Convincing GHC not to produce unfoldings during simplification

[Ben Gamari]

I'm currently trying to get the interface file bulk imposed by TTypeable
down. The branch will currently produce two top-level bindings for each TyCon.
For instance, given the type,

    data Proxy (a :: k) = Proxy

the branch will produce (ignoring the promoted datacon for a moment),

    $tcProxy :: TyCon
    $tcProxy
      = GHC.Types.TyCon
          fpr1 fpr2           -- fingerprints
          $trModule
          (GHC.Types.TrNameS "Proxy"#)
          1
          krep_aebr

    krep_aebr :: KindRep
    krep_aebr [InlPrag=NOINLINE CONLIKE]
      = GHC.Types.KindRepFun
          (GHC.Types.KindRepVar 0)
          (GHC.Types.KindRepTYPE GHC.Types.LiftedRep)

Note that the KindRep has been marked as NOINLINE; I do this
intentionally as these things can grow quite large (consider, for
instance, the kind of a promoted tuple constructor). This is especially
true as the simplifier tends to float out the constituents of the
KindRep. After the first simplifier phase we end up with,


    krep_sebQ :: GHC.Types.KindRep
    [LclId,
    Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
            WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 30 0}]
    krep_sebQ = GHC.Types.$WKindRepVar (GHC.Types.I# 0#)

    krep_sebR :: GHC.Types.KindRep
    [LclId,
    Unf=Unf{Src=<vanilla>, TopLvl=True, Value=False, ConLike=False,
            WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 20 0}]
    krep_sebR = GHC.Types.$WKindRepTYPE GHC.Types.LiftedRep

    krep_aebr [InlPrag=NOINLINE CONLIKE] :: GHC.Types.KindRep
    [LclId,
    Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True,
            WorkFree=True, Expandable=True, Guidance=IF_ARGS [] 10 30}]
    krep_aebr = GHC.Types.KindRepFun krep_sebQ krep_sebR

This means that GHC will now include each of the bindings floated out
from krep_aebr in the interface file, despite the NOINLINE pragma, as
they are all depended upon by the exported $tcProxy through their
unfoldings. This is Quite Bad.

I have observed that the floated bindings are not included in the
interface file with -O0. Moreover, the core2core output clearly shows
the unfoldings being added after the first simplifier phase. I haven't
yet determined where in the simplifier these unfoldings are being
introduced, but if anyone has ideas I'd love to hear them.

Cheers,

- Ben
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