[GHC] #7902: Add support for byte endianness swapping exposed as a primops

[GHC]

#7902: Add support for byte endianness swapping exposed as a primops
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Reporter:  tab               |          Owner:                  
    Type:  feature request   |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  7.7               |       Keywords:  bswap endianness
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
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 Add support for W32 and W64 endianness swapping as a new primops (bSwap32#
 and bSwap64#), supported by code generator change in llvm and ncg to
 generate efficient code (i.e. X86's bswap instruction support). For other
 NCG architectures (powerpc, sparc) provide support by 2 ghc-prim C
 functions.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7902>
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