From 623d6e8ca423e37daf435136da32697e3cdd605b Mon Sep 17 00:00:00 2001 From: Zalathar Date: Mon, 3 Feb 2025 21:31:06 +1100 Subject: Notes on types/traits used for in-memory query caching When the word "cache" appears in the context of the query system, it often isn't obvious whether that is referring to the in-memory query cache or the on-disk incremental cache. For these types, we can assure the reader that they are for in-memory caching. --- compiler/rustc_data_structures/src/vec_cache.rs | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'compiler/rustc_data_structures/src') diff --git a/compiler/rustc_data_structures/src/vec_cache.rs b/compiler/rustc_data_structures/src/vec_cache.rs index eb251b587c8..2ff60ab7f36 100644 --- a/compiler/rustc_data_structures/src/vec_cache.rs +++ b/compiler/rustc_data_structures/src/vec_cache.rs @@ -206,6 +206,19 @@ impl SlotIndex { } } +/// In-memory cache for queries whose keys are densely-numbered IDs +/// (e.g `CrateNum`, `LocalDefId`), and can therefore be used as indices +/// into a dense vector of cached values. +/// +/// (As of [#124780] the underlying storage is not an actual `Vec`, but rather +/// a series of increasingly-large buckets, for improved performance when the +/// parallel frontend is using multiple threads.) +/// +/// Each entry in the cache stores the query's return value (`V`), and also +/// an associated index (`I`), which in practice is a `DepNodeIndex` used for +/// query dependency tracking. +/// +/// [#124780]: https://github.com/rust-lang/rust/pull/124780 pub struct VecCache { // Entries per bucket: // Bucket 0: 4096 2^12 -- cgit 1.4.1-3-g733a5