ICE due to illegal move

[dlrobertson]

I was playing around with unsafe blocks with the code listed below and it failed with the following.
System Info:

rustc 1.0.0-nightly (d3732a12e 2015-02-06 23:30:17 +0000)
host: 3.18.5-1-ARCH
architecture: x86_64

Example:

extern crate libc;
pub struct TestBuffer<T> {
    start: *mut T,
    size: usize,
    curr: isize,
}

impl<T: Send> TestBuffer<T> {
    pub fn new(value: T, size: usize) -> TestBuffer<T> {
        unsafe {
            let start = libc::malloc(
                (std::mem::size_of::<T>() * size)
                as libc::size_t) as *mut T;
            std::ptr::write(&mut *start, value);
            TestBuffer{start: start, size: size, curr: 0}
        }
    }
}

impl<T> Iterator for TestBuffer<T> {
    type Item = T;
    fn next(&mut self) -> Option<T> {
        if self.curr < (self.size as isize) {
            self.curr += 1;
        } else {
            ()
        }
        unsafe { Some(*self.start.offset(self.curr - 1)) }
    }
}
```rust

Running with `RUST_BACKTRACE=1`:

Buff.rs:29:23: 29:56 error: internal compiler error: this path should not cause illegal move
Buff.rs:29 unsafe { Some(*self.start.offset(self.curr - 1)) }
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with RUST_BACKTRACE=1 for a backtrace
thread 'rustc' panicked at 'Box', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:129

stack backtrace:
1: 0x7f93ce6cd250 - sys::backtrace::write::h361f9c7ed16d6f6eUsy
2: 0x7f93ce6f0950 - failure::on_fail::h69f5f434699d11ccOWF
3: 0x7f93ce6507d0 - rt::unwind::begin_unwind_inner::hc4455d84b00b874blBF
4: 0x7f93cba20040 - rt::unwind::begin_unwind::h13236156776379767181
5: 0x7f93cba1ffd0 - diagnostic::SpanHandler::span_bug::h5ec31613fa5cf53fBUE
6: 0x7f93cc547270 - session::Session::span_bug::h5f8ab95419f97cb6xdq
7: 0x7f93cd8375e0 - borrowck::build_borrowck_dataflow_data::h3de5b29d7c85ab98gVe
8: 0x7f93cd833ed0 - borrowck::borrowck_fn::hac2da55ab2d59b33DSe
9: 0x7f93cd837440 - visit::walk_method_helper::h7515637727083481066
10: 0x7f93cd834ee0 - borrowck::borrowck_item::h918c0642f54f00c7BRe
11: 0x7f93cd8356f0 - borrowck::check_crate::h5c36e499d0e6ca76tMe
12: 0x7f93cecbfb20 - driver::phase_3_run_analysis_passes::h8f5a5e5500230bd1oGa
13: 0x7f93ceca5a40 - driver::compile_input::hcb43bced2a0b021bCba
14: 0x7f93ced77be0 - run_compiler::hb81cf958c2f963666ac
15: 0x7f93ced76270 - thunk::F.Invoke<A, R>::invoke::h6159218808669033746
16: 0x7f93ced751a0 - rt::unwind::try::try_fn::h8268217050585033268
17: 0x7f93ce75ca90 - rust_try_inner
18: 0x7f93ce75ca80 - rust_try
19: 0x7f93ced75450 - thunk::F.Invoke<A, R>::invoke::h8703575304585054118
20: 0x7f93ce6dce40 - sys::thread::thread_start::h35f66aa7ce5d7277LCB
21: 0x7f93c870f250 - start_thread
22: 0x7f93ce2d8219 - clone
23: 0x0 -

I'm still definitely a noobie just playing around, so this could definitely be my fault. Thanks in advance for the help. Any input or advice would also be appreciated.

[jdm]

Duplicate of #20801.