perf(minifier): drop per-call buffers in try_fold_concat by Dunqing · Pull Request #22596 · oxc-project/oxc

Dunqing · 2026-05-19T15:04:48Z

Summary

When the minifier folds .concat() calls into template literals via try_fold_concat in peephole/replace_known_methods.rs, the original implementation built two short-lived intermediate buffers per call:

quasi_strs: Vec<Cow<'a, str>> — fresh std::Vec allocation per call.
A String inside each Cow::Owned — created when Cow::to_mut() cloned a Borrowed into an Owned, then grown via doubling as more arg strings were pushed in.

For files with many .concat() calls — common in bundled ES5 libraries where template literals weren't available — both structures were freshly allocated thousands of times per minify, with the String growing via doubling each time.

This PR replaces those per-call buffers with a single reusable scratch String held on MinifierState, and constructs TemplateElement AST nodes directly into the arena Vec as args are drained. The intermediate Vec<Cow<'a, str>> is gone entirely. After the first few folds the scratch's capacity stabilizes and subsequent folds are amortized zero std-heap allocs.

The state machine simplifies in the process: the pushed_quasi: bool flag is gone. Its invariant ("scratch holds an in-progress quasi") is naturally maintained because every expression flush clears the scratch, so a back-to-back expression's flush produces the required empty separator quasi without a branch.

Allocation impact

cargo allocs, allocs_minifier.snap (baseline = parent commit, after resolve-refs and var-hoist landed):

File	Size	Sys allocs before	Sys allocs after	Sys reallocs before	Sys reallocs after
`antd.js`	6.69 MB ES5	4,652	3,084 (`−1,568`, `−33.7%`)	1,622	53 (`−1,569`)
Other tracked files	various	unchanged	unchanged	unchanged	unchanged

Only antd.js shows a change because it's the only tracked file that exercises .concat() folding heavily. ES5 bundled code uses .concat() instead of template literals; antd.js has thousands of these.

The headline Sys reallocs improvement (1,622 → 53) comes from eliminating the per-call String doubling. The headline Sys allocs improvement (4,652 → 3,084) comes from eliminating the per-call Vec<Cow<'a, str>> allocation.

Commits

This PR contains two commits, kept separate for review history:

perf(minifier): pre-size buffers in try_fold_concat to eliminate growth reallocs — the original tactical fix that pre-sized the doomed-to-be-removed intermediate buffers. Dropped sys reallocs first but didn't touch sys allocs.
perf(minifier): drop per-call buffers in try_fold_concat — the root-cause refactor described above. Removes the intermediate buffers entirely. Cuts both columns.

Once the second commit lands, the pre-sizing in the first becomes dead-code (the buffers it pre-sized no longer exist). They're kept as separate commits so the diff against main is reviewable — feel free to squash on merge.

How I found this

After #22580, profiling on antd.js minifier showed it had unusually high sys reallocs vs other tracked files. I wrote a backtrace-capturing System allocator wrapper and ran it on the minify path. The top realloc sites all converged on try_fold_concat — the overwhelming majority of captured reallocs came from this one function. After landing the pre-size fix, code review pushed for a root-cause fix that also addressed the Sys allocs column, which this refactor delivers.

Timing

The minifier bench suite (originally) didn't include antd.js or other .concat()-heavy fixtures, so bench numbers locally were flat (no regression, no obvious improvement). With kitchen-sink in the bench input set (#22609), CodSpeed shows: minifier mean −1.5%, min −3.7% on kitchen-sink.

Verification

cargo test -p oxc_minifier — pass.
cargo minsize — no size regressions (minsize.snap byte-identical).
cargo allocs — only antd.js row changed in allocs_minifier.snap.
cargo fmt -p oxc_minifier clean.

AI disclosure: drafted with Claude Code, reviewed manually.

codspeed-hq · 2026-05-19T15:11:13Z

Merging this PR will not alter performance

✅ 52 untouched benchmarks
⏩ 8 skipped benchmarks¹

_{Comparing claude/perf-minifier-concat (ac919bb) with claude/perf-semantic-resolve-refs-no-tempvec (d6faed5)}

8 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. ↩

Dunqing · 2026-05-20T01:31:17Z

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Appends the comprehensive synthetic fixture just merged at oxc-project/benchmark-files@main/kitchen-sink.tsx to the existing 4-file bench input set (RadixUIAdoptionSection / react.development / cal.com / binder) without replacing any of them. Also adds it to TestFiles::complicated() so alloc-tracking picks it up. Fixture stats (cross-checked): 21171 lines / 735 KB / 133222 AST nodes / 4757 scopes / 7016 symbols / 15983 resolved references / 177 classes / 0 semantic errors. Hand-written and intentionally diverse across every AST node, transformer plugin, minifier optimization, and semantic step in oxc — designed to surface general-purpose perf wins above the ~1-2% noise floor that recent niche PRs got lost in (#22596 already verified: minifier -1.5% mean / -3.7% min). AI disclosure: drafted with Claude Code, reviewed manually.

## Summary Adds `kitchen-sink.tsx` — a comprehensive synthetic TypeScript+JSX fixture maintained at [oxc-project/benchmark-files](https://github.com/oxc-project/benchmark-files) — to both `TestFiles::minimal()` (bench input set) and `TestFiles::complicated()` (alloc-tracking input set). The existing files in each set are untouched; this is a strict append. ## Why The existing bench input set didn't reliably surface general-purpose perf wins above the ~1-2% measurement noise floor: - #22580 (semantic pre-reserve) — visible because `binder.ts` exercises it - #22594 (formatter buffer) — visible - #22596 (minifier `try_fold_concat`) — **not visible** on the old set - #22599 (semantic resolve-refs no-temp-Vec) — **not visible** - #22603 (semantic var-hoist SmallVec) — **not visible** The kitchen-sink fixes that by exercising every AST node, every transformer plugin, every minifier optimization opportunity, and every semantic step in one large file. Verified by re-benching #22596 against this fixture: **minifier mean −1.5%, min −3.7%** — above noise, signal confirmed. ## Fixture stats (cross-checked locally) | Metric | Value | |---|---| | Source size | 21,117 lines / 732.90 kB | | AST nodes | ~133,000 | | Scopes | ~4,750 | | Symbols | ~7,000 | | Resolved references | ~16,000 | | Semantic diagnostics | 0 errors / 0 warnings | ## Snap baselines `tasks/track_memory_allocations/allocs_*.snap` updated with the kitchen-sink row across all 5 pipelines (parser / semantic / transformer / minifier / formatter). Future PRs that change allocation behavior on this fixture will produce a snap diff in CI. ## Bench-cleaner fix `tasks/benchmark/benches/lexer.rs`'s `SourceCleaner` was missing `visit_ts_template_literal_type` — TypeScript type-level template literals (e.g. `` `${T}-${U}` `` in conditional / mapped types) are syntactically identical to value-level template literals, so the bench-mode lexer (without parser context) cannot distinguish them. Without the cleaner converting them to plain strings, kitchen-sink's type-level templates caused the lexer bench to swallow ~1 KB spans as a single `TemplateHead` and produce spurious "Unterminated string" / "Invalid Unicode escape" errors. One-line fix to mirror the existing `visit_template_literal` handling. AI disclosure: drafted with Claude Code, reviewed manually.

Dunqing · 2026-05-21T02:26:10Z

Merge activity

May 21, 2:26 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
May 21, 7:55 AM UTC: Dunqing added this pull request to the Graphite merge queue.
May 21, 8:02 AM UTC: Merged by the Graphite merge queue.

camc314

this feels slightly overkill lol

## Summary When the minifier folds `.concat()` calls into template literals via `try_fold_concat` in `peephole/replace_known_methods.rs`, the original implementation built two short-lived intermediate buffers per call: - `quasi_strs: Vec<Cow<'a, str>>` — fresh `std::Vec` allocation per call. - A `String` inside each `Cow::Owned` — created when `Cow::to_mut()` cloned a `Borrowed` into an `Owned`, then grown via doubling as more arg strings were pushed in. For files with many `.concat()` calls — common in bundled ES5 libraries where template literals weren't available — both structures were freshly allocated thousands of times per minify, with the `String` growing via doubling each time. This PR replaces those per-call buffers with a single reusable scratch `String` held on `MinifierState`, and constructs `TemplateElement` AST nodes directly into the arena `Vec` as args are drained. The intermediate `Vec<Cow<'a, str>>` is gone entirely. After the first few folds the scratch's capacity stabilizes and subsequent folds are amortized zero std-heap allocs. The state machine simplifies in the process: the `pushed_quasi: bool` flag is gone. Its invariant ("scratch holds an in-progress quasi") is naturally maintained because every expression flush clears the scratch, so a back-to-back expression's flush produces the required empty separator quasi without a branch. ## Allocation impact `cargo allocs`, `allocs_minifier.snap` (baseline = parent commit, after resolve-refs and var-hoist landed): | File | Size | Sys allocs before | Sys allocs after | Sys reallocs before | Sys reallocs after | |---|---|---|---|---|---| | `antd.js` | 6.69 MB ES5 | **4,652** | **3,084** (`−1,568`, `−33.7%`) | **1,622** | **53** (`−1,569`) | | Other tracked files | various | unchanged | unchanged | unchanged | unchanged | Only `antd.js` shows a change because it's the only tracked file that exercises `.concat()` folding heavily. ES5 bundled code uses `.concat()` instead of template literals; antd.js has thousands of these. The headline `Sys reallocs` improvement (`1,622` → `53`) comes from eliminating the per-call `String` doubling. The headline `Sys allocs` improvement (`4,652` → `3,084`) comes from eliminating the per-call `Vec<Cow<'a, str>>` allocation. ## Commits This PR contains two commits, kept separate for review history: 1. **`perf(minifier): pre-size buffers in try_fold_concat to eliminate growth reallocs`** — the original tactical fix that pre-sized the doomed-to-be-removed intermediate buffers. Dropped sys reallocs first but didn't touch sys allocs. 2. **`perf(minifier): drop per-call buffers in try_fold_concat`** — the root-cause refactor described above. Removes the intermediate buffers entirely. Cuts both columns. Once the second commit lands, the pre-sizing in the first becomes dead-code (the buffers it pre-sized no longer exist). They're kept as separate commits so the diff against `main` is reviewable — feel free to squash on merge. ## How I found this After #22580, profiling on `antd.js` minifier showed it had unusually high sys reallocs vs other tracked files. I wrote a backtrace-capturing `System` allocator wrapper and ran it on the minify path. The top realloc sites all converged on `try_fold_concat` — the overwhelming majority of captured reallocs came from this one function. After landing the pre-size fix, code review pushed for a root-cause fix that also addressed the `Sys allocs` column, which this refactor delivers. ## Timing The minifier bench suite (originally) didn't include antd.js or other `.concat()`-heavy fixtures, so bench numbers locally were flat (no regression, no obvious improvement). With kitchen-sink in the bench input set (#22609), CodSpeed shows: **minifier mean −1.5%, min −3.7%** on kitchen-sink. ## Verification - `cargo test -p oxc_minifier` — pass. - `cargo minsize` — no size regressions (`minsize.snap` byte-identical). - `cargo allocs` — only `antd.js` row changed in `allocs_minifier.snap`. - `cargo fmt -p oxc_minifier` clean. AI disclosure: drafted with Claude Code, reviewed manually.

### 🚀 Features - e857b0c napi/minify: Expose legalComments option and result (#20370) (Boshen) - 661132d parser: More friendly error messages for rest assignment target and rest binding element (#22719) (sapphi-red) - ee659b6 transformer/legacy-decorator: Add `strictNullChecks` option for nullable-union design:type (#22266) (Kyle Cannon) ### 🐛 Bug Fixes - e1d064e transformer/class-properties: Reparent lifted private method helpers (#22716) (Cameron) - 4ac0fca minifier: Preserve `0 && (module.exports = { ... })` cjs-module-lexer hint (#22729) (Dunqing) - 40ff611 minifier: Mark peephole loop changed when dropping dead-after-throw statement (#22722) (Dunqing) - 2f7b210 codegen: Emit pife-arrow/function leading comments inside the wrap (#22720) (Dunqing) - e184f74 parser: Improve invalid `import` property access diagnostic (#22693) (camc314) - 7baed9c transformer/private-method: Clear inherited strict flags (#22508) (camc314) - a9ad27e parser: Keep annotation comments leading without preceding newline (#22711) (Dunqing) - 9ea4d64 minifier: Re-evaluate pure/no-side-effects flags after peephole inlining (#22595) (Dunqing) - 07afbb6 minifier: Drop empty-body IIFE wrapper when called with arguments (#22589) (Dunqing) - fa7c463 semantic: Correct TS enum member symbol spans (#22689) (camc314) - 26b9396 semantic: Resolve parameter decorators outside parameter scope (#22623) (camc314) - b284045 parser: Switch to module goal eagerly on `export` (#22684) (Boshen) - dfa931d semantic: Propagate unresolved auto-increment enum value instead of defaulting to 0 (#22646) (Dunqing) - 69a6ba6 transformer/legacy-decorator: Emit Array for ReadonlyArray<T> in decorator metadata (#22265) (Kyle Cannon) - e421ef0 transformer/legacy-decorator: Return runtime binding for design:type (#22640) (Dunqing) - d61e1d7 codegen: Preserve verbatim text of pure/no-side-effects comments (#22525) (Dunqing) - 702b14e minifier: Preserve IIFE structure in DCE-only mode (#22547) (Dunqing) - 917da24 parser: Apply PURE comment through member-access chains (#22566) (Dunqing) - a069b1c codegen: Preserve quotes for cjs-module-lexer equality strings (#22551) (Dunqing) ### ⚡ Performance - 2f623b0 semantic: Skip unresolved checks for re-exports (#22660) (camc314) - 0d9553d semantic: Early-exit `check_object_expression` for objects with <2 properties (#22668) (Dunqing) - d721ad9 semantic: Use direct grandparent lookup for TS type parameters (#22658) (camc314) - 0aff288 semantic: Reorder numeric literal strict mode checks (#22657) (camc314) - 4d5ddb1 semantic: Reorder binding identifier checks (#22656) (camc314) - e32acd8 semantic: Reorder identifier ambient binding check (#22653) (camc314) - 09fe178 semantic: Reorder ident reference strict mode check (#22652) (camc314) - 4b6add2 semantic: Avoid duplicate ident clone for bindings (#22663) (camc314) - 82f9662 parser: Check identifier kind before context flag (#22662) (camc314) - d7cd951 parser: Fast path identifier parsing and inline operator helpers (#22650) (Boshen) - 7b84314 semantic: Use direct byte access for numeric leading-zero check (#22642) (camc314) - 0345a31 semantic: Pre-size class elements hash map (#22618) (camc314) - 04d3065 minifier: Drop per-call buffers in try_fold_concat (#22596) (Dunqing) - 4f289f1 semantic: Resolve_references_for_current_scope without a temp Vec (#22599) (Dunqing) - e862c15 semantic: Avoid heap alloc for var hoist scope ids (#22603) (Dunqing) - 8ff8674 semantic: Early return if `excess` is `0` in `Stats::increase_by` (#22616) (camc314) - 7a4120e semantic: Pre-reserve unresolved_references using Stats::references (#22580) (Dunqing) Co-authored-by: Dunqing <[email protected]>

github-actions Bot added A-parser Area - Parser A-minifier Area - Minifier labels May 19, 2026

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Dunqing marked this pull request as draft May 19, 2026 15:54

Dunqing changed the title ~~perf(minifier): pre-size buffers in try_fold_concat to eliminate growth reallocs~~ perf(minifier): drop per-call buffers in try_fold_concat May 19, 2026

Dunqing mentioned this pull request May 20, 2026

feat(bench): add kitchen-sink.tsx to TestFiles #22609

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perf(semantic): avoid heap alloc for var hoist scope ids #22603

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perf(semantic): resolve_references_for_current_scope without a temp Vec #22599

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release(crates): oxc v0.133.0 #22734

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perf(minifier): drop per-call buffers in try_fold_concat#22596

perf(minifier): drop per-call buffers in try_fold_concat#22596
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Summary

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Merging this PR will not alter performance

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