April 2016 - ghc-tickets

[GHC] #11779: Merge "Skip TEST=TcCoercibleFail when compiler_debugged"
by GHC 06 Apr '16

06 Apr '16

#11779: Merge "Skip TEST=TcCoercibleFail when compiler_debugged" -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 8.0.1-rc2 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: -------------------------------------+------------------------------------- Hi, please merge 49c55e68aae9841c166430ae566b0d9bdc03c99d into ghc-8.0, to keep the test suite (and travis) useful. Thanks, Joachim -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11779> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11800: T9872d bytes allocated has regressed terribly on 32-bit Linux
by GHC 06 Apr '16

06 Apr '16

#11800: T9872d bytes allocated has regressed terribly on 32-bit Linux -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Test Suite | Version: 7.10.3 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: -------------------------------------+------------------------------------- While updating the performance testsuite numbers for 8.0.1-rc3 I noticed that `T9872d`'d bytes allocated metric has somehow regressed 350% but only on 32-bit Debian 8, {{{ =====> T9872d(normal) 22 of 30 [0, 0, 0] cd ./perf/compiler && "/home/ben/ghc/inplace/test spaces/ghc-stage2" -c T9872d.hs -fforce-recomp -dno-debug-output -fshow-warning-groups -no-user- package-db -rtsopts -fno-warn-tabs -fno-warn-missed-specialisations -fno- ghci-history +RTS -V0 -tT9872d.comp.stats --machine-readable -RTS > T9872d.comp.stderr 2>&1 bytes allocated value is too high: Expected T9872d(normal) bytes allocated: 59651432 +/-5% Lower bound T9872d(normal) bytes allocated: 56668860 Upper bound T9872d(normal) bytes allocated: 62634004 Actual T9872d(normal) bytes allocated: 264566040 Deviation T9872d(normal) bytes allocated: 343.5 % *** unexpected stat test failure for T9872d(normal) }}} The test passes on 64-bit Debian 8 and no similar jumps are seen in the test's history. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11800> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5850: Greater customization of GHCi prompt
by GHC 06 Apr '16

06 Apr '16

#5850: Greater customization of GHCi prompt -------------------------------------+------------------------------------- Reporter: JamesFisher | Owner: niksaz Type: feature request | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.4.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9994 | Differential Rev(s): Phab:D2084 Wiki Page: | -------------------------------------+------------------------------------- Changes (by niksaz): * differential: Phab:D623 => Phab:D2084 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5850#comment:17> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1168: Optimisation sometimes decreases sharing in IO code
by GHC 06 Apr '16

06 Apr '16

#1168: Optimisation sometimes decreases sharing in IO code -------------------------------------+------------------------------------- Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.6 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | nofib/spectral/calendar Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): See #10401 too -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1168#comment:25> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10401: state hack-related regression
by GHC 06 Apr '16

06 Apr '16

#10401: state hack-related regression -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Consider the following program `exp.hs`: {{{ import Control.Monad import Debug.Trace expensive :: String -> String expensive x = trace "$$$" x {-# NOINLINE expensive #-} main :: IO () main = do str <- fmap expensive getLine replicateM_ 3 $ print str }}} When run as `echo hi | ./exp`, it might print either {{{ $$$ "hi" "hi" "hi" }}} or {{{ $$$ "hi" $$$ "hi" $$$ "hi" }}} depending on the compiler version and optimization settings. In 7.8.4, building with `-O2` produces the second (bad) output, while building with `-O2 -fno-state-hack` produces the first output, not surprisingly. However in 7.10.1 and in HEAD both `-O2` and `-O2 -fno-state-hack` produce the second output. It seems this difference in behavior between 7.8.4 and 7.10.1 may be due to the following difference in the unfolding for IO's fmap. In 7.8.4 {{{ ba867929df0910f70431843781ad014d $fFunctorIO2 :: (a -> b) -> GHC.Types.IO a -> GHC.Prim.State# GHC.Prim.RealWorld -> (# GHC.Prim.State# GHC.Prim.RealWorld, b #) {- Arity: 3, HasNoCafRefs, Strictness: <L,1*C1(U)><C(S),1*C1(U(U,U))><L,U>, Unfolding: (\ @ a @ b f :: a -> b x :: GHC.Types.IO a s :: GHC.Prim.State# GHC.Prim.RealWorld -> case x `cast` (GHC.Types.NTCo:IO[0] <a>_R) s of ds { (#,#) ipv ipv1 -> (# ipv, f ipv1 #) }) -} }}} while in 7.10.1 {{{ d645bee15151bb50f2bad5912d533b38 $fFunctorIO2 :: (a -> b) -> IO a -> State# RealWorld -> (# State# RealWorld, b #) {- Arity: 3, HasNoCafRefs, Strictness: <L,1*C1(U)><C(S),1*C1(U(U,U))><L,U>, Unfolding: InlineRule (3, True, False) (\ @ a @ b f :: a -> b x :: IO a s :: State# RealWorld[OneShot] -> -- ^^^^^^^ case x `cast` (NTCo:IO[0] <a>_R) s of ds { (#,#) ipv ipv1 -> (# ipv, f ipv1 #) }) -} }}} I didn't completely confirm this, though, nor determine how that difference arose in the first place (I assume the libraries were built with `-O2` for both versions?) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10401> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1168: Optimisation sometimes decreases sharing in IO code
by GHC 06 Apr '16

06 Apr '16

#1168: Optimisation sometimes decreases sharing in IO code -------------------------------------+------------------------------------- Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.6 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | nofib/spectral/calendar Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): See #11271 for another example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1168#comment:24> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11271: Costly let binding gets duplicated in IO action value
by GHC 06 Apr '16

06 Apr '16

#11271: Costly let binding gets duplicated in IO action value -------------------------------------+------------------------------------- Reporter: dramforever | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code is much slower when optimized. {{{#!hs module Main where import Control.Monad import Data.Char import System.IO -- getInt: read a integer from stdin, skipping spaces {-# NOINLINE getInt #-} -- to simplify generated core getInt :: IO Int getInt = skipSpaces >> go 0 where skipSpaces = do next <- hLookAhead stdin if isSpace next then getChar >> skipSpaces else return () go n = do next <- hLookAhead stdin if isNumber next then getChar >> go (10 * n + digitToInt next) else return n {-# NOINLINE generateSlowList #-} generateSlowList :: Int -> [Int] generateSlowList 0 = [1] generateSlowList n = scanl (+) 1 (generateSlowList (n-1)) main = do n <- getInt let ls = generateSlowList n --- !!! replicateM_ n $ do i <- getInt print (ls !! i) }}} How to run: {{{ (echo 10000; yes 5000) | time ./slow > /dev/null }}} After a rough look through the generated core, it seems that the `ls` was moved into the argument to `replicateM_`, which is a lambda taking a `State# RealWorld`. It means that a list is rebuilt every time it's indexed, even though a let binding could have caused sharing. By the way it seems that `-fno-state-hack`, which seems related, doesn't seem to help. Interesting to note that using a bang pattern (`let !ls = ...`) would make the problem go away. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11271> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1168: Optimisation sometimes decreases sharing in IO code
by GHC 06 Apr '16

06 Apr '16

#1168: Optimisation sometimes decreases sharing in IO code -------------------------------------+------------------------------------- Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.6 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime | Test Case: performance bug | nofib/spectral/calendar Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): See #11795 for another example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1168#comment:23> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10752: Print which warning-flag controls/enabled an emitted warning
by GHC 05 Apr '16

05 Apr '16

#10752: Print which warning-flag controls/enabled an emitted warning -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: feature | Status: new request | Priority: normal | Milestone: 7.12.1 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: | -------------------------------------+------------------------------------- Both `gcc` and `clang` tell which warning flag a reported warning can be controlled with, e.g. {{{ $ clang-3.5 -Wall -c hello.c hello.c:3:7: warning: unused variable 'x' [-Wunused-variable] int x; ^ 1 warning generated. }}} {{{ $ gcc -Wall -c hello.c hello.c: In function ‘main’: hello.c:3:7: warning: unused variable ‘x’ [-Wunused-variable] int x; ^ hello.c:4:1: warning: control reaches end of non-void function [-Wreturn- type] } ^ }}} With GHC however, we need to lookup the documentation (or memorise all warning flags) to find out which `-fno-warn-*` flag we need to use to silence a specific warning. I propose we augment GHC's warnings in a similar style to how `gcc`/`clang` report flags in compile warnings. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10752> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7411: Exceptions are optimized away in certain situations
by GHC 05 Apr '16

05 Apr '16

#7411: Exceptions are optimized away in certain situations -------------------------------------+------------------------------------- Reporter: SimonHengel | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.2 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: seq, deepseq, | evaluate, exceptions Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: Incorrect result | Test Case: at runtime | simplCore/should_fail/T7411 Blocked By: | Blocking: Related Tickets: #5129 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * milestone: 8.0.1 => 8.0.2 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7411#comment:11> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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