[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
-------------------------------------+-------------------------------------
           Reporter:  mrkkrp         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           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:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 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 7.10.3 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

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11666>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler