[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:
                                     |  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 simonpj):

 >  We should do the same thing to coercionKindRole. (Tiresomely.)

 Actually, looking at it, I think it'd be better to define
 {{{
 coercionRole :: Coercion -> Role
 }}}
 directly (a simple, fast recursive function), and then define
 {{{
 coercionKindRole :: Coercion -> (Pair Type, Role)
 coercionKindRole co = (coercionKind co, coercionRole co)
 }}}
 Less duplication, and (I strongly suspect) faster. Could you try that and
 check perf?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:6>
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