On Mar 14, 2020, at 20:03, Sandy Maguire <sandy@sandymaguire.me> wrote:
What GHC are you testing against? I suspect https://gitlab.haskell.org/ghc/ghc/merge_requests/668 <https://gitlab.haskell.org/ghc/ghc/merge_requests/668> will fix this.
I’ve tested against HEAD. I think the change you link is helpful, but it doesn’t quite get there: the usage gets dumped before specHeader even gets a chance to look at the call. The relevant bit of code is here: https://gitlab.haskell.org/ghc/ghc/blob/1de3ab4a147eeb0b34b24a3c0e91f174e6e5... <https://gitlab.haskell.org/ghc/ghc/blob/1de3ab4a147eeb0b34b24a3c0e91f174e6e5cb79/compiler/specialise/Specialise.hs#L2274-2302> Specifically, this line seals the deal: ClassPred cls _ -> not (isIPClass cls) -- Superclasses can't be IPs So maybe the right fix is just to change the role of type_determines_value so that it turns SpecDicts into UnspecArgs, and then with your change everything would just happily work out.