ICE: assertion failure in LLVM when returning a struct from "extern" function.

[vadimcn]

Repro:

#[repr(C)]
pub struct Foo(u32);

pub extern fn bar() -> Foo {
    Foo(0)
}

fn main() {}

ICE:

File: C:/rust/src/llvm/lib/IR/Instructions.cpp, Line 1086

Expression: getOperand(0)->getType() == cast<PointerType>(getOperand(1)->getType())->getElementType() && "Ptr must be a pointer to Val type!"

[skade]

#17257 tracks a number of cases that throw the same error.

[vhbit]

A couple of hints - it looks like it happens when structure size is actually smaller or equal to register of architecture.

I had the similar report for failing on iOS with the following sample:

#![crate_type = "staticlib"]

#[derive(Copy)]
pub struct Pair {
    foo: u32,
    bar: u32,
}

#[no_mangle]
pub extern fn get_pair() -> Pair {
    Pair {
        foo: 42,
        bar: 10,
    }
}

It fails on x86_64 and aarch64 if foo + bar <= 64 bits, i.e. they are u16 or u32.
When switching to armv7 it fails if foo + bar<= 32 bits

[vhbit]

@dotdash @Aatch after 6 hours bisecting the verdict is - 6ef0840, part of #20755

[dotdash]

sigh I actually saw that when I was working on #20755 but didn't come up with a test case that would trigger a problem here and then forgot about it. Will look into this.

[vhbit]

@dotdash will fix hit the upcoming beta?

[dotdash]

Sorry, fixing a few regressions in LLVM that affected rust had higher priority for me than this issue (because LLVM is very close to its 3.6 release), so I couldn't devote much time to this issue yet.

But given that the beta is still ~3 weeks away, I'm positive that I'll get around to have it fixed by then.

[vhbit]

Hmm, beta is on week of Feb 16 (i.e. next week), isn't it?

[skade]

@vhbit Yes. http://blog.rust-lang.org/2014/12/12/1.0-Timeline.html

Although, as someone hitting that bug, I'd be okay if that were flagged as a known bug and would prefer if semantic issues were cared about first.

[vhbit]

@skade @dotdash I have nothing against fixing regressions, still be extremely happy to see it fixed as I will be stuck on beta1 following 6 weeks till beta2 or rc1.

[vhbit]

@dotdash 🎉 thanks a lot!