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

[GHC]

#8793: Improve GHC.Event.IntTable performance
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        Reporter:  cdk               |                Owner:
            Type:  task              |               Status:  infoneeded
        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 tried to collect the relevant changes from the patch, but in most cases
 could not reproduce the speedups cdk reported. Only for the {{{lookup}}}
 function the runtime changed measurable (it improved even more, around 78%
 faster than the current implementation). Pulling the
 {{{ForeignPtr}}} out of the {{{IORef}}} could make sense, but I could not
 measure an impact on performance.

 A thing I find surprising is the first argument in {{{updateWith.go}}},
 which seems to be totally unused. Is this the correct behavior? Anyway, I
 created a second patch which removes the unused argument (and changes the
 first element of the return value to a {{{Bool}}}, as it is just tested
 for being {{{Nothing}}}), if it is just a leftover from an earlier version
 of the function. The change has no impact on performance, though.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8793#comment:9>
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