I opened a GHC ticket (https://gitlab.haskell.org/ghc/ghc/-/issues/18414) with full details.
-harendra On Tue, 30 Jun 2020 at 18:25, Harendra Kumar <harendra.ku...@gmail.com> wrote: > Hi Richard, > > I am glad that you are interested in it. It is the runtime performance > that degrades, and yes it is fully reproducible and publicly shareable, the > library is open source so anyone can run these benchmarks. I had postponed > the problem raising an issue to investigate it further here > https://github.com/composewell/streamly/issues/567 . Since you are > interested I will investigate it sooner. I have added some perf numbers in > that issue. > > I was also surprised by it, thinking what can type families possibly do to > degrade run time performance like that. I can try compiling one worst > affected benchmark code and look at the core-2-core passes to see where it > makes the difference. > > -harendra > > On Mon, 29 Jun 2020 at 19:45, Richard Eisenberg <r...@richarde.dev> wrote: > >> Hi Harendra, >> >> I saw your comment on a ghc proposal ( >> https://github.com/ghc-proposals/ghc-proposals/pull/343#issuecomment-650797297) >> that said you experienced perf regressions with -XTypeFamilies enabled (but >> no other changes). Are these reproducible in a way that can be shared >> publicly? And are the regressions in compile times or run times? >> >> -XTypeFamilies enables -XMonoLocalBinds, which disables >> let-generalization on some nested lets. It is thus just barely conceivable >> that different Core is produced depending on this extension, and that there >> may be a possibility of performance changes. But this would be unexpected, >> and something worth investigating. >> >> In other words: if you can, do please post a bug -- simply enabling >> -XTypeFamilies should not slow anything down! >> >> Thanks, >> Richard > >
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