Fix access to deleted memory.

When parameters are replaced, the expression that is replaced is deleted
so make sure the pointer in the map is properly updated. Also, make sure
the defparam expression itself is not deleted because it is used to
print messages, such as design dumps.

net_design.cc

@@ -227,6 +227,10 @@ void NetScope::run_defparams(Design*des)
 		  continue;
 	    }
 
+	      // Once placed in the parameter map, the expression may
+	      // be deleted when evaluated, so give it a copy of this
+	      // expression, not the original.
+	    val = val->dup_expr();
 	    bool flag = targ_scope->replace_parameter(perm_name, val);
 	    if (! flag) {
 		  cerr << val->get_fileline() << ": warning: parameter "
@@ -348,7 +352,7 @@ void NetScope::evaluate_parameter_logic_(Design*des, param_ref_t cur)
 		  tmp.has_sign ( (*cur).second.signed_flag );
 		  delete val;
 		  val = new NetEConst(tmp);
-		  expr = val;
+		  (*cur).second.expr = expr = val;
 	    }
       }