Error code E0093

An unknown intrinsic function was declared.

Erroneous code example:

#![feature(intrinsics)]
#![allow(internal_features)]

#[rustc_intrinsic]
unsafe fn foo(); // error: unrecognized intrinsic function: `foo`

fn main() {
    unsafe {
        foo();
    }
}

Please check you didn't make a mistake in the function's name. All intrinsic functions are defined in library/core/src/intrinsics in the Rust source code.