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

[GHC]

#13629: sqrt should use machine instruction on x86_64
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (NCG)    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime           |            Test Case:
  performance bug                    |  numeric/num009
      Blocked By:                    |             Blocking:
 Related Tickets:  #13570            |  Differential Rev(s):  Phab:D3508
       Wiki Page:                    |
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Comment (by bgamari):

 Perhaps I'll just start a table of the PMU counters before and after,

 ||= Metric     =||= Before patch =||= After patch =||
 || instructions || 12,346,134,565 || 9,146,722,334 ||
 || branches     || 1,308,583,802  || 908,661,442   ||
 || branch predict misses || || ||
 || cache-misses || 83,983 || 57,490 ||
 || L1-icache-load-misses || 138,869 || 156,777 ||

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13629#comment:18>
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