With certain opcache settings (php -d opcache.optimization_level=-1 -d opcache.opt_debug_level=0x20020000 -l script.php), fn would get optimized down to return 2;.

• Not familiar with what dead/redundant code elimination php 7.2 has.

<?php
class C { 
	public $i;
}

function fn(int $x) {
	$c = new C;
	$c->i = 1;
	if($x) {
		$a = [1, 2, 3];
	} else {
		$a = [3, 2, 1];
	}
	return $a[$c->i];
	$c->i++;
	return $x;
}
fn(1);

SCCP Values for "fn":
    #4.X3 = {}
    #5.CV1($c) = {}
    #6.CV1($c) = {"i" => int(1)}
    #7.CV2($a) = array(...)
    #8.CV2($a) = array(...)
    #9.CV2($a) = [1 => int(2)]
    #10.X4 = int(1)
    #11.X3 = int(2)

fn: ; (lines=2, args=1, vars=1, tmps=0)
    ; (after optimizer)
    ; script.php:6-17
L0:     CV0($x) = RECV 1
L1:     RETURN int(2)

This will be regression from older versions of PHP, where __get and __set could be added dynamically and they would work as expected.

Possible solution:

• Refuse to add/remove __get/__set based on opcache presence and opcache optimization flags used. Continue allowing modification.
• Refuse to add/remove __construct/__destruct based on opcache presence and opcache optimization flags. Continue allowing modification.

Depending on how aggressive function/method inlining becomes in PHP 7.3, users may have issues with methods similar to how constants behave within classes

• May affect self::static_method(), final methods, and methods called within final classes.
• constructors with empty bodies?