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[JSC] Temporal is 2.5× faster: JIT intrinsics, a sort fast path, cached options and time zone offsets - #901
A 272-row benchmark (62 cases, 8 time zones) compares each Temporal operation with the equivalent Date code. On main, Temporal lost to Date on 45 rows. The costs, by area:
No JIT support.Temporal.Instant.compare, equals and epochMilliseconds were C++ host calls; Date has DFG/FTL intrinsics for the same work. a < b took 11.0 ns (Date 4.1 ns).
Sorting.arr.sort(Temporal.Instant.compare) went through the generic comparator path for every pair: 156 µs for 1000 instants, against 78 µs for 1000 Dates.
Options bags. Every { smallestUnit, roundingMode, ... } read did a full property lookup for each option.
Time zones. Every ZonedDateTime field read, and every toZonedDateTimeISO(tz), asked ICU for the offset again (TimeZoneICUBridge.cpp). Reading the wall-clock fields in America/New_York took 852 ns.
Arithmetic. Int128 division where int64 suffices, loop-based DifferenceISODate, and CreateTemporalDuration re-validating results already known to be valid. PlainDate.until for whole months took 153 ns.
Fix
DFG/FTL intrinsics for compare/equals on Instant, ZonedDateTime, PlainDate, PlainDateTime and PlainTime, for Instant/ZonedDateTimeepochMilliseconds, and for the Duration field getters.
New nodes TemporalCompare, TemporalEquals and TemporalGetNumber, with one shared TemporalIntrinsic that dispatches on the native function pointer, so the Intrinsic enum gains one value.
Operands are guarded with CheckJSCast. The fields read are const (immutable B3 heaps).
Inline epochMilliseconds uses an exact multiply-high division (static_asserts bound the error), with the C++ operation as the slow path.
Array.prototype.sort fast path when the comparator is one of the native Temporal compare functions and every element has the class's slots. It sorts the slots with arrayStableSort, and anything else falls back to the generic path. For native comparators the call count and order are unobservable, so the result is spec-identical.
Options reads
A shape cache for options bags (TemporalPropertyShapeCache, in JSGlobalObject::RareData), keyed on Weak<Structure> plus the Object.prototype structure.
Dictionaries and object-valued options always take the live path, so Get order and Proxy/getter behaviour are unchanged.
One GetOption implementation (intlOptionFromValue/intlStringOptionFromValue) is shared with Intl.
Time zones
A per-zone cache of offset periods (up to 256 per zone, with eviction) answers GetOffsetNanosecondsFor, GetPossibleEpochNanoseconds and transitions without ICU on a hit.
ZonedDateTime computes its ISO date-time once, on first use.
Time zone identifiers are found through a case-insensitive index.
Arithmetic
int64 fast paths for flooring, rounding and duration balancing.
A closed-form DifferenceISODate.
CreateTemporalDuration validation is skipped where the result already satisfies IsValidDuration, with an ASSERT at each site.
ISO strings are built into a fixed buffer.
Spec fix:PlainDateTime.from(plainDate) now throws a RangeError for dates outside the PlainDateTime limits, as ISODateTimeWithinLimits requires.
Verified
5 new JSTests/stress tests (JIT intrinsics, sort, options cache, offset cache, limits). All pass in the 17 run-jsc-stress-tests configurations. On main, only the limits test fails, which is the spec fix.
test262 Temporal (13,264 tests): failures unchanged at 5. These are pre-existing and also fail on main.
45 differential scripts (fuzzers across 455 time zones, option-order probes with Proxies, Int128 boundary sweeps) give byte-identical output on main and this branch.
In Bun, a 268,288-comparison check of every benchmark case gives identical output to the Date code on both builds.
macOS arm64, Bun 179664ea8 built from source with ThinLTO against WebKit main (680ef47) and this branch, identical flags; time per operation, fastest of 3 interleaved runs:
benchmark
Date
Temporal, main
Temporal, this branch
Temporal.Instant.compare(a, b) < 0
4.1 ns
11.0 ns
4.9 ns
a.equals(b)
4.5 ns
9.7 ns
4.5 ns
sort 1000 instants with Temporal.Instant.compare
78.4 µs
156.2 µs
25.3 µs
sort 1000 dates with Temporal.PlainDate.compare
75.2 µs
188.8 µs
23.1 µs
wall-clock fields in America/New_York
939.5 ns
851.8 ns
84.7 ns
calendar days between, in America/New_York
1.7 µs
402.8 ns
33.2 ns
withTimeZone
967.0 ns
463.5 ns
74.3 ns
start of day in America/New_York
2.9 µs
268.3 ns
50.1 ns
whole months between dates
7.1 ns
153.0 ns
42.9 ns
add 90 minutes (exact)
10.3 ns
76.2 ns
29.9 ns
round to nearest 15 minutes
8.6 ns
51.6 ns
37.1 ns
group 1000 events by local day
415.8 µs
257.5 µs
109.9 µs
Across all 272 rows, Temporal is 2.48× faster (geometric mean). Temporal ÷ Date goes from 0.34 to 0.135, and Temporal now beats Date on 223 rows (was 210) and loses on 31 (was 45). One row is more than 5% slower than on main: next DST transition in Asia/Jerusalem, 641 → 684 ns (0.94×), where Date's own time drifted 4% between the runs.
Reproduce
benchmark.ts is the benchmark above in one file: 62 cases, 8 time zones, seeded inputs, mitata.
bun add mitata
<bun built against main> benchmark.ts
<bun built against this branch> benchmark.ts
Downsides
The Intrinsic enum (uint8_t) now has one value of headroom left.
Each JSGlobalObject that uses Temporal options allocates a small shape cache, and each time zone that is used keeps up to 256 cached offset periods.
The x86-64 DFG epochMilliseconds path follows compileArithDiv's register handling and compiles for x86-64, but has only run on arm64 here. RISC-V always calls the operation.
Per-group results (geometric mean of Temporal speedup; Temporal ÷ Date before → after)
The pull request adds Temporal-specific DFG and FTL operations, updates Temporal runtime conversions, arithmetic, option handling, formatting, sorting, and time-zone caching, and adds stress tests for these paths.
Changes
Temporal JIT operations
Layer / File(s)
Summary
Operation model and compiler integration Source/JavaScriptCore/b3/*, Source/JavaScriptCore/dfg/*, Source/JavaScriptCore/ftl/*
The DFG adds Temporal operation nodes and recognizes supported comparison, equality, and getter calls. DFG and FTL add analysis, safety, lowering, and runtime fallback paths.
New tests exercise Temporal getters, comparison and equality, receiver and conversion behavior, polymorphic calls, and boundary values in optimized code.
Temporal runtime behavior
Layer / File(s)
Summary
Option reading and caching Source/JavaScriptCore/runtime/TemporalObject.*, JSGlobalObject.*, IntlObject.*, CommonIdentifiers.h, TemporalDuration.cpp, JSTests/stress/temporal-options-cache.js
Temporal option parsing uses shared value converters and a per-global property-shape cache. The tests cover property access order, object mutations, exceptions, and cross-realm inputs.
Date and date-time operations resolve ISO slots and calendar IDs for comparison, equality, and differences. PlainTime and year-month operations use direct conversion helpers. Tests cover date differences and representable limits.
Duration, instant, and ISO arithmetic Source/JavaScriptCore/runtime/TemporalDuration*, TemporalInstant*, ISO8601.*, FractionToDouble.cpp, temporal/core/DurationArithmetic.*, ISOArithmetic.cpp, Rounding.cpp
Duration operations add integer fast paths and use shared comparison conversion. Instant comparisons use exact-time values. ISO date arithmetic and rounding use integer calculations in covered fast paths.
Formatting and sorting Source/JavaScriptCore/runtime/ISO8601.*, ArrayPrototype.cpp, TemporalObject.*, JSTests/stress/temporal-iso-string-formatting.js, JSTests/stress/temporal-sort-with-compare-function.js
ISO formatting uses a fixed-buffer builder. Array sorting can use a stable Temporal-specific path for matching values, with the existing comparator path as fallback.
Temporal time-zone handling
Layer / File(s)
Summary
Offset caching and resolution Source/JavaScriptCore/runtime/temporal/core/TimeZoneICUBridge.cpp, IntlObject.cpp, TemporalObject.*, JSTests/stress/temporal-time-zone-offset-cache.js
Named time zones cache offset periods and use the cache for offset and local-time resolution when available. ICU remains a fallback, and UTC-equivalent named zones use zero-offset handling.
ZonedDateTime formatting and comparison Source/JavaScriptCore/runtime/TemporalZonedDateTime.*, JSTests/stress/temporal-iso-string-formatting.js
ZonedDateTime caches local date-time data and reuses it during formatting when rounding does not change the exact time. Time-zone parsing and option handling use shared helpers.
Possibly related PRs
oven-sh/WebKit#897: It changes legacy time-zone alias mapping and TimeZone::toICUString, which share the named-time-zone and ICU identifier path used here.
Suggested reviewers: hyjorc1, cdumez
Priority: Normal
Merge Risk: Low · up to d97c4
The Temporal performance changes show no confirmed correctness problem in the reviewed code. Several new stress tests use hard-coded iteration counts that could exceed the test time budget in slow configurations, and one sort test does not vary a duration field as intended. Both are bounded test-maintenance items.
Pre-merge checks: 3 · 1
Failed checks: 1 warning
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Reformat the description to the WebKit template. Add a bug title and a Bugzilla link (https://bugs.webkit.org/show_bug.cgi?id=#####). Add the 'Reviewed by' line, a short explanation in the template format, and a ChangeLog-style list of chan…
Passed checks: 3 passed
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The title names the main theme of the changeset: JSC Temporal performance work covering JIT intrinsics, a sort fast path, cached options, and time zone offset caching. The changes in the raw summary m…
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Full details: Title check
Explanation
The title names the main theme of the changeset: JSC Temporal performance work covering JIT intrinsics, a sort fast path, cached options, and time zone offset caching. The changes in the raw summary match each element, including DFG/FTL nodes, the Array.prototype.sort hook, TemporalPropertyShapeCache, and the ICU offset cache. The title is a single sentence, but it is long (101 characters) and contains a specific speedup claim. That claim is not verifiable from the diff alone, but it does not make the title unrelated.
Full details: Description check
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The description covers the problem, the fix, verification, benchmark results, and downsides, so the content is substantive. It does not follow the WebKit template. It has no Bugzilla bug link or title line, no 'Reviewed by' line, and no changelog-style list of changed paths with function names. The description also points to a benchmark attachment and a linked benchmark file that the reviewer cannot verify from the diff.
Resolution
Reformat the description to the WebKit template. Add a bug title and a Bugzilla link (https://bugs.webkit.org/show_bug.cgi?id=#####). Add the 'Reviewed by' line, a short explanation in the template format, and a ChangeLog-style list of changed paths with their functions or classes. Keep the performance results and the verification notes below that structure.
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Actionable comments posted: 6
🪄 Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix review comments
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Inline comments:
Review comments at @JSTests/stress/temporal-jit-duration-getters.js:
- Line 142: Replace the hard-coded 2000 loop bound in the stress-test loop with
testLoopCount so the iteration count follows the configured test setting.
Review comments at @JSTests/stress/temporal-jit-instant-intrinsics.js:
- Line 72: Replace the three fixed 2000 loop bounds in temporal JIT test flows
with the existing iterations value derived from testLoopCount, preserving each
loop’s body and behavior.
Review comments at @JSTests/stress/temporal-jit-plaindate-intrinsics.js:
- Line 151: Replace the hard-coded iteration limit in the loop with the
repository’s testLoopCount value so jsc configurations control the test’s
iteration count.
Review comments at @JSTests/stress/temporal-options-cache.js:
- Around line 318-330: Update the “Shapes that die between calls” loop to use
testLoopCount instead of fixed iteration counts, and reduce the number of
fullGC() calls while retaining a collection between the warm shape and
fresh-shape checks.
Review comments at @JSTests/stress/temporal-sort-with-compare-function.js:
- Line 62: Update the `durations` mapping so `hours` is derived from a varying
part of `ms` rather than `ms % 1000`, which is always zero for these values.
Preserve the existing positive and negative hour signs in the two branches and
keep the other duration fields unchanged.
Review comments at @JSTests/stress/temporal-time-zone-offset-cache.js:
- Around line 127-142: Update the outer round loop in the stress test to use the
JSTests iteration count, such as testLoopCount or wasmTestLoopCount, instead of
the fixed repeat count. Keep the sweep and revisit checks needed for
cache-eviction coverage, and adjust the repeated workload only as needed to stay
within the 200 ms limit across configurations.
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…metic in int64 where it fits
Options bags are read through a per-global shape cache; dictionaries and object values take the live path, so Get order is unchanged.
Flooring, rounding, duration balancing and DifferenceISODate use int64 or closed forms, and results known to satisfy IsValidDuration skip the re-check.
ISO strings are built into a fixed buffer. PlainDateTime.from(plainDate) now throws a RangeError outside the PlainDateTime limits.
…ate-time
Each time zone keeps up to 256 offset periods, so GetOffsetNanosecondsFor, GetPossibleEpochNanoseconds and transitions skip ICU on a hit.
A ZonedDateTime computes its ISO date-time once, and time zone identifiers are found through a case-insensitive index.
… the comparator is a Temporal compare function
When every element has the class's slots, the array is sorted with arrayStableSort on those slots; anything else takes the generic path.
For a native comparator the call count and order are unobservable, so the result is the same.
…nds and Duration getters
New TemporalCompare, TemporalEquals and TemporalGetNumber nodes, behind one TemporalIntrinsic that dispatches on the native function.
Operands are checked with CheckJSCast and only const fields are read; epochMilliseconds divides inline with an exact multiply-high.
…yle of JSTests/stress
Five tests remain: the DFG/FTL intrinsics, the sort fast path, the options cache, the offset cache, and the spec fix.
The ISO formatting and PlainDate difference tests are gone; they covered rewrites that keep behavior, which test262
covers. Loops use testLoopCount, and each test runs under 70 ms in every run-jsc-stress-tests configuration.
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Problem
Datecode. Onmain, Temporal lost toDateon 45 rows. The costs, by area:Temporal.Instant.compare,equalsandepochMillisecondswere C++ host calls;Datehas DFG/FTL intrinsics for the same work.a < btook 11.0 ns (Date 4.1 ns).arr.sort(Temporal.Instant.compare)went through the generic comparator path for every pair: 156 µs for 1000 instants, against 78 µs for 1000Dates.{ smallestUnit, roundingMode, ... }read did a full property lookup for each option.toZonedDateTimeISO(tz), asked ICU for the offset again (TimeZoneICUBridge.cpp). Reading the wall-clock fields in America/New_York took 852 ns.DifferenceISODate, andCreateTemporalDurationre-validating results already known to be valid.PlainDate.untilfor whole months took 153 ns.Fix
compare/equalson Instant, ZonedDateTime, PlainDate, PlainDateTime and PlainTime, forInstant/ZonedDateTimeepochMilliseconds, and for the Duration field getters.TemporalCompare,TemporalEqualsandTemporalGetNumber, with one sharedTemporalIntrinsicthat dispatches on the native function pointer, so theIntrinsicenum gains one value.CheckJSCast. The fields read areconst(immutable B3 heaps).epochMillisecondsuses an exact multiply-high division (static_asserts bound the error), with the C++ operation as the slow path.Array.prototype.sortfast path when the comparator is one of the native Temporalcomparefunctions and every element has the class's slots. It sorts the slots witharrayStableSort, and anything else falls back to the generic path. For native comparators the call count and order are unobservable, so the result is spec-identical.TemporalPropertyShapeCache, inJSGlobalObject::RareData), keyed onWeak<Structure>plus the Object.prototype structure.intlOptionFromValue/intlStringOptionFromValue) is shared with Intl.GetOffsetNanosecondsFor,GetPossibleEpochNanosecondsand transitions without ICU on a hit.DifferenceISODate.CreateTemporalDurationvalidation is skipped where the result already satisfiesIsValidDuration, with anASSERTat each site.PlainDateTime.from(plainDate)now throws a RangeError for dates outside the PlainDateTime limits, as ISODateTimeWithinLimits requires.JSTests/stresstests (JIT intrinsics, sort, options cache, offset cache, limits). All pass in the 17run-jsc-stress-testsconfigurations. Onmain, only the limits test fails, which is the spec fix.main.mainand this branch.Datecode on both builds.macOS arm64, Bun 179664ea8 built from source with ThinLTO against WebKit
main(680ef47) and this branch, identical flags; time per operation, fastest of 3 interleaved runs:mainTemporal.Instant.compare(a, b) < 0a.equals(b)Temporal.Instant.compareTemporal.PlainDate.comparewithTimeZoneAcross all 272 rows, Temporal is 2.48× faster (geometric mean). Temporal ÷ Date goes from 0.34 to 0.135, and Temporal now beats
Dateon 223 rows (was 210) and loses on 31 (was 45). One row is more than 5% slower than onmain:next DST transitionin Asia/Jerusalem, 641 → 684 ns (0.94×), whereDate's own time drifted 4% between the runs.Reproduce
benchmark.tsis the benchmark above in one file: 62 cases, 8 time zones, seeded inputs, mitata.Downsides
Intrinsicenum (uint8_t) now has one value of headroom left.epochMillisecondspath followscompileArithDiv's register handling and compiles for x86-64, but has only run on arm64 here. RISC-V always calls the operation.Per-group results (geometric mean of Temporal speedup; Temporal ÷ Date before → after)
main