November 2015 - ghc-tickets

[GHC] #9701: GADTs not specialized properly
by GHC 21 Mar '17

21 Mar '17

#9701: GADTs not specialized properly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Runtime Blocked By: | performance bug Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- This has probably been raised before, but I can't find a ticket. If I write {{{#!hs data Silly a where Silly :: Ord a => a -> Silly a isItSilly :: a -> Silly a -> Bool isItSilly a (Silly x) = a < x isItSillyInt :: Int -> Silly Int -> Bool isItSillyInt = isItSilly }}} then I get {{{ isItSilly isItSilly = \ @ a_aBq eta_B2 eta1_B1 -> case eta1_B1 of _ { Silly $dOrd_aBs x_aAy -> < $dOrd_aBs eta_B2 x_aAy } isItSillyInt isItSillyInt = isItSilly }}} Although GHC knows that `eta_B2` is an `Int`, and `x_aAy` therefore must be one as well, it looks up the `<` method in the `eta1_B1` dictionary instead of just using `ltInt`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9701> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8751: Show parenthesised output of expressions in ghci
by GHC 21 Mar '17

21 Mar '17

#8751: Show parenthesised output of expressions in ghci ------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Iceland_jack Type: feature request | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Operator fixity can be a source of bugs (even for experienced users!),[#point1 (1)] precedence levels may vary between languages and then there are user-defined operators. Attached is a patch for a ghci command allowing users to quickly parenthesise expressions as a sanity check (and as an alternative to using :info and parsing the result yourself). The command itself is activated with `:paren`: {{{ ghci> :paren 2 + 10 * 4 / 3 2 + ((10 * 4) / 3) ghci> :paren \a b → a == b || b && a == (b == a) || b \ a b -> (a == b) || ((b && (a == (b == a))) || b) ghci> :paren 5 + 1 `mod` 2 5 + (1 `mod` 2) ghci> :paren 5 * 1 `mod` 2 (5 * 1) `mod` 2 }}} A friend of mine also pointed out that this could eventually be integrated into `haskell-mode` where the user could temporarily replace an expression with a parenthesised version or have different colours indicate different levels of logical nesting. [=#point1 (1)] [http://www.knosof.co.uk/cbook/accu06.html Developer beliefs about binary operator precedence] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8751> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10143: Separate PprFlags (used by Outputable) from DynFlags
by GHC 18 Mar '17

18 Mar '17

#10143: Separate PprFlags (used by Outputable) from DynFlags -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- At the moment, SDoc computations have full access to the entirety of DynFlags, despite only a minusculely small amount of the data structure being relevant to them. This proposal is to split out a `PprFlags` structure which will be contained in a `DynFlags`, and contain dynamic flags JUST for pretty-printing. There will be a function `pprFlags :: DynFlags -> PprFlags`. This also helps eliminate the circular dependency between `DynFlags` and `Outputable`. This structure is not complete, but it should give a sense for some of the things that need to be put in here: {{{ data PprFlags = PprFlags { pprUserLength :: Int, pprCols :: Int, useUnicode :: Bool, useUnicodeSyntax :: Bool, targetPlatform :: Platform, suppressUniques :: Bool, errorSpans :: Bool, suppressModulePrefixes :: Bool } }}} I have a patch in-progress which factors this out, but I want to get some sign-offs that this is a good refactoring before I finish it. Thanks! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10143> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8255: GC Less Operation
by GHC 08 Mar '17

08 Mar '17

#8255: GC Less Operation ------------------------------+-------------------------------------------- Reporter: sirinath | Owner: Type: feature | Status: new request | Milestone: Priority: highest | Version: 7.6.3 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: Runtime performance bug Architecture: | Test Case: Unknown/Multiple | Blocking: Difficulty: Unknown | Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- Hi, Is it possible to eliminated GC through Automatic Reference Counting (ARC) like in Objective C / Clang. S -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8255> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10712: Regression: make TEST=exceptionsrun001 WAY=optasm is failing
by GHC 07 Mar '17

07 Mar '17

#10712: Regression: make TEST=exceptionsrun001 WAY=optasm is failing -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: high | Milestone: 7.12.1 Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: base/tests/exceptionsrun001 | Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- The following program, extracted from the test exceptionsrun001, should exit with exitcode 100. Instead, when compiled with `-O1`, it never gets past the ioTest and somehow manages to exit with exitcode 0. {{{ {-# LANGUAGE ScopedTypeVariables #-} module Main where import Control.Exception import System.IO.Error import System.Exit main = do ioTest exitWith (ExitFailure 100) ioTest :: IO () ioTest = (catch (ioError (userError "wibble")) (\(e::IOException) -> return ()) }}} I think this will require a git bisect: * last known good commit: 34bb4605d4ec5b131df57ca4c91d6840b7539194 * first known bad commit: f83aab95f59ae9b29f22fc7924e050512229cb9c. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10712> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11006: Warning: Glomming in Main
by GHC 07 Mar '17

07 Mar '17

#11006: Warning: Glomming in Main -------------------------------------+------------------------------------- Reporter: ezyang | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: 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 Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The Travis build bot is reporting a test failure with debugging on, relating to glomming: {{{ Actual stderr output differs from expected: --- /dev/null 2015-01-28 16:31:58.000000000 +0000 +++ ./lib/integer/integerConstantFolding.run.stderr.normalised 2015-10-22 20:31:03.287376925 +0000 @@ -0,0 +1,2 @@ +WARNING: file compiler/simplCore/OccurAnal.hs, line 66 + Glomming in Main: [s3k0 :->, s3kc :->, s3kq :->, s3kr :->] \ No newline at end of file *** unexpected failure for integerConstantFolding(normal) }}} Full log https://s3.amazonaws.com/archive.travis- ci.org/jobs/86899099/log.txt -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11006> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11076: Demand information of foreign calls is wrong
by GHC 06 Mar '17

06 Mar '17

#11076: Demand information of foreign calls is wrong -------------------------------------+------------------------------------- Reporter: luite | 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 Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Foreign calls of all types (including prim calls) use `mkFCallId` to create a fresh `Id` for each one. This Id claims to be strict in all arguments, which is not correct for foreign calls that allow lifted types to be passed. This also causes some trouble for GHCJS. I hope to get a fix in 7.10.3. Can we leave the strictness sig out entirely perhaps? Most arguments would be trivially strict since they're unboxed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11076> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10830: maximumBy has a space leak
by GHC 04 Mar '17

04 Mar '17

#10830: maximumBy has a space leak -------------------------------------+------------------------------------- Reporter: | Owner: NeilMitchell | Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.10.2 libraries/base | Keywords: | Operating System: Windows Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Given the program: {{{#!hs import Data.List main = print $ maximumBy compare [1..10000] }}} Compiling with {{{-O2}}}, on GHC 7.8.3 this runs in constant stack space (works fine with {{{+RTS -K1K}}}). With GHC 7.10.2 I get: {{{ $ ghc --make Test.hs -O2 -rtsopts [1 of 1] Compiling Main ( Test.hs, Test.o ) Linking Test.exe ... $ Test +RTS -K100K Stack space overflow: current size 33680 bytes. Use `+RTS -Ksize -RTS' to increase it. }}} Not sure why it's failing at 33K instead of 100K, but it's certainly taking more than 1K as GHC 7.8.3 did. See #3416 for previous discussion of this issue. My guess is that in older versions of GHC the strictness analysis managed to kick in and optimise things. With the burnt bridges that no longer works. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10830> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9729: GHCi accepts invalid programs when recompiling
by GHC 01 Mar '17

01 Mar '17

#9729: GHCi accepts invalid programs when recompiling -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: GHC Blocked By: | accepts invalid program Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Here's what's happening: Module A imports module B. Module B contains a function with constraints that are '''required''' to compile module B. If I load module A in GHCi, I can remove some (required) constraints on the function in module B and GHCi will successfully reload module B. My example uses the [https://hackage.haskell.org/package/syntactic syntactic] library. I attempted to recreate the situation I just described without syntactic, but I was unsuccessful. Module A.hs: {{{ #!haskell module A where import B import Data.Syntactic.Sugar.BindingT () main = print "hello" }}} Module B.hs: {{{ #!haskell {-# LANGUAGE GADTs, TypeOperators, FlexibleContexts #-} module B where import Data.Syntactic data Let x where Let :: Let (a :-> (a -> b) :-> Full b) share :: (Let :<: sup, sup ~ Domain b, sup ~ Domain a, Internal (a -> b) ~ (Internal a -> Internal b), -- remove me Syntactic a, Syntactic b, Syntactic (a -> b), SyntacticN (a -> (a -> b) -> b) (ASTF sup (Internal a) -> ASTF sup (Internal (a -> b)) -> ASTF sup (Internal b))) => a -> (a -> b) -> b share = sugarSym Let }}} Here's a terminal transcript: {{{ $ ghci A [1 of 2] Compiling B ( testsuite/B.hs, interpreted ) [2 of 2] Compiling A ( testsuite/A.hs, interpreted ) Ok, modules loaded: A, B. > (Now remove the constraint from B and save. This *should* break module B) > :r [1 of 2] Compiling B ( testsuite/B.hs, interpreted ) Ok, modules loaded: A, B. > :q $ ghci B [1 of 2] Compiling B ( testsuite/B.hs, interpreted ) testsuite/B.hs:21:9: Could not deduce (Internal (a -> b) ~ (Internal a -> Internal b)) }}} If I had to guess what's going on, it's that GHCi is remembering the instance that A imports from BindingT: {{{ instance (...) => Syntactic (a -> b) where type Internal (a -> b) = Internal a -> Internal b }}} This instance implies the constraint that module B needs, however it should never be visible to module B. GHCi seems to be ignoring that and using the instance to recompile module B. When compiling from scratch, module B is compiled first, so of course the instance (and therefore the constraint) are not visible. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9729> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10749: Boot file instances should imply superclasses
by GHC 01 Mar '17

01 Mar '17

#10749: Boot file instances should imply superclasses -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.11 Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Currently, if I write the following program: {{{ -- A.hs-boot module A where data T instance Ord T -- B.hs module B where import {-# SOURCE #-} A f :: T -> T -> Bool f x y = x == y }}} I get: {{{ B.hs:4:11: No instance for (Eq T) arising from a use of `==' Possible fix: add an instance declaration for (Eq T) In the expression: x == y In an equation for `f': f x y = x == y }}} This is a bit confusing, because Ord instances are supposed to imply Eq instances. GHC should either: 1. Reject A.hs-boot (claiming that it could not find evidence that T had an Eq instance), or 2. Accept B.hs, since the instance requirement for Ord should imply Eq. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10749> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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