If is not need convert, use zend_string_copy.

Author: youkidearitai

ext/mbstring/mbstring.c

@@ -2973,6 +2973,10 @@ static void php_mb_ulcfirst(INTERNAL_FUNCTION_PARAMETERS, php_case_mode mode)
 	zend_string *head = mbstring_convert_case(mode, ZSTR_VAL(first), ZSTR_LEN(first), enc);
 	zend_string_release_ex(first, false);
 
+	if (zend_string_equals(first, head)) {
+		RETVAL_STR(zend_string_copy(str));
+	}
+
 	zend_string *retval = zend_string_concat2(ZSTR_VAL(head), ZSTR_LEN(head), ZSTR_VAL(second), ZSTR_LEN(second));
 	zend_string_release_ex(head, false);
 	zend_string_release_ex(second, false);