[GHC] #13253: Exponential compilation time with RWST & ReaderT stack with `-02`

[GHC]

#13253: Exponential compilation time with RWST & ReaderT stack with `-02`
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        Reporter:  phadej            |                Owner:  (none)
            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 phadej):

 Simon, see the `bad.hs` attached. I can see the expontential behaviour
 with current `HEAD` too. Remember to use `-O2`.
 {{{
 time .../bin/ghc-stage2 -O2 -fforce-recomp       bad.hs # 38sec
 time .../bin/ghc-stage2 -O2 -fforce-recomp -DBIG bad.hs # 3min 16sec

 time .../bin/ghc-stage2 -O1 -fforce-recomp       bad.hs # 9.8sec
 time .../bin/ghc-stage2 -O1 -fforce-recomp -DBIG bad.hs # 9.9sec
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13253#comment:8>
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