June 2014 - ghc-tickets

[GHC] #8295: T4850 deadlocks when run with -Ds on Windows (also it's failing)
by GHC 03 Nov '14

03 Nov '14

#8295: T4850 deadlocks when run with -Ds on Windows (also it's failing) --------------------------+------------------------------------------------ Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.7 Runtime System | Operating System: Windows Keywords: | Type of failure: Incorrect result at runtime Architecture: x86_64 | Test Case: T4850 (amd64) | Blocking: Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ T4850 has been failing recently, reporting too *few* OS threads allocated. That's pretty odd. What is also odd (and much less good) is that T4850 is deadlocking when you run it with `-Ds`. Uh oh! {{{ bash.exe-3.1$ ./T4850 +RTS -Ds 7eb0: created capset 0 of type 2 7eb0: created capset 1 of type 3 7eb0: cap 0: initialised 7eb0: assigned cap 0 to capset 0 7eb0: assigned cap 0 to capset 1 7eb0: allocated 1 more capabilities 7eb0: new task (taskCount: 1) 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: created thread 1 7eb0: new bound thread (1) 7eb0: cap 0: schedule() 7eb0: cap 0: running thread 1 (ThreadRunGHC) 7eb0: cap 0: created thread 2 7eb0: cap 0: thread 1 stopped (finished) 7eb0: bound thread (1) finished 7eb0: starting new worker on capability 0 7eb0: new worker task (taskCount: 2) 7eb0: task exiting 7eb0: new task (taskCount: 2) 7eb0: returning; I want capability 0 7fc0: cap 0: schedule() 7fc0: giving up capability 0 7fc0: passing capability 0 to worker 0x7eb0 7eb0: resuming capability 0 7eb0: cap 0: created thread 3 7eb0: new bound thread (3) 7eb0: cap 0: schedule() 7eb0: giving up capability 0 7eb0: passing capability 0 to worker 0x7fc0 7fc0: woken up on capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to bound task 0x7eb0 7eb0: woken up on capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (suspended while making a foreign call) 7eb0: starting new worker on capability 0 7eb0: new worker task (taskCount: 3) 7eb0: returning; I want capability 0 7b50: cap 0: schedule() 7b50: giving up capability 0 7b50: passing capability 0 to bound task 0x7eb0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: created thread 4 7eb0: cap 0: thread 3 stopped (blocked on an MVar) thread 3 @ 00e03bbc is blocked on an MVar @ 00e021e4 (TSO_DIRTY) 7eb0: giving up capability 0 7eb0: passing capability 0 to worker 0x7b50 7b50: woken up on capability 0 7b50: resuming capability 0 7b50: cap 0: running thread 4 (ThreadRunGHC) 7b50: cap 0: thread 4 stopped (suspended while making a foreign call) 7b50: starting new worker on capability 0 7b50: new worker task (taskCount: 4) 7b50: new task (taskCount: 4) 7b50: returning; I want capability 0 7de4: cap 0: schedule() 7de4: giving up capability 0 7de4: passing capability 0 to worker 0x7b50 7b50: resuming capability 0 7b50: cap 0: created thread 5 7b50: new bound thread (5) 7b50: cap 0: schedule() 7b50: cap 0: running thread 5 (ThreadRunGHC) 7b50: cap 0: thread 5 stopped (finished) 7b50: bound thread (5) finished 7b50: freeing capability 0 7b50: task exiting 7b50: returning; I want capability 0 7b50: resuming capability 0 7b50: cap 0: running thread 4 (ThreadRunGHC) 7b50: cap 0: waking up thread 3 on cap 0 7b50: cap 0: thread 4 stopped (finished) 7b50: giving up capability 0 7b50: passing capability 0 to bound task 0x7eb0 7eb0: woken up on capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (suspended while making a foreign call) 7eb0: freeing capability 0 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (suspended while making a foreign call) 7eb0: freeing capability 0 4 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: created thread 6 7eb0: cap 0: thread 3 stopped (blocked on an MVar) thread 3 @ 00e03bbc is blocked on an MVar @ 00e021e4 (TSO_DIRTY) 7eb0: giving up capability 0 7eb0: passing capability 0 to worker 0x7b50 7b50: woken up on capability 0 7b50: resuming capability 0 7b50: cap 0: running thread 6 (ThreadRunGHC) 7b50: cap 0: thread 6 stopped (suspended while making a foreign call) 7b50: freeing capability 0 7b50: new task (taskCount: 4) 7b50: returning; I want capability 0 7b50: resuming capability 0 7b50: cap 0: created thread 7 7b50: new bound thread (7) 7b50: cap 0: schedule() 7b50: cap 0: running thread 7 (ThreadRunGHC) 7b50: cap 0: thread 7 stopped (finished) 7b50: bound thread (7) finished 7b50: freeing capability 0 7b50: task exiting 7b50: returning; I want capability 0 7b50: resuming capability 0 7b50: cap 0: running thread 6 (ThreadRunGHC) 7b50: cap 0: waking up thread 3 on cap 0 7b50: cap 0: thread 6 stopped (finished) 7b50: giving up capability 0 7b50: passing capability 0 to bound task 0x7eb0 7eb0: woken up on capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (suspended while making a foreign call) 7eb0: freeing capability 0 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (suspended while making a foreign call) 7eb0: freeing capability 0 4 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (yielding) 7eb0: cap 0: running thread 3 (ThreadRunGHC) 7eb0: cap 0: thread 3 stopped (finished) 7eb0: bound thread (3) finished 7eb0: freeing capability 0 7eb0: task exiting 7eb0: new task (taskCount: 4) 7eb0: returning; I want capability 0 7eb0: resuming capability 0 7eb0: cap 0: created thread 8 7eb0: new bound thread (8) 7eb0: cap 0: schedule() 7eb0: cap 0: running thread 8 (ThreadRunGHC) 7eb0: cap 0: thread 8 stopped (finished) 7eb0: bound thread (8) finished 7eb0: freeing capability 0 7eb0: task exiting 7eb0: new task (taskCount: 4) 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7eb0: returning; I want capability 0 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (suspended while making a foreign call) 7fc0: passing capability 0 to worker 0x7eb0 7fc0: returning; I want capability 0 7fc0: resuming capability 0 7fc0: cap 0: running thread 2 (ThreadRunGHC) 7fc0: cap 0: thread 2 stopped (yielding) 7fc0: SCHED_INTERRUPTING 7fc0: cap 0: requesting sequential GC 7fc0: grabbing all the capabilies (0/1) all threads: threads on capability 0: thread 2 @ 00e037bc is not blocked (TSO_DIRTY) other threads: 7fc0: deleting all threads 7fc0: cap 0: raising exception in thread 2. 7fc0: cap 0: starting GC 7fc0: cap 0: GC working 7fc0: cap 0: GC idle 7fc0: cap 0: GC done 7fc0: cap 0: GC idle 7fc0: cap 0: GC done 7fc0: cap 0: GC idle 7fc0: cap 0: GC done 7fc0: cap 0: all caps stopped for GC 7fc0: cap 0: finished GC 7fc0: SCHED_SHUTTING_DOWN 7fc0: giving up capability 0 7fc0: passing capability 0 to worker 0x7eb0 7eb0: resuming capability 0 7eb0: passing capability 0 to worker 0x7fc0 7eb0: shutting down capability 0, attempt 0 7fc0: woken up on capability 0 7eb0: runnable threads or workers still alive, yielding 7eb0: passing capability 0 to worker 0x7fc0 7eb0: shutting down capability 0, attempt 1 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 2 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 3 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 4 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 5 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 6 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 7 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 8 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 9 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 10 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 11 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 12 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 13 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 14 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 15 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 16 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 17 7eb0: not owner, yielding 7eb0: shutting down capability 0, attempt 18 7eb0: not owner, yielding ... }}} ad infinitum. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8295> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8571: Validation fails
by GHC 03 Nov '14

03 Nov '14

#8571: Validation fails ----------------------------------+--------------------------------- Reporter: khyperia | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 7.6.3 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------------+--------------------------------- {{{ =====> T5267(normal) 50 of 3812 [0, 0, 0] cd ./arrows/should_compile && 'c:/Users/Evan/Documents/ghc/bindisttest/install dir/bin/ghc.exe' -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-us er-package-db -rtsopts -fno-ghci-history -c T5267.hs >T5267.comp.stderr 2>&1 Compile failed (status 256) errors were: T5267.hs:11:15: tee: standard output: Permission denied }}} followed by an infinite hang. If I comment out that specific test, another test fails a few tests later. If I comment out that one, another one fails a few later. If I comment out *that* one... you get the picture. Running as administrator does not solve the permission denied issue. I am on Windows 8.1, if that matters. I think, I am not sure, that any test with expect_broken in them hangs without moving on. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8571> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8967: Add syntax for creating finite maps and sets
by GHC 02 Nov '14

02 Nov '14

#8967: Add syntax for creating finite maps and sets ------------------------------------+------------------------------------- Reporter: tibbe | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | 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: | ------------------------------------+------------------------------------- Many languages have syntax for creating maps. Commonly used syntax is either {{{ {key1: value1, key2: value2, ...} }}} or {{{ {key1 => value1, key2 => value2, ...} }}} Since few Haskellers (with the notable exception of SPJ) use the curly bracket Haskell syntax for layout, I thought we could co-opt it and instead use it for map (and set literals.) The feature would of course be protected by a language pragma as to not break old code. Strawman proposal: `{key1: value1, key2: value2, ...}` desugars to `fromList [(key1, value1), (key2, value2), ...]`, using a new type class: {{{#!haskell class IsMap m where type Key m type Value m fromList :: [(Key m, Value m)] -> m }}} `{:}` is the literal for empty maps. Analogously, `{value1, value2, ...}` desugars to `fromList [value1, value2, ...]`, using a new type class: {{{#!haskell class IsSet m where type Item m fromList :: [Item m] -> m }}} `{}` is the literal for empty sets. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8967> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9084: Template Haskell should warn when it encounters an unencodable pragma
by GHC 02 Nov '14

02 Nov '14

#9084: Template Haskell should warn when it encounters an unencodable pragma ------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- When I say this {{{ {-# LANGUAGE TemplateHaskell #-} {-# OPTIONS_GHC -Wall #-} module Bug where $([d| class C a where meth :: a -> a meth = undefined -- give a (silly) default {-# MINIMAL meth #-} |]) instance C Int }}} I get no warnings. I'm not surprised that TH doesn't handle every pragma that GHC knows about, but it should issue a (suppressable) warning when it discards one. I can fix this one. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9084> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9236: hGetContents leads to late/silent failures
by GHC 31 Oct '14

31 Oct '14

#9236: hGetContents leads to late/silent failures ------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | 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: | ------------------------------------+------------------------------------- A common newbie error: {{{ #!haskell withFile "file" ReadMode hGetContents >>= putStr }}} The problem, of course, is that the result of `withFile "file" ReadMode hGetContents` isn't forced until `putStr` is executed, at which point the file has already been closed. The Haskell report doesn't specify what it will find, and, at least in 7.6.3, it finds the string empty. The behavior that seems most correct to me would be to guarantee that if a file has not been completely read (or read up to an I/O error) when it is closed, then its contents should be reported as something like `"Four score and seven years ag"++error "Forcing a suspended computation led to an attempted read from a handle that was already closed."` Since the current system apparently puts an `[]` as a temporary marker while waiting to see what the rest of the list will be, I imagine that the fix is as simple as putting the error thunk there instead. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9236> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas
by GHC 31 Oct '14

31 Oct '14

#9242: Implement {-# OVERLAPPABLE #-} and {-# INCOHERENT #-} pragmas ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The language extensions `-XIncoherentInstances` and `-XOverlappingInstances` (described in [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class- extensions.html#instance-overlap the user manual]) apply to every instance declaration in the module. Internally, however, GHC records this information on a per-instance-declaration basis. It would be much better for the programmer to be able to control these matters on a per-instance-declaration basis. Thus: {{{ instance Show a => Show [a] where {-# OVERLAPPABLE #-} ... instance Show [Char] where ... }}} We came across the need for this when discussing the `Typeable` instances. We have a generic instance like this: {{{ instance (Typeable f, Typeable a) => Typeable (f a) where .... }}} but also want {{{ instance KnownNat n => Typeable (n :: Nat) where ... }}} If we seek `(Typeable (x::Nat))`, we should pick the second instance even though in principle you might imagine that `x` might be instantiated to `(f a)`, for some `f` and `a`. But we know that there are no type constructors `f` of kind `blah -> Nat`, so this can never happen and it's safe to pick the second instance. So a local `{-# INCOHERENT #-}` pragma for this particular instance declaration would be very useful to express this fact. {{{ instance KnownNat n => Typeable (n :: Nat) where {-# INCOHERENT #-} ... }}} Quite apart from this special case, it's plain better to have per-instance control * Rather than a remote per-module flag, the pragma draws attention that ''this particular instance'' is incoherent, overlappable or whatever. * The current situation almost certainly means that more instances are marked overlapping than are really necessary. I have some design questions. * Where should the pragma appear, syntactically? {{{ instance {-# OVERLAPPABLE #-} Show a => Show [a] where ... or instance Show a => Show [a] {-# OVERLAPPABLE #-} where ... or instance Show a => Show [a] where {-# OVERLAPPABLE #-} }}} Remember that `SPECIALISE INSTANCE` pragmas appear in the third of the above positions, so I mildly favour that. * The user manual (link above) allows overlap if ''either'' instance is compiled with `-XOverlappingInstances` (see the rules towards the end of [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class- extensions.html#instance-overlap 7.6.3.5). It would be more explicit to have two pragmas, one to say "I can be overlapped" and one to say "I can overlap something else". The rule would then be that "either IX is marked `{-# OVERLAPPABLE #-}` or IY is marked `{-# OVERLAPPING #-}`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9242> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8890: segfault on Windows 7 i386
by GHC 27 Oct '14

27 Oct '14

#8890: segfault on Windows 7 i386 ----------------------------+--------------------------------------- Reporter: ganesh | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc2 Keywords: | Operating System: Windows Architecture: x86 | Type of failure: Compile-time crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------+--------------------------------------- This minimal example causes the GHC 7.8.1 i386 RC1 and RC2 binaries to segafult on two different Window 7 machines. It doesn't happen with the x86_64 binaries and it doesn't happen on the one Windows 8.1 machine I tried. {{{ {-# LANGUAGE GADTs #-} module Test1 where data T t where T :: T () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8890> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9006: GHC accepts import of private data constructor if it has the same name as the type
by GHC 27 Oct '14

27 Oct '14

#9006: GHC accepts import of private data constructor if it has the same name as the type --------------------------+------------------------------------------------ Reporter: | Owner: Lemming | Status: new Type: bug | Milestone: Priority: normal | Version: 7.8.2 Component: | Operating System: Unknown/Multiple Compiler | Type of failure: GHC accepts invalid program Keywords: | Test Case: Architecture: | Blocking: Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ {{{ $ cat A.hs B.hs module A (T) where data T = T module B where import A (T(T)) }}} `ghci-7.8.2` accepts module B, whereas `ghci-7.6.3` and `ghci-7.4.2` say: {{{ B.hs:3:11: Module `A' does not export `T(T)' }}} For this bug to happen it is important, that the data constructor has the same name as the type. I.e. if you rename the data constructor to, say, `Cons`, then `ghci-7.8.2` will emit the same error as earlier versions. The bug is not dramatic, since if you try to actually use the imported data constructor then ghc will say {{{ B.hs:20:5: Not in scope: data constructor ‘T’ }}} However this error message is very confusing, because it suggests that `T` is not in scope although you imported it correctly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9006> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8345: A more efficient atomicModifyIORef'
by GHC 27 Oct '14

27 Oct '14

#8345: A more efficient atomicModifyIORef' ------------------------------------+------------------------------------- Reporter: parcs | Owner: Type: task | Status: new Priority: normal | Milestone: Component: libraries/base | 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: | ------------------------------------+------------------------------------- `atomicModifyIORef'` is currently defined as: {{{ #!haskell atomicModifyIORef' ref f = do b <- atomicModifyIORef ref (\x -> let (a, b) = f x in (a, a `seq` b)) b `seq` return b }}} This doesn't seem to be the best we can do, though. The following implementation exhibits a speedup of 1.7x (vanilla RTS) / 1.4x (threaded RTS) over the current implementation: {{{ #!haskell atomicModifyIORef' ref f = do b <- atomicModifyIORef ref $ \a -> case f a of v@(a',_) -> a' `seq` v b `seq` return b }}} The differences between this version and the current version are: 1. the lambda is now strict in `f a`, and 2. a new result tuple is no longer being allocated. Is there a good reason why `atomicModifyIORef'` is not already defined this way? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8345> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9031: ghc panic: RegAlloc.Liveness.computeLivenss
by GHC 27 Oct '14

27 Oct '14

#9031: ghc panic: RegAlloc.Liveness.computeLivenss -----------------------------------+--------------------------------------- Reporter: jwlato | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- I have some code where ghc consistently panics with {{{ RegAlloc.Liveness.computeLivenss SCCs aren't in reverse dependent order bad blockId c1kek }}} The only reference I can find to that block in the dumped output is here: {{{ REC c1kej: movq $block{v c1keo}_info,(%rbp) movsd 7(%rbx),%vSSE_s1ivM movsd 15(%rbx),%vSSE_s1ivN movq 96(%rbp),%rbx movsd %vSSE_s1ivN,88(%rbp) movsd %vSSE_s1ivM,96(%rbp) testq $7,%rbx jne _c1keo jmp _c1kep c1kpo: movq $block{v c1kej}_info,(%rbp) movq %vI_s1it5,%rbx movq $0,120(%rbp) testq $7,%rbx jne _c1kej jmp _c1kek, }}} There doesn't appear to be any reference to {{{c1kpo}}} either. Unfortunately I don't yet have a test case I can provide; I'll keep working on that. Building with -dcore-lint and -dcmm-lint don't show any extra errors. This is with ghc-7.8.2 using NCG. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9031> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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