They are in the process of marking them safe, which is enabled through the target_feature 1.1 RFC.

In fact, it has already been merged two weeks ago: https://github.com/rust-lang/stdarch/pull/1714

The change is already visible on nightly: https://doc.rust-lang.org/nightly/core/arch/x86/fn._mm_xor_s...

Compared to stable: https://doc.rust-lang.org/core/arch/x86/fn._mm_xor_si128.htm...

So this should be stable in 1.87 on May 15 (Rust's 10 year anniversary since 1.0)