Issue 1:
The code is probably invalid, but still generates an ICE.

$ rustc src/ice.rs
src/ice.rs:3:9: 3:12 warning: unused variable: `ptr`, #[warn(unused_variables)] on by default
src/ice.rs:3 let ptr = string as *const _ as *const u8;
^~~
error: internal compiler error: translating unsupported cast: *const str (cast_other) -> *const u8 (cast_pointer)
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 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libsyntax/diagnostic.rs:180

The code is very short:

fn main() {
let string: &str = "test1";
let ptr = string as *const _ as *const u8;
}

Backtrace:

$ gdb --args rustc src/ice.rs
Reading symbols from rustc...(no debugging symbols found)...done.
(gdb) b rust_panic
Function "rust_panic" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (rust_panic) pending.
(gdb) r
src/ice.rs:3:9: 3:12 warning: unused variable: `ptr`, #[warn(unused_variables)] on by default
src/ice.rs:3 let ptr = string as *const _ as *const u8;
^~~
error: internal compiler error: translating unsupported cast: *const str (cast_other) -> *const u8 (cast_pointer)

Breakpoint 1, 0x00007ffff7111440 in rust_panic () from /usr/local/lib/librustrt-4e7c5e5c.so
(gdb) bt
#0 0x00007ffff7111440 in rust_panic () from /usr/local/lib/librustrt-4e7c5e5c.so
#1 0x00007ffff7111b06 in unwind::begin_unwind_inner::hf044c6d185c5aca3tad () from /usr/local/lib/librustrt-4e7c5e5c.so
#2 0x00007ffff4e51529 in unwind::begin_unwind::h5761018185178914378 () from /usr/local/lib/libsyntax-4e7c5e5c.so
#3 0x00007ffff4e51c84 in diagnostic::Handler::bug::hfb9fa81ad3c3172cL3F () from /usr/local/lib/libsyntax-4e7c5e5c.so
#4 0x00007ffff5e5c935 in session::Session::bug::h176dff5b0ea34ba0Lt1 () from /usr/local/lib/librustc-4e7c5e5c.so
#5 0x00007ffff7932899 in trans::expr::trans_imm_cast::ha29135b513d0179aTLk () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#6 0x00007ffff7925c63 in trans::expr::trans_unadjusted::h4dd3a502f0c61d18iJi () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#7 0x00007ffff78e6287 in trans::expr::trans_into::h9ab7d00213095796hQh () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#8 0x00007ffff79de1bd in trans::_match::store_local::closure.49047 () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#9 0x00007ffff79dd5a4 in trans::_match::mk_binding_alloca::h3960520261142917360 () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#10 0x00007ffff7990094 in trans::_match::store_local::he5f9566f16d0e035w9x () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#11 0x00007ffff78e582e in trans::base::init_local::h305f837109a50408MIt () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#12 0x00007ffff78e4e42 in trans::controlflow::trans_stmt::h8e6bafcdf7128142cXd () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#13 0x00007ffff78e64f9 in trans::controlflow::trans_block::h7ed275868dcb5977k2d () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#14 0x00007ffff7998c40 in trans::base::trans_closure::h45d1af6bd984feb85Au () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#15 0x00007ffff78d9587 in trans::base::trans_fn::he30b79362e00aa4eVMu () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#16 0x00007ffff78d679e in trans::base::trans_item::hd3d39cc929783f51F8u () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#17 0x00007ffff79a21f8 in trans::base::trans_crate::h9cc619fc129272e2Z6v () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#18 0x00007ffff7a4cc45 in driver::driver::phase_4_translate_to_llvm::he2f0cbfd547d4bd4UtS () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#19 0x00007ffff7a3c4b5 in driver::driver::compile_input::h3764e7506ecf962760R () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#20 0x00007ffff7abfa87 in driver::run_compiler::hd5386abc6d794eaceZT () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#21 0x00007ffff7abe0ac in driver::run::closure.59712 () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#22 0x00007ffff78cbdfb in task::TaskBuilder::try_future::closure.38971 () from /usr/local/lib/librustc_trans-4e7c5e5c.so
#23 0x00007ffff743d43d in task::TaskBuilder::spawn_internal::closure.24316 () from /usr/local/lib/libstd-4e7c5e5c.so
#24 0x00007ffff710f4d2 in task::Task::spawn::closure.6079 () from /usr/local/lib/librustrt-4e7c5e5c.so
#25 0x00007ffff7169e3c in rust_try_inner () from /usr/local/lib/librustrt-4e7c5e5c.so
#26 0x00007ffff7169e26 in rust_try () from /usr/local/lib/librustrt-4e7c5e5c.so
#27 0x00007ffff710f583 in unwind::try::hc6a5679abcd17f59OYc () from /usr/local/lib/librustrt-4e7c5e5c.so
#28 0x00007ffff710f37c in task::Task::run::h56429f146a5c97ecX5b () from /usr/local/lib/librustrt-4e7c5e5c.so
#29 0x00007ffff710efc8 in task::Task::spawn::closure.6055 () from /usr/local/lib/librustrt-4e7c5e5c.so
#30 0x00007ffff7110d25 in thread::thread_start::hce41c81aad9e2f16Kpc () from /usr/local/lib/librustrt-4e7c5e5c.so
#31 0x00007ffff1c2c314 in start_thread () from /usr/lib/libpthread.so.0
#32 0x00007ffff6de63ed in clone () from /usr/lib/libc.so.6

Version info:

$ rustc --version=verbose
rustc 0.13.0-nightly (395901393 2014-11-24 00:46:30 +0000)
binary: rustc
commit-hash: 395901393c369c910a8ae36ace71402cb206d217
commit-date: 2014-11-24 00:46:30 +0000
host: x86_64-unknown-linux-gnu
release: 0.13.0-nightly

Happens also in:

$ rustc --version=verbose
rustc 0.13.0-nightly (fac5a0767 2014-11-26 22:37:06 +0000)
binary: rustc
commit-hash: fac5a07679cac21a580badc84b755b8df0f975cf
commit-date: 2014-11-26 22:37:06 +0000
host: x86_64-unknown-linux-gnu
release: 0.13.0-nightly

Issue 2:
Code:

fn f() -> u64 {
0
}

fn main() {
let n = f as f32;
}

Error with backtrace:

src/main.rs:6:9: 6:10 warning: unused variable: `n`, #[warn(unused_variable)] on by default
src/main.rs:6 let n = f as f32;
^
error: internal compiler error: translating unsupported cast: fn() -> u64 (cast_pointer) -> f32 (cast_float)
note: the compiler hit an unexpected failure path. 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' failed at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libsyntax/diagnostic.rs:163

stack backtrace:
1: 0x7f6e5389ced0 - rt::backtrace::imp::write::h3e02102493c7a1b79Hp::v0.11.0.pre
2: 0x7f6e538a3a00 - failure::on_fail::h73803e3fd7728138o3p::v0.11.0.pre
3: 0x7f6e55a06ef0 - unwind::begin_unwind_inner::h66e3981eb8555b96cZd::v0.11.0.pre
4: 0x7f6e54e4a4e0 - unwind::begin_unwind::h14114372353668361027::v0.11.0.pre
5: 0x7f6e54e4ae80 - diagnostic::Handler::bug::h163e51ddd1a017c2Dgc::v0.11.0.pre
6: 0x7f6e562f9520 - driver::session::Session::bug::h09f59f7b6f35750fdsr::v0.11.0.pre
7: 0x7f6e5637cbf0 - middle::trans::expr::trans_imm_cast::h261d15fd2f6453feLQh::v0.11.0.pre
8: 0x7f6e5636e380 - middle::trans::expr::trans_unadjusted::h37391b28c8fd0d0b60f::v0.11.0.pre
9: 0x7f6e5632a310 - middle::trans::expr::trans_into::hdc05c03d27b262d4JDf::v0.11.0.pre
10: 0x7f6e56434000 - middle::trans::_match::store_local::closure.85655
11: 0x7f6e56433cf0 - middle::trans::_match::mk_binding_alloca::h16257314354832004452::v0.11.0.pre
12: 0x7f6e563eaa70 - middle::trans::_match::store_local::h71f3ff230e537ab6JEu::v0.11.0.pre
13: 0x7f6e563297e0 - middle::trans::base::init_local::he8478d5bef2cef9cOZp::v0.11.0.pre
14: 0x7f6e56328d40 - middle::trans::controlflow::trans_stmt::h77aa44239cd8a9d8Mdc::v0.11.0.pre
15: 0x7f6e5632a940 - middle::trans::controlflow::trans_block::hf4faa65f79a4fae52ic::v0.11.0.pre
16: 0x7f6e563f0850 - middle::trans::base::trans_closure::hbab3416264edbe7aauq::v0.11.0.pre
17: 0x7f6e562fa790 - middle::trans::base::trans_fn::hd7d1d11484c269ccbCq::v0.11.0.pre
18: 0x7f6e562f3230 - middle::trans::base::trans_item::h40a4f8eccf6f8e7eCSq::v0.11.0.pre
19: 0x7f6e564011b0 - middle::trans::base::trans_crate::h470bfcf3cac093e1JMr::v0.11.0.pre
20: 0x7f6e56c06570 - driver::driver::phase_4_translate_to_llvm::h2fa30f4b120cdb579Aq::v0.11.0.pre
21: 0x7f6e56bfd2b0 - driver::driver::compile_input::h1d313b682f9ead2bDeq::v0.11.0.pre
22: 0x7f6e56cca0c0 - driver::run_compiler::hcc8540f7b478ad28b0s::v0.11.0.pre
23: 0x7f6e56cc9fd0 - driver::main_args::closure.117522
24: 0x7f6e56cdf0f0 - task::TaskBuilder<S>::try_future::closure.118663
25: 0x7f6e56cded10 - task::TaskBuilder<S>::spawn_internal::closure.118640
26: 0x7f6e55d5c590 - task::spawn_opts::closure.7462
27: 0x7f6e55a5f290 - rust_try
28: 0x7f6e55a03500 - unwind::try::h800fde6f36f3558bBNd::v0.11.0.pre
29: 0x7f6e55a031e0 - task::Task::run::hf743f122a6385418XYc::v0.11.0.pre
30: 0x7f6e55d5c350 - task::spawn_opts::closure.7408
31: 0x7f6e55a05da0 - thread::thread_start::hd9510588dd47efddvld::v0.11.0.pre
32: 0x7f6e53311060 - start_thread
33: 0x7f6e556cd489 - __clone
34: 0x0 - <unknown>