perf(allocator): move code into cold path in Arena::alloc_layout#21622
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Pull request overview
This PR optimizes Arena::alloc_layout by ensuring the “panic on OOM” logic is confined to the cold (slow) path, reducing the amount of code inlined into hot call sites and improving downstream inlining opportunities.
Changes:
- Refactors
alloc_layoutto calltry_alloc_layout_fastdirectly and delegate failures to a coldalloc_layout_slow. - Splits the prior slow-path implementation into
alloc_layout_slow(panicking) andtry_alloc_layout_slow(non-panicking) with a sharedtry_alloc_layout_slow_impl.
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…21622) Previously `Arena::alloc_layout` behaved as follows: 1. Call `try_alloc_layout_fast` (fast path for common case that allocation can be serviced by current chunk). 2. If that fails, call `alloc_layout_slow` (cold path). 3. Check that `alloc_layout_slow` succeeded, panic if not. Step 3 did not add instructions to the fast path, but it was inlined into all call sites. Since step 3 is only required if `try_alloc_layout_fast` fails (rare case), instead move step 3 into the cold path. This reduces the amount of code inlined into call sites, making those functions more likely to be eligible for inlining themselves.
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April 22, 2026 00:03
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### 💥 BREAKING CHANGES - 502e804 ast: [**BREAKING**] Reduce size of `TSTypePredicateName` (#21711) (overlookmotel) - 5651539 ast: [**BREAKING**] Reduce size of `JSXExpression` (#21710) (overlookmotel) - c44e280 ast: [**BREAKING**] Reduce size of `ArrayExpressionElement` (#21709) (overlookmotel) - c5b3deb syntax: [**BREAKING**] Remove `CommentNodeId` (#21679) (overlookmotel) ### 🚀 Features - b738a39 allocator: Add `Allocator::cursor_ptr` method (#21773) (overlookmotel) - 678767e ast: Generate node_id accessors for AST enum wrappers (#21653) (camc314) - f091d77 minifier: Inline constant spread elements into arrays (#21095) (Armano) ### 🐛 Bug Fixes - 0d608c2 minifier: Preserve raw CR in template literals (#21645) (Dunqing) - a889ea9 minifier: Track pure functions in DCE mode (#21722) (Dunqing) - 674dfac allocator: `Arena` retry allocation when chunk size approaches maximum (#21777) (overlookmotel) - f130cc0 allocator: Fix arithmetic overflow in `Arena::new_chunk_memory_details` (#21745) (overlookmotel) - b9bf239 allocator: Fix UB in `Arena::grow_zeroed` (#21739) (overlookmotel) - d2b9389 allocator: Clippy warning when building without `testing` feature (#21681) (camc314) - 503dc86 codegen: Map sourcemaps from visible output starts (#21662) (Dunqing) - c92bd3b transformer: Use SPAN for synthesized helper calls to prevent comment misattribution (#21578) (Dunqing) - 0d80441 codegen: Add mapping before printing `#` for private ident (#21619) (camc314) ### ⚡ Performance - 9fa362e napi/parser: Do not generate tokens except in tests (#21811) (overlookmotel) - 0044392 allocator: Reduce branches when allocating new chunk (#21776) (overlookmotel) - 7896bd0 allocator: `Allocator::used_bytes` do not use chunk iterator (#21771) (overlookmotel) - a5c562f allocator: Remove check in `Arena::new_chunk_memory_details` (#21750) (overlookmotel) - 35bbe1f allocator: `Arena` use unchecked size round up where guaranteed no overflow (#21743) (overlookmotel) - ffe229b allocator: Remove unnecessary check from `Arena::try_alloc_layout_slow_impl` (#21732) (overlookmotel) - 72fece5 allocator: Use `NonNull::offset_from_unsigned` in `Arena::chunk_capacity` (#21731) (overlookmotel) - cab32ae ast: Add `#[inline(always)]` to `node_id` methods on enums with all variants unboxed (#21707) (overlookmotel) - b179688 parser: Allocate `TriviaBuilder` comments in the arena (#21512) (Boshen) - 2290f31 lexer: Fix perf of `Token::set_*` methods on Rust 1.95.0 (#21659) (overlookmotel) - 1b58029 allocator: Move code into cold path in `Arena::alloc_layout` (#21622) (overlookmotel) - 3cf7cef allocator: Reduce instructions on allocation hot path (#21510) (overlookmotel) ### 📚 Documentation - ce65070 data_structures: Document why `as_ref` and `as_mut` on `NonNullConst` and `NonNullMut` take `self` (#21800) (overlookmotel) - 93b7dbd allocator: Improve doc comments for `ChunkFooter` (#21733) (overlookmotel) - 295db8d transformer: Fix comment (#21717) (overlookmotel) - 5c93af8 ast: Add comments explaining `#[inline(always)]` to `node_id` methods on enums (#21706) (overlookmotel) - e4cea25 transform: Use the `node:` namespace in the example (#19998) (루밀LuMir) ### 🛡️ Security - d8076c9 deps: Update rolldown (#21639) (renovate) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
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Previously
Arena::alloc_layoutbehaved as follows:try_alloc_layout_fast(fast path for common case that allocation can be serviced by current chunk).alloc_layout_slow(cold path).alloc_layout_slowsucceeded, panic if not.Step 3 did not add instructions to the fast path, but it was inlined into all call sites.
Since step 3 is only required if
try_alloc_layout_fastfails (rare case), instead move step 3 into the cold path. This reduces the amount of code inlined into call sites, making those functions more likely to be eligible for inlining themselves.