The underlying storage used during string formatting is StringBuilder.
To support UTF-16 strings, this patch allows callers to specify a mode
during StringBuilder construction. The default mode is UTF-8, for which
StringBuilder remains unchanged.
In UTF-16 mode, we treat the StringBuilder's internal ByteBuffer as a
series of u16 code units. Appending a single character will append 2
bytes for that character (cast to a char16_t). Appending a StringView
will transcode the string to UTF-16.
Utf16String also gains the same memory optimization that we added for
String, where we hand-off the underlying buffer to Utf16String to avoid
having to re-allocate.
In the future, we may want to further optimize for ASCII strings. For
example, we could defer committing to the u16-esque storage until we
see a non-ASCII code point.
This is a strictly UTF-16 string with some optimizations for ASCII.
* If created from a short UTF-8 or UTF-16 string that is also ASCII,
then the string is stored in an inlined byte buffer.
* If created with a long UTF-8 or UTF-16 string that is also ASCII,
then the string is stored in an outlined char buffer.
* If created with a short or long UTF-8 or UTF-16 string that is not
ASCII, then the string is stored in an outlined char16 buffer.
We do not store short non-ASCII text in the inlined buffer to avoid
confusion with operations such as `length_in_code_units` and
`code_unit_at`. For example, "😀" would be stored as 4 UTF-8 bytes
in short string form. But we still want `length_in_code_units` to
be 2, and `code_unit_at(0)` to be 0xD83D.
This is an active proposal at stage 3 of the TC39 proposal process.
See: https://tc39.es/proposal-dynamic-code-brand-checks/
See: https://github.com/tc39/proposal-dynamic-code-brand-checks
This proposal essentially adds support for the TrustedScript type from
the Trusted Types specification to eval and Function. This in turn
pipes support for the type into the CSP hook to check if the CSP allows
dynamic code compilation.
However, it currently doesn't support ShadowRealms, so the
implementation here is a close approximation, using PerformEval as the
basis.
See: https://github.com/tc39/proposal-dynamic-code-brand-checks/issues/19
This is required to support the new function signature for the CSP
hook, and will allow us to slot in Trusted Types support in the future.
Our floating point number parser was based on the fast_float library:
https://github.com/fastfloat/fast_float
However, our implementation only supports 8-bit characters. To support
UTF-16, we will need to be able to convert char16_t-based strings to
numbers as well. This works out-of-the-box with fast_float.
We can also use fast_float for integer parsing.
By definition, the web allows lonely surrogates by default. Let's have
our string APIs reflect this, so we don't have to pass an allow option
all over the place.
To prepare for an upcoming Utf16String, this migrates Utf16View to store
its data as a char16_t. Most function definitions are moved inline and
made constexpr.
This also adds a UDL to construct a Utf16View from a string literal:
auto string = u"hello"sv;
This let's us remove the NTTP Utf16View constructor, as we have found
that such constructors bloat binary size quite a bit.
By following the spec to the letter, our mapped arguments objects ended
up with many extra GC allocations:
- 1 extra Object for the internal [[ParameterMap]].
- 2 extra NativeFunctions for each mapped parameter accessor.
- 1 extra Accessor to hold the aforementioned NativeFunctions.
This patch removes all those allocations and lets ArgumentsObject model
the desired behavior in custom C++ instead of using script primitives.
1.06x speedup on Speedometer's TodoMVC-jQuery.
Instead of letting every [[Call]] implementation allocate an
ExecutionContext, we now make that a responsibility of the caller.
The main point of this exercise is to allow the Call instruction
to write function arguments directly into the callee ExecutionContext
instead of copying them later.
This makes function calls significantly faster:
- 10-20% faster on micro-benchmarks (depending on argument count)
- 4% speedup on Kraken
- 2% speedup on Octane
- 5% speedup on JetStream
This is better because:
- Better data locality
- Allocate vector for registers+constants+locals+arguments in one go
instead of allocating two vectors separately
Instead of using the more generic define_native_accessor() here,
we poke directly at indexed property storage for the parameter map.
We can also construct the NativeFunction objects directly, without
giving them names like "get 0" etc, since these are not observable
by userspace.
Finally, by using default property attributes (not observable anyway),
we get simple indexed storage instead of generic (hash map) storage.
We were doing way too much computation every time an ESFO was
instantiated. This was particularly sad, since the results of these
computations were identical every time!
This patch adds a new SharedFunctionInstanceData object that gets
shared between all instances of an ESFO instantiated from some kind of
AST FunctionNode.
~5% speedup on Speedometer 2.1 :^)
The special empty value (that we use for array holes, Optional<Value>
when empty and a few other other placeholder/sentinel tasks) still
exists, but you now create one via JS::js_special_empty_value() and
check for it with Value::is_special_empty_value().
The main idea here is to make it very unlikely to accidentally create an
unexpected special empty value.
PrimitiveString is now internally either UTF-8, UTF-16, or both.
We no longer convert them to/from ByteString anywhere, nor does VM have
a ByteString cache.
Instead of making a copy of the Vector<FunctionParameter> from the AST
every time we instantiate an ECMAScriptFunctionObject, we now keep the
parameters in a ref-counted FunctionParameters object.
This reduces memory usage, and also allows us to cache the bytecode
executables for default parameter expressions without recompiling them
for every instantiation. :^)
These are going to be included in the ECMA-262 AOs once Temporal reaches
stage 4. There's no need to keep them in the Temporal namespace. Some
upcoming Temporal editorial changes will get awkward without this patch.
While we don't yet have a working `using` implementation with our byte
code, we can still keep our DisposableStack implementation up to date.
The changes brought in here are all editorial, and set us up to start
an AsyncDisposableStack implementation.
From what I understand, the suspension steps are not required now,
or in the future for our implementation, or any other. The intent
is already implemented in the spec pushing on another execution
context to the stack and leaving the running execution context as-is.
The resume steps are a slightly different story as there is some subtle
behavior which the spec is trying to convey where some custom logic may
need to be done when one execution context changes from one to another.
It may be worth implementing those steps at a later point in time so
that this behavior is a bit easier to follow in those cases.
To make the situation more confusing - from what I can gather from the
spec, not all cases that the spec mentions resume actually means
anything normative. Resume is only _actually_ needed in a limited set
of locations.
For now, let's just remove the unneeded FIXMEs that indicate that there
is something to be done for the suspension steps, as there is not, and
leave the resume steps as is.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
Now that the heap has no knowledge about a JavaScript realm and is
purely for managing the memory of the heap, it does not make sense
to name this function to say that it is a non-realm variant.
The main motivation behind this is to remove JS specifics of the Realm
from the implementation of the Heap.
As a side effect of this change, this is a bit nicer to read than the
previous approach, and in my opinion, also makes it a little more clear
that this method is specific to a JavaScript Realm.
