[llvm] [Reassociate] Preserve NSW flags after expr tree rewriting (PR #93105)

[Akshay Deodhar via llvm-commits]

akshayrdeodhar wrote:

There is an internal OpenCL benchmark where the special case helps performance- I can't concretely say that this will generalize to most LLVM users.

https://github.com/llvm/llvm-project/pull/93105