March 2018 - ghc-tickets

[GHC] #14949: Perform builds on non-Debian-based systems on Circle CI
by GHC 27 Jul '18

27 Jul '18

#14949: Perform builds on non-Debian-based systems on Circle CI -------------------------------------+------------------------------------- Reporter: mrkkrp | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- I could not find already existing ticket and so I'm creating this one. Ben mentioned (in his latest status update on GHC devops mailing list) that we need to do building on non-Debian-based systems on CI. To quote: > e. Support for building on non-Debian-based systems (e.g. Fedora), which is necessary if we want to produce our binary distributions via CI. So this ticket is to track progress on that. I'm planning to start working on this tomorrow perhaps. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14949> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14185: Non-local bug reporting around levity polymorphism
by GHC 27 Jul '18

27 Jul '18

#14185: Non-local bug reporting around levity polymorphism -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Keywords: | Operating System: Unknown/Multiple LevityPolymorphism, | TypeErrorMessages | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- From comment:12:ticket:13105. In HEAD (or, at least, my version, on the `wip/rae` branch), this code {{{#!hs class Unbox (t :: *) (r :: TYPE k) | t -> r, r -> t where unbox :: t -> r box :: r -> t instance Unbox Int Int# where unbox (I# i) = i box i = I# i instance Unbox Char Char# where unbox (C# c) = c box c = C# c instance (Unbox a a', Unbox b b') => Unbox (a,b) (# a', b' #) where unbox (a,b) = (# unbox a, unbox b #) box (# a, b #) = (box a, box b) testInt :: Int testInt = box (unbox 1) testTup :: (Int, Char) testTup = box (unbox (1, 'a')) }}} fails with {{{ Bug.hs:27:11: error: • Couldn't match a lifted type with an unlifted type When matching types a' :: * Int# :: TYPE 'IntRep • In the expression: box (unbox 1) In an equation for ‘testInt’: testInt = box (unbox 1) | 27 | testInt = box (unbox 1) | ^^^^^^^^^^^^^ Bug.hs:27:16: error: • Couldn't match a lifted type with an unlifted type When matching types a' :: * Int# :: TYPE 'IntRep • In the first argument of ‘box’, namely ‘(unbox 1)’ In the expression: box (unbox 1) In an equation for ‘testInt’: testInt = box (unbox 1) | 27 | testInt = box (unbox 1) | ^^^^^^^ Bug.hs:42:11: error: • Couldn't match a lifted type with an unlifted type When matching types a' :: * Int# :: TYPE 'IntRep • In the expression: box (unbox (1, 'a')) In an equation for ‘testTup’: testTup = box (unbox (1, 'a')) | 42 | testTup = box (unbox (1, 'a')) | ^^^^^^^^^^^^^^^^^^^^ }}} I think it should succeed. Worse, when I comment out the `testTup` definition, the file succeeds... but note that two of the errors above are in `testInt`, which compiles fine on its own. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14185> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14627: qAddTopDecls: can't convert top-level declarations
by GHC 27 Jul '18

27 Jul '18

#14627: qAddTopDecls: can't convert top-level declarations -------------------------------------+------------------------------------- Reporter: tianxiaogu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following program crashes 8.2.2 and HEAD (8.5.20171228). {{{#!hs {-# LANGUAGE TemplateHaskell #-} import Language.Haskell.TH.Syntax (addTopDecls) $(do ds <- [d| f = Bool |] addTopDecls ds [d| g = cab |]) }}} Output: {{{ Exception when trying to run compile-time code: ghc: panic! (the 'impossible' happened) (GHC version 8.5.20171228 for x86_64-unknown-linux): qAddTopDecls: can't convert top-level declarations Illegal variable name: ‘Bool’ When splicing a TH declaration: f_0 = Bool Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcSplice.hs:886:27 in ghc:TcSplice Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14627> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13116: Allow Overloaded things in patterns
by GHC 26 Jul '18

26 Jul '18

#13116: Allow Overloaded things in patterns -------------------------------------+------------------------------------- Reporter: | Owner: facundo.dominguez | 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 ticket is motivated by the use of `OverloadedLabels` of the [http://hackage.haskell.org/package/choice-0.2.0 choice package]. One can use a type `Choice "block"` with values `Do #block` and `Don't #block` by using `OverloadedLabels`. However, in patterns this syntax is forbidden. {{{ case block of Do #block -> ... Don't #block -> ... }}} It would be nice if overloaded labels desugared to something sensible in patterns, perhaps {{{ case block of Do ((==) (fromLabel (proxy# :: Proxy# "foo")) -> True) -> ... Don't ((==) (fromLabel (proxy# :: Proxy# "foo")) -> True) -> ... }}} `OverloadedLists` and `OverloadedStrings` could benefit from a similar solution. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13116> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12736: Calling a complex Haskell function (obtained via FFI wrapper function) from MSVC 64-bit C code (passed in as FunPtr) can leave SSE2 registers in the XMM6-XMM15 range modified
by GHC 24 Jul '18

24 Jul '18

#12736: Calling a complex Haskell function (obtained via FFI wrapper function) from MSVC 64-bit C code (passed in as FunPtr) can leave SSE2 registers in the XMM6-XMM15 range modified -------------------------------------+------------------------------------- Reporter: bavism | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 (FFI) | Keywords: | Operating System: Windows ffi,registers,sse2,clobber,xmm | Architecture: x86_64 | Type of failure: Incorrect result (amd64) | at runtime Test Case: | Blocked By: https://github.com/bavis-m/raycast | Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- According to the [https://msdn.microsoft.com/en-us/library/9z1stfyw.aspx MSDN], in the Microsoft x64 architecture function calls must preserve the SSE2 registers in the range XMM6-XMM15. The Haskell FFI can produce a function pointer via dynamic wrapper that, when called from MSVC x64 C code, does not preserve these registers, causing further floating-point operations in the C code to fail. I can reproduce this error in [https://github.com/bavis-m/raycast this project], which is a DOOM-style raycasting engine written in Haskell, that imports a C DLL with glue for rendering and window management. The Haskell executable generates a FunPtr to a frame update function using the dynamic import mechanism, and passes this to a long-lived C function that runs the update loop. Any time this update function is called from the C loop, subsequent floating point operations produce incorrect results (in this case, the next operations compute a view matrix for the OpenGL window). The output on every frame showing the view matrix should be: {{{ viewM: 0.003125 0.000000 0.000000 -1.000000 0.000000 0.004167 0.000000 -1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 1.000000 }}} Running the raycaster with the Release version of the DLL causes the value of this matrix to be corrupted. There is a patch provided (stub.patch in the root folder) that turns the Haskell update function into an empty stub. This causes the program to work. When stepping through the assembly code with this patch applied, I can see in the function prologue where the XMM registers are saved. Without the patch, these registers are not saved. Running the Debug version does not show this error; the register allocation must be different. I have been attempting to create a much simpler test case to reveal this code-generation issue, however it has been difficult. Even seemingly trivial changes can cause the bug to not show up, it is clearly dependent on the register allocation used internally to produce the assembly code. Instructions for building the project are in the readme. (You will need the Haskell Stack Tool, and Visual Studio 15). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12736> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8128: Standalone deriving fails for GADTs due to inaccessible code
by GHC 24 Jul '18

24 Jul '18

#8128: Standalone deriving fails for GADTs due to inaccessible code -------------------------------------+------------------------------------- Reporter: adamgundry | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.7 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: Unknown/Multiple | valid program Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- Consider the following: {{{ {-# LANGUAGE StandaloneDeriving, GADTs, FlexibleInstances #-} module StandaloneDerivingGADT where data T a where MkT1 :: T Int MkT2 :: (Bool -> Bool) -> T Bool deriving instance Show (T Int) }}} This gives the error: {{{ StandaloneDerivingGADT.hs:9:1: Couldn't match type ‛Int’ with ‛Bool’ Inaccessible code in a pattern with constructor MkT2 :: (Bool -> Bool) -> T Bool, in an equation for ‛showsPrec’ In the pattern: MkT2 b1 In an equation for ‛showsPrec’: showsPrec a (MkT2 b1) = showParen ((a >= 11)) ((.) (showString "MkT2 ") (showsPrec 11 b1)) When typechecking the code for ‛showsPrec’ in a standalone derived instance for ‛Show (T Int)’: To see the code I am typechecking, use -ddump-deriv In the instance declaration for ‛Show (T Int)’ }}} The derived instance declaration matches on all the constructors, even if they cannot possibly match. It should omit obviously inaccessible constructors so that this example is accepted. For reference, the derived code is: {{{ instance GHC.Show.Show (StandaloneDerivingGADT.T GHC.Types.Int) where GHC.Show.showsPrec _ StandaloneDerivingGADT.MkT1 = GHC.Show.showString "MkT1" GHC.Show.showsPrec a_aij (StandaloneDerivingGADT.MkT2 b1_aik) = GHC.Show.showParen ((a_aij GHC.Classes.>= 11)) ((GHC.Base..) (GHC.Show.showString "MkT2 ") (GHC.Show.showsPrec 11 b1_aik)) GHC.Show.showList = GHC.Show.showList__ (GHC.Show.showsPrec 0) }}} The same problem applies to other derivable classes (e.g. `Eq`). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8128> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8740: Code conditionally compiles
by GHC 24 Jul '18

24 Jul '18

#8740: Code conditionally compiles ----------------------------+---------------------------------------------- Reporter: | Owner: thomaseding | Status: new Type: bug | Milestone: Priority: normal | Version: 7.6.3 Component: Compiler | Operating System: MacOS X Keywords: | Type of failure: GHC rejects valid program Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- {{{ {-# LANGUAGE GADTs #-} {-# LANGUAGE StandaloneDeriving #-} data Abstract data Reified data Player data Elect p a where ElectRefAsTypeOf :: Int -> Elect Abstract a -> Elect Abstract a ElectHandle :: a -> Elect Reified a Controller :: Elect Abstract Player Owner :: Elect Abstract Player You :: Elect Abstract Player deriving instance (Eq a) => Eq (Elect p a) deriving instance (Ord a) => Ord (Elect p a) }}} As is, the above code fails to compile. But if I move `ElectRefAsTypeOf` to be the last constructor for the GADT, the code does compile. If I remove one of the `Elect Abstract Player` constructors, the code still won't compile even if the `ElectRefAsTypeOf` is moved. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8740> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14333: GHC doesn't use the fact that Coercible is symmetric
by GHC 23 Jul '18

23 Jul '18

#14333: GHC doesn't use the fact that Coercible is symmetric -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- {{{#!hs {-# Language ScopedTypeVariables, GADTs, DeriveGeneric #-} import GHC.Generics import Data.Type.Coercion data AB = A | B deriving (Generic) data XY = X | Y deriving (Generic) data This ab xy where At :: This AB XY foo :: This ab xy -> Coercion (Rep ab a) (Rep xy a) foo At = Coercion bar :: forall ab xy a. This ab xy -> Coercion (Rep ab a) (Rep xy a) bar at | Coercion <- foo at :: Coercion (Rep ab a) (Rep xy a) = Coercion }}} This compiles on 8.2.1 and 8.3.20170920 but flipping the arguments to `Coercion` fails {{{#!hs -- ... -- • Could not deduce: Coercible (Rep xy a) (Rep ab a) -- arising from a use of ‘Coercion’ -- from the context: Coercible (Rep ab a) (Rep xy a) -- bound by a pattern with constructor: bar :: forall ab xy a. This ab xy -> Coercion (Rep xy a) (Rep ab a) bar at | Coercion <- foo at :: Coercion (Rep ab a) (Rep xy a) = Coercion }}} Conceptually there should be an (`Undecidable`) superclass constraint for `Coercible` {{{#!hs class Coercible b a => Coercible a b }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14333> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14414: Profiled program runs 2.5x faster than non-profiled
by GHC 23 Jul '18

23 Jul '18

#14414: Profiled program runs 2.5x faster than non-profiled -------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- I was looking at benchmarks game (attached as fasta.ghc-2.hs). I have found that with the flags give there, this program on GHC 8.2.1 runs in about a second with `-prof -fprof-auto` and 2.5 seconds without! To run without profiling: {{{ ghc --make -Wall -fforce-recomp -fllvm -O2 -XBangPatterns -threaded -rtsopts -XOverloadedStrings fasta.ghc-2.hs -o fasta.ghc-2.ghc_run && ./fasta.ghc-2.ghc_run +RTS -N4 -s -RTS 250000 > /dev/null }}} Same program with profiling {{{ ghc --make -fforce-recomp -fllvm -prof -fprof-auto -O2 -XBangPatterns -threaded -rtsopts -XOverloadedStrings fasta.ghc-2.hs -o fasta.ghc-2.ghc_run && ./fasta.ghc-2.ghc_run +RTS -N4 -p -s -RTS 250000 > /dev/null }}} I also attach Core outputs for both profiled and unprofiled version. To me this seems very strange: profiled version is somehow faster. Perhaps what's worse is that this means that there's some optimisation GHC is performing when profiling is not on that makes the program a lot slower than it could be! This program is not minimised. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14414> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12714: T9405 fails on Windows
by GHC 22 Jul '18

22 Jul '18

#12714: T9405 fails on Windows --------------------------------------+--------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Runtime System | Version: 8.0.1 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+--------------------------------- The `T9405` testcase currently fails on Windows, {{{ }}} Contrary to what was suggested in ticket:12004#comment:3 it looks like the problem is that an empty `.ticky` file is produced. Even increasing the `sleep` time to 10 seconds (after bumping the sleep in `T9405.hs` accordingly) doesn't change this, so I suspect there is a runtime system bug here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12714> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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