Inconsistent refcount of array object

[YuanchengJiang]

Description

The following code:

<?php
$obj = (object)['a' => 1, 'b' => 2];
$ao = new ArrayObject($obj);
$arr = (array) $obj;
debug_zval_dump($arr);

Resulted in this output: the refcount is 4 in non-JIT.

array(2) refcount(4){
  ["a"]=>
  int(1)
  ["b"]=>
  int(2)
}

while is 3 in JIT

array(2) refcount(3){
  ["a"]=>
  int(1)
  ["b"]=>
  int(2)
}

PHP Version

nightly

Operating System

ubuntu 22.04

[nielsdos]

I haven't checked this yet, but note that the JIT contains optimizations to skip updating the refcount sometimes. So it's possible that this is legit and not a bug.

[iluuu1994]

This difference also occurs without JIT. I believe this code is to blame:

php-src/Zend/zend_vm_def.h

Lines 6463 to 6466 in 7aeafe4

	if (GC_FLAGS(ht) & IS_ARRAY_IMMUTABLE) {
	/* TODO: try not to duplicate immutable arrays as well ??? */
	ht = zend_array_dup(ht);
	}

When the array in (object) $array is immutable, we always duplicate it. This causes the refcount to go down to 1. Because all array literals are immutable when using opcache, that explains the drop in refcount. Hence, this doesn't seem to be a bug. Thanks for the report nonetheless.