print vs echo, which one is faster?

As most of us, I am tired to read blog posts about non-sense micro-optimizations like replacing print by echo, ++$i by $i++, or double quotes by single quotes. Why? Because 99.999999% of the time, it is irrelevant. Why? Because 99.99% of the time, you’d better install a PHP accelerator like APC, or add these missing indexes on your database columns, or try to avoid those 1000 database requests you have on the homepage.

But let’s pretend you really want to know the answer to this question. Instead of trying to write a script and execute it a million times to find the fastest, I want to show you some interesting tools you might find useful from time to time as they allow you to better understand the PHP code you write.

Enter VLD, the “Vulcan Logic Disassembler”. VLD is written by Derrick Rethans and as you can read on the VLD homepage, it “hooks into the Zend Engine and dumps all the opcodes (execution units) of a script”.

Installing VLD is simple enough. Download the latest version, and install it as you would have done for any other PHP extension:

$ phpize
$ ./configure
$ sudo make install

Enable the extension in your php.ini file:

extension=vld.so

Time to look under the hood. Create two simple files, one uses echo, and the other one uses print:

// print.php
<?php print 'foo';

// echo.php
<?php echo 'foo';

Execute these scripts from the command-line with the -d vld.activate=1 argument to activate VLD output and let’s have a look at the opcodes generated by these scripts:

$ php -d vld.active=1 print.php

number of ops:  4
compiled vars:  none
line     #  op                           fetch          ext  return  operands
-------------------------------------------------------------------------------
   1     0  PRINT                                            ~0      'foo'
         1  FREE                                                     ~0
   2     2  RETURN                                                   1
         3* ZEND_HANDLE_EXCEPTION                                    

$ php -d vld.active=1 echo.php

number of ops:  3
compiled vars:  none
line     #  op                           fetch          ext  return  operands
-------------------------------------------------------------------------------
   1     0  ECHO                                                     'foo'
   2     1  RETURN                                                   1
         2* ZEND_HANDLE_EXCEPTION                                    

Spot the difference? Yes, print uses one more opcode because it actually returns something. We can conclude that echo is faster than print. But one opcode costs nothing, really nothing. Even if a script have hundreds of calls to print.

 [php]
 <?php $isFoo and print 'foo'; ?>

Want to know the number of opcodes executed when running a script that has a lot of includes? Try this:

$ php -d vld.active=1 print.php 2> output
$ grep "number of ops" output | cut -f 5 -d ' ' | (tr '\n' +; echo 0) | bc

I have tried on a fresh Wordpress installation. The script halts before it ends with a “Bus Error” on my laptop, but the number of opcodes was already at more than 2.3 millions. Enough said.