[GHC] #9805: Use TrieMaps to speed up type class instance lookup

[GHC]

#9805: Use TrieMaps to speed up type class instance lookup
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        Reporter:  ezyang            |                   Owner:  ezyang
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.9
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by ezyang):

 simonpj: The key (ahem) part where we need the keys is we compute
 substitutions. In the prototype, it's line 696. Essentially, you have a
 sub-trie, and want to extract all the expressions corresponding to entries
 in the sub-trie, since those are your substitutions.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9805#comment:4>
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