Performance of preg_match varies depending on how subject string is initialized #24380

<?php

/*
 * Run pinned to specific CPU core:
 * taskset -c 3 php perf-regex-strings.php
 */

$pattern = '/[&]/u'; // This will not produce any match in test subject.

$textA = 'weengahhoghecho1eeSheeG5el9cie5b';
$textB = sprintf('%s', 'weengahhoghecho1eeSheeG5el9cie5b');
$textC = 'weengahhoghecho1eeSheeG5el9cie5' . 'b';

$textD_1 = 'weengahhoghecho1eeSheeG5el9cie5';
$textD = $textD_1 . 'b';

$tests = ['A', 'A', 'B', 'C', 'D', 'A', 'B', 'C', 'D'];

foreach ($tests as $test) {
    $subject = '';
    switch ($test) {
        case 'A':
            $subject = $textA;
            break;
        case 'B':
            $subject = $textB;
            break;
        case 'C':
            $subject = $textC;
            break;
        case 'D':
            $subject = $textD;
            break;
    }

    $start = microtime(true);

    for ($i = 0; $i < 1000000; $i++) {
        preg_match($pattern, $subject);
    }

    $diff = sprintf('%.6f sec.', microtime(true) - $start);
    echo "Execution time $test: $diff\n";

    gc_collect_cycles();
}