perf(formatter_core): stage IR buffers on the heap to reduce arena memory by leaysgur · Pull Request #24582 · oxc-project/oxc

leaysgur · 2026-07-16T03:23:52Z

Adds HeapVecBuffer to oxc_formatter_core: a staging twin of VecBuffer that grows on a pooled heap vector and moves the finished sequence into the arena as one exactly-sized allocation.

Converted JS formatter call sites: Formatter::intern, BestFitting variant construction, and the three grouped-call-argument variant builders.

The other formatters would automatically benefit from this as well, and there was no need to make any individual changes.

TIL: antd.js is a bundled file and is not intended for general formatting.

leaysgur · 2026-07-16T03:24:07Z

perf(formatter): stage assignment-like left hand side on the heap #24613 : 3 dependent PRs (#24631 , #24754 , #24793 )
perf(formatter): accumulate JSX child-list builders on the heap #24585
perf(formatter_core): share one thread-cached scratch vector across staging buffers #24583
perf(formatter_core): stage IR buffers on the heap to reduce arena memory #24582 👈 (View in Graphite)
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codspeed-hq · 2026-07-16T03:28:17Z

Merging this PR will improve performance by 4.94%

⚠️

Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
✅ 55 untouched benchmarks
⏩ 19 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	Simulation	`formatter[types.ts]`	12.5 ms	11.8 ms	+6.17%
⚡	Simulation	`formatter[App.tsx]`	47.4 ms	45.7 ms	+3.72%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory (d7cedab) with main (8eb9eca)²}

19 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
No successful run was found on main (7c46346) during the generation of this report, so 8eb9eca was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

oxc-guard · 2026-07-16T03:35:45Z

Oxfmt Ecosystem CI

suite	oxfmt@latest	main	refs/pull/24582/head branch
cnpm/cnpmcore	❌	✅	✅
fuma-nama/fumadocs	✅	✅	✅
vercel/turborepo	✅	✅	✅
eggjs/egg	❌	✅	✅
monkeytypegame/monkeytype	❌	✅	✅
AmanVarshney01/create-better-t-stack	✅	✅	✅
formatjs/formatjs	❌	✅	✅
actualbudget/actual	❌	✅	✅
fastify/fastify-vite	❌	✅	✅
vuejs/pinia	❌	✅	✅
getsentry/sentry-javascript	❌	✅	✅
tale/headplane	❌	✅	✅
openclaw/openclaw	❌	✅	✅
huggingface/huggingface.js	❌	✅	✅
cloudflare/agents	❌	✅	✅
rolldown/rolldown	❌	✅	✅
npmx-dev/npmx.dev	❌	✅	✅
lichess-org/lila	❌	✅	✅
aidenybai/react-grab	✅	✅	✅
vuejs/core	❌	✅	✅
mastodon/mastodon	✅	✅	✅
cloudflare/workers-sdk	❌	✅	✅
dyad-sh/dyad	❌	✅	✅
mantinedev/mantine	❌	✅	✅
Comfy-Org/ComfyUI_frontend	⚠️	✅	✅

💥 = panic, ⚠️ = error e.g. parse error (main/branch columns: only new errors), ❌ = diff or exit code mismatch, 🟨 = differs from oxfmt@latest (merged-but-unreleased changes)

graphite-app · 2026-07-22T06:31:29Z

Merge activity

Jul 22, 6:31 AM UTC: leaysgur added this pull request to the Graphite merge queue.
Jul 22, 6:36 AM UTC: Merged by the Graphite merge queue.

…mory (#24582) Part of #24558 Adds `HeapVecBuffer` to `oxc_formatter_core`: a staging twin of `VecBuffer` that grows on a pooled heap vector and moves the finished sequence into the arena as one exactly-sized allocation. Converted JS formatter call sites: `Formatter::intern`, `BestFitting` variant construction, and the three grouped-call-argument variant builders. The other formatters would automatically benefit from this as well, and there was no need to make any individual changes. --- TIL: `antd.js` is a bundled file and is not intended for general formatting.

The JSX child-list builders (`MultilineBuilder` / `FlatBuilder` in `child_list.rs`) were the last IR staging path still growing vectors in the arena. They accumulate elements across the whole child-list loop while arbitrary child content is formatted in between, so every growth stranded its old allocation (the same pattern #24582 removed from `intern` / `BestFitting` / grouped arguments). They can't use `HeapVecBuffer`: the flat and multiline builders write *alternately* for each child, which would interleave their segments in the shared scratch vector and break its LIFO watermark discipline. The thread-local cache behind it has no such requirement though. So each builder now checks out its own `ScratchBuffer` and writes into it through a small private `Buffer` adapter (`ChildListBuffer`); the finished result reaches the arena as one exactly-sized copy via the new `Formatter::intern_elements`, which clears the source so its capacity returns to the cache on drop. Now arena reallocs for `RadixUIAdoptionSection.jsx` is 0.

leaysgur requested a review from overlookmotel as a code owner July 16, 2026 03:23

github-actions Bot added the A-formatter Area - Formatter label Jul 16, 2026

leaysgur added the run-oxfmt-ecosystem-ci label Jul 16, 2026

oxc-guard Bot removed the run-oxfmt-ecosystem-ci label Jul 16, 2026

leaysgur force-pushed the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch from bf07076 to aa1921c Compare July 16, 2026 05:04

This was referenced Jul 16, 2026

perf(formatter_core): share one thread-cached scratch vector across staging buffers #24583

Merged

perf(formatter): accumulate JSX child-list builders on the heap #24585

Merged

leaysgur force-pushed the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch from aa1921c to 12a1158 Compare July 17, 2026 06:03

This was referenced Jul 17, 2026

perf(formatter): stage assignment-like left hand side on the heap #24613

Merged

perf(formatter_core): pack FormatElement 24B to 16B #24631

Closed

formatter: IR build allocates 45-80x the source size in the arena (525 MB for antd.js) #24558

Open

leaysgur force-pushed the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch from 12a1158 to 8039aca Compare July 21, 2026 06:11

leaysgur mentioned this pull request Jul 21, 2026

perf(formatter_core): take assignment staging from a state-owned spare slot #24754

Closed

leaysgur force-pushed the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch 2 times, most recently from c880bce to d7cedab Compare July 22, 2026 05:04

This was referenced Jul 22, 2026

perf(formatter_core): bound the thread-local scratch cache #24793

Merged

refactor(formatter_core): drop unused HeapVecBuffer methods #24796

Merged

graphite-app Bot added the 0-merge Merge with Graphite Merge Queue label Jul 22, 2026

graphite-app Bot force-pushed the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch from d7cedab to c191f51 Compare July 22, 2026 06:32

graphite-app Bot merged commit c191f51 into main Jul 22, 2026
30 checks passed

graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Jul 22, 2026

graphite-app Bot deleted the 07-16-perf_formatter_core_stage_ir_buffers_on_the_heap_to_reduce_arena_memory branch July 22, 2026 06:36

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perf(formatter_core): stage IR buffers on the heap to reduce arena memory#24582

perf(formatter_core): stage IR buffers on the heap to reduce arena memory#24582
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