Error code E0668

Note: this error code is no longer emitted by the compiler.

Malformed inline assembly rejected by LLVM.

Erroneous code example:

#![feature(llvm_asm)]

fn main() {
    let rax: u64;
    unsafe {
        llvm_asm!("" :"={rax"(rax));
        println!("Accumulator is: {}", rax);
    }
}

LLVM checks the validity of the constraints and the assembly string passed to it. This error implies that LLVM seems something wrong with the inline assembly call.

In particular, it can happen if you forgot the closing bracket of a register constraint (see issue #51430), like in the previous code example.