[GHC] #12506: Compile time regression in GHC 8.

[GHC]

#12506: Compile time regression in GHC 8.
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        Reporter:  deech             |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by tdammers):

 Replying to [comment:28 simonpj]:
 > > I can confirm that this *is* a regression; I'm seeing ~34 seconds
 overall compilation time on 7.10.3, vs. ~341 seconds on GHC HEAD.
 >
 > Aha! Excellent. Does that show on (some version of) the repro case
 test.hs?
 >
 > PS: maybe comment:27 answers that affirmatively; I missed that.

 Yes on both; `test1000.hs` is pretty much an exact replica of the code in
 the original test case, I really just unrolled the imports to get it into
 one file, and played with the number of repetitions in `main`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12506#comment:29>
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