Fix edge case for STL bit string termination

Since the RLO is only modeled implicitly, changing a value that was
pushed on the RLO previously modifies the RLO post hoc. This fix should
allow for correct results when a value that contributes to the RLO is
modified.

Author: MatWise

src/statement-list/statement_list_typecheck.cpp

@@ -1046,6 +1046,9 @@ void statement_list_typecheckt::typecheck_statement_list_assign(
   tia_element.value.add_to_operands(assignment);
   fc_bit = false;
   or_bit = false;
+  // Set RLO to assigned operand in order to prevent false results if a symbol
+  // that's implicitly part of the RLO was changed by the assignment.
+  rlo_bit = lhs;
 }
 
 void statement_list_typecheckt::typecheck_statement_list_set_rlo(
@@ -1078,6 +1081,9 @@ void statement_list_typecheckt::typecheck_statement_list_set(
   tia_element.value.add_to_operands(ifthen);
   fc_bit = false;
   or_bit = false;
+  // Set RLO to assigned operand in order to prevent false results if a symbol
+  // that's implicitly part of the RLO was changed by the assignment.
+  rlo_bit = lhs;
 }
 
 void statement_list_typecheckt::typecheck_statement_list_reset(
@@ -1092,6 +1098,9 @@ void statement_list_typecheckt::typecheck_statement_list_reset(
   tia_element.value.add_to_operands(ifthen);
   fc_bit = false;
   or_bit = false;
+  // Set RLO to assigned operand in order to prevent false results if a symbol
+  // that's implicitly part of the RLO was changed by the assignment.
+  rlo_bit = lhs;
 }
 
 void statement_list_typecheckt::typecheck_statement_list_call(