Tweak variable declaration reconstruction -- big code-gen quality imp…

…rovement

lib/Cleanup1.ml

@@ -85,7 +85,10 @@ let remove_assignments = object(self)
           with_type e.typ @@ close_now_over not_yet_closed (
             (* We must now bind: *)
               (count e) ++ (* whichever variables were in the condition *)
-              (AtomSet.inter (count e') (count e''))) (* variables that appear in both branches *)
+              AtomSet.empty) (* unlike below, we are in terminal position, so we do not need to
+              close immediately variables that appear in both branches -- we can simply declare them
+              twice in each branch! is this a better code-gen choice? yes, absolutely -- owing to
+              the structure of MIR, NOT doing this generates awful code *)
             (fun not_yet_closed ->
               EIfThenElse (self#visit_expr_w not_yet_closed e,
                 recurse_or_close not_yet_closed e',
@@ -98,12 +101,8 @@ let remove_assignments = object(self)
       | ESwitch (e, branches) ->
           with_type e.typ @@ close_now_over not_yet_closed (
             (* We must now bind: *)
-              (count e) ++
-                (* i.e., whichever variables were in the condition *)
-              (Krml.KList.reduce AtomSet.inter (List.map (fun (_p, e) -> count e) branches)))
-                (* i.e., variables that appear in all branches -- note that
-                   switches don't bind variables in their branches so it's simpler
-                   than the match below*)
+              (count e) ++ (* i.e., whichever variables were in the condition *)
+              AtomSet.empty) (* see above *)
             (fun not_yet_closed ->
               ESwitch (
                 self#visit_expr_w not_yet_closed e,
@@ -113,11 +112,8 @@ let remove_assignments = object(self)
       | EMatch (c, e, branches) ->
           with_type e.typ @@ close_now_over not_yet_closed (
             (* We must now bind: *)
-              (count e) ++
-                (* i.e., whichever variables were in the condition *)
-              (Krml.KList.reduce AtomSet.inter (List.map (fun (_bs, _p, e) -> count e) branches)))
-                (* i.e., variables that appear in all branches -- note that we
-                   don't open _bs meaning that we don't collect bound variables in this branch *)
+              (count e) ++ (* i.e., whichever variables were in the condition *)
+              AtomSet.empty) (* see above *)
             (fun not_yet_closed ->
               EMatch (
                 c,