rust/compiler/rustc_transmute/src/lib.rs, branch cargo_update

transmutability: shift abstraction boundary

2025-06-09T14:08:12+00:00

Previously, `rustc_transmute`'s layout representations were genericized over `R`, a reference. Now, it's instead genericized over representations of type and region. This allows us to move reference transmutability logic from `rustc_trait_selection` to `rustc_transmutability` (and thus unit test it independently of the compiler), and — in a follow-up PR — will make it possible to support analyzing function pointer transmutability with minimal surgery.

transmutability: Mark edges by ranges, not values

2025-04-23T18:45:00+00:00

In the `Tree` and `Dfa` representations of a type's layout, store byte ranges rather than needing to separately store each byte value. This permits us to, for example, represent a `u8` using a single 0..=255 edge in the DFA rather than using 256 separate edges. This leads to drastic performance improvements. For example, on the author's 2024 MacBook Pro, the time to convert the `Tree` representation of a `u64` to its equivalent DFA representation drops from ~8.5ms to ~1us, a reduction of ~8,500x. See `bench_dfa_from_tree`. Similarly, the time to execute a transmutability query from `u64` to `u64` drops from ~35us to ~1.7us, a reduction of ~20x. See `bench_transmute`.

transmutability: remove NFA intermediate representation

2025-04-20T03:06:59+00:00

Prior to this commit, the transmutability analysis used an intermediate NFA representation of type layout. We then determinized this representation into a DFA, upon which we ran the core transmutability analysis. Unfortunately, determinizing NFAs is expensive. In this commit, we avoid NFAs entirely by observing that Rust `union`s are the only source of nondeterminism and that it is comparatively cheap to compute the DFA union of DFAs. We also implement Graphviz DOT debug formatting of DFAs. Fixes rust-lang/project-safe-transmute#23 Fixes rust-lang/project-safe-transmute#24

Remove `recursion_limit` increases.

2025-04-02T05:25:27+00:00

These are no longer needed now that `Nonterminal` is gone.

Auto merge of #138414 - matthiaskrgr:rollup-9ablqdb, r=matthiaskrgr

2025-03-12T17:27:43+00:00

Rollup of 7 pull requests Successful merges: - #137314 (change definitely unproductive cycles to error) - #137701 (Convert `ShardedHashMap` to use `hashbrown::HashTable`) - #138269 (uefi: fs: Implement FileType, FilePermissions and FileAttr) - #138331 (Use `RUSTC_LINT_FLAGS` more) - #138345 (Some autodiff cleanups) - #138387 (intrinsics: remove unnecessary leading underscore from argument names) - #138390 (fix incorrect tracing log) r? `@ghost` `@rustbot` modify labels: rollup

Remove `#![warn(unreachable_pub)]` from all `compiler/` crates.

2025-03-11T02:14:21+00:00

It's no longer necessary now that `-Wunreachable_pub` is being passed.

Revert "Use workspace lints for crates in `compiler/` #138084"

2025-03-10T10:12:47+00:00

Revert to buy time to consider options that avoids breaking downstream usages of cargo on distributed `rustc-src` artifacts, where such cargo invocations fail due to inability to inherit `lints` from workspace root manifest's `workspace.lints` (this is only valid for the source rust-lang/rust workspace, but not really the distributed `rustc-src` artifacts). This breakage was reported in . This reverts commit 48caf81484b50dca5a5cebb614899a3df81ca898, reversing changes made to c6662879b27f5161e95f39395e3c9513a7b97028.

Remove `#![warn(unreachable_pub)]` from all `compiler/` crates.

2025-03-07T21:41:43+00:00

(Except for `rustc_codegen_cranelift`.) It's no longer necessary now that `unreachable_pub` is in the workspace lints.

Increase recursion_limit in numerous crates.

2025-03-07T03:51:07+00:00

This is temporarily needed for `x doc compiler` to work. They can be removed once the `Nonterminal` is removed (#124141).

Remove `allow(unused_variables)` for `rustc_transmute`.

2025-02-28T06:31:31+00:00

This was hiding some genuine sins, including unused arguments in numerous functions/methods (incl. trait methods), and some unnecessary computation.