[GHC] #13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)

[GHC]

#13604: regression in ghc 8.2.1-rc1 (8.2.0.20170404)
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        Reporter:  George            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.2.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3514
       Wiki Page:                    |
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Changes (by ezyang):

 * differential:   => Phab:D3514


Comment:

 I don't think a proper fix can make it for 8.2, so I've put up a revert
 for review.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13604#comment:13>
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