[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:  patch           
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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Comment(by tibbe):

 Some comments:

  * Why is there no 16-bit version? LLVM support it and it can be
 implemented using the XCHG instruction, like so: `xchg al, ah`
  * Are you also going to make the changes to base (e.g. in Data.Bits) to
 expose this to the world?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7902#comment:3>
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