I didn't say "is wrong", I said "looks wrong" (yes, I know you didn't say I said that either, but you seem to have reacted as though I did). It looks wrong to the extent that it should either be rewritten to "look right" or be commented. However the only appropriate comment effectively says "I did a dumb thing that needs an even dumber comment so that you know I'm being silly". Much better to rewrite it as:

$x = $y;
if ($x) {
    ...
}
[download]

which makes it quite clear that the assignment is intended and also quite clear what is being tested. Most countries don't tax code by the line so the cost of being clear is pretty low. ;)