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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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24
Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
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@ -1027,7 +1027,7 @@ Object* create_mapped_arguments_object(GlobalObject& global_object, FunctionObje
}
// 7.1.21 CanonicalNumericIndexString ( argument ), https://tc39.es/ecma262/#sec-canonicalnumericindexstring
Value canonical_numeric_index_string(GlobalObject& global_object, PropertyKey const& property_key)
Optional<u32> canonical_numeric_index_string(PropertyKey const& property_key)
{
// NOTE: If the property name is a number type (An implementation-defined optimized
// property key type), it can be treated as a string property that has already been
@ -1035,25 +1035,11 @@ Value canonical_numeric_index_string(GlobalObject& global_object, PropertyKey co
VERIFY(property_key.is_string() || property_key.is_number());
// If property_key is a string containing a canonical numeric index
// the act of calling is_number() will return true
if (property_key.is_number())
return Value(property_key.as_number());
// 1. Assert: Type(argument) is String.
auto argument = Value(js_string(global_object.vm(), property_key.as_string()));
// 2. If argument is "-0", return -0𝔽.
if (argument.as_string().string() == "-0")
return Value(-0.0);
// 3. Let n be ! ToNumber(argument).
auto n = MUST(argument.to_number(global_object));
// 4. If SameValue(! ToString(n), argument) is false, return undefined.
if (!same_value(MUST(n.to_primitive_string(global_object)), argument))
return js_undefined();
// 5. Return n.
return n;
return property_key.as_number();
return {};
}
// 22.1.3.17.1 GetSubstitution ( matched, str, position, captures, namedCaptures, replacement ), https://tc39.es/ecma262/#sec-getsubstitution