October 2016 - ghc-tickets

[GHC] #12522: GHC 8.0.1 hangs, looping forever in type-checker
by GHC 26 Oct '16

26 Oct '16

#12522: GHC 8.0.1 hangs, looping forever in type-checker -------------------------------------+------------------------------------- Reporter: clinton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'm not sure if this is a bug or hanging the compiler is expected here. This was the minimal example that causes GHC to hang: {{{#!hs {-# LANGUAGE TypeFamilyDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE AllowAmbiguousTypes #-} main = return $ f (Just 'c') data D1 x data D2 type family TF x = t | t -> x type instance TF (D1 x, a) = Maybe (TF (x, a)) type instance TF (D2, ()) = Char class C p where f :: TF (x, a) -> () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12522> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9858: Typeable instance for datatype and its promoted constructor is the same
by GHC 26 Oct '16

26 Oct '16

#9858: Typeable instance for datatype and its promoted constructor is the same -------------------------------------+------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 | Type of failure: hour) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- {{{ {-# LANGUAGE DataKinds #-} {-# LANGUAGE AutoDeriveTypeable #-} import Data.Typeable data A = A main = print $ typeRep (Proxy :: Proxy A) == typeRep (Proxy :: Proxy 'A) }}} This returns `True`, but it should return `False`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9858> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4162: GHC API messes up signal handlers
by GHC 26 Oct '16

26 Oct '16

#4162: GHC API messes up signal handlers -------------------------------------+------------------------------------- Reporter: jcpetruzza | Owner: Type: bug | Status: patch Priority: low | Milestone: Component: GHC API | Version: 6.12.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): phab:D2633 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): Good point, maybe use a reference count instead? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4162#comment:16> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4162: GHC API messes up signal handlers
by GHC 26 Oct '16

26 Oct '16

#4162: GHC API messes up signal handlers -------------------------------------+------------------------------------- Reporter: jcpetruzza | Owner: Type: bug | Status: patch Priority: low | Milestone: Component: GHC API | Version: 6.12.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): phab:D2633 Wiki Page: | -------------------------------------+------------------------------------- Changes (by hsyl20): * differential: D2633 => phab:D2633 Comment: Note that my patch in comment:14 doesn't make `runGhc` thread-safe if several `runGhc` are executed concurrently. E.g., in the following case: {{{#!haskell runGhc (1) install handlers runGhc (2) install handlers runGhc (1) uninstall handlers runGhc (2) uninstall handlers -- reinstall handlers installed by `runGhc (1)` -- overwriting initial handlers }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4162#comment:15> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1687: A faster (^)-function.
by GHC 26 Oct '16

26 Oct '16

#1687: A faster (^)-function. --------------------------------------------+----------------------------- Reporter: moonlite@… | Owner: Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Prelude | Version: 6.6.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86 Type of failure: Runtime performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | --------------------------------------------+----------------------------- Comment (by siddhanathan): rwbarton explained this earlier, but it took a while to wrap my head around it. I find this a bit clearer to understand: {{{ {-# SPECIALISE [1] (^) :: Integer -> Integer -> Integer, Integer -> Int -> Integer, Int -> Int -> Int #-} {-# INLINABLE [1] (^) #-} -- See Note [Inlining (^)] (^) :: (Num a, Integral b) => a -> b -> a x0 ^ y0 | y0 < 0 = errorWithoutStackTrace "Negative exponent" | y0 == 0 = 1 | otherwise = f x0 y0 1 where f x y z | even y = let k = f x (y `quot` 2) z in k * k | y == 1 = x * z | otherwise = let k = f x ((y - 1) `quot` 2) z in k * k * x }}} This has identical performance to the version in the description above. This makes use of the fact that x^2a^ = x^a+a^ = x^a^ * x^a^ ; and x^2a+1^ = x^a^ * x^a^ * x -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1687#comment:18> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12765: Don't optimize coercions with -O0
by GHC 25 Oct '16

25 Oct '16

#12765: Don't optimize coercions with -O0 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- During the call today Simon and I discussed the possibility of omitting coercion optimization from the desugarer's simple optimization (`simpleOptPgm`) when compiling with `-O0`. The justification here was to perhaps speed-up unoptimized compilation times for programs like that of #12506, which has very large coercions (presumably due to #8095). The rationale was that while this first pass of coercion simplification during desugaring may reduce the size of some of these coercions, we only walk over them once more during code generation, so there's little benefit given the cost. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12765> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #2721: Newtype deriving doesn't work with type families
by GHC 25 Oct '16

25 Oct '16

#2721: Newtype deriving doesn't work with type families -------------------------------------+------------------------------------- Reporter: rl | Owner: Type: feature request | Status: patch Priority: lowest | Milestone: 8.2.1 Component: Compiler (Type | Version: 6.10.1 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | deriving/should_fail/T2721 Blocked By: | Blocking: Related Tickets: #8165 | Differential Rev(s): Phab:D2636 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => patch * differential: => Phab:D2636 * milestone: => 8.2.1 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2721#comment:25> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4114: Add a flag to remove/delete intermediate files generated by GHC
by GHC 25 Oct '16

25 Oct '16

#4114: Add a flag to remove/delete intermediate files generated by GHC -------------------------------------+------------------------------------- Reporter: guest | Owner: kaiha Type: feature request | Status: closed Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 6.10.4 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | driver/T4114a,b,c,d Blocked By: | Blocking: Related Tickets: #2258 | Differential Rev(s): Phab:D2021 Wiki Page: | Phab:D2050 -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => closed * resolution: => fixed -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4114#comment:32> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4815: Instance constraints should be used when deriving on associated data types
by GHC 25 Oct '16

25 Oct '16

#4815: Instance constraints should be used when deriving on associated data types -------------------------------------+------------------------------------- Reporter: batterseapower | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler | Version: 6.12.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Replying to [comment:17 simonpj]: > So I'm unconvinced that this is worth the bother. I completely agree, not only because it might be over-constraining, but in some cases it might even yield redundant constraints, as in this example: {{{#!hs {-# LANGUAGE TypeFamilies #-} class C a where data D a c :: a -> a -> Bool instance Eq a => C [a] where newtype D [a] = DList [a] deriving Show c = (==) }}} This would, under the proposal in this ticket, yield: {{{#!hs instance (Eq a, Show a) => Show (D [a]) }}} which isn't what we want at all. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4815#comment:18> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4815: Instance constraints should be used when deriving on associated data types
by GHC 25 Oct '16

25 Oct '16

#4815: Instance constraints should be used when deriving on associated data types -------------------------------------+------------------------------------- Reporter: batterseapower | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler | Version: 6.12.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I think it's more than just #11008. The question of this ticket is just "what context should GHC infer for a 'deriving' clause." But the ticket concerns the specific case of a `data instance` inside a `class` instance decl, thus: {{{ instance <context> => C (T a b) where data D (T a b) = D1 a | D2 b }}} Now arguably, whether or not the `deriving Eq` part ''needs'' `<context>` it would do no harm to add it, so we get the derived instance {{{ instance <context> => Eq (DT a b) where (==) = <blah> }}} (where `DT` is the representation data type for `D (T a b)`). The point is that `<context>` might help satisfy the `Eq` constraints arising from `<blah>`. Max argues that `<context>` must already be satisfied (because the class instance holds). But that's not really true {{{ f x y = D1 x == D2 y }}} Here we need equality on `DT` but we don't need `C (T a b)`. So `<context>` might be over-constraining. So I'm unconvinced that this is worth the bother. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4815#comment:17> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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