Since AST interpreter switches to bytecode to execute generator
functions, arguments stored in local variables always need to be
initialized for such functions.
Using local variables to store function parameters makes Kraken tests
run 7-10% faster.
For now this optimization is limited to only be applied if:
- Parameter does not use destructuring assignment
- None of the function params has default value
- There is no access to "arguments" variable inside function body
Converting a base value to an Object is performed by Reference::delete_.
Doing this early in the bytecode operator could be observable, although
it would likely be the first observable step in Reference::delete_
anyways. This will just align these operators with upcoming operators
for super references, where doing this coercion first will be observable
(we need to throw an exception for deleting a super property before this
coercion).
This is (part of) a normative change in the ECMA-262 spec. See:
d09532c
We recently implemented other parts of that commit in LibJS, but missed
this change:
442ca4f9b42b19d1b5ab
These are not strictly unresolvable references. Treating them as such
fails an assertion in the `delete UnaryExpression` semantic (which is
Reference::delete_ in our implementation) - we enter the unresolvable,
branch, which then asserts that the [[Strict]] slot of the reference is
false.
Invariants 5 and 6 of the `EnumerateObjectProperties` AO mean that we
must not include an enumerate property if there is a non-enumerable
property higher up the prototype chain with the same name. The previous
implementation did not adhere to this, as `EnumerableOwnPropertyNames`
does not carry information about present but non-enumerable properties.
This is part of an old normative change that happened soon after
Andreas made `super` closer to spec in 1270df2.
See https://github.com/tc39/ecma262/pull/2267/
This was introduced into bytecode by virtue of copy and paste :^)
Bytecode results:
Summary:
Diff Tests:
+2 ✅ -2 ❌
- Update ECMAScriptFunctionObject::function_declaration_instantiation
to initialize local variables
- Introduce GetLocal, SetLocal, TypeofLocal that will be used to
operate on local variables.
- Update bytecode generator to emit instructions for local variables
Now ExecutionContext has vector of values that will represent values
of local variables.
This vector is initialized in ECMAScriptFunctionObject::internal_call()
or ECMAScriptFunctionObject::internal_const() using number of local
variables provided to ECMAScriptFunctionObject by the parser.
Saving vector of local variables names in ECMAScriptFunctionObject
will allow to get a name by index in case message of ReferenceError
needs to contain a variable name.
This modification enables the parser to determine whether an identifier
used within a function refers to a local variable or not. In this
context, a local identifier means that it is not captured by any nested
function declaration which means it modified only from inside a
function.
The information about whether identifier is local is stored inside
Identifier AST node and also contains information about the index of
local variable inside a function and information about total number
of local variables used by a function is stored in function nodes.
By using Identifier class to represent the name of a class expression,
it becomes possible to consistently store information within the
identifier object, indicating whether the name refers to a local
variable or not.
The flag indicating the presence of an await expression should be
passed up to the parent scope until the nearest function scope is
reached. This resolves several problems related to identifying
top-level awaits, which are currently not recognized correctly
when used within a nested scope.
This makes the behavior of `Symbol` correct in strict mode, wherein if
the receiver is a symbol primitive, assigning new properties should
throw a TypeError.
ECMA-262 implies that `MIN_VALUE` should be a denormalized value if
denormal arithmetic is supported. This is the case on x86-64 and AArch64
using standard GCC/Clang compilation settings.
test262 checks whether `Number.MIN_VALUE / 2.0` is equal to 0, which
only holds if `MIN_VALUE` is the smallest denormalized value.
This commit renames the existing `NumericLimits<FloatingPoint>::min()`
to `min_normal()` and adds a `min_denormal()` method to force users to
explicitly think about which one is appropriate for their use case. We
shouldn't follow the STL's confusingly designed interface in this
regard.
This avoids the overhead of allocating a new Array on every function
call, saving a substantial amount of time and avoiding GC thrash.
This patch only makes use of Op::Call in CallExpression. There are other
places we should codegen this op. We should also do the same for super
expression calls.
~5% speed-up on Kraken/stanford-crypto-ccm.js
Forcing every function call to allocate a new Array just to accommodate
spread parameters is not very nice, so let's start moving towards making
this a special case rather than the general (and only) case.
The var environments will unwind as needed with the ExecutionContext
and there's no need to include it in the unwind info.
We still need to do this for lexical environments though, since they
can have short local lifetimes inside a function.
Since the relationship between VM and Bytecode::Interpreter is now
clear, we can have VM ask the Interpreter for roots in the GC marking
pass. This avoids having to register and unregister handles and
MarkedVectors over and over.
Since GeneratorObject can also own a RegisterWindow, we share the code
in a RegisterWindow::visit_edges() helper.
~4% speed-up on Kraken/stanford-crypto-ccm.js :^)
While the completion value of a variable declaration is specified to be
empty, we might already have a completion value in the accumulator from
a previous statement. Preserve it so as to avoid clobbering it.
This fixes 6 tests on test262.
