perf(react_compiler): keep small hot-path collections inline#24514
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Boshen merged 2 commits intoJul 14, 2026
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The HIR operand/lvalue visitors (`each_instruction_value_operand`, `each_terminal_operand`, and friends) returned a fresh `Vec<Place>` for every instruction visited, and nearly every pass in the pipeline calls them in a loop. Operand lists are almost always one to four entries, so return a `SmallVec<[Place; 4]>` (aliased as `PlaceList`) and keep them on the stack. Element order and contents are unchanged. This introduces the crate's `smallvec` dependency (already a workspace dependency).
… helpers - `terminal_successors` returns a `SmallVec<[BlockId; 2]>` so the back-edge scan and the queue loop no longer heap-allocate per block; - `EffectKey::Apply` args and `CreateFunction` captures use inline small vectors, making typical key construction allocation-free.
Merging this PR will not alter performance
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Jul 21, 2026
### 💥 BREAKING CHANGES - 54cc121 ast: [**BREAKING**] Split `MetaProperty` into `ImportMeta` and `NewTarget` (#24557) (camc314) ### 🚀 Features - 4c71560 parser: More friendly error for spread element in dynamic imports (#24705) (sapphi-red) - 7b045cd minfier: Drop last break from last switch case (#24673) (Armano) - 7d3c178 minifier: Remove unreachable recursive functions (#24125) (Dunqing) - 94f99b3 ast: Allow `NONE` to be passed to AST builder methods where `Option<ArenaVec>` is expected (#24629) (overlookmotel) - 77230c5 ast: Accept arrays for `ArenaVec` params of AST builder methods (#24621) (overlookmotel) - f08b152 allocator: Implement `FromIn` for array to `Vec` conversion (#24620) (overlookmotel) - 2338c13 track-memory-allocations: Track heap deallocs, alloc bytes, and peak growth (#24619) (Boshen) - 7aa4739 syntax,transformer: Move JSX entity decoder to `oxc_syntax` (#24617) (camc314) - 2b097c4 str: Export `Str` as `ArenaStr` (#24604) (overlookmotel) - 3acf4c1 minifier: Expand switch optimiation to remove empty cases (#24520) (Armano) - 129b759 parser: Improve diagnostics for unparenthesized LHS on exponential expr (#24569) (camc314) - 4d0c601 minifier: Fold arithmetic over undefined and null operands (#24485) (Dunqing) - 91541dd minifier: Drop empty switch statements (#24527) (Armano) - d05224d ast_visit: Generate VisitJs visitor that skips TypeScript type-space (#24499) (Boshen) - 3d22307 parser: Add `ParseOptions::enable_ident_hashes` (#24491) (Boshen) ### 🐛 Bug Fixes - 64c2241 minifier: Align class heritage removal with assumptions (#24533) (Dunqing) - 48b59f4 parser: Span ambient generator diagnostics (#24711) (camc314) - e750a82 ecmascript: Fix false negative for may_have_side_effects on dynamic property access (#24709) (sapphi-red) - f145d73 minifier: Guard reordered identifier reads (#24698) (Dunqing) - a2ef382 isolated-declarations: Reject `window.Symbol` as global symbol reference (#24689) (camc314) - b1bcf72 minifier: Invalidate facts for redeclared bindings (#24658) (Dunqing) - 921b834 minifier: Don't treat a conditionally-assigned var as write-once (#24650) (Dunqing) - 061af1f minifier: Avoid stale pure function summaries (#24636) (Dunqing) - 40c2f43 allocator: `Vec::from_array_in` do not allocate zero-length array (#24628) (overlookmotel) - 70994ae codegen: Preserve comments before expression operands (#24510) (Dunqing) - 7b4baff parser: Reject new import member access (#23459) (camc314) - 128b385 minifier: Clippy warning with no-debug-assertions (#24547) (camc314) - 8421feb parser: Use first `as` span for imported name (#24537) (leaysgur) - c517aa0 parser: Reject invalid accessor assertions (#24504) (camc314) ### ⚡ Performance - 884d9eb parser: Pre-size cover-grammar assignment target buffers (#24683) (Boshen) - d3f07a0 diagnostics: Box OxcDiagnosticInner to reduce binary size (#24665) (Boshen) - bcc9de0 parser: Defer diagnostic creation until parse exit (#24663) (Boshen) - c35d8ab allocator: Mark `ReplaceWith` panic path cold (#24515) (camc314) - ba65790 semantic, allocator: Branchless `clone_in` for semantic IDs (#24564) (overlookmotel) - 747feec parser: Build AST nodes with the AST builder instead of cloning (#24540) (Boshen) - ba35a0d react_compiler: Use IndexVec for dense id-keyed maps (#24549) (Boshen) - b685062 react_compiler: Keep small hot-path collections inline (#24514) (Marius Schulz) - a149e95 transformer: Outline rare expression exits (#24512) (camc314) - 7808a6e react_compiler: Make aliasing effects cheap to intern and clone (#24506) (Marius Schulz) - 3a36f2a react_compiler: Store AbstractValue reasons as a u16 bitmask (#24480) (Boshen) - 1c96753 react_compiler: Use FxHashMap for the lookup-only aliasing node map (#24490) (Boshen) Co-authored-by: Cameron <[email protected]>
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What
Two kinds of small, hot collections in the react-compiler pass get heap-allocated on every use:
each_instruction_value_operand,each_terminal_operand, and friends) build a freshVec<Place>for every instruction they're called on, and nearly every pass calls them in a loop. The lists almost always hold one to four entries.terminal_successors) and an args/captures list per interned effect (EffectKey).Change
PlaceList = SmallVec<[Place; 4]>; element order and contents are unchanged.terminal_successorsreturns aSmallVec<[BlockId; 2]>, andEffectKey::Applyargs /CreateFunctioncaptures are inline small vectors, so building a typical key no longer allocates.smallvecto the crate (already a workspace dependency).Numbers from the stock release profile (fat LTO), linting cal.com with
react/react-compileras the only enabled rule,--threads=1:Verification
reportAllBailoutsboth on and off (full stdout/stderr and exit codes, single-threaded).cargo test -p oxc_react_compiler(including the fixture snapshot suite), clippy, and rustfmt are all clean.This PR was assisted by Claude Code.