ICE: No kind for cast

[DutchGhost]

The following only ICE's on stable, beta and nightly:

fn main() {
    let f = [();  { &loop { break } as *const _ as usize } ];
}

playground: https://play.rust-lang.org/?gist=b35ac8a560e0cc448e95e2a62598208a&version=stable&mode=release&edition=2015
Backtrace (stable):

error[E0019]: constant contains unimplemented expression type
   --> src\lib.rs:164:26
    |
164 |         let f = [();  { &loop { break } as *const _ as usize } ];
    |                          ^^^^^^^^^^^^^^

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: EvalError { kind: a raw memory access tried to access part of a pointer value as raw bytes, backtrace: None }', libcore\result.rs:945:5
stack backtrace:
   0: <u128 as compiler_builtins::int::Int>::min_value
   1: core::alloc::<impl core::alloc::::Opaque>::null_mut
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: rustc::ty::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::middle::const_val::ErrKind<'a>>::lift_to_tcx
   5: std::panicking::rust_panic_with_hook
   6: std::panicking::begin_panic_fmt
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: <rustc::util::common::ProfileQueriesMsg as core::fmt::Debug>::fmt
  10: rustc::ty::maps::on_disk_cache::<impl serialize::serialize::SpecializedDecoder<rustc::ty::maps::on_disk_cache::IntEncodedWithFixedSize> for serialize::opaque::Decoder<'enc>>::specialized_decode
  11: rustc::ty::maps::on_disk_cache::<impl serialize::serialize::SpecializedDecoder<rustc::ty::maps::on_disk_cache::IntEncodedWithFixedSize> for serialize::opaque::Decoder<'enc>>::specialized_decode
  12: <rustc::infer::combine::Generalizer<'cx, 'gcx, 'tcx> as rustc::ty::relate::TypeRelation<'cx, 'gcx, 'tcx>>::tys
  13: rustc::ich::caching_codemap_view::CachingCodemapView::byte_pos_to_line_and_col
  14: <rustc::infer::sub::Sub<'combine, 'infcx, 'gcx, 'tcx> as rustc::ty::relate::TypeRelation<'infcx, 'gcx, 'tcx>>::tys
  15: rustc_typeck::hir_trait_to_predicates
  16: rustc_typeck::hir_trait_to_predicates
  17: <rustc::hir::HirId as rustc_typeck::check::writeback::Locatable>::to_span
  18: rustc_typeck::hir_trait_to_predicates
  19: <unknown>
  20: <unknown>
  21: <unknown>
  22: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_impl_item
  23: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_impl_item
  24: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_impl_item
  25: <rustc_typeck::outlives::implicit_infer::InferVisitor<'cx, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_impl_item
  26: <rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx> as rustc_typeck::astconv::AstConv<'gcx, 'tcx>>::record_ty
  27: <rustc_typeck::check::GatherLocalsVisitor<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::visit_pat
  28: <rustc_typeck::collect::has_late_bound_regions::LateBoundRegionsDetector<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_lifetime
  29: <rustc_typeck::check::CheckItemTypesVisitor<'a, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_item
  30: rustc::ty::maps::<impl rustc::ty::maps::config::QueryConfig<'tcx> for rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute
  31: rustc::ty::context::tls::track_diagnostic
  32: rustc::dep_graph::graph::DepGraph::assert_ignored
  33: rustc::ty::context::tls::track_diagnostic
  34: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  35: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  36: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  37: <rustc_typeck::check::Diverges as core::fmt::Debug>::fmt
  38: <rustc_typeck::check::CheckItemTypesVisitor<'a, 'tcx> as rustc::hir::itemlikevisit::ItemLikeVisitor<'tcx>>::visit_item
  39: rustc::ty::context::tls::track_diagnostic
  40: rustc::dep_graph::graph::DepGraph::assert_ignored
  41: rustc::ty::context::tls::track_diagnostic
  42: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  43: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_mark_green_and_read
  44: rustc_typeck::check_crate
  45: <humantime::duration::Error as std::error::Error>::cause
  46: <rustc_driver::pretty::UserIdentifiedItem as core::fmt::Debug>::fmt
  47: <unknown>
  48: rustc_driver::driver::compile_input
  49: rustc_driver::run_compiler
  50: rustc_driver::driver::build_output_filenames
  51: <unknown>
  52: rustc_driver::driver::build_output_filenames
  53: _rust_maybe_catch_panic
  54: rustc_driver::profile::trace::write_style
  55: rustc_driver::main
  56: <unknown>
  57: std::panicking::update_panic_count
  58: _rust_maybe_catch_panic
  59: std::rt::lang_start_internal
  60: <unknown>
  61: <unknown>
  62: BaseThreadInitThunk
  63: RtlUserThreadStart
query stack during panic:
#0 [typeck_tables_of] processing `internal_compiler_errors::no_kind_for_cast`
#1 [typeck_item_bodies] type-checking all item bodies
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0019`.

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

note: rustc 1.27.1 (5f2b325f6 2018-07-07) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `test_bugs`.

To learn more, run the command again with --verbose.

The backtrace on nightly is verry different:

warning: unreachable expression
   --> src\lib.rs:164:25
    |
164 |         let f = [();  { &loop { break } as *const _ as usize } ];
    |                         ^^^^^^^^^^^^^^^
    |
    = note: #[warn(unreachable_code)] on by default

error: internal compiler error: no kind for cast
   --> src\lib.rs:164:25
    |
164 |         let f = [();  { &loop { break } as *const _ as usize } ];
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

error: Could not compile `test_bugs`.

To learn more, run the command again with --verbose.

[DutchGhost]

After some more playing around, I found that break as _ gave the same ICE on nightly, but stable and beta refused to compile:

fn main() {
    
    [(); loop { break as _ } ];
}

[eddyb]

rust/src/librustc_passes/rvalue_promotion.rs

Line 373 in 38168a7

v.tcx.sess.delay_span_bug(e.span, "no kind for cast");