[GHC] #8623: Strange slowness when using async library with FFI callbacks

[GHC]

#8623: Strange slowness when using async library with FFI callbacks
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        Reporter:  JohnWiegley              |            Owner:  simonmar
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  Runtime System           |          Version:  7.6.3
      Resolution:                           |         Keywords:
Operating System:  MacOS X                  |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Description changed by hvr:

Old description:

> I've attached a Haskell and a C file, when compiled as such:
>
>     ghc -DSPEED_BUG=0 -threaded -O2 -main-is SpeedTest SpeedTest.hs
> SpeedTestC.c
>
> You should find that with 7.4.2, 7.6.3 or a recent build of 7.8, building
> with SPEED_BUG=0 produces an executable that takes more than a second to
> run, while building with SPEED_BUG=1 runs very quickly.  I've also
> attached the Core for both scenarios.

New description:

 I've attached a Haskell and a C file, when compiled as such:

 {{{
 ghc -DSPEED_BUG=0 -threaded -O2 -main-is SpeedTest SpeedTest.hs
 SpeedTestC.c
 }}}

 You should find that with 7.4.2, 7.6.3 or a recent build of 7.8, building
 with `SPEED_BUG=0` produces an executable that takes more than a second to
 run, while building with `SPEED_BUG=1` runs very quickly.  I've also
 attached the Core for both scenarios.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8623#comment:2>
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