Performance optimization by replacing is_null with === null

[SchumacherFM]

According to http://framework.zend.com/issues/browse/ZF-5413 the usage of is_null is slow.
So I replaced every occurrences of is_null or !is_null with === null or !== null

Unit test are running "normal".

First time for me, so I do accept your Contributor License Agreement.

PS: This pull request contains all commits. Sorry.

[magento-team]

Have you tried benchmarking this change? we have previously tried to change even more significant parts of the code but in the whole rendering time that speed difference was negligible (even though if the code itself repeated many times was much faster)

[mtdowling]

A quick google search shows that the overhead of the is_null function call vs using === null does make a small difference. Magento is such a large framework that you shouldn't turn down these really easy micro-optimizations.

<?php

$i = $argv[1];
$a = null;

$s = microtime(true);
for ($j = 0; $j < $i; $j++) {
    is_null($a);
}
echo (microtime(true) - $s) . "\n";

$s = microtime(true);
for ($j = 0; $j < $i; $j++) {
    $a === null;
}
echo (microtime(true) - $s) . "\n";

Benchmark:

$ php ~/projects/perf/is_null_vs_null.php 100000
0.15766286849976
0.034035205841064

[magento-team]

Hello. We did a small test and it showed that there is no noticeable improvement for real page rendering and is_null is more readable. We appreciate your work on this contribution but we will not accept it.