[GHC] #15519: Minor code refactoring leads to drastic performance degradation

[GHC]

#15519: Minor code refactoring leads to drastic performance degradation
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        Reporter:  danilo2           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by danilo2):

 Btw it seems like an inlining problem (but tbh I don't get where so big
 slowdown comes from!). If I replicate the code using type classes (each
 constructor of `Grammar` is separate type) and I create multiple instances
 which have to be resolved during compilation time and I mark them to be
 INLINED, the performance is the same as native.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15519#comment:1>
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