ICE comparing unsized type as raw pointer

[murarth]

Attempting to cast &str or a slice to a raw pointer results in a proper error message. Attempting to compare two such invalid casts, however, generates an ICE.
(And I realize now that .as_ptr() is the right way to do what I was trying to do.)

fn main() {
    let a: &[i32] = &[];
    (a as *const _) == (a as *const _);
    ("" as *const _) == ("" as *const _);
}

Results in:

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 'assertion failed: self.appropriate_rvalue_mode(bcx.ccx()) == ByValue', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/librustc/middle/trans/datum.rs:644

stack backtrace:
   1:     0x7f2610acd880 - rt::backtrace::imp::write::h7a90f4ef1aa5a81fsbq
   2:     0x7f2610ad0900 - failure::on_fail::he9ef851a069b43543wq
   3:     0x7f2615036d40 - unwind::begin_unwind_inner::ha2afab22d4dc49ed8Rd
   4:     0x7f261567bb30 - unwind::begin_unwind::h15560861862153460913
   5:     0x7f2615a1eb20 - middle::trans::datum::Datum<K>::to_llscalarish::h5300527991557390520
   6:     0x7f2615a3f650 - middle::trans::expr::trans_binary::h6c193beb06d7e93dcG7
   7:     0x7f2615a34ab0 - middle::trans::expr::trans_unadjusted::h02c4b8f1c6b87a22SZ5
   8:     0x7f26159fbac0 - middle::trans::expr::trans_into::h4971d03ccde714e0Ue5
   9:     0x7f26159faf20 - middle::trans::controlflow::trans_stmt_semi::h8fa1003152ba3849Gu1
  10:     0x7f26159fa4d0 - middle::trans::controlflow::trans_stmt::h98ee011c11c8d6d8tq1
  11:     0x7f26159fbee0 - middle::trans::controlflow::trans_block::h9afd935ec02d5d88zv1
  12:     0x7f2615a9e510 - middle::trans::base::trans_closure::h3e4483ae2d8e884bAGh
  13:     0x7f26159ef140 - middle::trans::base::trans_fn::h7f9774a3926fbf34nSh
  14:     0x7f26159ec9a0 - middle::trans::base::trans_item::h07f36bd67b211f81Bbi
  15:     0x7f2615aa8ce0 - middle::trans::base::trans_crate::hda78095df6dfa8bfC9i
  16:     0x7f2615efa840 - driver::driver::phase_4_translate_to_llvm::h3f7adb4e900158acqyC
  17:     0x7f2615ef16e0 - driver::driver::compile_input::h1c18718eb06a01d2k5B
  18:     0x7f2615f744e0 - driver::run_compiler::hcc1eba405fd576deBVF
  19:     0x7f2615f743d0 - driver::run::closure.146438
  20:     0x7f26156b0c20 - task::TaskBuilder<S>::try_future::closure.104848
  21:     0x7f26156b0a10 - task::TaskBuilder<S>::spawn_internal::closure.104819
  22:     0x7f261537d540 - task::NativeSpawner.Spawner::spawn::closure.8448
  23:     0x7f261508bc50 - rust_try_inner
  24:     0x7f261508bc40 - rust_try
  25:     0x7f26150346c0 - unwind::try::h2eeb8f95c58da3ccQGd
  26:     0x7f2615034550 - task::Task::run::hcb23459dab25134dGMc
  27:     0x7f261537d280 - task::NativeSpawner.Spawner::spawn::closure.8386
  28:     0x7f2615035d60 - thread::thread_start::h033f0420ecdbeed0V7c
  29:     0x7f260fe7d0c0 - start_thread
  30:     0x7f2614cfff89 - __clone
  31:                0x0 - <unknown>

[steveklabnik]

This no longer ICEs for me, and gives the right error:

hello.rs:2:21: 2:23 error: mismatched types:
 expected `&[isize]`,
    found `[_; 0]`
(expected &-ptr,
    found array of 0 elements)

[murarth]

@steveklabnik: No, that's just the array [] no longer being implicitly coerced to &[int]. I'm on nightly 2015-01-15 and still get an ICE. I've updated the original comment accordingly. (Added the str case, too.)

[steveklabnik]

Oops, sorry about that! Re-opened, and your new sample does ICE for me. Thanks!

[tamird]

Still ICEs.

[arielb1]

cc rust-lang/rfcs#1135