[GHC] #13739: Very slow linking of profiled executables
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While building profiled executables with 8.2.1rc2 I've noticed the link times seem to have significantly regressed. I don't have a minimal test case. Testing on cabal head source tree {{{ cabal --version
cabal-install version 2.1.0.0 compiled using version 2.1.0.0 of the Cabal library cabal new-configure --enable-profiling --enable-newer --with- ghc=/opt/ghc-8.2.1/bin/ghc cabal build cabal-install
# hit Ctrl-C during linking time cabal build cabal-install }}} gives real 1m54.833s user 1m52.936s sys 0m1.620s doing the same with 8.0.2 links in less than a second -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): What `cabal` commit are you looking at? I tried building b3af711a492970718d31ffdc46d31110109ddc42 but was unable to reproduce this. Link times are long (`real 0m5.947s user 0m0.028s sys 0m5.909s`) but nothing like you report. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): I tried 8.2.1-rc2 and it took a similar amount of time (`real 0m6.241s user 0m0.013s sys 0m6.227s`) to link. However, then I tried 8.0.2 and indeed saw it was quite a bit faster (`real 0m2.888s user 0m0.009s sys 0m2.878s`). I still don't know you ended up seeing two minute link times though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): I am working on github/haskell/cabal commit 0b5f13d71e3282df03495e1db75cd8375b0879ab I believe I have not been testing with rc2, but various releases from the rc2 branch obtained from https://launchpad.net/~hvr/+archive/ubuntu/ghc. I replicated this again with ghc-8.2.0.20170521. I am running ubuntu 16.04 with all my packages upgraded. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by niteria): I'm getting 2 minute compile times when linking profiled GHC HEAD. Running with `-v` reveals that GHC is stuck on gcc doing linking Here's the stuck command: https://phabricator.haskell.org/P151, it takes 135s to complete. When I remove `-Wl,--gc-sections`, it's only 11s. It's part of this GHC invocation: {{{ "inplace/bin/ghc-stage1" -o ghc/stage2/build/tmp/ghc-stage2 -hisuf p_hi -osuf p_o -hcsuf p_hc -static -prof -eventlog -O0 -H64m -Wall -hide-all-packages - i -ighc/. -ighc/stage2/build -Ighc/stage2/build -ighc/stage2/build/ghc/autogen -Ighc/stage2/build/ghc/autogen -optP- DGHCI -optP-include -optPghc/stage2/build/ghc/autogen/cabal_macros.h -package-id base-4.10.0.0 -package-id array-0.5.1.2 -package-id bytestring-0.10.8.2 -package-id directory-1.3.0.2 -package-id process-1.6.0.0 -package-id filepath-1.4.1.2 -pack age-id ghc-boot-8.3 -package-id ghc-8.3 -package-id unix-2.7.2.2 -package- id containers-0.5.10.2 -package-id deepseq-1.4.3.0 -package-id ghci-8.3 -package-id haskeline-0.7.4.0 -packa ge-id time-1.8.0.1 -package-id transformers-0.5.2.0 -Wall -fno-warn-name- shadowing -XHaskell2010 -O -no-hs-main -threaded -no-user-package-db -rtsopts -Wnoncanonical-monad-inst ances -odir ghc/stage2/build -hidir ghc/stage2/build -stubdir ghc/stage2/build -split-sections -static -prof -eventlog -O0 -H64m -Wall -hide-all-packages -i -ighc/. -ighc/ stage2/build -Ighc/stage2/build -ighc/stage2/build/ghc/autogen -Ighc/stage2/build/ghc/autogen -optP-DGHCI -optP-include -optPghc/stage2/build/ghc/autogen/cabal_macros.h -package-id base-4.10.0.0 -package-id array-0.5.1.2 -package-id bytestring-0.10.8.2 -package-id directory-1.3.0.2 -package-id process-1.6.0.0 -package-id filepath-1.4.1.2 -package-id ghc-boot- 8.3 -package-id ghc-8.3 -package-id unix-2.7.2.2 -package-id containers-0.5.10.2 -package-id deepseq-1.4.3.0 -package-id ghci-8.3 -package-id haskeline-0.7.4.0 -package-id time-1.8.0 .1 -package-id transformers-0.5.2.0 -Wall -fno-warn-name-shadowing -XHaskell2010 -O -no-hs-main -threaded -no-user-package-db -rtsopts -Wnoncanonical-monad-instances ghc/stage 2/build/Main.p_o ghc/stage2/build/GHCi/UI.p_o ghc/stage2/build/GHCi/UI/Info.p_o ghc/stage2/build/GHCi/UI/Monad.p_o ghc/stage2/build/GHCi/UI/Tags.p_o ghc/stage2/build/hschooks.p_o -v -keep- tmp-files }}} My gcc version: {{{ $ gcc --version gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11) Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. }}} @doug: Can you run the command that hangs with: `cabal build cabal-install --ghc-options='-v'` to check if it's an instance of the same problem? If it's also stuck on `gcc` you can run it with `cabal build cabal-install --ghc-options='-v -keep-tmp-files'` and run the `gcc` command by itself. Then try removing `-Wl,--gc-sections`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by niteria): Running the ld command with `--print-gc-sections` gives me 254934 lines. I don't know if that's big or small. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): I just tried building a profiled executable with -fwhole-archive-hs-libs, which seems to only control the -Wl,--gc-sections flag, and it is much faster. I'll replicate my previous setup and try this later today. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by niteria): * cc: niteria (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "out" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): I have attached a script and my output that exhibits a large slowdown in linking a trivial profiled executable. It times linking a file Main.hs with {{{main = return ()}}} with ghc-8.0.2 and ghc-8.2.0.2017.0522. It shows that the linking times irrespective of -fwhole-archive-hs-libs has slowed considerably, and that -fwhole-archive-hs-libs slows down linking by 4-5x on both ghc versions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test.2" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "out" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "out" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "out" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "run-test" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Thanks for the script, duog! It'll help me figure out what commit(s) introduced this regression. I did some quick testing on my Ubuntu machine with `gcc-4.8.4`. As baselines, I tested GHC 8.0.2: {{{ real 0m0.299s user 0m0.256s sys 0m0.028s }}} and GHC 8.2.1-rc2: {{{ (Without -fwhole-archive-hs-libs) real 0m12.946s user 0m12.816s sys 0m0.136s (With -fwhole-archive-hs-libs) real 0m2.676s user 0m2.436s sys 0m0.220s }}} I noticed a significant difference around commit b207b536ded40156f9adb168565ca78e1eef2c74 (Generalize kind of the (->) tycon). Before that commit, we have: {{{ Commit efeaf9e436109cb35b491e08b5407c0598108186 (Bump nofib submodule) ------ (Without -fwhole-archive-hs-libs) real 0m4.686s user 0m4.600s sys 0m0.068s (With -fwhole-archive-hs-libs) real 0m0.055s user 0m0.040s sys 0m0.008s }}} And after: {{{ Commit b207b536ded40156f9adb168565ca78e1eef2c74 (Generalize kind of the (->) tycon) ------ (Without -fwhole-archive-hs-libs) real 0m13.047s user 0m12.948s sys 0m0.104s (With -fwhole-archive-hs-libs) real 0m2.696s user 0m2.480s sys 0m0.196s }}} However, the times for commit efeaf9e436109cb35b491e08b5407c0598108186 are still not at parity with GHC 8.0.2, so an earlier commit must have contributed as well. I'll try to track down which one(s). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: rwbarton (added) Comment: Commit 283acec1d7307fdbd8cd7b3f1d984a036366d6b4 (Make split sections by default work again) is what caused the other regression. Before that commit, I obtained these times with duog's script: {{{ (Without -fwhole-archive-hs-libs) real 0m0.306s user 0m0.260s sys 0m0.028s (With -fwhole-archive-hs-libs) real 0m0.056s user 0m0.036s sys 0m0.012s }}} Notice that the `-fwhole-archive-hs-libs` times are pretty much identical to the GHC 8.0.2 times I found in comment:9. After that commit, I obtained: {{{ (Without -fwhole-archive-hs-libs) real 0m4.656s user 0m4.548s sys 0m0.088s (With -fwhole-archive-hs-libs) real 0m0.056s user 0m0.040s sys 0m0.008s }}} Which is basically identical to the times I found pre- b207b536ded40156f9adb168565ca78e1eef2c74. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): For reference, I decided to compare two builds of GHC 8.2.1-rc2 with and without reverting commit 283acec1d7307fdbd8cd7b3f1d984a036366d6b4, and the difference is astounding. If you revert commit 283acec1d7307fdbd8cd7b3f1d984a036366d6b4, you get: {{{ (Without -fwhole-archive-hs-libs) real 0m0.277s user 0m0.224s sys 0m0.036s (With -fwhole-archive-hs-libs) real 0m5.447s user 0m5.104s sys 0m0.328s }}} And if you use plain 8.2.1-rc2 (without reverting commit 283acec1d7307fdbd8cd7b3f1d984a036366d6b4), you get: {{{ (Without -fwhole-archive-hs-libs) real 0m13.648s user 0m12.716s sys 0m0.156s (With -fwhole-archive-hs-libs) real 0m3.077s user 0m2.500s sys 0m0.216s }}} So that commit at least explains the differences without the use of the `-fwhole-archive-hs-libs` flag. However, it doesn't account for the jump in times _with_ the the `-fwhole-archive-hs-libs` flag. I'll try investigating that next. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Oops, please ignore the noise about `-fwhole-archive-hs-libs` above. I forgot that the commit which introduced `-fwhole-archive-hs-libs` (a6874e546294173c166859769dd8054887a6ded7) didn't come until //after// 283acec1d7307fdbd8cd7b3f1d984a036366d6b4 (Make split sections by default work again), so the times I got above were just from GHC erroring out. (I suppressed the stdout/stderr to avoid flooding my terminal, so I didn't notice this happening.) Also, an observation that I meant to make earlier is that I think that b207b536ded40156f9adb168565ca78e1eef2c74 (Generalize kind of the (->) tycon), which I singled out in comment:9, is a red herring. I think commit 283acec1d7307fdbd8cd7b3f1d984a036366d6b4 (Make split sections by default work again) is the true culprit that causes a bad constant factor for each additional linked symbol, and commit b207b536ded40156f9adb168565ca78e1eef2c74 just happened to add a bunch of extra symbols. This is further evidenced by the fact that reverting 283acec1d7307fdbd8cd7b3f1d984a036366d6b4 alone brings the link time back down to the same as what I get with GHC 8.0.2. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): That patch is a one-liner to a configure script that sets SplitSections=Yes by default while building ghc. Perhaps the problem is caused by how the libraries being linked with SplitSections=YES? If bgamari had SplitSections = NO in his .mk, then this would explain why he couldn't replicate the issue. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): See https://phabricator.haskell.org/D1242#40188 Is it plausible that profiling libraries would have 100x more sections than non-profiling libraries? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Well, I certainly can't rule it out. Surely if this is the case it is avoidable, however. Can you run `objdump` on an affected object file? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I tried `objdump`-ing object files produced by 8.0.2 and 8.2.1, and they look almost identical. I have to wonder how much of this is due to GCC differences. For comparison, I just tried compiling a simple profiled executable on my machine with GCC 6.2.0, and the whole process only took about 1.5 seconds. (Compare that to the 13-second times that I experienced on my other machine with GCC 4.8.4.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): I have done some investigation and think I understand this now. Linking against libraries built with -split-sections is slow, and seems to be superlinear in the number of sections. I have been testing on HEAD, using BuildFlavour = Validate. By default, profiling libraries are not built, and SplitSections = No. Setting BUILD_PROF_LIBS = YES in build.mk and Linking the trivial program is only slightly slower than with 8.0.2 with and without -prof. I have been using the following command to count sections in library files, this is counting the sections in the profiled base I built without SplitSections: {{{ objdump -xw libraries/base/dist-install/build/libHSbase-4.10.0.0_p.a | wc -l 524008 }}} This is counting the sections in the profiled base I got from launchpad: {{{ objdump -xw /opt/ghc/8.2.1/lib/ghc-8.2.0.20170522/base-4.10.0.0/libHSbase-4.10.0.0_p.a | wc -l 1022947 }}} Now setting SplitSections = YES, cleaning and building libraries {{{ objdump -xw libraries/base/dist-install/build/libHSbase-4.10.0.0_p.a | wc -l 1031190 }}} And the test case is as slow as it has been in my previous testing. I tried upgrading my gcc to 6.3.0, and this does not change the results. I haven't tried upgrading ld, I can't see how to do that. It looks like the libraries from launchpad, both profiled and unprofiled, were built with SplitSections = Yes. The prof build flavour does not set SplitSections = No, unlike all of the other ones, so I suspect they came from a prof build. I believe that the above explains what causes linking to be very slow, and why we have had difficulty reliably reproducing it. I don't know why many sections slows linking. My only idea comes from [http://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking]: link, the library is rescanned again - it's possible that symbols imported by the included object can be found in other objects within the same library. That algorithm sounds quadratic in the worst case. The following are the file sizes produced in various cases (83 has SplitSections libraries): {{{ -rwxr-xr-x 1 doug fileservs 1507544 May 29 00:09 profiled_80 -rwxr-xr-x 1 doug fileservs 1511320 May 29 00:09 profiled_83 -rwxr-xr-x 1 doug fileservs 13138024 May 29 00:09 profiled_nogcsections_83 -rwxr-xr-x 1 doug fileservs 1040752 May 29 00:09 unprofiled_80 -rwxr-xr-x 1 doug fileservs 903616 May 29 00:09 unprofiled_83 -rwxr-xr-x 1 doug fileservs 7923416 May 29 00:09 unprofiled_nogcsections_83 }}} and the times taken to produce them: {{{ 8.0 profiled command real 0m0.183s user 0m0.168s sys 0m0.012s 8.2 profiled command real 0m14.764s user 0m14.616s sys 0m0.144s 8.2 profiled command no gc-section s real 0m2.138s user 0m1.940s sys 0m0.192s 8.0 unprofiled command real 0m0.179s user 0m0.140s sys 0m0.036s 8.2 unprofiled command real 0m1.749s user 0m1.656s sys 0m0.088s 8.2 unprofiled command no gc-sections real 0m1.373s user 0m1.220s sys 0m0.148s }}} ---- I think SplitSections should not be enabled in prof.mk (or any others), at least for libraries. There is good reason to pass -Wl,--gc-sections to the linker always, since it lets you leverage libraries that have been compiled with -split- sections, but perhaps this is too dangerous while we don't understand exactly what causes the slowdown. There should be better interface than -fwhole-archive-hs-libs to disable --gc-sections while doing a profiling build. One or many of: * Don't pass --gc-sections if profiling is enabled * * unless another flag is passed * A warning if -prof is passed without -fwhole-archive-hs-libs * * add another flag that only disables --gc-sections -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by niteria): I wanted to compare `gold` to `collect2`, so I run linking of profiled `ghc-stage2` under both with and without `--gc-sections`. The results: {{{ no --gc-sections, collect2 real 0m9.456s user 0m8.248s sys 0m1.168s 161M ghc/stage2/build/tmp/ghc-stage2 no --gc-sections, gold real 0m3.122s user 0m2.680s sys 0m0.441s 161M ghc/stage2/build/tmp/ghc-stage2 --gc-sections, collect2 real 2m14.460s user 2m13.356s sys 0m1.087s 129M ghc/stage2/build/tmp/ghc-stage2 --gc-sections, gold real 0m3.118s user 0m2.691s sys 0m0.411s 129M ghc/stage2/build/tmp/ghc-stage2 }}} Looks like `gold` doesn't even break a sweat. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Really, you don't even need profiled code to notice a difference. On my machine with `gcc-4.8.4`/`ld-2.24`, I experience longer linking times with an ordinary, non-profiled `main=return ()` executable: {{{ $ time /opt/ghc/8.0.2/bin/ghc -fforce-recomp -O0 Bug.hs [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... real 0m0.441s user 0m0.360s sys 0m0.060s $ time /opt/ghc/8.2.1/bin/ghc -fforce-recomp -O0 Bug.hs [1 of 1] Compiling Main ( Bug.hs, Bug.o ) Linking Bug ... real 0m1.616s user 0m1.476s sys 0m0.116s }}} On larger programs, the delay is more noticeable. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * priority: normal => high * milestone: => 8.2.1 Comment: Bumping the priority, as it would be nice to get some kind of resolution to this before GHC 8.2.1 is released. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "T13739-check-ld" added. Script to time ghc with different versions of ld -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * Attachment "T13739-check-ld-output" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): I've attached timings with 3 versions of ld obtained from [http://ftp.gnu.org/gnu/binutils/]. These show that 2.27 fixes the issue we're running into. Still much slower than 8.0.2 though. I would also note that I find the very large file sizes of 8.2.1-no-gc- sections relative to 8.0.2 in comment 17 weird. It looks, to my untrained eye, like many more .o files from the archives are getting pulled in. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: Very slow linking of profiled executables -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): Another note: -split-sections does not apply to shared libraries, and passing -dynamic to ghc shows no difference between 8.0.2 and 8.2.1. Profiled dynamic libraries do not appear to be packaged, so I have not tested the -dynamic -prof case, but I'd expect there to be no difference there either. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): This problem rears its head in an ugly fasion while configuring packages that have custom setups: {{{ cabal unpack distributive-0.5.2 cd distributive-0.5.2 cabal sandbox init cabal install --only-dependencies time cabal configure }}} gives: {{{ [1 of 1] Compiling Main ( dist/setup/setup.hs, dist/setup/Main.o ) Linking ./dist/setup/setup ... Configuring distributive-0.5.2... real 0m21.580s user 0m20.928s sys 0m0.560s }}} while {{{ time cabal configure --ghc-options=-dynamic }}} gives: {{{ Resolving dependencies... [1 of 1] Compiling Main ( dist/setup/setup.hs, dist/setup/Main.o ) Linking ./dist/setup/setup ... Configuring distributive-0.5.2... real 0m1.830s user 0m1.460s sys 0m0.228s }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by nh2): * cc: nh2 (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nh2): I have filed an upstream GNU ld bug to ask whether they are aware what could have brought the 10x performance improvement that ld 2.27 brought over 2.26: https://sourceware.org/bugzilla/show_bug.cgi?id=21677 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: infoneeded Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => infoneeded * cc: nh2 (removed) Comment: I don't think there's much else that we can do about this. binutils 2.27 seems to fix the majority of the issue and ultimately the plan is to use `gold` more often anyways (see #13541). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: infoneeded Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * cc: nh2 (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: infoneeded Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: 13541 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by duog): * related: => 13541 Comment: I don't know whether anyone has investigated whether there is anything we are doing which is exasperating the problem. Executables produced by removing -Wl,--gc-sections from the linker invocation look like they're pulling in most of the archives. This does not occur with 8.0.2. I will see if it happens with gold once support it lands in the ghc-8.2 branch. I would like to see the configure scripts disable split sectioned libraries if the linker is ld.bfd < 27, or at least warn that the user is in for an unpleasant experience. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:28 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: infoneeded Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: 13541 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by duog): Also, would anyone be able to check whether this occurs for non ELF targets? The thread linked to in comment 25 suggests some candidates for the fix in 2.27, both of which are ELF specific. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:29 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13739: very slow linking of executables with ld.bfd < 2.27 -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: infoneeded Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #13541 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * related: 13541 => #13541 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13739#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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