I have a local project in which blackfire reports the slowest part (7% of everything) as Cache/FileCacheStorage.php which get invoked mostly via PhpMethodReflection->getVariants():

the 2 most callers of PhpMethodReflection->getVariants() are

1st

2nd

I was looking at the sources for a few hours and did not yet have an idea whether this could be made more efficient.
maybe others have a idea, therefore I thought I will leave it here.

Tested on PHPStan 1.12.4 windows11:

$ php -v
PHP 8.2.12 (cli) (built: Oct 24 2023 21:15:35) (NTS Visual C++ 2019 x64)
Copyright (c) The PHP Group
Zend Engine v4.2.12, Copyright (c) Zend Technologies