[GHC] #13212: Support abs as a primitive operation on floating point numbers.

[GHC]

#13212: Support abs as a primitive operation on floating point numbers.
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        Reporter:  dominic           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
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 rwbarton):

 See also #7858, which fixed the definition of `abs` and `signum`. There it
 was suggested that a ticket be created for making the implementation more
 efficient, but as far as I can tell no one ever did so (until now).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13212#comment:2>
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