Make the _string, _fly_string, _utf16, and _utf16_fly_string UDL
operators constexpr, with a fast path for short (<= 7 byte) ASCII
literals that folds directly into an inline ShortString. Previously,
every "foo"_fly_string (and friends) involved an out-of-line call
into the string factory, even though the result is entirely known
at compile time.
We specialize `Optional<T>` for value types that inherently support some
kind of "empty" value or whose value range allow for a unlikely to be
useful sentinel value that can mean "empty", instead of the boolean flag
a regular Optional<T> needs to store. Because of padding, this often
means saving 4 to 8 bytes per instance.
By extending the new `SentinelOptional<T, Traits>`, these
specializations are significantly simplified to just having to define
what the sentinel value is, and how to identify a sentinel value.
When T in HashTable<T> has a potentially slow equality check, it can be
very profitable to check for a matching hash before full equality.
This patch adds may_have_slow_equality_check() to AK::Traits and
defaults it to true. For trivial types (pointers, integers, etc) we
default it to false. This means we skip the hash check when the equality
check would be a single-CPU-word compare anyway.
This synergizes really well with things like HashMap<String, V> where
collisions previously meant we may have to churn through multiple O(n)
equality checks.
This first pass only applies to the following two cases:
- Public functions returning a view type into an object they own
- Public ctors storing a view type
This catches a grand total of one (1) issue, which is fixed in
the previous commit.
We added this for String some time ago, so let's give Utf16String the
same optimization. Note that Utf16String was already handling its data
member potentially being null as of 5af99f4dd0.
For the web, we allow a wobbly UTF-16 encoding (i.e. lonely surrogates
are permitted). Only in a few exceptional cases do we strictly require
valid UTF-16. As such, our `validate(AllowLonelySurrogates::Yes)` calls
will always succeed. It's a wasted effort to ever make such a check.
This patch eliminates such invocations. The validation methods will now
only check for strict UTF-16, and are only invoked when needed.
Utf16FlyString more or less works exactly the same as FlyString. It will
store the raw encoded data of the string instance. If the string is a
short ASCII string, Utf16FlyString holds the ShortString bytes; else,
Utf16FlyString holds a pointer to the Utf16StringData.
