Does returning values from functions affect performance in PHP?

Question

Let's take a look at this class and method:

class Test {
    protected $storage;

    public function rng() {
        $random = random_bytes(100);

        $this->storage = $random;
    }
}

Some random bytes are being calculated using PHP7's random_bytes() function, and the result isn't returned; it's only being stored in a property.

Let's take a look at a slightly different version of the above method:

class Test {
    protected $storage;

    public function rng() {
        $random = random_bytes(100);

        $this->storage = $random;

        return $random;
    }
}

This time, the result is returned. I am wondering if there's any performance hit when a value is being returned.

Answer 1

Test script #1: not returning value

<?php

class Test {
    protected $storage;

    public function rng() {
        $random = random_bytes(100);

        $this->storage = $random;
    }
}

$instance = new Test;

$start = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $instance->rng();
}

$end = microtime(true);

$diff = $end - $start;

printf('Not returning: %.25f', $diff);

print PHP_EOL;

Test script #2: returning value

<?php

class Test {
    protected $storage;

    public function rng() {
        $random = random_bytes(100);

        $this->storage = $random;

        return $random;
    }
}

$instance = new Test;

$start = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $instance->rng();
}

$end = microtime(true);

$diff = $end - $start;

printf('Returning: %.25f', $diff);

print PHP_EOL;

Results:

$ php -f functions-returning-values-benchmark.php
Not returning: 0.0937850475311279296875000

$ php -f functions-returning-values-benchmark.php
Not returning: 0.0939409732818603515625000

$ php -f functions-returning-values-benchmark.php
Not returning: 0.0953028202056884765625000

$ php -f functions-returning-values-benchmark.php
Returning: 0.0947949886322021484375000

$ php -f functions-returning-values-benchmark.php
Returning: 0.0930099487304687500000000

$ php -f functions-returning-values-benchmark.php
Returning: 0.0935621261596679687500000

Conclusion

There is no performance hit.

Tested on AWS Debian Jessie t2.micro instance (1vCore, 1 GiB RAM) running PHP 7.0.7.