July 2017 - ghc-tickets

[GHC] #9274: GHC panic with UnliftedFFITypes+CApiFFI
by GHC 16 Oct '17

16 Oct '17

#9274: GHC panic with UnliftedFFITypes+CApiFFI -----------------------------------+--------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- The following code fails to compile with at least GHC 7.6, 7.8 and HEAD: {{{#!hs import GHC.Prim import Foreign.C type GmpLimb = CULong type GmpSize = CLong -- mp_limb_t mpn_add_1 (mp_limb_t *rp, const mp_limb_t *s1p, mp_size_t n, mp_limb_t s2limb) foreign import capi unsafe "gmp.h mpn_add_1" c_mpn_add_1 :: MutableByteArray# s -> ByteArray# -> GmpSize -> GmpLimb -> IO GmpLimb }}} with the following compile error message: {{{ ghc: panic! (the 'impossible' happened) (GHC version 7.9.20140704 for x86_64-unknown-linux): toCType MutableByteArray# s Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Otoh, replacing `capi` with `ccall` makes the code compile just fine -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9274> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13955: Backpack does not handle unlifted types
by GHC 16 Oct '17

16 Oct '17

#13955: Backpack does not handle unlifted types -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.2.1-rc2 Keywords: backpack | Operating System: Unknown/Multiple LevityPolymorphism | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In the code snippet below, I attempt to use backpack with levity polymorphism: {{{ {-# LANGUAGE MagicHash #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE DataKinds #-} unit number-unknown where signature NumberUnknown where import GHC.Types data Number plus :: Number -> Number -> Number multiply :: Number -> Number -> Number module NumberStuff where import NumberUnknown funcA :: Number -> Number -> Number funcA x y = plus x (multiply x y) unit number-int where module NumberUnknown where type Number = Int plus :: Int -> Int -> Int plus = (+) multiply :: Int -> Int -> Int multiply = (*) unit number-unboxed-int where module NumberUnknown where import GHC.Prim type Number = Int# plus :: Int# -> Int# -> Int# plus = (+#) multiply :: Int# -> Int# -> Int# multiply = (*#) unit main where dependency number-unknown[NumberUnknown=number-unboxed- int:NumberUnknown] module Main where import NumberStuff main = putStrLn "Hello world!" }}} Compiling this with `ghc --backpack packer.bkp` fails with the following error: {{{ - Type constructor ‘Number’ has conflicting definitions in the module and its hsig file Main module: type Number = GHC.Prim.Int# :: TYPE 'GHC.Types.IntRep Hsig file: data Number The types have different kinds - while checking that number-unboxed-int:NumberUnknown implements signature NumberUnknown in number-unknown[NumberUnknown=number-unboxed- int:NumberUnknown] type Number = Int# }}} The error is pretty clear: `Number` can only be instantiated by types of kind `Type` (aka `TYPE LiftedRep`). Even while remaining levity monomorphic, there doesn't seem to be a way to pick a different kind. For example, redefining `Number` in the signature as {{{ data Number :: TYPE IntRep }}} leads to the following immediate failure: {{{ Kind signature on data type declaration has non-* return kind TYPE 'IntRep }}} I do not understand any of the internals of backpack, so I do not understand if there's anything fundamental that makes this impossible. Going one step further, I would like to be able to do something like this (the syntax here is not even currently valid for a backpack signature): {{{ type MyRep :: RuntimeRep data Number :: TYPE MyRep }}} This may be instantiated with something like this: {{{ type MyRep = IntRep type Number = Int# }}} And then end users would be able to monomorphize levity-polymorphic functions. This would be really neat because there is currently no way to do this in GHC. So, I guess there are really two feature requests in here. One is the ability to use unlifted data types with backpack. The other is the ability to use backpack to monomorphize levity-polymorphic functions. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13955> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13875: ApplicativeDo desugaring is lazier than standard desugaring
by GHC 15 Oct '17

15 Oct '17

#13875: ApplicativeDo desugaring is lazier than standard desugaring -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Keywords: ApplicativeDo | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Suppose I write {{{#!hs import Data.Maybe (isJust) bangy m = do (_,_) <- m return () main = print $ isJust (bangy (Just undefined)) }}} If I compile this with `ApplicativeDo`, it prints `True`. Otherwise, it throws an exception. The basic problem is that the (correct) `bangy` function ''requires'' a `Monad` constraint, but `ApplicativeDo` replaces it with a lazier function that can get by with `Functor`. I believe it should desugar correctly, and impose a `Monad` constraint here. To get the `Functor` constraint should require an explicit lazy pattern match: {{{#!hs bangy m = do ~(_,_) <- m return () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13875> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12822: Cleanup GHC verbosity flags
by GHC 14 Oct '17

14 Oct '17

#12822: Cleanup GHC verbosity flags -------------------------------------+------------------------------------- Reporter: hsyl20 | Owner: Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple newcomer,flags | Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- 1) In the discussion of Phab:D2679#77898, Simon Marlow suggested that we make verbosity levels (`-v0`, `-v1`...) work just like optimization levels (`-O0`, `-O1`...), i.e., that we make each verbosity level a collection of verbosity flags. Currently the verbosity level is tested against explicitly in several places in GHC's code. 2) Homogenize verbosity flags: currently, flags that change GHC's reporting have various prefixes: - `-fprint-*` - `-fshow-*` - `-dshow-passes` - `-ddump-*` - `-dppr-*` - `-dverbose-*` Maybe we should homogenize (some of) them by using a common `-v` prefix as in `-vshow-source-paths`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12822> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14043: GHC.Stack.callStack throws exception
by GHC 11 Oct '17

11 Oct '17

#14043: GHC.Stack.callStack throws exception -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 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: -------------------------------------+------------------------------------- This program, {{{#!hs import GHC.Stack main :: IO () main = putStrLn (prettyCallStack $ id (\_ -> callStack) ()) }}} terminates with, {{{ Hi: popCallStack: empty stack }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14043> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13678: Overhaul the linker
by GHC 11 Oct '17

11 Oct '17

#13678: Overhaul the linker -------------------------------------+------------------------------------- Reporter: angerman | Owner: (none) Type: bug | Status: new Priority: lowest | Milestone: ⊥ Component: Compiler | Version: 8.3 (Linking) | 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 linker has gained support for aarch64/macho, and aarch64/elf, as well as improved arm/elf code, this code introduces separate mapping of sections into different pages, to allow for `W^X` protection. This is essentially a requirement on iOS, and I believe a sane default to have. To this extend the symbol extras logic needed to be split up into GOT and PLTs, where the PLTs are allocated alongside the sections, as the architecture may not allow arbitrary jumps (arm/aarch64). The introduction aarch64/elf has also been done through a pseudo interface so that the actual relocation logic can be contained within it's own files. Ideally we'd improve the linker by migrating the existing (heavily #ifdef'd) to the new separate section mapping (`W^X`) and pseudo interface approach. The separate section mapping logic has an inherent memory inefficiency (which might be improved a bit by aggregating similar sections into the same page), and might also cause a performance penalty due to separate mapping instead of a single file mmap. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13678> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11654: User Guide: Generate command line options table from ghc-flags directives
by GHC 11 Oct '17

11 Oct '17

#11654: User Guide: Generate command line options table from ghc-flags directives -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Documentation | Version: 7.10.3 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: -------------------------------------+------------------------------------- Since the move to ReStructuredText and Sphinx we've generated the options summary tables and manpage with `utils/mkUserGuidePart`. The options are described in a set of Haskell modules which are a pain to edit and may easily fall out of date. It would be far better if we could generate these tables from the `.. ghc- flags` directives already present in the users guide. This will involve a bit of hacking with Sphinx, although it should be more than up to the task. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11654> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14003: Allow more worker arguments in SpecConstr
by GHC 11 Oct '17

11 Oct '17

#14003: Allow more worker arguments in SpecConstr -------------------------------------+------------------------------------- Reporter: choenerzs | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.2.2 Component: Compiler | Version: 8.2.1-rc3 Keywords: JoinPoints, | Operating System: Unknown/Multiple Fusion | Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Starting with GHC 8.2 (rc1 -- head) I noticed that the SpecConstr pass does not always optimize completely with SpecConstr-heavy code. Setting ```-fmax-worker-args=100``` leads to complete specialization again. However, given that code annotated with ```SPEC``` should be optimized until no more ```SPEC``` arguments are alive, shouldn't ```callToNewPats``` in ```compiler/specialise/SpecConstr.hs``` specialize *irrespective* of the size of the worker argument list? Code that actually fails to specialize is fairly large, hence no test case -- though I have some files with core output showing insufficient specialization. (I'd be willing to write a patch for this) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14003> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10816: Fixity declaration for associated type rejected
by GHC 11 Oct '17

11 Oct '17

#10816: Fixity declaration for associated type rejected -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: 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: Differential Revisions: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE TypeOperators, TypeFamilies #-} module Bug where class C a where type a # b infix 4 # }}} I get {{{ Bug.hs:7:11: ‘#’ is not a (visible) method of class ‘C’ }}} But it really should just assign a fixity to the type `#`. It works if the fixity declaration is outside of the class. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10816> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13652: Add integer division to GHC.TypeLits
by GHC 08 Oct '17

08 Oct '17

#13652: Add integer division to GHC.TypeLits -------------------------------------+------------------------------------- Reporter: vagarenko | Owner: (none) Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- GHC.TypeLits currently lacks integer division type families and I can't see why. What is the reason for not having these methods of the `Integral` class at type level: {{{#!hs quot rem div mod quotRem divMod }}} ? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13652> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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