[GHC] #14626: No need to enter a scrutinised value

[GHC]

#14626: No need to enter a scrutinised value
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        Reporter:  heisenbug         |                Owner:  heisenbug
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:  performance
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13861            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alexbiehl):

 I think I know what is happening:

 - When generating code for `f` the CodeGenerator wants to know the
 `LambdaFormInfo` (the closure type) of `defaultUserStyle1`.

 - Since `defaultUserStyle1` is defined in another module we end up calling
 `mkLFImported` in `StgCmmClosure` which ultimatively gives an `LFUnknown`
 which always gets a `DynTag` 0 from `lfDynTag`.

 I think we lack a bit of information here to give `defaultUserStyle1` the
 correct `LFCon` lambda form. Maybe top-level binders should know its
 LambdaForm and include them in their interfaces.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14626#comment:38>
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