Can you check what the actual value of opline->opcode is?

(gdb) print opline->opcode 
$1 = 188 '\274'

repro:

class a
{
	protected function x(): bool
	{
		try
		{
			$credentials = something();
		}
		catch (Exception $e)
		{
			switch (get_class($e))
			{
				case Ex1::class:
				case Ex2::class:
					throw new Exception('');
				default:
					throw $e;
			}
		}

		return true;
	}
}

Slightly tweaked test case:

<?php
function test($foo) {
    switch ($foo . 'Bar') {
        case 'A':
            throw new Exception('A');
        default:
            throw new Exception('Default');
    }
}
try { 
    test('Foo');
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}

Asserts on master and 7.4. I had hoped it would show a leak on 7.3, but everything is alright there.

The problem is that the FREE for the SWITCH_STRING is optimized away, which shouldn't happen, as it is a loop free.