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.
Instead of crashing on the spot, return a descriptive error that will
eventually continue its days as a javascript "InternalError" exception.
This should make random crashes with BC less likely.
This removes a number of vm.exception() checks which are now caught
directly by TRY. Make use of these checks in
{Global, Eval}DeclarationInstantiation and while we're here add spec
comments.
It seems the stack search does not find all functions because they are
kept in variants and other structs. This meant some function could be
cleaned up while we were evaluating a class meaning it would fail/crash
when attempting to run the functions.
The hard part of parsing them in import statements and calls was already
done so this is just removing some check which threw before on
assertions. And filtering the assertions based on the result of a new
host hook.
Because we can have arbitrary in- and export names with strings we can
have '*' and '' which means using '*' as an indicating namespace imports
failed / behaved incorrectly for string imports '*'.
We now use more specific types to indicate these special states instead
of these 'magic' string values.
Do note that 'default' is not actually a magic string value but one
specified by the spec. And you can in fact export the default value by
doing: `export { 1 as default }`.
The big changes are:
- Allow strings as Module{Export, Import}Name
- Properly track declarations in default export statements
However, the spec is a little strange in that it allows function and
class declarations without a name in default export statements.
This is quite hard to fully implement without rewriting more of the
parser so for now this behavior is emulated by faking things with
function and class expressions. See the comments in
parse_export_statement for details on the hacks and where it goes wrong.
This includes:
- Parsing proper LabelledStatements with try_parse_labelled_statement()
- Removing LabelableStatement
- Implementing the LoopEvaluation semantics via loop_evaluation() in
each IterationStatement subclass; and IterationStatement evaluation
via {For,ForIn,ForOf,ForAwaitOf,While,DoWhile}Statement::execute()
- Updating ReturnStatement, BreakStatement and ContinueStatement to
return the appropriate completion types
- Basically reimplementing TryStatement and SwitchStatement according to
the spec, using completions
- Honoring result completion types in AsyncBlockStart and
OrdinaryCallEvaluateBody
- Removing any uses of the VM unwind mechanism - most importantly,
VM::throw_exception() now exclusively sets an exception and no longer
triggers any unwinding mechanism.
However, we already did a good job updating all of LibWeb and userland
applications to not use it, and the few remaining uses elsewhere don't
rely on unwinding AFAICT.
Instead of slapping 0..N labels on a statement like the current
LabelableStatement does, we need the spec's LabelledStatement for a
proper implementation of control flow using only completions - it always
has one label and one labelled statement - what appears to be 'multiple
labels' on the same statement is actually nested LabelledStatements.
Note that this is unused yet and will fully replace LabelableStatement
in the next commit.
This is another major milestone on our journey towards removing global
VM exception state :^)
Does pretty much exactly what it says on the tin: updating
ASTNode::execute() to return a Completion instead of a plain value. This
will *also* allow us to eventually remove the non-standard unwinding
mechanism and purely rely on the various completion types.
This allows us to only perform checks like export bindings existing only
for modules. Also this makes it easier to set strict and other state
variables with TemporaryChanges.
This commit adds support for the most bare bones version of async
functions, support for async generator functions, async arrow functions
and await expressions are TODO.
This is necessary as we might have to perform named evaluation with the
field name.
Ideally we would also skip some setup parts of the function like
function_declaration_instantiation however this would require bigger
changes to ECMAScriptFunctionObject.
We now propagate this flag to FunctionDeclaration, and then also into
ECMAScriptFunctionObject.
This will be used to disable optimizations that aren't safe in the
presence of direct eval().
Instead of going through an environment record, make arguments of the
currently executing function generate references via the argument index,
which can later be resolved directly through the ExecutionContext.
This patch introduces the "environment coordinate" concept, which
encodes the distance from a variable access to the binding it ends up
resolving to.
EnvironmentCoordinate has two fields:
- hops: The number of hops up the lexical environment chain we have
to make before getting to the resolved binding.
- index: The index of the resolved binding within its declarative
environment record.
Whenever a variable lookup resolves somewhere inside a declarative
environment, we now cache the coordinates and reuse them in subsequent
lookups. This is achieved via a coordinate cache in JS::Identifier.
Note that non-strict direct eval() breaks this optimization and so it
will not be performed if the resolved environment has been permanently
screwed by eval().
This makes variable access *significantly* faster. :^)
The idea here is simple: If the block statement doesn't contain any
lexical declarations, we don't need to allocate, initialize and
eventually garbage collect a new declarative environment.
This even makes lookups across nested blocks slightly faster as we don't
have to traverse a chain of empty environments anymore - instead, the
execution context just stores the outermost non-empty one.
This doesn't speed up test-js considerably, but has a noticeable effect
on test262 and real-world web content :^)
This gives FunctionNode a "might need arguments object" boolean flag and
sets it based on the simplest possible heuristic for this: if we
encounter an identifier called "arguments" or "eval" up to the next
(nested) function declaration or expression, we won't need an arguments
object. Otherwise, we *might* need one - the final decision is made in
the FunctionDeclarationInstantiation AO.
Now, this is obviously not perfect. Even if you avoid eval, something
like `foo.arguments` will still trigger a false positive - but it's a
start and already massively cuts down on needlessly allocated objects,
especially in real-world code that is often minified, and so a full
"arguments" identifier will be an actual arguments object more often
than not.
To illustrate the actual impact of this change, here's the number of
allocated arguments objects during a full test-js run:
Before:
- Unmapped arguments objects: 78765
- Mapped arguments objects: 2455
After:
- Unmapped arguments objects: 18
- Mapped arguments objects: 37
This results in a ~5% speedup of test-js on my Linux host machine, and
about 3.5% on i686 Serenity in QEMU (warm runs, average of 5).
The following microbenchmark (calling an empty function 1M times) runs
25% faster on Linux and 45% on Serenity:
function foo() {}
for (var i = 0; i < 1_000_000; ++i)
foo();
test262 reports no changes in either direction, apart from a speedup :^)
