Strange deadlock bug on Rust nightly

[bvssvni]

rustc 1.13.0-nightly (91f057de3 2016-09-04)

This runs forever on Rust stable (1.11) but hangs on Rust nightly.

Reduced case:

use std::sync::{Arc, Mutex};
use std::any::Any;

fn main() {
    let mut counter = 0;
    loop {
        let _ = foo();
        counter += 1;
        println!("counter {}", counter); // stops at ~ 495 - 499
    }
}

fn foo() -> Arc<Mutex<Any>> {
    Arc::new(Mutex::new(false)) as Arc<Mutex<Any>>
}

[nagisa]

This is more minimised:

use std::sync::{Arc, Mutex};
use std::any::Any;

fn main() {
    loop {
        drop(foo());
    }
}

fn foo() -> Box<Mutex<Any>> {
    Box::new(Mutex::new(0u32)) as Box<Mutex<Any>>
}

This tries to take a futex in a single threaded program for some reason:

futex(0x7f3b9ca02b40, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7f3b9ca02b40, FUTEX_WAIT_PRIVATE, 2, NULL…

Only fails at optimisation levels 0 and 1, but not 2 or 3. Also doesn’t fail if inner data is () or u64, but will fail with u8, u16, u32.

[eddyb]

This looks like it might be #36278.