Description:
------------
When a function both
* specifies an explicit return type
* AND uses an explicit cast of the return value,
then the PHP interpreter segfaults non-deterministically with high probability.

To reproduce, execute the following script with the PHP interpreter several times in a row. Sometimes it works, sometimes it segfaults.


Test script:
---------------
<?php

foo();

function foo() : string {
  return (string) 42;
}


Expected result:
----------------
PHP interpreter should not crash, no matter how many times the script is run.


Actual result:
--------------
The PHP interpreter segfaults when running this script. Not always, but very often:

$ php crash.php
Segmentation fault (core dumped)


gdb backtrace:

Core was generated by `php crash.php'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x0000000000888c20 in execute_ex (ex=0x7fa8daa14030) at /home/malte/php7/php-src/Zend/zend_vm_execute.h:406
#2  0x0000000000888d32 in zend_execute (op_array=0x7fa8daa75100, return_value=0x0) at /home/malte/php7/php-src/Zend/zend_vm_execute.h:450
#3  0x000000000082ee86 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /home/malte/php7/php-src/Zend/zend.c:1399
#4  0x000000000079aefc in php_execute_script (primary_file=0x7ffdb976c850) at /home/malte/php7/php-src/main/main.c:2475
#5  0x00000000008ec6ac in do_cli (argc=2, argv=0x2f6b0e0) at /home/malte/php7/php-src/sapi/cli/php_cli.c:971
#6  0x00000000008ed870 in main (argc=2, argv=0x2f6b0e0) at /home/malte/php7/php-src/sapi/cli/php_cli.c:1338