[GHC] #8647: Reduce allocations in `integer-gmp`

[GHC]

#8647: Reduce allocations in `integer-gmp`
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        Reporter:  hvr                      |            Owner:
            Type:  task                     |           Status:  new
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  libraries (other)        |          Version:  7.6.3
      Resolution:                           |         Keywords:  integer-
Operating System:  Unknown/Multiple         |  gmp
 Type of failure:  Runtime performance bug  |     Architecture:  x86_64
       Test Case:                           |  (amd64)
        Blocking:                           |       Difficulty:  Unknown
                                            |       Blocked By:
                                            |  Related Tickets:  #8638
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"baeeef7af6e37441d1fa28f4197a8cb878a9ef0b/integer-gmp"]:
 {{{
 #!CommitTicketReference repository="integer-gmp"
 revision="baeeef7af6e37441d1fa28f4197a8cb878a9ef0b"
 Add new `mpz_mul_si`-based primop (re #8647)

 This primop helps reducing allocation by being able to pass one `S#`
 argument directly to the GMP multiplication primitive without needing to
 promote (and thus allocate a `ByteArray#` as well) the `J#` first.

 This benefits a few nofib benchmarks wrt to allocations (having most
 impact on `kahan` resulting in about 10% less allocations)

 Signed-off-by: Herbert Valerio Riedel <hvr at gnu.org>
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8647#comment:3>
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