[GHC] #9233: Compiler performance regression

[GHC]

#9233: Compiler performance regression
---------------------------------+------------------------------------
        Reporter:  augustss      |            Owner:
            Type:  bug           |           Status:  new
        Priority:  low           |        Milestone:
       Component:  Compiler      |          Version:  7.8.2
      Resolution:                |         Keywords:
Operating System:  Windows       |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown  |       Difficulty:  Unknown
       Test Case:                |       Blocked By:
        Blocking:                |  Related Tickets:
---------------------------------+------------------------------------

Comment (by goldfire):

 I, too, have noticed that GHC has gotten slower to compile between 7.6.3
 and 7.8.2. And, I have a nice file that demonstrates the slowness.

 First, 7.6.3:

 {{{
 rae:10:40:52 ~/temp/th-desugar> ghc --version
 The Glorious Glasgow Haskell Compilation System, version 7.6.3
 rae:10:43:47 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    0m2.674s
 user    0m2.512s
 sys     0m0.131s
 rae:10:43:53 ~/temp/th-desugar> rm -f `find . -name '*.o' -or -name '*.hi'
 -or -name '*.dyn*'`
 rae:10:43:58 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs -O2
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    0m9.089s
 user    0m8.648s
 sys     0m0.241s
 rae:10:44:13 ~/temp/th-desugar> rm -f `find . -name '*.o' -or -name '*.hi'
 -or -name '*.dyn*'`
 rae:10:44:17 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs -O2 -fno-spec-constr
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    0m9.351s
 user    0m8.180s
 sys     0m0.242s
 }}}

 Now, 7.8.2:

 {{{
 rae:10:44:41 ~/temp/th-desugar> ghc --version
 The Glorious Glasgow Haskell Compilation System, version 7.8.2
 rae:10:44:45 ~/temp/th-desugar> rm -f `find . -name '*.o' -or -name '*.hi'
 -or -name '*.dyn*'`
 rae:10:44:49 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    1m5.906s
 user    0m7.972s
 sys     0m0.449s
 rae:10:45:58 ~/temp/th-desugar> rm -f `find . -name '*.o' -or -name '*.hi'
 -or -name '*.dyn*'`
 rae:10:46:05 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs -O2
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    0m58.498s
 user    0m18.374s
 sys     0m0.566s
 rae:10:47:06 ~/temp/th-desugar> rm -f `find . -name '*.o' -or -name '*.hi'
 -or -name '*.dyn*'`
 rae:10:47:14 ~/temp/th-desugar> time ghc
 Language/Haskell/TH/Desugar/Core.hs -O2 -fno-spec-constr
 [1 of 2] Compiling Language.Haskell.TH.Desugar.Util (
 Language/Haskell/TH/Desugar/Util.hs, Language/Haskell/TH/Desugar/Util.o )
 [2 of 2] Compiling Language.Haskell.TH.Desugar.Core (
 Language/Haskell/TH/Desugar/Core.hs, Language/Haskell/TH/Desugar/Core.o )

 real    1m32.710s
 user    0m17.552s
 sys     0m0.637s
 }}}

 The relevant files are attached. I don't have data for it, but I've
 noticed that compiling these files in GHCi is relatively snappy.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9233#comment:9>
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