June 2016 - ghc-tickets

[GHC] #8732: Global big object heap allocator lock causes contention
by GHC 16 Jul '16

16 Jul '16

#8732: Global big object heap allocator lock causes contention ------------------------------------+------------------------------------- Reporter: tibbe | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The lock allocate() takes when allocating big objects hurts scalability of I/O bound application. Network.Socket.ByteString.recv is typically called with a buffer size of 4096, which causes a ByteString of that size to be allocate. The size of this ByteString causes it to be allocated from the big object space, which causes contention of the global lock that guards that space. See http://www.yesodweb.com/blog/2014/02/new-warp for a real world example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8732> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12113: ghc-8.0.1-rc4: unification false positive?
by GHC 14 Jul '16

14 Jul '16

#12113: ghc-8.0.1-rc4: unification false positive? -------------------------------------+------------------------------------- Reporter: _deepfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE UnicodeSyntax #-} module Foo () where type family TF x ∷ * data ADT x type instance TF (ADT x) = x class (a ~ ADT (TF a)) ⇒ TC2 a b | a → b data Forget = ∀ a b. TC2 a b ⇒ Forget a -- ~ Forget (ADT (TF a)) data PhantomF a b = Constr Forget -- ~ Constr (Forget (ADT (TF a))) f ∷ ∀ a b. TC2 a b ⇒ ADT (TF a) → [Forget] f _ = case ((undefined) ∷ (PhantomF a b)) of Constr m → [Forget m] -- Here GHC 8.0.1-rc4 unifies, whereas GHC 7.10.3 (properly?) fails with: -- ghc8-unification-false-positive.hs:20:21: -- Couldn't match type ‘Forget’ with ‘ADT (TF Forget)’ -- In the expression: Forget m -- In the expression: [Forget m] -- In a case alternative: Constr m -> [Forget m] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12113> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12057: TypeFamilyDependencies on GHC.Generic's `Rep`
by GHC 14 Jul '16

14 Jul '16

#12057: TypeFamilyDependencies on GHC.Generic's `Rep` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | Keywords: TypeFamilies, | Operating System: Unknown/Multiple Injective | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With `TypeFamilyDependencies` (`InjectiveTypeFamilies`) can't `Rep` from `Generic` have a dependency? {{{#!hs class Generic a where type Rep a = (res :: Type -> Type) | res -> a ... }}} Assuming the meta data is always unique. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12057> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12240: Common Sense for Type Classes
by GHC 13 Jul '16

13 Jul '16

#12240: Common Sense for Type Classes -------------------------------------+------------------------------------- Reporter: Mathnerd314 | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC erroneously reports that there is "No instance of C". But, in fact, there is an instance, `C Int Char`; furthermore, it is the only instance. So GHC should use it! {{{#!hs {-# LANGUAGE MultiParamTypeClasses #-} module T4921 where class C a b where f :: (a,b) instance C Int Char where f = undefined x = fst f y = fst f :: Int }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12240> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11835: ApplicativeDo failed to desugar last line with pure $ <expr>
by GHC 12 Jul '16

12 Jul '16

#11835: ApplicativeDo failed to desugar last line with pure $ <expr> -------------------------------------+------------------------------------- Reporter: Cosmia | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc2 Keywords: ApplicativeDo | Operating System: MacOS X Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: #11607 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs {-# LANGUAGE ApplicativeDo #-} f m = do x <- m 1 y <- m 2 return $ x + y }}} f should have type (Applicative f, Num a, Num b) => (a -> f b) -> f b but ghc considers f a monad maybe similar with #11607 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11835> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10647: Notice about lack of SIMD support.
by GHC 12 Jul '16

12 Jul '16

#10647: Notice about lack of SIMD support. -------------------------------------+------------------------------------- Reporter: mniip | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- In some cases, when SIMD primitives are used without the `-fllvm` flag, instead of giving the friendly `SIMD vector instructions require the LLVM back-end.`, GHC crashes with varying messages. The simplest example is {{{#!hs {-# LANGUAGE MagicHash #-} module Foo where import GHC.Prim data V = V Int8X16# }}} In 7.8.4 this crashes with {{{ ghc: panic! (the 'impossible' happened) (GHC version 7.8.4 for x86_64-unknown-linux): Size.intSize W128 }}} According to osa1, in HEAD this still crashes, but with {{{ ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.11.20150717 for x86_64-unknown-linux): Format.intFormat W128 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10647> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8308: Resurrect ticky code for counting constructor arity
by GHC 12 Jul '16

12 Jul '16

#8308: Resurrect ticky code for counting constructor arity ----------------------------------------------+---------------------------- Reporter: jstolarek | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Profiling | Version: 7.7 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less than a day) | Type of failure: Other Blocked By: | Test Case: Related Tickets: | Blocking: ----------------------------------------------+---------------------------- There is a dead piece of ticky profiling code that computes histograms of data constructor arities (including tuples) and size of vector returns. The function responsible is `bumpHistogram` in [[GhcFile(compiler/codeGen/StgCmmTicky.hs)]], which masks the commented out function `bumpHistogramE`. We can improve ticky profiling by resurrecting this dead code. There are following things that need to be done: 1. Replace current no-op `bumpHistogram` with `bumpHistogramE`. Note that current implementation of `bumpHistogramE` computes constructor arity at runtime. This is unnecessary because we know arity at compile time so we can avoid runtime check by doing sth like this: {{{ bumpHistogram lbl n = do let offset = n `min` 8 emit (addToMem cLong (cmmIndexExpr cLongWidth (CmmLit (CmmLabel (mkRtsDataLabel lbl))) (CmmReg (CmmInt (fromIntegral offset) cLongWidth))) 1) }}} Note that `mkRtsDataLabel` function does not exist anymore but we should be able to replace that call with `mkCmmDataLabel rtsPackageId lbl` (speculation). 2. We need to declare arrays that will store histogram values. Declarations of variables used for storing ticky statistics are in [[GhcFile(includes/stg/Ticky.h)]]. We also need to initialize the declared array to contain only zeros. 3. Having declared the arrays we need to fix printing of computed arities. This is done in [[GhcFile(rts/Ticky.c)]]. Note that there is a lot of code that is commented out (`/* krc: comment out some of this stuff temporarily */`) or disabled with `#if FALSE` pragma. We need to resurect *some* of it. There is a `PR_HST` macro for printing one histogram entry. This seems bad. We should probably rework the part of code responsible for printing out results of historgams. 4. Current code counts arities from 0 to 8. Everything above 8 is put into the same bin as 8. This magical 8 is spread all over the code. We should declare a constant that is visible both in Haskell sources (see `bumpHistogram` in 1.) and RTS files and have all code behave properly depending on that constant - we should have loops instead of statically printing 9 elements of histogram array. 5. Some ticky functions that count arity histograms are not used. For example `tickyReturnNewCon` should probably be called by `cgConApp` like this: {{{ ; emit =<< fcode_init ; tickyReturnNewCon ; emitReturn [idInfoToAmode idinfo] } }}} The above is a an outline, which should be fairly accurate, but unexpected things may show up along the way. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8308> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12127: ghc-8.0.1: panic! (the 'impossible' happened) filterImports/combine (double import)
by GHC 12 Jul '16

12 Jul '16

#12127: ghc-8.0.1: panic! (the 'impossible' happened) filterImports/combine (double import) -------------------------------------+------------------------------------- Reporter: slyfox | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It's a distilled example or repa-devil-0.3.2.6 build failure: {{{#!hs -- Cursored.hs: {-# LANGUAGE TypeFamilies #-} module Cursored where class Source r where data Array r instance Source () where data Array () = F { f :: Int } }}} {{{#!hs -- Bug.hs: module DevIL () where import Cursored (Array(..), Source(..)) }}} {{{ [1 of 2] Compiling Cursored ( Cursored.hs, Cursored.o ) [2 of 2] Compiling DevIL ( Bug.hs, Bug.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): filterImports/combine (Array, Array{Array, F, f}, Nothing) (Array, Source{Source, Array}, Nothing) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} The error is the same as #11959 but involved entities are slightly different. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12127> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11554: Self quantification in GADT data declarations
by GHC 12 Jul '16

12 Jul '16

#11554: Self quantification in GADT data declarations -------------------------------------+------------------------------------- Reporter: Rafbill | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc2 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: -------------------------------------+------------------------------------- GHC hangs on this (it was panicking on the same code before : [https://github.com/goldfirere/ghc/issues/56](https://github.com/goldfirere/… : {{{#!hs {-# LANGUAGE GADTs, TypeInType #-} import Data.Kind data A :: Type where B :: forall (a :: A). A }}} I guess the typechecker tries to infer the kind of A from the type of the constructors and hangs. Maybe recursive occurrences of a type as a kind in its constructors should only be allowed when its kind signature is specified and can be used to typecheck the constructors. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11554> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12026: Pattern match failure in RnNames.hs
by GHC 12 Jul '16

12 Jul '16

#12026: Pattern match failure in RnNames.hs -------------------------------------+------------------------------------- Reporter: davean | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When compiling dimensional-1.0.1.1 after patching numtype-dk with the patch at https://github.com/bjornbm/numtype-dk/issues/12 GHC does the "impossible": [ 3 of 16] Compiling Numeric.Units.Dimensional.Dimensions.TypeLevel ( src/Numeric/Units/Dimensional/Dimensions/TypeLevel.hs, dist/dist-sandbox- 68389a1a/build/Numeric/Units/Dimensional/Dimensions/TypeLevel.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.0.20160421 for x86_64-unknown-linux): Pattern match failure in do expression at compiler/rename/RnNames.hs:902:12-50 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12026> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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