October 2018 - ghc-tickets

[GHC] #13595: Should ‘coerce’ be levity polymorphic?
by GHC 14 Feb '19

14 Feb '19

#13595: Should ‘coerce’ be levity polymorphic? -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) 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: #13592 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'm not able to write `coerce @Int# @Int#` or `coerce :: Double# -> Double#`, just checking to see if its intentional or not {{{ >>> :set -XTypeApplications >>> :set -XMagicHash >>> import Data.Coerce >>> import GHC.Exts >>>> :t coerce @Int coerce @Int :: Coercible b Int => Int -> b >>> :t coerce @Int# <interactive>:1:1: error: Couldn't match a lifted type with an unlifted type When matching types b :: * Int# :: TYPE 'IntRep <interactive>:1:9: error: • Expecting a lifted type, but ‘Int#’ is unlifted • In the type ‘Int#’ In the expression: coerce @Int# }}} This was needed for #13592. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13595> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15219: Implement UnliftedNewtypes proposal
by GHC 14 Feb '19

14 Feb '19

#15219: Implement UnliftedNewtypes proposal -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple UnliftedNewtypes | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The unlifted newtypes proposal is described here: https://github.com/ghc- proposals/ghc-proposals/blob/master/proposals/0013-unlifted-newtypes.rst I am going to be working on it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15219> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15622: Generalize `E{0,1,2,3,6,9,12}` from `Data.Fixed`
by GHC 11 Feb '19

11 Feb '19

#15622: Generalize `E{0,1,2,3,6,9,12}` from `Data.Fixed` -------------------------------------+------------------------------------- Reporter: rockbmb | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: Core | Version: 8.4.3 Libraries | Keywords: base, | Operating System: Unknown/Multiple Data.Fixed | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Hello; I'm creating this email to propose a change to `Data.Fixed`. Full credit for this idea goes to Bhavik Mehta (@b-mehta on GitHub), who implemented it in this [https://github.com/dmcclean/exact-pi/pull/8 PR] for `exact- pi`. In `Data.Fixed` there are several `E`-prefixed datatypes used to represent a certain number of digits of precision in fixed-precision arithmetic. For example, `E1` has 1 decimal place, `E12` has 12. Each of them, `E{0,1,2,3,6,9,12}` is hardcoded. If more precision types are to be provided, they have to be hardcoded as well, and all of these types resemble each other. I think there is room for improvement here. Instead of having {{{#!hs data E0 instance HasResolution E0 where resolution _ = 1 }}} and repeating it as many times as there are `E` datatypes, I propose to add the following type: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} import GHC.TypeLits (Nat, KnownNat, natVal) data E (n :: Nat) }}} and then do {{{#!hs instance KnownNat n => HasResolution (E n) where resolution _ = 10^natVal (undefined :: E n) }}} just once, replacing `data E0` with `type E0 = E 0` (and the same for the rest of them) to continue reexporting these types. `E` should also be exported. I've sent an email to the Core Libraries Committee regarding this issue. This is my first contribution to GHC, if I'm doing something incorrectly please tell me. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15622> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14848: -XDuplicateRecordFields breaks record expression splices
by GHC 10 Feb '19

10 Feb '19

#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | 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: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ {-# language TemplateHaskell #-} {-# language DuplicateRecordFields #-} module Lib where import Language.Haskell.TH import Language.Haskell.TH.Syntax data A = A {x :: Int, y :: String} a = A 3 "test" test = $([e|case a of A {x = b} -> b|]) }}} Without `DuplicateRecordFields` it compiles correctly so `test = 3` but with `DuplicateRecordFields` enabled it gives: {{{ • Illegal variable name: ‘$sel:x:A’ When splicing a TH expression: case Lib.a of (Lib.A {Lib.$sel:x:A = b_0}) -> b_0 • In the untyped splice: $([| case a of { A {x = b} -> b } |]) }}} Additionally, there doesn't seem to be a workaround for munging the name manually, since the `$sel:x:A` name is the one actually in scope, there is no `A.x` like there would be normally, even when the label is not a duplicate. Is there a way to get around this? Ex: by changing the binding name somehow manually? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14848> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15091: Better occurrence analysis for join points
by GHC 10 Feb '19

10 Feb '19

#15091: Better occurrence analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Keywords: JoinPoints | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider this {{{ let x = ... in join j y = x+y in case v of A -> x B -> j 1 C -> j 2 D -> 3 }}} What does `OccAnal` say about `x`'s usage? It says `ManyOccs`! But it's plain as a pikestaff that `x` is used at most once: * Either in the `A` branch, * or in the `B` or `C` branches via `j`. If instead we had inlined `j` we'd have {{{ let x = ... in join j y = x+y in case v of A -> x B -> x + 1 C -> x + 2 D -> 3 }}} and now it's all more obvious: `x`'s occurrence info should be `OneOcc { occ_one_br = False }`, not `ManyOccs`. Does this matter? Not a great deal, but there is a reason for having `OneOcc` with `occ_one_br = False`, and it seems a shame not to take advantage. One case in point is the definition of `SimplUtils.isExitJoinId {{{ isExitJoinId :: Var -> Bool isExitJoinId id = isJoinId id && isOneOcc (idOccInfo id) && occ_in_lam (idOccInfo id) }}} Something does not cease to be an exit-join-point if it is mentioned in multiple places as above. Another use for this info is `postInlineUnconditionally`. Could we improve this situation? I think it'd be quite easy. For non- recursive join points `j = rhs` * Gather occurrence info from the RHS * Bind `j` to its occurrence info * Unleash that occurrence info at each jump-site for `j`, just as if it had been inlined. See Trac #14152, comment:40. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15091> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15449: Nondeterministic Failure on aarch64 with -jn, n > 1
by GHC 10 Feb '19

10 Feb '19

#15449: Nondeterministic Failure on aarch64 with -jn, n > 1 -------------------------------------+------------------------------------- Reporter: tmobile | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Linux Architecture: aarch64 | Type of failure: Compile-time | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC releases 8.2.1 through 8.4.3 exhibit various crashes when invoked with '-jn' where n > 1. GHCHQ's binary releases have this behavior, as well as GHCs I've cross-built on my own. In order to reproduce this issue there must be some parallelism in the module dependency graph; I've attached a test package for easily reproducing this. Use of deriving in the test modules isn't necessary to trigger this; it merely gives the compiler some work to do. The 'hscolour' package also triggers this issue reliably. To trigger the bad behavior, simply run: ghc --make -jn Main.hs -o test with n > 1 in the test-package. Running this repeatedly (removing .hi and .o files in between runs, of course), I've observed these outcomes with varying frequencies: - Segmentation fault. - Bus fault. - Compiler process sleeps indefinitely. - {{{ <no location info>: error: ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for aarch64-unknown-linux): Binary.UserData: no put_binding_name }}} - {{{ ghc: internal error: MUT_VAR_CLEAN object entered! (GHC version 8.4.3 for aarch64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted (core dumped) }}} - And most strangely: {{{ A.hs:3:1: error: • Kind signature on data type declaration has non-* return kind * • In the data declaration for ‘A’ | 3 | data A = A | ^^^^^^^^^^... }}} I have not noticed issues with any other concurrent Haskell programs on aarch64. I'm using the NVIDIA Jetson TX2 for these tests. I have not yet tried GHC 8.0.x, 8.6.x, or HEAD. I'm having trouble reproducing this in GDB; I'll report back when I've got that working. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15449> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12658: GHC 7.10.3 sometimes reports unimplemented/strange closure type 63270
by GHC 09 Feb '19

09 Feb '19

#12658: GHC 7.10.3 sometimes reports unimplemented/strange closure type 63270 --------------------------------+--------------------------------------- Reporter: clint | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: powerpc | Type of failure: Compile-time crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------+--------------------------------------- This happened when building http-link-header. {{{ ghc: internal error: scavenge: unimplemented/strange closure type 63270 @ 0xf36de0a8ghc: internal error: scavenge: unimplemented/strange closure type 63270 @ 0xf36de0a8 (GHC version 7.10.3 for powerpc_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Sometimes it segfaults instead. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12658> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15336: ./System/IO.hs accidentally overridden when running ghci
by GHC 08 Feb '19

08 Feb '19

#15336: ./System/IO.hs accidentally overridden when running ghci -------------------------------------+------------------------------------- Reporter: luqui | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: GHCi | Version: 8.2.2 Keywords: | Operating System: MacOS X Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Running ghci fails if there is a System/IO.hs module present in the current directory. Doesn't seem like desirable behavior. {{{ % mkdir System % touch System/IO.hs % ghci GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help <interactive>:1:19: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:43: error: Not in scope: ‘System.IO.stdin’ No module named ‘System.IO’ is imported. <interactive>:1:60: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:99: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:123: error: Not in scope: ‘System.IO.stdout’ No module named ‘System.IO’ is imported. <interactive>:1:140: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:179: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:203: error: Not in scope: ‘System.IO.stderr’ No module named ‘System.IO’ is imported. <interactive>:1:220: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15336> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9370: large blowup in memory usage and time when doing parallel build of xmlhtml package
by GHC 08 Feb '19

08 Feb '19

#9370: large blowup in memory usage and time when doing parallel build of xmlhtml package -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I've observed a blowup in ghc memory usage when invoked with parallel build flags. to reproduce {{{ cabal get xmlhtml-0.2.3.2 cabal install xmlhtml-0.2.3.2 --only-dependencies cd xmlhtml-0.2.3.2 }}} then {{{ cabal clean ; cabal configure --ghc-options="-j4" ; time cabal build -j4 -v3 }}} will take quite a while and use > 1gb of ram whereas {{{ cabal clean ; cabal configure --ghc-options="-j1 ; time cabal build -j1 -v3 }}} will use < 150mb of ram. Based upon the output of cabal build -j4 -v3, it looks like the parallel build is spending a lottt more time in the simplifier passes. I'm not sure what changes between the parallel and sequential builds to change this. I'll try to dig into this more in a few days, but recording this problem now before i forget. (though of course any insights would be appreciated) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9370> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8635: GHC optimisation flag ignored when importing a local module with derived type classes
by GHC 08 Feb '19

08 Feb '19

#8635: GHC optimisation flag ignored when importing a local module with derived type classes ------------------------------------+------------------------------------- Reporter: NeilMitchell | Owner: Type: bug | 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: | ------------------------------------+------------------------------------- Given Foo.hs and Bar.hs: {{{ module Foo where data Food = Food -- deriving Eq {-# OPTIONS_GHC -O2 -ddump-simpl #-} module Bar where import Foo bar :: Int -> Bool bar x = x == 72 }}} If I run: {{{ ghc --make Bar -fforce-recomp }}} I get (snipped): {{{ Bar.bar = \ (x_afk :: GHC.Types.Int) -> case x_afk of _ { GHC.Types.I# x1_alo -> case x1_alo of _ { __DEFAULT -> GHC.Types.False; 72 -> GHC.Types.True } } }}} `bar` now looks pretty well optimised. However, if I uncomment the `deriving Eq` I get: {{{ Bar.bar1 = GHC.Types.I# 72 Bar.bar2 = GHC.Classes.== @ GHC.Types.Int GHC.Classes.$fEqInt Bar.bar = \ (x_amD :: GHC.Types.Int) -> Bar.bar2 x_amD Bar.bar1 }}} Now `bar` looks like terrible code, using dictionaries, boxing etc. It seems adding `deriving` in the imported and unused module makes it ignore the optimisation level. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8635> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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