Warn when coercing NAN to other types

[Girgias]

RFC: https://wiki.php.net/rfc/warnings-php-8-5#coercing_nan_to_other_types

[github-actions]

AWS x86_64 (c7i.24xl)

Attribute	Value
Environment	aws
Runner	host
Instance type	c7i.metal-24xl (dedicated)
Architecture	x86_64
CPU	48 cores
CPU settings	disabled deeper C-states, disabled turbo boost, disabled hyper-threading
RAM	188 GB
Kernel	6.1.147-172.266.amzn2023.x86_64
OS	Amazon Linux 2023.8.20250818
GCC	14.2.1
Time	2025-08-29 17:20:09 UTC

Laravel 12.2.0 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	Instr count	Memory
PHP - baseline@fc46	0.46565	0.46818	0.00045	0.10%	0.46637	0.00%	0.46629	0.00%	1.515	0.999	176423932	44.01 MB
PHP - 8.5-warn-nan-coercion	0.45876	0.46679	0.00075	0.16%	0.46494	-0.31%	0.46499	-0.28%	-5.442	0.000	176485965	44.07 MB

Symfony 2.7.0 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	Instr count	Memory
PHP - baseline@fc46	0.72046	0.73259	0.00155	0.21%	0.72261	0.00%	0.72217	0.00%	3.109	0.999	287234974	40.16 MB
PHP - 8.5-warn-nan-coercion	0.72253	0.72854	0.00100	0.14%	0.72405	0.20%	0.72384	0.23%	1.831	0.000	287280133	40.53 MB

Wordpress 6.2 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	Instr count	Memory
PHP - baseline@fc46	0.57464	0.58357	0.00228	0.39%	0.58060	0.00%	0.58151	0.00%	-1.225	0.999	1119139470	43.91 MB
PHP - 8.5-warn-nan-coercion	0.57682	0.58512	0.00218	0.37%	0.58209	0.26%	0.58298	0.25%	-1.361	0.000	1119813967	43.91 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	Instr count	Memory
PHP - baseline@fc46	0.42476	0.55444	0.02724	6.28%	0.43407	0.00%	0.42786	0.00%	4.179	0.999	2020744423	26.98 MB
PHP - 8.5-warn-nan-coercion	0.42534	0.58863	0.03210	7.34%	0.43703	0.68%	0.42765	-0.05%	3.477	0.582	2020694323	27.05 MB

[arnaud-lb]

Triggered a benchmark to check the effect of this: valgrind shows no regression (changes are under 0.0x%).

[Girgias]

I do wonder if this is not actually a problem for switch cases too now that I think of.

[arnaud-lb]

It would be worth it to check

[Girgias]

Yeah, it seems I completely broke switch statements...

<?php

$nan = fdiv(0, 0);
switch ($nan) {
    case true:
        echo "true";
        break;
    case false:
        echo "false";
        break;
}
?>

Returns nothing now, even without opcache :|

[iluuu1994]

I wonder if this is important for canonicalization.

[arnaud-lb]

It would be worth it to check

[iluuu1994]

Couldn't see anything obviously incorrect.

[iluuu1994]

I wonder if this is important for canonicalization.

[edorian]

No RM objections 👍

[TimWolla]

Did look in particular detail. Not happy about the optimizations we lose 😔

[staabm]

was this change intentionally only implemented for NAN, but not for INF?

it seems INF has similar cast semantics: https://3v4l.org/lYIng

[Girgias]

was this change intentionally only implemented for NAN, but not for INF?

it seems INF has similar cast semantics: https://3v4l.org/lYIng

Yes, that's normal. NAN is meant to be "uncomparable" and only occurs in "nonsensical" FP operations, +-INF is just a very large value, however if you try to cast them to INT you would get another warning (done in a separate PR).