February 2016 - ghc-tickets

[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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[GHC] #10614: Show constraints in ``Found hole...''
by GHC 15 Dec '16

15 Dec '16

#10614: Show constraints in ``Found hole...'' -------------------------------------+------------------------------------- Reporter: bjmprice | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Currently it is not clear when types are known equal. Consider writing castWith: {{{#!hs {-# LANGUAGE GADTs , TypeOperators #-} import Data.Type.Equality hiding (castWith) castWith :: a :~: b -> a -> b castWith Refl x = _ }}} which results in {{{ TypeEq.hs:5:19: error: Found hole: _ :: b Where: ‘b’ is a rigid type variable bound by the type signature for: castWith :: a :~: b -> a -> b at TypeEq.hs:4:13 Relevant bindings include x :: a (bound at TypeEq.hs:5:15) castWith :: a :~: b -> a -> b (bound at TypeEq.hs:5:1) In the expression: _ In an equation for ‘castWith’: castWith Refl x = _ }}} Filling the hole with x is correct, but it is not clear from the message that GHC knows this. It would be useful to have a section "Constraints include" e.g. {{{ TypeEq.hs:5:19: error: Found hole: _ :: b Where: ‘b’ is a rigid type variable bound by the type signature for: castWith :: a :~: b -> a -> b at TypeEq.hs:4:13 Relevant bindings include x :: a (bound at TypeEq.hs:5:15) castWith :: a :~: b -> a -> b (bound at TypeEq.hs:5:1) Constraints include <------ NEW LINE a ~ b (from Refl :: a :~: a at TypeEq.hs:5:10) <------ NEW LINE In the expression: _ In an equation for ‘castWith’: castWith Refl x = _ }}} And show class constraints (Show a etc.) similarly -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10614> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9696: readRawBufferPtr and writeRawBufferPtr allocate memory
by GHC 13 Dec '16

13 Dec '16

#9696: readRawBufferPtr and writeRawBufferPtr allocate memory -------------------------------------+------------------------------------- Reporter: mergeconflict | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: x86_64 (amd64) | Unknown/Multiple Difficulty: Unknown | Type of failure: Runtime Blocked By: | performance bug Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I initially filed this as a [http://stackoverflow.com/questions/26333815 /why-do-hgetbuf-hputbuf-etc-allocate-memory question on StackOverflow], assuming that the behavior I'm seeing was intentional, or that I was misinterpreting the profiler results... but Kazu Yamamoto [https://twitter.com/kazu_yamamoto/status/522583112249663488 suggested] I should file this as an issue here. It's my first GHC ticket, so here goes: {{{#!hs main :: IO () main = do buf <- mallocArray 1 echo buf echo :: Ptr Word8 -> IO () echo buf = forever $ do len <- readRawBufferPtr "read" stdin buf 0 1 writeRawBufferPtr "write" stdout buf 0 (fromIntegral len) }}} I expect the only heap allocation here should be my explicit `mallocArray`, but profiling with `+RTS -P` indicates this isn't the case: both the read and write operations do appear to allocate some short-lived heap objects. In contrast: {{{#!hs echo :: Ptr Word8 -> IO () echo buf = forever $ do threadWaitRead $ Fd 0 len <- c_read 0 buf 1 c_write 1 buf (fromIntegral len) yield }}} does not appear to allocate. I did a bit of digging (copying bits of source code from `base` into my own project, to get cost center annotations) and it seems like the allocation might be happening in `throwErrnoIfRetryMayBlock`. See [https://gist.github.com/anonymous/3ba3cfa118e1d05870d4 this gist] for more detail, including core output from `-ddump-simpl`. In all honesty, I don't know whether this is a bug. I was just surprised by it, when I first encountered it using `hGetBuf` / `hPutBuf`, so I'm trying to understand whether this is expected behavior and why. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9696> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8248: GHCi should not warn if group writable
by GHC 13 Dec '16

13 Dec '16

#8248: GHCi should not warn if group writable ----------------------------+---------------------------------------------- Reporter: afcowie | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.6.3 Keywords: | Operating System: Linux Architecture: | Type of failure: GHC rejects valid program Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- Any number of Linux distros support the idea of user groups, whereby when a new user is created there is also simultaneously a group created with the same name; ie, instead of {{{ -rw-r--r--. 1 andrew users 19 Sep 5 08:29 ghci.conf }}} as us old traditionalists would have it, you get {{{ -rw-rw-r--. 1 andrew andrew 19 Sep 5 08:29 ghci.conf }}} because the umask in such cases is 0002 instead of 0022. There is entirely nothing unusual or incorrect about this approach, and it is followed, for example, in the Fedora family of distros. GHC, however, is being a bit silly in emitting the following: {{{ $ ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. *** WARNING: /home/andrew/.ghc/ghci.conf is writable by someone else, IGNORING! Prelude> }}} Foremost the fact that the file is group writable is not a problem and the user's choice, //particularly// in this case because it's group writable in the user's group! Regardless of that, GHCi should not be ignoring files with other than 0644 permissions; this isn't `.ssh/`. Can this check and attendant behaviour be removed? AfC -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8248> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9308: nofib fannkuch-redux runs perpetually with -fllvm
by GHC 09 Dec '16

09 Dec '16

#9308: nofib fannkuch-redux runs perpetually with -fllvm ------------------------------------+------------------------------------- Reporter: jrp | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Running the nofib benchmarks with make -k EXTRA_HC_OPTS=-fllvm on a HEAD build of ghc configured with perf-llvm (3.4.2) results in fannkuch-redux running in an infinite loop. The benchmark runs in about 3.5s without the -fllvm {{{ HC = /Users/xx/Projects/ghc/inplace/bin/ghc-stage2 HC_OPTS = -O2 -Rghc-timing -H32m -hisuf hi -fllvm -rtsopts -XBangPatterns -O2 RUNTEST_OPTS = -ghc-timing ==nofib== fannkuch-redux: time to compile Main follows... /Users/jrp/Projects/ghc/inplace/bin/ghc-stage2 -O2 -Rghc-timing -H32m -hisuf hi -fllvm -rtsopts -XBangPatterns -O2 -c Main.hs -o Main.o <<ghc: 358716248 bytes, 313 GCs, 10827462/27497216 avg/max bytes residency (6 samples), 57M in use, 0.00 INIT (0.00 elapsed), 0.20 MUT (0.53 elapsed), 0.21 GC (0.23 elapsed) :ghc>> ==nofib== fannkuch-redux: size of Main.o follows... __TEXT __DATA __OBJC others dec hex 10333 497 0 0 10830 2a4e ==nofib== fannkuch-redux: time to link fannkuch-redux follows... <<ghc: 19914544 bytes, 16 GCs, 1005021/2239600 avg/max bytes residency (3 samples), 25M in use, 0.00 INIT (0.00 elapsed), 0.01 MUT (0.53 elapsed), 0.02 GC (0.02 elapsed) :ghc>> ==nofib== fannkuch-redux: size of fannkuch-redux follows... __TEXT __DATA __OBJC others dec hex 4075520 446464 0 4295945496 4300467480 10053ed18 ==nofib== fannkuch-redux: time to run fannkuch-redux follows... ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9308> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9504: LLVM backend TBAA is too aggressive
by GHC 09 Dec '16

09 Dec '16

#9504: LLVM backend TBAA is too aggressive -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Incorrect Blocked By: | result at runtime Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- At https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVM/Ali… there is written > It [a memory load/store] is very rarely of the form: > {{{ > x = Sp + 8 > I64[x] = ... > }}} > And when it is, 'it is' (unconfirmed) always deriving a "heap" pointer, "stack" pointers are always of the in-line variety. In fact commit e10589a505b44f4f0394500c6a0d2db5baa7f3f4 treats any memory access through a Cmm local variable as having the "other" type, which cannot alias any non-"other" address. But it turns out that a Cmm local might be either an offset from Sp (#9125, though TBAA doesn't seem to have been the cause of the bad code there) or an offset from a Cmm global variable (#9308). In general, we don't know anything about what it might be so we should conservatively use the "top" "type". -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9504> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9125: int-to-float conversion broken on ARM - 7.8.1-rc2
by GHC 09 Dec '16

09 Dec '16

#9125: int-to-float conversion broken on ARM - 7.8.1-rc2 --------------------------+------------------------------------------------ Reporter: | Owner: Ansible | Status: new Type: bug | Milestone: Priority: normal | Version: 7.8.1 Component: | Operating System: Linux Compiler | Type of failure: Incorrect result at runtime Keywords: | Test Case: Architecture: arm | Blocking: Difficulty: | Unknown | Blocked By: | Related Tickets: | --------------------------+------------------------------------------------ I compiled ghc on the raspberry pi. See this bug for more about that build of ghc: [https://ghc.haskell.org/trac/ghc/ticket/8896 8896]. A simple test program: {{{ main = do mapM_ (print . (fromInteger :: Integer -> Float)) [0..100] }}} And the result: {{{ 0.0 127.0 256.0 257.0 516.0 517.0 518.0 519.0 1040.0 1041.0 1042.0 1043.0 1044.0 1045.0 1046.0 1047.0 2096.0 2097.0 2098.0 2099.0 2100.0 2101.0 2102.0 2103.0 2104.0 2105.0 2106.0 2107.0 2108.0 2109.0 2110.0 2111.0 4224.0 4225.0 4226.0 4227.0 4228.0 4229.0 4230.0 4231.0 4232.0 4233.0 4234.0 4235.0 4236.0 4237.0 4238.0 4239.0 4240.0 4241.0 4242.0 4243.0 4244.0 4245.0 4246.0 4247.0 4248.0 4249.0 4250.0 4251.0 4252.0 4253.0 4254.0 4255.0 8512.0 8513.0 8514.0 8515.0 8516.0 8517.0 8518.0 8519.0 8520.0 8521.0 8522.0 8523.0 8524.0 8525.0 8526.0 8527.0 8528.0 8529.0 8530.0 8531.0 8532.0 8533.0 8534.0 8535.0 8536.0 8537.0 8538.0 8539.0 8540.0 8541.0 8542.0 8543.0 8544.0 8545.0 8546.0 8547.0 8548.0 8538.0 }}} This code, however, works normally: {{{ main = do mapM_ (print . (fromInteger :: Integer -> Double)) [0..100] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9125> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8953: Reifying poly-kinded type families misses kind annotations
by GHC 09 Dec '16

09 Dec '16

#8953: Reifying poly-kinded type families misses kind annotations ------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Consider the following two modules: {{{ {-# LANGUAGE DataKinds, PolyKinds, TypeFamilies #-} module A where type family Poly (a :: k) :: * type instance Poly (x :: Bool) = Int type instance Poly (x :: Maybe k) = Double }}} {{{ {-# LANGUAGE TemplateHaskell #-} module B where import Language.Haskell.TH import A $( do info <- reify ''Poly runIO $ putStrLn $ pprint info return [] ) }}} Compiling with HEAD yields this output: {{{ type family A.Poly (a_0 :: k_1) :: * type instance A.Poly x_2 = GHC.Types.Double type instance A.Poly x_3 = GHC.Types.Int }}} The problem is that the type patterns in the reified instances are just plain variables, without their kind annotations. This omission makes the instance declarations unfaithful to the original meaning. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8953> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8925: :print and :sprint sometimes fully evaluates strings
by GHC 09 Dec '16

09 Dec '16

#8925: :print and :sprint sometimes fully evaluates strings ------------------------------------+------------------------------------- Reporter: soapie | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Not too confident in my terminology but `:sprint`ing a string that has been evaluated down to its spine seems to fully evaluate the string: {{{ Prelude> let a = map (Debug.Trace.trace "!!!") "abc" Prelude> a `seq` () () Prelude> :sprint a a = _ : _ -- looks fine Prelude> length a 3 Prelude> :sprint a a = "!!! -- strange! a!!! b!!! c" }}} What I expect to see is `a = [_,_,_]`. `:print` behaves similarly. Since neither `:print` nor `:sprint` is supposed to force any evaluation this seems like a bug. At least it can make debugging quite confusing if you're not aware of it! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8925> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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