[GHC] #3966: Warn about useless UNPACK pragmas

[GHC]

#3966: Warn about useless UNPACK pragmas
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  Reporter:  tibbe                        |          Owner:                  
      Type:  feature request              |         Status:  new             
  Priority:  normal                       |      Milestone:  7.4.3           
 Component:  Compiler                     |        Version:  6.12.1          
Resolution:                               |       Keywords:                  
        Os:  Unknown/Multiple             |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown                 |     Difficulty:  Unknown         
  Testcase:  typecheck/should_fail/T3966  |      Blockedby:                  
  Blocking:                               |        Related:                  
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Comment(by tibbe):

 Since -O is on by default I don't feel strongly about this. It'd probably
 be better if it was always on.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3966#comment:8>
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