[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 simonpj):

 You don't need to propagate the change into `IfaceCoercion`: it's just a
 cache, so you can recompute it when turning `IfaceNthCo` into `NthCo`.  On
 the whole I think it'd be better not to change `IfaceCoercion`: less
 redundancy in the `Iface` data types.

 Shaving off 4 seconds is fantastic.  Take it!

 Also:

 * Yes `CoreTidy` is worth looking into
 * But also so is `simplCast`. See comment:10.  '''Richard''' I need your
 help!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:28>
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