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LibJS: Reduce UTF-8 to UTF-16 transcoding when only UTF-16 is wanted

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When appending two strings together to form a new string, if both of the
strings are already UTF-16, create the new string as UTF-16 as well.

This shaves about 0.5 seconds off the following test262 test:
  RegExp/property-escapes/generated/General_Category_-_Decimal_Number.js
This commit is contained in:
Timothy Flynn 2021-08-09 18:00:38 -04:00 • committed by Andreas Kling
parent 66264f7c2a
commit b85b8ca350
2 changed files with 17 additions and 0 deletions
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15
Userland/Libraries/LibJS/Runtime/Value.cpp
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@ -1100,6 +1100,21 @@ Value add(GlobalObject& global_object, Value lhs, Value rhs)
if (vm.exception())
return {};
if (lhs_primitive.is_string() && rhs_primitive.is_string()) {
auto const& lhs_string = lhs_primitive.as_string();
auto const& rhs_string = rhs_primitive.as_string();
if (lhs_string.has_utf16_string() && rhs_string.has_utf16_string()) {
auto const& lhs_utf16_string = lhs_string.utf16_string();
auto const& rhs_utf16_string = rhs_string.utf16_string();
Vector<u16> combined;
combined.ensure_capacity(lhs_utf16_string.length_in_code_units() + rhs_utf16_string.length_in_code_units());
combined.extend(lhs_utf16_string.string());
combined.extend(rhs_utf16_string.string());
return js_string(vm.heap(), Utf16String(move(combined)));
}
}
if (lhs_primitive.is_string() || rhs_primitive.is_string()) {
auto lhs_string = lhs_primitive.to_string(global_object);
if (vm.exception())