[GHC] #11822: Pattern match checker exceeded (2000000) iterations

[GHC]

#11822: Pattern match checker exceeded (2000000) iterations
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        Reporter:  j.waldmann        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc3
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by NeilMitchell):

 I've ran into this two times, both regressions since GHC rc3. The two
 cases are:

 * https://github.com/ndmitchell/hlint/blob/master/src/HSE/Bracket.hs
 needBracket (currently at a438ba0e45697e65bbcd9fb996d350b07394a45f)
 *
 https://github.com/ndmitchell/derive/blob/master/src/Language/Haskell/TH/Peephole.hs
 peep (currently at 6a703a9f71986232bbb1e54853a548af2b53b706)

 Is there any recommendation on how I can avoid this warning without CPP in
 a way that works on older versions of GHC?

 In contrast to the original reporter, I do not welcome that GHC emits this
 warning. It seems a warning about GHC, not my code, and not something that
 I can do much about, other than turn off warnings, which seems a little
 sad.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11822#comment:3>
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