[GHC] #8578: Improvements to SpinLock implementation

[GHC]

#8578: Improvements to SpinLock implementation
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        Reporter:  parcs             |            Owner:  parcs
            Type:  task              |           Status:  patch
        Priority:  normal            |        Milestone:
       Component:  Runtime System    |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by thoughtpolice):

 Ah, yes, you're right - I did some more digging. The tricky bit is that
 `rep; nop` and `pause` actually have the same opcodes (`F390`) for
 backwards compatibility, but on newer CPUs, `rep; nop` is treated
 magically (allowing other hyperthreads on the same core), and `pause` is
 simply an alias to make it more clear.

 In that case, ignore me and my inability to keep up with Intel
 shenanigans.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8578#comment:6>
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