php double if statement

I'm new to learning how to program. And I'm wondering what the best way is to handle the problem where you got a double if statement, with both having the same Else result.

Take for instance the following double if statement.

if (isset($x)) {
    $y = doSomething($x);
    if ($y == "something") {
        do result A;
    }
    else {
        do result B;
    }
}
else {
    do result B;
}

It doesn't seem like a smart idea to write result B multiple times. Now what are the different ways to prevent having to write result B multiple times?

One can try making 1 combined if statement, but this doesn't seem always possible (for instance when checking with isset() if a variable exists).

if (isset($x) && $y) { etc. }

What other options are there?

PS. I'm also open for other suggestions to help improve my code, like how to write if(isset($x)) in a nicer way.