inline asm opt-level 3 where function incorrectly marked as dead_code

[mark3982]

#![feature(asm)]

fn main() {
    unsafe {
        asm!("call foobar");
    }
}

#[no_mangle]
fn foobar() {

}

The symbol and function foobar are dropped on highest optimization level, because I assume that rustc does not detect that it is referenced.

I believe that it could make sense for it to determine that it is indeed referenced.

[mark3982]

However, after careful thought I came to the conclusion that it may also be difficult to offer detection, and considering that the assembly shoots straight through to LLVM it may require additional complexity in rustc and I would rather keep things simple and clean and find other ways to achieve the result if possible - but I will leave this issue open because just maybe someone might have a different view or more accurate thought on the issue.

[kmcallister]

Related: #13365, but that one's pub.

I agree that this is hard to fix for private items, and probably not worth it.

[steveklabnik]

Triage: this is the same today.

Given that nobody has commented on this issue in a year, and both of you aren't even sure it's worth it, giving this a close.