December 2017 - ghc-tickets

[GHC] #14519: Exponential runtime performance regression in GHC 8.2 + Data.Text.Lazy + Text.RE.TDFA
by GHC 22 Jan '18

22 Jan '18

#14519: Exponential runtime performance regression in GHC 8.2 + Data.Text.Lazy + Text.RE.TDFA -------------------------------------+------------------------------------- Reporter: ntc2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: https://github.com/ntc2/ghc-8.2.1 | -regex-lazy-text-bug | Blocking: | Related Tickets: 13745 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When using `Text.RE.TDFA` from the regex-tdfa package on GHC 8.2 to match trivial regexes against `Data.Text.Lazy` strings, I see **exponential runtime**. On GHC 8.0, or using `Data.Text` strict strings or `String` strings, the runtime is as expected. Here's my repo with simple test code illustrating the regression and timing stats: https://github.com/ntc2/ghc-8.2.1-regex-lazy-text-bug. In summary, for the problematic combination of GHC version and libraries, the run times are 3s, 10s, 22s, and 40s for counting regex matches in files with 10000, 20000, 30000, and 40000 lines, respectively. For all of the unproblematic combinations -- i.e. GHC 8.0.2, `String`, strict `Data.Text`, or building with profiling -- the run time is always about 1s! And **this is a Heisenbug**, in that the performance problem goes away if I build with profiling support! There is the separate Issue #13745 about **compile-time regressions** in GHC 8.2 + the regex-tdfa package, that [https://ghc.haskell.org/trac/ghc/ticket/13745#comment:18 I commented on]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14519> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13891: forkIO can trivially defeat bracket
by GHC 22 Jan '18

22 Jan '18

#13891: forkIO can trivially defeat bracket -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new 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: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider this program, {{{#!hs import Control.Concurrent import Control.Exception main = do putStrLn "forking" forkIO $ bracket (putStrLn "forked") (const $ putStrLn "finalize") (const $ putStrLn "hello" >> threadDelay 100000000) threadDelay 10000 putStrLn "done" }}} Would you predict that it would print `finalize`? Answer: no. It will print, {{{ forking forked hello done }}} It would pointed out by an author of a cryptographic library (`raaz`) that this is quite bad as it means that secure memory could leak out uncleared. It's not entirely clear how best to deal with this. Perhaps raise a `ThreadKilled` async exception to all running threads during RTS shutdown, followed by a synchronization? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13891> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14206: Add bit deposit and bit extraction primops
by GHC 22 Jan '18

22 Jan '18

#14206: Add bit deposit and bit extraction primops -------------------------------------+------------------------------------- Reporter: newhoggy | 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: -------------------------------------+------------------------------------- Modern CPUs (on x86, Haswell and newer) have a PDEP instruction for efficient bit deposit and a PEXT instruction for efficient bit extraction. These instructions can be used to implement various data structures. I propose we add the following set of primops {{{#!hs pdep8# :: Word# -> Word# -> Word# pdep16# :: Word# -> Word# -> Word# pdep32# :: Word# -> Word# -> Word# pdep64# :: Word64# -> Word64# -> Word64# pdep# :: Word# -> Word# -> Word# pext8# :: Word# -> Word# -> Word# pext16# :: Word# -> Word# -> Word# pext32# :: Word# -> Word# -> Word# pext64# :: Word64# -> Word64# -> Word64# pext# :: Word# -> Word# -> Word# }}} Each primop compiles into either a single PDEP/PEXT instruction or a call to some fallback function, implemented in C. For reference, see the following library that implements FFI wrapper 32-bit and 64-bit functions for these instructions: https://github.com/haskell-works/hw-prim-bits -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14206> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9885: ghc-pkg parser eats too much memory
by GHC 22 Jan '18

22 Jan '18

#9885: ghc-pkg parser eats too much memory -------------------------------------+------------------------------------- Reporter: gnezdo | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: ghc-pkg | Version: 7.8.3 Keywords: | Operating System: Linux Architecture: Unknown/Multiple | Type of failure: Runtime Difficulty: Moderate (less | performance bug than a day) | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Parsing of spec files in ghc-pkg scales very poorly. The following script demonstrates memory consumption growth as a function of the number of tokens in ld-options (16K leads to ~6G) #!/bin/bash # Demonstrates memory consumption behavior of ghc-pkg as a function of # the number of ld-options arguments. for i in {10..14}; do size=$((1 << $i)) echo $size rm -fr a.packages /usr/bin/ghc-pkg init a.packages cat > a.spec <<EOF name: project id: project license: AllRightsReserved version: 1.0 EOF echo -n ld-options: >> a.spec for i in $(seq 1 $size); do echo -n "x "; done >> a.spec /usr/bin/time /usr/bin/ghc-pkg --global-package-db a.packages register --force a.spec done exit 0 # This was collected with ghc-7.6.3. 7.8.3 fares as badly. % bash a.sh 1024 Reading package info from "a.spec" ... done. 0.03user 0.00system 0:00.03elapsed 97%CPU (0avgtext+0avgdata 17848maxresident)k 0inputs+32outputs (0major+4973minor)pagefaults 0swaps 2048 Reading package info from "a.spec" ... done. 0.09user 0.01system 0:00.10elapsed 99%CPU (0avgtext+0avgdata 60872maxresident)k 0inputs+56outputs (0major+15723minor)pagefaults 0swaps 4096 Reading package info from "a.spec" ... done. 0.41user 0.07system 0:00.49elapsed 99%CPU (0avgtext+0avgdata 294340maxresident)k 0inputs+104outputs (0major+74090minor)pagefaults 0swaps 8192 Reading package info from "a.spec" ... done. 1.72user 0.30system 0:02.04elapsed 99%CPU (0avgtext+0avgdata 1168836maxresident)k 0inputs+192outputs (0major+292716minor)pagefaults 0swaps 16384 Reading package info from "a.spec" ... done. 9.11user 1.38system 0:10.51elapsed 99%CPU (0avgtext+0avgdata 5396932maxresident)k 0inputs+376outputs (0major+1349736minor)pagefaults 0swaps -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9885> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14385: Clarify error message when missing GADTs extension
by GHC 21 Jan '18

21 Jan '18

#14385: Clarify error message when missing GADTs extension -------------------------------------+------------------------------------- Reporter: lyxia | Owner: (none) Type: bug | Status: new 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: -------------------------------------+------------------------------------- If we write a GADT declaration and forget to enable `GADTs` we get the following error message: {{{ ww.hs:1:1: error: • Illegal generalised algebraic data declaration for ‘T’ (Use GADTs to allow GADTs) • In the data declaration for ‘T’ }}} It could be made more explicit for new users that the suggestion is to use the '''extension''' `GADTs`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14385> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11645: Heap profiling - hp2ps: samples out of sequence
by GHC 21 Jan '18

21 Jan '18

#11645: Heap profiling - hp2ps: samples out of sequence -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | 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: #664 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- `make TEST=hpc_fork WAY=prof` is failing, but it has nothing to do with `hpc`. {{{ hp2ps: hpc_fork.hp, line 9, samples out of sequence hp2ps error when processing heap profile for hpc_fork }}} hpc_fork.hs: {{{ module main where import system.posix.process import control.concurrent main = do pid1 <- forkprocess $ do threaddelay 100000 pid2 <- forkprocess $ do threaddelay 100000 print () }}} To reproduce: {{{ $ ghc-8.0.1 hpc_fork.hs -fforce-recomp -prof $ ./hpc_fork +RTS -hc $ hp2ps hpc_fork.hp }}} Example hpc_fork.hp: {{{ JOB "hpc_fork +RTS -hc" DATE "Thu Feb 25 22:37 2016" SAMPLE_UNIT "seconds" VALUE_UNIT "bytes" BEGIN_SAMPLE 0.000000 END_SAMPLE 0.000000 BEGIN_SAMPLE 0.005672 END_SAMPLE 0.005672 BEGIN_SAMPLE 0.003167 END_SAMPLE 0.003167 BEGIN_SAMPLE 0.003311 END_SAMPLE 0.003311 }}} This is a regression from 7.10.3. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11645> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14056: Figure out what to do about libffi
by GHC 21 Jan '18

21 Jan '18

#14056: Figure out what to do about libffi -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.4.1 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: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- For some platform GHC depends upon `libffi` for foreign call support in the bytecode interpreter. Unfortunately `libffi`'s upstream seems to be unresponsive and there has not been a release in nearly three years. This means that there is currently no release which has, e.g., support for AArch64 and iOS's compact debug information. While we obviously want to avoid shipping our own patched libffi, at this point we are starting to run out of options. Consider options for resolving this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14056> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14495: Relocatable GHC
by GHC 21 Jan '18

21 Jan '18

#14495: Relocatable GHC -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.4.1 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: -------------------------------------+------------------------------------- Moritz Angerman has recently been working on [[https://github.com/snowleopard/hadrian/pull/445|enabling]] relocatable builds of GHC in Hadrian. This will enable a user to extract a bindist anywhere in their file system and expect it to work. Moreover, it should simplify our installation procedure -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14495> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14122: Core lint error while compiling GHC.IO.Handle
by GHC 21 Jan '18

21 Jan '18

#14122: Core lint error while compiling GHC.IO.Handle -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 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: -------------------------------------+------------------------------------- While compiling `GHC.IO.Handle` with `-g3 -dcore-lint -O` I encountered the following, {{{ *** Core Lint errors : in result of Simplifier *** <no location info>: warning: [RHS of w1_s8qY :: Addr#] Recursive or top-level binder has strict demand info: w1_s8qY Binder's demand info: <L,U> }}} The binding in question is, {{{#!hs w1_s8qY :: Addr# [LclId, Unf=Unf{Src=<vanilla>, TopLvl=False, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 20 0}] w1_s8qY = src<libraries/base/GHC/IO/Handle.hs:745:37-50> src<libraries/base/GHC/IO/Handle.hs:739:9-10> "}"# }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14122> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14006: Heap profiling ghc gives hp2ps error
by GHC 21 Jan '18

21 Jan '18

#14006: Heap profiling ghc gives hp2ps error -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Runtime | Version: 8.3 System | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Debugging Unknown/Multiple | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Running GHC with heap profiling and then running `hp2ps` on the result gives {{{ hp2ps: ghc-stage2.hp, line 17405, samples out of sequence }}} Reproduction (GHC commit 4700baaf8f9bf3c44a53a595d840c7c14cfd6f98) {{{ cabal unpack skylighting-0.1.1.5 cd skylighting-0.1.1.5 cabal configure --with-ghc=$HOME/src/ghc-clean-july12/inplace/bin/ghc- stage2 \ --enable-profiling -fexecutable cabal build touch src/Skylighting/Syntax/Php.hs /home/dfeuer/src/ghc-clean-july12/inplace/bin/ghc-stage2 --make -i \ -isrc -idist/build -O -prof -fprof-auto-exported -osuf p_o -hisuf \ p_hi -optPdist/build/autogen/cabal_macros.h -hide-all-packages \ -package-db dist/package.conf.inplace -package-id aeson-1.2.1.0 \ -package base-4.10.0.0 -package blaze-html-0.9.0.1 -package \ bytestring-0.10.8.2 -package case-insensitive-1.2.0.10 -package \ containers-0.5.10.2 -package directory-1.3.0.2 -package \ filepath-1.4.1.2 -package hxt-9.3.1.16 -package mtl-2.2.1 -package \ regex-pcre-builtin-0.94.4.8.8.35 -package safe-0.3.15 -package \ text-1.2.2.2 -package utf8-string-1.0.1.1 -XHaskell2010 \ Skylighting.Types Skylighting.Regex \ Skylighting.Tokenizer Skylighting.Syntax.Php -j1 +RTS \ -s -h -N1 hp2ps ghc-stage2.hp }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14006> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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