[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_compile/T3966  |      Blockedby:                  
  Blocking:                                  |        Related:                  
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Comment(by simonmar):

 Ah, the warning is only emitted when `-O` is on.  I think it was always
 that way.

 Do we want to leave it like that?  I think the reasoning is that without
 `-O`, `UNPACK` does nothing anyway.  On the other hand, a warning that
 depends on the optimisation level is rather unpleasant.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3966#comment:6>
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