zend_compile: Optimize array_map() with callable convert callback into foreach

[TimWolla]

For:

<?php

function plus1($x) {
	return $x + 1;
}

$array = array_fill(0, 100, 1);

$count = 0;
for ($i = 0; $i < 100_000; $i++) {
	$count += count(array_map(plus1(...), $array));
}

var_dump($count);

This is ~1.1× faster:

Benchmark 1: /tmp/test/before -d opcache.enable_cli=1 /tmp/test/test6.php
  Time (mean ± σ):     172.2 ms ±   0.5 ms    [User: 167.8 ms, System: 4.2 ms]
  Range (min … max):   171.6 ms … 173.1 ms    17 runs

Benchmark 2: /tmp/test/after -d opcache.enable_cli=1 /tmp/test/test6.php
  Time (mean ± σ):     155.1 ms ±   1.3 ms    [User: 150.6 ms, System: 4.2 ms]
  Range (min … max):   154.2 ms … 159.3 ms    18 runs

Summary
  /tmp/test/after -d opcache.enable_cli=1 /tmp/test/test6.php ran
    1.11 ± 0.01 times faster than /tmp/test/before -d opcache.enable_cli=1 /tmp/test/test6.php

With JIT it becomes ~1.7× faster:

Benchmark 1: /tmp/test/before -d opcache.enable_cli=1 -d opcache.jit=tracing /tmp/test/test6.php
  Time (mean ± σ):     166.9 ms ±   0.6 ms    [User: 162.7 ms, System: 4.1 ms]
  Range (min … max):   166.1 ms … 167.9 ms    17 runs

Benchmark 2: /tmp/test/after -d opcache.enable_cli=1 -d opcache.jit=tracing /tmp/test/test6.php
  Time (mean ± σ):      94.5 ms ±   2.7 ms    [User: 90.4 ms, System: 3.9 ms]
  Range (min … max):    92.5 ms … 103.1 ms    31 runs

Summary
  /tmp/test/after -d opcache.enable_cli=1 -d opcache.jit=tracing /tmp/test/test6.php ran
    1.77 ± 0.05 times faster than /tmp/test/before -d opcache.enable_cli=1 -d opcache.jit=tracing /tmp/test/test6.php

[bwoebi]

I like this!
Though, in ZEND_TYPE_ASSERT I'd avoid fetching the function name / the zend_internal_function for non-errors and directly store the expected type (e.g. in the lower 16 bits of extended_value and put the operand num into the higher 16 bits).

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I assume something similar is also possible for Closures passed directly as arg, like array_map(fn($x) => $x + 1, $array) and inline the closure code itself directly (as long as it doesn't create new variables), which probably is a much more common scenario?

[bwoebi]

On that note, I wonder whether it would make sense to expose this as API, add a function pointer on zend_internal_function, and whenever a function is encountered during compilation and it has this function pointer, it's called with the ast of its arguments and can emit opcodes by itself (or just return false and normal compilation happens). Rather than centralizing this in compiler (the file is big enough :-P, and it would make it extensible; extensions could play around with this too).

[TimWolla]

I wonder whether it would make sense to expose this as API,

It probably would for all the reasons that you mentioned.

[TimWolla]

I assume something similar is also possible for Closures passed directly as arg, like array_map(fn($x) => $x + 1, $array) and inline the closure code itself directly (as long as it doesn't create new variables), which probably is a much more common scenario?

I assume getting scoping right is getting complicated quickly. Even preserving the Closure and compiling it as:

$c = fn ($x) => $x + 1;
foreach ($array as $key => $val) $result[$key] = $c($val);

is not immediately obvious to me that it is safe (e.g. with regard to variable capturing and scoping).

---

I've opted to support only CALLABLE_CONVERT for now, since those should already be pretty useful once PFA lands and they don't come with the concerns above.