"Unreachable definition" warning after infallible expression in `if`-block

[fnetz]

The following snippet generates an "unreachable definition" warning at let _x = 1 (godbolt at 1.69):

fn infallible() -> std::convert::Infallible {
    loop {}
}

fn main() {
    if false {
        infallible();
    }

    let _x = 1;
}

Full output:

warning: unreachable definition
  --> <source>:10:9
   |
7  |         infallible();
   |         ------------ any code following this expression is unreachable
...
10 |     let _x = 123;
   |         ^^ unreachable definition
   |
note: this expression has type `Infallible`, which is uninhabited
  --> <source>:7:9
   |
7  |         infallible();
   |         ^^^^^^^^^^^^
   = note: `#[warn(unreachable_code)]` on by default

Runtime behaviour is as expected (it exits), so this warning seems wrong.

This occurs in rustc 1.71.0-nightly (c4190f2 2023-05-07) all the way back to rustc 1.56.

A similar issue (with an expression instead of a definition) has been brought up in #89779. However, that specific case disappeared in rustc 1.60.

[danjl1100]

It's interesting that adding an explicit panic satisfies the unreachable_code warning:

     if false {
         infallible();
+        unreachable!();
     }
 
     let _x = 1;

(current stable rustc 1.80.1 on the playground)

[JonathanBrouwer]

This is a duplicate of #88393

[JonathanBrouwer]

@rustbot claim
Together with @Bryntet

[JonathanBrouwer]

@rustbot release-assignment