Compiling and running the following code with -C opt-level=0 for 32-bit Linux on a recent nightly (2020-06-07) results in a failing assertion.

fn main() {
    let masked_nan2 = f32::NAN.to_bits() ^ 0x0055_5555;
    assert_eq!(f32::from_bits(masked_nan2).to_bits(), masked_nan2);
}

rustc +nightly --target=i686-unknown-linux-gnu test.rs && ./test

Output:

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `2144687445`,
 right: `2140493141`', test.rs:3:5

However, this code is taken directly from a unit test for libstd added in #46012, so presumably it should succeed.