Ganesh It's an old bug that has somehow reappeared. I opened https://gitlab.haskell.org/ghc/ghc/issues/17140 But it seems OK in HEAD, and hence probably in GHC 8.8. Can you try? Maybe put further comments on the issue tracker, rather than here. thanks Simon | -----Original Message----- | From: Glasgow-haskell-users On | Behalf Of Ganesh Sittampalam | Sent: 05 August 2019 14:02 | To: glasgow-haskell-users@haskell.org | Subject: exhausted simplifier ticks and hs-boot files | | Hi, | | The code below (also attached - unzip and run go.sh) triggers the GHC | panic "Simplifier ticks exhausted", and I'm unsure whether I should view | it as an instance of the known infelicity in the inliner | (https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/bugs.html | #bugs-ghc) | | My code does have a recursive datatype, but the recursion isn't | contravariant, which is the case described in "Secrets of the GHC inliner" | (https://www.microsoft.com/en-us/research/wp- | content/uploads/2002/07/inline.pdf, | section 4). | | It's cut down from some real code where I have a mutually recursive | datatype that I want to define across two modules for code structuring | reasons, meaning I need a .hs-boot file. I haven't been able to reproduce | it without the .hs-boot file - if I put everything in one module it stops | happening. | | I've tried with a range of GHC versions from 8.2.x to an early version of | 8.8. It happens with -O1 and not -O0, but I haven't managed to find a | specific optimisation that triggers it. | | Is this just an instance of the known problem in a different guise, or is | it something different and worth a bug report? | | Cheers, | | Ganesh | | T2.hs-boot | ----------- | module T2 where | | data T2 | | mapP_T2 :: (Int -> Int) -> T2 -> T2 | | T1.hs | ----- | module T1 where | | import {-# SOURCE #-} T2 | | data T1 = T1 T2 | | mapP_T1 :: (Int -> Int) -> T1 -> T1 | mapP_T1 _ (T1 xs) = T1 (mapP_T2 id xs) | | T2.hs | ----- | | module T2 where | | import T1 | | data T2 = T2 T1 | | mapP_T2 :: (Int -> Int) -> T2 -> T2 | mapP_T2 f (T2 t) = T2 (mapP_T1 f t) | | go :: T1 -> T1 | go = mapP_T1 id | | GHC output | ---------- | $ ghc --make T2.hs -O1 -fsimpl-tick-factor=1000 -ddump-simpl-stats) [...] | ghc.exe: panic! (the 'impossible' happened) | (GHC version 8.2.2 for x86_64-unknown-mingw32): | Simplifier ticks exhausted | When trying UnfoldingDone mapP_T2 | To increase the limit, use -fsimpl-tick-factor=N (default 100) | If you need to do this, let GHC HQ know, and what factor you needed | Total ticks: 61203 | | 24481 PreInlineUnconditionally | 6121 ds_i17h | 6120 f_a16p | 6120 ds_d17d | 6120 ds1_i17i | 12241 UnfoldingDone | 6121 mapP_T1 | 6120 mapP_T2 | 24481 BetaReduction | 6121 ds_i17h | 6120 f_a16p | 6120 ds_d17d | 6120 ds1_i17i