[GHC] #8095: TypeFamilies painfully slow

[GHC]

#8095: TypeFamilies painfully slow
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        Reporter:  MikeIzbicki       |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.6.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  5321              |  Differential Rev(s):
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Comment (by goldfire):

 The blowup in coercions is fixed in the simplifier, yes? That means that
 coercion optimization is working.

 When you vary `N`, what changes in the output? The long sequence of
 coercions in the middle of that dump looks correct to me. I'm less sure
 about the two casts at the end. The unoptimized Core term for this program
 may truly grow quadratically. Maybe the solution is to be more eager with
 the coercion optimizer? I don't see any harm in doing so, if we can
 observe a speedup.

 Let me know if I can be of further assistance.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8095#comment:11>
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