[GHC] #5210: Add primops for copying/cloning byte arrays

[GHC]

#5210: Add primops for copying/cloning byte arrays
---------------------------------+------------------------------------------
    Reporter:  tibbe             |       Owner:  tibbe       
        Type:  bug               |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  7.0.3             |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 Add primops for copying/cloning byte arrays so that we can unroll such
 copies in the backends. Even if we don't unroll in the backend, this will
 allow us to use `memcpy` for copying parts of the byte array, which is
 difficult today as while `ByteArray#` can be passed in an FFI call, the
 pointer that gets passed refers to the based of the array when we might
 want it to refer to somewhere in the middle of the array.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5210>
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