September 2018 - ghc-tickets

Re: [GHC] #4022: GHC Bindist is Broken on FreeBSD/amd64
by GHC 21 Sep '18

21 Sep '18

#4022: GHC Bindist is Broken on FreeBSD/amd64 -------------------------------------+------------------------------------- Reporter: pgj | Owner: pgj Type: bug | Status: new Priority: lowest | Milestone: Component: Core Libraries | Version: 6.13 Resolution: | Keywords: GMP,integer- | gmp, sharedlibs Operating System: FreeBSD | Architecture: x86_64 Type of failure: Building GHC | (amd64) failed | Test Case: Blocked By: | Blocking: Related Tickets: #8156 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Unfortunately I'm finding that the FreeBSD bindist for 8.6.1 fails to pass `bindisttest`: {{{ [1 of 1] Compiling Main ( bindisttest/HelloWorld.lhs, bindisttest/HelloWorld.o ) Linking bindisttest/HelloWorld ... /usr/local/bin/ld.gold: error: /usr/home/ben/bin- dist-8.6.1-FreeBSD/ghc/bindisttest/install dir/lib/ghc-8.6.1/rts/libHSrts.a(RTS.o): unexpected reloc 8 in object file ... (many more messages of the same form) }}} I suspect this is due to our insistence on using `ld.gold`. I'm going to try doing another build with `--disable-ld-override`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4022#comment:41> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Looking for student ticket to GHC
by Virashree Patel 21 Sep '18

21 Sep '18

Hi, I am looking to buy a student ticket to GHC 2018. If you are selling still please contact me. Thank you! Best, Vira Patel, Graduate Research Assistant at *Kansas State University * LinkedIn: *linkedin.com/in/virashreepatel <http://linkedin.com/in/virashreepatel> <http://twitter.com/>*

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Re: [GHC] #3427: control what sort of entity a deprecated pragma applies to
by GHC 21 Sep '18

21 Sep '18

#3427: control what sort of entity a deprecated pragma applies to -------------------------------------+------------------------------------- Reporter: igloo | Owner: nineonine Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 6.10.4 Resolution: | Keywords: deprecate | warning, newcomer, GHCProposal Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D5126 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: deprecate warning, newcomer => deprecate warning, newcomer, GHCProposal -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3427#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8281: The impossible happened: primRepToFFIType
by GHC 21 Sep '18

21 Sep '18

#8281: The impossible happened: primRepToFFIType -----------------------------------+--------------------------------------- Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- I ran into this error while trying to use GHCi on the hashable package: {{{ $ cabal repl Preprocessing library hashable-1.2.0.10... GHCi, version 7.6.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.4.0.1 ... linking ... done. Loading package deepseq-1.3.0.1 ... linking ... done. Loading package bytestring-0.10.0.2 ... linking ... done. Loading package text-0.11.3.1 ... linking ... done. Loading object (static) dist/build/cbits/fnv.o ... done Loading object (static) dist/build/cbits/getRandomBytes.o ... done final link ... done [1 of 4] Compiling Data.Hashable.RandomSource ( Data/Hashable/RandomSource.hs, interpreted ) [flags changed] [2 of 4] Compiling Data.Hashable.Class ( Data/Hashable/Class.hs, interpreted ) [flags changed] ghc: panic! (the 'impossible' happened) (GHC version 7.6.2 for x86_64-apple-darwin): primRepToFFIType Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8281> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15610: GHCi command to list instances a (possibly compound) type belongs to
by GHC 21 Sep '18

21 Sep '18

#15610: GHCi command to list instances a (possibly compound) type belongs to -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: lowest | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This command (`:instances`) would be very useful to me (for deriving in particular). People on Twitter were digging it, I believe some are interested in implementing it {{{ >> import Data.Functor.Sum (Sum) >> >> :instances Sum [] [] Eq a => Eq (Sum [] [] a) Ord a => Ord (Sum [] [] a) Show a => Show (Sum [] [] a) Read a => Read (Sum [] [] a) Functor (Sum [] []) Foldable (Sum [] []) Eq1 (Sum [] []) Ord1 (Sum [] []) Show1 (Sum [] []) Read1 (Sum [] []) FunctorWithIndex (Either Int Int) (Sum [] []) FoldableWithIndex (Either Int Int) (Sum [] []) TraversableWithIndex (Either Int Int) (Sum [] []) }}} Not a precise algorithm, but the command `:instances <ty>` lists what classes `<ty>` is an instance of. This is something I usually do by hand and is useful for finding what instances I can expect to derive with `-XDerivingVia`: {{{#!hs data ... deriving (???) via (F A B) -- >> :instances F A B -- Cls1 (F A B) -- Cls2 (F A B) .. data ... deriving (Cls1, Cls2, ..) via (F A B) }}} I expect something like `:instances Sum Endo` to return no instances, but I currently rely on my own mind to derive a contradiction for each type. I would cross-reference `:info Sum`, `:info Endo` which blows up when the types are complex and deeply nested. partial type signature (`_`):: the command `:instances Either _ Int` should match `Eq a => Eq (Either a Int)` trace info:: I find it noisy but we can {{{ >> :instances Sum [] [] .. Functor (Sum [] []) -- (Functor f, Functor g) => Functor (Sum f g) -- Defined in ‘Data.Functor.Sum’ .. }}} This would be more natural in a interactive environment where we can toggle/expand and collapse it. negative results:: There is a `.. => Comonad (Sum f g)` instance but we don't have `Comonad (Sum [] [])` because there is no `Comonad []`. It may be valuable to query negative results {{{ >> :noinstance Sum [] [] NO (instance Comonad (Sum [] [])) because NO (instance Comonad []) }}} multi-parameter type class:: I cheekily listed `FunctorWithIndex` example of, I am fine dropping MPTCs but listing `Coercible` instances might be useful {{{ >> newtype List_or_List a = L_or_L (Sum [] [] a) >> >> :instance Sum [] [] .. Coercible (Sum [] [] a) (List_or_List a) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15610> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13700: GHCi command listing possible type class instances
by GHC 21 Sep '18

21 Sep '18

#13700: GHCi command listing possible type class instances -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a reminder ticket, I want to be able to list possible instances, {{{ >>> :insts Product (Functor f, Functor g) => Functor (Product f g) (Applicative f, Applicative g) => Applicative (Product f g) ... >>> :insts Product Identity Functor g => Functor (Product Identity g) Applicative g => Applicative (Product Identity g) Monad g => Monad (Product Identity g) MonadFix g => MonadFix (Product Identity g) MonadZip g => MonadZip (Product Identity g) ... >>> :insts Product Identity Identity Functor (Product Identity Identity) Applicative (Product Identity Identity) Monad (Product Identity Identity) MonadFix (Product Identity Identity) MonadZip (Product Identity Identity) }}} Would be so useful for `GeneralizedNewtypeDeriving` {{{#!hs newtype Pair a = P (Product Identity Identity a) deriving (Functor, Applicative, Monad, MonadFix, MonadZip, ...) -- pattern (:#) :: a -> a -> Pair a -- pattern a1 :# a2 = P (Identity a1 `Pair` Identity a2) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13700> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11671: Allow labels starting with uppercase with OverloadedLabels
by GHC 21 Sep '18

21 Sep '18

#11671: Allow labels starting with uppercase with OverloadedLabels -------------------------------------+------------------------------------- Reporter: inaki | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following program {{{#!hs {-# LANGUAGE OverloadedLabels, DataKinds, FlexibleInstances, MultiParamTypeClasses #-} import GHC.OverloadedLabels instance IsLabel "Three" Int where fromLabel _ = 3 test :: Int test = #Three main :: IO () main = print test }}} fails to compile in ghc 8.0 with a parse error (while it works as expected if we replace "Three" -> "three"). This may be a conscious design decision, but if not I figured I would ask if it would be possible to allow such labels starting with uppercase letters. I run into this when working on adding support for OverloadedLabels to the gobject-introspection bindings (autogenerated bindings for gtk, etc.), where it would be natural in a few places to write overloaded labels starting with a capital letter. Not hugely important, but sometimes aesthetically more pleasing (imho), and I am not aware of a good reason to forbid them. Perhaps there is one? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11671> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13233: typePrimRep panic while compiling GHC with profiling
by GHC 20 Sep '18

20 Sep '18

#13233: typePrimRep panic while compiling GHC with profiling -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I am seeing this panic while compiling GHC stage2, {{{ ghc-stage1: panic! (the 'impossible' happened) (GHC version 8.1.20170124 for x86_64-unknown-linux): runtimeRepPrimRep typePrimRep (a :: TYPE k0) k0 Call stack: ?callStack, called at compiler/utils/Util.hs:1352:50 in ghc:Util prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1166:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1170:37 in ghc:Outputable pprPanic, called at compiler/simplStg/RepType.hs:360:5 in ghc:RepType Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug <<ghc: 1038844096 bytes, 158 GCs, 21564561/73278928 avg/max bytes residency (8 samples), 148M in use, 0.000 INIT (0.000 elapsed), 1.113 MUT (1.125 elapsed), 0.935 GC (0.940 elapsed) :ghc>> compiler/ghc.mk:582: recipe for target 'compiler/stage2/build/StgCmmMonad.p_o' failed }}} This appears to be due to my enabling of profiling. `build.mk` contains, {{{ BuildFlavour=prof ifneq "$(BuildFlavour)" "" include mk/flavours/$(BuildFlavour).mk endif HADDOCK_DOCS=YES compiler_HC_OPTS += -fprof-auto-exported }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13233> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14941: Switching direct type family application to EqPred (~) prevents inlining in code using vector (10x slowdown)
by GHC 19 Sep '18

19 Sep '18

#14941: Switching direct type family application to EqPred (~) prevents inlining in code using vector (10x slowdown) -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs selectVectorDestructive2 :: (PrimMonad m, VG.Vector v e, Ord e, Show e, VG.Mutable v ~ vm) => Int -> v e -> vm (PrimState m) e -> Int -> Int -> m () -- slow selectVectorDestructive2 :: (PrimMonad m, VG.Vector v e, Ord e, Show e) => Int -> v e -> VG.Mutable v (PrimState m) e -> Int -> Int -> m () -- fast }}} These two functions are identical except one has `VG.Mutable v ~ vm` as a constraint, the other one has it in the type signature right of the `=>`. The second function is 10x faster. I would expect them to be equally fast. The code of the functions is identical, I change only the type declaration. The slowness happens because with the first function, inlining of primitives like `unsafeRead` does not happen, and thus also it boxes the `Int#`s back to `Int`s when calling `unsafeRead`. In particular, in `-ddump-simpl`, the slow version has {{{#!hs $wpartitionLoop2_rgEy :: forall (m :: * -> *) (vm :: * -> * -> *) e. (PrimMonad m, MVector vm e, Ord e) => vm (PrimState m) e -> GHC.Prim.Int# -> e -> GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int# -> m Int $wpartitionLoop2_rgEy = \... -> let { endIndex_a7Ay :: Int ... endIndex_a7Ay = GHC.Types.I# ww2_sfZn } in ... (VGM.basicUnsafeRead ... endIndex_a7Ay) ... }}} while the fast version has {{{#!hs $w$spartitionLoop2_rgUN :: GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.MutableByteArray# GHC.Prim.RealWorld -> GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, Int #) ... $spartitionLoop2_rgUP :: VG.Mutable VU.Vector (PrimState IO) Int -> Int -> Int -> Int -> Int -> Int -> GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, Int #) }}} So with `VG.Mutable v (PrimState m) e` in the type signature, GHC managed to inline + specialise it all the way down to concrete types (`VUM.MVector`, `IO`, and `Int` as the element type), and consequently inline `basicUnsafeRead` on unboxed `Int#`. But with `VG.Mutable v ~ vm`, ghc keeps `vm (PrimState m) e` all the way, passes around dictionaries, thus eventually cannot inline `basicUnsafeRead` and re-packs already unboxed values, like `endIndex_a7Ay = GHC.Types.I# ww2_sfZn`, before passing them into the non-inlined call of `basicUnsafeRead`, thus making a tight loop allocate that normally wouldn't allocate. Why might rewriting the type signature in such a trivial way make this happen? ---- I have tested this on GHC 8.0.2, GHC 8.2.2, and GHC 8.5 HEAD commit cc4677c36ee. Reproducer: * https://github.com/nh2/haskell-quickselect-median-of- medians/blob/0efd6293e779fda2d864ec3d75329fb16b8af6d9/Main.hs#L506 * Running instructions are [https://github.com/nh2/haskell-quickselect- median-of-medians/commit/7a49d673990dfaebdb0ba837c3fbbaae0455dba0 in this commit message]; for short: `stack exec -- ghc -O --make Main.hs -rtsopts -ddump-simpl -dsuppress-coercions -fforce-recomp -ddump-to-file -fno-full- laziness && ./Main +RTS -sstderr` * For that file, I have pregenerated `-dverbose-core2core` output here: https://github.com/nh2/haskell-quickselect-median-of- medians/tree/0efd6293e779fda2d864ec3d75329fb16b8af6d9/slowness-analysis * I originally just wanted to write a fast median-of-medians implementation on ZuriHac 2017, but got totally derailed by this performance problem. The version of it that I link here is a total mess because of me mauling it to track down this performance issue. Trying to increase `-funfolding-use-threshold` or `-funfolding-keeness- factor` did not change the situation. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14941> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15544: Possible segmentation fault in cryptohash-sha256 testsuite
by GHC 19 Sep '18

19 Sep '18

#15544: Possible segmentation fault in cryptohash-sha256 testsuite -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ $ cabal get cryptohash-sha256-0.11.101.0 $ cabal new-run -w ghc-8.6.1 --enable-test --allow-newer=cryptohash- sha256:base,*:stm,*:tasty,async:base test:test-sha256 -- -j 8 --quickcheck-tests 9999 }}} Eventually the program will start spamming stderr with `test-sha256: lost signal due to full pipe: 11` repeatedly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15544> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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