[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 heisenbug):

 Replying to [comment:26 simonpj]:
 > I think you believe that there is a heap-allocated `Name` with an un-
 evaluated `n_occ` field.

 Yes. `n_occ` is a strict field and it appears to be non-WHNF when reading
 it. I was suspecting that this is because of deserialisation doing some
 dirty `unsafeCoerce` tricks when loading dictionaries, which contain the
 `Name` values, but there are other culprits too. I had to remove two
 further bangs on datatype fields on order to get a ''quick'' build with
 `make GhcStage2HcOpts="-O1 -g"` through.
 (https://github.com/ghc/ghc/commit/57a57f2f8cef2ea67588edd1f09f73981e86c889)
 So all evidence point towards a GHC defect in allocation of heap objects
 with strict fields.


 > There is only one place in the code generator namely
 `StgCmmCon.buildDynCon'`.  You could perhaps add (runtime) assertions
 there to see if any strict fields had un-tagged pointers.

 I'll look into the assertion which you suggest. Btw. this might be a
 recent regression or something ancient. I'll find out and file another
 ticket if this gets confirmed.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14626#comment:27>
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