use high-level numerical conversion

Direct access to the value of a constant_exprt is prone to error; the
already existing functions should be used instead.

Author: Daniel Kroening

jbmc/src/java_bytecode/java_bytecode_concurrency_instrumentation.cpp

@@ -86,7 +86,7 @@ static const std::string get_thread_block_identifier(
 {
   PRECONDITION(f_code.arguments().size() == 1);
   const exprt &expr = f_code.arguments()[0];
-  mp_integer lbl_id = bv2integer(expr.op0().get_string(ID_value), false);
+  const mp_integer lbl_id = numeric_cast_v<mp_integer>(expr.op0());
   return integer2string(lbl_id);
 }
 

src/goto-programs/goto_convert.cpp

@@ -1830,8 +1830,13 @@ bool goto_convertt::get_string_constant(
       forall_operands(it, index_op)
         if(it->is_constant())
         {
-          unsigned long i = integer2ulong(
-            bv2integer(id2string(to_constant_expr(*it).get_value()), true));
+          mp_integer int_value;
+          if(to_integer(to_constant_expr(*it), int_value))
+            return true;
+
+          const auto i = numeric_cast<std::size_t>(*it);
+          if(!i.has_value())
+            return true;
 
           if(i!=0) // to skip terminating 0
             result+=static_cast<char>(i);