October 2015 - ghc-tickets

[GHC] #10319: Eta expand PAPs
by GHC 20 Oct '15

20 Oct '15

#10319: Eta expand PAPs -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- SPJ writes in ticket:10260#comment:11: But see this note in SimplUtils: {{{ Note [Do not eta-expand PAPs] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We used to have old_arity = manifestArity rhs, which meant that we would eta-expand even PAPs. But this gives no particular advantage, and can lead to a massive blow-up in code size, exhibited by Trac #9020. Suppose we have a PAP foo :: IO () foo = returnIO () Then we can eta-expand do foo = (\eta. (returnIO () |> sym g) eta) |> g where g :: IO () ~ State# RealWorld -> (# State# RealWorld, () #) But there is really no point in doing this, and it generates masses of coercions and whatnot that eventually disappear again. For T9020, GHC allocated 6.6G beore, and 0.8G afterwards; and residency dropped from 1.8G to 45M. But note that this won't eta-expand, say f = \g -> map g Does it matter not eta-expanding such functions? I'm not sure. Perhaps strictness analysis will have less to bite on? }}} The worse code for the un-eta-expanded code for last is perhaps an example of the last paragraph! And yet the comment is reasonably convincing. I'm not sure what to do here. One thing that might be worth trying is to eta-expand as far as poss without bumping into a coercion. That would expand last but not foo. Want to try that? We may fix last but there are sure to be other cases, and the more robust the optimisations the better. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10319> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10350: Should be able to specify path for eventlog output.
by GHC 20 Oct '15

20 Oct '15

#10350: Should be able to specify path for eventlog output. -------------------------------------+------------------------------------- Reporter: literon | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 7.10.1 System | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Currently it is a fixed path, but the binary might run in an env where write access is restricted. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10350> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10971: ExtendedDefaultRules defaults to [] for Foldable/Traversable
by GHC 20 Oct '15

20 Oct '15

#10971: ExtendedDefaultRules defaults to [] for Foldable/Traversable -------------------------------------+------------------------------------- Reporter: kanetw | Owner: Type: feature | Status: new request | Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: 10963 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- From goldfire: > Extend -XExtendedDefaultRules to allow defaulting when one of the classes involved is Foldable or Traversable. (See the current rules here.) This will mean, essentially, that there will be two lists of default types, one list at kind * and one at kind * -> *. Both lists should be settable by the user by the default directive. (GHC can figure out which list is being set quite easily.) The default default list for * -> * will be []. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10971> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10457: Revise/remove custom mapM implementation for lists
by GHC 20 Oct '15

20 Oct '15

#10457: Revise/remove custom mapM implementation for lists -------------------------------------+------------------------------------- Reporter: dolio | Owner: Type: task | Status: new Priority: normal | Milestone: 7.10.2 Component: | Version: 7.10.1 libraries/base | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Recently, Simon Marlow asked why the list instance for Traversable had a custom mapM implementation that used the Monad operations. Having looked a bit, I don't think there's any good reason. The only fusion that the custom mapM can participate in is due to it being written as foldr, but traverse is, as well. So as long as 'mapM = traverse' is able to inline appropriately, there should be no difference. Further, this can be changed, in principle, for 7.10.2. It doesn't change any types, only the implementation. mapM = traverse is the class default definition, so this could possibly be completed by just removing the custom definition. Link to the libraries thread: https://mail.haskell.org/pipermail/libraries/2015-May/025708.html -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10457> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10975: At program exit, finalizer runs while foreign function is running
by GHC 20 Oct '15

20 Oct '15

#10975: At program exit, finalizer runs while foreign function is running -------------------------------------+------------------------------------- Reporter: akio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Incorrect result (amd64) | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code prints "finalized", which means the finalizer runs while the "call" function is still running. Steps to reproduce: {{{ % ghc finalizer.hs foreign.c -threaded % ./finalizer }}} finalizer.hs: {{{#!hs import Control.Concurrent import Control.Monad import Foreign.C.Types import Foreign.ForeignPtr import Foreign.Ptr main :: IO () main = do _ <- forkIO $ do fptr <- newForeignPtr finalizer nullPtr forever $ withForeignPtr fptr call threadDelay 1000000 foreign import ccall "&finalizer" finalizer :: FunPtr (Ptr CInt -> IO ()) foreign import ccall "call" call :: Ptr CInt -> IO () }}} foreign.c {{{#!c #include <stdio.h> int finalized = 0; void finalizer(int *a) { finalized = 1; puts("finalizer"); } void call(int *a) { int i; unsigned w = 0; puts("begin call"); for(i = 0; i < 100000000; i++) { if(finalized) puts("finalized"); w += i; } printf("end call: %u\n", w); } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10975> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4012: Compilation results are not deterministic
by GHC 20 Oct '15

20 Oct '15

#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: patch Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, Wiki Page: | Phab:D1268 -------------------------------------+------------------------------------- Comment (by nomeata): > #10424 is related: "Build path leaks into ABI hashes". Are all tickets matching the regex `#[4012]+` related? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:125> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10380: "thread blocked indefinitely" exception while blocking on a socket
by GHC 20 Oct '15

20 Oct '15

#10380: "thread blocked indefinitely" exception while blocking on a socket -------------------------------------+------------------------------------- Reporter: akio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.10.1 libraries/base | Operating System: Linux Keywords: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- First start a TCP server, e.g. nc. {{{ % nc localhost -l 1234 > /dev/null }}} On another shell, compile the following program and run it: {{{ % ghc -threaded sock.hs % ./sock localhost 1234 receiver: thread blocked indefinitely in an MVar operation }}} {{{#!hs {-# LANGUAGE ViewPatterns #-} import Control.Applicative -- GHC 7.8 compatibility import Control.Concurrent import qualified Control.Exception as Ex import Control.Monad import qualified Data.ByteString.Char8 as S import Network.Socket import qualified Network.Socket.ByteString as Sock import Network.BSD (getHostByName, hostAddresses) import System.Environment import System.Mem main :: IO () main = do [host, read -> fromInteger -> port] <- getArgs sock <- connectTo host port forkVerbose "sender" $ forever $ do _ <- Sock.send sock $ S.replicate 40000 '0' return () forkVerbose "receiver" $ forever $ do dat <- Sock.recv sock 2048 putStrLn $ "received: " ++ show dat forever $ do threadDelay 1000000 performGC forkVerbose :: String -> IO () -> IO () forkVerbose name act = void $ forkIO $ do act; msg "exiting normally" `Ex.catch` \e -> msg $ show (e :: Ex.SomeException) where msg s = putStrLn $ name ++ ": " ++ s connectTo :: HostName -> PortNumber -> IO Socket connectTo hostName port = do addr <- SockAddrInet port <$> lookupHost hostName sock <- socket AF_INET Stream 0 connect sock addr return sock lookupHost :: String -> IO HostAddress lookupHost name = do hostInfo <- getHostByName name case hostAddresses hostInfo of [] -> error ("Invalid host name: " ++ name) (a:_) -> return a }}} GHC 7.8.3 doesn't have this problem. I suspect that this is a regression in the event manager. When there is an event, `GHC.Event.Manager.onFdEvent` seems to remove all callbacks associated to the `fd`, whether or not they match the current event. In the program above, the callback for `recv` may be removed permanently when the socket becomes ready for `send`ing, causing the "receiver" thread to deadlock. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10380> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10388: GHC panic when compiling Yesod app
by GHC 20 Oct '15

20 Oct '15

#10388: GHC panic when compiling Yesod app -------------------------------------+------------------------------------- Reporter: chfi | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: MacOS X Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- When compiling a Yesod app, using 'yesod devel', GHC crashes with the following error: {{{ <no location info>: ghc: panic! (the 'impossible' happened) (GHC version 7.10.1 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/yb/98yhr6bj5fg3z68prq2gxs6w0000gn/T/ghc99761_0/libghc99761_51.dylib, 5): Symbol not found: _adverzuGWP0VNzzhgmvBNANratclKO_SubscriptionType_zdfPersistFieldKey_closure Referenced from: /var/folders/yb/98yhr6bj5fg3z68prq2gxs6w0000gn/T/ghc99761_0/libghc99761_51.dylib Expected in: flat namespace in /var/folders/yb/98yhr6bj5fg3z68prq2gxs6w0000gn/T/ghc99761_0/libghc99761_51.dylib }}} Specifically, I'm using Yesod's mkPersist to create a data type, and it works fine, until I make said type an instance of FromJSON, in which case the above panic occurs. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10388> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10390: Constraint order must match with RankNTypes
by GHC 20 Oct '15

20 Oct '15

#10390: Constraint order must match with RankNTypes -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.8.4 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- In the following code, GHC will not compile unless the constraints on the higher-rank function have the same *order* as the method declaration in `ApPair`. {{{#!hs {-# LANGUAGE RankNTypes #-} class ApPair r where apPair :: (forall a . (ApPair a, Num a) => Maybe a) -> Maybe r instance (ApPair a, ApPair b) => ApPair (a,b) where apPair = apPair' apPair' :: (ApPair b, ApPair c) => (forall a . (ApPair a, Num a) => Maybe a) -> Maybe (b,c) apPair' f = let (Just a) = apPair f (Just b) = apPair f in Just $ (a, b) }}} That is, the following does *not* compile: {{{#!hs apPair' :: (ApPair b, ApPair c) => (forall a . (Num a, ApPair a) => Maybe a) -> Maybe (b,c) apPair' f = let (Just a) = apPair f (Just b) = apPair f in Just $ (a, b) }}} GHC probably shouldn't care about lexical matching when checking constraints. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10390> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #4012: Compilation results are not deterministic
by GHC 20 Oct '15

20 Oct '15

#4012: Compilation results are not deterministic -------------------------------------+------------------------------------- Reporter: kili | Owner: niteria Type: bug | Status: patch Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 6.12.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: #10424 | Differential Rev(s): Phab:D910, | Phab:D1073, Phab:D1133, Phab:D1192, Wiki Page: | Phab:D1268 -------------------------------------+------------------------------------- Changes (by thomie): * related: => #10424 Comment: #10424 is related: "Build path leaks into ABI hashes". -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/4012#comment:124> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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