[GHC] #7771: RTS should provide stg_sel_n_noupd_closure

[GHC]

#7771: RTS should provide stg_sel_n_noupd_closure
---------------------------------+------------------------------------------
    Reporter:  simonpj           |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  Compiler          |     Version:  7.6.2           
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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 In `StgStdThunks.cmm` we define info tables `stg_sel_1_upd_info`, etc, for
 "selector thunks", thus:
 {{{
 #define SELECTOR_CODE_UPD(offset)                                       \
   INFO_TABLE_SELECTOR(stg_sel_##offset##_upd, offset, THUNK_SELECTOR,
 "stg_sel_upd", "stg_sel_upd") \
       (P_ node)                                                         \
 ...etc...
 }}}
 But we should ALSO define info tables for ''non-updatable'' selector
 thunks, thus `stg_sel_1_nonupd_info` etc.  We didn't generate any such
 selectors before, but now I'm implementing cardinality analysis, we are.

 Would it be possible to beef up this macro to to generate both info
 tables?  Simply omit the update for the `nonupd` version.  (It wasn't
 quite obvious to me how to do this.)

 That would allow me to get rid of this hack in `CLabel`
 {{{
 pprCLbl (RtsLabel (RtsSelectorInfoTable _upd_reqd offset))
   = hcat [ptext (sLit "stg_sel_"), text (show offset),
                   ptext (sLit "_upd_info")
 -- RTS only has updatable selector thunks at the moment
 -- so we use just them
 --                ptext (if upd_reqd
 --                        then (sLit "_upd_info")
 --                        else (sLit "_noupd_info"))
         ]
 }}}
 Thanks

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7771>
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