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Simonas Kazlauskas 6db94dbc25 abi: add a rust-preserve-none calling convention 
This is the conceptual opposite of the rust-cold calling convention and
is particularly useful in combination with the new `explicit_tail_calls`
feature.

For relatively tight loops implemented with tail calling (`become`) each
of the function with the regular calling convention is still responsible
for restoring the initial value of the preserved registers. So it is not
unusual to end up with a situation where each step in the tail call loop
is spilling and reloading registers, along the lines of:

    foo:
        push r12
        ; do things
        pop r12
        jmp next_step

This adds up quickly, especially when most of the clobberable registers
are already used to pass arguments or other uses.

I was thinking of making the name of this ABI a little less LLVM-derived
and more like a conceptual inverse of `rust-cold`, but could not come
with a great name (`rust-cold` is itself not a great name: cold in what
context? from which perspective? is it supposed to mean that the
function is rarely called?)
2026-01-24 19:23:17 +02:00
..
src abi: add a rust-preserve-none calling convention 2026-01-24 19:23:17 +02:00
Cargo.toml rustc_public: Make Id types !Send / !Sync 2025-11-19 19:46:18 +00:00
README.md rename stable_mir to rustc_public, and rustc_smir to rustc_public_bridge 2025-07-14 09:25:54 +00:00
rust-toolchain.toml rename stable_mir to rustc_public, and rustc_smir to rustc_public_bridge 2025-07-14 09:25:54 +00:00

README.md

This crate is currently developed in-tree together with the compiler.

Our goal is to start publishing stable_mir into crates.io. Until then, users will use this as any other rustc crate, by installing the rustup component rustc-dev, and declaring stable-mir as an external crate.

See the StableMIR "Getting Started" guide for more information.

Stable MIR Design

The stable-mir will follow a similar approach to proc-macro2. Its implementation is split between two main crates:

  • stable_mir: Public crate, to be published on crates.io, which will contain the stable data structure as well as calls to rustc_smir APIs. The translation between stable and internal constructs will also be done in this crate, however, this is currently implemented in the rustc_smir crate.1.
  • rustc_smir: This crate implements the public APIs to the compiler. It is responsible for gathering all the information requested, and providing the data in its unstable form.

I.e., tools will depend on stable_mir crate, which will invoke the compiler using APIs defined in rustc_smir.

I.e.:

    ┌──────────────────────────────────┐           ┌──────────────────────────────────┐
    │   External Tool     ┌──────────┐ │           │ ┌──────────┐   Rust Compiler     │
    │                     │          │ │           │ │          │                     │
    │                     │stable_mir| │           │ │rustc_smir│                     │
    │                     │          │ ├──────────►| │          │                     │
    │                     │          │ │◄──────────┤ │          │                     │
    │                     │          │ │           │ │          │                     │
    │                     │          │ │           │ │          │                     │
    │                     └──────────┘ │           │ └──────────┘                     │
    └──────────────────────────────────┘           └──────────────────────────────────┘

More details can be found here: https://hackmd.io/XhnYHKKuR6-LChhobvlT-g?view

  1. This is currently implemented in the rustc_smir crate, but we are working to change that. ↩︎