February 2017 - ghc-tickets

[GHC] #10648: Some 64-vector SIMD primitives are absolutely useless
by GHC 03 Jul '17

03 Jul '17

#10648: Some 64-vector SIMD primitives are absolutely useless -------------------------------------+------------------------------------- Reporter: mniip | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The primitives `packInt8X64#`, `packWord8X64#`, `unpackInt8X64#`, `unpackWord8X64#` cannot be used because their types include unboxed 64-tuples, but any haskell code using them does not compile due to the 62-tuple limitation. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10648> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12610: Emit tab warning promptly
by GHC 03 Jul '17

03 Jul '17

#12610: Emit tab warning promptly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.2 Component: Compiler | Version: 8.0.1 (Parser) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs p = let x = 4 [tab]y = 5 in 12 }}} produces `error: parse error on input ‘y’` and nothing else. The problem is caused by a tab appearing to the user to line up `x` with `y` but actually placing `y` in the wrong column. The user typically will scratch their head and then post a question on StackOverflow. There they'll be told to use `-fwarn-tabs`, but ''that option won't help'' (and it's probably already on) because GHC will exit with a parse error before it gets around to giving the warning. I suspect the solution is probably to emit the tab warning in the lexer, but one of the parsing gurus will probably know better. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12610> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12203: Allow constructors on LHS of (implicit) bidirectional pattern synonym
by GHC 01 Jul '17

01 Jul '17

#12203: Allow constructors on LHS of (implicit) bidirectional pattern synonym -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.0.1 (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: -------------------------------------+------------------------------------- Inspired by the recent Ghostbuster paper http://www.cs.ox.ac.uk/people/timothy.zakian/ghostbuster.pdf , I was experimenting with using pattern synonyms to simulate GADTs. In the process, I noticed that we should be able to generalize the implicit bidirectional synonyms to allow constructors on the LHS. Consider this program: {{{ {-# LANGUAGE KindSignatures #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE TypeOperators #-} {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} module GhostBuster where import GHC.TypeLits newtype Vec a (n :: Nat) = Vec { unVec :: [a] } pattern VNil :: Vec a 0 pattern VNil = Vec [] pattern VCons :: a -> Vec a n -> Vec a (n + 1) pattern VCons x xs <- Vec (x : (Vec -> xs)) where VCons x (Vec xs) = Vec (x : xs) headVec :: Vec a (n + 1) -> a headVec (VCons x _) = x }}} In effect, we simulate a vector GADT using pattern synonyms to handle the newtype `Vec`. I would like it if I could specify the `VCons` pattern more simply, as just: {{{ pattern VCons :: a -> Vec a n -> Vec a (n + 1) pattern VCons x (Vec xs) = Vec (x : xs) }}} And GHC would infer the correct pattern (the constructor can be read off immediately), automatically replacing occurrences of `xs` with a view pattern that reconstructs the constructors that were stripped off on the LHS. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12203> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13220: Performance regressions in testsuite from join points
by GHC 29 Jun '17

29 Jun '17

#13220: Performance regressions in testsuite from join points -------------------------------------+------------------------------------- Reporter: lukemaurer | Owner: lukemaurer Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: -------------------------------------+------------------------------------- Need to look at, among others: * `perf/compiler/T9961` * `deriving/perf/T10858` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13220> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9588: Add `MonadPlus {IO, Either e}` and `Alternative (Either e)` instances
by GHC 29 Jun '17

29 Jun '17

#9588: Add `MonadPlus {IO,Either e}` and `Alternative (Either e)` instances -------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: 7.10.1 Component: libraries/base | Version: Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following 3 instances are currently Orphans in `transformers` but shall be defined in `base` instead: {{{#!hs instance MonadPlus IO instance MonadPlus (Either e) instance Alterantive (Either e) }}} This proposal by SPJ already passed the CLC back in April and only needs implementing. I'll submit a patch shortly to Phab -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9588> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11990: Custom Type Error not getting triggered in the nested Type function call
by GHC 27 Jun '17

27 Jun '17

#11990: Custom Type Error not getting triggered in the nested Type function call -------------------------------------+------------------------------------- Reporter: magesh.b | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc3 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: -------------------------------------+------------------------------------- I have partial type function which is invoked by another type function. When the inner type function fails with TypeError, outer type function is not been able to propagate that type error to its caller. As a result of it, I'm getting following error • No instance for (KnownSymbol (NestedPartialTF (TypeError ...))) instead of • Unexpected type @ NestedPartialTF: Char {{{#!hs {-# LANGUAGE DataKinds, TypeOperators, TypeFamilies, UndecidableInstances, ScopedTypeVariables, FlexibleContexts #-} -- | module CErrs where import GHC.TypeLits import Data.Proxy type family PartialTF t :: Symbol where PartialTF Int = "Int" PartialTF Bool = "Bool" PartialTF a = TypeError (Text "Unexpected type @ PartialTF: " :<>: ShowType a) type family NestedPartialTF (tsym :: Symbol) :: Symbol where NestedPartialTF "Int" = "int" NestedPartialTF "Bool" = "bool" NestedPartialTF a = TypeError (Text "Unexpected type @ NestedPartialTF: " :<>: ShowType a) testPartialTF :: forall a.(KnownSymbol (PartialTF a)) => a -> String testPartialTF t = symbolVal (Proxy :: Proxy (PartialTF a)) --t1 = testPartialTF 'a' {- Above code rightly fails with the following error: • Unexpected type: Char • In the expression: testPartialTF 'a' In an equation for ‘t1’: t1 = testPartialTF 'a' -} -- Bug? testNesPartialTF :: forall a.(KnownSymbol (NestedPartialTF (PartialTF a))) => a -> String testNesPartialTF t = symbolVal (Proxy :: Proxy (NestedPartialTF (PartialTF a))) t2 = testNesPartialTF 'a' {- Above code fails with the following error: • No instance for (KnownSymbol (NestedPartialTF (TypeError ...))) arising from a use of ‘testNesPartialTF’ • In the expression: testNesPartialTF 'a' In an equation for ‘t2’: t2 = testNesPartialTF 'a' -} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11990> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13337: GHC doesn't think a type is of kind *, despite having evidence for it
by GHC 27 Jun '17

27 Jun '17

#13337: GHC doesn't think a type is of kind *, despite having evidence for it -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The easiest way to illustrate this bug is this: {{{#!hs {-# LANGUAGE PolyKinds #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} module Foo where import Data.Kind (Type) blah :: forall (a :: k). k ~ Type => a -> a blah x = x }}} {{{ $ ghci Foo.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Foo ( Foo.hs, interpreted ) Foo.hs:8:43: error: • Expected a type, but ‘a’ has kind ‘k’ • In the type signature: blah :: forall (a :: k). k ~ Type => a -> a }}} I find this behavior quite surprising, especially since we have evidence that `k ~ Type` in scope! If the program above looks too contrived, consider a similar program that uses `Typeable`. I want to write something like this: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE TypeOperators #-} module Foo where import Data.Kind (Type) import Data.Typeable foo :: forall k (a :: k) proxy. (Typeable k, Typeable a) => proxy a -> String foo _ = case eqT :: Maybe (k :~: Type) of Nothing -> "Non-Type kind" Just Refl -> case eqT :: Maybe (a :~: Int) of Nothing -> "Non-Int type" Just Refl -> "It's an Int!" }}} This exhibits the same problem. Despite the fact that we pattern-matched on a `Refl` of type `k :~: Type`, GHC refuses to consider the possibility that `a :~: Int` is well kinded, even though `(a :: k)`, and we learned from the first `Refl` that `k ~ Type`! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13337> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12912: IO library should not use select()
by GHC 27 Jun '17

27 Jun '17

#12912: IO library should not use select() -------------------------------------+------------------------------------- Reporter: simonmar | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: | Version: 8.0.1 libraries/base | 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 IO library uses `select()` in `fdReady()`, which fails in processes with more than 1024 file descriptors. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12912> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12412: SIMD things introduce a metric ton of known key things
by GHC 26 Jun '17

26 Jun '17

#12412: SIMD things introduce a metric ton of known key things -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In #12357 we were looking at reducing the number of entries in the `knownKeyNames`. This has the potential to improve compiler performance since this set of things is always present in the original name cache, which is often referred to. #12357 reduced the number of elements in `knownKeyNames` from 2017 to 1834. Not a bad improvement. That being said, the SIMD operations introduce nearly four times that number. These include things like `readWord64OffAddrAsWord64X2#`, `indexInt16OffAddrAsInt16X16#`, and `remInt16X16#`. All in all these operations constitute nearly a third of the known key names. I'm not really sure what can be done about this, but I thought it should be noted. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12412> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10286: native code generator: GHC crash at GHC.Prim SIMD vector
by GHC 26 Jun '17

26 Jun '17

#10286: native code generator: GHC crash at GHC.Prim SIMD vector -------------------------------------+------------------------------------- Reporter: hkanai | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- When compiling attached source file, GHC panics. The following is the error message. {{{ $ ghc -Wall Vec3.hs [1 of 1] Compiling Data.Vector.Vec3 ( Vec3.hs, Vec3.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.10.1 for x86_64-unknown-linux): Size.intSize W256 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Currently native code generator does not support SIMD operations, and my computer does not support AVX instructions. Therefore ghc cannot compile the source at any case. So I think this bug is not so important. My system environment. {{{ $ uname -a Linux think 3.19.2-1-ARCH #1 SMP PREEMPT Wed Mar 18 16:21:02 CET 2015 x86_64 GNU/Linux $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.10.1 $ cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Core(TM)2 Duo CPU L9300 @ 1.60GHz stepping : 6 microcode : 0x60c cpu MHz : 1601.000 cache size : 6144 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm ida dtherm tpr_shadow vnmi flexpriority bugs : bogomips : 3193.86 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: processor : 1 vendor_id : GenuineIntel cpu family : 6 model : 23 model name : Intel(R) Core(TM)2 Duo CPU L9300 @ 1.60GHz stepping : 6 microcode : 0x60c cpu MHz : 1601.000 cache size : 6144 KB physical id : 0 siblings : 2 core id : 1 cpu cores : 2 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 10 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl aperfmperf pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm ida dtherm tpr_shadow vnmi flexpriority bugs : bogomips : 3193.86 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management: }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10286> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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