Oh, it seems can't be resolved by check first stmt as first stmt can be multiple condition, for example:

        echo 'test';

        while (true !== false) {
        }

that still added. I added more failing fixture for it e78c0ee

I am not sure about this, the question is why create abvious infinite loop on early code in the first place :)

        while (true !== false) {
        }

        $a = [];

        if ($b = $yes) {
            $a[] = 'test';
        }

        return $a;

I am closing this for now.

Re-open, @jackbentley it seems it can be resolved by check parent Node of Stmt is an Unreachable stmt on PHPStanNodeScopeResolver

Finally, All checks have passed 🎉 @TomasVotruba it is ready for review.

@TomasVotruba I am merging it ;)