[GHC] #9203: Perf regression in 7.8.2 relative to 7.6.3, possibly related to HashMap

[GHC]

#9203: Perf regression in 7.8.2 relative to 7.6.3, possibly related to HashMap
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        Reporter:  simonmar                 |            Owner:
            Type:  bug                      |           Status:  merge
        Priority:  high                     |        Milestone:  7.8.3
       Component:  Compiler                 |          Version:  7.8.2
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by Simon Marlow <marlowsd@…>):

 In [changeset:"5ffc68bb75d34414987b5d1e5aa4f9061a7a7383/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="5ffc68bb75d34414987b5d1e5aa4f9061a7a7383"
 Fix recomputation of TypeRep in the instance for Typeable (s a) (#9203)

 Summary:
 Every time we called typeRep on a type application, we were
 recomputing the TypeRep.  This showed up in a benchmark I had: #9203.

 Test Plan: Benchmark from #9203.

 Reviewers: simonpj, austin

 Subscribers: simonmar, relrod

 Differential Revision: https://phabricator.haskell.org/D19
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9203#comment:7>
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