So in this case we want that the *only* uses of n are in case statements.
+Note [Good arguments]
+~~~~~~~~~~~~~~~~~~~~~
So we look for
* A self-recursive function. Ignore mutual recursion for now,
simplifier. That gives the simplest possible program for SpecConstr to
chew on; and it virtually guarantees no shadowing.
+-----------------------------------------------------
+ Stuff not yet handled
+-----------------------------------------------------
+
+Here are notes arising from Roman's work that I don't want to lose.
+
+Example 1
+~~~~~~~~~
+ data T a = T !a
+
+ foo :: Int -> T Int -> Int
+ foo 0 t = 0
+ foo x t | even x = case t of { T n -> foo (x-n) t }
+ | otherwise = foo (x-1) t
+
+SpecConstr does no specialisation, because the second recursive call
+looks like a boxed use of the argument. A pity.
+
+ $wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
+ $wfoo_sFw =
+ \ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) ->
+ case ww_sFo of ds_Xw6 [Just L] {
+ __DEFAULT ->
+ case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] {
+ __DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq;
+ 0 ->
+ case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] ->
+ case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] ->
+ $wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy
+ } } };
+ 0 -> 0
+
+Example 2
+~~~~~~~~~
+ data a :*: b = !a :*: !b
+ data T a = T !a
+
+ foo :: (Int :*: T Int) -> Int
+ foo (0 :*: t) = 0
+ foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) }
+ | otherwise = foo ((x-1) :*: t)
+
+Very similar to the previous one, except that the parameters are now in
+a strict tuple. Before SpecConstr, we have
+
+ $wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
+ $wfoo_sG3 =
+ \ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T
+ GHC.Base.Int) ->
+ case ww_sFU of ds_Xws [Just L] {
+ __DEFAULT ->
+ case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] {
+ __DEFAULT ->
+ case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] ->
+ $wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1
+ };
+ 0 ->
+ case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] ->
+ case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] ->
+ $wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2
+ } } };
+ 0 -> 0 }
+
+We get two specialisations:
+"SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#}
+ Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB)
+ = Foo.$s$wfoo1 a_sFB sc_sGC ;
+"SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#}
+ Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp))
+ = Foo.$s$wfoo y_aFp sc_sGC ;
+
+But perhaps the first one isn't good. After all, we know that tpl_B2 is
+a T (I# x) really!
+
+
+Example 3
+~~~~~~~~~
+This one is about specialising on a *lambda* argument
+
+ foo :: Int -> (Int -> Int) -> Int
+ foo 0 f = 0
+ foo m f = foo (f m) (+1)
+
+It produces
+
+ lvl_rmV :: GHC.Base.Int -> GHC.Base.Int
+ lvl_rmV =
+ \ (ds_dlk :: GHC.Base.Int) ->
+ case ds_dlk of wild_alH { GHC.Base.I# x_alG ->
+ GHC.Base.I# (GHC.Prim.+# x_alG 1)
+
+ T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
+ GHC.Prim.Int#
+ T.$wfoo =
+ \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) ->
+ case ww_sme of ds_Xlw {
+ __DEFAULT ->
+ case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz ->
+ T.$wfoo ww1_Xmz lvl_rmV
+ };
+ 0 -> 0
+ }
+
+Of course, it would be much nicer if the optimiser specialised $wfoo for
+when lvl_rmV is passed as the second argument and then inlined it.
+
+Example 4
+~~~~~~~~~
+ foo :: Int -> (Int -> Int) -> Int
+ foo 0 f = 0
+ foo m f = foo (f m) (\n -> n-m)
+
+This is subtly different from the previous one in that we get an
+explicit lambda as the argument:
+
+ T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
+ GHC.Prim.Int#
+ T.$wfoo =
+ \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) ->
+ case ww_sm8 of ds_Xlr {
+ __DEFAULT ->
+ case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq ->
+ T.$wfoo
+ ww1_Xmq
+ (\ (n_ad3 :: GHC.Base.Int) ->
+ case n_ad3 of wild_alB { GHC.Base.I# x_alA ->
+ GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr)
+ })
+ };
+ 0 -> 0
+ }
+
+I wonder if SpecConstr couldn't be extended to handle this? After all,
+lambda is a sort of constructor for functions and perhaps it already
+has most of the necessary machinery?
+
%************************************************************************
%* *
scBind env (Rec [(fn,rhs)])
| notNull val_bndrs
= scExpr env_fn_body body `thenUs` \ (usg, body') ->
- specialise env fn bndrs body usg `thenUs` \ (rules, spec_prs) ->
+ specialise env fn bndrs body' usg `thenUs` \ (rules, spec_prs) ->
+ -- Note body': the specialised copies should be based on the
+ -- optimised version of the body, in case there were
+ -- nested functions inside.
let
SCU { calls = calls, occs = occs } = usg
in
---------------------
good_arg :: ConstrEnv -> IdEnv ArgOcc -> (CoreBndr, CoreArg) -> Bool
+-- See Note [Good arguments] above
good_arg con_env arg_occs (bndr, arg)
= case is_con_app_maybe con_env arg of
Just _ -> bndr_usg_ok arg_occs bndr arg
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