[GHC] #11195: New pattern-match check can be non-performant

[GHC]

#11195: New pattern-match check can be non-performant
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1676,
       Wiki Page:                    |  Phab:D1795
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Comment (by rwbarton):

 It's very strange. I also see `OptCoercion` taking several minutes and
 gobs of memory to compile, when I copy it somewhere and build it with
 `-package ghc`; but according to my logs from investigating join points it
 never takes particularly long to compile as part of the ghc build.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11195#comment:16>
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