Merge pull request #2977 from KodrAus/simd-pg

[RFC]: Portable SIMD Libs Project Group

Author: Mark-Simulacrum

text/2977-stdsimd.md

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+- Feature Name: stdsimd_project_group
+- Start Date: 2020-08-28
+- RFC PR: [rust-lang/rfcs#2977](https://github.com/rust-lang/rfcs/pull/2977)
+- Rust Issue: [rust-lang/rust-libs#4](https://github.com/rust-lang/libs-team/issues/4)
+
+# Summary
+[summary]: #summary
+
+This is a project group RFC version of [`lang-team#29`].
+
+This RFC establishes a new project group, under the libs team, to produce a portable SIMD API in a new `rust-lang/stdsimd` repository, exposed through a new `std::simd` (and `core::simd`) module in the standard library in the same manner as [`stdarch`]. The output of this project group will be the finalization of [RFC 2948] and stabilization of `std::simd`.
+
+# Motivation
+[motivation]: #motivation
+
+The current stable `core::arch` module is described by [RFC 2325], which considers a portable API desirable but out-of-scope. The current [RFC 2948] provides a good motivation for this API. Various ecosystem implementations of portable SIMD have appeared over the years, including [`packed_simd`], and [`wide`], each taking a different set of trade-offs in implementation while retaining some similarities in their public API. The group will pull together a "blessed" implementation in the standard library with the explicit goal of stabilization for the [2021 edition].
+
+# Charter
+[charter]: #charter
+
+## Goals
+
+- Determine the shape of the portable SIMD API.
+- Get an unstable `std::simd` and `core::simd` API in the standard library. This may mean renaming `packed_simd` to `stdsimd` and working directly on it, or creating a new repository and pulling in chunks of code as needed.
+- Produce a stabilization plan to allow portions of `std::simd` to be stabilized when they're ready, and coordinate with other unstable features.
+- Respond to user feedback and review contributions to the API.
+- Update [RFC 2948] based on the final API and stabilization plan.
+- Stabilize `std::simd`!
+
+## Non Goals
+
+- This group isn't directly attempting to build out more `core::arch` APIs.
+
+## Membership Requirements
+
+- Group membership is open, any interested party can participate in discussions, repeat contributors will be added to appropriate teams.
+
+## Additional Questions
+
+### What support do you need, and separately want, from the Rust organization?
+
+Support scaffolding a space to work and integrating `stdsimd` into `libcore` and input from engineers who are familiar with this space.
+
+### Why should this be a project group over a community effort?
+
+Community efforts have already produced libraries that are in use, but pulling those together in the standard library needs a group with permissions to get things merged.
+
+### What do you expect the relationship to the team be?
+
+The project group will regularly update libs on how things are going, whether there are any blockers
+
+### Who are the initial shepherds/leaders? (This is preferably 2–3 individuals, but not required.)
+
+- @BurntSushi
+- @calebzulawski
+- @hsivonen
+- @KodrAus
+- @Lokathor
+
+### Is your group long-running or temporary?
+
+Temporary
+
+### If it is temporary, how long do you see it running for?
+
+Until the 2021 edition, which is probably mid 2021.
+
+### If applicable, which other groups or teams do you expect to have close contact with?
+
+The project group will interact with:
+
+- libs
+- compiler
+
+### Where do you see your group needing help?
+
+There will be lots of feedback to gather from users and input from compiler developers on how to approach implementation.
+
+[`packed_simd`]: https://github.com/rust-lang/packed_simd
+[`wide`]: https://github.com/Lokathor/wide
+[`stdarch`]: https://github.com/rust-lang/stdarch
+[2021 edition]: https://github.com/rust-lang/rfcs/pull/2966
+[RFC 2948]: https://github.com/rust-lang/rfcs/pull/2948
+[RFC 2325]: https://rust-lang.github.io/rfcs/2325-stable-simd.html
+[`lang-team#29`]: https://github.com/rust-lang/lang-team/issues/29