or_patterns: incorrect unreachable pattern warning

[lcnr]

#![feature(or_patterns)]

enum F {
    A,
    B,
}

fn main() {
    let a = F::A;
    let b = F::B;
    match (a, b) {
        (F::A, F::A) => (),
        (F::B | F::A, F::B | F::A) => (),
    }
}

Results in the following incorrect warning:

warning: unreachable pattern
  --> src/main.rs:13:30
   |
13 |         (F::B | F::A, F::B | F::A) => (),
   |                              ^^^^
   |
   = note: `#[warn(unreachable_patterns)]` on by default

warning: 1 warning emitted

Removing F::A causes a non-exhaustive patterns error as expected.

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