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LibJS: Cache the result of parsing time zone identifiers

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The result of parsing an identifier cannot change. It is not cheap to do
so, so let's cache the result.

This is hammered in a few test262 tests. On my machine, this reduces the
runtime of each test/staging/sm/Date/dst-offset-caching-{N}-of-8.js by
0.3 to 0.5 seconds. For example:

dst-offset-caching-1-of-8.js: Reduces from 1.2s -> 0.9s
dst-offset-caching-3-of-8.js: Reduces from 1.5s -> 1.1s
This commit is contained in:
Timothy Flynn 2026-02-18 12:55:34 -05:00 committed by Jelle Raaijmakers
parent 6e433f0d10
commit d1ed361239
2 changed files with 20 additions and 10 deletions
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28
Libraries/LibJS/Runtime/Temporal/TimeZone.cpp
View file

@ -244,7 +244,7 @@ ThrowCompletionOr<String> to_temporal_time_zone_identifier(VM& vm, StringView te
i64 get_offset_nanoseconds_for(String const& time_zone, Crypto::SignedBigInteger const& epoch_nanoseconds)
{
// 1. Let parseResult be ! ParseTimeZoneIdentifier(timeZone).
auto parse_result = parse_time_zone_identifier(time_zone);
auto const& parse_result = parse_time_zone_identifier(time_zone);
// 2. If parseResult.[[OffsetMinutes]] is not empty, return parseResult.[[OffsetMinutes]] × (60 × 10**9).
if (parse_result.offset_minutes.has_value())
@ -323,7 +323,7 @@ ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanosecon
Vector<Crypto::SignedBigInteger> possible_epoch_nanoseconds;
// 1. Let parseResult be ! ParseTimeZoneIdentifier(timeZone).
auto parse_result = parse_time_zone_identifier(time_zone);
auto const& parse_result = parse_time_zone_identifier(time_zone);
// 2. If parseResult.[[OffsetMinutes]] is not empty, then
if (parse_result.offset_minutes.has_value()) {
@ -421,9 +421,15 @@ bool time_zone_equals(StringView one, StringView two)
return false;
}
// OPTIMIZATION: The result of parsing a time zone identifier will not change, so we can cache the result.
static HashMap<String, ParsedTimeZoneIdentifier> s_time_zone_id_cache;
// 11.1.16 ParseTimeZoneIdentifier ( identifier ), https://tc39.es/proposal-temporal/#sec-parsetimezoneidentifier
ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM& vm, String const& identifier)
{
if (auto result = s_time_zone_id_cache.get(identifier); result.has_value())
return *result;
// 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, identifier);
@ -431,19 +437,23 @@ ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM& vm, S
if (!parse_result.has_value())
return vm.throw_completion<RangeError>(ErrorType::TemporalInvalidTimeZoneString, identifier);
return parse_time_zone_identifier(*parse_result);
auto result = parse_time_zone_identifier(*parse_result);
s_time_zone_id_cache.set(identifier, result);
return result;
}
// 11.1.16 ParseTimeZoneIdentifier ( identifier ), https://tc39.es/proposal-temporal/#sec-parsetimezoneidentifier
ParsedTimeZoneIdentifier parse_time_zone_identifier(String const& identifier)
ParsedTimeZoneIdentifier const& parse_time_zone_identifier(String const& identifier)
{
// OPTIMIZATION: Some callers can assume that parsing will succeed.
return s_time_zone_id_cache.ensure(identifier, [&]() {
// 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, identifier);
VERIFY(parse_result.has_value());
// 1. Let parseResult be ParseText(StringToCodePoints(identifier), TimeZoneIdentifier).
auto parse_result = parse_iso8601(Production::TimeZoneIdentifier, identifier);
VERIFY(parse_result.has_value());
return parse_time_zone_identifier(*parse_result);
return parse_time_zone_identifier(*parse_result);
});
}
// 11.1.16 ParseTimeZoneIdentifier ( identifier ), https://tc39.es/proposal-temporal/#sec-parsetimezoneidentifier

2
Libraries/LibJS/Runtime/Temporal/TimeZone.h
View file

@ -35,7 +35,7 @@ ThrowCompletionOr<Vector<Crypto::SignedBigInteger>> get_possible_epoch_nanosecon
ThrowCompletionOr<Crypto::SignedBigInteger> get_start_of_day(VM&, String const& time_zone, ISODate);
bool time_zone_equals(StringView one, StringView two);
ThrowCompletionOr<ParsedTimeZoneIdentifier> parse_time_zone_identifier(VM&, String const& identifier);
ParsedTimeZoneIdentifier parse_time_zone_identifier(String const& identifier);
ParsedTimeZoneIdentifier const& parse_time_zone_identifier(String const& identifier);
ParsedTimeZoneIdentifier parse_time_zone_identifier(ParseResult const&);
}