[llvm] [SCEV] Teach SCEVExpander to use zext nneg when possible (PR #70815)

[Nikita Popov via llvm-commits]

nikic wrote:

There is a test failure in CodeGen/partial_write_in_region_with_loop.ll.

(We should really drop polly from the monorepo...)

https://github.com/llvm/llvm-project/pull/70815