perf(parser): shrink-wrap cold diagnostic tails out of hot frames#23159
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…3159) ## Finding (Pattern A from assembly audit — highest-leverage) An assembly audit found several hot lexer/parser functions carrying a large stack frame + callee-saved register spills **unconditionally**, purely to construct a ~232-byte `OxcDiagnostic` buffer on a cold error arm that almost never runs. Classic missed shrink-wrapping: the rare path's frame is paid on every hot return. ## Change Move each cold diagnostic arm out of line — `cold_branch(...)` (already the idiom for the sibling string-escape / line-break arms), or `#[inline(never)]` for the destructuring `cover` impls. | Function | frame before → after | notes | |---|---|---| | `QOD` / `QOS` (string handlers) | 288 B → **0 B** | now frameless leaves | | `LSS` (the `<` byte handler) | 288 B → **32 B** | `<!--` HTML-comment arm outlined | | `cursor::asi` | 288 B → **64 B** | ASI-failure diagnostic → closure | | `check_after_numeric_literal` | 336 B frame → **fully inlined** | invalid-number tail outlined | | `AssignmentTarget::cover` | 3066 instr / 448 B / 3 panic-sites → **225 / 176 B / 0** | `#[inline(never)]` on `Array`/`ObjectAssignmentTarget::cover` | These are the hottest-frame offenders the audit surfaced; the underlying pattern recurs elsewhere and could be pushed into the byte-handler macros as a follow-up. ## Verification - **Pure codegen change, no behavior change.** Conformance: **byte-identical** to `main` across all 31 snapshot suites (test262/babel/typescript × parser/semantic/codegen/estree/transformer/minifier/formatter). - Each frame shrink re-verified by disassembling before/after (ARM64, release codegen). ## Caveat Frame-size wins are instruction-count-scale; net effect on the per-token path must be confirmed on **CodSpeed** before merge. The `AssignmentTarget::cover` change moves the (rare) destructuring-target conversion out of line — confirm that path doesn't regress. 🤖 Generated with [Claude Code](https://claude.com/claude-code)
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### 💥 BREAKING CHANGES - 7a24911 codegen: [**BREAKING**] Borrow sourcemaps from codegen (#23422) (Boshen) - bb0ed44 transformer: [**BREAKING**] Disable styled-components transpileTemplateLiterals by default (#23171) (Boshen) ### 🚀 Features - 1490a0a linter/react: Implement react-compiler rule (#23202) (Boshen) - 6c0bdf0 transformer/react-refresh: Support `module.property.useHook()` (#23190) (Dunqing) - 47991bd semantic: Report TS1228 for invalid type predicates (#23174) (camc314) - 1d3af58 parser: Add TS2398 parameter property diagnostic (#23216) (camc314) - 44313da semantic: Add `scope_is_descendant_of` api (#22313) (camc314) - e5050c0 parser: Improve diagnostic for rest initializer (#23205) (camc314) - ec266bb transformer: Run React Compiler as a feature-gated transform pass (#23201) (Boshen) - e7374fe parser: Report error for `const` modifier on interface type parameter (#23173) (camc314) - a7c1c9b parser: Report ambient definite variable assertions (#23165) (camc314) - d169fcd parser: Report invalid class definite assertions (#23164) (camc314) - 00244d8 parser: Report definite property initializer errors (#23160) (camc314) ### 🐛 Bug Fixes - 52d0c31 transformer: Replace ambient dot defines (#23231) (camc314) - 2c28748 transformer/class: Parent generated constructors to class scope (#23222) (camc314) - 8edd234 parser: Report accessor definite assertion on token (#23203) (camc314) - de38a3f react_compiler: Keep imports referenced only by a local re-export (#23176) (Boshen) - f5721c2 codegen: Preserve parentheses around `intrinsic` type reference (#23156) (Boshen) - e89f81d parser: Don't emit TS1477 for parenthesized instantiation expression (#23147) (Boshen) - 8a04149 parser: Reject module-referencing imports/exports in a namespace body (#22829) (Boshen) ### ⚡ Performance - 2783295 parser: Table-driven operator precedence lookup (#23346) (Boshen) - 231d5de parser: Single-match member expression dispatch (#23347) (Boshen) - e89729b codegen: Accept one-shot wrap closures (#23265) (camc314) - a6c11fa parser: Force-inline read_non_decimal to fold per-digit number dispatch (#23157) (Boshen) - d74964c parser: Store class definite assertion offset (#23170) (camc314) - f0fda4d parser: Shrink-wrap cold diagnostic tails out of hot frames (#23159) (Boshen) - a082180 parser: Store definite assertion offset (#23167) (camc314) - 534f9c6 oxc: Conditionally rebuild semantic in compiler pipeline (#23153) (Boshen) - b435c6a parser: Skip checkpoint for `infer T extends U` constraint in disallow context (#23128) (Boshen) - 7464dce parser: Peek instead of checkpoint/rewind for `export default` modifier (#23124) (Boshen) - 80a9a32 parser: Fast-path single-keyword TS declarations (#23083) (Boshen) - da1a6c6 diagnostics: Migrate to allocation-optimized oxc-miette (#23094) (Boshen) - b7b08ce parser: Peek once for the static modifier disambiguation (#23079) (Boshen) - e7e07a3 parser: Fold unary dispatch into a single match (#23076) (Boshen) ### 📚 Documentation - d241add semantic: Add `AGENTS.md` test guidance for agents (#23441) (camc314) - 026f1ae parser: Add `AGENTS.md` test guidance for agents (#23440) (camc314) - 09755ac transformer: Add `AGENTS.md` test guidance for agents (#23439) (camc314) - e6bdfd4 lexer: Correct reference link for `byte_handlers!` (#23313) (Dunqing) - 65b6d7a allocator: Fix memory leaks in `Arena` examples (#23257) (overlookmotel) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
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Finding (Pattern A from assembly audit — highest-leverage)
An assembly audit found several hot lexer/parser functions carrying a large stack frame + callee-saved register spills unconditionally, purely to construct a ~232-byte
OxcDiagnosticbuffer on a cold error arm that almost never runs. Classic missed shrink-wrapping: the rare path's frame is paid on every hot return.Change
Move each cold diagnostic arm out of line —
cold_branch(...)(already the idiom for the sibling string-escape / line-break arms), or#[inline(never)]for the destructuringcoverimpls.QOD/QOS(string handlers)LSS(the<byte handler)<!--HTML-comment arm outlinedcursor::asicheck_after_numeric_literalAssignmentTarget::cover#[inline(never)]onArray/ObjectAssignmentTarget::coverThese are the hottest-frame offenders the audit surfaced; the underlying pattern recurs elsewhere and could be pushed into the byte-handler macros as a follow-up.
Verification
mainacross all 31 snapshot suites (test262/babel/typescript × parser/semantic/codegen/estree/transformer/minifier/formatter).Caveat
Frame-size wins are instruction-count-scale; net effect on the per-token path must be confirmed on CodSpeed before merge. The
AssignmentTarget::coverchange moves the (rare) destructuring-target conversion out of line — confirm that path doesn't regress.🤖 Generated with Claude Code