September 2017 - ghc-tickets

[GHC] #14251: LLVM Code Gen messes up registers
by GHC 07 Dec '18

07 Dec '18

#14251: LLVM Code Gen messes up registers -------------------------------------+------------------------------------- Reporter: angerman | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.3 (LLVM) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Due to the way the LLVM Code Gen generates Function Singnatures, it is possible to end up mixed up registers. A slightly adapted T8064 {{{#!hs {-# LANGUAGE MagicHash, BangPatterns #-} module Main where import GHC.Exts {-# NOINLINE f #-} f :: (Int# -> Float# -> Double# -> Float# -> Double# -> String) -> String f g = g 3# 4.0# 5.0## 6.0# 6.9## ++ " World!" {-# NOINLINE p #-} p :: Int# -> Float# -> Double# -> Float# -> Double# -> String p i j k l m = "Hello" {-# NOINLINE q #-} q :: Int# -> Int# -> Float# -> Double# -> Float# -> Double# -> String q _ i j k l m = "Hello " ++ show (F# l) ++ " " ++ show (D# m) {-# NOINLINE r #-} r :: Int# -> Float# -> Double# -> Float# -> Double# -> String r i = let !(I# z) = length [I# 1# .. I# i] in \j k l m -> p z j k l m -- ghc won't eta-expand around the length, because it has unknown cost main = do putStrLn (f p) -- fast call putStrLn (f r) -- slow call: function but wrong arity let g = last [q 1#] putStrLn (f g) -- slow call: thunk }}} will produce the following results: {{{ ../inplace/bin/ghc-stage1 -fllvm -fforce-recomp T6084.hs -O2 -o T6084-llvm && ./T6084-llvm [1 of 1] Compiling Main ( T6084.hs, T6084.o ) Linking T6084-llvm ... Hello World! Hello World! Hello 4.0 5.0 World! ../inplace/bin/ghc-stage1 -fasm -fforce-recomp T6084.hs -O2 -o T6084-asm && ./T6084-asm [1 of 1] Compiling Main ( T6084.hs, T6084.o ) Linking T6084-asm ... Hello World! Hello World! Hello 6.0 6.9 World! }}} The underlying reason is that (at least for X86_64) the Float and Double registers alternate. The llvm code gen creates function signatures based on the live registers (instead of all). For `q` only the last Float and Double register are `live`. However when calling `q` we pass `f1: Float -> d1: Double -> f2: Float -> d2: Double`. `f2` and `d2` are silently ignored, and in the function body, we now have `f2 <- f1` and `d2 <- d1`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14251> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13786: GHC panic on Mac OS X with "cabal repl" / "stack repl" on GHC 8.0.2 and 7.8.3
by GHC 07 Dec '18

07 Dec '18

#13786: GHC panic on Mac OS X with "cabal repl" / "stack repl" on GHC 8.0.2 and 7.8.3 -------------------------------------+------------------------------------- Reporter: ppelleti | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.2 Keywords: | Operating System: MacOS X Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Using [https://github.com/ppelleti/hs-mercury-api this package], I tried doing "stack repl" with GHC 8.0.2: {{{ whiteandnerdy:hs-mercury-api ppelleti$ stack repl The following GHC options are incompatible with GHCi and have not been passed to it: -threaded * * * * * * * * The main module to load is ambiguous. Candidates are: 1. Package `mercury-api' component exe:tmr-firmware with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr- firmware.hs 2. Package `mercury-api' component exe:tmr-gpio with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-gpio.hs 3. Package `mercury-api' component exe:tmr-lock with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-lock.hs 4. Package `mercury-api' component exe:tmr-params with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-params.hs 5. Package `mercury-api' component exe:tmr-read with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-read.hs 6. Package `mercury-api' component exe:tmr-write with main-is file: /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-write.hs You can specify which one to pick by: * Specifying targets to stack ghci e.g. stack ghci mercury-api:exe:tmr- firmware * Specifying what the main is e.g. stack ghci --main-is mercury-api:exe :tmr-firmware * Choosing from the candidate above [1..6] * * * * * * * * Specify main module to use (press enter to load none): 4 Loading main module from cadidate 4, --main-is /Users/ppelleti/programming/haskell/hs-mercury-api/examples/tmr-params.hs Configuring GHCi with the following packages: mercury-api GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91859_0/libghc_5.dylib, 5): Symbol not found: _TMR_SR_cmdStopReading Referenced from: /var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91859_0/libghc_5.dylib Expected in: flat namespace in /var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91859_0/libghc_5.dylib Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This bug appears to have been around a while, because it also happens with GHC 7.8.3: {{{ whiteandnerdy:hs-mercury-api ppelleti$ cabal repl Preprocessing library mercury-api-0.1.0.0... GHCi, version 7.8.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. 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 binary-0.7.1.0 ... linking ... done. Loading package text-1.2.2.1 ... linking ... done. Loading package hashable-1.2.6.0 ... linking ... done. Loading package unordered-containers-0.2.8.0 ... linking ... done. Loading package clock-0.7.2 ... linking ... done. Loading package old-locale-1.0.0.6 ... linking ... done. Loading package time-1.4.2 ... linking ... done. Loading package unix-2.7.0.1 ... linking ... done. Loading package ansi-terminal-0.6.2.3 ... linking ... done. Loading object (static) dist/build/cbits/api/tmr_strerror.o ... done Loading object (static) dist/build/cbits/api/tmr_param.o ... done Loading object (static) dist/build/cbits/api/hex_bytes.o ... done Loading object (static) dist/build/cbits/api/tm_reader.o ... ghc: panic! (the 'impossible' happened) (GHC version 7.8.3 for x86_64-apple-darwin): Loading temp shared object failed: dlopen(/var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91576_0/ghc91576_4.dylib, 9): Symbol not found: _TMR_SR_SerialTransportNativeInit Referenced from: /var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91576_0/ghc91576_4.dylib Expected in: flat namespace in /var/folders/d1/v9ptqpx12mdcxj77509440rc0000gn/T/ghc91576_0/ghc91576_4.dylib Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I'm using Mac OS X 10.9.5: {{{ whiteandnerdy:hs-mercury-api ppelleti$ uname -a Darwin whiteandnerdy.lan 13.4.0 Darwin Kernel Version 13.4.0: Mon Jan 11 18:17:34 PST 2016; root:xnu-2422.115.15~1/RELEASE_X86_64 x86_64 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13786> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13104: runRW# ruins join points
by GHC 06 Dec '18

06 Dec '18

#13104: runRW# ruins join points -------------------------------------+------------------------------------- Reporter: lukemaurer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: JoinPoints | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Found this while poking around in the example for #12781. Suppose we have code like this: {{{ let loop :: Int -> State# RealWorld -> (State# RealWorld, Int) loop n = ... loop (n+1) {- tail call -} ... in runRW# @ 'PtrRepLifted @ Int (loop 0) }}} We would love for `loop` to be a join point, but it can't be because it's invoked in the argument to `runRW#`. In this situation, we're often rescued by Float In, which we might hope to give us this: {{{ runRW# @ 'PtrRepLifted @ Int ( let loop :: Int -> State# RealWorld -> (State# RealWorld, Int) loop n s = ... loop (n+1) s' {- tail call -} ... in loop 0 ) }}} Two problems: 1. Float In won't do this to begin with because `loop 0` is a partial application. 2. It's still not eligible to be a join point, again because `loop 0` is a partial application. What we would //like// to see is this: {{{ runRW# @ 'PtrRepLifted @ Int ( \s0 -> let loop :: Int -> State# RealWorld -> (State# RealWorld, Int) loop n s = ... loop (n+1) s' {- tail call -} ... in loop 0 s0 ) }}} Now we're golden. But someone has to have thought to eta-expand the argument to `runRW#` first. (Float In should then float `loop` into the lambda because, due to the state hack, the lambda is considered one-shot.) Perhaps the simplifier should //always// eta-expand the argument to `runRW#`? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13104> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12088: Promote data family instance constructors
by GHC 06 Dec '18

06 Dec '18

#12088: Promote data family instance constructors -------------------------------------+------------------------------------- Reporter: alexvieth | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: #11348 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In `TcEnv.hs` there is a note AFamDataCon: not promoting data family constructors. It states that we can't use a promoted data family instance constructor because we would have to interleave the checking of instances and data types. But with the fix of #11348, we now do exactly this. In the example from the note {{{#!hs data family T a data instance T Int = MkT data Proxy (a :: k) data S = MkS (Proxy 'MkT) }}} -ddump-rn-trace shows these groups {{{ rnTycl dependency analysis made groups [[data family T a_apG] [] [data instance T Int = MkT], [data Proxy (a_apF :: k_apE)] [] [], [data S = MkS (Proxy MkT)] [] []] }}} That's to say, the instance `T Int` will in fact be checked before `S`. So let's remove this restriction. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12088> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9091: print and/or apply constraints when showing info for typed holes
by GHC 05 Dec '18

05 Dec '18

#9091: print and/or apply constraints when showing info for typed holes -------------------------------------------+------------------------------- Reporter: kosmikus | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- Typed holes are fantastic already, but could be even better. Consider the following three examples: == Example 1 == {{{ f :: Eq a => a -> a -> Bool f x y = _ }}} GHC-7.8.2 shows: {{{ Found hole ‘_’ with type: Bool Relevant bindings include y :: a (bound at THC.hs:4:5) x :: a (bound at THC.hs:4:3) f :: a -> a -> Bool (bound at THC.hs:4:1) In the expression: _ In an equation for ‘f’: f x y = _ }}} GHC additionally knows that `Eq a` holds. It would be great if it would print that, too. == Example 2 == {{{ g :: (forall a. Eq a => a -> Bool) -> Bool g f = f _ }}} GHC-7.8.2 shows: {{{ Found hole ‘_’ with type: a0 Where: ‘a0’ is an ambiguous type variable Relevant bindings include f :: forall a. Eq a => a -> Bool (bound at THC.hs:7:3) g :: (forall a. Eq a => a -> Bool) -> Bool (bound at THC.hs:7:1) In the first argument of ‘f’, namely ‘_’ In the expression: f _ In an equation for ‘g’: g f = f _ }}} GHC additionally knows the `Eq a0` must hold. It would be nice if it could indicate that. == Example 3 == {{{ data X a where Y :: X Int h :: X a -> a -> a h Y x = _ }}} GHC-7.8.2 shows: {{{ Found hole ‘_’ with type: Int Relevant bindings include x :: a (bound at THC.hs:13:5) h :: X a -> a -> a (bound at THC.hs:13:1) In the expression: _ In an equation for ‘h’: h Y x = _ }}} Interestingly, GHC shows that we have to produce an `Int`. Unfortunately, it shows that `x` is of type `a`. GHC additionally knows that `a ~ Int`. It would be nice if GHC could either apply the constraint to show that `x :: Int` or at least show the constraint. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9091> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13480: GHCi display visible type application
by GHC 05 Dec '18

05 Dec '18

#13480: GHCi display visible type application -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | 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: #8751 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Similar to #8751, have a way to get GHCi to dump which types an expression is applied to: {{{ ghci> :tyapp length [1,2,3] length @[] @Integer [1,2,3] }}} It could also function as the [https://downloads.haskell.org/~ghc/master /users-guide/ghci.html#ghci-cmd-:all-types :all-types], [https://downloads.haskell.org/~ghc/master/users-guide/ghci.html#ghci-cmd -:type-at :type-at] commands where we can specify a region of code (from [https://www.researchgate.net/publication /282487445_Combining_Deep_and_Shallow_Embedding_of_Domain- Specific_Languages?ev=pubitem-pub_cit_inc Combining Deep and Shallow Embedding of Domain-Specific Languages]) {{{#!hs fromFunC :: FunC (m (Internal a)) -> Mon m a fromFunC m = M $ \k -> fromFunC Bind m k }}} displays {{{#!hs fromFunC :: FunC (m (Internal a)) -> Mon m a fromFunC m = M @m @a $ \(k :: a -> FunC (m b)) -> fromFunC @(FunC (m (Internal a)) -> (a -> FunC (m b)) -> FunC (m b)) (Bind @m @(Internal a) @b) m k }}} Would be great to get this feature as an IDE support. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13480> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13064: Incorrect redudant imports warning
by GHC 05 Dec '18

05 Dec '18

#13064: Incorrect redudant imports warning -------------------------------------+------------------------------------- Reporter: phadej | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With a simple package: issue.cabal: {{{ name: issue version: 0 cabal-version: >= 1.10 build-type: Simple library build-depends: base, binary, binary-orphans==0.1.5.2 exposed-modules: Issue }}} Issue.hs: {{{ {-# LANGUAGE DeriveGeneric #-} {-# OPTIONS_GHC -Wall #-} module Issue (T (..)) where import Prelude () import Data.Binary.Orphans import Data.Binary (Binary (..)) import GHC.Generics (Generic) import Data.Aeson (Value) data T = T Value deriving (Generic) instance Binary T }}} GHC 7.10.3 correctly reports: {{{ Issue.hs:7:1: Warning: The import of ‘Data.Binary’ is redundant except perhaps to import instances from ‘Data.Binary’ To import instances alone, use: import Data.Binary() }}} GHC 8.0.1 incorrectly (!!!) reports: {{{ Issue.hs:6:1: warning: [-Wunused-imports] The import of ‘Data.Binary.Orphans’ is redundant except perhaps to import instances from ‘Data.Binary.Orphans’ To import instances alone, use: import Data.Binary.Orphans( }}} but `Binary Value` instance is imported from `Data.Binary.Orphans`. --- In real life while compiling https://github.com/futurice/haskell-mega- repo/blob/93c3f111f39c973769c35725d90c9b8ef9a57de3/futurice- github/src/Futurice/GitHub.hs the `Data.Binary` redundant import isn't reported, as `Futurice.Prelude` exports other stuff, which is used. See https://gist.github.com/phadej/bb26df19c611260ab8f867729def39b9 for minimal imports reported with `-ddump-minimal-imports`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13064> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9221: (super!) linear slowdown of parallel builds on 40 core machine
by GHC 04 Dec '18

04 Dec '18

#9221: (super!) linear slowdown of parallel builds on 40 core machine -------------------------+------------------------------------------------- Reporter: | Owner: carter | Status: new Type: bug | Milestone: Priority: high | Version: 7.8.2 Component: | Operating System: Unknown/Multiple Compiler | Type of failure: Compile-time performance bug Keywords: | Test Case: Architecture: | Blocking: Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | -------------------------+------------------------------------------------- im seeing slowdowns in parallel builds of a (simple!!) 6 module project when I build it on a 40 core server i'm using for work. for any given ghc invocation with -jn, once n>10, i start to see a super linear slow down as a function of n heres some basic numbers at -j1 0m2.693s at -j4 0m2.507s at -j10 0m2.763s at -j25 0m12.634s at -j30 : 0m39.154s at -j40 : 0m57.511s at -j60 : 2m21.821s these timings are another 2-4x worse if ghc is invoked indirectly via cabal-install / setup.hs according to the linux utility latencytop, 100% of ghc's cpu time was spent on user-space lock contention when I did the -j40 invocation. the timing in the -j40 case stayed the same even when ghc was also passed -O0 (and -fforce-recomp to ensure it did the same ) a bit of experimentation makes me believe that in *ANY* cabalized project on a 40 core machine will exhibit this perf issue. cabal clean ; cabal configure --ghc-options="-j" ; cabal build -j1 should be enough to trigger the lock contention. That said, I'll try to cook up a minimal repro that i can share the source for post haste. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9221> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10739: Resuscitate the humble ticky-ticky profiler
by GHC 04 Dec '18

04 Dec '18

#10739: Resuscitate the humble ticky-ticky profiler -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | 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 Revisions: | -------------------------------------+------------------------------------- The [https://ghc.haskell.org/trac/ghc/wiki/Debugging/TickyTicky ticky- ticky profiler] is known to be quite bit-rotted. Indeed there currently isn't even a definitive list of the counters, much less what they counter and whether they are still accurate. That being said, it can be quite useful and is worth putting effort into bringing back up to grade. There are a few things that need to be done here, 1. Collect a list of the existing counters 2. Work out what they are supposed to be measuring 3. Decide which still have a chance of being useful and accurate 4. ??? 5. Profile! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10739> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14252: ApplicativeDo: Add compiler message about irrefutable pattern matches and Monad constraints
by GHC 03 Dec '18

03 Dec '18

#14252: ApplicativeDo: Add compiler message about irrefutable pattern matches and Monad constraints -------------------------------------+------------------------------------- Reporter: mutantmell | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: -------------------------------------+------------------------------------- Add an error message to the compiler when ApplicativeDo desugaring: * requires a Monad constraint when a Functor/Applicative constraint is expected * Adding a lazy pattern match could allow the Functor/Applicative constraint bgamari suggests something like the following message: {{{#!hs ApplicativeDo is enabled yet Monad is required due to irrefutable pattern match; perhaps you want to make the match refutable by adding a ~? }}} Background: In GHC 8.2.1, ApplicativeDo desugaring was changed to require monad constraints when using a strict pattern match (see #13875 for details). While this behavior is a requirement for maintaining the intended semantics of ApplicativeDo, it is both a breaking change, and somewhat unintuitive (see #14249). Adding a message would provide both clarification around the requirement, and provide a simple resolution for the common use case. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14252> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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