[GHC] #11597: Optimize cmpTypeX

[GHC]

#11597: Optimize cmpTypeX
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           Reporter:  goldfire       |             Owner:  goldfire
               Type:  task           |            Status:  new
           Priority:  highest        |         Milestone:  8.0.1
          Component:  Compiler       |           Version:  7.10.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Simon and I observed that we could skip the kind-check in `cmpTypeX` if
 the type has no casts, which is the vastly common case. I will collect
 this information while checking the type and omit the kind check if
 possible.

 Putting on "highest" priority basically because this is so easy to do.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11597>
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