Broken MIR with immovable generators

[Nemo157]

#![feature(conservative_impl_trait)]
#![feature(generators)]
#![feature(generator_trait)]

use std::ops::Generator;

#[derive(Debug)]
pub struct Beacon;

fn listen() -> impl Iterator<Item=Beacon> {
    Some(Beacon).into_iter()
}

pub fn main() -> impl Generator<Yield=(), Return=Result<(), ()>> {
    #[allow(unused_unsafe)]
    unsafe {
        static move || {
            let mut stream = listen();

            loop {
                let beacon = {
                    match stream.next() {
                        Some(e) => e,
                        None => break,
                    }
                };
                println!("Saw beacon {:?}", beacon);
            }

            loop {
                yield ();
            }
        }
    }
}

when compiled with rustc src/lib.rs --crate-type lib gives error:

error: internal compiler error: librustc_mir/transform/generator.rs:495: Broken MIR: generator contains type Beacon in MIR, but typeck only knows about {impl std::iter::Iterator, ()}
  --> src/lib.rs:17:9
   |
17 | /         static move || {
18 | |             let mut stream = listen();
19 | |
20 | |             loop {
...  |
32 | |             }
33 | |         }
   | |_________^

thread 'rustc' panicked at 'Box<Any>', librustc_errors/lib.rs:488:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.26.0-nightly (a04b88d19 2018-03-19) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib

[Zoxc]

The problem here is that we don't generate a StorageDead(beacon) instruction when we break from the loop to match the previous StorageLive(beacon), so the beacon variable appears live outside the loop. This can be seen from the MIR of this simpler code:

fn main() {
    loop {
        let beacon = {
            match true {
                false => 4,
                true => break,
            }
        };
        drop(&beacon);
    }
}