Internal compiler error with unreachable nested if-expression

[nmsmith]

The following code causes a compiler error:

fn main() {
    not(true);
}

fn not(b: bool) -> bool {
    if b {
        !b
    } else {
        fail!("Break the compiler");
        if !b {

        }
    }
}

The error message:

error: internal compiler error: unexpected failure
This message reflects a bug in the Rust compiler. 
We would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: the compiler hit an unexpected failure path. this is a bug
task 'rustc' failed at 'assertion failed: dest == expr::Ignore || bcx.unreachable.get()', /home/nick/workspace/rust/src/librustc/middle/trans/controlflow.rs:91

[Armavica]

I can reproduce it with the latest build, but not with

virgile@Serenno:~/tmp$ rustc -v
rustc 0.10-pre (77eedda 2014-01-13 23:26:36 -0800)
host: x86_64-unknown-linux-gnu

So the problem probably comes from something that happened meanwhile.

[huonw]

cc #11709

(They fail on the same assertion, but the triggering code seems quite different.)