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

[GHC]

#9447: Add support for resizing `MutableByteArray#`s
-------------------------------------+-------------------------------------
       Reporter:  hvr                |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.2
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:  Phab:D133
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 This is motivated by #9281 which changes how memory is allocated, and
 gives rise to the need to be able to efficiently shrink or grow
 `MutableByteArray#`s before they're frozen into `ByteArray#` while
 retaining their original byte content to avoid a major bottle-neck.

 This ticket is for tracking/documenting all changes related to this new
 facility.

 Here's the current road-map:

  1. Implement
     {{{#!hs
     shrinkMutableByteArray# :: MutableByteArray# s -> Int# -> State# s ->
 State# s
     resizeMutableByteArray# :: MutableByteArray# s -> Int# -> State# s ->
 (# State# s, MutableByteArray# s #)
     }}}
     (see Phab:D133)

  2. As suggested by Johan,
     {{{#!hs
     getSizeofMutableByteArray# :: MutableByteArray# s -> State# s -> (#
 State# s Int# #)
     }}}
     This is similar in spirit to `numCapabilities` and
 `getNumCapabilities`.
     Add a deprecate pragma (or equivalent) for `sizeofMutableByteArray#`.
     Add a note to `sizeofMutableByteArray#` stating that it's unsafe in
 the presence of calls to resize-operations on the same MBA.

  3. Submit patches to upstream libraries replacing calls to
 `sizeofMutableByteArray#` with `getSizeofMutableByteArray#`

  4. Investigate how to provide in-place (zero-copy) growing of MBAs (step
 1. only implements in-place shrinking).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9447>
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