[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:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13570            |  Differential Rev(s):  Phab:D3508
       Wiki Page:                    |
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Comment (by bgamari):

 It's made in the native code generator, `genCCall` in
 `compiler/nativeGen/X86/CodeGen.hs`. While we use the `fsin` instruction
 on i386, we don't on x86_64 (and i386 with `-msse2`).

 See Phab:D3508 for a quick attempt at fixing the `sqrt` situation. In the
 case of trigonometric functions I'm afraid we have little choice but to
 fall back on `libm` since SSE provides no trig instructions.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13629#comment:4>
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