validaçao login PHP

<?php
$x="";
if(isset($_GET['btn'])){
    $user = $_GET['user'];
    $pass = $_GET['pass'];
    /*
    echo $user."<br>";
    echo $pass."<br>";*/
    $x=verificalogin($user,$pass);
}


function verificalogin($user, $pass){
    if($user == "andre" && $pass == "abc123"){
        return 'Sucesso';
    }else{
        return 'Erro';
    }
}
?>
<!DOCTYPE html>
<html lang="pt-br">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    <form action="formulario.php" method="GET">
        <input type="text" name="user">
        <input type="pass" name="pass">
        <input type="submit" name="btn">
    </form>
    <?php
    if($x=="Erro"){
        echo "login invalido";
    }else{
        echo "OK";
    }
    ?>
</body>
</html>