perf(semantic): skip checking redeclarations for function expressions by overlookmotel · Pull Request #18291 · oxc-project/oxc

overlookmotel · 2026-01-20T12:26:46Z

Function expressions can't have redeclarations, so exit check_function_redeclaration early for function expressions, rather than proceeding through more expensive checks which can't pass anyway.

Marginal improvement (0.1% - 0.2%) on most semantic benchmarks. Or perhaps it's just noise.

overlookmotel · 2026-01-20T12:27:02Z

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codspeed-hq · 2026-01-20T12:33:09Z

Merging this PR will not alter performance

✅ 42 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing om/01-20-perf_semantic_skip_checking_redeclarations_for_function_expressions (df3236a) with om/01-19-refactor_semantic_simplify_checking_if_function_is_part_of_if_statement (3f602f0)²}

3 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 om/01-19-refactor_semantic_simplify_checking_if_function_is_part_of_if_statement (3f602f0) during the generation of this report, so 79fed6c was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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Pull request overview

This PR optimizes the check_function_redeclaration function by adding an early exit for function expressions. Since function expressions cannot have redeclarations (only function declarations can), the optimization skips expensive redeclaration checks that would never produce errors for expressions anyway.

Changes:

Added an early return check in check_function_redeclaration to exit immediately for function expressions
Added clarifying comment about function declarations and identifiers

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graphite-app · 2026-01-20T14:02:46Z

Merge activity

Jan 20, 2:02 PM UTC: Boshen added this pull request to the Graphite merge queue.
Jan 20, 2:16 PM UTC: The Graphite merge queue removed this pull request due to downstack failures on PR #18290.
Jan 21, 1:08 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Jan 21, 1:08 AM UTC: Dunqing added this pull request to the Graphite merge queue.
Jan 21, 1:16 AM UTC: Merged by the Graphite merge queue.

…#18291) Function expressions can't have redeclarations, so exit `check_function_redeclaration` early for function expressions, rather than proceeding through more expensive checks which can't pass anyway. Marginal improvement (0.1% - 0.2%) on most semantic benchmarks. Or perhaps it's just noise.

…on_part_of_if_statement` (#18292) Small optimization. After #18291, one of the callers of `is_function_part_of_if_statement` has already done the check for whether the `Function` is a declaration. So move that repeated check out of `is_function_part_of_if_statement`. As that function now only applies to function declarations, rename it to `is_function_decl_part_of_if_statement`.

…#18291) Function expressions can't have redeclarations, so exit `check_function_redeclaration` early for function expressions, rather than proceeding through more expensive checks which can't pass anyway. Marginal improvement (0.1% - 0.2%) on most semantic benchmarks. Or perhaps it's just noise.

…on_part_of_if_statement` (#18292) Small optimization. After #18291, one of the callers of `is_function_part_of_if_statement` has already done the check for whether the `Function` is a declaration. So move that repeated check out of `is_function_part_of_if_statement`. As that function now only applies to function declarations, rename it to `is_function_decl_part_of_if_statement`.

### 💥 BREAKING CHANGES - 22dec6a semantic: [**BREAKING**] Remove `Scoping::scope_build_child_ids` and all related APIs (#18362) (Dunqing) - 30a4899 oxc: [**BREAKING**] Remove `CompilerInterface::semantic_child_scope_ids` (#18361) (Dunqing) - 777fc40 ast: [**BREAKING**] Add `Ident` type (#18354) (Boshen) - af0ca46 span: [**BREAKING**] Use `ModuleKind::CommonJS` for `SourceType::cjs()` (#18276) (sapphi-red) ### 🚀 Features - 0a02026 semantic: Add TS1499 code to diagnostic (#18557) (camc314) - 8b4618f parser: Add TS1500 code to diagnostic (#18547) (camc314) - 866b6b3 parser: Add TS1048 code to diagnostic (#18546) (camc314) - 1117c44 parser: Add TS1054 code to diagnostic (#18541) (camc314) - e4fcdde semantic: Add TS1053 code to diagnostic (#18539) (camc314) - bcbf396 semantic: Add TS1052 code to diagnostic (#18538) (camc314) - 8155edf semantic: Add TS1049 code to diagnostic (#18535) (camc314) - 51d3b3f parser: Add TS1502 code to diagnostic (#18534) (camc314) - 00854e8 semantic: Add TS2337 error code to super call diagnostic (#18531) (camc314) - 993fd2b parser: Parse unambiguous await with better error messages (#18480) (Boshen) - 8db0e78 linter/plugins: Handle BOMs (#18376) (overlookmotel) - 6ac09e2 linter/plugins: Support source text not being at start of buffer (#18375) (overlookmotel) - 2ef5647 ast: Add escape_raw parameter to template_element builders (#18121) (Boshen) ### 🐛 Bug Fixes - 74d0998 semantic: Update error msg for multiple `default` cases in switch stmt (#18526) (camc314) - c205b0d ast: Remove `ThisExpression` from `TSModuleReference` (#18489) (Boshen) - aed3669 parser: Parse HTML-like comments in unambiguous mode (#18442) (Boshen) - c4132fb parser: Validate accessor parameters in interface method signatures (#18391) (Boshen) - b0cd74d semantic: Allow `var` and `function` with same name in static blocks (#18358) (Boshen) - 6037995 semantic: Allow `new.target` in class field initializers (#18349) (Boshen) - 9a15c6a semantic: Do not rely on spans for node comparison in `Function::bind` (#18296) (overlookmotel) ### ⚡ Performance - 6b600c4 semantic: Skip parent lookup for function declarations in `Function::bind` (#18293) (overlookmotel) - c27ad2d semantic: Move check for function declaration out of `is_function_part_of_if_statement` (#18292) (overlookmotel) - 63eb89e semantic: Skip checking redeclarations for function expressions (#18291) (overlookmotel) - 7c12743 semantic: Skip checking unresolved exports in CommonJS files (#18250) (overlookmotel) - 2349031 allocator: Increase initial chunk size from 512B to 16KB (#18234) (Boshen) ### 📚 Documentation - 8ccd853 npm: Update package homepage URLs and add keywords (#18509) (Boshen) - 9b3165f napi/parser: Clarify when to use `parseAsync` vs `parseSync` (#18486) (Boshen) - 1b59f63 napi/parser: Correct typo in README (#18251) (overlookmotel) - 00ff75f mangler: Fix `top_level` option in example (#18233) (overlookmotel) - 2ddc073 semantic: Fix typo in comment (#18238) (overlookmotel) Co-authored-by: Boshen <[email protected]>

github-actions bot added A-semantic Area - Semantic C-performance Category - Solution not expected to change functional behavior, only performance labels Jan 20, 2026

overlookmotel mentioned this pull request Jan 20, 2026

test(semantic): add test cases for function redeclaration check #18288

Merged

This was referenced Jan 20, 2026

refactor(semantic): simplify checking if function is part of if statement #18290

Merged

perf(semantic): move check for function declaration out of is_function_part_of_if_statement #18292

Merged

overlookmotel marked this pull request as ready for review January 20, 2026 12:36

overlookmotel requested a review from Dunqing as a code owner January 20, 2026 12:36

Copilot AI review requested due to automatic review settings January 20, 2026 12:36

Copilot started reviewing on behalf of overlookmotel January 20, 2026 12:37 View session

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This was referenced Jan 20, 2026

perf(semantic): skip parent lookup for function declarations in Function::bind #18293

Merged

refactor(semantic): move code into if block #18294

Merged

overlookmotel assigned Dunqing Jan 20, 2026

This was referenced Jan 20, 2026

perf(semantic): single call to Function::bind for functions #18295

Closed

fix(semantic): do not rely on spans for node comparison in Function::bind #18296

Merged

graphite-app bot added the 0-merge Merge with Graphite Merge Queue label Jan 20, 2026

graphite-app bot force-pushed the om/01-19-refactor_semantic_simplify_checking_if_function_is_part_of_if_statement branch from 3f602f0 to 90e93ab Compare January 20, 2026 14:09

graphite-app bot force-pushed the om/01-20-perf_semantic_skip_checking_redeclarations_for_function_expressions branch from df3236a to b02673e Compare January 20, 2026 14:10

graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Jan 20, 2026

Dunqing approved these changes Jan 21, 2026

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Dunqing added the 0-merge Merge with Graphite Merge Queue label Jan 21, 2026

graphite-app bot force-pushed the om/01-19-refactor_semantic_simplify_checking_if_function_is_part_of_if_statement branch from 90e93ab to fde1dc7 Compare January 21, 2026 01:09

graphite-app bot force-pushed the om/01-20-perf_semantic_skip_checking_redeclarations_for_function_expressions branch from b02673e to 63eb89e Compare January 21, 2026 01:09

Base automatically changed from om/01-19-refactor_semantic_simplify_checking_if_function_is_part_of_if_statement to main January 21, 2026 01:15

graphite-app bot merged commit 63eb89e into main Jan 21, 2026
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graphite-app bot deleted the om/01-20-perf_semantic_skip_checking_redeclarations_for_function_expressions branch January 21, 2026 01:16

graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Jan 21, 2026

Boshen mentioned this pull request Jan 26, 2026

release(crates): oxc v0.111.0 #18572

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perf(semantic): skip checking redeclarations for function expressions#18291

perf(semantic): skip checking redeclarations for function expressions#18291
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Merging this PR will not alter performance

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