Hi, I'm Derick. And this is PHP internals news, a weekly podcast dedicated to demystifying the development of the PHP language. This is Episode 48. Today I'm talking with Sara Golemon about PHP 8 and JIT. Sara, would you please introduce yourself?

Hi there. Hi there, everybody listening to PHP internals podcast. I'm Sara. I've been on this podcast before. But in case you're just getting here to for the first time, welcome to the podcast. You have a nice backlog to go through. I am a lapsed web developer, come database security engineer by day, and an opinionated open source dev slash PHP 7.2 release manager by night and also day. I've been involved with the project for about 20 years now off and on. Somehow I just keep coming back for more punishment.

We're leading up to PHP 8, with lots of new features being added. But one of the biggest thing in PHP 8 that I've spoken about on the podcast on before all the way back last year in Episode 7, is that PHP eight is going to get a JIT engine. Would you care to explain what a JIT engine does again?

Well, I'm going to give you the short, you can look this up on Wikipedia in two seconds definition of JIT, means just in time compilation. That doesn't really tell you much, unless you listen to it on the sort of other half of that of AOT, or ahead of time compilation. AOT is what you expect from applications like GCC, you know, you just make an application that you've got C or C++ kind of source code to that's ahead of time. JIT is saying, well, let's take the source for application. And let's just run with it. Let's just start executing it as fast as I can. And eventually we're going to get down to some compiled code. That's going to run a little bit quicker than the initial stuff did. PHP already has this nice little virtual machine built into it. We call it the Zend engine. That takes your script and immediately just says: All right, well, what does this say in computer terms? Well, a computer readable term is a series of these op codes, they're also called byte codes in other languages that give you instructions for: run this type of instruction at this time and get something done. The PHP runtime interpreter interprets that one instruction at a time basically pretending to be a CPU. This works quite well, it runs quite efficiently. But there's still this sort of bottleneck in the middle there of a program pretending to be a CPU running on top of a CPU in order to run other code. The idea of JIT is that this thing sitting in the middle is going to gradually figure out what your program really is trying to do and how it's intended to run, and It's going to take those PHP instructions and it's going to turn them all the way down into CPU instructions, so that it can get out of the way and let the CPU run your code natively as if it had been written in a compiled AOT kind of language. What that actually means for execution of PHP code in PHP 8 is still sort of a, you know, a question that's, that's left to be answered here. I listened to your interview with Zeev. Episode 7, is a good episode of getting some good information on that. We do definitely agree on what the status of the JIT within PHP is, right now we can. It's subjective facts like this is how much work has been done largely by Dmitri, where we can kind of expect to see the best gains come from. I personally think I might be a little bit more pessimistic than him in terms of the actual