pub struct Foo {
    x: isize,
    y: isize
}

impl Foo {
    pub extern fn foo_new() -> Foo {
        Foo { x: 21, y: 33 }
    }
}

rustc 1.3.0-nightly (67256dff6 2015-07-09)
binary: rustc
commit-hash: 67256dff6dd7526f0be9da5092a6b3e390654c8c
commit-date: 2015-07-09
host: x86_64-unknown-linux-gnu
release: 1.3.0-nightly

$ RUST_BACKTRACE=1 rustc --crate-type dylib lib.rs 
lib.rs:2:5: 2:13 warning: struct field is never used: `x`, #[warn(dead_code)] on by default
lib.rs:2     x: isize,
             ^~~~~~~~
lib.rs:3:5: 3:13 warning: struct field is never used: `y`, #[warn(dead_code)] on by default
lib.rs:3     y: isize
             ^~~~~~~~
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
thread 'rustc' panicked at 'assertion failed: index < LLVMCountParams(llfn)', ../src/librustc_llvm/lib.rs:2250

stack backtrace:
   1:     0x7f12dd59817e - sys::backtrace::write::h3ecf23ae317178b4Qqs
   2:     0x7f12dd59fe14 - panicking::on_panic::hffb5f62afcb56dacQ9w
   3:     0x7f12dd562d9e - rt::unwind::begin_unwind_inner::ha7a91c9abe288335uPw
   4:     0x7f12d7f2d413 - rt::unwind::begin_unwind::h16605897156115720580
   5:     0x7f12d7f2d3aa - get_param::hb188514a1386c943URc
   6:     0x7f12dc398104 - trans::base::init_function::hf129fb24e7ecd471MEh
   7:     0x7f12dc39c962 - trans::base::trans_closure::ha8dd63d3ab902b61WTh
   8:     0x7f12dc3a0927 - trans::base::trans_fn::hc037a1ceab32bd37J3h
   9:     0x7f12dc3a4518 - trans::base::trans_item::h3f8065230582e652Usi
  10:     0x7f12dc3b0c28 - trans::base::trans_crate::hf1e6e2ced94af1d9Rgj
  11:     0x7f12ddb06d14 - driver::phase_4_translate_to_llvm::h76638dba7a6bfe525Oa
  12:     0x7f12ddb01445 - driver::phase_3_run_analysis_passes::closure.15879
  13:     0x7f12ddafb69b - middle::ty::ctxt<'tcx>::create_and_enter::h9374423159988670676
  14:     0x7f12ddaf6641 - driver::phase_3_run_analysis_passes::h16611790442000187316
  15:     0x7f12ddad58bc - driver::compile_input::h518a192813f7b6ceTba
  16:     0x7f12ddbbc1a3 - run_compiler::h2692f9bb80088600A7b
  17:     0x7f12ddbb9b7e - boxed::F.FnBox<A>::call_box::h1854161409259061273
  18:     0x7f12ddbb93c9 - rt::unwind::try::try_fn::h13481957482458181815
  19:     0x7f12dd61ae78 - rust_try_inner
  20:     0x7f12dd61ae65 - rust_try
  21:     0x7f12dd58b4b7 - rt::unwind::try::inner_try::h497973a2166ac637nLw
  22:     0x7f12ddbb95db - boxed::F.FnBox<A>::call_box::h18176717890739738257
  23:     0x7f12dd59ea71 - sys::thread::Thread::new::thread_start::h1bd024404d1992a3aVv
  24:     0x7f12d723c353 - start_thread
  25:     0x7f12dd1f8bfc - __clone
  26:                0x0 - <unknown>