C: Fix an issue with assigning to unitialized variables at end of blocks

Assigning to an uninitialized variable as the last statement in a
block is almost certainly a type, and if that occurs then the
lift_assign re-write will introduce empty blocks causing this error to
occur. Now when we see such an empty block when converting to A-normal
form we turn it into unit, and emit a warning stating that an empty
block has been found as well as the probable cause (uninitialized
variable).

1 files changed, 4 insertions, 0 deletions

diff --git a/src/anf.ml b/src/anf.ml
index e87f2bfd..38be1127 100644
--- a/src/anf.ml
+++ b/src/anf.ml
@@ -509,6 +509,10 @@ let rec anf (E_aux (e_aux, ((l, _) as exp_annot)) as exp) =
   match e_aux with
   | E_lit lit -> mk_aexp (ae_lit lit (typ_of exp))
 
+  | E_block [] ->
+     Util.warn (Reporting_basic.loc_to_string l
+                ^ "\n\nTranslating empty block (possibly assigning to an uninitialized variable at the end of a block?)");
+     mk_aexp (ae_lit (L_aux (L_unit, l)) (typ_of exp))
   | E_block exps ->
      let exps, last = split_block l exps in
      let aexps = List.map anf exps in