[GHC] #14447: Add unaligned ByteArray# access primops

[GHC]

#14447: Add unaligned ByteArray# access primops
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           Reporter:  reinerp        |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I would like unaligned store and unaligned load primops in GHC.Prim.
 Specifically: for X in
 {Int,Int16,Int32,Int64,Word,Word16,Word32,Word64,Float,Double,WideChar,Addr,StablePtr}
 and where X# is the corresponding
 Int#/Word#/Float#/Double#/Char#/Addr#/StablePtr# type, I'd like the
 following primitives:

 {{{#!hs
 -- | Reads an 'X#', offset in bytes
 indexXArrayOffBytes# :: ByteArray# -> Int# -> X#
 -- | Reads an 'X#', offset in bytes
 readXArrayOffBytes# :: MutableByteArray# s -> Int# -> State# s -> (#State#
 s, X# #)
 -- | Writes an 'X#', offset in bytes
 writeXArrayOffBytes# :: MutableByteArray# s -> Int# -> X# -> State# s ->
 State# s
 }}}

 Note that the indexXOffAddr# family of functions already provides
 unaligned loads and similarly writeXOffAddr# provides unaligned stores, so
 GHC's code generator must handle these already. For example, we could use
 these to provide unaligned loads for pinned ByteArray#s:

 {{{#!hs
 indexWord16ArrayOffBytes# :: ByteArray# -> Int# -> Word#
 indexWord16ArrayOffBytes# arr offset =
   indexWord16OffAddr# (byteArrayContents# arr `plusAddr#` offset) 0#
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14447>
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