`#[inline]` functions do not have their inline asm syntax checked

I tried this code:

#![no_std]

#[inline(always)]
pub fn checkasm() {
    unsafe {
        core::arch::asm!("nonsense");
    }
}

#[unsafe(no_mangle)]
fn foo() {
    // checkasm();
}

https://rust.godbolt.org/z/qWYnefq5a

I expected to see this happen: the lib would fail to compile

Instead, this happened: the lib compiles OK. But, if the function is actually called, then it does fail.

It is non-obvious that you can compile a library containing bad assembly if the function is marked inline(always).

See chat on Zulip: https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/inline.28always.29.20caused.20inline.20assembly.20to.20not.20get.20checked/near/541817357

Meta

I've seen this on 1.89 in Godbolt and on my desktop.

Start by reproducing the minimal #![no_std] example with #[inline(always)] and core::arch::asm!("nonsense"), both with and without a call to checkasm(). Investigate the compiler path that validates inline assembly for unused inline functions; done means the library is rejected for invalid assembly even when checkasm() is not called, with regression coverage for this example.