[GHC] #7116: Missing optimisation: strength reduction of floating-point multiplication

[GHC]

#7116: Missing optimisation: strength reduction of floating-point multiplication
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    Reporter:  simonmar          |       Owner:                         
        Type:  bug               |      Status:  new                    
    Priority:  normal            |   Milestone:  7.8.1                  
   Component:  Compiler          |     Version:  7.4.2                  
    Keywords:                    |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple  |     Failure:  Runtime performance bug
  Difficulty:  Unknown           |    Testcase:                         
   Blockedby:                    |    Blocking:                         
     Related:                    |  
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 e.g. `x * 2.0` should turn into `x + x`.  See #2253 (program 6) for an
 example.

 Whether this is best done as a builtin RULE or in `cmmMachOpFold`, or
 possibly both, I don't know.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7116>
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