October 2015 - ghc-tickets

[GHC] #10838: hsig files don't have good enough error checking for wired-in types
by GHC 05 Jan '17

05 Jan '17

#10838: hsig files don't have good enough error checking for wired-in types -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 (Type checker) | Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- If I have the signature: {{{ {-# LANGUAGE NoImplicitPrelude #-} module MyPrelude where data Int a }}} And I compile it with `ghc MyPrelude.hsig -sig-of "MyPrelude is base:Prelude"` this won't actually give an error, despite `Int` having the wrong kind. The bug seems to be because `Int` is wired in and this case is not handled. Filing this so I don't forget to fix. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10838> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8107: need types to express constant argument for primop correctness
by GHC 22 Dec '16

22 Dec '16

#8107: need types to express constant argument for primop correctness ------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | 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: | ------------------------------------+------------------------------------- (not sure if this is a bug or a feature request, or a task, or a dialogue, filing as a bug for now) a number of compiler intrinsics that GHC has started to support (prefetch) and will come to support (concurrent memory operations a la http://ghc.haskell.org/trac/ghc/ticket/7883) require certain arguments to be statically fixed at compile time {{{ primop PrefetchAddrOp "prefetchAddr#" GenPrimOp Addr# -> Int# -> Addr# with llvm_only = True }}} consider the specification on the llvm side for prefetch http://llvm.org/docs/LangRef.html#llvm-prefetch-intrinsic {{{ Syntax:¶ declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>, i32 <cache type>) Overview: The ‘llvm.prefetch‘ intrinsic is a hint to the code generator to insert a prefetch instruction if supported; otherwise, it is a noop. Prefetches have no effect on the behavior of the program but can change its performance characteristics. Arguments: address is the address to be prefetched, rw is the specifier determining if the fetch should be for a read (0) or write (1), and locality is a temporal locality specifier ranging from (0) - no locality, to (3) - extremely local keep in cache. The cache type specifies whether the prefetch is performed on the data (1) or instruction (0) cache. The rw, locality and cache type arguments must be constant integers. }}} the punch line is that we're starting add primops that REALLY require certain arguments to be compile time constants to work correctly, otherwise there will by definition be compiler errors after the c-- phase when operations are passed along to the llvm backend and friends. (for the atomicity ops, i'll be looking into adding them to the native code gen, but the point being it will likely trigger an error at code gen time). a strawman approach would look like adding a type {{{ ReallyActuallyConstant :: * or unliftedtype -> * unliftedtype}}} roughly, then prefetch could have the type {{{ primop PrefetchAddrOp "prefetchAddr#" GenPrimOp Addr# ->ReallyActuallyConstant Int# -> Addr# with llvm_only = True }}} a way of emulating something like this functionality now, would be some template haskell that lets you lift a compile time constant of type t into the type ReallyActuallyConstant t, and is the only way to build a value of that type "ReallyActuallyConstant t". That said, that approach seems like a bad way of providing type safetype for making sure primops actually compile! Point being, some sort of way of nicely enforcing that a value needs to be available at compile time, that doesn't require doing abusing template haskell, is the idea i'm pointing at. Might also be useful for other things, but for now, i'm merely remarking on an invariant these primops have -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8107> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9509: No automatic specialization of inlinable imports in 7.8
by GHC 21 Dec '16

21 Dec '16

#9509: No automatic specialization of inlinable imports in 7.8 -------------------------------------+------------------------------------- Reporter: dolio | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 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: -------------------------------------+------------------------------------- According to the GHC manual, any uses of an imported definition that is overloaded and INLINABLE will automatically cause a SPECIALIZE to be generated for those uses, if appropriate. However, this no longer appears to be the case in 7.8(.3). Here is a simple test case: {{{#!hs module A (foo) where import Data.IORef foo :: Ord a => a -> IO a foo x = newIORef x >>= readIORef >>= \y -> case compare x y of LT -> return x ; _ -> return y {-# INLINABLE foo #-} }}} {{{#!hs module Main (main) where import A main = foo (5 :: Int) >>= print }}} `foo` is constructed to be long enough that GHC 7.8.3 will elect to not inline it. When compiling with 7.6.3, the core contains the following: {{{ Main.$sfoo1 :: GHC.Types.Int -> GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, GHC.Types.Int #) [GblId, Arity=2, Caf=NoCafRefs, Str=DmdType LL, Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=2, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [20 0] 55 30}] Main.$sfoo1 = \ (x_XkE :: GHC.Types.Int) (eta_B1 :: GHC.Prim.State# GHC.Prim.RealWorld) -> case GHC.Prim.newMutVar# @ GHC.Types.Int @ GHC.Prim.RealWorld x_XkE eta_B1 of _ { (# ipv_amT, ipv1_amU #) -> case GHC.Prim.readMutVar# @ GHC.Prim.RealWorld @ GHC.Types.Int ipv1_amU ipv_amT of ds1_amJ { (# ipv2_Xn8, ipv3_Xna #) -> case x_XkE of wild_axu { GHC.Types.I# x#_axw -> case ipv3_Xna of _ { GHC.Types.I# y#_axA -> case GHC.Prim.<# x#_axw y#_axA of _ { GHC.Types.False -> ds1_amJ; GHC.Types.True -> (# ipv2_Xn8, wild_axu #) } } } } } Main.$sfoo :: GHC.Types.Int -> GHC.Types.IO GHC.Types.Int [GblId, Arity=2, Caf=NoCafRefs, Str=DmdType LL, Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=True)}] Main.$sfoo = Main.$sfoo1 `cast` (<GHC.Types.Int> -> Sym <(GHC.Types.NTCo:IO <GHC.Types.Int>)> :: (GHC.Types.Int -> GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, GHC.Types.Int #)) ~# (GHC.Types.Int -> GHC.Types.IO GHC.Types.Int)) ... ------ Local rules for imported ids -------- "SPEC A.foo [GHC.Types.Int]" [ALWAYS] forall ($dOrd_sxj :: GHC.Classes.Ord GHC.Types.Int) A.foo @ GHC.Types.Int $dOrd_sxj = Main.$sfoo }}} However, in 7.8.3 and newer (I'm actually using 7.9.20140725 for this particular output, but 7.8.3 is similar), we see the following: {{{ Main.main1 :: GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, () #) [GblId, Arity=1, Str=DmdType <L,U>, Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [0] 100 0}] Main.main1 = \ (s_aIb :: GHC.Prim.State# GHC.Prim.RealWorld) -> case ((A.foo @ GHC.Types.Int GHC.Classes.$fOrdInt Main.main2) `cast` (GHC.Types.NTCo:IO[0] <GHC.Types.Int>_R :: GHC.Types.IO GHC.Types.Int ~R# (GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, GHC.Types.Int #)))) s_aIb of _ [Occ=Dead] { (# ipv_aIe, ipv1_aIf #) -> GHC.IO.Handle.Text.hPutStr2 GHC.IO.Handle.FD.stdout (GHC.Show.$fShowInt_$cshow ipv1_aIf) GHC.Types.True ipv_aIe } }}} There is no local rules section in 7.8.3. Putting a manual SPECIALIZE pragma in the main module generates comparable code to 7.6.3, so it does not appear to be a failure at that level. Rather, GHC seems to just not be generating the SPECIALIZE equivalent. Presumably this is a regression, but even if not, the manual should be revised. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9509> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10007: Fix misattribution of Cost Centre profiles to lintAnnots
by GHC 19 Dec '16

19 Dec '16

#10007: Fix misattribution of Cost Centre profiles to lintAnnots -------------------------------------+------------------------------------- Reporter: | Owner: scpmw thoughtpolice | Status: new Type: bug | Milestone: 7.10.1 Priority: high | Version: 7.10.1-rc1 Component: Profiling | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #9961 Blocking: | Differential Revisions: Phab:D616 | -------------------------------------+------------------------------------- Split off from #9961 - the profiling results while debugging erroneously reported that most cost centre profiles were a result of `lintAnnots`, as opposed to `CSE`. This is a bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10007> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10723: Make declarations in signatures "weakly bound" until they are used
by GHC 17 Dec '16

17 Dec '16

#10723: Make declarations in signatures "weakly bound" until they are used -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature | Status: new request | Priority: normal | Milestone: Component: Package | Version: 7.11 system | Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Suppose you are the author of a library in a Backpack world, and you publish a signature package which defines the entire public facing interface of your library. The library `foo` which uses of your library decides to `include` the signature package for convenience, but actually only uses a small portion of the API. Later, you make a BC-breaking change in one part of the library and release a new signature package. The library `bar` which uses your library includes this NEW signature package, using a different portion of the API which was unaffected by the by the BC change. Now, a hapless user tries to use `foo` and `bar`, but Backpack complains that the requirements are not compatible. What's the problem here? The practice of writing reusable signature packages for people to use caused the requirements of `foo` and `bar` to become too large, since they included a lot of junk that these libraries didn't actually use. It would be far better if you could `include` a signature package, but only "require" the bits of it that you actually used! How can we achieve this? 1. We augment the `ModIface` of signature merges (#10690) to record whether or not a declaration was (transitively) used or not by some module. Used declarations must be filled, but unused ones are treated more flexibly: if they are merged with a different, incompatible but used requirement, they disappear, and we don't check if an implementing module actually implemented the declaration. (If two unused incompatible requirements are merged, we just erase the name.) 2. How do we compute the usage info? I think it will have to be done during shaping (which runs the renamer). We only need to annotate each declaration a signature with the transitive set of names from other signatures that it has used--this can be incrementally computed. (It's not necessary to annotate declarations in modules, since they are always assumed to use holes). Then whenever a declaration from a signature is used in a module, we mark its transitive set as used. This information can then be used later when constructing the merged `ModIface` which represents the "public requirement" of the package. So, for example, a package containing only signatures would contain all unused declarations (however, they may start being used by a package which includes them). Any unused declaration which isn't mixed with another incompatible declaration can be imported (causing it to be used), but we will complain if you try to use a name and we can't tell which declaration to use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10723> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9601: Make the rewrite rule system more powerful
by GHC 16 Dec '16

16 Dec '16

#9601: Make the rewrite rule system more powerful -------------------------------------+------------------------------------- Reporter: spacekitteh | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more | Type of failure: than a week) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- It would be amazing if the current RULES system could be upgraded to include various predicates, or even into a full-on strategic programming system. This would allow far far more optimisations to be possible, rather than the current conservative system where you have to make sure that the optimisations ALWAYS apply. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size)
by GHC 16 Dec '16

16 Dec '16

#8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size) ----------------------------------------------+---------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more than a week) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: 8287 ----------------------------------------------+---------------------------- currently GHC's internals and code gen don't provide a strong distinction between Ints as data, and Ints for pointer / address arithmetic. This also comes up as being problematical in a number of ways. 1. We wind up having many portability issues around Int and pointer / address sizes. 2. adds some inessential complexity / problems to adding new architectures to ghc. eg x32 ABI which has 32bit pointers and 64bit ints somewhat breaks current assumptions in the GHC primops (because arrays are indexed by a byte offset, and the valid range for those is determined by the ABI pointer size!) 3. this Ints and Ptrs confusion we currently have, also means we can't leverage the Integer support in SIMD registers that is in most modern CPUs! If we could have those two separated better, theres a lot of low leve optimizations we could do for Int/Word data that we currently cant do! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8299> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10301: Plugins/dynamic loading subtly broken (it seems)
by GHC 15 Dec '16

15 Dec '16

#10301: Plugins/dynamic loading subtly broken (it seems) -------------------------------------+------------------------------------- Reporter: | Owner: thoughtpolice | Status: new Type: bug | Milestone: 7.10.2 Priority: normal | Version: 7.8.2 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: Compile-time Architecture: | crash Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #8276 Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Imported from #8276, which was originally about a Haddock bug (that was different in nature but appeared similarly): > I still experience this panic on GHC 7.8.2 with Windows x86_64: > > {{{ > $ ghci > GHCi, version 7.8.2: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > λ> import StaticFlags > λ> import Data.IORef > λ> readIORef v_opt_C_ready > Loading package array-0.5.0.0 ... linking ... done. > Loading package deepseq-1.3.0.2 ... linking ... done. > Loading package bytestring-0.10.4.0 ... linking ... done. > Loading package containers-0.5.5.1 ... linking ... done. > Loading package Win32-2.3.0.2 ... linking ... done. > Loading package filepath-1.3.0.2 ... linking ... done. > Loading package old-locale-1.0.0.6 ... linking ... done. > Loading package time-1.4.2 ... linking ... done. > Loading package directory-1.2.1.0 ... linking ... done. > Loading package pretty-1.1.1.1 ... linking ... done. > Loading package process-1.2.0.0 ... linking ... done. > Loading package Cabal-1.18.1.3 ... linking ... done. > Loading package binary-0.7.1.0 ... linking ... done. > Loading package bin-package-db-0.0.0.0 ... linking ... done. > Loading package hoopl-3.10.0.1 ... linking ... done. > Loading package hpc-0.6.0.1 ... linking ... done. > Loading package template-haskell ... linking ... done. > Loading package transformers-0.3.0.0 ... linking ... done. > Loading package ghc-7.8.2 ... linking ... done. > False > λ> staticFlags > ghc.exe: panic! (the 'impossible' happened) > (GHC version 7.8.2 for x86_64-unknown-mingw32): > Static flags have not been initialised! > Please call GHC.parseStaticFlags early enough. > > Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} > > But not with GHC 7.8.2 on Linux x86_64: > > {{{ > $ ghci > GHCi, version 7.8.2: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > λ> import StaticFlags > λ> import Data.IORef > λ> readIORef v_opt_C_ready > Loading package array-0.5.0.0 ... linking ... done. > Loading package deepseq-1.3.0.2 ... linking ... done. > Loading package bytestring-0.10.4.0 ... linking ... done. > Loading package containers-0.5.5.1 ... linking ... done. > Loading package filepath-1.3.0.2 ... linking ... done. > Loading package old-locale-1.0.0.6 ... linking ... done. > Loading package time-1.4.2 ... linking ... done. > Loading package directory-1.2.1.0 ... linking ... done. > Loading package pretty-1.1.1.1 ... linking ... done. > Loading package process-1.2.0.0 ... linking ... done. > Loading package Cabal-1.18.1.3 ... linking ... done. > Loading package binary-0.7.1.0 ... linking ... done. > Loading package bin-package-db-0.0.0.0 ... linking ... done. > Loading package hoopl-3.10.0.1 ... linking ... done. > Loading package hpc-0.6.0.1 ... linking ... done. > Loading package template-haskell ... linking ... done. > Loading package transformers-0.3.0.0 ... linking ... done. > Loading package ghc-7.8.2 ... linking ... done. > True > λ> staticFlags > [] > }}} > > This has caused problems for me when running programs such as [https://github.com/ku-fpg/hermit/ HERMIT] on Windows, since at some point, {{{parseStaticFlagsFull}}} seems to be called during program execution. A workaround is to call {{{initStaticOpts}}} manually somewhere in the program, but I feel like that shouldn't be necessary. The one above was on Windows. Also reported: > Hello, > > A similar panic also happens when running Liquid Haskell [http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/about/] on a file that uses the Units of Measure plugin [https://github.com/adamgundry/uom- plugin] > > > {{{ > liquid: liquid: panic! (the 'impossible' happened) > (GHC version 7.10.1 for x86_64-unknown-linux): > Static flags have not been initialised! > Please call GHC.parseStaticFlags early enough. > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10301> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10294: Missing instances if compiling with -fplugin
by GHC 15 Dec '16

15 Dec '16

#10294: Missing instances if compiling with -fplugin -------------------------------------+------------------------------------- Reporter: jscholl | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 (Type checker) | Operating System: Linux Keywords: | Type of failure: GHC rejects Architecture: x86_64 | valid program (amd64) | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Using the example from "9.3.3.2. Using Annotations" of the GHC user manual does not work correctly with GHC 7.10. The following fails: $ ghc -c Bug1.hs -fplugin=SayAnnNames.Plugin {{{ Bug1.hs:5:1: No instance for (Data SomeAnn) arising from an annotation In the annotation: {-# ANN foo SomeAnn #-} }}} It does not seem to matter why the type class is required: $ ghc -c Bug2.hs -fplugin=SayAnnNames.Plugin {{{ Bug2.hs:10:7: No instance for (Data SomeAnn) arising from a use of ‘bar’ In the expression: bar SomeAnn In an equation for ‘baz’: baz = bar SomeAnn }}} Compiling without -fplugin works fine, though. If SomeAnn is defined in a different module than SayAnnNames.Plugin and reexported from it, the instances are in scope, too. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10294> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9890: RTS -qa option is helpful but under-documented
by GHC 15 Dec '16

15 Dec '16

#9890: RTS -qa option is helpful but under-documented -------------------------------------+------------------------------------- Reporter: adamgundry | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | Documentation bug Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The entire documentation for the RTS `-qa` option is Use the OS's affinity facilities to try to pin OS threads to CPU cores. This is an experimental feature, and may or may not be useful. Please let us know whether it helps for you! It does help for us: enabling it on a multithreaded, moderately GC-heavy web server led to a sizeable improvement (~20%) in throughput benchmarks. However, it would be nice if the GHC documentation was a little more descriptive about what exactly this option does and how experimental it is now considered! (Relatedly, perhaps it would be worth adding a single index of RTS options in the user's guide, much like the flag reference for GHC itself.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9890> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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