[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 (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:                    |
-------------------------------------+-------------------------------------

Comment (by bgamari):

 So `perf stat` reveals a rather interesting picture. With the patch we
 retire few instructions (9,146,722,334 vs. 12,346,134,565), perform far
 fewer branches (908,661,442 compared to 1,308,583,802 without, the
 predictor missing around 0.01% in both cases), yet see a significantly
 higher runtime.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13629#comment:17>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler