Description:
------------
Earliest tested version: 7.3.7, also tested: 7.4.15 (Debian package) 8.0.2 (Compiled from src)
Propably all versions affected.

Defining a function in an include file seems to break/disable some kind of cache cleaning and results in a memory leak.
In most cases this might not hurt, since it only occurs once. I found this on an run-time editable script where the include file gets reloaded on every loop and after years of using it this way, it suddently broke and instead of a few kbyte of ram it crashed after a day reaching the 125mb limit.
After searching and fiddling with the prior changes i made i reduced the code to a minimal test for this specific problem.


Test script:
---------------
main.php:
<?php
function checkmem($name = "") { global $oldmem; $newmem = memory_get_usage(false); if ($newmem > $oldmem) { echo "\n".$oldmem." -> ".$newmem." (".($newmem-$oldmem).") Checkpoint $name\n"; $oldmem = $newmem; }
}

while (!usleep(10000)) {
checkmem("Preinclude");
include("inc.php");
checkmem("Postinclude");
}
?>

inc.php:
<?php
checkmem("inner begin");
if (1 == 0) function test() {}
checkmem("inner end");
?>

Expected result:
----------------
The memory size shouldn't increase unlimited (The code is never reached, the include is left successfully, etc..)
The result is the same whether or not the function exists.

Actual result:
--------------
php main.php
 -> 394136 (394136) Checkpoint Preinclude
394136 -> 395256 (1120) Checkpoint inner begin
395256 -> 460792 (65536) Checkpoint inner begin
460792 -> 526328 (65536) Checkpoint inner begin
526328 -> 591864 (65536) Checkpoint inner begin
.... until OOM

Just re-including a file unlimited times is no problem until a user defined function is declared within. Then some kind of optimization seems to fail and the used memory get's bigger and bigger. Without the user defined function definition in the include, the memory amount is almost unchanged even when the file is changed during runtime (and reincluded ...)