⚡ PHP Opcode: Optimize Performance Without Rewriting Code

OPcache is the native PHP extension (included since PHP 5.5) that caches compiled bytecode in memory. Without OPcache, PHP would recompile code on every request, wasting CPU and memory.

; php.ini or php.d/opcache.ini
opcache.enable=1
opcache.memory_consumption=128
opcache.interned_strings_buffer=8
opcache.max_accelerated_files=10000
opcache.revalidate_freq=0
opcache.validate_timestamps=0
opcache.fast_shutdown=1

// Deployment script
<?php
opcache_reset(); // Full cache purge
// or
opcache_invalidate('/path/to/file.php', true);

To optimize, you must first see the generated opcode. Three methods:

<?php
// Force compilation
opcache_compile_file(__DIR__.'/script.php');

// Get OPcache status
$status = opcache_get_status();

// Inspect script
print_r($status['scripts'][__DIR__.'/script.php']);

# Installation
pecl install vld

# Usage
php -d vld.active=1 -d vld.execute=0 script.php

Here's the most surprising aspect: two logically identical syntaxes can generate very different opcodes in terms of complexity and number of operations.

<?php
namespace App;

strlen('hello'); // ❌ Bad

line  #* op                        fetch  ext  return  operands
------------------------------------------------------------------------
  5   0  INIT_NS_FCALL_BY_NAME              'App%5Cstrlen'
      1  SEND_VAL_EX                        'hello'
      2  DO_FCALL                    0
      3  RETURN                             1

<?php
namespace App;

\strlen('hello'); // ✅ Good

line  #* op         fetch  ext  return  operands
----------------------------------------------------
  5   0  RETURN                      1

<?php
namespace App;

use function strlen;

strlen('hello'); // ✅ Good too

Since PHP 7.x, the engine includes many automatic optimizations that evaluate static expressions ahead of time. Being aware of these mechanisms allows you to leverage them.

<?php
namespace App;

if (PHP_OS === 'Linux') {
  echo "Linux";
}

FETCH_CONSTANT  ~0  'App%5CPHP_OS'
IS_IDENTICAL    ~0, 'Linux'
JMPZ            ~1, ->4
ECHO            'Linux'

<?php
namespace App;

if (\PHP_OS === 'Linux') {
  echo "Linux";
}

ECHO 'Linux'
RETURN 1

At VOID, we applied these optimizations to a banking platform processing over 1 million transactions per day. Here are measured results: