+ ------------------------------
+ [Inline dfuns] Inlining dfuns unconditionally
+ ------------------------------
+
+The code above unconditionally inlines dict funs. Here's why.
+Consider this program:
+
+ test :: Int -> Int -> Bool
+ test x y = (x,y) == (y,x) || test y x
+ -- Recursive to avoid making it inline.
+
+This needs the (Eq (Int,Int)) instance. If we inline that dfun
+the code we end up with is good:
+
+ Test.$wtest =
+ \r -> case ==# [ww ww1] of wild {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True ->
+ case ==# [ww1 ww] of wild1 {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True -> PrelBase.True [];
+ };
+ };
+ Test.test = \r [w w1]
+ case w of w2 {
+ PrelBase.I# ww ->
+ case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+ };
+
+If we don't inline the dfun, the code is not nearly as good:
+
+ (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
+ PrelBase.:DEq tpl1 tpl2 -> tpl2;
+ };
+
+ Test.$wtest =
+ \r [ww ww1]
+ let { y = PrelBase.I#! [ww1]; } in
+ let { x = PrelBase.I#! [ww]; } in
+ let { sat_slx = PrelTup.(,)! [y x]; } in
+ let { sat_sly = PrelTup.(,)! [x y];
+ } in
+ case == sat_sly sat_slx of wild {
+ PrelBase.False -> Test.$wtest ww1 ww;
+ PrelBase.True -> PrelBase.True [];
+ };
+
+ Test.test =
+ \r [w w1]
+ case w of w2 {
+ PrelBase.I# ww ->
+ case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
+ };
+
+Why doesn't GHC inline $fEq? Because it looks big:
+
+ PrelTup.zdfEqZ1T{-rcX-}
+ = \ @ a{-reT-} :: * @ b{-reS-} :: *
+ zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
+ zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
+ let {
+ zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
+ zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
+ let {
+ zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
+ zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
+ let {
+ zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
+ zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
+ ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
+ case ds{-rf5-}
+ of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
+ case ds1{-rf4-}
+ of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
+ PrelBase.zaza{-r4e-}
+ (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
+ (zeze{-rf0-} a2{-reZ-} b2{-reY-})
+ }
+ } } in
+ let {
+ a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
+ a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
+ b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
+ PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
+ } in
+ PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
+
+and it's not as bad as it seems, because it's further dramatically
+simplified: only zeze2 is extracted and its body is simplified.