False postive: warning of unnecessary `unsafe` block

[zjp-CN]

Code

I tried this code:

fn main() {
    let a = unsafe { core::arch::x86_64::__cpuid_count(0, 0) };
    dbg!(a);
}

I expected to see this happen: it compiles without warnings.

Instead, this happened: it compiles with a warning of unnecessary unsafe block

warning: unnecessary `unsafe` block
 --> src/main.rs:2:13
  |
2 |     let a = unsafe { core::arch::x86_64::__cpuid_count(0, 0) };
  |             ^^^^^^ unnecessary `unsafe` block
  |
  = note: `#[warn(unused_unsafe)]` (part of `#[warn(unused)]`) on by default

Version it worked on

Stable channel 1.93.0 doesn't emit that.

Version with regression

Beta channel 1.94.0-beta.2 emits that. (2026-01-25 23a44d3)

Nightly channel 1.95.0-nightly emits that. (2026-02-08 6efa357)

The code can be reproduced on the present plaground: stable vs beta.

[zjp-CN]

It's because __cpuid_count turns safe on beta and nightly, while it's unsafe on stable.

It was changed since 3e8185f . Is it intended with ACP?

[inkreasing]

github.com/rust-lang/stdarch/pull/1935 there was FCP on it

[jieyouxu]

Reported already as rust-lang/stdarch#1990

The lint itself is not a FP, it's whether cpuid should be safe (which as correctly noted above was dual-FCP'd by libs-api and lang) or use some other mechanism.