[GHC] #11270: "Unusable UNPACK pragma" warnings should be printed even without -O

[GHC]

#11270: "Unusable UNPACK pragma" warnings should be printed even without -O
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        Reporter:  osa1              |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 @thomie, it shouldn't get any slower - all the information is already
 there. (unless we end up forcing a thunk that otherwise wouldn't be
 forced. Even in this case there shouldn't be any measurable difference,
 the code is not doing anything fancy)

 @rwbarton, good point. I just tried using HEAD:

 {{{
 ➜  ghc-stage1 -fno-code -fforce-recomp -Wall --make Main.hs
 [1 of 1] Compiling Main             ( Main.hs, nothing )

 ➜  ghc-stage1 -fforce-recomp -Wall --make Main.hs
 [1 of 1] Compiling Main             ( Main.hs, Main.o )

 Main.hs:6:1: warning:
     Pattern match(es) are non-exhaustive
     In an equation for ‘showD’: Patterns not matched: C
 Linking Main ...
 }}}

 I think ideally this shouldn't happen, but we should probably discuss this
 further in the mailing list.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11270#comment:5>
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