[GHC] #11666: Severe performance degradation in GHC 8.0.1 compared to GHC 7.10.x

[GHC]

#11666: Severe performance degradation in GHC 8.0.1 compared to GHC 7.10.x
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        Reporter:  mrkkrp            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by mrkkrp:

@@ -11,1 +11,1 @@
- and 7.10.3 demonstrated similar results (77 seconds).
+ and 7.10.1 demonstrated similar results (77 seconds).

New description:

 While working on a project, I have noticed that GHC 8 takes too long to
 run
 my test suite on CI server, see for example here:

 https://travis-ci.org/mrkkrp/zip/builds/113059190

 GHC 8 finished in 370
 [seconds](https://travis-ci.org/mrkkrp/zip/jobs/113059197#L599), while GHC
 7.10.3 in
 [82 seconds](https://travis-ci.org/mrkkrp/zip/jobs/113059195#L608), 7.10.2
 and 7.10.1 demonstrated similar results (77 seconds).

 There are minor differences in versions of libraries used, mainly those
 that
 are shipped with GHC, I read their changelogs and it seems like it's not
 likely that this sort of slow-down (× 4.5) happened because of one of
 those
 libraries.

 Note that due to the nature of the project I test it does fair amount of
 IO
 in temporary directories, I'll be happy to provide more information if you
 like. BTW, here is the test suite:

 https://github.com/mrkkrp/zip/blob/master/tests/Main.hs

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11666#comment:1>
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