[GHC] #11735: Optimize coercionKind

[GHC]

#11735: Optimize coercionKind
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14683 #14975     |  Differential Rev(s):  D4394 D4395
       Wiki Page:                    |
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Comment (by simonpj):

 Yes!!  `simplCast` should not take 73% of compiler time!!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:84>
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