/ is not the same as f64::div for NaN

[jyn514]

I tried this code (playground):

use std::ops::Div;

fn main() {
    let slash: f64 = 0.0_f64 / 0.0_f64;
    let div: f64 = f64::div(0.0_f64, 0.0_f64);
    assert_eq!(slash.to_bits(), div.to_bits());
}

I expected to see this happen: The assert succeeds.

Instead, this happened: The assert fails.

thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `9221120237041090560`,
 right: `18444492273895866368`', src/main.rs:6:5

Note that this only happens in debug mode, the second you turn on -C opt-level=1 the assertion passes.

Meta

1.45.0-nightly (2020-05-19 3a7dfda)
The bug is also present on 1.43 stable.

[jyn514]

Closing as duplicate of #55131 (but I hope that issue gets some love!)