Three standalone Cell creation functions remain in the JS namespace:
- js_bigint()
- js_string()
- js_symbol()
All of them are leftovers from early iterations when LibJS still took
inspiration from JSC, which itself has jsString(). Nowadays, we pretty
much exclusively use static create() functions to construct types
allocated on the JS heap, and there's no reason to not do the same for
these.
Also change the return type from BigInt* to NonnullGCPtr<BigInt> while
we're here.
This is patch 1/3, replacement of js_string() and js_symbol() follow.
This makes more sense as an Object method rather than living within the
VM class for no good reason. Most of the other 7.3.xx AOs already work
the same way.
Also add spec comments while we're here.
This will make it easier to support both string types at the same time
while we convert code, and tracking down remaining uses.
One big exception is Value::to_string() in LibJS, where the name is
dictated by the ToString AO.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
This patch does two things:
- We now use u32 instead of size_t for the hops and index fields
in EnvironmentCoordinate. This means we're limited to an environment
nesting level and variable count of 4Gs respectively.
- Instead of wrapping it in an Optional, EnvironmentCoordinate now has
a custom valid/invalid state using a magic marker value.
These two changes reduce the size of Identifier by 16 bytes. :^)
Before this change, each AST node had a 64-byte SourceRange member.
This SourceRange had the following layout:
filename: StringView (16 bytes)
start: Position (24 bytes)
end: Position (24 bytes)
The Position structs have { line, column, offset }, all members size_t.
To reduce memory consumption, AST nodes now only store the following:
source_code: NonnullRefPtr<SourceCode> (8 bytes)
start_offset: u32 (4 bytes)
end_offset: u32 (4 bytes)
SourceCode is a new ref-counted data structure that keeps the filename
and original parsed source code in a single location, and all AST nodes
have a pointer to it.
The start_offset and end_offset can be turned into (line, column) when
necessary by calling SourceCode::range_from_offsets(). This will walk
the source code string and compute line/column numbers on the fly, so
it's not necessarily fast, but it should be rare since this information
is primarily used for diagnostics and exception stack traces.
With this, ASTNode shrinks from 80 bytes to 32 bytes. This gives us a
~23% reduction in memory usage when loading twitter.com/awesomekling
(330 MiB before, 253 MiB after!) :^)
This is only visible with something like `Object.getOwnPropertyNames` on
the global object. All other declaration instantiations put the
functions on an environment making the order invisible.
Note that spec order is not quite tree order as in non-strict mode
functions which get hoisted out of blocks appear before top level
functions.
Co-authored-by: Hendiadyoin1 <leon.a@serenityos.org>
This has to get quite messy because we currently do evaluation to value
and reference separately meaning we have to deal with a lot of edge
cases here.
This patch adds a special EnvironmentCoordinate::global_marker value
that signifies that a binding lookup ended up searching the global
environment. It doesn't matter if we find it there or not, the global
marker is always returned. This allows us to bypass other environments
on subsequent access, going directly to the global environment.
This gives us better debug output when analysing calls to `undefined`
and also fixes multiple test-js cases expecting an
`(evaluated from $Expression)` in the error message.
This also refactors out the generation of that string, to avoid code
duplication with the AST interpreter.
A struct with three raw pointers to other GC'd types is a pretty big
liability, let's just turn this into a Cell itself.
This comes with the additional benefit of being able to capture it in
a lambda effortlessly, without having to create handles for individual
members.
This is an export which looks like `export {} from "module"`, and
although it doesn't have any real export entries it should still add
"module" to the required modules to load.
Intrinsics, i.e. mostly constructor and prototype objects, but also
things like empty and new object shape now live on a new heap-allocated
JS::Intrinsics object, thus completing the long journey of taking all
the magic away from the global object.
This represents the Realm's [[Intrinsics]] slot in the spec and matches
its existing [[GlobalObject]] / [[GlobalEnv]] slots in terms of
architecture.
In the majority of cases it should now be possibly to fully allocate a
regular object without the global object existing, and in fact that's
what we do now - the realm is allocated before the global object, and
the intrinsics between both :^)
- Prefer VM::current_realm() over GlobalObject::associated_realm()
- Prefer VM::heap() over GlobalObject::heap()
- Prefer Cell::vm() over Cell::global_object()
- Prefer Wrapper::vm() over Wrapper::global_object()
- Inline Realm::global_object() calls used to access intrinsics as they
will later perform a direct lookup without going through the global
object
This is a continuation of the previous five commits.
A first big step into the direction of no longer having to pass a realm
(or currently, a global object) trough layers upon layers of AOs!
Unlike the create() APIs we can safely assume that this is only ever
called when a running execution context and therefore current realm
exists. If not, you can always manually allocate the Error and put it in
a Completion :^)
In the spec, throw exceptions implicitly use the current realm's
intrinsics as well: https://tc39.es/ecma262/#sec-throw-an-exception
This is a continuation of the previous four commits.
Passing a global object here is largely redundant, we definitely need
the interpreter but can get the VM and (later) current active realm from
there - and also the global object while we still need it, although I'd
like to remove Interpreter::global_object() in the future.
This now matches the bytecode interpreter's execute_impl() functions.
This is a continuation of the previous two commits.
As allocating a JS cell already primarily involves a realm instead of a
global object, and we'll need to pass one to the allocate() function
itself eventually (it's bridged via the global object right now), the
create() functions need to receive a realm as well.
The plan is for this to be the highest-level function that actually
receives a realm and passes it around, AOs on an even higher level will
use the "current realm" concept via VM::current_realm() as that's what
the spec assumes; passing around realms (or global objects, for that
matter) on higher AO levels is pointless and unlike for allocating
individual objects, which may happen outside of regular JS execution, we
don't need control over the specific realm that is being used there.
We already did this but it called the @@iterator method of
%Array.prototype% visible to the user for example by overriding that
method. This should not be visible so we use a special version of
SuperCall now.
We cache on the AST node side as this is easier to track a position, we
just have to take care to wrap the values in a handle to make sure they
are not garbage collected.
Since tagged template literals can inspect the raw string it is not a
syntax error to have invalid escapes. However the cooked value should be
`undefined`.
We accomplish this by tracking whether parse_string_literal
fails and then using a NullLiteral (since UndefinedLiteral is not a
thing) and finally converting null in tagged template execution to
undefined.
Using the fact that there are 2^52-2 NaN representations we can
"NaN-box" all the Values possible. This means that Value no longer has
an explicit "Type" but that information is now stored in the bits of a
double. This is done by "tagging" the top two bytes of the double.
For a full explanation see the large comment with asserts at the top of
Value.
We can also use the exact representation of the tags to make checking
properties like nullish, or is_cell quicker. But the largest gains are
in the fact that the size of a Value is now halved.
The SunSpider and other benchmarks have been ran to confirm that there
are no regressions in performance compared to the previous
implementation. The tests never performed worse and in some cases
performed better. But the biggest differences can be seen in memory
usage when large arrays are allocated. A simple test which allocates a
1000 arrays of size 100000 has roughly half the memory usage.
There is also space in the representations for future expansions such as
tuples and records.
To ensure that Values on the stack and registers are not lost during
garbage collection we also have to add a check to the Heap to check for
any of the cell tags and extracting the canonical form of the pointer
if it matches.
This commit moves the length calculations out to be directly on the
StringView users. This is an important step towards the goal of removing
StringView(char const*), as it moves the responsibility of calculating
the size of the string to the user of the StringView (which will prevent
naive uses causing OOB access).
This was defined twice, despite being the very same thing:
- ClassElement::ClassFieldDefinition
- ECMAScriptFunctionObject::InstanceField
Move the former to a new header and use it everywhere. Also update the
define_field() AO to take a single field instead of separate name and
initializer arguments.
Having all spec comments verbatim on their own line with no additions
made by us will make it easier to automate comparing said comments to
their current spec counterparts.
While adding spec comments to PerformEval, I noticed we were missing
multiple steps.
Namely, these were:
- Checking if the host will allow us to compile the string
(allowing LibWeb to perform CSP for eval)
- The parser's initial state depending on the environment around us
on direct eval:
- Allowing new.target via eval in functions
- Allowing super calls and super properties via eval in classes
- Disallowing the use of the arguments object in class field
initializers at eval's parse time
- Setting ScriptOrModule of eval's execution context
The spec allows us to apply the additional parsing steps in any order.
The method I have gone with is passing in a struct to the parser's
constructor, which overrides the parser's initial state to (dis)allow
the things stated above from the get-go.
This fixes 2 bugs in our current implementation:
* Properties deleted during iteration were still being iterated
* Properties with the same name in both the object and it's prototype
were iterated twice
