November 2018 - ghc-tickets

[GHC] #10892: ApplicativeDo should use *> and <*
by GHC 05 Mar '19

05 Mar '19

#10892: ApplicativeDo should use *> and <* -------------------------------------+------------------------------------- Reporter: simonmar | Owner: Type: task | Status: new Priority: normal | Milestone: 8.0.1 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 Revisions: | -------------------------------------+------------------------------------- From @ekmett: Would it be possible to tweak the generation to use `(<*)` or `(*>)` where appropriate when the result isn't being used? For many Applicatives this can be a massive asymptotic win in terms of sharing and/or computational cost. When desugaring using (<*) you'd just omit any handling of the unused result instead. {{{ (\x y -> ...) <$> foo <* bar <*> baz }}} corresponds to {{{ do x <- foo bar y <- baz return ... }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10892> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13633: testwsdeque failure on POWER8
by GHC 04 Mar '19

04 Mar '19

#13633: testwsdeque failure on POWER8 ---------------------------------------+---------------------------------- Reporter: trommler | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.1 Keywords: SMP | Operating System: Linux Architecture: powerpc64 | Type of failure: Runtime crash Test Case: rts/testwsdeque | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ---------------------------------------+---------------------------------- On a POWER8 `testwsdeque` fails occasionally under load: {{{ Wrong exit code for testwsdeque(threaded1)(expected 0 , actual 134 ) Stderr ( testwsdeque ): internal error: FAIL: 277808608 3 13 (GHC version 8.3.20170430 for powerpc64le_unknown_linux) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13633> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15658: strange inferred kind with TypeInType
by GHC 04 Mar '19

04 Mar '19

#15658: strange inferred kind with TypeInType -------------------------------------+------------------------------------- Reporter: dmwit | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.2 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: -------------------------------------+------------------------------------- This type family has a strange kind to begin with: {{{ {-# Language TypeFamilies , TypeInType #-} type family F f a :: a }}} But it gets even stranger when you ask ghci what it thinks about F: {{{ > :k F F :: * -> forall a -> a }}} There is a forall which doesn't seem to bind any variables and hasn't got the customary delimiting dot. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15658> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14037: Fix fusion for GHC's utility functions
by GHC 04 Mar '19

04 Mar '19

#14037: Fix fusion for GHC's utility functions -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In a patchset I'm working on, I encountered a smallish "bytes allocated" regression in `perf/compiler/T5631`. After some sleuthing, I discovered that the regression is caused by using a `zipWith3M` where previously there was a `zipWithM`. Interestingly, it was not the zipped function that caused the problem, but the `zipWith3M` itself. Further sleuthing found that `zipWithM` is inlined into a combination of `sequenceA` and `zipWith`, both of which have been taught to work nicely with fusion. I thought of doing the same to GHC's `zipWith3M`, but I discovered that `base`'s `zipWith3` has no rules or inlining pragmas, suggesting that it does not fuse. I was quite surprised to find this, thinking that all functions as basic as `zipWith3` in `base` would play nicely with fusion. (Perhaps it does fuse -- I didn't actually check.) I then checked out GHC's `MonadUtils`, which defines a bunch of functions, some of which must be hammered on, and only one of which has any kind of performance- enhancing pragma. (The one is `zipWithAndUnzipM`, whose `INLINABLE` pragma was added only after much pain suffered by your dear author.) So: this ticket is a request to sweep through `MonadUtils` and `Util` and perhaps `ListSetOps`, looking for performance enhancements via fusion, tighter definitions, and such. Also, get `zipWith3` (and the other `zipWith`s) to fuse in `base`. I figure this is all some fairly low-hanging fruit for performance improvements in GHC. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14037> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15072: Teach the testsuite driver about response files
by GHC 04 Mar '19

04 Mar '19

#15072: Teach the testsuite driver about response files -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 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: -------------------------------------+------------------------------------- Currently `T14697` is disabled on Windows as that test produces a long enough command-line (mostly `-D` flags) that it runs amok of the Windows command-line length limit. It seems like the solution here will be to teach the testsuite driver to invoke GHC with a response file. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15072> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15508: concprog001 fails with various errors when compiled with -prof
by GHC 04 Mar '19

04 Mar '19

#15508: concprog001 fails with various errors when compiled with -prof -------------------------------------+------------------------------------- Reporter: osa1 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Profiling | Version: 8.5 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): Phab:D5051 | Wiki Page: -------------------------------------+------------------------------------- I'm observing a few different runtime errors. I'm not sure if they're because of different bugs so I'm filing one ticket for now. Reproduce with GHC HEAD: {{{ prog001 git:(master) $ ghc-stage2 Mult.hs -prof -fprof-auto -fforce-recomp -debug [1 of 7] Compiling Stream ( Stream.hs, Stream.o ) [2 of 7] Compiling Converter ( Converter.hs, Converter.o ) [3 of 7] Compiling Thread ( Thread.hs, Thread.o ) [4 of 7] Compiling Utilities ( Utilities.hs, Utilities.o ) [5 of 7] Compiling Trit ( Trit.hs, Trit.o ) [6 of 7] Compiling Arithmetic ( Arithmetic.hs, Arithmetic.o ) [7 of 7] Compiling Main ( Mult.hs, Mult.o ) Linking Mult ... prog001 git:(master) $ ./Mult +RTS -DS Mult: internal error: ASSERTION FAILED: file rts/sm/Sanity.c, line 210 (GHC version 8.7.20180809 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug zsh: abort (core dumped) ./Mult +RTS -DS }}} I tried to fix this in Phab:D5051 but it's causing a segfault in test `T11108` when run with profiling. Not sure what the problem is yet. It's very easy to trigger other kind of panics in `concprog001`, just try different compile and runtime flag combinations: {{{ prog001 git:(master) $ ghc-stage2 Mult.hs -prof -fprof-auto -fforce-recomp -threaded [1 of 7] Compiling Stream ( Stream.hs, Stream.o ) [2 of 7] Compiling Converter ( Converter.hs, Converter.o ) [3 of 7] Compiling Thread ( Thread.hs, Thread.o ) [4 of 7] Compiling Utilities ( Utilities.hs, Utilities.o ) [5 of 7] Compiling Trit ( Trit.hs, Trit.o ) [6 of 7] Compiling Arithmetic ( Arithmetic.hs, Arithmetic.o ) [7 of 7] Compiling Main ( Mult.hs, Mult.o ) Linking Mult ... prog001 git:(master) $ ./Mult +RTS -N2 zsh: segmentation fault (core dumped) ./Mult +RTS -N2 }}} Yet another way: {{{ prog001 git:(master) $ ghc-stage2 Mult.hs -prof -fprof-auto -fforce-recomp -threaded -debug [1 of 7] Compiling Stream ( Stream.hs, Stream.o ) [2 of 7] Compiling Converter ( Converter.hs, Converter.o ) [3 of 7] Compiling Thread ( Thread.hs, Thread.o ) [4 of 7] Compiling Utilities ( Utilities.hs, Utilities.o ) [5 of 7] Compiling Trit ( Trit.hs, Trit.o ) [6 of 7] Compiling Arithmetic ( Arithmetic.hs, Arithmetic.o ) [7 of 7] Compiling Main ( Mult.hs, Mult.o ) Linking Mult ... prog001 git:(master) $ ./Mult +RTS -N2 Mult: internal error: invalid closure, info=0x947edc (GHC version 8.7.20180809 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug zsh: abort (core dumped) ./Mult +RTS -N2 }}} It seems to work fine when not compiled for profiling so marking this bug as a profiler bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15508> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14671: Make the Template Haskell class Lift work over typed expressions
by GHC 04 Mar '19

04 Mar '19

#14671: Make the Template Haskell class Lift work over typed expressions -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Template | Version: 8.2.2 Haskell | Keywords: | Operating System: Unknown/Multiple TemplateHaskell | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- At the moment we have the `Lift` class in TH: {{{ class Lift t where lift :: t -> Q Exp }}} But that loses type information. What we want is this: {{{ Lift t where typedLift :: t -> Q (TExp t) lift :: Lift t => t -> Q Exp lift = fmap unType . typedLift }}} Otherwise, when you want the typed version, people resort to unsafe-coerce operations, which are entirely unnecessary. See [https://mail.haskell.org/pipermail/libraries/2018-January/028409.html this thread on the libraries list]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14671> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15840: Inline data constructor wrappers very late
by GHC 04 Mar '19

04 Mar '19

#15840: Inline data constructor wrappers very late -------------------------------------+------------------------------------- Reporter: aspiwack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.7 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: -------------------------------------+------------------------------------- This came up in the context of the implementation of linear types, where more data constructors have wrapper. But this should be of more general use. I want to share this in case someone can find an objection to this approach. Currently, writing a RULE involving a data constructor with a wrapper is perilous: the wrapper will be inlined in phase 2, probably before the RULE is even triggered (necessarily if the RULE only runs in phase 1). I want to remedy this situation. This proposal is mainly from Simon Peyton Jones, any misrepresentation is, of course, my own. The proposal is to inline all data constructor wrappers in phase 0. After all the RULE business has been dealt with. If we do that, we need to be quite careful about case-of-know-constructor: In {{{#!hs case $WK u of { K x -> e; … } }}} `$WK` wouldn't unfold until very late. But we don't want the `case` expression to be blocked! Otherwise we may, for instance, prevent the function's size to be small enough to be inlined. Hence a maybe some rules will not trigger. That would not be acceptable. Fortunately, in order to decide whether case-of-known-constructor can perform, the simplifier calls `exprIsConApp_maybe`. Also fortunate is that in the situation above, we really don't care about any RULE stuff (at least not in relation with `K`). So what we can do is make `exprIsConApp_maybe` a bit smarter and teach it to see through data constructor wrappers. Let's take an unpacking wrapper as an example: {{{#!hs data T = MkT {-# UNPACK #-} !(Int, Bool) $WMkT p = case p of (i,b) -> MkT i b }}} We have to see that `$WMkT u` is a constructor application. Hence we need to be able to peek through cases. We also need to be able to witness that we have done so. So the type of `exprIsConApp_maybe` would change from {{{#!hs exprIsConApp_maybe :: InScopeEnv -> CoreExpr -> Maybe (DataCon, [Type], [CoreExpr]) }}} to {{{#!hs exprIsConApp_maybe :: InScopeEnv -> CoreExpr -> Maybe ([Float],DataCon, [Type], [CoreExpr]) }}} Where `Float`-s are lets or cases with a single alternative (much like in the FloatOut pass). We then need to change case-of-known-constructor to also perform case-of- lets and case-of-cases when such floats are found. In summary: data constructor wrappers would be inlined in phase 0, except when they can trigger a case-of-known constructor, in which case they would be inlined immediately. Does anyone sees something which could go wrong with this plan? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15840> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15952: Reduce zonking-related invariants in the type checker
by GHC 04 Mar '19

04 Mar '19

#15952: Reduce zonking-related invariants in the type checker -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 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: -------------------------------------+------------------------------------- The type checker currently maintains two invariants, documented in `Note [The well-kinded type invariant]` in TcType and `Note [The tcType invariant]` in TcHsType. These are a pain to maintain, and Simon and I cooked up a plan not to. Step 1. The tcType invariant is all about `tcInferApps`, at least according to the Note. Previously, we couldn't zonk in `tcInferApps`, because types were knot-tied. But now we can! So, `tcInferApps` could take the type only (not its kind), zonk it, then get the type's (zonked) kind. This might also mean that `tc_infer_hs_type` no longer needs to return a type/kind pair, but could just return a type. After this is done, we can likely remove all the zonks that are in service to the tcType invariant, findable by a search. Step 2. The well-kinded type invariant is also about the need to zonk sometimes. But, instead, we could just always zonk on-the-fly. That is, we introduce new functions like `tcTypeKind` and `tcSubstTy` that zonk as they go. To make sure we're calling the right function at the right time, we introduce `newtype TcType = TcType { unTcType :: Type }`. Then, we're forced to call monadic functions on `TcType`s. This will likely lead to code duplication between `Type` and `TcType`, but we might be able to banish `zonkTcType` (and its many friends) entirely. Also gone would be the `naked` functions, which are all about maintaining the well-kinded type invariant. This step would, as a side effect, fix #15799 and #15918, which is about treating `TcType`s differently from `Type`s. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15952> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8657: -fregs-graph still has a limit on spill slots
by GHC 04 Mar '19

04 Mar '19

#8657: -fregs-graph still has a limit on spill slots -----------------------------------+--------------------------------------- Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Compiler (NCG) | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time crash Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -----------------------------------+--------------------------------------- The limit on spill slots was removed for the linear register allocator in 7.8, but not for `-fregs-graph`. SHA-1 fails to compile with `-fregs-graph` in 7.8. Related: #7679 (`-fregs-graph` generates poor code with the new codegen). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8657> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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