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LibJS: Get rid of unnecessary work from canonical_numeric_index_string

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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 is contained in:
Anonymous 2022-02-12 12:51:06 -08:00 • committed by Andreas Kling
parent 44a2ebea00
commit 3a184f7841
8 changed files with 57 additions and 98 deletions
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27
Userland/Libraries/LibJS/Runtime/StringObject.cpp
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@ -44,7 +44,7 @@ void StringObject::visit_edges(Cell::Visitor& visitor)
}
// 10.4.3.5 StringGetOwnProperty ( S, P ), https://tc39.es/ecma262/#sec-stringgetownproperty
static Optional<PropertyDescriptor> string_get_own_property(GlobalObject& global_object, StringObject const& string, PropertyKey const& property_key)
static Optional<PropertyDescriptor> string_get_own_property(StringObject const& string, PropertyKey const& property_key)
{
// 1. Assert: S is an Object that has a [[StringData]] internal slot.
// 2. Assert: IsPropertyKey(P) is true.
@ -57,17 +57,14 @@ static Optional<PropertyDescriptor> string_get_own_property(GlobalObject& global
return {};
// 4. Let index be ! CanonicalNumericIndexString(P).
auto index = canonical_numeric_index_string(global_object, property_key);
// 5. If index is undefined, return undefined.
if (index.is_undefined())
return {};
// 6. If IsIntegralNumber(index) is false, return undefined.
if (!index.is_integral_number())
return {};
// 7. If index is -0𝔽, return undefined.
if (index.is_negative_zero())
return {};
auto index = canonical_numeric_index_string(property_key);
if (!index.has_value()) {
// 5. If index is undefined, return undefined.
// 6. If IsIntegralNumber(index) is false, return undefined.
// 7. If index is -0𝔽, return undefined.
return {};
}
// 8. Let str be S.[[StringData]].
// 9. Assert: Type(str) is String.
auto str = string.primitive_string().utf16_string_view();
@ -76,11 +73,11 @@ static Optional<PropertyDescriptor> string_get_own_property(GlobalObject& global
auto length = str.length_in_code_units();
// 11. If ℝ(index) < 0 or len ≤ ℝ(index), return undefined.
if (index.as_double() < 0 || length <= index.as_double())
if (length <= static_cast<u64>(*index))
return {};
// 12. Let resultStr be the String value of length 1, containing one code unit from str, specifically the code unit at index ℝ(index).
auto result_str = js_string(string.vm(), str.substring_view(index.as_double(), 1));
auto result_str = js_string(string.vm(), str.substring_view(*index, 1));
// 13. Return the PropertyDescriptor { [[Value]]: resultStr, [[Writable]]: false, [[Enumerable]]: true, [[Configurable]]: false }.
return PropertyDescriptor {
@ -104,7 +101,7 @@ ThrowCompletionOr<Optional<PropertyDescriptor>> StringObject::internal_get_own_p
return descriptor;
// 4. Return ! StringGetOwnProperty(S, P).
return string_get_own_property(global_object(), *this, property_key);
return string_get_own_property(*this, property_key);
}
// 10.4.3.2 [[DefineOwnProperty]] ( P, Desc ), https://tc39.es/ecma262/#sec-string-exotic-objects-defineownproperty-p-desc
@ -114,7 +111,7 @@ ThrowCompletionOr<bool> StringObject::internal_define_own_property(PropertyKey c
VERIFY(property_key.is_valid());
// 2. Let stringDesc be ! StringGetOwnProperty(S, P).
auto string_descriptor = string_get_own_property(global_object(), *this, property_key);
auto string_descriptor = string_get_own_property(*this, property_key);
// 3. If stringDesc is not undefined, then
if (string_descriptor.has_value()) {