October 2017 - ghc-tickets

[GHC] #11791: Remove the `isInlinePragma prag` test
by GHC 19 Feb '18

19 Feb '18

#11791: Remove the `isInlinePragma prag` test -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | 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: #11781, #5928 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a spin off of tickjet:11781#comment:9, where simonpjs writes: > What is more mysterious to me is why the unfolding for `$fApplicativeIO_$c*>` doesn't have `bindIO`, and then `bindIO` inlined into it, which would allow a cascade of further improvements, which would, I think, produce essentially the same code as `thenIO`. > > The offending corner is this > {{{ > active_unfolding_gentle id > = isInlinePragma prag -- WHY?? > && isEarlyActive (inlinePragmaActivation prag) > }}} > So I tried removing the `isInlinePragma prag` test, and indeed the code becomes identical. > > Conclusion: > * I'd love to make the above change to `active_unfolding_gentle` and see if any other performance numbers budge. I doubt that anything will change a lot -- it really only affects whether optimisation happens before or after inlining -- but it should improve compiler performance a bit for that very reason. This could be a separate ticket > > Incidentally, see #5928 which is somewhat related. This ticket tracks that idea. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11791> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 3

[GHC] #13994: STG lint failure on master
by GHC 18 Feb '18

18 Feb '18

#13994: STG lint failure on master -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 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: -------------------------------------+------------------------------------- As of 4700baaf8f9bf3c44a53a595d840c7c14cfd6f98 building with this `build.mk` results in an STG lint failure, {{{ BuildFlavour = devel2 include mk/flavours/$(BuildFlavour).mk GhcLibHcOpts += -g3 -ddump-to-file -ddump-stg -dcore-lint -dstg-lint -dcmm-lint GhcRtsHcOpts += -g3 GhcStage2HcOpts += -g3 -ddump-to-file -ddump-stg -dcore-lint -dstg-lint -dcmm-lint }}} The failures occurs while building `libraries/integer-gmp/dist- install/build/GHC/Integer/Type.o` and are of the form, {{{ *** Stg Lint ErrMsgs: in Stg2Stg *** <no location info>: warning: [in body of lambda with binders m0_scBi :: State# s_a2Ej -> State# s_a2Ej, s1_scBj :: State# s_a2Ej] s'_scBk is out of scope <no location info>: warning: [RHS of $j1_sdij :: (# BigNat, GmpLimb# #)] Let(rec) binder ‘$j1_sdij’ has unlifted type ‘(# BigNat, GmpLimb# #)’ RHS: (elided for brevity) <no location info>: warning: [RHS of $j4_sdQ1 :: (# BigNat, BigNat #)] Let(rec) binder ‘$j4_sdQ1’ has unlifted type ‘(# BigNat, BigNat #)’ RHS: (elided) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13994> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 7

[GHC] #13185: haskell-relational-query: ghc: panic! (the 'impossible' happened)
by GHC 18 Feb '18

18 Feb '18

#13185: haskell-relational-query: ghc: panic! (the 'impossible' happened) -------------------------------------+------------------------------------- Reporter: LocutusOfBorg | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Linux Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: build | Blocked By: relational-query with ghc 8.0.2 | Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Hello, this seems a regression of ghc 8.0.2 since 8.0.1 was building it fine: https://launchpadlibrarian.net/303858976/buildlog_ubuntu-zesty-amd64 .haskell-relational-query_0.8.3.2-2build1_BUILDING.txt.gz as you can see in the build log: Preprocessing test suite 'sqls' for relational-query-0.8.3.2... [1 of 3] Compiling Model ( test/Model.hs, dist-ghc/build/sqls /sqls-tmp/Model.o ) [2 of 3] Compiling Lex ( test/Lex.hs, dist-ghc/build/sqls /sqls-tmp/Lex.o ) [3 of 3] Compiling Main ( test/sqlsEq.hs, dist-ghc/build/sqls /sqls-tmp/Main.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): Simplifier ticks exhausted When trying UnfoldingDone runReaderT To increase the limit, use -fsimpl-tick-factor=N (default 100) If you need to do this, let GHC HQ know, and what factor you needed To see detailed counts use -ddump-simpl-stats Total ticks: 405365 Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug /usr/share/cdbs/1/class/hlibrary.mk:147: recipe for target 'build-ghc- stamp' failed make: *** [build-ghc-stamp] Error 1 dpkg-buildpackage: error: debian/rules build gave error exit status 2 thanks, Gianfranco -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13185> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 21

[GHC] #9429: Alternative to type family Any
by GHC 18 Feb '18

18 Feb '18

#9429: Alternative to type family Any -------------------------------------+------------------------------------- Reporter: mboes | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: 9097, 9380 | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- In GHC HEAD, `Any` is no longer a datatype. There are good reasons for this change, one of which was explained in #9097, the original ticket, and another in #9380. Unfortunately, a casualty of this change is that it is no longer easy to generalize the [https://hackage.haskell.org/package/rank1dynamic|rank1dynamic package] to rank-1 types with type variables of arbitrary kind (not just `*`). We submitted a way to do so [here], that exploits the fact that `Any` has the very magical property of inhabiting *all* kinds, including closed ones. This works for GHC 7.8, but won't work in HEAD, because we require that there exists a `Typeable` instance for `Any`, just as there are `Typeable` instances for any other type one wishes to have instances for. The reason is that now that `Any` is a type family, `Any` is no longer a legal instance head. There are several possible solutions that I see: * while it's clearly dangerous for the compiler to be inserting the old `Any` during typechecking from the moment that we have computation in types over closed kinds, we may still want the old `Any`, say under a different name, as a backdoor. It wouldn't be used by the compiler during type checking - only by packages such as rank1dynamic. I believe that furthermore, if we restrict the old `Any` to not inhabit closed kinds, then none of the problems cited in the above tickets arise. * Instead of making the new `Any` a type family, keep it a datatype, but ban it from inhabiting closed kinds. I don't know if such an `Any` would be sufficient for the purposes of GHC, however. * Hardwire a `Typeable` instance for the `Any` type family (not sure if this makes sense). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9429> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 33

[GHC] #13852: Can we have more SIMD primops, corresponding to the untapped AVX etc. instructions?
by GHC 17 Feb '18

17 Feb '18

#13852: Can we have more SIMD primops, corresponding to the untapped AVX etc. instructions? -------------------------------------+------------------------------------- Reporter: | Owner: (none) leftaroundabout | Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (LLVM) | Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: None/Unknown (amd64) | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- [http://hackage.haskell.org/package/ghc-prim-0.5.0.0/docs/GHC- Prim.html#g:28 GHC.Prim] contains a good couple of vectorised instructions, which can be [http://hackage.haskell.org/package/primitive- simd-0.1.0.0/docs/Data-Primitive-SIMD.html used by libraries] for generating nice fast e.g. sums of floating-point vectors. However, several instructions that modern processors could vectorise are missing there. In particular, I would like to be able to use the VPSLLVD...VPSRAVD shifting operations, and at some point perhaps VPMAXSQ...VPMINUQ maximum/minimum operations. It would be great if corresponding primops could be added. Else I would like to know – where is this stuff even defined? [http://hackage.haskell.org/package/ghc- prim-0.5.0.0/docs/src/GHC.Prim.html GHC.Prim] as such seems to be merely an automatically-generated dummy module, mostly for Haddock. (On the other hand, I find it also a bit strange that there are primops for [http://hackage.haskell.org/package/ghc-prim-0.5.0.0/docs/GHC- Prim.html#v:quotInt8X16-35- integer division], which is apparently [https://stackoverflow.com/questions/16822757/sse-integer-division not supported by SSE/AVX] at all!) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13852> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 7

[GHC] #13943: Compiler infinite loop with GHC-8.2
by GHC 15 Feb '18

15 Feb '18

#13943: Compiler infinite loop with GHC-8.2 -------------------------------------+------------------------------------- Reporter: vagarenko | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-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: -------------------------------------+------------------------------------- GHC-8.0.1 compile this module in less than one seconds on my machine. Both GHC-8.2rc2 and GHC-8.2rc3 eat all 8GB of memory and don't show any signs of stopping. -dshow-passes shows this: {{{ [1 of 1] Compiling Data.List.Unrolled ( unrolled.hs, unrolled.o ) *** Parser [Data.List.Unrolled]: !!! Parser [Data.List.Unrolled]: finished in 0.00 milliseconds, allocated 3.434 megabytes *** Renamer/typechecker [Data.List.Unrolled]: }}} and then nothing. Only memory consumption grows. Code: {{{#!hs {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE TypeApplications #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE AllowAmbiguousTypes #-} {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE GADTs #-} module Data.List.Unrolled where import GHC.TypeLits -- | Drop @n@ elements from a list class Drop (n :: Nat) where drop :: [a] -> [a] instance {-# OVERLAPPING #-} Drop 0 where drop xs = xs {-# INLINE drop #-} instance {-# OVERLAPPABLE #-} (Drop (n - 1)) => Drop n where drop [] = [] drop (_ : xs) = drop @(n - 1) xs {-# INLINE drop #-} -- | Take @n@ elements from a list class Take (n :: Nat) where take :: [a] -> [a] instance {-# OVERLAPPING #-} Take 0 where take _ = [] {-# INLINE take #-} instance {-# OVERLAPPABLE #-} (Take (n - 1)) => Take n where take [] = [] take (x : xs) = x : take @(n - 1) xs {-# INLINE take #-} -- | Split list at @n@-th element. splitAt :: forall (n :: Nat) a. (Take n, Drop n) => [a] -> ([a], [a]) splitAt xs = (take @n xs, drop @n xs) -- | Split list into chunks of the given length @c@. @n@ is length of the list. class ChunksOf (n :: Nat) (c :: Nat) where chunksOf :: [a] -> [[a]] instance {-# OVERLAPPING #-} ChunksOf 0 0 where chunksOf _ = [] {-# INLINE chunksOf #-} instance {-# OVERLAPPABLE #-} ChunksOf 0 c where chunksOf _ = [] {-# INLINE chunksOf #-} instance {-# OVERLAPPABLE #-} ChunksOf n 0 where chunksOf _ = [] {-# INLINE chunksOf #-} instance {-# OVERLAPPABLE #-} (Take c, Drop c, ChunksOf (n - 1) c) => ChunksOf n c where chunksOf xs = let (l, r) = splitAt @c xs in l : chunksOf @(n - 1) @c r {-# INLINE chunksOf #-} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13943> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 16

[GHC] #8258: GHC accepts `data Foo where` in H2010 mode
by GHC 14 Feb '18

14 Feb '18

#8258: GHC accepts `data Foo where` in H2010 mode --------------------------+------------------------------------------------ Reporter: hvr | Owner: Type: bug | Status: new Priority: low | Milestone: 7.8.1 Component: | Version: 7.0.4 Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC accepts invalid program Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ According to the Haskell2010 report, The grammar productions relevant for `data` declarations are the following: {{{ topdecl → data [context =>] simpletype [= constrs] [deriving] }}} (from [http://www.haskell.org/onlinereport/haskell2010/haskellch4.html#x10-680004.2 4.2.1 Algebraic Datatype Declarations]) However, GHC 7.0.4/7.4.2/7.6.3/HEAD all happily compile the following Haskell module without any warning when using `-XHaskell2010 -Wall`, even though this is not valid Haskell2010 afaik: {{{#!hs module Foo where data Foo where }}} The trailing `where` in the `data` declaration is not valid Haskell2010 (without language extensions such as `GADT`). At the very least, this divergence from the Haskell Report should be mentioned in [http://www.haskell.org/ghc/docs/latest/html/users_guide /bugs-and-infelicities.html#haskell-standards-divergence 14.1.1. Divergence from Haskell 98 and Haskell 2010]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8258> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 5

[GHC] #9269: Type families returning quantified types
by GHC 14 Feb '18

14 Feb '18

#9269: Type families returning quantified types ------------------------------------+------------------------------------- Reporter: pumpkin | Owner: Type: feature request | 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: | ------------------------------------+------------------------------------- Is there a fundamental reason for not being able to use quantification in a type family? I'd very much like to be able to do it, obviously turning on RankNTypes if necessary. I'm looking for things like this: {{{#!haskell type family Foo (x :: Bool) where Foo True = forall a. [a] Foo False = () }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9269> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 7

[GHC] #12422: Add decidable equality class
by GHC 14 Feb '18

14 Feb '18

#12422: Add decidable equality class -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Core | Version: 8.0.1 Libraries | 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: -------------------------------------+------------------------------------- Currently, we have a `TestEquality` class {{{#!hs class TestEquality f where testEquality :: f a -> f b -> Maybe (a :~: b) }}} It would be nice to add a class for fully decidable equality. There are a few options, but this one gets to the point rather quickly: {{{#!hs data EqDec a b where NotEqual :: (forall c . a :~: b -> c) -> EqDec a b Equal :: EqDec a a class DecEq f where decEq :: f a -> f b -> EqDec a b }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12422> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 9

[GHC] #12262: Binary output is not deterministic
by GHC 07 Feb '18

07 Feb '18

#12262: Binary output is not deterministic -------------------------------------+------------------------------------- Reporter: niteria | 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: -------------------------------------+------------------------------------- The goal of DeterministicBuilds (#4012) was to get ABI-compatible binaries given the same sources, flags and the environment. There's a stronger goal of getting bit-for-bit identical binaries and this ticket will track that. Known causes of binary nondeterminism: * Unique comparison * Uniques converted to strings for symbol names * everything else from #4012 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12262> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

1 5