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perf(semantic): reorder identifier ambient binding check#22653

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c/05-21-perf_semantic_reorder_identifier_ambient_binding_check
May 22, 2026
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perf(semantic): reorder identifier ambient binding check#22653
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c/05-21-perf_semantic_reorder_identifier_ambient_binding_check

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@camc314

@camc314 camc314 commented May 21, 2026

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check_identifier runs for every identifier seen during semantic checking, but the ambient-binding exception only matters for the small set of names that can produce reserved-keyword diagnostics.

Previously we called is_current_node_ambient_binding before checking the identifier name, so every identifier paid for the ambient-context lookup even though most identifiers cannot trigger any of this function’s diagnostics. Moving the ambient check into the relevant match arms keeps the same behavior while making the common path cheaper: ordinary identifiers now fall through after the name match without querying scope flags, symbol flags, or the current AST node.

camc314 commented May 21, 2026

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@github-actions github-actions Bot added the A-semantic Area - Semantic label May 21, 2026
@camc314 camc314 marked this pull request as ready for review May 21, 2026 16:59
@camc314 camc314 requested a review from Dunqing as a code owner May 21, 2026 16:59
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Pull request overview

This PR optimizes the JavaScript semantic checker’s hot-path identifier validation by deferring the ambient-binding lookup until it’s actually needed for reserved-keyword diagnostics. This reduces overhead for the common case where identifier names cannot trigger these diagnostics.

Changes:

  • Avoids calling is_current_node_ambient_binding for most identifiers by moving the ambient check into the "await" branch and the strict-mode reserved-word guard.
  • Preserves existing behavior for .d.ts sources and for ambient bindings suppressing "await" / strict-mode reserved-word diagnostics.

Comment thread crates/oxc_semantic/src/checker/javascript.rs
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codspeed-hq Bot commented May 21, 2026

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Merging this PR will not alter performance

✅ 57 untouched benchmarks
⏩ 3 skipped benchmarks1


Comparing c/05-21-perf_semantic_reorder_identifier_ambient_binding_check (f6673e8) with c/05-21-perf_semantic_reorder_ident_strict_mode_check (8f137c2)

Open in CodSpeed

Footnotes

  1. 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.

@camc314

camc314 commented May 21, 2026

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performance goes brrrrrrrr

Screenshot 2026-05-21 at 18 18 41

Comment thread crates/oxc_semantic/src/checker/javascript.rs
@graphite-app graphite-app Bot added the 0-merge Merge with Graphite Merge Queue label May 22, 2026
@graphite-app graphite-app Bot changed the base branch from c/05-21-perf_semantic_reorder_ident_strict_mode_check to graphite-base/22653 May 22, 2026 00:52
@graphite-app graphite-app Bot force-pushed the c/05-21-perf_semantic_reorder_identifier_ambient_binding_check branch from f6673e8 to 80bd1b6 Compare May 22, 2026 00:55
@graphite-app graphite-app Bot force-pushed the graphite-base/22653 branch from 8f137c2 to 09fe178 Compare May 22, 2026 00:55
@graphite-app graphite-app Bot changed the base branch from graphite-base/22653 to main May 22, 2026 00:56
@graphite-app graphite-app Bot force-pushed the c/05-21-perf_semantic_reorder_identifier_ambient_binding_check branch from 80bd1b6 to 062956f Compare May 22, 2026 00:56
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graphite-app Bot commented May 22, 2026

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Merge activity

`check_identifier` runs for every identifier seen during semantic checking, but the ambient-binding exception only matters for the small set of names that can produce reserved-keyword diagnostics.

Previously we called `is_current_node_ambient_binding` before checking the identifier name, so every identifier paid for the ambient-context lookup even though most identifiers cannot trigger any of this function’s diagnostics. Moving the ambient check into the relevant match arms keeps the same behavior while making the common path cheaper: ordinary identifiers now fall through after the  name match without querying scope flags, symbol flags, or the current AST node.
@graphite-app graphite-app Bot force-pushed the c/05-21-perf_semantic_reorder_identifier_ambient_binding_check branch from 062956f to e32acd8 Compare May 22, 2026 04:21
@graphite-app graphite-app Bot merged commit e32acd8 into main May 22, 2026
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@graphite-app graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label May 22, 2026
@graphite-app graphite-app Bot deleted the c/05-21-perf_semantic_reorder_identifier_ambient_binding_check branch May 22, 2026 04:24
graphite-app Bot pushed a commit that referenced this pull request May 22, 2026
… <2 properties (#22668)

## Summary

A duplicate `__proto__` entry needs at least two property definitions — empty and single-property objects can't violate the rule. JSX/TSX call sites compile to enormous numbers of single-property object literals (`<Foo prop={x}>` → `{prop: x}`), so bailing before the loop setup and `prop_name()` call skips per-call overhead for the vast majority of `ObjectExpression` nodes seen during semantic checking.

## Context

The original version of this PR also reordered `check_identifier`, `check_identifier_reference`, and `check_binding_identifier` to defer expensive scope/symbol-flag loads behind a cheap name-match. While I was working on it, @camc314 shipped equivalent changes as three separate PRs (#22652, #22653, #22656). After rebasing onto `main`, only the `check_object_expression` early-exit remains as new work; the rest of the checker hot path is already covered.

This single change shows no measurable delta in `cargo bench --bench semantic` against current `main` (all five files within criterion's noise threshold) — JSX/TSX-heavy benches have already been driven down by the related PRs, and the property loop on a 1-property object is a fast path already. Pushing for completeness; happy to close if the maintainers would prefer to skip a change with no benchmark signal.

Verified by `cargo test -p oxc_semantic --features cfg` (72 tests) and `cargo clippy -p oxc_semantic --all-features`.

AI assisted.
Dunqing added a commit that referenced this pull request May 26, 2026
### 🚀 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]>
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