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Add a 1-char fastpath to implode() #19276

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Add a 1-char fastpath to implode() #19276

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@alexandre-daubois alexandre-daubois commented Jul 28, 2025 •
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I think it's worth adding a 1 char fast path for implode(). A quick search on Github reveals the following stats:

  • Implode usage with one char glue: /implode\(\s*["'][^"']{1}["']\s*,\s*/ language:PHP reveals 1.4 million occurrences
  • Implode usage with 2+ char glue: /implode\(\s*["'][^"']{2,}["']\s*,\s*/ language:PHP reveals 1.1 million occurrences

Here is the benchmark code:

<?php

$iterations = 1000;
$array = array_fill(0, 10000, 'item');

for ($i = 0; $i < $iterations; $i++) {
    implode(',', $array);
}

And the results:

Benchmark 1: ./sapi/cli/php.branch bench.php
  Time (mean ± σ):      33.7 ms ±   1.2 ms    [User: 30.8 ms, System: 2.1 ms]
  Range (min … max):    32.7 ms …  41.4 ms    82 runs
 
Benchmark 2: ./sapi/cli/php.master bench.php
  Time (mean ± σ):      45.1 ms ±   6.7 ms    [User: 41.4 ms, System: 2.2 ms]
  Range (min … max):    42.9 ms …  97.5 ms    65 runs

Summary
  ./sapi/cli/php.branch bench.php ran
    1.34 ± 0.21 times faster than ./sapi/cli/php.master bench.php

No change for multi char glue, but a nice improved performance for single char glue especially one big arrays.

@alexandre-daubois alexandre-daubois requested a review from bukka as a code owner July 28, 2025 12:27
@alexandre-daubois alexandre-daubois mentioned this pull request Jul 28, 2025
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1-char bench on an i7-4790:

Benchmark 1: ./sapi/cli/php x.php 
  Time (mean ± σ):      47.9 ms ±   0.7 ms    [User: 45.5 ms, System: 2.0 ms]
  Range (min … max):    46.5 ms …  49.3 ms    60 runs
 
Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):      69.8 ms ±   1.1 ms    [User: 67.7 ms, System: 1.8 ms]
  Range (min … max):    67.4 ms …  73.0 ms    42 runs
 
Summary
  ./sapi/cli/php x.php  ran
    1.46 ± 0.03 times faster than ./sapi/cli/php_old x.php

Curiously a large difference with your measurement, did you benchmark a release build?

2-char glue is slightly slower:

Benchmark 1: ./sapi/cli/php x.php 
  Time (mean ± σ):      72.5 ms ±   1.9 ms    [User: 70.2 ms, System: 1.9 ms]
  Range (min … max):    70.2 ms …  82.4 ms    40 runs
 
Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):      66.4 ms ±   0.8 ms    [User: 63.9 ms, System: 2.0 ms]
  Range (min … max):    64.5 ms …  68.9 ms    45 runs
 
Summary
  ./sapi/cli/php_old x.php ran
    1.09 ± 0.03 times faster than ./sapi/cli/php x.php

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alexandre-daubois commented Aug 10, 2025 •
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I checked again and --enable-debug was used in configure. Removing it reveals results very close to yours. 2-char glue results on about the same perf on Apple M4:

Summary
  ./sapi/cli/php.branch bench.php ran
    1.01 ± 0.03 times faster than ./sapi/cli/php.master bench.php

Given the number of occurrences of 1 char glue as written in the description, I think this fast path would still worth it?

Description updated with the non-debug numbers for 1-char glue.

nielsdos
nielsdos approved these changes Aug 10, 2025
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Ok for me

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@nielsdos nielsdos nielsdos approved these changes

@bukka bukka Awaiting requested review from bukka bukka is a code owner

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