ICE when doing some casts on constant expressions

[LeoTestard]

The following code does not compile :

extern
{
    fn foo();
}

static a: u64 = foo as u64;

fn main()
{
    println!("{:u}", a};
}

It fails with the following message :

test.rs:6:18: 6:28 error: internal compiler error: Impossible case reached: bad combination of types for cast
test.rs:6 static baz: u64 = foo as u64;

Where as the following code, that does the same type of cast but in a non-constant expression, is valid :

extern
{
    fn foo();
}

fn main()
{
    let a: u64 = foo as u64;
    println!("{:u}", a};
}

Maybe I'm missing some point, but I don't see any good reason to disallow this type of casts at compile-time.

[flaper87]

Triage bump, updated example:

extern {
    fn read();
}

static a: u64 = read as u64;

fn main() {
    println!("{:u}", a);
}

This hits rustc::middle::trans::consts

[cceckman]

Getting a similar issue in my code. Alternative example:

static foo : *mut u32 = (0x10) as *mut u32;
static bar : u32 = foo as u32;
fn main() {}

Version is 0.10-pre (50e3aa3 2014-03-17 05:17:02 -0700)
A little bit of the rustc backtrace (provided by RUST_BACKTRACE):

6:     0x7ffcb4e3e640 -driver::session::Session::impossible_case::hd4ebc2a653541a9ccAg::v0.10.pre
7:     0x7ffcb4e36d90 - middle::trans::consts::const_expr_unadjusted::h278e8dbd89fc1c82Dbj::v0.10.pre
8:     0x7ffcb4e34850 - middle::trans::consts::const_expr::hd4588a552760e28daVi::v0.10.pre
9:     0x7ffcb4d8fb90 - middle::trans::base::get_item_val::h705f0e0ab9002b63C9o::v0.10.pre
10:     0x7ffcb4e36770 - middle::trans::consts::trans_const::h2bcd0d481971109blJj::v0.10.pre
11:     0x7ffcb4d8e950 - middle::trans::base::trans_item::haca992924f705714zPo::v0.10.pre

NB this is for the arm-none-eabi target, but looks like the same issue- at least related. Can file a separate bug if it seems to be unrelated.

[jdm]

What is VIC_INT in your example?

[cceckman]

Oops- had renamed to foo in one place, not the other. Fixed in above comment. Thanks for the catch.

[bkoropoff]

I think all the examples in here were fixed when issue #17458 was fixed.

[alexcrichton]

🎆