ICE when updating tuples

[gavinb]

Playing around with some simple code which is clearly wrong:

fn gcd(n: uint, m: uint) -> uint {
    while m > 0 {
        (m, n) = (n, n%m)
    }
    n
}

fn main() {
    let a = 75;
    let b = 15;
    println!("gcd({}, {}) = {}", a, b, gcd(a, b));
}

This triggered an internal compiler error:

test.rs:4:8: 4:14 error: internal compiler error: trans_lvalue reached fall-through case: expr_tup(~[@{id: 15, node: expr_path({span: {lo: {__field__: 63}, hi: {__field__: 64}, expn_info: None}, global: false, idents: ~[{name: 70, ctxt: 0}], rp: None, types: ~[]}), span: {lo: {__field__: 63}, hi: {__field__: 64}, expn_info: None}}, @{id: 16, node: expr_path({span: {lo: {__field__: 66}, hi: {__field__: 67}, expn_info: None}, global: false, idents: ~[{name: 68, ctxt: 0}], rp: None, types: ~[]}), span: {lo: {__field__: 66}, hi: {__field__: 67}, expn_info: None}}])
test.rs:4         (m, n) = (n, n%m)
                  ^~~~~~

This is running Rust 1ac7d80 on Mac OS X 10.8.4.

Incidentally, when trying to check the version, I noticed this error:

$ rust --version
rust 0.8-pre (1ac7d80 2013-08-26 15:51:15 -0700)
host: x86_64-apple-darwin
pthread_mutex_lock(&_mutex) failed in /Users/abcdef/src/rust/src/rt/sync/lock_and_signal.cpp at line 79, result = 22 (Invalid argument) 
Abort trap: 6

[alexcrichton]

Huh, that's an odd ICE. I was under the impression that rust didn't support destructuring assignment into existing locals.

[gavinb]

It doesn't. :) I should say, that's why I mentioned that the code was wrong in attempting to mutate the immutable parameters (it was converted from Python code where this would be fine). I fixed it by declaring two local mutable shadow vars.

The pthread failure is a bit of a worry, too. Haven't had a chance to dig into that yet.

[alexcrichton]

Opened #8870 to continue discussion about the pthreads failure, that is disturbing...

[alexcrichton]

For the original issue, closing this as a dupe of #7507