[php-src] Issue #8283: Performance: array_reduce is drastically slower (~1000x) than implementing the same logic with foreach

Issue: https://github.com/php/php-src/issues/8283 Comment Author: kamil-tekiela I don't think big O notation applies here. FWIW, your examples are not comparable, because the one with foreach doesn't use function calls or array reassignment. If you create the same example, the performance is identical. See these two examples: ``` <?php declare(strict_types=1); // generate a large sample of pseudo-random data which may have duplicates $data = []; for ($i = 0; $i < 40000; $i++) { $data[] = crc32((string) $i); } echo 'Foreach'; function reduce($carry, $item) { @$carry[$item]++; return $carry; } $start = hrtime(true); $result = []; foreach ($data as $item) { $result = reduce($result, $item); } $durationNs = hrtime(true) - $start; echo sprintf('%f s', $durationNs / 1_000_000_000); echo "\n\n"; unset($start, $result, $item, $durationNs); echo 'Array reduce'; $start = hrtime(true); $result = array_reduce($data, function ($carry, $item) { @$carry[$item]++; return $carry; }, []); $durationNs = hrtime(true) - $start; echo sprintf('%f s', $durationNs / 1_000_000_000); ``` array_reduce isn't the culprit. It's the function calls and constant reassignment of arrays; the latter being the biggest offender. So, I am not sure what exactly you consider to be a bug. In terms of performance array_reduce is almost identical to naive foreach loop if implemented exactly the same way. If you compare apples to oranges, then obviously, you will notice a difference.