Rust programming giving signal 4 (Illegal instruction) while modifying value inside a match statement

[daboross]

I'm getting "An unknown error occurred" when trying to use a value that I got out of a match statement - when I set the thing being matched upon to None.

Here's the code to reproduce this:

struct Client {
    option: Option<String>,
}

fn main() {
    let mut client = Client {
        option: Some("address".into_string())
    };
    let address = match client.option {
        Some(v) => {
            // This seems to make 'v' invalid, but still lets me use it
            client.option = None;
            v
        },
        None => return
    };
    println!("Cloning")
    // This is where the error occurs
    address.clone();
}

The output when running via cargo:

$ cargo run
   Compiling test-irc v0.0.1 (file:///home/daboross/Projects/Rust/Learn/test-irc)
     Running `target/test-irc`
Cloning
An unknown error occurred

To learn more, run the command again with --verbose.

The output when running via gdb:

Starting program: /home/daboross/Projects/Rust/test-irc/target/test-irc 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Cloning

Program received signal SIGSEGV, Segmentation fault.
0x000055555555bf0e in ptr::write::h984757489268428869 ()

Here's a rust playpen share with the code in it: http://is.gd/GCa24t

This occurs when using the above code in the playpen, though here are my system details in case it matters:

$ rustc --version=verbose
rustc 0.13.0-nightly (fac5a0767 2014-11-26 22:37:06 +0000)
binary: rustc
commit-hash: fac5a07679cac21a580badc84b755b8df0f975cf
commit-date: 2014-11-26 22:37:06 +0000
host: x86_64-unknown-linux-gnu
release: 0.13.0-nightly
$ uname -a
Linux M14x 3.13.0-39-generic #66-Ubuntu SMP Tue Oct 28 13:30:27 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: elementary OS
Description:    elementary OS Freya
Release:    0.3
Codename:   freya

[daboross]

Noting that when using --opt-level 1, there is no error, but it does occur with --opt-level 0, --opt-level 2, --opt-level 3, and without a --opt-level parameter.

[huonw]

cc @luqmana, I have a feeling this is related to the by-value optimisations you(I think?) added a while ago.

stl on IRC gave a slight variation:

struct S { o: Option<String> }

fn main() {
    let mut s = S{ o: Some("right".into_string()) };  
    let b = match s.o {
        Some(v) => {
            s.o = Some("wrong".into_string());
            v
        }
        None => String::new(),
    }; 
    println!("{}", b);
}

It prints wrong.

[luqmana]

Yea... I know what's wrong here (basically same issue as in #15571). Fun fact, it'd also fail if that were tuple indexing. Anyways, I'll have a fix up soon.