Comment by DonHopkins

NIT linter warning: That’s not really a JIT compiler.

PHP parses the whole file and compiles it to Zend opcodes before executing it, so syntax errors are caught up front. But "JIT" means compiling an intermediate representation/opcodes into native machine code at runtime, when the functions are called, not at load time when the source file is parsed. If you just load a file and never call any of its code, the JIT compiler should never compile it.

PHP 8's OPcache JIT can do that optionally, but the normal load/parse/compile-to-opcodes step isn't JIT.