What PHP7 Brings: New Features and Massive Performance Gains Explained

At the 2015 PHPCON conference, PHP expert "Bird" presented the new features and performance improvements of PHP7, and this article consolidates those insights for PHP developers.

New Features and Changes

Scalar Type Declarations & Return Type Declarations PHP now optionally supports strict typing via declare(strict_types=1); , allowing developers to enforce exact parameter and return types, reducing implicit type coercion.

More Errors as Catchable Exceptions PHP7 introduces a global Throwable interface, making many previously fatal errors catchable as exceptions, improving error handling flexibility.

Abstract Syntax Tree (AST) The engine now builds an AST before compilation, decoupling parsing from opcode generation and simplifying maintenance.

Native Thread‑Local Storage (TLS) PHP7 replaces the large global array used for thread‑specific data with a dedicated thread‑local variable, streamlining multithreaded environments.

Other New Features

Int64 support for large integers, strings, and file uploads.

Uniform variable syntax.

Consistent foreach behavior.

New operators <=> and ??.

Unicode code point syntax \u{xxxxx}.

Anonymous classes.

Performance Breakthroughs

Benchmarks show PHP7 reducing execution time from 2.991 s to 1.186 s (≈60% faster) and increasing WordPress QPS by 2.77× compared with PHP5.6.

Although a JIT engine was experimented with in PHP5.5, the generated bytecode was too large for real‑world projects like WordPress, causing CPU cache misses and negating performance gains. The analysis concluded that JIT benefits depend heavily on the project’s bottlenecks.

Memory Layout Optimizations

Zval Changes – The Zval structure shrank from 24 bytes to 16 bytes by using a union, reducing memory consumption.

zend_string – Stores the string directly in a fixed‑size char array, improving cache locality.

Array (HashTable) Redesign – PHP7’s Zend Array packs buckets and values together, cutting bucket size from 72 bytes to 32 bytes and reducing overall HashTable size, which lowers CPU cache misses.

Function Calling Convention – Redundant instructions were removed, streamlining parameter passing.

Macros and Inline Functions – Compile‑time evaluation of parameter parsing and other checks reduces runtime overhead.

Conclusion

PHP7 delivers a dramatic performance uplift through language‑level type safety, memory layout refinements, and engine optimizations, enabling higher request throughput on fewer servers. The release promises continued evolution for PHP‑based web applications.