December 2017 - ghc-tickets

[GHC] #8642: Allow GHCi to print non-pretty forms of things.
by GHC 29 Dec '17

29 Dec '17

#8642: Allow GHCi to print non-pretty forms of things. ------------------------------------+------------------------------------- Reporter: Fuuzetsu | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Currently when we ask GHCi for :info or :type of something, it will do things like splitting over multiple lines and all that eye candy that people like to see. This however makes it more difficult for people to write text editor plugins &c that rely on GHCi output. Currently one has to write parsers to stitch the GHCi output back together which is fairly error prone and not really future-proof. Is there any chance for a more machine-friendly output? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8642> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14621: GHC 8.2 GCed too early
by GHC 29 Dec '17

29 Dec '17

#14621: GHC 8.2 GCed too early -------------------------------------+------------------------------------- Reporter: kazu-yamamoto | 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: -------------------------------------+------------------------------------- The network package uses mkWeakVar so that unreachable Sockets can be GCed. See the master branch of https://github.com/haskell/network {{{ mkSocket :: CInt -> Family -> SocketType -> ProtocolNumber -> SocketStatus -> IO Socket mkSocket fd fam sType pNum stat = do mStat <- newMVar stat withSocketsDo $ return () let sock = Socket fd fam sType pNum mStat ##if MIN_VERSION_base(4,6,0) _ <- mkWeakMVar mStat $ close sock ##endif return sock }}} The following code cause "threadWait: invalid argument (Bad file descriptor)" in accept: {{{ module Main where import Control.Concurrent (forkIO) import Control.Monad (void, forever) import Network.Socket hiding (recv) import Network.Socket.ByteString (recv, sendAll) main :: IO () main = do let localhost = "localhost" listenPort = "9876" connectPort = "6789" proxy localhost listenPort connectPort proxy :: HostName -> ServiceName -> ServiceName -> IO () proxy localhost listenPort connectPort = do fromClient <- serverSocket localhost listenPort toServer <- clientSocket localhost connectPort void $ forkIO $ relay toServer fromClient relay fromClient toServer relay :: Socket -> Socket -> IO () relay s1 s2 = forever $ do payload <- recv s1 4096 sendAll s2 payload serverSocket :: HostName -> ServiceName -> IO Socket serverSocket host port = do let hints = defaultHints { addrFlags = [AI_PASSIVE] , addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) bind sock (addrAddress addr) listen sock 1 fst <$> accept sock clientSocket :: HostName -> ServiceName -> IO Socket clientSocket host port = do let hints = defaultHints { addrSocketType = Stream } addr:_ <- getAddrInfo (Just hints) (Just host) (Just port) sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr) connect sock (addrAddress addr) return sock }}} GC frees sock while accepting. This occurs with GHC 8.2 or higher. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14621> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9291: Don't reconstruct sum types if the type subtly changes
by GHC 28 Dec '17

28 Dec '17

#9291: Don't reconstruct sum types if the type subtly changes ----------------------------------------------+---------------------------- Reporter: schyler | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Moderate (less than a day) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: ----------------------------------------------+---------------------------- Consider this test case: {{{ module Main (main) where fun :: Either Int String -> Either String String fun x = case x of Left int -> Left (show int) Right str -> Right str {-# NOINLINE fun #-} main :: IO () main = do l <- getLine print $ fun (Right l) }}} The core we get for fun looks like: {{{ Main.fun [InlPrag=NOINLINE] :: Data.Either.Either GHC.Types.Int GHC.Base.String -> Data.Either.Either GHC.Base.String GHC.Base.String [GblId, Arity=1, Caf=NoCafRefs, Str=DmdType <S,1*U>] Main.fun = \ (x_aur :: Data.Either.Either GHC.Types.Int GHC.Base.String) -> case x_aur of _ [Occ=Dead] { Data.Either.Left int_aus -> Data.Either.Left @ GHC.Base.String @ GHC.Base.String (GHC.Show.$fShowInt_$cshow int_aus); Data.Either.Right str_aCG -> Data.Either.Right @ GHC.Base.String @ GHC.Base.String str_aCG } }}} There would be less allocations and probably perform better if we just coerced `x` into the new type. Because the coercion is common code, this also means that if hypothetically some other sum type which had 15 constructors, and only 3 had subtle type changes, 12 of the case branches could be CSE'd into the single coerce greatly reducing code generated and also hinting the inliner better. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9291> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14618: Higher rank typechecking is broken
by GHC 28 Dec '17

28 Dec '17

#14618: Higher rank typechecking is broken -------------------------------------+------------------------------------- Reporter: mniip | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.2.2 (Type checker) | 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: -------------------------------------+------------------------------------- The oddity was noticed when someone asked the type of `lens` from lambdabot and it replied with {{{#!hs 1514165211 [04:26:51] <lambdabot> Functor f => (s1 -> a1) -> (s1 -> b1 -> t1) -> (a2 -> f b2) -> s2 -> f t2 }}} This disagrees with `lens`'s type per definition (way too many foralls and unconstrained type variables), and if handled carefully it could be used to implement `unsafeCoerce` within SafeHaskell. The minimalest example I could come up with: {{{#!hs {-# LANGUAGE RankNTypes #-} safeCoerce :: a -> b safeCoerce = f' where f :: d -> forall c. d f x = x f' = f }}} This compiles and typechecks on GHC 8.2.2, 8.2.1 (courtesy of hydraz) and HEAD. But not on 8.0.2 (hydraz) or 7.10.3. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14618> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14622: Add `joinState# :: State# s -> State# s -> State# s` primop
by GHC 28 Dec '17

28 Dec '17

#14622: Add `joinState# :: State# s -> State# s -> State# s` primop -------------------------------------+------------------------------------- Reporter: reinerp | Owner: (none) Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- The state threading in GHC.Prim requires the user to impose a total order on memory reads and writes within a state thread. In some cases, this total order constrains the compiler more than necessary. For example, if the programmer knows that `addr1` and `addr2` don't alias, then they might like to express that the two writes in the following can be reordered relative to each other: {{{#!hs doTwoWrites :: Addr# -> Addr# -> State# s -> State# s doTwoWrites addr1 addr2 s = writeWord8OffAddr# addr2 0# 123## ( writeWord8OffAddr# addr1 0# 234## s) }}} If we had the following primop, then we could express that flexibility in reordering: {{{#!hs -- | Produces a state that has a data dependency on the two input -- states. Generates no machine code. joinState# :: State# s -> State# s -> State# s }}} That is, we'd write the above function as: {{{#!hs doTwoWrites :: Addr# -> Addr# -> State# s -> State# s doTwoWrites addr1 addr2 s = joinState# (writeWord8OffAddr# addr2 0# 123## s) (writeWord8OffAddr# addr1 0# 234## s) }}} This would give us fine-grained fork/join of `State#` threads, with fork provided by copying of `State# s` objects and join provided by `joinState#`. This lets the programmer express arbitrary DAGs of dependencies between memory operations, rather than just linear chains of dependencies. Low priority; I don't have a specific use case with a missed optimization. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14622> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #8033: add AVX register support to llvm calling convention
by GHC 27 Dec '17

27 Dec '17

#8033: add AVX register support to llvm calling convention -------------------------------------+------------------------------------- Reporter: carter | Owner: (none) Type: task | Status: closed Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 7.7 Resolution: fixed | Keywords: SIMD Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => closed * resolution: => fixed * milestone: => 8.4.1 Comment: Indeed they were in 15f788f5e5096641245a4f060600a6db9cbc2c4e. A note about this was added to the release notes in c1bc923b08860101d0b74795ff42f6022c7fec0b. Thanks for noticing this, George! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8033#comment:38> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14615: Segfault when printing a simple string
by GHC 27 Dec '17

27 Dec '17

#14615: Segfault when printing a simple string -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: Christmas | 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 segfaults on GHC 8.2.1 and 8.3.20171208 {{{#!hs -- Segfault.hs main = do let xs = [1,1,1,1,1,1,5,0,1,1,1,1,1,4,2,4,0,1,1,1,1,4,2,2,2,4,0,1,1,1,4,2,3,2,2,3,4,0,1,1,4,3,2,2,3,2,2,2,4,0,1,4,2,2,3,2,2,2,3,2,2,4,0,4,2,3,2,2,2,3,2,2,3,2,2,4,0,1,1,1,1,1,1,2,0,1,1,1,1,1,1,2] let f ?? x = fmap ($ x) f putStrLn (traverse ((??) (!!)) xs "\n #%.t") }}} when running it as {{{ $ runghc -ignore-dot-ghci -dcore-lint -fdefer-type-errors Segfault.hs Segmentation fault: 11 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14615> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14612: unsolved constraints, panic during compilation
by GHC 26 Dec '17

26 Dec '17

#14612: unsolved constraints, panic during compilation -------------------------------------+------------------------------------- Reporter: msk | 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: -------------------------------------+------------------------------------- Code: {{{#!hs import Graphics.X11.Xlib getWindowRect :: Display -> Window -> IO Rectangle getWindowRect dpy w = fmap makeRect (getWindowAttributes dpy w) }}} Error: {{{ # ghc main.hs [1 of 1] Compiling Main ( main.hs, main.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): initTc: unsolved constraints WC {wc_insol = [W] makeRect_a1LX :: t_a1LW[tau:1] (CHoleCan: makeRect) [W] getWindowAttributes_a1M2 :: t_a1M1[tau:1] (CHoleCan: getWindowAttributes)} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Compiler: {{{ ghc --version The Glorious Glasgow Haskell Compilation System, version 8.0.2 }}} Graphics.X11.Xlib from the ArchHaskell package: {{{ haskell-x11 1.8.x0-1 }}} Frankly, I'm just following the request made by the compiler output "Please report this as a GHC bug" and have no idea what's going on. Hopefully this isn't spurious. Let me know if I can help at all. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14612> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14620: Polymorphic functions not easily recognized as join points
by GHC 26 Dec '17

26 Dec '17

#14620: Polymorphic functions not easily recognized as join points -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 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: #14610 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This grew out of ticket:14610#comment:3. If I write {{{#!hs foo :: forall a. (Int -> Bool) -> Int -> a -> a foo p = go where go :: Int -> a -> a go !n a | p n = a | otherwise = go (n + 1) a }}} then I get {{{ foo = \ (@ a_aYZ) (p_aWO :: Int -> Bool) (eta_B2 :: Int) (eta1_B1 :: a_aYZ) -> case eta_B2 of { GHC.Types.I# ww1_s1bZ -> joinrec { $wgo_s1c1 [InlPrag=NOUSERINLINE[0], Occ=LoopBreaker] :: GHC.Prim.Int# -> a_aYZ -> a_aYZ [LclId[JoinId(2)], Arity=2, Str=<L,U><S,1*U>, Unf=OtherCon []] $wgo_s1c1 (ww2_X1cu :: GHC.Prim.Int#) (w_s1bW :: a_aYZ) = case p_aWO (GHC.Types.I# ww2_X1cu) of { False -> jump $wgo_s1c1 (GHC.Prim.+# ww2_X1cu 1#) w_s1bW; True -> w_s1bW }; } in jump $wgo_s1c1 ww1_s1bZ eta1_B1 } }}} But if I make `go` polymorphic, {{{#!hs foo :: (Int -> Bool) -> Int -> a -> a foo p = go where go :: Int -> b -> b go !n a | p n = a | otherwise = go (n + 1) a }}} I get a wrapper and this worker: {{{#!hs T14610.$wfoo = \ (@ a_s1cm) (w_s1cn :: Int -> Bool) (ww_s1cs :: GHC.Prim.Int#) (w1_s1cp :: a_s1cm) -> letrec { $wgo_s1cl [InlPrag=NOUSERINLINE[0], Occ=LoopBreaker] :: forall b. GHC.Prim.Int# -> b -> b [LclId, Arity=2, Str=<L,U><S,1*U>, Unf=OtherCon []] $wgo_s1cl = \ (@ b_s1ce) (ww1_s1cj :: GHC.Prim.Int#) (w2_s1cg :: b_s1ce) -> case w_s1cn (GHC.Types.I# ww1_s1cj) of { False -> $wgo_s1cl @ b_s1ce (GHC.Prim.+# ww1_s1cj 1#) w2_s1cg; True -> w2_s1cg }; } in $wgo_s1cl @ a_s1cm ww_s1cs w1_s1cp }}} This distinction remains as `let` vs. `let-no-escape` in STG. As Joachim Breitner's comments seem to suggest, we could probably recognize this by applying the static argument transformation to the type argument of `go`. But we don't currently have any machinery for doing that, I don't think. Furthermore, that would fail with polymorphic recursion even if the only type changes are from `newtype`. That said, the SAT approach would presumably help when the worker has a non-essential type signature for clarity. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14620> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14616: panic! initTc: unsolved constraints
by GHC 25 Dec '17

25 Dec '17

#14616: panic! initTc: unsolved constraints -------------------------------------+------------------------------------- Reporter: w-j-w | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 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: -------------------------------------+------------------------------------- New haskeller here, I was doing an exercise at http://exercism.io/exercises/haskell /rotational-cipher/readme and got the following error message from the compiler. {{{ Compiling Main ( RotationalCipher.hs, .stack-work/dist/x86_64 -linux-tinfo6/Cabal-1.24.2.0/build/Main.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): initTc: unsolved constraints WC {wc_insol = [W] find_a7hU :: t_a7hT[tau:1] (CHoleCan: find) [W] find_a7iF :: t_a7iE[tau:1] (CHoleCan: find)} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Progress: 16/17 -- While building custom Setup.hs for package rotational-cipher-1.1.0.1 using: /home/websterw/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal- simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2 --builddir=.stack-work/dist/x86_64 -linux-tinfo6/Cabal-1.24.2.0 build lib:rotational-cipher test:test --ghc- options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 }}} I was using the normal project setup that exercism uses for this problem, with my code residing a file called `RotationalCipher.hs`. The contents of this file are as follows. {{{ rotate :: Int -> String -> String rotate n = map (rot n) rot :: Int -> Char -> Char rot i c | c `elem` ['a'..'z'] = let translate = zip (lowershift n) ['a'..'z'] in fst (find (\x -> snd x == c) translate) | c `elem` ['A'..'Z'] = let translate = zip (uppershift n) ['A'..'Z'] in fst (find (\x -> snd x == c) translate) | otherwise = c where lowershift n = take 26 $ drop n $ cycle ['a'..'z'] uppershift n = take 26 $ drop n $ cycle ['A'..'Z'] }}} The error occured when I ran `stack test` I am using fedora linux as my operating system on x86_64 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14616> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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