March 2018 - ghc-tickets

[GHC] #11441: RFC: Inline intermediate languages (Core, STG, Cmm, even StrictCore)
by GHC 08 Mar '19

08 Mar '19

#11441: RFC: Inline intermediate languages (Core, STG, Cmm, even StrictCore) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- Allow intermediate code inline. == Inline ''Core'' == Typeable/WithTypeable: > {{{#!hs > withTypeable :: TTypeRep a -> (Typeable a => r) -> r > }}} > > Currently, `withTypeable` cannot be written in Haskell, but it is straightforward to write in Core. Can we fix this? [http://www.seas.upenn.edu/~sweirich/papers/wadlerfest2016.pdf A reflection on types] (''2016''): > We cannot implement ''withTypeable'' in Haskell source. But we ''can'' implement it in GHC's statically-typed intermediate language, System FC. The definition is simple, roughly like this: > > {{{#!hs > withTypeable tr k = k tr -- Not quite right > }}} > > Its second argument ''k'' expects a ''Typeable'' dictionary as its value argument. But since > a ''Typeable'' dictionary is represented by a ''TypeRep'', we can simply pass ''tr'' to ''k''. > When written in System FC there is a type-safe coercion to move from ''TypeRep a'' to ''Typeable a'', > but that coercion is erased at runtime. Since the definition can be statically type checked, > ''withTypeable'' does not form part of the trusted code base. == Inline ''Cmm'' == Edkward Kmett writes his own `.cmm` [https://github.com/ekmett/concurrent/blob/master/cbits/hashmap.cmm hither], [https://github.com/ekmett/concurrent/blob/master/cbits/array.cmm yon]. == Inline ''Strict Core'' == Should [http://research.microsoft.com/en-us/um/people/simonpj/papers /strict-core/tacc-hs09.pdf Types are calling conventions] (''2009'') be implemented: > === '''4.4 The ''`seq`'' function''' === > > A nice feature of Strict Core,,ANF,, is that it is possible to give a straightforward definition of the primitive ''seq'' function of Haskell: > {{{#!hs > seq : {a:* -> b:* -> {a} -> {b} -> b} > = { \a:*. \b:*. \x:{a}. \y:{b}. let _:a = x <> in y <> } > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11441> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11315: GHC doesn't restore split objects
by GHC 08 Mar '19

08 Mar '19

#11315: GHC doesn't restore split objects -------------------------------------+------------------------------------- Reporter: snowleopard | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: -------------------------------------+------------------------------------- While working on the new Shake-based build system I came across an annoying problem related to missing split objects ([#note see note]). I still don't fully understand the reasons behind the problem, but I found that GHC doesn't restore missing split objects, as explained in the example below. I think this is a bug, but maybe this is actually a missing feature. I think it shouldn't be difficult to fix. {{{#!hs module Test (test) where test :: Int test = 0 }}} I compile the above with `ghc -split-objs Test.hs` and get two split object files in `Test_o_split`. Then if I delete any of these files, or even the whole folder, and rerun `ghc -split-objs Test.hs` the compiler doesn't bother to restore split objects, pretending that everything is up- to-date. However, if I delete `Test.o` all object files are restored. Another related issue reported by Neil Mitchell (which may be worth a separate ticket) is that even if we corrupt `Test.o` and rerun `ghc -split-objs Test.hs`, the compiler doesn't restore the object file (nor missing split objects) to the consistent state. ---- [=#note Note:] The problem I have is described here: https://github.com/snowleopard/shaking-up-ghc/issues/30. It's not necessary to follow the link to understand this ticket, however I'd appreciate any insight you might have about the reasons behind the problem and/or a possible solution. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11315> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9832: Get rid of PERL dependency of `ghc-split`
by GHC 08 Mar '19

08 Mar '19

#9832: Get rid of PERL dependency of `ghc-split` -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: task | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: Keywords: | Operating System: Windows Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- (writeme) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9832> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8964: split_marker_entry assert breaks -split-objs and -ddump-opt-cmm
by GHC 08 Mar '19

08 Mar '19

#8964: split_marker_entry assert breaks -split-objs and -ddump-opt-cmm -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: lowest | Milestone: ⊥ Component: Compiler | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Compile-time Difficulty: Easy (less than 1 | crash hour) | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- ...since the pretty-printer attempts to force the blocks list of the split_marker_entry proc. I'm not really sure what the right way to fix this is: just provide an empty block list, or hack the pretty-printer to treat split markers specially. But should be easy to fix. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8964> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8685: -split-objs doesn't work for executables
by GHC 08 Mar '19

08 Mar '19

#8685: -split-objs doesn't work for executables ------------------------------------+------------------------------------- Reporter: refold | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Driver | 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: | ------------------------------------+------------------------------------- While investigating [this bug report](https://github.com/haskell/cabal/issues/1611), I've noticed that the `-split-objs` option only works for libraries, but not for executables. That is, unlike in the case of libraries, the driver feeds only `A.o B.o ...` files to the linker instead of `A_split_0.o A_split_1.o ... B_split_0.o B_split_1.o ...`. It'd be nice if `-split-objs` could be changed to also work on executables. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8685> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8629: Option 'split-objs' being ignored when trying to reduce object code size in iOS cross-compilation
by GHC 08 Mar '19

08 Mar '19

#8629: Option 'split-objs' being ignored when trying to reduce object code size in iOS cross-compilation ------------------------------------+--------------------------------- Reporter: f1rstmistake | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Keywords: ios | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+--------------------------------- I have been trying to statically link Pandoc packages to iOS application following the guide in https://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling/iOS and it's great so far! I have finally successfully use Pandoc library in iOS app, but the binary size is very big! 1. More than 50MB when using Pandoc library. 2. Around 5MB for simple haskell code. I try to add “split-objs: True” in .cabal/config file, but when running cabal I got this message: {{{ Preprocessing library pandoc-1.12.2.1... unused terminals: 1 on the commandline: Warning: ignoring -fsplit-objs }}} And if I ignore that, at the end of build, I get another error message that stop the build. {{{ cabal: dist-i386/build/Text/Pandoc_o_split: does not exist }}} I try with another package and got similar error message. It seems that split-objs not only being ignored by cross-compilation ghc, but will also fail the build. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8629> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8095: TypeFamilies painfully slow
by GHC 08 Mar '19

08 Mar '19

#8095: TypeFamilies painfully slow -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.6.3 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: Compile-time Architecture: Unknown/Multiple | performance bug Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: 5321 | -------------------------------------+------------------------------------- I'm using the TypeFamilies extension to generate types that are quite large. GHC can handle these large types fine when they are created manually, but when type families get involved, GHC's performance dies. Unlike in ticket #5321, using tail recursion does not eliminate the problem, and the order of arguments greatly affects compile time. I've attached a file Types.hs that demonstrates the problems. This file generates another Haskell file which has the problems. It takes 3 flags. The first is the size of the type to generate, the second is which type family function to use, and the third is whether to call the type family or just use a manually generated type. Here are my performance results: Using non-tail recursion, I get these results. I have to increase the stack size based on the size of the type I want to generate. {{{ $ ./Types 200 a a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=250 real 0m2.973s $ ./Types 300 a a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=350 real 0m6.018s $ ./Types 400 a a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=450 real 0m9.995s $ ./Types 500 a a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=550 real 0m15.645s }}} Tail recursion generates much slower compile times for some reason, and I still need to adjust the stack size: {{{ $ ./Types 200 b a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=250 real 0m16.120s }}} Changing the order of arguments to the recursive type family greatly changes the run times: {{{ $ ./Types 200 c a > test.hs && time ghc test.hs > /dev/null -fcontext- stack=250 real 0m6.095s }}} Without the type family, I get MUCH better performance: {{{ $ ./Types 10000 a d > test.hs && time ghc test.hs > /dev/null real 0m2.271s }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8095> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11715: There's something fishy going on with Constraint
by GHC 07 Mar '19

07 Mar '19

#11715: There's something fishy going on with Constraint -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc1 (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: -------------------------------------+------------------------------------- I first noticed something was a bit odd with `Constraint` when chasing #11334. Consider this testcase, {{{#!hs import Data.Typeable main = do print $ typeRep (Proxy :: Proxy Eq) print $ typeOf (Proxy :: Proxy Eq) }}} With `ghc-8.0` this will produce, {{{ Eq Proxy (* -> *) Eq }}} Notice the second line; GHC seems to be claiming that `Eq :: * -> *`, which is clearly nonsense. I believe this issue may be the cause of some of the testsuite failures that I'm seeing on #11011. Unfortunately I haven't the foggiest where this issue might originate. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11715> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12509: ghci -XSafe fails in an inscrutable way
by GHC 06 Mar '19

06 Mar '19

#12509: ghci -XSafe fails in an inscrutable way -------------------------------------+------------------------------------- Reporter: int-e | 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: -------------------------------------+------------------------------------- Trying to run `ghci -XSafe` produces the following output: {{{ GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help <interactive>:1:6: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:30: error: Not in scope: ‘System.IO.stdin’ No module named ‘System.IO’ is imported. <interactive>:1:46: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:70: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:94: error: Not in scope: ‘System.IO.stdout’ No module named ‘System.IO’ is imported. <interactive>:1:111: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:135: error: Not in scope: ‘System.IO.hSetBuffering’ No module named ‘System.IO’ is imported. <interactive>:1:159: error: Not in scope: ‘System.IO.stderr’ No module named ‘System.IO’ is imported. <interactive>:1:176: error: Not in scope: data constructor ‘System.IO.NoBuffering’ No module named ‘System.IO’ is imported. }}} I'm not sure whether this should work, but in any case the error message is horrible. I tried adding `-trust base` to no avail. For comparison, ghc-7.10.3 starts with no trouble: {{{ > ghci -XSafe GHCi, version 7.10.2: http://www.haskell.org/ghc/ :? for help Prelude> }}} (Motivation: I'm using ghci in Safe mode to track down import problems with SafeHaskell. As a workaround, I can use `:set -XSafe` after ghci's startup is done.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12509> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12102: “Constraints in kinds” illegal family application in instance (+ documentation issues?)
by GHC 06 Mar '19

06 Mar '19

#12102: “Constraints in kinds” illegal family application in instance (+ documentation issues?) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: TypeInType | 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 8.0.0.20160511. Example from the user guide: [https://downloads.haskell.org/~ghc/8.0.1/docs/html/users_guide/glasgow_exts… #constraints-in-kinds Constraints in kinds] {{{#!hs type family IsTypeLit a where IsTypeLit Nat = 'True IsTypeLit Symbol = 'True IsTypeLit a = 'False data T :: forall a. (IsTypeLit a ~ 'True) => a -> * where MkNat :: T 42 MkSymbol :: T "Don't panic!" }}} Deriving a standalone `Show` instance *without* the constraint works fine {{{#!hs deriving instance Show (T a) }}} but I couldn't define a `Show` instance given the constraints: {{{#!hs -- • Couldn't match expected kind ‘'True’ -- with actual kind ‘IsTypeLit a0’ -- The type variable ‘a0’ is ambiguous -- • In the first argument of ‘Show’, namely ‘T a’ -- In the stand-alone deriving instance for ‘Show (T a)’ deriving instance Show (T a) }}} let's add constraints {{{#!hs -- • Couldn't match expected kind ‘'True’ -- with actual kind ‘IsTypeLit lit’ -- • In the first argument of ‘Show’, namely ‘T (a :: lit)’ -- In the instance declaration for ‘Show (T (a :: lit))’ instance IsTypeLit lit ~ 'True => Show (T (a :: lit)) where }}} let's derive for a single literal {{{#!hs -- • Illegal type synonym family application in instance: -- T Nat -- ('Data.Type.Equality.C:~ -- Bool -- (IsTypeLit Nat) -- 'True -- ('GHC.Types.Eq# Bool Bool (IsTypeLit Nat) 'True <>)) -- 42 -- • In the stand-alone deriving instance for ‘Show (T (42 :: Nat))’ deriving instance Show (T (42 :: Nat)) }}} same happens with {{{#!hs instance Show (T 42) where }}} ---- The documentation > Note that explicitly quantifying with `forall a` is not necessary here. seems to be wrong since removing it results in {{{ tVDv.hs:10:17-18: error: … • Expected kind ‘a’, but ‘42’ has kind ‘Nat’ • In the first argument of ‘T’, namely ‘42’ In the type ‘T 42’ In the definition of data constructor ‘MkNat’ Compilation failed. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12102> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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