Description:
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See https://github.com/php/php-src/pull/2215 for a description and a fix.

The objects(keys) used for the null coalescing operator are leaked if the entry does not exist in the map.

PHP 7.0.13(and 7.0.12, probably others) are affected, along with php 7.1.0RC6. (The null coalescing operator was introduced in 7.0)

Test script:
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<?php

$b = new stdClass();
$map = new SplObjectStorage();
var_export($map[$b] ?? null); // /usr/local/php-7.0.12-src/Zend/zend_objects.c(162) :  Freeing 0x7F3957875A00 (40 bytes), script=/path/to/test.php


Expected result:
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No memory leaks. Null coalescing operator continues behaving equivalently to isset($hash[$obj]) ? $hash[$obj] : $default (which currently does not leak)

Actual result:
--------------
The return value of the coalescing operator was correct, but memory leaks are observed (visible in debug builds), of the form

/usr/local/php-7.0.12-src/Zend/zend_objects.c(162) :  Freeing 0x7F3957875A00 (40 bytes), script=/path/to/test.php