March 2018 - ghc-tickets

[GHC] #12758: Bring sanity to our performance testsuite
by GHC 28 Jan '19

28 Jan '19

#12758: Bring sanity to our performance testsuite -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Test Suite | 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: -------------------------------------+------------------------------------- The GHC testsuite's performance tests tends to be a constant source of busy-work as it requires that contributors manually bump performance numbers and propagate these changes across platforms. Moreover, the testsuite is poor at noticing performance regressions due to false positive failures (due to spurious environmental differences) and false negatives (due to the rather generous acceptance windows that many tests have). Joachim and I briefly discussed this at Hac Phi and came up with the following proposal: * We rip expected performance numbers out of the `.T` files * -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12758> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13512: GHC incorrectly warns that a variable used in a type application is unused
by GHC 27 Jan '19

27 Jan '19

#13512: GHC incorrectly warns that a variable used in a type application is unused -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple TypeApplications | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This bug is reproducible on GHC 8.0.1, 8.0.2, 8.2, and HEAD. {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeInType #-} {-# OPTIONS_GHC -Wunused-foralls #-} module Bug where import Data.Proxy proxy :: forall k (a :: k). Proxy a proxy = Proxy data SomeProxy where SomeProxy :: forall k (a :: k). Proxy a -> SomeProxy someProxy :: forall k (a :: k). SomeProxy someProxy = SomeProxy (proxy @k @a) }}} {{{ $ /opt/ghc/head/bin/ghci Bug.hs GHCi, version 8.3.20170327: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:17:23: warning: [-Wunused-foralls] Unused quantified type variable ‘(a :: k)’ In the type ‘forall k (a :: k). SomeProxy’ | 17 | someProxy :: forall k (a :: k). SomeProxy | ^^^^^^^^ Ok, modules loaded: Bug. }}} But that `a` is used in `proxy @k @a`! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13512> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9173: Better type error messages
by GHC 27 Jan '19

27 Jan '19

#9173: Better type error messages ------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | 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: | ------------------------------------+------------------------------------- Generating better type-error messages is a hoary chestnut, but Herbert brought my attention to [https://pay.reddit.com/r/haskell/comments/26tcrk/curious_with_a_bit_of_begi… this thread on reddit], which has the following idea. At the moment, from {{{ module Foo where addThree = \x -> x + 3 :: Int y = addThree $ Just 5 }}} we get this error: {{{ Foo.hs:2:20 Couldn't match expected type `Int' with actual type `Maybe a0' In the return type of a call of `Just' In the second argument of `($)', namely `Just 5' In the expression: addThree $ Just 5 }}} Maybe we could generate this instead {{{ Foo.hs:2:20 inferred: "Just 5" has type "Maybe a0" expected: second argument of "($)" must have type "Int" in the expression: addThree $ Just 5 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9173> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14259: Worker/Wrapper for sum return
by GHC 26 Jan '19

26 Jan '19

#14259: Worker/Wrapper for sum return -------------------------------------+------------------------------------- Reporter: jheek | Owner: (none) Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- GHC version 8.2 introduces Unboxed Sum types. It would be great if the worker/wrapper transformation could make use of this new functionality. For clarification I would expect a function like this: {{{#!haskell maybeEven :: Int -> Maybe Int maybeEven n = case even n of True -> Just n False -> Nothing }}} to be transformed into (the core equivalent) of {{{#!haskell maybeEven :: Int -> Maybe Int MaybeEven (I# n#) = case workerMaybeEven n# of (# | x #) -> Just x (# (# #) | #) -> Nothing workerMaybeEven :: Int# -> (# (# #) | Int #) {-# NOINLINE workerMaybeEven #-} workerMaybeEven n# = case even (I# n#) of True -> (# | I# n# #) False -> (# (# #) | #) }}} Currently the core output for the maybeEven worker is: {{{#!haskell Main.$wmaybeEven :: Int# -> Maybe Int Main.$wmaybeEven = \ (ww_s4WH :: Int#) -> case remInt# ww_s4WH 2# of { __DEFAULT -> GHC.Base.Nothing @ Int; 0# -> GHC.Base.Just @ Int (GHC.Types.I# ww_s4WH) } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14259> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12364: Demand analysis for sum types
by GHC 25 Jan '19

25 Jan '19

#12364: Demand analysis for sum types -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | Status: new 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: -------------------------------------+------------------------------------- While working on #10613 it crossed my mind that it might be worthwhile to expand the demand type also onto sum types. So instead of {{{ | UProd [ArgUse] -- Product }}} we would have {{{ | UData [[ArgUse]] -- Data type }}} and a function like {{{ fromMaybe :: a -> Maybe a -> b }}} would have a signature of {{{ <1*U><1*U(;1*U)> }}} which indicates that the second argument of `fromMaybe` is evaluated at most once; the first constructor of the result has no arguments, the second (separated by `;`) has one argument which is also used at most once. I could imagine that this gives a lot of useful information with parsers and other code that repeatedly retuns stuff wrapped in a `Maybe` or similar type. Now, sum types are often recursive (`[]`…), and we probably want to be smarter about recursion here. But note that this is not a new problem. If you write {{{ data Stream = Stream Int Stream Stream Stream foo (Stream 0 x y z) = 0 foo (Stream 1 x y z) = foo x foo (Stream 2 x y z) = foo y foo (Stream _ x y z) = foo z }}} you already get huge demand signatures. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12364> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12599: Add Hadrian build artifacts to gitignore
by GHC 25 Jan '19

25 Jan '19

#12599: Add Hadrian build artifacts to gitignore -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new 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: -------------------------------------+------------------------------------- Andrey wrote requesting the following, > For top-level `.gitignore`: > {{{ > # ------------------------------------------------------------------------------------- > # Hadrian's stuff. Note, **/stageN/ folders will be relocated to _build/ after > # resolving https://github.com/snowleopard/hadrian/issues/113 > # ------------------------------------------------------------------------------------- > _build/ > hadrian/ > **/stage?/ > }}} > > For `.gitignore` in affected submodules (array, deepseq, directory, filepath, > hoopl, hpc, process, utils/hsc2hs): > > {{{ > # ------------------------------------------------------------------------------------- > # Hadrian's stuff. Note, stageN/ folders will be relocated to top-level _build/ > # after resolving https://github.com/snowleopard/hadrian/issues/113 > # ------------------------------------------------------------------------------------- > stage?/ > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12599> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9476: Implement late lambda-lifting
by GHC 25 Jan '19

25 Jan '19

#9476: Implement late lambda-lifting -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- This ticket exists to coordinate work on Nick Frisby's '''late lambda- lifting''' optimisation. * Wiki page: [wiki:LateLamLift]. All the details are here. * Branch in GHC repo: `wip/llf` * Related tickets * #9279: local closure remains in final program * #9374: static argument transformation -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9476> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13253: Exponential compilation time with RWST & ReaderT stack with `-02`
by GHC 24 Jan '19

24 Jan '19

#13253: Exponential compilation time with RWST & ReaderT stack with `-02` -------------------------------------+------------------------------------- Reporter: phadej | Owner: Type: bug | Status: new 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: -------------------------------------+------------------------------------- See the attached file. The compilation time grows exponentially with additional fields in `HuteStruct`. Tried with GHC-8.0.1 and quite recent HEAD (8.2) adding a field doubles the compilation time with `-O2`. - 9: 17s - 10: 34s - 11: 83s on my machine. With `-01` around 3sec, independently of the struct size. The original issue: https://github.com/yesodweb/yesod/issues/1348 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13253> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12920: Overzealous unused-top-binds
by GHC 23 Jan '19

23 Jan '19

#12920: Overzealous unused-top-binds -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following example produces three warnings: {{{ module Foo () where type A = Int type B = A foo :: IO () foo = print (bar 3 :: B) bar :: a -> a bar = id }}} `ghci Foo -Wall` produces {{{ GHCi, version 8.0.1.20161117: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Foo ( Foo.hs, interpreted ) Foo.hs:5:1: warning: [-Wunused-top-binds] Defined but not used: type constructor or class ‘B’ Foo.hs:8:1: warning: [-Wunused-top-binds] Defined but not used: ‘foo’ Foo.hs:11:1: warning: [-Wunused-top-binds] Defined but not used: ‘bar’ Ok, modules loaded: Foo. }}} The three errors reported are inconsistent because GHC reports that `B` is unused, but somehow feels that `A` *is* used. It seems to me that two possibilities could work: 1. GHC reports 1 error: GHC should only report that `foo` is unused, since `A` is used in `B`, `B` is used in `foo`, and `bar` is used in `foo`. This seems like the best approach to me. 2. GHC reports 4 errors: One might choose to apply the definition of "unused" transitively so that, since `foo` is unused, everything used in `foo` is considered unused (unless "used" elsewhere). In this case, `A` should also be reported as unused, but it currently isn't. This definition would be exceedingly useful for removing dead code, but it also produces very noisy output when there is a lot of dead code. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12920> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13586: ghc --make seems to leak memory
by GHC 22 Jan '19

22 Jan '19

#13586: ghc --make seems to leak memory -------------------------------------+------------------------------------- Reporter: | Owner: (none) MikolajKonarski | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: #13379 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (This is probably not reproducible with a small example.) When I build this project with `cabal build` https://github.com/LambdaHack/LambdaHack/commit/138123ab13edd4db6c8143720af… the peek memory, as observed with `top`, is 10G*. When I instead interrupt the compilation with `^C` at the following point (compilation of this file take a couple of minutes, so it's easy to interrupt): {{{ [123 of 123] Compiling Game.LambdaHack.SampleImplementation.SampleMonadServer ( Game/LambdaHack/SampleImplementation/SampleMonadServer.hs, dist/build/Game/LambdaHack/SampleImplementation/SampleMonadServer.o ) }}} and then restart and continue to the end, peek memory usage in either of the two compilation parts is 5G*. So it seems `ghc --make` keeps some data that is either eventually not used or could as well be read on demand instead of kept in memory. Confirmed with 8.2.1-rc1 as well, but it's not trivial to compile due to restrictive upper bounds of many packages. *exact numerical values are made up -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13586> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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