[llvm] [SCEV] Fix NSW flag propagation in getGEPExpr, getMulExpr, and getAddExpr (PR #155145)

[Nikita Popov via llvm-commits]

nikic wrote:

For flag propagation changes, I'd really recommend writing alive2 proofs for the propagation rules you are claiming. You can't directly prove something on addrecs, but you can at least prove it for one step of the addrec.

https://github.com/llvm/llvm-project/pull/155145