Improve inlining for local functions

[simonpj]

I found that boyer2/Rewritefuns.onewayunify1 has a join point that really should be inlined. It should get a big discount from scrutinizing free variables. But the inlining mechanism only take account of arguments, not free variables. There's a small optimisation opportunity here, which this ticket records.

Here's the code:

Rewritefns.onewayunify1 =
  \ (t1_acm :: Lisplikefns.Lisplist)
    (t2_acn :: Lisplikefns.Lisplist)
    (u_aco :: Lisplikefns.Lisplist) ->
    case t2_acn of wild_ao1 {
      __DEFAULT ->
        case t1_acm of wild_Xok {
          __DEFAULT ->
            let {
              $j_spS
                :: GHC.Prim.State# GHC.Prim.RealWorld
                   -> (GHC.Bool.Bool, Lisplikefns.Lisplist)
              [LclId,
               Arity=1,
               Unf=Unf{Src=<vanilla>, TopLvl=False, Arity=1, Value=True,
                       ConLike=True, Cheap=True, Expandable=True,
                       Guidance=IF_ARGS [0] 10 0}]
              $j_spS =
                \ _ ->
                  Rewritefns.onewayunify1lst
                    (case wild_Xok of _ {
                       Lisplikefns.Nil -> Lisplikefns.Nil;
                       Lisplikefns.Cons ds1_anT ->
                         case ds1_anT of _ { (_, y_anY) -> y_anY }
                     })
                    (case wild_ao1 of _ {
                       Lisplikefns.Nil -> Lisplikefns.Nil;
                       Lisplikefns.Cons ds1_anT ->
                         case ds1_anT of _ { (_, y_anY) -> y_anY }
                     })
                    u_aco } in
            case wild_Xok of _ {
              Lisplikefns.Nil ->
                case wild_ao1 of _ {
                  Lisplikefns.Nil ->
                    case Lisplikefns.$fEqLisplist_$c== Lisplikefns.Nil Lisplikefns.Nil
                    of _ {
                      GHC.Bool.False -> (GHC.Bool.False, u_aco);
                      GHC.Bool.True -> $j_spS GHC.Prim.realWorld#
                    };
                  Lisplikefns.Cons ds1_anJ ->
                    case ds1_anJ of _ { (x_anN, _) ->
                    case Lisplikefns.$fEqLisplist_$c== Lisplikefns.Nil x_anN of _ {
                      GHC.Bool.False -> (GHC.Bool.False, u_aco);
                      GHC.Bool.True -> $j_spS GHC.Prim.realWorld#
                    }
                    }
                };
              Lisplikefns.Cons ds1_anJ ->
                case ds1_anJ of _ { (x_anN, _) ->
                case wild_ao1 of _ {
                  Lisplikefns.Nil ->
                    case Lisplikefns.$fEqLisplist_$c== x_anN Lisplikefns.Nil of _ {
                      GHC.Bool.False -> (GHC.Bool.False, u_aco);
                      GHC.Bool.True -> $j_spS GHC.Prim.realWorld#
                    };
                  Lisplikefns.Cons ds1_Xof ->
                    case ds1_Xof of _ { (x_Xom, _) ->
                    case Lisplikefns.$fEqLisplist_$c== x_anN x_Xom of _ {
                      GHC.Bool.False -> (GHC.Bool.False, u_aco);
                      GHC.Bool.True -> $j_spS GHC.Prim.realWorld#
                    }
                    }
                }
                }
            };
          Lisplikefns.Atom x_ao3 -> (GHC.Bool.False, u_aco)
        };

You can see that $j_sps scrutinises wild_Xok and wild_ao1, but it currently gets no discount for doing so.

[nfrisby]

Small example abstracting nofib boyer2, where discounting FVs is a win

[nfrisby]

For the record, we re-discovered this while investigating a late lambda float. If we move forward with that, it would partially achieve the functionality of discounting FVs, as discussed in #7664; see attached FVDiscountSim.hs