perf(parser): reserve cap 2 for sequence expressions vec#22374
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2 for sequence expressions2 for sequence expressions vec
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Pull request overview
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This PR optimizes parsing of JavaScript sequence expressions by avoiding an initial 1-element arena vector allocation and reserving capacity for the minimum valid sequence length (2), reducing arena reallocations.
Changes:
- Allocate sequence-expression
Vecwith capacity 2 instead of creating a 1-element vec. - Update the memory allocation snapshot to reflect fewer reallocations during parsing.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| tasks/track_memory_allocations/allocs_parser.snap | Updates allocation/reallocation counts to match the optimization impact. |
| crates/oxc_parser/src/js/expression.rs | Changes sequence-expression collection initialization to reserve capacity 2. |
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it's impossible to have a sequence expression with a length of 1, so there is no point in creating a vec of len 1, only to re allocate. This change is visible in the parser via the fewer number of arena re-allocs.
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overlookmotel
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May 15, 2026
### 🚀 Features - bc91a17 codegen: Expose `Codegen::with_source_type` method (#22432) (camc314) ### 🐛 Bug Fixes - 5ac7e79 minifier: Drop unused-var-init pure IIFEs and preserve annotation for downstream (#22349) (Dunqing) - 4ab57eb allocator: Fixed-size allocators use `VirtualAlloc` on Windows (#22124) (overlookmotel) - 66d77eb allocator: Fix segfault on Linux MUSL with fixed-size allocators (#22388) (overlookmotel) - b8fbc1f transformer/object-rest-spread: Correct scope id when moving bindings (#22419) (camc314) - 18edc2c codegen: Keep `Object.defineProperty` property name as plain string in minify (#22400) (Dunqing) - dda33de transformer/explicit-resource-management: Align lexical binding scopes (#22320) (camc314) - 8e79de8 transformer: Preserve for-await statement bodies (#22361) (camc314) - 0cba210 transformer/class: Replace `new.target` in static blocks (#22360) (camc314) - 67ab1c9 transformer/es2018/for-await: Hoist for-await generated bindings (#22355) (camc314) - c3ceb4a transformer/object-rest-spread: Use hoisted scope for `for-of` temp refs (#22347) (camc314) ### ⚡ Performance - 73a9043 allocator/bitset: Avoid temp heap `String` allocation (#22403) (camc314) - 8b2f4f9 transformer/object-rest-spread: Collect `Vec<SymbolId` over `Vec<BindingIdentifier>` (#22418) (camc314) - 83679ea parser: Split TriviaBuilder::handle_token hot/cold paths (#22415) (Boshen) - 2c7d781 codegen: Inline identifier-name accessors (#22411) (Boshen) - 618bc76 diagnostics: Inline `OxcDiagnosticInner` to avoid heap allocation (#22406) (Boshen) - 0b4e158 parser: Reserve cap `2` for sequence expressions vec (#22374) (camc314) - 5f3bdd0 codegen: Add `#[inline]` to `code`, `code_len` (#22373) (camc314) Co-authored-by: overlookmotel <557937+overlookmotel@users.noreply.github.com>
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it's impossible to have a sequence expression with a length of 1, so there is no point in creating a vec of len 1, only to re allocate.
This change is visible in the parser via the fewer number of arena re-allocs.