[llvm] [IndVars] Mark truncs as nuw/nsw (PR #88686)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

One of the thoughts I'd had when seeing this langref proposal was that it might allow us to simplify this code significantly.  I believe one of the things which makes this code complex is that we have to "commit" to our signed or unsigned interpretation by performing all rewrites at once since we couldn't materialize a wide IV + truncate and preserve the information about the choice.  With this IR change, we now have that possibility.  This might not fully work out - there's other reasons for complexity in this code - but mentioning it in case it inspires you.  :)

https://github.com/llvm/llvm-project/pull/88686