[llvm] [IndVars] Preserve flags of narrow IV inc if replacing with wider inc. (PR #80446)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

(This question also goes for the similar change at https://github.com/llvm/llvm-project/pull/79512...)

Are we guaranteed matching increments at this point? I.e. do we know that both instructions actually increment by the same amount, and we don't have, say, a `iv.next = iv - 7 + 12` sequence on one end and `iv.next = iv + 5` on the other?

https://github.com/llvm/llvm-project/pull/80446