Description:
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If make the situation described in the docs of "Collecting Cycles" (http://php.net/manual/en/features.gc.collecting-cycles.php) the gc_collect_cycles() doesn't collect garbage cycle reference.

After we made an array which is referenced only by itself element (cycle reference) the gc_collect_cycles() call returns 0. That means there are not collected cycles and we have a memory leak.

If we replace "$a = $a[0]" on "unset($a)" the garbage collector works correctly and the gc_collect_cycles() call returns 1.

Test script:
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<?php
echo "Memory usage before memory leak:\t",
memory_get_usage()," bytes",PHP_EOL;

$a = ['one'];
$a[] = &$a;
$a = $a[0];

echo "Memory usage after memory leak:\t\t",
memory_get_usage()," bytes",PHP_EOL;

echo "Number of collected cycles: ",
gc_collect_cycles(),PHP_EOL;

echo "Memory usage after gc_collect_cycles():\t",
memory_get_usage()," bytes",PHP_EOL;

Actual result:
--------------
Memory usage before memory leak:        353368 bytes
Memory usage after memory leak:         353392 bytes
Number of collected cycles: 0
Memory usage after gc_collect_cycles(): 353392 bytes