A closer look at JIT (Just In Time Compiler)
JIT is arguably the biggest change in PHP 8, in order to understand how it works you need to understand compilation. Compilation is a translation of human-readable code to machine code, translating human-readable code to machine code can happen in three different ways: Ahead Of Time (e.g C++) , Just In Time or Interpretation.
PHP has traditionally been an interpreted language however it is now not only interpreted but also Just In Time compiled. Capable of compiling this intermediate representation of code into binary objects in runtime operating in a hybrid mode where code is partially compiled and interpreted.
When using JIT in PHP 8, parts of your php code will be compiled into machine code so your PHP handler won’t interpret these parts anymore. Your php code will talk directly to the CPU thus improving performance.