December 2013 - ghc-tickets

[GHC] #8532: Hyperbolic arc cosine fails on (-1) :: Complex r.
by GHC 14 Sep '17

14 Sep '17

#8532: Hyperbolic arc cosine fails on (-1) :: Complex r. -------------------------------------+------------------------------------- Reporter: leftaroundabout | Owner: Type: bug | Status: new Priority: low | Milestone: Component: libraries/base | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Incorrect result Difficulty: Easy (less than 1 | at runtime hour) | Test Case: acosh(-1) :: Blocked By: | Complex Double Related Tickets: | Blocking: -------------------------------------+------------------------------------- When allowing for complex results, the hyperbolic arc cosine is continuously defined on all ℝ. In the {{{(x < (-1))}}} real ray of the complex plane, {{{acosh}}} equals {{{\z -> i * pi + acosh(abs z)}}}, which works fine for almost all arguments. Thus, {{{acosh (-1)}}} should equal {{{i * pi}}}; however due to the implementation as {{{ acosh z = log (z + (z+1) * sqrt ((z-1)/(z+1))) }}} where the denominator in the root becomes zero at {{{z = -1}}}, this comes out as {{{NaN :+ NaN}}}. Could be fixed trivially by adding a special case {{{ acosh ((-1):+0) = 0:+pi }}} to the {{{instance (RealFloat a) => Floating (Complex a)}}} in {{{Data.Complex}}}. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8532> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8583: Associated pattern synonyms
by GHC 11 Sep '17

11 Sep '17

#8583: Associated pattern synonyms ------------------------------------+------------------------------------- Reporter: cactus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: 5144 | Blocking: Related Tickets: | ------------------------------------+------------------------------------- The PatternSynonyms wiki page has a section on (typeclass-)associated pattern synonyms: {{{ class ListLike l where pattern Nil :: l a pattern Cons :: a -> l a -> a isNil :: l a -> Bool isNil Nil = True isNil (Cons _ _) = False append :: l a -> l a -> l a instance ListLike [] where pattern Nil = [] pattern Cons x xs = x:xs append = (++) headOf :: (ListLike l) => l a -> Maybe a headOf Nil = Nothing headOf (Cons x _) = Just x }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8583> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8317: Optimize tagToEnum# at Core level
by GHC 30 Aug '17

30 Aug '17

#8317: Optimize tagToEnum# at Core level ------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #6135 | ------------------------------------+------------------------------------- Old comparison primops that returned Bool were implemented by inserting call to `tagToEnum#` in the code generator. This call to `tagToEnum#` was later optimized away by a special case in the code geenrator (see [[GhcFile(compiler/codeGen/StgCmmExpr.hs)]], Note [case on bool])). Now that we have new comparison primops (see #6135) we no longer insert `tagToEnum#` in the code generator - all uses of `tagToEnum#` come from explicit calls in a source program. But we still have that special case in the code generator to optimize away `tagToEnum#`. We should drop that special case in the code generator and handle scrutinizing of `tagToEnum#` at the Core level by: 1. removing call to `tagToEnum#` in the scrutinee 2. adding calls to `dataToTag#` in case branches 3. constant-folding inserted `dataToTag#` Here is an example. This Haskell code: {{{ if tagToEnum# (a ># b) then E1 else E2 }}} will be translated to this Core: {{{ case tagToEnum# (a ># b) of True -> E1 False -> E2 }}} and optimized like this: {{{ case a ># b of dataToTag# True -> E1 dataToTag# False -> E2 }}} ====> {{{ case a ># b of 1 -> E1 0 -> E2 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8317> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8472: Primitive string literals prevent optimization
by GHC 16 Aug '17

16 Aug '17

#8472: Primitive string literals prevent optimization ------------------------------+-------------------------------------------- Reporter: akio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Runtime performance bug (amd64) | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- Using an Addr# literal seems to result in less aggressive optimization. If I compile the attached program like this: {{{ ghc -O2 -fforce-recomp -ddump-simpl addr.hs }}} the code is optimized nicely. Everything are inlined into {{{t}}}, intermediate pairs are eliminated, etc. However, when I replace the Int# literals in the code with Addr# literals by defining the {{{ADDR}}} macro: {{{ ghc -O2 -fforce-recomp -ddump-simpl -DADDR addr.hs }}} GHC now creates 2 extra top-level bindings, each of which allocates a pair. I don't see why the presence of Addr# literals should prevent inlining, so I'm reporting a bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8472> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8147: Exponential behavior in instance resolution on fixpoint-of-sum
by GHC 08 Aug '17

08 Aug '17

#8147: Exponential behavior in instance resolution on fixpoint-of-sum -------------------------+------------------------------------------------- Reporter: | Owner: jkoppel | Status: new Type: bug | Milestone: Priority: | Version: 7.6.3 normal | Operating System: Unknown/Multiple Component: | Type of failure: Compile-time performance bug Compiler | Test Case: Keywords: | Blocking: performance, | Architecture: | Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | -------------------------+------------------------------------------------- Doing instance resolution on a fixpoint-of-sum type takes a very long time. This is possibly the same issue as issue #5642. These are the numbers I see for various n: {{{ 10 : 0.329s 20 : 0.479s 40 : 0.935s 80 : 2.821s 160 : 11.694s 320 : 1m30.39s 640: Ran for over 1 hour without terminating }}} This uses a couple of attached support files. Apologies for not being able to reduce further. {{{ -- Test.hs {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances, OverlappingInstances, TypeOperators, DeriveFunctor, TemplateHaskell #-} module Test where import Control.Monad import Lib import TH {- With n=3, produces data X1 e = X1 e deriving (Functor) data X2 e = X2 e deriving (Functor) data X3 e = X3 e deriving (Functor) type X = X1 :+: X2 :+: X3 -} $(let n = 320 in liftM concat $ sequence [liftM concat $ mapM mkDec $ map (('X':).show) [1..n] , makeSumType "X" (map (('X':).show) [1..n])]) data Y0 e = Y0 e deriving ( Functor ) type X' = Y0 :+: X class Lift f g where lift' :: f (Fix g) -> Fix g instance (Lift f g, Lift f' g) => Lift (f :+: f') g where lift' x = case x of L e -> lift' e R e -> lift' e instance (Functor f, f :<: g) => Lift f g where lift' = In . inj cata :: (Functor f) => (f a -> a) -> Fix f -> a cata f = f . fmap (cata f) . out lift :: Fix X -> Fix X' lift = cata lift' }}} Virtually all the time is spent in compiling lift. For example, with n=640, commenting out lift makes it compile in around 2 seconds. Interestingly, when I add the following code, compilation times only increase by 10-20%. In the original code where I encountered this issue, doing so doubles compilation time. {{{ instance Lift Y0 X where lift' = undefined lower :: Fix X' -> Fix X lower = cata lift' }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8147> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8631: Need ImpredicativeTypes for GeneralizedNewtypeDeriving?
by GHC 02 Aug '17

02 Aug '17

#8631: Need ImpredicativeTypes for GeneralizedNewtypeDeriving? ------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Nathan Howell posts this code: {{{ {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE RankNTypes #-} -- Uncomment to compile on GHC 7.8 -- {-# LANGUAGE ImpredicativeTypes #-} module Repro where import Control.Monad.Trans.Cont import Control.Monad.Trans.State.Lazy newtype AnyContT m a = AnyContT { unAnyContT :: forall r . ContT r m a } class MonadAnyCont b m where anyContToM :: (forall r . (a -> b r) -> b r) -> m a instance MonadAnyCont b (AnyContT m) where anyContToM _ = error "foo" data DecodeState = DecodeState newtype DecodeAST a = DecodeAST { unDecodeAST :: AnyContT (StateT DecodeState IO) a } deriving (MonadAnyCont IO) }}} Compiling on HEAD produces {{{ [1 of 1] Compiling Repro ( repro.hs, interpreted ) repro.hs:24:13: Cannot instantiate unification variable ‛b0’ with a type involving foralls: (forall r. (a1 -> IO r) -> IO r) -> DecodeAST a1 Perhaps you want ImpredicativeTypes In the expression: GHC.Prim.coerce (anyContToM :: (forall (r :: *). (a -> IO r) -> IO r) -> AnyContT (StateT DecodeState IO) a) :: forall (a :: *). (forall (r :: *). (a -> IO r) -> IO r) -> DecodeAST a In an equation for ‛anyContToM’: anyContToM = GHC.Prim.coerce (anyContToM :: (forall (r :: *). (a -> IO r) -> IO r) -> AnyContT (StateT DecodeState IO) a) :: forall (a :: *). (forall (r :: *). (a -> IO r) -> IO r) -> DecodeAST a Failed, modules loaded: none. }}} Two questions: 1. Should we require users to specify !ImpredicativeTypes here? Or, should the !GeneralizedNewtypeDeriving mechanism (which sometimes is impredicative) just assume the extension? 2. Can we improve the error message? I'd like to note that the original example really ''does'' require impredicativity -- the question is whether and how to bother the user with this technicality. Small program note: I've done a lot of stuff with !GeneralizedNewtypeDeriving lately but am on holiday until Jan. 6, so don't expect responses! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8631> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8346: Rank 1 type signature still requires RankNTypes
by GHC 12 Jul '17

12 Jul '17

#8346: Rank 1 type signature still requires RankNTypes ----------------------------+---------------------------------------------- Reporter: | Owner: tinctorius | Status: new Type: bug | Milestone: Priority: normal | Version: 7.6.3 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects valid program Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: #2605 | ----------------------------+---------------------------------------------- When trying to figure out which type variable names are *actually* bound in `ScopedTypeVariables`, I tried floating `forall`s into the covariant argument of the function type. Essentially, I ran into the problem that programs like the following are rejected: {{{ #!hs {-# LANGUAGE ExplicitForAll #-} tuple :: forall a. a -> (forall b. b -> (a, b)) tuple = (,) }}} The message is as follows: {{{ Main.hs:2:10: Illegal polymorphic or qualified type: forall b. b -> (a, b) Perhaps you intended to use -XRankNTypes or -XRank2Types In the type signature for `tuple': tuple :: forall a. a -> (forall b. b -> (a, b)) }}} As far as I know, the rank of a type is defined by how deep quantifiers are nested in contravariant parts of that type. Or something like that. Also, as far as I know, `forall a. a -> (forall b. b -> (a, b))` is equivalent to `forall a b. a -> b -> (a, b)`, and more importantly, both are rank-1 polymorphic. There should be no need to use extensions that allow higher-ranked polymorphism. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8346> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8048: Register spilling produces ineffecient/highly contending code
by GHC 21 May '17

21 May '17

#8048: Register spilling produces ineffecient/highly contending code -------------------------------------+------------------------------------- Reporter: schyler | Owner: Type: bug | Status: new Priority: normal | Milestone: _|_ Component: Compiler | Version: 7.6.3 Keywords: register | Operating System: Unknown/Multiple allocator spill | Type of failure: Runtime Architecture: Unknown/Multiple | performance bug Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- The native codegen and llvm both produce ineffecient code for functions using structures with many strict fields or unboxed values. Consider the following program: {{{ {-# LANGUAGE BangPatterns #-} module Spill where import GHC.Exts data S = S !Int !Int !Int !Int !Int !Int !Int !Int !Int spill :: S -> S -> S -> S spill (S !a !b !c !d !e !f !g !h !i) (S !j !k !l !m !n !o !p !q !r) (S !s !t !u !v !w !x !y !z _) = S (a + j + s) (b + c) (k + r) (a + b + c + d + e + f + g + h + i) (j + k + l + m + n + o + p + q + r) (s + t + u + v + w + x + y + z) (a + b + c) (j + k + l) (s + t + u) }}} Parts of the code produced for this (which is identical regardless of -funbox-strict-fields) looks like: {{{ _cnc: addq $80,%r12 cmpq 144(%r13),%r12 ja _cni movq $Spill.S_con_info,-72(%r12) movq 32(%rbp),%rax movq %rax,-64(%r12) movq 24(%rbp),%rax movq %rax,-56(%r12) movq 16(%rbp),%rax movq %rax,-48(%r12) movq 8(%rbp),%rax movq %rax,-40(%r12) movq 40(%rbp),%rax movq %rax,-32(%r12) movq 48(%rbp),%rax movq %rax,-24(%r12) movq 56(%rbp),%rax movq %rax,-16(%r12) movq 64(%rbp),%rax movq %rax,-8(%r12) movq 7(%rbx),%rax movq %rax,0(%r12) leaq -71(%r12),%rbx addq $72,%rbp jmp *0(%rbp) }}} {{{ _csv: movq 63(%rbx),%rax movq %rax,-56(%rbp) movq 55(%rbx),%rax movq %rax,-48(%rbp) movq 47(%rbx),%rax movq %rax,-40(%rbp) movq 39(%rbx),%rax movq %rax,-32(%rbp) movq 31(%rbx),%rax movq %rax,-24(%rbp) movq 23(%rbx),%rax movq %rax,-16(%rbp) movq 71(%rbx),%rax movq %rax,-8(%rbp) movq 15(%rbx),%rax movq %rax,0(%rbp) }}} And likewise for LLVM: {{{ .LBB10_1: # %coZ movq 7(%rbx), %rcx movq $Spill_S_con_info, 8(%rax) movq 8(%rbp), %rdx movq %rdx, 16(%rax) movq 16(%rbp), %rdx movq %rdx, 24(%rax) movq 24(%rbp), %rdx movq %rdx, 32(%rax) movq 32(%rbp), %rdx movq %rdx, 40(%rax) movq 40(%rbp), %rdx movq %rdx, 48(%rax) movq 48(%rbp), %rdx movq %rdx, 56(%rax) movq 56(%rbp), %rdx movq %rdx, 64(%rax) movq 64(%rbp), %rdx movq %rdx, 72(%rax) movq %rcx, (%r12) movq 72(%rbp), %rax leaq 72(%rbp), %rbp leaq -71(%r12), %rbx jmpq *%rax # TAILCALL }}} Quoting from #ghc "the [register allocator] core algo is '96 vintage". Improvements are needed; * Take into consideration pipelining and handle spills less dramatically, attempting to reduce register contention * Sink memory reads in order to reduce register pressure -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8048> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8396: cleanup / refactor native code gens
by GHC 10 May '17

10 May '17

#8396: cleanup / refactor native code gens ----------------------------------------+---------------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: None/Unknown Blocked By: | Test Case: Related Tickets: #8299 , #8287 ,#8272 | Blocking: ----------------------------------------+---------------------------------- the native code gen could use some cleanup / love. 1. Catchup with feature parity of the llvm a. this includes adding SIMD support on applicable native code gen architectures, starting with x86_64 2. make it easier to extend / modify experiment with the native code gen 3. make it easier to add new primops (maybe even a magic inline asm primop?!) 4. other things i'm overlooking right now this also overlaps with a number of related tickets i've been adding to trac. a more ambitious strategic goal that won't be the initial goal, that simon marlow suggested when i chatted with him at ICFP, is to make the native code gen codebase a sort of "mini-llvm". I think thats a bit ambitious for the near term, but maybe thats the point on the horizon we may want to aim towards. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8396> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8573: "evacuate: strange closure type 0" when creating large array
by GHC 10 May '17

10 May '17

#8573: "evacuate: strange closure type 0" when creating large array ----------------------------+---------------------------------- Reporter: nad | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Linux Architecture: x86 | Type of failure: Runtime crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ----------------------------+---------------------------------- Consider the following code: {{{ module Main where import Data.Array xs :: [Int] xs = [0 .. 64988] crash :: Int -> IO () crash m = array (0, m) [ (x, x) | x <- xs ] `seq` return () strangeClosureType = do print (sum xs) crash (maxBound - 1) segFault1 = crash (maxBound - 1) segFault2 = do print (sum xs) crash (maxBound - 2) }}} If I compile the program using `ghc --make Main.hs -O -main-is strangeClosureType`, then I get the following error message: {{{ Main: internal error: evacuate: strange closure type 0 (GHC version 7.6.3 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted (core dumped) }}} If I don't use `-O`, or if I let `segFault1` or `segFault2` be `main`, then I get the following error message instead: {{{ Segmentation fault (core dumped) }}} If the number `30000` is replaced by some other number, then the strange closure error may be replaced by a segfault, or even no error at all. Perhaps this is another instance of bug #7762; I have only tested using GHC 7.6.3. I am using base 4.6.0.1 and array 0.4.0.1. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8573> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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