[GHC] #13629: sqrt should use machine instruction on x86_64

[GHC]

#13629: sqrt should use machine instruction on x86_64
-------------------------------------+-------------------------------------
           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.4.1
          Component:  Compiler       |           Version:  8.0.1
  (NCG)                              |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime
  Unknown/Multiple                   |  performance bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):  Phab:D3265     |         Wiki Page:
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 The NCG currently implements the square root MachOp with an out-of-line
 call. This resulted in a large performance regression in `n-body` (see
 #13570). Fix this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13629>
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