perf(parser): allocate AST nodes in arena directly by overlookmotel · Pull Request #23712 · oxc-project/oxc

overlookmotel · 2026-06-22T12:31:04Z

Same as #23709.

Small perf optimizations around AST builder calls.

AST nodes which end up in Boxes, allocate into the Box as early as possible, to increase chance compiler sees the type can be built directly in arena, rather than built on the stack, and then copied from stack into arena.
Functions return Box<T> rather than T where the value needs to be boxed anyway. If function is not inlined, this avoids stack allocation + copy.

Also, shorten code where possible by using more specific AstBuilder methods.

overlookmotel · 2026-06-22T12:31:14Z

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codspeed-hq · 2026-06-22T12:39:58Z

Merging this PR will not alter performance

✅ 62 untouched benchmarks
⏩ 9 skipped benchmarks¹

_{Comparing om/06-21-perf_parser_allocate_ast_nodes_in_arena_directly (0090ac3) with om/06-21-perf_minifier_allocate_ast_nodes_in_arena_directly (86b4184)}

9 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. ↩

Copilot

Pull request overview

This PR applies small performance-focused refactors in oxc_parser to allocate AST nodes directly in the arena (and/or return already-boxed nodes) to reduce intermediate stack allocations and copies during parsing.

Changes:

Return Box<'a, T> from several parsing helpers when the produced AST node is always boxed in the AST (e.g. literals, using declarations, TS import attributes object).
Replace “build then alloc” patterns with AstBuilder::alloc_* constructors (e.g. alloc_identifier_name, alloc_object_expression, alloc_*_literal).
Thread boxed nodes through call sites to avoid extra self.alloc(...) steps.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/oxc_parser/src/ts/types.rs	Allocate TS import type option/attribute AST nodes directly in the arena; return boxed object expressions where required.
crates/oxc_parser/src/js/statement.rs	Pass already-boxed `using` declarations into `parse_any_for_loop` without re-boxing.
crates/oxc_parser/src/js/expression.rs	Return boxed literal nodes and construct `Expression::*Literal` variants without intermediate allocations.
crates/oxc_parser/src/js/declaration.rs	Make `parse_using_declaration` return a boxed `VariableDeclaration` and propagate that to statement construction.
crates/oxc_parser/src/js/binding.rs	Make rest-element parsing return boxed rest elements and pass them through binding-pattern builders directly.
crates/oxc_parser/src/cursor.rs	Update `parse_delimited_list_with_rest` to return an optional boxed rest element to match binding parser changes.

) Optimization to parsing JSX. When parsing JSX element names `parse_jsx_element_name` has to determine if the identifier: 1. starts with a lowercase letter, and 2. contains a `-`. The 2nd check is relatively expensive - string search. Avoid the search by making the lexer feed this information (which it already has) to the parser. This reduces the check in the parser to just `!contains_dash`. (came across this while working #23712)

graphite-app · 2026-06-23T00:59:36Z

Merge activity

Jun 23, 12:59 AM UTC: overlookmotel added this pull request to the Graphite merge queue.
Jun 23, 1:06 AM UTC: Merged by the Graphite merge queue.

Same as #23709. Small perf optimizations around AST builder calls. - AST nodes which end up in `Box`es, allocate into the `Box` as early as possible, to increase chance compiler sees the type can be built directly in arena, rather than built on the stack, and then copied from stack into arena. - Functions return `Box<T>` rather than `T` where the value needs to be boxed anyway. If function is not inlined, this avoids stack allocation + copy. Also, shorten code where possible by using more specific `AstBuilder` methods.

### 💥 BREAKING CHANGES - 94fbacb ast: [**BREAKING**] Only export `AstBuilder` and `NONE` in `builder` module (#23876) (overlookmotel) - 8de5122 ecmascript: [**BREAKING**] Switch to new `AstBuilder` (#23834) (overlookmotel) - dc0ef38 transformer: [**BREAKING**] Switch to new `AstBuilder` (#23831) (overlookmotel) - 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take `&GetAllocator` (#23781) (overlookmotel) - 36009dd allocator: [**BREAKING**] `GetAllocator::allocator` take `&self` (#23676) (overlookmotel) - bd74f9d allocator: [**BREAKING**] Rename `AllocatorAccessor` trait to `GetAllocator` (#23675) (overlookmotel) ### 🚀 Features - 326fe25 transformer_plugins: Support `typeof` `define` keys (#23605) (Alexander Lichter) - f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel) - cd1fd12 codegen: Expose `Codegen::print_string` API (#23785) (camc314) - 785461b ast: Add custom builder methods to AST types (#23651) (overlookmotel) - 05d1357 ast: Add AST creation methods to AST types (#23650) (overlookmotel) - 2580eda str: Add `Str::from_str_in` and `Ident::from_str_in` methods (#23767) (overlookmotel) - 6883fcf minifier: Fold write-once falsy var to false in boolean context (#23540) (Dunqing) - fcbf993 allocator: Add `Vec::from_value_in` method (#23718) (overlookmotel) - 989ddb7 allocator: Add `Vec::from_box_in` method (#23717) (overlookmotel) - 9d1aa7f allocator: Improve `PartialEq` for `Vec` (#23716) (overlookmotel) ### 🐛 Bug Fixes - da0e5bf minifier: Don't reorder a closed-over TDZ read when inlining a var (#23771) (Dunqing) - 0b3021f allocator: Remove `Vec::from_box_in` (#23873) (overlookmotel) - 0ab64ec ast: Silence deprecation warnings within files defining deprecated `AstBuilder` methods (#23889) (overlookmotel) - 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast` crate in tests (#23888) (overlookmotel) - 3800f01 ast: Legacy `AstBuilder` methods take `self` not `&self` (#23891) (overlookmotel) - 869ac20 semantic/cfg: Connect for update exit to loop test (#23791) (camc314) - d3e92d5 semantic/cfg: Connect while branches from condition exit (#23790) (camc314) - 025045d ast: `ExportNamedDeclaration` plain builder methods return boxed nodes (#23783) (overlookmotel) - 7537c58 ast: Fix name of `AstBuilder` method for `Expression::V8IntrinsicExpression` (#23766) (overlookmotel) - 3f574f5 traverse: Fix unsoundness in `Traverse` walk functions (#23745) (overlookmotel) - 585760f parser: String in AST reference arena (#23721) (overlookmotel) - 7231d55 allocator: Fix unsound lifetime extension in `Box::new_in` (#23685) (overlookmotel) ### ⚡ Performance - d5c916a semantic: Flatten hoisting_variables to avoid per-scope map allocation (#23927) (Lawrence Lin) - e71609d minifier: Bail member-expr folding before the side-effect walk (#23924) (Lawrence Lin) - e1f89ab minifier: Reduce string allocations folding addition (#23846) (overlookmotel) - 9f6ee3b isolated-declarations: Pool scope maps to avoid per-scope alloc/rehash (#23761) (Boshen) - 0b07c4c semantic: Avoid heap alloc for catch-clause binding ids (#23911) (Lawrence Lin) - c5eef8b regular_expression: Skip capturing-group pre-parse when pattern has no `(` (#23908) (Lawrence Lin) - b4f5b4b isolated_declarations: Remove redundant clone of formal parameter pattern (#23912) (Lawrence Lin) - 53d083f isolated_declarations: Use `TakeIn` not `CloneIn` (#23847) (overlookmotel) - 3ea9304 react_compiler: Use faster API to arena allocate strings (#23849) (overlookmotel) - a6d8e45 parser: Avoid span lookup for arrow expression body (#23788) (camc314) - e1886a0 transformer, minifier: Use `static_ident!` macro to create static `Ident`s (#23727) (overlookmotel) - 5527bef transformer/object-rest-spread: Reduce iteration (#23720) (overlookmotel) - 680ffbc transformer: Allocate AST nodes in arena directly (#23711) (overlookmotel) - 1c63c66 parser: Allocate AST nodes in arena directly (#23712) (overlookmotel) - 3855f0c minifier: Allocate AST nodes in arena directly (#23710) (overlookmotel) - d025887 isolated_declarations: Allocate AST nodes in arena directly (#23709) (overlookmotel) - 10b96c6 parser: Remove string search from parsing JSX element name (#23713) (overlookmotel) ### 📚 Documentation - 3d61dea all: Correct capitalization in comments (#23887) (overlookmotel) - aa1ad74 ast: Add `#[deprecated]` to legacy `AstBuilder` methods (#23877) (overlookmotel) - a4676db ast: Correct doc comment for `NONE` (#23765) (overlookmotel) - 419ec80 syntax: Fix typo in doc comment (#23674) (overlookmotel) ### 🛡️ Security - 3cdd18f deps: Update npm packages (#23690) (renovate[bot]) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com> Co-authored-by: Cameron <cameron.clark@hey.com>

) Optimization to parsing JSX. When parsing JSX element names `parse_jsx_element_name` has to determine if the identifier: 1. starts with a lowercase letter, and 2. contains a `-`. The 2nd check is relatively expensive - string search. Avoid the search by making the lexer feed this information (which it already has) to the parser. This reduces the check in the parser to just `!contains_dash`. (came across this while working #23712)

Same as #23709. Small perf optimizations around AST builder calls. - AST nodes which end up in `Box`es, allocate into the `Box` as early as possible, to increase chance compiler sees the type can be built directly in arena, rather than built on the stack, and then copied from stack into arena. - Functions return `Box<T>` rather than `T` where the value needs to be boxed anyway. If function is not inlined, this avoids stack allocation + copy. Also, shorten code where possible by using more specific `AstBuilder` methods.

### 💥 BREAKING CHANGES - 94fbacb ast: [**BREAKING**] Only export `AstBuilder` and `NONE` in `builder` module (#23876) (overlookmotel) - 8de5122 ecmascript: [**BREAKING**] Switch to new `AstBuilder` (#23834) (overlookmotel) - dc0ef38 transformer: [**BREAKING**] Switch to new `AstBuilder` (#23831) (overlookmotel) - 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take `&GetAllocator` (#23781) (overlookmotel) - 36009dd allocator: [**BREAKING**] `GetAllocator::allocator` take `&self` (#23676) (overlookmotel) - bd74f9d allocator: [**BREAKING**] Rename `AllocatorAccessor` trait to `GetAllocator` (#23675) (overlookmotel) ### 🚀 Features - 326fe25 transformer_plugins: Support `typeof` `define` keys (#23605) (Alexander Lichter) - f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel) - cd1fd12 codegen: Expose `Codegen::print_string` API (#23785) (camc314) - 785461b ast: Add custom builder methods to AST types (#23651) (overlookmotel) - 05d1357 ast: Add AST creation methods to AST types (#23650) (overlookmotel) - 2580eda str: Add `Str::from_str_in` and `Ident::from_str_in` methods (#23767) (overlookmotel) - 6883fcf minifier: Fold write-once falsy var to false in boolean context (#23540) (Dunqing) - fcbf993 allocator: Add `Vec::from_value_in` method (#23718) (overlookmotel) - 989ddb7 allocator: Add `Vec::from_box_in` method (#23717) (overlookmotel) - 9d1aa7f allocator: Improve `PartialEq` for `Vec` (#23716) (overlookmotel) ### 🐛 Bug Fixes - da0e5bf minifier: Don't reorder a closed-over TDZ read when inlining a var (#23771) (Dunqing) - 0b3021f allocator: Remove `Vec::from_box_in` (#23873) (overlookmotel) - 0ab64ec ast: Silence deprecation warnings within files defining deprecated `AstBuilder` methods (#23889) (overlookmotel) - 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast` crate in tests (#23888) (overlookmotel) - 3800f01 ast: Legacy `AstBuilder` methods take `self` not `&self` (#23891) (overlookmotel) - 869ac20 semantic/cfg: Connect for update exit to loop test (#23791) (camc314) - d3e92d5 semantic/cfg: Connect while branches from condition exit (#23790) (camc314) - 025045d ast: `ExportNamedDeclaration` plain builder methods return boxed nodes (#23783) (overlookmotel) - 7537c58 ast: Fix name of `AstBuilder` method for `Expression::V8IntrinsicExpression` (#23766) (overlookmotel) - 3f574f5 traverse: Fix unsoundness in `Traverse` walk functions (#23745) (overlookmotel) - 585760f parser: String in AST reference arena (#23721) (overlookmotel) - 7231d55 allocator: Fix unsound lifetime extension in `Box::new_in` (#23685) (overlookmotel) ### ⚡ Performance - d5c916a semantic: Flatten hoisting_variables to avoid per-scope map allocation (#23927) (Lawrence Lin) - e71609d minifier: Bail member-expr folding before the side-effect walk (#23924) (Lawrence Lin) - e1f89ab minifier: Reduce string allocations folding addition (#23846) (overlookmotel) - 9f6ee3b isolated-declarations: Pool scope maps to avoid per-scope alloc/rehash (#23761) (Boshen) - 0b07c4c semantic: Avoid heap alloc for catch-clause binding ids (#23911) (Lawrence Lin) - c5eef8b regular_expression: Skip capturing-group pre-parse when pattern has no `(` (#23908) (Lawrence Lin) - b4f5b4b isolated_declarations: Remove redundant clone of formal parameter pattern (#23912) (Lawrence Lin) - 53d083f isolated_declarations: Use `TakeIn` not `CloneIn` (#23847) (overlookmotel) - 3ea9304 react_compiler: Use faster API to arena allocate strings (#23849) (overlookmotel) - a6d8e45 parser: Avoid span lookup for arrow expression body (#23788) (camc314) - e1886a0 transformer, minifier: Use `static_ident!` macro to create static `Ident`s (#23727) (overlookmotel) - 5527bef transformer/object-rest-spread: Reduce iteration (#23720) (overlookmotel) - 680ffbc transformer: Allocate AST nodes in arena directly (#23711) (overlookmotel) - 1c63c66 parser: Allocate AST nodes in arena directly (#23712) (overlookmotel) - 3855f0c minifier: Allocate AST nodes in arena directly (#23710) (overlookmotel) - d025887 isolated_declarations: Allocate AST nodes in arena directly (#23709) (overlookmotel) - 10b96c6 parser: Remove string search from parsing JSX element name (#23713) (overlookmotel) ### 📚 Documentation - 3d61dea all: Correct capitalization in comments (#23887) (overlookmotel) - aa1ad74 ast: Add `#[deprecated]` to legacy `AstBuilder` methods (#23877) (overlookmotel) - a4676db ast: Correct doc comment for `NONE` (#23765) (overlookmotel) - 419ec80 syntax: Fix typo in doc comment (#23674) (overlookmotel) ### 🛡️ Security - 3cdd18f deps: Update npm packages (#23690) (renovate[bot]) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com> Co-authored-by: Cameron <cameron.clark@hey.com>

This was referenced Jun 22, 2026

refactor(ast): remove AstBuilder::alloc calls #23708

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perf(isolated_declarations): allocate AST nodes in arena directly #23709

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perf(minifier): allocate AST nodes in arena directly #23710

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overlookmotel mentioned this pull request Jun 22, 2026

perf(transformer): allocate AST nodes in arena directly #23711

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github-actions Bot added the A-parser Area - Parser label Jun 22, 2026

overlookmotel marked this pull request as ready for review June 22, 2026 12:46

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overlookmotel requested a review from Dunqing June 22, 2026 12:49

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graphite-app Bot force-pushed the om/06-21-perf_transformer_allocate_ast_nodes_in_arena_directly branch from c94b543 to ca1a2ae Compare June 22, 2026 12:55

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overlookmotel changed the base branch from om/06-21-perf_transformer_allocate_ast_nodes_in_arena_directly to graphite-base/23712 June 22, 2026 12:56

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This was referenced Jun 22, 2026

perf(parser): remove string search from parsing JSX element name #23713

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perf(transformer/object-rest-spread): reduce iteration #23720

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overlookmotel force-pushed the om/06-21-perf_parser_allocate_ast_nodes_in_arena_directly branch from 4149490 to b57ac10 Compare June 22, 2026 14:59

camc314 approved these changes Jun 22, 2026

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overlookmotel force-pushed the om/06-21-perf_minifier_allocate_ast_nodes_in_arena_directly branch from 644b3d0 to 86b4184 Compare June 23, 2026 00:31

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overlookmotel mentioned this pull request Jun 23, 2026

refactor(parser): switch parser to new AstBuilder #23730

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release(crates): oxc v0.138.0 #23934

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perf(parser): allocate AST nodes in arena directly#23712

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