PHP - to copy, or not to copy, that is the variable?

Question

I landed up on this link: https://developers.google.com/speed/articles/optimizing-php

And then did a search about variable copies and found this: Copy or don't copy extra variables in PHP?

So I understand the above concepts but to my understanding the below code is actually good practice but sorta goes against the don't copy statement. Its almost like "don't copy" must have a condition. Ive always understood that doing a function call on every loop is more resource intensive than storing (copy).

$total = total();
for($i=0; $i<$total; $i++){
}

Same applies for (best example I could think of using Google's example):

<?php
$description = strip_tags($_POST['description']);
?>
<img src="" alt="<?php echo $description ?>" title="<?php echo $description ?>" data-description="<?php echo $description ?>" />

I find it hard to believe making a variable copy has more of a performance hit then:

<img src="" alt="<?php echo strip_tags($_POST['description']) ?>" title="<?php echo strip_tags($_POST['description']) ?>" data-description="<?php echo strip_tags($_POST['description']) ?>" />

So I guess the "for no reason" is relevant above?

Answer 1

If copying variables becomes a performance issue, then something is severely wrong with your application and you've got much bigger issues to worry about. In 99.99999% of cases, this will never be your bottle neck. Going out of your way to purposely avoid copying variables is an act of micro-optimization. Focus on writing clean readable code that makes sense instead of worrying about small micro-optimizations like this. The Google article in question has actually received a lot of criticism in the past as it looks as though it was quickly thrown together by somebody who was grabbing random information from other random misinformed articles.