Rewrite rules failing to fire in package streamly
@harendra writes (in #19557 (closed)): FWIW we have seen severe regressions when using GHC 9.0 in https://github.com/composewell/streamly. Streamly uses stream fusion extensively so I guess it might be the same issue or something related. I have added the perf regressions and some observations here: https://github.com/composewell/streamly/issues/1061 . It looks pretty bad, hopefully it is some simple issue rather than something major. I am now going to take one example out of these and inspect the core.
This repository (https://github.com/composewell/streamly-ghc9-regression) has a minimal example reproducing the issue. On the "fast" branch in the same repo I have added the "Operations" module code in the Main module itself which makes the problem go away. It depends only on ghc-prim and base.