[GHC] #9067: Optimize clearNursery by short-circuiting when we get to currentNursery

[GHC]

#9067: Optimize clearNursery by short-circuiting when we get to currentNursery
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        Reporter:  ezyang                   |            Owner:  ezyang
            Type:  task                     |           Status:  new
        Priority:  low                      |        Milestone:
       Component:  Runtime System           |          Version:  7.9
      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 simonmar):

 Andreas Voellmy and I talked about some similar ideas.  I doubt that you
 want to rely on `CurrentNursery`, because we want to reset that after
 every GC, but instead I think the right approach is to assume that every
 block from `CurrentNursery` onwards needs to have its free pointer reset
 before we use it.  It's a somewhat subtle invariant and something else we
 have to get right, but the win seems to be worthwhile.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9067#comment:1>
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