[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 goldfire):

 I'm not still working on this. I pushed the changes I had in mind to the
 tdammers branch. If the performance is OK there, could you please Phab and
 then commit? As for `simplCast`, the changes I had in mind are all on your
 branch, including removing the inefficient one-variable substitution. If
 my changes aren't an improvement, try undoing the change I made to the
 ordering of cases in `simplCast`: I moved the `isReflexiveCo` case to the
 top, but perhaps that check is too expensive and is better at the bottom.
 Regardless, the changes I made in CoreOpt should be enough to improve
 performance.

 Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11735#comment:71>
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