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Rollup merge of #155778 - kevinheavey:perf-mk-place-elem-avoid-vec-alloc, r=cjgillot,JohnTitor

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Avoid Vec allocation in TyCtxt::mk_place_elem

`mk_place_elem` appends a single `PlaceElem` to an existing (interned) projection. The current implementation copies the projection into a fresh `Vec`, pushes the new element, and re-interns the slice, which allocates on every call.

Feed the elements through `mk_place_elems_from_iter` so that `CollectAndApply`'s hand-unrolled stack fast path (up to 9 elements, in `rustc_type_ir::interner`) kicks in for the common case of short projections and the `Vec` allocation is skipped entirely. The behavior is identical for longer projections (the fast path falls back to a `Vec` internally).
This commit is contained in:
Jacob Pratt
2026-04-26 21:56:42 -04:00
committed by GitHub
parent f4043f8c09 5cd9d929a9
commit c20a92efd9
1 changed files with 4 additions and 4 deletions
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compiler/rustc_middle/src/ty/context.rs
+4 -4
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@@ -2416,10 +2416,10 @@ pub fn mk_place_index(self, place: Place<'tcx>, index: Local) -> Place<'tcx> {
/// to build a full `Place` it's just a convenient way to grab a projection and modify it in
/// flight.
pub fn mk_place_elem(self, place: Place<'tcx>, elem: PlaceElem<'tcx>) -> Place<'tcx> {
let mut projection = place.projection.to_vec();
projection.push(elem);
Place { local: place.local, projection: self.mk_place_elems(&projection) }
Place {
local: place.local,
projection: self.mk_place_elems_from_iter(place.projection.iter().chain([elem])),
}
}
pub fn mk_poly_existential_predicates(