Hi, I'm not sure I see all the context of the conversation, but it is entirely possible that code with many local constraints regresses the pattern-match checker (which is accounted to Desugaring in the profile emitted by -v2), I'm afraid. That simply has to do with the fact that we now actually care about them, previously they were mostly discarded.
I'd be glad if you submitted a relatively isolated reproducer of what is fast with 8.8 and slow with 8.10 (even better 9.0). I hope that things have improved since we fixed https://gitlab.haskell.org/ghc/ghc/-/issues/17836, which is part of 9.0 but not of 8.10. Cheers, Sebastian Am Mo., 15. Feb. 2021 um 19:04 Uhr schrieb Troels Henriksen < at...@sigkill.dk>: > Carter Schonwald <carter.schonw...@gmail.com> writes: > > > Ccing ghc devs since that’s a better forum perhaps > > Crazy theory: > > > > this is a regression due the the partial changes to pattern matching > > coverage checking in 8.10 that finished / landed in ghc 9 > > > > Why: > > Desugaring is when pattern/ case statement translation happens I think? > > And the only obvious “big thing” is that you have some huge , albeit sane > > for a compiler, pattern matching > > > > I’d first check if the new ghc 9 release doesn’t have that regression in > > build time that you experienced. And if it does file a ticket. > > > > I may be totally wrong, but that seems like a decent likelihood ! > > You may be right! Another module that regressed is also mainly > characterised by large-but-not-insane case expressions: > > https://github.com/diku-dk/futhark/blob/d0839412bdd11884d75a1494dd5de5191833f39e/src/Futhark/Optimise/Simplify/Rules.hs > > I'll try to split these modules up a little bit (I should have done so a > while ago anyway) and maybe that will make the picture even clearer. > > -- > \ Troels > /\ Henriksen > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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