[GHC] #8345: A more efficient atomicModifyIORef'

[GHC]

#8345: A more efficient atomicModifyIORef'
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              Reporter:  parcs       |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:              |          Version:  7.6.3
  libraries/base                     |         Keywords:  IORef
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Moderate (less
  Unknown/Multiple                   |  than a day)
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:  #5926
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by dfeuer):

 Actually, one possible complication (maybe): the current version
 guarantees allocation (and therefore an opportunity to switch threads). I
 don't think the proposed one does this. I also don't know if that's a
 problem.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8345#comment:8>
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