Atomic fetch_or fails to optimize right shift mask while left shift works

[SUPERCILEX]

use core::sync::atomic::*;

pub fn left(a: &AtomicU32, shift: u32) -> bool {
    let mask = 1 << shift;
    a.fetch_or(mask, Ordering::Relaxed) & mask == mask
}

pub fn right(a: &AtomicU32, shift: u32) -> bool {
    let mask = (1 << (u32::BITS - 1)) >> shift;
    a.fetch_or(mask, Ordering::Relaxed) & mask == mask
}

https://rust.godbolt.org/z/oYW1Y47EK

[SUPERCILEX]

Hmmm, left also seems to fail with let mask = 2 << shift;. Very finicky.