[GHC] #13647: Tidy up TcTypeable

[GHC]

#13647: Tidy up TcTypeable
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
      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 bgamari):

 Indeed I had considered giving tuple `KindRep`s special treatment, but was
 reluctant to implement a solution that would only target `GHC.Types`. Yes,
 `GHC.Types` does get larger,

 > Once that is done, I suspect that the entire machinery of tyring to
 share KindReps (which makes my head hurt) would be unnecessary

 I am not convinced it would be wise to drop the sharing. Afterall, the
 problem that you describe above above does not affect only `GHC.Types`.
 There were some programs in `nofib` whose compiler allocations increased
 drastically due to `TTypeable` as well. The patches introducing sharing
 (a694cee77b64235b42029fea248453ddf6b17d17) and "canned" KindReps
 (c1dacb8a9c18677495bbe7e41391f8ca7a573070) both helped immensely.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13647#comment:1>
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