[GHC] #14731: Document alignment & underlying size invariants for array types in GHC.Prim

[GHC]

#14731: Document alignment & underlying size invariants for array types in GHC.Prim
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        Reporter:  jberryman         |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Documentation     |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #2917 #9806       |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by jberryman):

 Documenting `newAlignedPinnedByteArray#` is also relevant. It seems that
 the alignment argument is only important for data that needs to be aligned
 to greater than word size (i.e. all byte arrays, pinned or not are word
 aligned). It's awkward to future-proof code for the case where GHC starts
 storing pinned arrays more tightly aligned.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14731#comment:5>
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