[GHC] #12234: 'deriving Eq' on recursive datatype makes ghc eat a lot of CPU and RAM

[GHC]

#12234: 'deriving Eq' on recursive datatype makes ghc eat a lot of CPU and RAM
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        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      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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Comment (by vladki):

 Just in case,  removing one of the parameters in the `ExprF` constructor
 makes the problem go away:
 {{{
 data ExprF rT = ExprF rT deriving Eq
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12234#comment:3>
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