[GHC] #8793: Improve GHC.Event.IntTable performance

[GHC]

#8793: Improve GHC.Event.IntTable performance
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        Reporter:  cdk               |                Owner:
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Core Libraries    |              Version:  7.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by jscholl):

 I attached the modified benchmark from cdk which compares the current
 implementation found in base with cdks and my changes.

 Note that the {{{loopV_}}} function does not evaluate the returned
 results, so if someone wants to use that and makes {{{insertWith}}}
 somehow return its result lazy instead of in WHNF, these will be thrown
 away.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8793#comment:16>
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