Perf: Defer per-row reactive allocations [perf-eval]

[jlukic]

Isolated perf eval; close after CI.

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Project	Deployment	Actions	Updated (UTC)
semantic-next	Ready	Preview, Comment	May 22, 2026 7:41pm

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Project	Deployment	Actions	Updated (UTC)
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[semantic-performance-bot]

🟡 Mixed (mostly faster) for f139dec on Benchmark Suite 📊

Base: main · Action: #26308265750 · Raw: bench-report.json

^{Perf: Defer per-row reactive allocations [perf-eval]}

Warning

This PR improves ✅ 7 tests while regressing on ❌ 6 tests.

✅ 7 faster · ❌ 6 slower · 🔍 26 unsure · ⚪ 28 no change · 🏆 1 new peak · 📜 2 reopened

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✅ Faster (7)

Metrics where this PR confidently improved performance compared to main.

metric	Improvement
krausest:remove-row-back-100	-43% (10ms) 🌟
todo:remove-middle-100	-31% (5ms) ⭐
krausest:update-10th-50	-31% (10ms) ⭐
todo:toggle-middle-100	-26% (3ms) ⭐
krausest:replace-1k	-10% (10ms)
krausest:select-40	-4% (2ms)
krausest:clear-10k	-4% (5ms)

❌ Slower (6)

Metrics where this PR confidently regressed performance compared to main.

metric	Regression
krausest:remove-row-middle-20	+95% (5ms) 🚨
hydrate:helper-100-mount	+48% (14ms) ‼️
krausest:remove-row-front-20	+28% (4ms) ❗
template:each-mount-1000	+5% (3ms)
hydrate:helper-100-state-change-1k	+5% (0ms)
template:subtemplate-helpers-heavy-100x500	+3% (1ms)

🏆 New peaks (1)

These metrics hit a new best on this PR. The most recent candidate is usually the cause.

metric	improvement	prior peak	likely candidates
krausest:select-40	4%	46a0764	—

📜 Regressions from peak (2)

These metrics were faster on an earlier push to this PR. The most recent candidate is usually where to look.

metric	regression	prior peak	likely candidates
krausest:remove-row-middle-20	53%	46a0764	—
todo:toggle-middle-100	8%	46a0764	—

⚪ No Change (28)

Metrics where this PR measured within ±2% of main — no meaningful performance change detected.

metric	Change
renderer-micros:build-html-string-10k	-1.2% – +1.1%
todo:clear-completed-250	-0.8% – +1.8%
signal:computed-chain-10x60k	-0.1% – +1.7%
signal:computed-unobserved-200x500	-1.9% – +0.5%
krausest:create-10k	-0.3% – +0.6%
krausest:create-1k	-1.8% – +0.3%
hydrate:each-100	-2.0% – -0.2%
hydrate:each-100-mount	-0.8% – +1.1%
todo:edit-start-10	-1.3% – +0.4%
renderer-micros:expr-js-10k	-1.3% – +1.3%
renderer-micros:expr-lisp-50k	-0.9% – +1.1%
renderer-micros:expr-simple-100k	-1.3% – +1.4%
todo:filter-cycle-20	-0.8% – +0.5%
signal:reaction-coalesce-400x100	-1.7% – +1.1%
signal:reaction-dep-diff-45k	-0.9% – +1.8%
signal:reaction-flush-noop-5m	-1.6% – +0.4%
signal:reactive-fanout-500x1200	-1.1% – +0.6%
signal:reactive-list-replace-1000x1000	-0.5% – +0.5%
signal:reactive-multi-read-5x160k	-1.1% – +0.3%
signal:reactive-stable-deps-3reads-5000x100	-1.4% – -0.1%
signal:reactive-stable-fanout-5000x100	-1.4% – +0.5%
signal:set-same-10m	-1.4% – +0.9%
template:snippet-args-per-key-100x500	-1.1% – +1.1%
template:subtemplate-data-blob-100	-0.7% – +0.9%
template:subtemplate-helpers-light-100x500	-0.8% – +1.9%
template:subtemplate-reactive-data-100x500	-1.9% – +0.5%
template:subtemplate-shorthand-props-100x500	-1.5% – +1.0%
todo:toggle-all-200	-0.4% – +0.5%

🔍 Unsure (26)

Too Fast to Measure Precisely (26)

On benches this short, OS jitter, GC, and JIT pauses drown out anything under 4%. Bigger changes than that still show up.

metric	Change	Test Time	Expected Noise
template:active-indicator-200	-2.4% – +1.7%	~32ms	±6%
template:active-indicator-nested-200	+1.3% – +6.2%	~17ms	±7%
todo:add-20	+1.1% – +2.9%	~8ms	±3%
krausest:append-1k	-2.3% – +1.9%	~84ms	±5%
todo:bulk-add-500	-2.2% – -0.6%	~200ms	±2%
signal:computed-subscribe-unsubscribe-10k	-3.4% – +2.0%	~8ms	±9%
renderer-micros:dom-walker-1000x15	-2.3% – +0.0%	~50ms	±5%
todo:edit-cycle-5	-1.3% – +2.2%	~62ms	±4%
signal:flush-fanout-allocation-1000x500	-2.6% – -0.5%	~79ms	±3%
signal:reactive-list-filter-1000x300	-2.1% – +4.1%	~5ms	±10%
signal:reactive-push-2000x20	-3.0% – +0.6%	~36ms	±5%
signal:reactive-set-index-300	-8.1% – +3.7%	~2ms	±18%
signal:reactive-set-property-by-id-200	-8.6% – -1.8%	~3ms	±11%
todo:remove-50-back	-5.1% – +3.8%	~3ms	±11%
todo:remove-50-front	-0.9% – +2.9%	~3ms	±6%
todo:remove-50-middle	-8.5% – -0.6%	~4ms	±6%
todo:remove-first-100	-2.7% – +2.7%	~13ms	±8%
todo:remove-last-100	-5.8% – +10.0%	~11ms	±20%
todo:rename-500	-1.3% – +7.8%	~17ms	±12%
template:snippet-in-subtemplate-100x1k	-3.9% – +0.8%	~21ms	±7%
template:stable-ref-mutate-500	-5.3% – +0.8%	~12ms	±10%
signal:sub-unsub-100k	-0.0% – +4.1%	~29ms	±5%
krausest:swap-rows-20	-4.8% – -1.9%	~117ms	±4%
todo:toggle-100	-3.5% – +4.3%	~7ms	±10%
todo:toggle-first-100	-1.5% – +5.5%	~13ms	±9%
todo:toggle-last-100	-0.2% – +6.9%	~12ms	±9%

📖 Bench glossary (67 metrics)

metric	what it tests
hydrate:each-100	Reassigns the items of a hydrated 1000-item list to a fresh array with the same keys and data.
hydrate:each-100-mount	Hydrates a server-rendered 1000-item list and waits for it to become interactive without re-rendering.
hydrate:helper-100-mount	Hydrates a 1000-item list where each item calls a helper that reads state shared across the list.
hydrate:helper-100-state-change-1k	Walks the shared activeID across every item in a hydrated 1000-item list so two items repaint per cycle.
krausest:append-1k	Appends 1000 new rows onto an existing 1000-row table.
krausest:clear-10k	Clears a 10000-row table back to empty in a single operation.
krausest:create-10k	Renders a fresh 10000-row table into an empty parent at ten times the create-1k scale.
krausest:create-1k	Renders a fresh 1000-row table into an empty parent.
krausest:remove-row-back-100	Removes the last row 100 times from a 1000-row table, with no other rows needing to move.
krausest:remove-row-front-20	Removes the first row 20 times from a 1000-row table, with all remaining rows sliding up each time.
krausest:remove-row-middle-20	Removes the middle row 20 times from a 1000-row table, with the rows below it sliding up each time.
krausest:replace-1k	Replaces 1000 rows with a fresh 1000-row set, diffing the keyed list against a populated table.
krausest:select-40	Highlights one row at a time across 40 rows so only the previous and newly highlighted rows update.
krausest:swap-rows-20	Swaps the second and second-to-last rows in a 1000-row table, repeated 20 times.
krausest:update-10th-50	Updates the label on every tenth row of a 1000-row table, looped 50 times to lift the work above noise.
renderer-micros:build-html-string-10k	Builds the HTML string for a realistic card AST 10000 times. Raw assembly throughput.
renderer-micros:dom-walker-1000x15	Runs bindMarkers across a 1000-node card fragment 15 times. TreeWalker pass and binding dispatch.
renderer-micros:expr-js-10k	Evaluates one arithmetic expression and one ternary 10000 times each. JS-eval hot path.
renderer-micros:expr-lisp-50k	Evaluates one Lisp-style helper call 50000 times. Parse-cache lookup and helper dispatch.
renderer-micros:expr-simple-100k	Evaluates one simple identifier and one dotted path 100000 times each. Property-lookup hot path.
signal:computed-chain-10x60k	Propagates a value change from root to leaf through a 10-deep chain of derived signals 60000 times.
signal:computed-subscribe-unsubscribe-10k	10000 create-computed + attach-observer + detach cycles. Lifecycle cost the refcount path must keep acceptable.
signal:computed-unobserved-200x500	200 unobserved computed signals, root updated 500 times. Measures the eager-recompute cost the refcount removes.
signal:flush-fanout-allocation-1000x500	500 subscribers fanout across 1000 flush cycles. Each flush spreads pendingReactions; tests per-flush allocation churn.
signal:reaction-coalesce-400x100	Sets one signal 100 times then flushes once across 400 bursts so 100 subscribers wake one time per burst.
signal:reaction-dep-diff-45k	Toggles which of two signals a subscriber reads across 45000 cycles. Per-run dep-set diffing.
signal:reaction-flush-noop-5m	Calls Reaction.flush() 5000000 times with no pending work. Scheduler dispatch overhead.
signal:reactive-fanout-500x1200	Fans out one signal's value change to 500 subscribers across 1200 successive updates.
signal:reactive-list-filter-1000x300	Changes a search-term signal 300 times, re-scanning a 1000-item list on each change.
signal:reactive-list-replace-1000x1000	Replaces a 1000-item list signal with a fresh 1000-item array and rescans it 1000 times.
signal:reactive-multi-read-5x160k	Changes five signals in turn for 32000 rounds with one subscriber reading all five.
signal:reactive-push-2000x20	Appends 20 items onto an empty list signal with a subscriber, across 2000 reset cycles.
signal:reactive-set-index-300	Replaces one item by index in a 1000-item list signal across 300 updates, with a subscriber.
signal:reactive-set-property-by-id-200	Finds an item by id and updates one field in a 1000-item list signal across 200 alternating updates.
signal:reactive-stable-deps-3reads-5000x100	5000 reactions × 3 signals × 100 cycles. Each run clears + re-adds 3 stable dep edges.
signal:reactive-stable-fanout-5000x100	5000 reactions × 1 signal × 100 invalidations. Per-run Set.delete + add on a stable dep edge.
signal:set-same-10m	Sets a signal to its current value 10000000 times. Exercises the no-op fast path when nothing changes.
signal:sub-unsub-100k	Creates and tears down a subscriber on one signal across 100000 cycles. Subscription churn cost.
template:active-indicator-200	Cycles selectedId across 200 list items. Only the previously and newly active items update their class.
template:active-indicator-nested-200	Cycles currentUrl through 50 leaf urls in a 5×10×4 nav. Only the previously and newly active leaves should update their…
template:each-mount-1000	Mounts a fresh 1000-item each block with five-field items so per-record allocation cost dominates the wall clock.
template:snippet-args-per-key-100x500	Mutates one snippet arg's source across 100 invocations, 500 cycles. Adjacent no-signal expressions stay quiet.
template:snippet-in-subtemplate-100x1k	Mutates one subtemplate prop's source across 25 cards each invoking 4 inner snippets, 1000 cycles. Snippet bodies shoul…
template:stable-ref-mutate-500	Replaces one item by index in a 500-item list across 100 cycles. Only that item's expressions re-render.
template:subtemplate-data-blob-100	Mutates one field inside data=expression on 100 children. Every child re-renders by design.
template:subtemplate-helpers-heavy-100x500	100 subtemplates, 4 inner bindings where three call helpers shaped like userland reality — Intl.NumberFormat, Array.fin…
template:subtemplate-helpers-light-100x500	100 subtemplates, 4 inner bindings each calling formatDate / classIf / capitalize, 500 cycles. Mutates one source signa…
template:subtemplate-reactive-data-100x500	Mutates one verbose reactiveData field across 100 child subtemplates, 500 cycles. Only the changed field re-evaluates.
template:subtemplate-shorthand-props-100x500	Mutates one shorthand prop's source across 100 child subtemplates, 500 cycles. Only that prop re-evaluates.
todo:add-20	Appends 20 todo items one at a time, like a user typing entries in a row.
todo:bulk-add-500	Renders 500 todo items added at once from a single data load.
todo:clear-completed-250	Clears 250 completed items from a 500-item list in one action, like clicking clear completed.
todo:edit-cycle-5	Runs 5 full edit-then-save cycles on different items, like editing a row and saving it.
todo:edit-start-10	Enters edit mode on 10 different items in a row, like double-clicking each one.
todo:filter-cycle-20	Cycles through active, completed, and all filters 20 times on a 100-item list.
todo:remove-50-back	Deletes 50 items from the end of a 100-item list, one click at a time.
todo:remove-50-front	Deletes 50 items from the front of a 100-item list, one click at a time.
todo:remove-50-middle	Deletes 50 items from the middle of a 100-item list, one click at a time.
todo:remove-first-100	Deletes the first item 100 times from a 200-item list, with remaining items moving up each time.
todo:remove-last-100	Deletes the last item 100 times from a 200-item list, with no other items needing to move.
todo:remove-middle-100	Deletes the middle item 100 times from a 200-item list, walking halfway through to find each target.
todo:rename-500	Renames items in a 100-item list 500 times via single-field setProperty without editingId co-fires.
todo:toggle-100	Cycles through the first 10 items 10 times each, like a user toggling items repeatedly down a list.
todo:toggle-all-200	Toggles all 100 items completed and back across 200 cycles via the master checkbox.
todo:toggle-first-100	Toggles the first item in a 100-item list 100 times, alternating completed on and off.
todo:toggle-last-100	Toggles the last item in a 100-item list 100 times, alternating completed on and off.
todo:toggle-middle-100	Toggles a middle item in a 100-item list 100 times, alternating completed on and off.

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_{Sample size: 80 floor / 270 max · Noise floor: ±2% · Timeout: 3min · Wall-clock: 10m54s}