Issue 1:
@rillian and @evanmcc have both encountered a build failure -- same place -- stage1 segfaults when building optimized on atom. Seems independent of distribution, (happens on FC17 and Ubuntu oneiric). Both machines were atoms. Tried builds on emulated non-atoms, same distros, no fault. Think it's atom-specific. Might be a duplicate of #1879 (requirement for subtargets).

Issue 2:
This code:

#![feature(if_let, while_let)]

use std::io;

pub struct Test<W: Writer> {
writer: W,
}

impl<W: Writer> Test<W> {

pub fn new(writer: W) -> Test<W> {
Test {
writer: writer,
}
}

pub fn write_something(&mut self) -> io::IoResult<()> {
try!(writeln!(self.writer, ""));
Ok(())
}
}

Produces this very hard to understand error:

<std macros>:3:24: 18:34 error: type `W` cannot be dereferenced
<std macros>:3 let dst = &mut *$dst;
<std macros>:4 format_args!(|args| { dst.write_fmt(args) }, $($arg)*)
<std macros>:5 })
<std macros>:6 )
error: internal compiler error: unexpected panic
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
task 'rustc' panicked at 'index out of bounds: the len is 6 but the index is 6', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libsyntax/lib.rs:1

stack backtrace:
1: 0x10e61aba2 - rt::backtrace::imp::write::h90a8813e205226e59it
2: 0x10e61dd3d - failure::on_fail::h02cd561a89cb7027gBt
3: 0x10e88df65 - unwind::begin_unwind_inner::h4bc3350c0517820112c
4: 0x10e88dbaf - unwind::begin_unwind_fmt::hd106a62827b11c87c0c
5: 0x10e88d952 - rust_begin_unwind
6: 0x10e8d8fec - panicking::panic_fmt::h17addcbe3c55edecaOl
7: 0x10e8e15b1 - panicking::panic_bounds_check::he446012f6f64f624IMl
8: 0x10c59c015 - codemap::FileMap::get_line::h765ba394c07c5a54m4E
9: 0x10c5ca703 - diagnostic::emit::hb066201a777f2165wvG
10: 0x10c5c6f98 - diagnostic::EmitterWriter.Emitter::emit::h165058475e3b3ec5lrG
11: 0x10c5c5785 - diagnostic::Handler::emit::hde0ac2d5b40efe25F8F
12: 0x10c5981ab - diagnostic::SpanHandler::span_err::h2eaa3c8ca5c5b97cEWF
13: 0x10b9df920 - middle::typeck::infer::InferCtxt<'a, 'tcx>::type_error_message_str_with_expected::h6ee55cab43056003TKF
14: 0x10b92f921 - middle::typeck::infer::InferCtxt<'a, 'tcx>::type_error_message::h3d8733aff7464519dQF
15: 0x10b940539 - middle::typeck::check::check_expr_with_unifier::h40fb1c6e261626f5Nzm
16: 0x10b93e934 - middle::typeck::check::check_expr_with_unifier::h40fb1c6e261626f5Nzm
17: 0x10b96d0b3 - middle::typeck::check::check_decl_local::hfecf573d1629e05egto
18: 0x10b96d2a3 - middle::typeck::check::check_stmt::h837abcc8fc4466f6gvo
19: 0x10b8f41e8 - middle::typeck::check::check_block_with_expected::hb5675eefe857af90vzo
20: 0x10b93a760 - middle::typeck::check::check_expr_with_unifier::h40fb1c6e261626f5Nzm
21: 0x10b82e2db - middle::typeck::check::_match::check_match::h3caf386ed888768e5P8
22: 0x10b93a683 - middle::typeck::check::check_expr_with_unifier::h40fb1c6e261626f5Nzm
23: 0x10b8f4522 - middle::typeck::check::check_block_with_expected::hb5675eefe857af90vzo
24: 0x10b93a760 - middle::typeck::check::check_expr_with_unifier::h40fb1c6e261626f5Nzm
25: 0x10b96d2fa - middle::typeck::check::check_stmt::h837abcc8fc4466f6gvo
26: 0x10b8f41e8 - middle::typeck::check::check_block_with_expected::hb5675eefe857af90vzo
27: 0x10b8cdf00 - middle::typeck::check::check_fn::hd44de11a490be98ce0i
28: 0x10b8f0aae - middle::typeck::check::check_bare_fn::h3c7a1f5d35e30589jPi
29: 0x10b8f754f - middle::typeck::check::check_method_body::he0c86eb88bb45c1blkj
30: 0x10b8edb88 - middle::typeck::check::check_item::h4ddfa2a018f36791t9i
31: 0x10b8f07d0 - middle::typeck::check::check_item_types::h1ade2b1cc61bf6batOi
32: 0x10bc74826 - util::common::time::h8028586279873844585
33: 0x10bc73ca4 - middle::typeck::check_crate::h3a5b374f87cce2eecwM
34: 0x10b265393 - driver::driver::phase_3_run_analysis_passes::hdc8c835c5059844etfS
35: 0x10b2598bc - driver::driver::compile_input::h1998d439bb2aa565dWR
36: 0x10b2d7bc5 - driver::run_compiler::h8a3c490c622774caHUT
37: 0x10b2d639e - driver::run::closure.59807
38: 0x10b0edc5b - task::TaskBuilder<S>::try_future::closure.39061
39: 0x10b0edb53 - task::TaskBuilder<S>::spawn_internal::closure.39032
40: 0x10b0b17bd - task::NativeSpawner.Spawner::spawn::closure.2475
41: 0x10e8f082c - rust_try_inner
42: 0x10e8f0816 - rust_try
43: 0x10e88b707 - unwind::try::h9549aa28335b576amRc
44: 0x10e88b59c - task::Task::run::h7f22cfdcfa218bd192b
45: 0x10b0b15e3 - task::NativeSpawner.Spawner::spawn::closure.2399
46: 0x10e88cdd7 - thread::thread_start::h08cb83a10e608715foc
47: 0x7fff9260c2fc - _pthread_body
48: 0x7fff9260c279 - _pthread_body