Understanding Rust Error E0511: Invalid Monomorphization of Intrinsic Functions

Rust Error E0511 Explanation

Rust Error E0511 occurs when there is an invalid monomorphization of an intrinsic function, specifically when a non-SIMD type is passed to a platform intrinsic function that expects a SIMD type.

What are Platform-Intrinsic Functions?

Platform-intrinsic functions are low-level functions that provide direct access to hardware-specific SIMD operations. These functions are usually platform-specific and have names that match the underlying instruction set.

What is SIMD?

SIMD (Single Instruction Multiple Data) is a class of parallel computers where the same operation is performed on multiple data points simultaneously. In this context, SIMD refers to vector or tuple data types that represent multiple values in parallel.

What is Monomorphization?

Monomorphization is the process of generating specific implementations of generic functions or data structures for the required concrete types. In Rust, this happens at compile time.

Erroneous Code Example

#![feature(platform_intrinsics)]

extern "platform-intrinsic" {
    fn simd_add<T>(a: T, b: T) -> T;
}

fn main() {
    unsafe { simd_add(0, 1); }
    // error: invalid monomorphization of `simd_add` intrinsic
}

In the erroneous code example above, a SIMD type is expected by the platform-intrinsic function simd_add, but instead, plain integers are passed. This results in Rust Error E0511.

Correct Code Example

#![allow(unused)]
#![feature(repr_simd)]
#![feature(platform_intrinsics)]

fn main() {
#[repr(simd)]
#[derive(Copy, Clone)]
struct i32x2(i32, i32);

extern "platform-intrinsic" {
    fn simd_add<T>(a: T, b: T) -> T;
}

unsafe { simd_add(i32x2(0, 0), i32x2(1, 2)); } // ok!
}

In this corrected code example, a proper SIMD type, i32x2, is defined and used as the input type for the simd_add function. This resolves the E0511 error.

Conclusion

To fix Rust Error E0511, ensure that you're using valid SIMD types as inputs for platform-intrinsic functions that require them. Defining and using appropriate SIMD types in your code will prevent this error from occurring.