March 2015 - ghc-tickets

[GHC] #9805: Use TrieMaps to speed up type class instance lookup
by GHC 17 Jul '17

17 Jul '17

#9805: Use TrieMaps to speed up type class instance lookup -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: task | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.9 checker) | Operating System: Keywords: | Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Currently, type class instance resolution is performed by doing a map lookup by type class, and then linearly matching against every instance. This is not great, and for a while, simonpj has been keen on using the TrieMap data structure in GHC, which has been previously used to implement a map from CoreExprs to various things (e.g. for CSE). What makes this a little tricky is that instance lookup isn't intended to be an exact match: we should unify so-called template variables and provide a substitution; furthermore, there may be multiple matches. After some prototyping, I think we should be able to make this work. The primary refactoring we have to do is *maintain the key associated with an entry in a TrieMap*. Unlike the current uses of TrieMaps, where it's acceptable to lose the underlying key associated with an entry in the TrieMap, we need to know the key when doing unification, because it may be reported in the substitution. There are a few knock-on effects of this: * We should add a method `foldWithKeyTM :: (Key m -> a -> b -> b) -> m a -> b -> b` to the `TrieMap` type class. * We need a variant of `UniqFM` which tracks the original key that was used. I propose we name it `UniqKM` (unique key map). A number of implementations of `TrieMap` need to be adjusted to use this instead of `UniqFM`. * Why can't we just represent keyed TrieMaps as `TypeMap (Type, a)`? It might be possible. An insurmountable difficulty would be if we need to know the partial key PRIOR to having finished traversing the TrieMap; however, for the parts of the unification algorithm I've implemented, this does not seem to be the case. The primary actual difficulty is that `Type` uses a named representation, whereas `TypeMap` keys are on-the-fly deBruijn numbered. There would at least be some annoying fiddliness. * Reversing the deBruijn numbered key into a `Type` is a bit goofy. Essentially, you need the reverse of the current `CmEnv`: a mapping from de Bruijn levels to the `Var` you've decided to allocate. (I've called this `CfEnv` in my prototype) * When we represent a TrieMap binder, we have to put the binder map on the OUTSIDE, as opposed to the inside as it is currently. Otherwise, we can't update the `CfEnv` with the new mapping before making the recursive call to fold-with-key. I'll attach the standalone Haskell file I used to prototype this, wherein I copy-pasted a lot of Haskell from GHC's source and implemented fuzzy map on a simplified version of `Type`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9805> 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 11 Jul '17

11 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] #10150: Suppress orphan instance warning per instance
by GHC 11 Jul '17

11 Jul '17

#10150: Suppress orphan instance warning per instance -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | Milestone: Priority: low | Version: 7.11 Component: Compiler | Operating System: Unknown/Multiple (Type checker) | Type of failure: None/Unknown Keywords: | Blocked By: Architecture: | Related Tickets: Unknown/Multiple | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- In the same way we have overlapping/incoherent instance pragmas which can be applied on a per instance basis, it would be good to have a `-fno-warn- orphan-instance` pragma which can be applied on a per-instance basis. Annoyingly, there is not an obvious syntax to use for this case, since SOP for a module with orphan instances is `{-# GHC_OPTIONS -fno-warn-orphans #-}` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10150> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9588: Add `MonadPlus {IO, Either e}` and `Alternative (Either e)` instances
by GHC 29 Jun '17

29 Jun '17

#9588: Add `MonadPlus {IO,Either e}` and `Alternative (Either e)` instances -------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: 7.10.1 Component: libraries/base | Version: Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following 3 instances are currently Orphans in `transformers` but shall be defined in `base` instead: {{{#!hs instance MonadPlus IO instance MonadPlus (Either e) instance Alterantive (Either e) }}} This proposal by SPJ already passed the CLC back in April and only needs implementing. I'll submit a patch shortly to Phab -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9588> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8697: Type rationals
by GHC 16 Jun '17

16 Jun '17

#8697: Type rationals ------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: Type: feature request | 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: | ------------------------------------+------------------------------------- I've used GHC's Type Nats to implement my own type level rationals (code below). This works fine, but the syntax is a little funky because you have to write out the number as a fraction. For example, you must write 13/10 instead of 1.3; or even worse, 13/1 instead of 13. It would be nice to just write the decimal notation. I only see one potential problem with this feature: the dot in the decimal notation could interfere with the dot in forall statements. I guess this can be parsed unambiguously, but maybe not. {{{ data Frac = Frac Nat Nat data instance Sing (n::Frac) = SFrac Integer Integer instance (SingI a, SingI b) => SingI ('Frac a b) where sing = SFrac (fromSing (sing :: Sing a)) (fromSing (sing :: Sing b)) instance Fractional r => SingE (Kind :: Frac) r where fromSing (SFrac a b) = fromIntegral a/fromIntegral b type (/) a b = 'Frac a b }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8697> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8703: Use guard pages rather than heap checks
by GHC 07 Jun '17

07 Jun '17

#8703: Use guard pages rather than heap checks ------------------------------------+------------------------------------- Reporter: schyler | Owner: simonmar Type: feature request | Status: new Priority: normal | Milestone: Component: Runtime System | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- By mmap'ing memory using MAP_ANONYMOUS (or /dev/zero) as PROT_NONE (Windows has an equivalent functionality with VirtualAlloc), it's possible to create a page that will fault when read or written to. It may be possible to remove the heap checks in the runtime, speeding up allocations, and instead expand the heap when a fault is raised. This is likely cheaper for large pages full of many small allocations than the cost of the heap checking branch. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8703> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8905: Function arguments are always spilled/reloaded if scrutinee is already in WHNF
by GHC 26 May '17

26 May '17

#8905: Function arguments are always spilled/reloaded if scrutinee is already in WHNF ------------------------------+-------------------------------------------- Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime performance bug Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- The code generator unnecessarily spills and reloads function arguments if the scrutinee turns out to be already evaluated (i.e. has non-zero tag bits). Here's the beginning of a function body, taken from the `insert` function at https://github.com/tibbe/unordered- containers/blob/master/Data/HashMap/Base.hs#L303: {{{ c2wQ: // stack check if ((Sp + -72) < SpLim) goto c2wR; else goto c2wS; c2wR: // stack check failure R1 = PicBaseReg + $wpoly_go_closure; I64[Sp - 40] = R2; I64[Sp - 32] = R3; P64[Sp - 24] = R4; I64[Sp - 16] = R5; P64[Sp - 8] = R6; Sp = Sp - 40; call (I64[BaseReg - 8])(R1) args: 48, res: 0, upd: 8; c2wS: // stack check success I64[Sp - 40] = PicBaseReg + block_c2my_info; // return addr for eval R1 = R6; // t I64[Sp - 32] = R2; // spill: s I64[Sp - 24] = R3; // spill: x P64[Sp - 16] = R4; // spill: k I64[Sp - 8] = R5; // spill: h Sp = Sp - 40; if (R1 & 7 != 0) goto c2my; else goto c2mz; // eval check of t c2mz: // eval check failed call (I64[R1])(R1) returns to c2my, args: 8, res: 8, upd: 8; // eval c2my: // eval check succeeded _s2b1::I64 = I64[Sp + 8]; // reload: h _s2b2::I64 = I64[Sp + 16]; // reload: k _s2b3::P64 = P64[Sp + 24]; // reload: x _s2b4::I64 = I64[Sp + 32]; // reload: s switch [0 .. 4] (R1 & 7 - 1) { case 0 : goto c2wK; case 1 : goto c2wL; case 2 : goto c2wM; case 3 : goto c2wN; case 4 : goto c2wO; } }}} It seems to me that all the spills/reloads could be pushed into the `c2mz` block. The `c2my` block, in its current form, is reused for a heap check failure case, so the heap check most likely will have to do its own spilling/reloading. However, since the scrutinee not having tags bit or the eval checking failing is not the common case, they should be out of the common path. If it matters the data type is spine strict so GHC should have enough information to know that the common case (e.g. self-recursive calls) already have an evaluated argument (although there might be an indirection in some cases). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8905> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9287: changed dependency generation
by GHC 23 May '17

23 May '17

#9287: changed dependency generation ------------------------------------+-------------------------------------- Reporter: maeder | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Documentation | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Documentation bug Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+-------------------------------------- "ghc -M" for ghc-7.8.x changed in that an error occurs: {{{ You must specify at least one -dep-suffix }}} By chance (#8746) I found that {{{ ghc -M -dep-suffix "" B.hs }}} works, but only for the new ghc-7.8.x. For module B importing module A the following dependencies are generated: {{{ # DO NOT DELETE: Beginning of Haskell dependencies A.o : A.hs B.o : B.hs B.o : A.hi # DO NOT DELETE: End of Haskell dependencies }}} The same command used with ghc-7.6.x produces wrong dependencies: {{{ # DO NOT DELETE: Beginning of Haskell dependencies A.o A._o : A.hs B.o B._o : B.hs B.o : A.hi B._o : A._hi # DO NOT DELETE: End of Haskell dependencies }}} Obviously, only for dynamic linking a dep-suffix should be needed. However for ghc-7.6. this must be "dyn" and for ghc-7.8.x this must "dyn_" plus the empty suffix! {{{ ghc-7.6.3 -M -dep-suffix dyn B.hs ghc-7.8.2 -M -dep-suffix dyn_ -dep-suffix "" B.hs }}} Both calls produce: {{{ # DO NOT DELETE: Beginning of Haskell dependencies A.o A.dyn_o : A.hs B.o B.dyn_o : B.hs B.o : A.hi B.dyn_o : A.dyn_hi # DO NOT DELETE: End of Haskell dependencies }}} The changed behavior is not documented in http://www.haskell.org/ghc/docs/7.8.2/html/users_guide/separate- compilation.html#makefile-dependencies The (accidental?) change should also be documented in the release notes! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9287> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9445: GHC Panic: Tick Exhausted with high factor
by GHC 22 May '17

22 May '17

#9445: GHC Panic: Tick Exhausted with high factor -------------------------------------+------------------------------------- Reporter: adinapoli | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: panic | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: Difficulty: Unknown | None/Unknown Blocked By: | Test Case: Related Tickets: 5539 | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Hello guys, this is an old bug which has been reported so many times that I'm not sure this will be noise or something useful. In a nutshell I have been hit by this bug installing the library "SFML", which relies heavily on FFI. The only interesting thing of this report is that it was necessary an very high simpl-factor to make the installation go through! Pre-bump: {{{ Resolving dependencies... In order, the following will be installed: SFML-0.2.0.0 (reinstall) Warning: Note that reinstalls are always dangerous. Continuing anyway... Configuring SFML-0.2.0.0... Building SFML-0.2.0.0... Preprocessing library SFML-0.2.0.0... [...] [34 of 71] Compiling SFML.Graphics.Transform ( dist/build/SFML/Graphics/Transform.hs, dist/build/SFML/Graphics/Transform.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Simplifier ticks exhausted When trying UnfoldingDone $j_sZQW{v} [lid] 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: 2655928 }}} And this was the magic line: {{{ cabal install SFML --ghc-option=-fsimpl-tick-factor=1630 }}} HTH, it turns out it's quite an annoying one! And yes, "1630" was the smaller factor which made the installation possible. Alfredo -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9445> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9700: Support C structures in Haskell FFI
by GHC 22 May '17

22 May '17

#9700: Support C structures in Haskell FFI -------------------------------------+------------------------------------- Reporter: Yuras | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: Phab:D252 -------------------------------------+------------------------------------- This ticket is for tracking progress on [[CStructures]] language extension proposal. The idea is to support C structures in Haskell FFI. See wiki for details. If it will be accepted, I'm going to implement it in few steps. The first one is to support structures as return value. Platform specific part for that is already implemented, see Phab:D252 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9700> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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