[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:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by tdammers):

 The caching approach implemented directly (i.e., adding a `Role` field to
 the `NthCo` constructor) is a fairly pervasive one; it turns out that many
 modules depend on that constructor, either directly o via the isomorphic
 `IfaceCoercion` type (which, I believe, should inherit the additional
 field, correct me if I'm wrong), so adding the extra fields is going to
 touch a lot of source files.

 Not a fundamental problem per se, but it means that this will take a
 little while and will deserve some extra scrutinity before unleashing it.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:26>
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