January 2019 - ghc-tickets

[GHC] #15872: Odd pretty printing of equality constraint in kind ('GHC.Types.Eq# <>)
by GHC 06 Mar '19

06 Mar '19

#15872: Odd pretty printing of equality constraint in kind ('GHC.Types.Eq# <>) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Maybe indicative of deeper issues: {{{#!hs {-# Language RankNTypes #-} {-# Language DataKinds #-} {-# Language PolyKinds #-} {-# Language GADTs #-} import Data.Kind data WHICH = OP | OPOP data Fun :: forall (a :: WHICH). a ~ OP => Type -> Type -> Type where MkFun :: (a -> b) -> Fun a b }}} There are some artifacts `Fun ('GHC.Type.Eq# <>)` in the type of `MkFun` that shouldn't be there {{{ $ ~/code/unmodifiedghc/inplace/bin/ghc-stage2 --interactive -ignore-dot- ghci ~/hs/655_bug.hs GHCi, version 8.7.20181029: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /home/baldur/hs/655_bug.hs, interpreted ) Ok, one module loaded. *Main> :t MkFun MkFun :: (a -> b) -> Fun ('GHC.Types.Eq# <>) a b *Main> :k Fun Fun :: (a ~ 'OP) => * -> * -> * *Main> }}} ---- Tangent: Omitting `{-# Language GADTs #-}` we get the term "equational constraint" which is not the term I have seen in the wild {{{ $ latestbug 655_bug.hs GHCi, version 8.7.20181017: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( 655_bug.hs, interpreted ) 655_bug.hs:9:1: error: Illegal equational constraint a ~ 'OP (Use GADTs or TypeFamilies to permit this) | 9 | data Fun :: forall (a :: WHICH). a ~ OP => Type -> Type -> Type where | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... Failed, no modules loaded. Prelude> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15872> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13208: Do two-phase inlining in simpleOptPgm
by GHC 06 Mar '19

06 Mar '19

#13208: Do two-phase inlining in simpleOptPgm -------------------------------------+------------------------------------- Reporter: lukemaurer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- As of #12988, having `simpleOptPgm` leave β-redexes lying around is painful because it requires a special loophole in Core Lint to allow a jump inside a β-redex. We'd rather use a two-phase approach, mirroring the simplifier's `preInlineUnconditionally` and `postInlineUnconditionally`, so we can aggressively eliminate β-redexes without fear of exponential blowup. Consider: {{{ joinrec j1 x = e1 in join j2 x y = jump j1 e2 in jump j2 e3 e4 }}} Since `j2` is only used once, it gets inlined. But `simpleOptPgm` only performs inlining //after// a binding is simplified, so we end up here: {{{ joinrec j1 x = e1' in (\x y -> jump j1 e2') e3' e4' }}} Since `e2'` was already simplified, performing the β-reduction here risks exponential blowup for the same reason it can happen in the simplifier (see the Secrets paper; `perf/compiler/T783` is a live example, increasing in allocs by over 80% if we re-simplify here). We //could// just `let`-bind `e3'` and `e4'` (carefully avoiding capturing free occurrences of `x` in `e4'`), but not if one them is actually a type argument. Well, okay, we //could// introduce a type `let`, but doing that here means the desugarer can now return a type `let` and we're not prepared for that. (Specifically, under certain circumstances, the simplifier never runs in between the desugarer and Float Out, and the latter breaks in the presence of type `let`.) So for the moment, we leave the β-redex there, but this needs a special rule just for β-redexes because normally you can't have a jump under a lambda (or an application, for that matter). In the long term, we'd prefer to take the simplifier's approach instead: If we want to inline something because it only occurs once (even though it may be big), we add it to the substitution //before// simplifying it so that we only simplify it once. This means the substitution has to carry lexical closures around, though, just like the simplifier does (see `SimplSR`'s `ContEx` disjunct), so it's not trivial. The `simpleOptPgm` β-redexes are the only reason for the special rule in Core Lint (see Note [Beta redexes] in `CoreLint.hs`), so once this is done we can be rid of that. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13208> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16113: T14740 fails in debugged compiler
by GHC 05 Mar '19

05 Mar '19

#16113: T14740 fails in debugged compiler -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.8.1 Component: Compiler | Version: 8.6.3 (Type checker) | 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: -------------------------------------+------------------------------------- {{{#!patch --- parser/should_fail/T14740.run/T14740.stderr.normalised 2018-12-30 16:06:27.120170052 +0000 +++ parser/should_fail/T14740.run/T14740.comp.stderr.normalised 2018-12-30 16:06:27.120170052 +0000 @@ -1,4 +1,5 @@ +ghc: panic! (the 'impossible' happened) + (GHC version 8.7.20181230 for x86_64-unknown-linux): + ASSERT failed! file compiler/types/TyCoRep.hs, line 911 -T14740.hs:5:7: - Expecting a lifted type, but ‘(# #)’ is unlifted - In the type signature: x :: ((# #)) => () +Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16113> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16084: Improve link times on Windows
by GHC 05 Mar '19

05 Mar '19

#16084: Improve link times on Windows -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Windows Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Currently the Windows CI builds are typically lasting over 3 hours. The primary cause of this appears to be poor performance in `ld.bfd`, especially when linking testsuite tests. One option to fix this is to try using LLD for linking. Unfortunately the msys2 `gcc` does not support `-fuse-ld=lld`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16084> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16251: T5515 broken in devel2 flavour
by GHC 05 Mar '19

05 Mar '19

#16251: T5515 broken in devel2 flavour -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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 `T5515` testcase is broken in the `devel2` build flavour: {{{ --- indexed-types/should_fail/T5515.run/T5515.stderr.normalised 2019-01-27 16:01:12.703091135 +0000 +++ indexed-types/should_fail/T5515.run/T5515.comp.stderr.normalised 2019-01-27 16:01:12.703091135 +0000 @@ -1,24 +1,12 @@ +ghc: panic! (the 'impossible' happened) + (GHC version 8.7.20190127 for x86_64-unknown-linux): + ASSERT failed! + rhs axiom D:R:Argf :: + Arg f = a_asO[sk:1] -- Defined at T5515.hs:15:8 + Call stack: + CallStack (from HasCallStack): + callStackDoc, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + pprPanic, called at compiler/utils/Outputable.hs:<line>:<column> in <package-id>:Outputable + assertPprPanic, called at compiler/typecheck/FamInst.hs:<line>:<column> in <package-id>:FamInst -T5515.hs:6:16: - Expecting one more argument to ‘ctx’ - Expected a type, but ‘ctx’ has kind ‘* -> Constraint’ - In the first argument of ‘Arg’, namely ‘ctx’ - In the first argument of ‘ctx’, namely ‘(Arg ctx)’ - In the class declaration for ‘Bome’ - -T5515.hs:14:1: - Type variable ‘a’ is mentioned in the RHS, - but not bound on the LHS of the family instance - In the type instance declaration for ‘Arg’ - In the instance declaration for ‘Some f’ - -T5515.hs:14:10: - Could not deduce (C f a0) - from the context: C f a - bound by an instance declaration: - forall f a. C f a => Some f - at T5515.hs:14:10-24 - The type variable ‘a0’ is ambiguous - In the ambiguity check for an instance declaration - To defer the ambiguity check to use sites, enable AllowAmbiguousTypes - In the instance declaration for ‘Some f’ +Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16251> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #16208: map/coerce does not fire with all newtypes
by GHC 05 Mar '19

05 Mar '19

#16208: map/coerce does not fire with all newtypes -------------------------------------+------------------------------------- Reporter: monoidal | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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: -------------------------------------+------------------------------------- Consider a slightly modified version of T2110, compiled with -O: {{{ #!haskell {-# LANGUAGE GADTs #-} {-# LANGUAGE MagicHash #-} {-# LANGUAGE RankNTypes #-} import GHC.Exts import Unsafe.Coerce newtype Age a b where Age :: forall a b. Int -> Age a b foo :: [Int] -> [Int] foo = map id fooAge :: [Int] -> [Age a b] fooAge = map Age fooCoerce :: [Int] -> [Age a b] fooCoerce = map coerce fooUnsafeCoerce :: [Int] -> [Age a b] fooUnsafeCoerce = map unsafeCoerce same :: a -> b -> IO () same x y = case reallyUnsafePtrEquality# (unsafeCoerce x) y of 1# -> putStrLn "yes" _ -> putStrLn "no" main = do let l = [1,2,3] same (foo l) l same (fooAge l) l same (fooCoerce l) l same (fooUnsafeCoerce l) l }}} This code correctly prints "yes" four times, as required by #2110. However, changing the order of type arguments in the definition of Age to: {{{ Age :: forall b a. Int -> Age a b }}} causes the test to fail in one case: `map Age` is no longer simplified to `Age`. The reason is that this change causes the newtype `Age` to have a wrapper, and the map/coerce rule is not detecting it (see Note [Getting the map/coerce RULE to work] and Note [Data con wrappers and GADT syntax]) This ticket is a prerequisite to linear types (since in linear types, all newtypes have wrappers). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16208> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14030: Implement the "Derive Lift instances for data types in template-haskell" proposal
by GHC 05 Mar '19

05 Mar '19

#14030: Implement the "Derive Lift instances for data types in template-haskell" proposal -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.4.1 Component: Template | Version: 8.3 Haskell | 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: -------------------------------------+------------------------------------- Back in September 2015, I [https://mail.haskell.org/pipermail/libraries/2015-September/026117.html proposed] using the `DeriveLift` extension to, well, derive `Lift` instance for data types in the `template-haskell` library. The proposal was well received, but I was unable to implement it at the time due to `DeriveLift`'s newness (having only been introduced in GHC 8.0). Now that GHC 8.0 is the oldest version of GHC that we support bootstrapping with, this is no longer an obstacle. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14030> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12596: can't find interface-file declaration
by GHC 05 Mar '19

05 Mar '19

#12596: can't find interface-file declaration -------------------------------------+------------------------------------- Reporter: mwotton | 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: -------------------------------------+------------------------------------- full repro at https://github.com/mwotton/liftwoes/issues/1 ``` /home/mark/projects/liftwoes/src/Lib.hs:14:11: error: • Can't find interface-file declaration for variable Data.Text.Internal.pack Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error • In the first argument of ‘(:)’, namely ‘Data.Text.Internal.pack ((:) 'A' [])’ In the first argument of ‘HS.fromList’, namely ``` {{{#!hs {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE TemplateHaskell #-} module Lib where import Data.Data import qualified Data.Set as HS import qualified Data.Text as T import qualified Data.Text.IO as T import Data.Time -- import Instances.TH.Lift import Instances import Language.Haskell.TH.Syntax table = $(do r <- runIO (HS.fromList . T.lines <$> T.readFile "/usr/share/dict/words") [|r|] ) someFunc = do print $ HS.member "foo" table }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12596> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10892: ApplicativeDo should use *> and <*
by GHC 05 Mar '19

05 Mar '19

#10892: ApplicativeDo should use *> and <* -------------------------------------+------------------------------------- Reporter: simonmar | Owner: Type: task | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- From @ekmett: Would it be possible to tweak the generation to use `(<*)` or `(*>)` where appropriate when the result isn't being used? For many Applicatives this can be a massive asymptotic win in terms of sharing and/or computational cost. When desugaring using (<*) you'd just omit any handling of the unused result instead. {{{ (\x y -> ...) <$> foo <* bar <*> baz }}} corresponds to {{{ do x <- foo bar y <- baz return ... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10892> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13633: testwsdeque failure on POWER8
by GHC 04 Mar '19

04 Mar '19

#13633: testwsdeque failure on POWER8 ---------------------------------------+---------------------------------- Reporter: trommler | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.1 Keywords: SMP | Operating System: Linux Architecture: powerpc64 | Type of failure: Runtime crash Test Case: rts/testwsdeque | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ---------------------------------------+---------------------------------- On a POWER8 `testwsdeque` fails occasionally under load: {{{ Wrong exit code for testwsdeque(threaded1)(expected 0 , actual 134 ) Stderr ( testwsdeque ): internal error: FAIL: 277808608 3 13 (GHC version 8.3.20170430 for powerpc64le_unknown_linux) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13633> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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