Rule source on GitHub

DowngradeFreadFwriteFalsyToNegationRector

Changes fread() or fwrite() compare to false to negation check

-fread($handle, $length) === false;
-fwrite($fp, '1') === false;
+!fread($handle, $length);
+!fwrite($fp, '1');

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp74\Rector\Identical\DowngradeFreadFwriteFalsyToNegationRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeFreadFwriteFalsyToNegationRector::class,
    ]);