[GHC] #2598: Avoid excessive specialisation in SpecConstr

[GHC]

#2598: Avoid excessive specialisation in SpecConstr
---------------------------------+------------------------------------------
    Reporter:  simonpj           |       Owner:                  
        Type:  feature request   |      Status:  new             
    Priority:  lowest            |   Milestone:  7.6.2           
   Component:  Compiler          |     Version:  6.8.3           
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by morabbin):

  * failure:  => None/Unknown


Comment:

 Is this moot now? With GHC 7.6.2:
 {{{
 ghc --make -fforce-recomp -c -ddverbose-core2core -dshow-passes -O2
 DropComment.hs
 }}}
 on the attached `DropComment.hs` produces (among other things):
 {{{
 ==================== Tidy Core ====================
 Result size of Tidy Core = {terms: 70, types: 50, coercions: 0}

 Rec {
 lvl_rid :: [GHC.Types.Char]
 [GblId]
 lvl_rid = DropComment.dropComment (GHC.Types.[] @ GHC.Types.Char)

 DropComment.dropComment [Occ=LoopBreaker]
   :: [GHC.Types.Char] -> [GHC.Types.Char]
 [GblId, Arity=1, Str=DmdType S]
 DropComment.dropComment =
   \ (ds_deO :: [GHC.Types.Char]) ->
     case ds_deO of _ {
       [] -> GHC.Types.[] @ GHC.Types.Char;
       : ds1_deP ds2_deQ ->
         case ds1_deP of wild1_X7 { GHC.Types.C# ds3_deR ->
         case ds3_deR of _ {
           __DEFAULT ->
             GHC.Types.:
               @ GHC.Types.Char wild1_X7 (DropComment.dropComment ds2_deQ);
           ' ' ->
             case ds2_deQ of wild2_Xa {
               [] -> GHC.Types.: @ GHC.Types.Char wild1_X7 lvl_rid;
               : ds5_deS ds6_deT ->
                 case ds5_deS of _ { GHC.Types.C# ds7_deU ->
                 case ds7_deU of _ {
                   __DEFAULT ->
                     GHC.Types.:
                       @ GHC.Types.Char wild1_X7 (DropComment.dropComment
 wild2_Xa);
                   '-' ->
                     case ds6_deT of _ {
                       [] ->
                         GHC.Types.:
                           @ GHC.Types.Char wild1_X7
 (DropComment.dropComment wild2_Xa);
                       : ds9_deV ds10_deW ->
                         case ds9_deV of _ { GHC.Types.C# ds11_deX ->
                         case ds11_deX of _ {
                           __DEFAULT ->
                             GHC.Types.:
                               @ GHC.Types.Char wild1_X7
 (DropComment.dropComment wild2_Xa);
                           '-' ->
                             case ds10_deW of _ {
                               [] ->
                                 GHC.Types.:
                                   @ GHC.Types.Char wild1_X7
 (DropComment.dropComment wild2_Xa);
                               : ds13_deY ds14_deZ ->
                                 case ds13_deY of _ { GHC.Types.C# ds15_df0
 ->
                                 case ds15_df0 of _ {
                                   __DEFAULT ->
                                     GHC.Types.:
                                       @ GHC.Types.Char wild1_X7
 (DropComment.dropComment wild2_Xa);
                                   ' ' -> GHC.Types.[] @ GHC.Types.Char
                                 }
                                 }
                             }
                         }
                         }
                     }
                 }
                 }
             }
         }
         }
     }
 end Rec }
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2598#comment:17>
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