[GHC] #12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level lists and -O)

[GHC]

#12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level
lists and -O)
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        Reporter:                    |                Owner:
  mikhail.vorozhtsov                 |
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Inlining
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 mpickering):

 The interface file produced by both versions is absolutely huge (17mb). A
 very large number of coercions are generated by the instance declarations
 in Regression.hs.

 Interestingly, one way to improve the performance is marking `elemWitness`
 as inlinable.. This stops the unfoldings being optimised but it doesn't
 bring performance to the same level as omitting unfoldings completely.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12545#comment:4>
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