Description:
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Noticed serious performance issues while reading non-existing values from multi-dimensional array. 

Adding ISSET() check before the array read makes the script at least 3 times faster. 

However the main concern is that there are lots of non-optimized scripts that do not have ISSET() around multi-dimensional arrays.



Reproduce code:
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error_reporting(0);

$start = date('H:m:s');

$myArr = array('a');
$test = 'a';

// performance killer loop
for($i = 0; $i < 1000000; $i++)
  if ($myArr[$test][$fieldName] == 5);

/* optimized code
  if (isset($myArr[$test][$fieldName]) && $myArr[$test][$fieldName] == 5) */

$end = date('H:m:s');
echo $start . ' ' . $end;

Expected result:
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I expect the code with ISSET (commented out) run close to as fast as the code without ISSET. 

Actual result:
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Serious performance difference while running code that has ISSET() around multi-dimensional array read vs. code without ISSET().