[GHC] #14254: The Binary instance for TypeRep smells a bit expensive

[GHC]

#14254: The Binary instance for TypeRep smells a bit expensive
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  Typeable
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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Description changed by dfeuer:

Old description:

> In particular, `get` uses `getSomeTypeRep`. `getSomeTypeRep`, in turn,
> calls `typeRepKind` through its recursion. But `typeRepKind` is itself
> recursive, fully inspecting the spine of its argument. That smells
> quadratic to me. The solution, I believe, is to change the type of
> `getSomeTypeRep` to `BinHandle -> IO (SomeTypeRep, TypeRep Type)`.

New description:

 In particular, `get` uses `getSomeTypeRep`. `getSomeTypeRep`, in turn,
 calls `typeRepKind` through its recursion. But `typeRepKind` is itself
 recursive, fully inspecting the spine of its argument. That smells
 quadratic to me. The solution, I believe, is to change the type of
 `getSomeTypeRep` to `BinHandle -> IO (SomeTypeRep, SomeTypeRep)`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14254#comment:1>
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