$filename = "test.ini";
$handle = @fopen($filename, "r");
$result = [];
if ($handle) {
    while (($buffer = fgets($handle, 4096)) !== false) { //строка до 4КБ
        list($inikeys, $value) = explode('=', $buffer);
        $inikeys = explode('.', $inikeys);
        $current = &$result;
        foreach ($inikeys as $key => $inikey){
            if(!array_key_exists( $inikey, $current ) && $key + 1 < count($inikeys)){
                $current[$inikey] = [];
            }
            $current = &$current[$inikey];
        }
        $current = str_replace("\n", '', str_replace("\r", '', $value));
        unset($current);
    }
    fclose($handle);
}