[GHC] #8704: Use GHC.Exts.build in randoms, randomRs to achieve fusion

[GHC]

#8704: Use GHC.Exts.build in randoms, randomRs to achieve fusion
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        Reporter:  ion1              |            Owner:
            Type:  feature request   |           Status:  patch
        Priority:  normal            |        Milestone:
       Component:  libraries/random  |          Version:  7.6.3
      Resolution:                    |         Keywords:  fusion
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #4218
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Comment (by nomeata):

 Thanks for the patch, ion1.

 Just checking: Did you make sure that the fusion works as desired, e.g. by
 writing a very small example and comparing the resulting Core before and
 after?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8704#comment:2>
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