Check for lvalue in assigns clause after type checking

Signed-off-by: Felipe R. Monteiro <felisous@amazon.com>

Author: feliperodri

src/ansi-c/ansi_c_convert_type.cpp

@@ -256,13 +256,7 @@ void ansi_c_convert_typet::read_rec(const typet &type)
 
     for(const exprt &target : to_unary_expr(as_expr).op().operands())
     {
-      if(!is_lvalue(target))
-      {
-        error().source_location = target.source_location();
-        error() << "illegal target in assigns clause" << eom;
-        throw 0;
-      }
-      else if(has_subexpr(target, ID_side_effect))
+      if(has_subexpr(target, ID_side_effect))
       {
         error().source_location = target.source_location();
         error() << "Assigns clause is not side-effect free." << eom;

src/ansi-c/c_typecheck_base.cpp

@@ -739,7 +739,21 @@ void c_typecheck_baset::typecheck_declaration(
         }
 
         for(auto &target : code_type.assigns())
+        {
           typecheck_expr(target);
+          if(target.type().id() == ID_empty)
+          {
+            error().source_location = target.source_location();
+            error() << "void-typed targets not permitted" << eom;
+            throw 0;
+          }
+          if(!target.get_bool(ID_C_lvalue))
+          {
+            error().source_location = target.source_location();
+            error() << "illegal target in assigns clause" << eom;
+            throw 0;
+          }
+        }
 
         if(!as_const(code_type).ensures().empty())
         {