[GHC] #7837: Rules involving equality constraints don't fire

[GHC]

#7837: Rules involving equality constraints don't fire
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Reporter:  akio                     |          Owner:                           
    Type:  bug                      |         Status:  new                      
Priority:  normal                   |      Component:  Compiler                 
 Version:  7.6.2                    |       Keywords:  equality constraint,rules
      Os:  Unknown/Multiple         |   Architecture:  Unknown/Multiple         
 Failure:  Runtime performance bug  |      Blockedby:                           
Blocking:                           |        Related:                           
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 In the attached program, the "normalize/Double" rule doesn't fire, whereas
 "normalize'/Double" does.

 In general, it seems that a rule doesn't fire if it involves discharging
 an equality constraint that is required by the LHS.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7837>
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