"argument never used" in new asm! syntax

[cesarb]

When trying to use the new asm! syntax to implement something similar to std::hint::black_box, it fails with an "argument never used" error. For example (https://godbolt.org/z/mG9AMg):

#![feature(asm)]

pub fn black_box(dummy: i32) -> i32 {
    unsafe {
        asm!("", in(reg) &dummy, options(nostack));
        dummy
    }
}

error: argument never used

 --> <source>:5:18

  |

5 |         asm!("", in(reg) &dummy, options(nostack));

  |                  ^^^^^^^^^^^^^^ argument never used


error: aborting due to previous error


Compiler returned: 1

This makes it impossible to use the new asm! syntax in one of my crates (cesarb/clear_on_drop@43cd2be with CI output at https://travis-ci.org/github/cesarb/clear_on_drop/jobs/694467164).

[Amanieu]

Fixed by #73230