The spec version of canonical_numeric_index_string is absurdly complex,
and ends up converting from a string to a number, and then back again
which is both slow and also requires a few allocations and a string
compare.
Instead this patch moves away from using Values to represent canonical
a canonical index. In most cases all we need to know is whether a
PropertyKey is an integer between 0 and 2^^32-2, which we already
compute when we construct a PropertyKey so the existing is_number()
check is sufficient.
The more expensive case is handling strings containing numbers that
don't roundtrip through string conversion. In most cases these turn
into regular string properties, but for TypedArray access these
property names are not treated as normal named properties.
TypedArrays treat these numeric properties as magic indexes that are
ignored on read and are not stored (but are evaluated) on assignment.
For that reason there's now a mode flag on canonical_numeric_index_string
so that only TypedArrays take the cost of the ToString round trip test.
In order to improve the performance of this path this patch includes
some early returns to avoid conversion in cases where we can quickly
know whether a property can round trip.
This reverts commit 3a184f7841.
This broke a number of test262 tests under "TypedArrayConstructors".
The issue is that the CanonicalNumericIndexString AO should not fail
for inputs like "1.1", despite them not being integral indices.
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.
The spec version of canonical_numeric_index_string is absurdly complex,
and ends up converting from a string to a number, and then back again
which is both slow and also requires a few allocations and a string
compare.
Instead lets use the logic we already have as that is much more
efficient.
This improves performance of all non-numeric property names.
This commit removes all exception related code:
Remove VM::exception(), VM::throw_exception() etc. Any leftover
throw_exception calls are moved to throw_completion.
The one method left is clear_exception() which is now a no-op. Most of
these calls are just to clear whatever exception might have been thrown
when handling a Completion. So to have a cleaner commit this will be
removed in a next commit.
It also removes the actual Exception and TemporaryClearException classes
since these are no longer used.
In any spot where the exception was actually used an attempt was made to
preserve that behavior. However since it is no longer tracked by the VM
we cannot access exceptions which were thrown in previous calls.
There are two such cases which might have different behavior:
- In Web::DOM::Document::interpreter() the on_call_stack_emptied hook
used to print any uncaught exception but this is now no longer
possible as the VM does not store uncaught exceptions.
- In js the code used to be interruptable by throwing an exception on
the VM. This is no longer possible but was already somewhat fragile
before as you could happen to throw an exception just before a VERIFY.
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.
Using an Optional was extremely wasteful for function objects that don't
even have a bytecode executable.
This allows ECMAScriptFunctionObject to fit in a smaller size class.
This also refactors interpreter creation to follow
InitializeHostDefinedRealm, but I couldn't fit it in the title :^)
This allows us to follow the spec much more closely rather than being
completely ad-hoc with just the parse node instead of having all the
surrounding data such as the realm of the parse node.
The interpreter creation refactor creates the global execution context
once and doesn't take it off the stack. This allows LibWeb to take the
global execution context and manually handle it, following the HTML
spec. The HTML spec calls this the "realm execution context" of the
environment settings object.
It also allows us to specify the globalThis type, as it can be
different from the global object type. For example, on the web, Window
global objects use a WindowProxy global this value to enforce the same
origin policy on operations like [[GetOwnProperty]].
Finally, it allows us to directly call Program::execute in perform_eval
and perform_shadow_realm_eval as this moves
global_declaration_instantiation into Interpreter::run
(ScriptEvaluation) as per the spec.
Note that this doesn't evalulate Source Text Modules yet or refactor
the bytecode interpreter, that's work for future us :^)
This patch was originally build by Luke for the environment settings
object change but was also needed for modules. So I (davidot) have
modified it with the new completion changes and setup for that.
Co-authored-by: davidot <davidot@serenityos.org>
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.
The spec has a note stating that resolve binding will always return a
reference whose [[ReferencedName]] field is name. However this is not
correct as the underlying method GetIdentifierReference may throw on
env.HasBinding(name) thus it can throw. However, there are some
scenarios where it cannot throw because the reference is known to exist
in that case we use MUST with a comment.
Now that only ECMAScriptFunctionObject uses this, we can remove the
FunctionObject::new_function_environment() pure virtual method and just
implement it as a standalone AO with an ECMAScriptFunctionObject
parameter, next to the other NewFooEnvironment AOs.
This patch implements:
- Spec compliant [[Call]] and [[Construct]] internal slots, as virtual
FunctionObject::internal_{call,construct}(). These effectively replace
the old virtual FunctionObject::{call,construct}(), but with several
advantages:
- Clear and consistent naming, following the object internal methods
- Use of completions
- internal_construct() returns an Object, and not Value! This has been
a source of confusion for a long time, since in the spec there's
always an Object returned but the Value return type in LibJS meant
that this could not be fully trusted and something could screw you
over.
- Arguments are passed explicitly in form of a MarkedValueList,
allowing manipulation (BoundFunction). We still put them on the
execution context as a lot of code depends on it (VM::arguments()),
but not from the Call() / Construct() AOs anymore, which now allows
for bypassing them and invoking [[Call]] / [[Construct]] directly.
Nothing but Call() / Construct() themselves do that at the moment,
but future additions to ECMA262 or already existing web specs might.
- Spec compliant, standalone Call() and Construct() AOs: currently the
closest we have is VM::{call,construct}(), but those try to cater to
all the different function object subclasses at once, resulting in a
horrible mess and calling AOs with functions they should never be
called with; most prominently PrepareForOrdinaryCall and
OrdinaryCallBindThis, which are only for ECMAScriptFunctionObject.
As a result this also contains an implicit optimization: we no longer
need to create a new function environment for NativeFunctions - which,
worth mentioning, is what started this whole crusade in the first place
:^)
Since non-strict direct eval() can insert new bindings into a
surrounding var scope, we cannot safely cache some assumptions about
environment chain layout after eval() has taken place.
Since eval() is rare, let's do what other engines do and simply
deoptimize in its presence. This patch adds a new "permanently screwed"
flag to JS::Environment that will be set on the entire variable
environment chain upon non-strict direct eval().
