perf(allocator): add #[cold] annotations to error handling functions#18181
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Pull request overview
This PR adds performance optimization attributes (#[cold] and #[inline(never)]) to error handling and panic functions in the oxc_allocator crate to improve branch prediction and code layout for hot allocation paths.
Changes:
- Added
#[cold]attribute toallocation_size_overflowinbump.rs(already had#[inline(never)]) - Added both
#[cold]and#[inline(never)]attributes tonew_layout_errandhandle_alloc_errorinbumpalo_alloc.rs - Added both
#[cold]and#[inline(never)]attributes tocapacity_overflowinvec2/raw_vec.rs
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
crates/oxc_allocator/src/bump.rs |
Added #[cold] to allocation_size_overflow function |
crates/oxc_allocator/src/bumpalo_alloc.rs |
Added #[cold] and #[inline(never)] to new_layout_err and handle_alloc_error functions |
crates/oxc_allocator/src/vec2/raw_vec.rs |
Added #[cold] and #[inline(never)] to capacity_overflow function |
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…18181) ## Summary - Add `#[cold]` and `#[inline(never)]` annotations to error/panic functions in oxc_allocator - Improves branch prediction and code layout for hot allocation paths ### Functions annotated | File | Function | Change | |------|----------|--------| | `bump.rs` | `allocation_size_overflow` | Added `#[cold]` | | `bumpalo_alloc.rs` | `new_layout_err` | Added `#[cold]` + `#[inline(never)]` | | `bumpalo_alloc.rs` | `handle_alloc_error` | Added `#[cold]` + `#[inline(never)]` | | `vec2/raw_vec.rs` | `capacity_overflow` | Added `#[cold]` + `#[inline(never)]` | ### Impact The `#[cold]` attribute tells the compiler to: 1. Assume branches leading to these functions are unlikely 2. Move cold code away from hot paths (improves i-cache locality) 3. Avoid inlining cold functions into hot callers ## Test plan - [x] `cargo test -p oxc_allocator` passes 🤖 Generated with [Claude Code](https://claude.com/claude-code)
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This was referenced Apr 2, 2026
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#18168 copied `bumpalo`'s code for `Bump` into `oxc_allocator` crate. #18172, #18181, and #18234 made a few improvements to the implementation. However, #18168 removed various things, and altered others. Notably, it removed the`MIN_ALIGN` generic param, which we definitely want to keep. I'm going to be working on the allocator, and would like to start with a clean slate, beginning with the "known good" implementation of `bumpalo`. This PR removes the previous modified `bumpalo` implementation, and copies latest version of `bumpalo` from main branch into the repo. It then makes the absolute minimum changes necessary just to make CI pass. Note: Unlike #18168, this PR keeps all the doctests for `Bump`, using a trick of adding the crate to it's own `dev-dependencies` with `testing` feature enabled, and exposing `Bump` only with that feature. This PR is broken into multiple commits, so we have an exact "trail of breadcrumbs" of how we've diverged from `bumpalo`. I intend to manually merge this PR, so that record remains on Github (instead of Graphite squashing all the commits). Later PRs in this stack reapply the changes made in #18172, #18181, and #18234 on top of the fresh base implementation. This PR is a small perf regression, but that will be won back once those other changes are reapplied.
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Repeat of #18181. #20963 wiped all changes to `bumpalo_alloc.rs`, going back to a fresh copy of `bumpalo`. Re-apply changes from #18181 which were lost in the process - marking error handling functions as `#[cold]`. This PR differs from #18181 in one minor respect. `new_layout_err` is not marked `#[inline(never)]` in this PR. The function is a no-op (unconditionally returns a ZST), so we do want it inlined, but with the`#[cold]`attribute to hint to compiler that it's a cold path.
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Summary
#[cold]and#[inline(never)]annotations to error/panic functions in oxc_allocatorFunctions annotated
bump.rsallocation_size_overflow#[cold]bumpalo_alloc.rsnew_layout_err#[cold]+#[inline(never)]bumpalo_alloc.rshandle_alloc_error#[cold]+#[inline(never)]vec2/raw_vec.rscapacity_overflow#[cold]+#[inline(never)]Impact
The
#[cold]attribute tells the compiler to:Test plan
cargo test -p oxc_allocatorpasses🤖 Generated with Claude Code