[GHC] #12442: Pure unifier usually doesn't need to unify kinds

[GHC]

#12442: Pure unifier usually doesn't need to unify kinds
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2433
       Wiki Page:                    |
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Comment (by simonpj):

 Status (see Phab:D2433 comment): Richard says: Please don't merge yet.
 When I validated, there were some hiccups, including around performance.
 IIRC, there were actually three performance improvements along with one
 regression, but I have to investigate properly. (A performance improvement
 is certainly not unexpected with this patch.) When I saw these problems, I
 prioritized other tasks, but will return to this eventually.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12442#comment:2>
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