I recently noticed a performance problem
... What worries me is that such a regression
had been sitting there for over a year
There are 215 open runtime performance https://ghc.haskell.org/trac/ghc/query?status=!closed&failure=Runtime+performance+bug&order=id tickets (out of a total of 1655 open tickets, that makes 13%). Compared to say new typesystem features, they don't get much attention. Only a few were fixed https://ghc.haskell.org/trac/ghc/query?failure=Runtime+performance+bug&resolution=fixed&milestone=8.0.1&milestone=7.10.3&milestone=7.10.2 this year, most of them by Joachim Breitner (the new performance tsar https://ghc.haskell.org/trac/ghc/wiki/CodeOwners#CurrentOwners?). He also created https://perf.haskell.org/ghc. In case you want to help out, start here: https://ghc.haskell.org/trac/ghc/wiki/Newcomers.