[GHC] #7337: GHC does not generate great code for bit-level rotation

[GHC]

#7337: GHC does not generate great code for bit-level rotation
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 Reporter:  bos               |          Owner:                  
     Type:  feature request   |         Status:  new             
 Priority:  normal            |      Component:  Compiler        
  Version:  7.6.1             |       Keywords:                  
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
  Failure:  None/Unknown      |       Testcase:                  
Blockedby:                    |       Blocking:                  
  Related:                    |  
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 I'm working on some hashing functions at the moment, and I notice that GHC
 generates an {{{or}}} and a pair of shifts for a rotate. The LLVM back end
 is smart enough to recover the code's intent via strength reduction and
 emit a single {{{rot}}} instruction, but the regular code generator emits
 three instructions.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7337>
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