[llvm] [unroll-and-jam] Document dependency patterns in dependencies.ll (NFC) (PR #156577)

[Sjoerd Meijer via llvm-commits]

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

Thanks, explaining these test-cases looks very useful to me, LGTM.

https://github.com/llvm/llvm-project/pull/156577