Multiversion

Function multiversioning attribute macros for Rust.

What is function multiversioning?

Many CPU architectures have a variety of instruction set extensions that provide additional functionality. Common examples are single instruction, multiple data (SIMD) extensions such as SSE and AVX on x86/x86-64 and NEON on ARM/AArch64. When available, these extended features can provide significant speed improvements to some functions. These optional features cannot be haphazardly compiled into programs--executing an unsupported instruction will result in a crash.

Function multiversioning is the practice of compiling multiple versions of a function with various features enabled and safely detecting which version to use at runtime.

Features

• Dynamic dispatching, using runtime CPU feature detection
• Static dispatching, avoiding repeated feature detection for nested multiversioned functions (and allowing inlining!)
• Support for all functions, including generic and async

Example

Automatic function multiversioning with the clone attribute, similar to GCC's target_clones attribute:

use multiversion::multiversion;

#[multiversion]
#[clone(target = "[x86|x86_64]+avx")]
#[clone(target = "x86+sse")]
fn square(x: &mut [f32]) {
    for v in x {
        *v *= *v;
    }
}

Manual function multiversioning with the multiversion and target attributes:

use multiversion::{multiversion, target};

#[target("[x86|x86_64]+avx")]
unsafe fn square_avx(x: &mut [f32]) {
    for v in x {
        *v *= *v;
    }
}

#[target("x86+sse")]
unsafe fn square_sse(x: &mut [f32]) {
    for v in x {
        *v *= *v;
    }
}

#[multiversion]
#[specialize(target = "[x86|x86_64]+avx", fn = "square_avx", unsafe = true)]
#[specialize(target = "x86+sse", fn = "square_sse", unsafe = true)]
fn square(x: &mut [f32]) {
    for v in x {
        *v *= *v;
    }
}

License

Multiversion is distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.