[GHC] #8638: Optimize by demoting "denormalized" Integers (i.e. J# -> S#)

[GHC]

#8638: Optimize by demoting "denormalized" Integers (i.e. J# -> S#)
--------------------------------------------+------------------------------
        Reporter:  hvr                      |            Owner:  hvr
            Type:  feature request          |           Status:  patch
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  libraries (other)        |          Version:  7.7
      Resolution:                           |         Keywords:  integer-
Operating System:  Unknown/Multiple         |  gmp
 Type of failure:  Runtime performance bug  |     Architecture:
       Test Case:                           |  Unknown/Multiple
        Blocking:                           |       Difficulty:  Unknown
                                            |       Blocked By:
                                            |  Related Tickets:  #8647
--------------------------------------------+------------------------------
Changes (by hvr):

 * related:   => #8647


Comment:

 I've investigated some more how to optimize `integer-gmp`, see also #8647

 The scary part is, that the `Integer` is involved in seemingly unrelated
 operations, such as operating on `Double` or `show`ing `Double` values,
 causing several avoidable allocations.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8638#comment:12>
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