Performance impact: sizzle don't use querySelectorAll for specific selector after using $('...').filter('selector')

[miflinak]

Steps to reproduce

1. Use filter, for example $('any selector').filter('a, div') (useless but it's just an example).
2. Call $('a, div') and sizzle wouldn't use querySelectorAll!

That happends because there compilerCache exists for that selector (it was cached when we called filter).

Example: http://jsbin.com/qidopuhiro/1/edit?js,console,output
1 ms vs 15 ms in my case (desktop).

Why that happends?

See

sizzle/src/sizzle.js

Line 295 in abde99f

!compilerCache[ selector + " " ] &&

We can just remove this line. Or do something more complex (like marking cache as filter-only).

You can say "hey, that's just a 15 ms!". But that's much slower on mobile (for example 10 ms vs 150 ms) or when there's many selectors or selectors are complex.
Anyway, why not to use querySelectorAll in cases when we can use it.