the pair as SIV (you can confirm this in the debug output of DA). I'm not sure why ScalarEvolution fails to transfer the `nsw` flags, but DA can't perform any analysis unless they're attached. That is, we can't prove that `%n` is smaller than `2^62`, beyond which `{0,+,4}` would wrap around to 0 once (or more).

https://github.com/llvm/llvm-project/pull/206425