[GHC] #9279: Local wrapper function remains in final program; result = extra closure allocation

[GHC]

#9279: Local wrapper function remains in final program; result = extra closure
allocation
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        Reporter:  simonmar          |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.2
      Resolution:                    |             Keywords:  LateLamLift
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by sgraf):

 Here's a diff that handles all `UnliftedRep`s uniformly:

 {{{
 diff --git a/compiler/basicTypes/Literal.hs
 b/compiler/basicTypes/Literal.hs
 index 21f4a92290..0e9f25f51e 100644
 --- a/compiler/basicTypes/Literal.hs
 +++ b/compiler/basicTypes/Literal.hs
 @@ -62,6 +62,7 @@ import Binary
  import Constants
  import DynFlags
  import Platform
 +import RepType
  import UniqFM
  import Util

 @@ -614,11 +615,14 @@ literalType (LitNumber _ _ t) = t
  absentLiteralOf :: TyCon -> Maybe Literal
  -- Return a literal of the appropriate primitive
  -- TyCon, to use as a placeholder when it doesn't matter
 -absentLiteralOf tc = lookupUFM absent_lits (tyConName tc)
 +absentLiteralOf tc
 +  | tyConPrimRep tc == [UnliftedRep]
 +  = ASSERT (isUnliftedTyCon tc) Just MachNullAddr
 +  | otherwise
 +  = lookupUFM absent_lits (tyConName tc)

  absent_lits :: UniqFM Literal
 -absent_lits = listToUFM [ (addrPrimTyConKey,    MachNullAddr)
 -                        , (charPrimTyConKey,    MachChar 'x')
 +absent_lits = listToUFM [ (charPrimTyConKey,    MachChar 'x')
                          , (intPrimTyConKey,     mkMachIntUnchecked 0)
                          , (int64PrimTyConKey,   mkMachInt64Unchecked 0)
                          , (wordPrimTyConKey,    mkMachWordUnchecked 0)
 }}}

 But now `MachNullAddr` isn't always a literal of type `Addr#`. In
 particular, the definition

 {{{
 -- | Find the Haskell 'Type' the literal occupies
 literalType :: Literal -> Type
 literalType MachNullAddr      = addrPrimTy
 literalType (MachChar _)      = charPrimTy
 literalType (MachStr  _)      = addrPrimTy
 }}}

 is probably a lie. But then it also lies for `MachStr` and `MachLabel`s,
 so maybe this isn't such a bad thing? The binding should be immediately
 eliminated by the simplifier, after all.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9279#comment:15>
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