[llvm] [CGP] Fix missing sign extension for base offset in optimizeMemoryInst (PR #161377)

[Nikita Popov via llvm-commits]

nikic wrote:

We need to implement this TODO to catch these issues: https://github.com/llvm/llvm-project/blob/4c2b1d495aa26fa80833fa1508736df984b6f55e/llvm/lib/IR/Constants.cpp#L954-L957

https://github.com/llvm/llvm-project/pull/161377