array_unshift: Add fast optimized case for packed arrays #20353

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ndossche wants to merge 1 commit into php:master

from ndossche:array-unshift-packed

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array_unshift: Add fast optimized case for packed arrays #20353

ndossche wants to merge 1 commit into php:master from ndossche:array-unshift-packed

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@ndossche ndossche commented Nov 1, 2025 •

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Packed arrays are likely common in this case, as with array_shift which already has a similar optimization.

For the following benchmark:

<?php
for ($i = 0; $i < 10000000; $i++) {
 $a = [0, 1, 2, 3, 4, 5];
 array_unshift($a, -3, -2, -1);
}

On an i7-4790:

Benchmark 1: ./sapi/cli/php x.php
 Time (mean ± σ): 753.8 ms ± 23.8 ms [User: 749.8 ms, System: 2.1 ms]
 Range (min ... max): 734.3 ms ... 818.6 ms 10 runs
Benchmark 2: ./sapi/cli/php_old x.php
 Time (mean ± σ): 972.5 ms ± 5.0 ms [User: 968.8 ms, System: 1.4 ms]
 Range (min ... max): 967.8 ms ... 984.3 ms 10 runs
Summary
 ./sapi/cli/php x.php ran
 1.29 ± 0.04 times faster than ./sapi/cli/php_old x.php

On an i7-1185G7:

Benchmark 1: ./sapi/cli/php x.php
 Time (mean ± σ): 507.9 ms ± 6.7 ms [User: 504.7 ms, System: 2.6 ms]
 Range (min ... max): 498.3 ms ... 519.3 ms 10 runs
 
Benchmark 2: ./sapi/cli/php_old x.php
 Time (mean ± σ): 627.1 ms ± 7.2 ms [User: 624.0 ms, System: 2.3 ms]
 Range (min ... max): 616.6 ms ... 640.2 ms 10 runs
 
Summary
 ./sapi/cli/php x.php ran
 1.23 ± 0.02 times faster than ./sapi/cli/php_old x.php

@ndossche


 array_unshift: Add fast optimized case for packed arrays

cc04158

Packed arrays are likely common in this case, as with array_shift which
already has a similar optimization.
For the following benchmark:
```php
<?php
for ($i = 0; $i < 10000000; $i++) {
 $a = [0, 1, 2, 3, 4, 5];
 array_unshift($a, -3, -2, -1);
}
```
On an i7-4790:
```
Benchmark 1: ./sapi/cli/php x.php
 Time (mean ± σ): 753.8 ms ± 23.8 ms [User: 749.8 ms, System: 2.1 ms]
 Range (min ... max): 734.3 ms ... 818.6 ms 10 runs
Benchmark 2: ./sapi/cli/php_old x.php
 Time (mean ± σ): 972.5 ms ± 5.0 ms [User: 968.8 ms, System: 1.4 ms]
 Range (min ... max): 967.8 ms ... 984.3 ms 10 runs
Summary
 ./sapi/cli/php x.php ran
 1.29 ± 0.04 times faster than ./sapi/cli/php_old x.php
```