Rust SIMD tokens prove which CPU instructions are available

Sergey Davidoff explains how fearless_simd uses unforgeable, zero-sized tokens to represent successful CPU feature checks. Safe wrappers pass those tokens to functions whose required instruction sets Rust verifies, concentrating unsafe code into fewer places. The design supports ordinary vector arithmetic, but correct inlining remains crucial: code can still compile while losing the performance benefit. This June article is a library-design deep dive.

Sergey Davidoff · Jun 19, 2026

Why it matters

A practical example of making invalid operations difficult to express through a type-safe interface.

More context

Try the linked fearless_simd example and inspect generated assembly for the target CPU. The article describes version 0.5 and Rust 1.87’s target-feature changes; check current compatibility before integrating it.

Keep in mind

The approach reduces the unsafe surface rather than eliminating it, and callers must still respect documented inlining requirements.

Original read