> On Mar 14, 2020, at 20:03, Sandy Maguire <sa...@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/1de3ab4a147eeb0b34b24a3c0e91f174e6e5cb79/compiler/specialise/Specialise.hs#L2274-2302
<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._______________________________________________
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