this tests the performance of count inside the loop or outside of the loop

performance-for-loop.php

<?php

function test1($arr)
{
    $arr = array_fill(0, 10000, true);

    $start = microtime();
    for ($i = 0; $i < count($arr); $i++) {
        array_fill(0, 500, "abc");
    }
    return ((float) microtime() - (float) $start);
}

function test2($arr)
{
    $start = microtime();
    $iCount = count($arr);
    for ($i = 0; $i < $iCount; $i++) {
        array_fill(0, 500, "abc");
    }
    
    return ((float) microtime() - (float) $start);
}

$iTries = 10;
$aResult1 = [];
$aResult2 = [];

$arr = array_fill(0, 100, true);
for($i = 0; $i < $iTries; $i++) {
    $aResult1[] = test1($arr);
    $aResult2[] = test2($arr);
}

echo "with count: " . round(array_sum($aResult1) / count($aResult1), 5) . "\n";
echo "without count: " . round(array_sum($aResult2) / count($aResult2), 5) . "\n";