[GHC] #9350: Consider using xchg instead of mfence for CS stores

[GHC]

#9350: Consider using xchg instead of mfence for CS stores
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              Reporter:  tibbe       |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.9
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by tibbe):

 Herb Sutter argues for using `xchg` over `mfence` in
 [http://channel9.msdn.com/Shows/Going+Deep/Cpp-and-Beyond-2012-Herb-
 Sutter-atomic-Weapons-2-of-2 C++ and Beyond 2012: Herb Sutter - atomic<>
 Weapons, 2 of 2], around 0:38:20.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9350#comment:1>
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