[GHC] #13570: CoreFVs patch makes n-body slower

[GHC]

#13570: CoreFVs patch makes n-body slower
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by hsyl20):

 With the floating-in of the array-indexing primop, instead of having the
 following order:

 {{{
 1) A <- load from address @XXX
 2) compute several things (sqrt,mul,div,sub,add) independent of A
 3) store (A - ..) at address @XXX
 }}}

 We have this order: 2, 1, 3.

 As this is n-body, could it be a prefetching issue?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13570#comment:3>
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