[GHC] #9447: Add support for resizing `MutableByteArray#`s

[GHC]

#9447: Add support for resizing `MutableByteArray#`s
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                   Owner:
            Type:  feature request   |                  Status:  patch
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D133,
                                     |  Phab:D1139
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"9e8562ae02701270e2c1dfcee3279d862dc5b7b6/ghc" 9e8562a/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9e8562ae02701270e2c1dfcee3279d862dc5b7b6"
 Implement getSizeofMutableByteArrayOp primop

 Now since ByteArrays are mutable we need to be more explicit about when
 the size is queried.

 Test Plan: Add testcase and validate

 Reviewers: goldfire, hvr, austin

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1139

 GHC Trac Issues: #9447
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9447#comment:5>
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