Infer static for closures by iluuu1994 · Pull Request #19941 · php/php-src

iluuu1994 · 2025-09-23T22:32:28Z

RFC: https://wiki.php.net/rfc/closure-optimizations

This PR implements static inference for closures, with some restrictions. The closure must not:

Use $this. That's the obvious case.
Use $$var, given $var could be 'this'.
Use Foo::bar(), given this could be a hidden instance call to a (grand-)parent method.
Use $f(), for the same reason as 3.
Use call_user_func(), for the same reason as 3.
Declare another non-static (explicit or inferred) closure, where $this flows from parent to child.
Use require, include or eval, given the called code might do any of the above.

In a Symfony Demo run specifically, static inference works for 68/87 (~78%) closures that were explicitly marked as static by Symfony. That seems quite decent.

The PR also adds caching for static closures that don't have any bindings and don't declare static variables. Instances of such closures can be re-used almost without side-effects (except for object identity).

For Symfony Demo (with static removed from all closures), I measured an improvemend of ~0.1%, so definitely not very significant. Synthetic benchmarks can improve quite a bit, though this will also apply to real-world code that creates closures in loops.

function test() {
    $x = function () {};
}
for ($i = 0; $i < 10_000_000; $i++) {
    test();
}

improves by ~78% in my test runs.

If persistent objects are ever implemented, the instantiation could be done fully at compile-time.

iluuu1994 · 2025-09-23T22:35:17Z

@dktapps Ping. I haven't done any benchmarking yet.

Zend/zend_compile.c

dktapps · 2025-09-23T23:12:26Z

This isn't caching static closures yet, right? So there should be no observable effect on performance

iluuu1994 · 2025-09-23T23:13:20Z

This isn't caching static closures yet, right?

Right. IIRC static closures themselves have a small benefit, though I didn't see it in the CI benchmark. I'm not sure if maybe Symfony already uses linting to add static.

iluuu1994 · 2025-09-24T00:55:27Z

Okay, testing Symfony Demo with all static closures turned into non-static ones shows virtually no improvement. Regardless, they should benefit if we can cache them. I'll try this in the same PR then, given this one isn't useful on its own.

arnaud-lb · 2025-09-24T08:50:21Z

One drawback of non-static closures is that they retain $this, which can increase memory usage when the lifetime of $this is supposed to be shorter and references a large graph. I believe this is why coding guidelines and IDEs recommend to manually declare closure as static.

Big +1 on this.

Zend/zend_closures.c

Zend/tests/bug75079_2.phpt

iluuu1994 · 2025-09-24T12:35:41Z

Quick test: In Symfony Demo with all static closures turned into non-static ones, this patch can turn 122/283 into static ones. That's ~43%, so not bad at all. How many of those can also be cached remains to be seen.

dktapps · 2025-09-27T14:05:29Z

Some other weird cases that might need to be considered:

Variable variables
include,require et al
eval()

Source: https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/blame/b0a17bf1288a696cba2c8492126f0a485d5637f0/src/Fixer/FunctionNotation/StaticLambdaFixer.php#L110

dktapps · 2025-09-27T14:07:54Z

To be honest I start to wonder if this actually makes sense considering the number of obscure conditions that might cause an unintended $this binding just for a potential usage. It'd avoid some unnecessary refs but there'd still be plenty of cases where static would be needed to avoid cycles and accidental refs. (I suppose it'd still benefit for common array_map() style cases where a throwaway closure is used, but 🤷 )

Has there been any discussion about a shorter syntax for static closures? e.g. something like sfn() (idk)

iluuu1994 · 2025-09-27T14:17:25Z

Var var is already handled in this patch. I forgot about eval, but that's quite rare as well, especially in closures.

Girgias

Ack for ext/spl test changes

dktapps · 2026-01-05T20:37:02Z

Is there any movement on caching static stateless closures generally? I know the 1cc cache was merged, but there's plenty of cases where explicitly static closures could be cached too without the need for this inference. This inference would just be an added benefit to auto-static stuff in certain cases.

iluuu1994 · 2026-01-05T20:42:17Z

Ofc, explicitly static closures will be cached too, assuming they are stateless.

dktapps · 2026-01-05T20:46:20Z

Ok, I hadn't realised caching was also in this PR. Good stuff

arnaud-lb

This looks right to me!

Zend/zend_compile.c

Zend/zend_closures.c

github-actions · 2026-01-13T16:11:18Z

AWS x86_64 (c7i.24xl)

Attribute	Value
Environment	aws
Runner	host
Instance type	c7i.metal-24xl (dedicated)
Architecture	x86_64
CPU	Intel(R) Xeon(R) Platinum 8488C, 48 cores @ 2400 MHz
CPU settings	disabled deeper C-states, disabled turbo boost, disabled hyper-threading
RAM	188 GB
Kernel	6.1.158-178.288.amzn2023.x86_64
OS	Amazon Linux 2023.9.20251117
GCC	14.2.1
Time	2026-01-13 15:22:54 UTC

Laravel 12.11.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@8c4f	0.45921	0.46365	0.00054	0.12%	0.45990	0.00%	0.45976	0.00%	3.659	0.999	26.93 MB
PHP - auto-static-closures	0.44028	0.44333	0.00038	0.09%	0.44077	-4.16%	0.44072	-4.14%	3.351	0.000	26.93 MB

Symfony 2.8.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@8c4f	0.77489	0.79602	0.00311	0.40%	0.78241	0.00%	0.78270	0.00%	0.509	0.999	26.96 MB
PHP - auto-static-closures	0.77087	0.78412	0.00246	0.32%	0.77873	-0.47%	0.77924	-0.44%	-1.452	0.000	26.96 MB

Wordpress 6.9 main page - 100 consecutive runs, 20 warmups, 20 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@8c4f	0.66211	0.68058	0.00297	0.45%	0.66357	0.00%	0.66299	0.00%	5.430	0.999	26.98 MB
PHP - auto-static-closures	0.65689	0.65935	0.00042	0.06%	0.65784	-0.86%	0.65778	-0.79%	0.512	0.000	26.96 MB

bench.php - 100 consecutive runs, 10 warmups, 2 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@8c4f	0.43121	0.43999	0.00163	0.37%	0.43559	0.00%	0.43556	0.00%	-0.041	0.999	7.95 MB
PHP - auto-static-closures	0.42158	0.42797	0.00136	0.32%	0.42483	-2.47%	0.42492	-2.44%	-0.003	0.000	7.95 MB

ext/reflection/tests/closures_005.phpt

ext/reflection/tests/ReflectionFunction__toString_bound_variables.phpt

github-actions · 2026-01-19T15:51:30Z

AWS x86_64 (c7i.24xl)

Attribute	Value
Environment	aws
Instance type	c7i.metal-24xl (dedicated)
Architecture	x86_64
CPU	Intel(R) Xeon(R) Platinum 8488C, 48 cores @ 2400 MHz
CPU settings	disabled deeper C-states, disabled turbo boost, disabled hyper-threading
RAM	188 GB
Kernel	6.1.158-178.288.amzn2023.x86_64
OS	Amazon Linux 2023.9.20251117
GCC	14.2.1
Time	2026-01-19 15:00:50 UTC
Job details	https://github.com/php/php-src/actions/runs/21142128198 (Artifacts)
Changeset	https://github.com/php/php-src/compare/0caebc..96ca7f

Laravel 12.11.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0cae	0.45726	0.46371	0.00069	0.15%	0.45797	0.00%	0.45785	0.00%	6.056	0.999	27.03 MB
PHP - auto-static-closures	0.44219	0.44421	0.00043	0.10%	0.44275	-3.32%	0.44265	-3.32%	1.570	0.000	27.03 MB

Symfony 2.8.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0cae	0.75879	0.77172	0.00220	0.29%	0.76755	0.00%	0.76812	0.00%	-1.834	0.999	27.06 MB
PHP - auto-static-closures	0.75747	0.77009	0.00249	0.33%	0.76599	-0.20%	0.76654	-0.21%	-1.652	0.000	27.06 MB

Wordpress 6.9 main page - 100 consecutive runs, 20 warmups, 20 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0cae	0.66644	0.68717	0.00207	0.31%	0.66804	0.00%	0.66772	0.00%	8.183	0.999	27.06 MB
PHP - auto-static-closures	0.66228	0.68300	0.00216	0.33%	0.66365	-0.66%	0.66326	-0.67%	7.484	0.000	27.06 MB

bench.php - 100 consecutive runs, 10 warmups, 2 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0cae	0.42379	0.43149	0.00150	0.35%	0.42667	0.00%	0.42661	0.00%	0.470	0.999	7.94 MB
PHP - auto-static-closures	0.43164	0.43861	0.00134	0.31%	0.43417	1.76%	0.43395	1.72%	0.531	0.000	7.95 MB

github-actions · 2026-01-20T00:08:24Z

AWS x86_64 (c7i.24xl)

Attribute	Value
Environment	aws
Instance type	c7i.metal-24xl (dedicated)
Architecture	x86_64
CPU	Intel(R) Xeon(R) Platinum 8488C, 48 cores @ 2400 MHz
CPU settings	disabled deeper C-states, disabled turbo boost, disabled hyper-threading
RAM	188 GB
Kernel	6.1.158-178.288.amzn2023.x86_64
OS	Amazon Linux 2023.9.20251117
GCC	14.2.1
Time	2026-01-19 23:24:29 UTC
Job details	https://github.com/php/php-src/actions/runs/21154141728 (Artifacts)
Changeset	https://github.com/php/php-src/compare/0caebcd196..96ca7fa073

Laravel 12.11.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0caebcd	0.44661	0.45030	0.00044	0.10%	0.44720	0.00%	0.44713	0.00%	3.736	0.999	27.00 MB
PHP - auto-static-closures	0.43096	0.43464	0.00046	0.11%	0.43155	-3.50%	0.43145	-3.51%	3.433	0.000	27.00 MB

Symfony 2.8.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0caebcd	0.76308	0.77568	0.00265	0.34%	0.77247	0.00%	0.77328	0.00%	-1.988	0.999	27.01 MB
PHP - auto-static-closures	0.76260	0.77571	0.00284	0.37%	0.77207	-0.05%	0.77291	-0.05%	-1.870	0.008	27.01 MB

Wordpress 6.9 main page - 100 consecutive runs, 20 warmups, 20 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0caebcd	0.66457	0.66720	0.00042	0.06%	0.66540	0.00%	0.66534	0.00%	1.027	0.999	27.01 MB
PHP - auto-static-closures	0.66029	0.68065	0.00302	0.46%	0.66168	-0.56%	0.66114	-0.63%	5.744	0.000	27.01 MB

bench.php - 100 consecutive runs, 10 warmups, 2 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@0caebcd	0.42382	0.43063	0.00135	0.32%	0.42676	0.00%	0.42671	0.00%	0.064	0.999	27.01 MB
PHP - auto-static-closures	0.43190	0.45228	0.00284	0.65%	0.43486	1.90%	0.43450	1.83%	4.165	0.000	27.01 MB

iluuu1994 · 2026-01-20T21:17:45Z

Pretty cool, I was able to confirm the ~3% improvement for the Laravel default page locally. They use a lot of closures, and this patch is able to avoid instantiation for 2384 out of 3637.

Zend/tests/gc/bug60139.phpt

Zend/zend_compile.c

Zend/zend_vm_def.h

This field is still unused on master, but required for GH-19941.

See php#19754 (comment)

… dump

DanielEScherzer · 2026-03-14T01:58:38Z

ext/reflection/tests/closures_006.phpt

@@ -0,0 +1,46 @@
+--TEST--


this tests a bunch of cases that are not inferred as static, can we also test a few that are inferred as static?

ext/reflection/tests/closures_005.phpt contains some rudimentary ones, but I'll add some more standard cases that can be inferred in a new test.

DanielEScherzer · 2026-03-14T01:59:59Z

ext/spl/tests/ArrayObject/ArrayObject_sort_different_backing_storage.phpt


 Deprecated: ArrayObject::__construct(): Using an object as a backing array for ArrayObject is deprecated, as it allows violating class constraints and invariants in %s on line %d
-object(ArrayObject)#3 (1) {
+object(ArrayObject)#%d (1) {


the changes in this file to replace hard-coded numbers with %d are fine, but unrelated to the actual functionality change - can you send a separate PR if you want to adjust these? I'd be happy to review that, but it makes this PR bigger than it needs to be. Applies to a few other files too

Also not all of the object ids were updated with placeholders, just some

I think the object IDs have changed as they are declared earlier - at compile time. I personally would like to keep hardcoded numbers to be able to review possible changes of the declaration order earlier in the future.

DanielEScherzer · 2026-03-14T02:02:24Z

ext/standard/tests/array/compact_this.phpt

 var_dump(
    (new class {
        function test(){
            return (function(){ return compact('this'); })();


shouldn't this maintain the non-static-ness of the function, given the access to $this via compact()? I'd say that any use of compact() should be treated the same as $$var - if we aren't going to analyze the possible values to make sure $this is not included, then we should be conservative and not infer static

I think there are much more cases. Like uasort($arr, 'Foo::bar'). IMO they are not worth to be pursued.

Yeah you're both correct. compact() needs to be excluded, and so do any calls to internal functions using Z_PARAM_FUNC(), i.e. those that accept callable, and are passed something that could be a string. I'll think about how to best address those cases.

DanielEScherzer · 2026-03-14T02:03:27Z

Zend/tests/arrow_functions/005.phpt


 class Test {
    public function method() {
        // It would be okay if this is NULL, but the rest should work


this comment needs some update, now it is NULL

DanielEScherzer · 2026-03-14T02:05:44Z

Zend/tests/closures/closure_020.phpt

    public $a;

    public function x() {
        $a = &$this;


should this be marked as static? Doesn't it give access to $this via the closure?

$this is not the scope, but a bound variable. This PR does two things, it "infer static" and "cache not bound closures". The case here allows the 1st one but not the 2nd one.

So I expect the l31 unchanges and prefer to keep it hardcoded.

DanielEScherzer · 2026-03-14T02:06:34Z

Zend/tests/closures/closure_026.phpt

  array(1) {
    [0]=>
-    object(Closure)#%d (4) {
+    object(Closure)#%d (%d) {


same as closure_20, don't these still need $this ?

DanielEScherzer · 2026-03-14T02:09:37Z

Zend/zend_closures.c

+				zend_error(E_WARNING, "Cannot bind an instance to a static closure, this will be an error in PHP 9");
+				return false;
+			} else {
+				*newthis_ptr = NULL;


got confused reading this for the first time wondering why no warning was needed here - can I suggest adding some comment explaining this with a reference to the RFC, which specified that

Of note is that Closure::bind() and Closure::bindTo() usually throw when attempting to bind an object to a static closure. In this RFC, passing an object to these methods is explicitly allowed and discarded only for closures that are inferred as static, but not those that are explicitly static. The aim is to retain backward compatibility when a closure can suddenly be inferred as static due to seemingly unrelated changes, such as removing a static method call.

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Un-static closures for testing of php/php-src#19941

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static_lambda should not add static if outside class PHP-CS-Fixer/PHP-CS-Fixer#7262

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Use static callback for TypeTraverser::map() phpstan/phpstan-src#4701

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[skip ci] Fix uninitialized fn_flags2 for internal functions

80b1ede

This field is still unused on master, but required for GH-19941.

iluuu1994 added 4 commits March 13, 2026 20:29

Infer static for closures and add stateless closure cache

8365f5c

See php#19754 (comment)

[skip ci] Add return to prevent optimization in the future

9088615

Skip closure caching in main

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Differentiate inferred and explicit staticness in reflection function…

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