ctype_alnum 5 times slower in PHP 8.1 or greater

[joanhey]

Description

The following code:

<?php

$foo = '112312312312323';

$start_time = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $foo = $foo.'1';
    preg_match('/^[a-zA-Z0-9]+$/', $foo);
}

$end_time = microtime(true);

echo 'preg_match Result: ' . ($end_time - $start_time).PHP_EOL;

$foo = '112312312312323';

$start_time = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $foo = $foo.'1';
    ctype_alnum($foo);
}

$end_time = microtime(true);

echo 'ctype Result: ' . ($end_time - $start_time).PHP_EOL;

Resulted in this output:
A lot slower in 8.1 and 8.2

But I expected this output instead:
The same that in 8.0 or smaller.

Here start the performance degradation:

https://3v4l.org/fjSaZ
https://onlinephp.io/code/e3b9ddc370fdb0f00ff40447eadc24def0dd1abe

PD: I didn't test other ctype_* functions

PHP Version

8.1

Operating System

No response

[ndossche]

Strangely, it was already way slower in 8.0.30 on my system. In 8.1.0 there is additional slowdown that seems to come from the indirect call when the code was refactored from macro into function: dc80ea7
However, even after reverting that change, it's only a little bit faster, still almost a factor of 5 slower...
Maybe your environment is smart enough to create an inline version of isalnum.

If I apply the following patch, the ctype_isalnum becomes almost twice as fast as the regex solution. Probably because it avoid C library call overhead:

diff --git a/ext/ctype/ctype.c b/ext/ctype/ctype.c
index 939959bc09..a0a09f0cf1 100644
--- a/ext/ctype/ctype.c
+++ b/ext/ctype/ctype.c
@@ -61,7 +61,7 @@ static PHP_MINFO_FUNCTION(ctype)
 }
 /* }}} */
 
-static void ctype_impl(
+static zend_always_inline void ctype_impl(
 		INTERNAL_FUNCTION_PARAMETERS, int (*iswhat)(int), bool allow_digits, bool allow_minus) {
 	zval *c;
 
@@ -99,10 +99,15 @@ static void ctype_impl(
 	}
 }
 
+static zend_always_inline int php_isalnum(int c)
+{
+	return (c >= '0' && c <= '9') || ((unsigned int) c | 32) - 'a' < 26;
+}
+
 /* {{{ Checks for alphanumeric character(s) */
 PHP_FUNCTION(ctype_alnum)
 {
-	ctype_impl(INTERNAL_FUNCTION_PARAM_PASSTHRU, isalnum, 1, 0);
+	ctype_impl(INTERNAL_FUNCTION_PARAM_PASSTHRU, php_isalnum, 1, 0);
 }
 /* }}} */
 

Could even be further improved by moving the deprecated code section into a separate no-inline function such that the code cache pressure doesn't increase too much.

We could make our own version for each of the iswhatever functions, but idk if we want this? Maybe some other people can voice there opinion here :-) EDIT: this may be undesirable because they depend on the locale, even for the isalnum case...

[Girgias]

Meh, I don't really mind.

However, a large part of the complexity of those functions is related to needing to deal with integers.

When this is removed and a proper string ZPP check can be used, it might make more sense to just inline everything instead of passing by a common generic implementation.

[ndossche]

However, a large part of the complexity of those functions is related to needing to deal with integers.

According to callgrind, the most time is spent in the isalnum call and the if check. The overhead of the C library call is quite high.

That being said, hand-rolling our own iswhatever functions would give the biggest speedup, but would also introduce complexity because we actually have to take into account the current C locale...

@joanhey If you compiled PHP yourself, are you able to test what the performance difference is on your system when you add zend_always_inline to ctype_impl (like I did in the patch, but without the other additions).

[Girgias]

I maybe should go forward with actually deprecating setlocale() and forcing the C locale to be used. As this is a constant source of pain

[bwoebi]

@Girgias Probably we can just refer to the Locale class from intl. And rip out setlocale() support everywhere else.
However this also means every printf("%f") for example will be affected, which may not be desirable. I don't think the path to deprecation is as simple as it seems, as locales are still involved in core places of PHP.

[Girgias]

I don't think it's simple, but is probably worthwhile. Also printf() for useland uses our own implementation, for C extensions I'm not sure this is something widely used within php-src (I do have a script somewhere to check) but even then they probably shoud use the custom version.

[morrisonlevi]

Note that on musl's libc, these functions don't take into account locale. You can see the sources here: https://git.musl-libc.org/cgit/musl/plain/src/ctype/ though I've copied relevant pieces here:

int isalnum(int c)
{
	return isalpha(c) || isdigit(c);
}

int isalpha(int c)
{
	return ((unsigned)c|32)-'a' < 26;
}

int isdigit(int c)
{
	return (unsigned)c-'0' < 10;
}

Of course, their locale support is... well I'll just quote them:

Locale support is very limited, and barely works.

Just adding this as more background information when making a decision.

[morrisonlevi]

LLVM's libc implementation also does not support locales here, which is expected there since they don't support locales yet.

Honestly, I'm not certain locale support is even desirable for these newer libc implementations. The only system which is not totally bonkers broken is UTF-8, and ctypes are definitely not that, so...