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Last week, Joe Watkins, a PHP developer, shared that PHP 8 will support the Just-in-Time (JIT) compilation. This decision was the result of voting among the PHP core developers for supporting JIT in PHP 8 and also in PHP 7.4 as an experimental feature.

If you don’t know what JIT is, it is a compiling strategy in which a program is compiled on the fly into a form that’s usually faster, typically the host CPU’s native instruction set. To do this the JIT compiler has access to dynamic runtime information whereas a standard compiler doesn’t.

How PHP programs are compiled?

PHP comes with a virtual machine named the Zend VM. The human-readable scripts are compiled into instructions, which are called opcodes that are understandable to the virtual machine. Opcodes are low-level, and hence faster to translate to machine code as compared to the original PHP code. This stage of execution is called compile time. These opcodes are then executed by the Zend VM in the runtime stage.

JIT is being implemented as an almost independent part of OPcache, an extension to cache the opcodes so that compilation happens only when it is required. In PHP, JIT will treat the instructions generated for the Zend VM as the intermediate representation. It will then generate an architecture dependent machine code so that the host of your code is no longer the Zend VM, but the CPU directly.

Why JIT is introduced in PHP?

PHP hits the brick wall

Many improvements have been done to PHP since its 7.0 version including optimizations for HashTable, specializations in the Zend VM for certain opcodes, specializations in the compiler for certain sequences, and many more. After so many improvements, now PHP has reached the extent of its ability to be improved any further.

PHP for non-Web scenarios

Adding support for JIT in PHP will allow its use in scenarios for which it is not even considered today, i.e., in other non-web, CPU-intensive scenarios, where the performance benefits will be very substantial.

Faster innovation and more secure implementations

With JIT support, the team will be able to develop built-in functions in PHP instead of C without any huge performance penalty. This will make PHP less susceptible to memory management, overflows, and other similar issues associated with C-based development.

We can expect the release of PHP 7.4 later this year, which will debut JIT in PHP.  Though there is no official announcement about the release schedule of PHP 8, many are speculating its release in late 2021.

Read Joe Watkins’ announcement on his blog.

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