[GHC] #15304: Huge increase of compile time and memory use from 8.0.2 to 8.2.2 or 8.4.2

[GHC]

#15304: Huge increase of compile time and memory use from 8.0.2 to 8.2.2 or 8.4.2
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        Reporter:  NathanWaivio      |                Owner:  tdammers
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.2
      Resolution:                    |             Keywords:
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 tdammers):

 It seems that the `Eq` instance is at the core of the problem: replacing
 it with the following allows GHC to compile the module in a timely
 fashion, and compilation succeeds even with a heap limit of only 128M:

 {{{#!haskell
 instance Eq Cl3 where
     (==) = undefined
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15304#comment:7>
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