[GHC] #9960: Performance problem with TrieMap

[GHC]

#9960: Performance problem with TrieMap
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        Reporter:  simonpj           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:  Phab:D606
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Comment (by Edward Z. Yang <ezyang@…>):

 In [changeset:"da64ab530512c36acd17c1dbcd3b5fcc681d128b/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="da64ab530512c36acd17c1dbcd3b5fcc681d128b"
 Compress TypeMap TrieMap leaves with singleton constructor.

 Suppose we have a handful H of entries in a TrieMap, each with a very
 large
 key, size K. If you fold over such a TrieMap you'd expect time O(H). That
 would
 certainly be true of an association list! But with TrieMap we actually
 have to
 navigate down a long singleton structure to get to the elements, so it
 takes
 time O(K*H).  The point of a TrieMap is that you need to navigate to the
 point
 where only one key remains, and then things should be fast.

 This is a starting point: we can improve the patch by generalizing the
 singleton constructor so it applies to CoercionMap and CoreMap; I'll do
 this
 in a later commit.

 Summary: Signed-off-by: Edward Z. Yang <ezyang at cs.stanford.edu>

 Test Plan: validate

 Reviewers: simonpj, austin

 Subscribers: carter, thomie

 Differential Revision: https://phabricator.haskell.org/D606

 GHC Trac Issues: #9960
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9960#comment:8>
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