Nightly support for ergonomic SIMD multiversioning

[nikomatsakis]

Metadata
Point of contact	@veluca93
Team(s)	lang
Goal document	2025h1/simd-multiversioning

Summary

Figure out the best way for Rust to support generating code for multiple SIMD targets in a safe and ergonomic way.

Tasks and status

• Design meeting (lang )
• Lang-team experiment (lang )
• Experimental implementation (@veluca93)
• Author RFC (@veluca93)
• RFC decision (lang )

[nikomatsakis]

This issue is intended for status updates only.

For general questions or comments, please contact the owner(s) directly.

[veluca93]

Key developments: Further discussions on implementation details of the three major proposed ways forward. Requested a design meeting in rust-lang/lang-team#309.

[veluca93]

Key developments: Started investigating how the proposed SIMD multiversioning options might fit in the context of the efforts for formalizing a Rust effect system

[veluca93]

Key developments: nothing substantial.

[veluca93]

Key developments: rust-lang/rust#139368 was opened, which poses some possibly-relevant questions on the interaction between the target_feature attribute and traits. Otherwise, still trying to get a better understanding of the interaction between target feature and effects.