ICE: Rvalue::Discriminant on Lvalue of type

[sinkuu]

Compiling this code with mir-opt-level=2 or higher produces an ICE.

pub enum Enum {
    A,
    B,
}

fn foo(s: &[Enum]) {
    match s[1-1] { Enum::A => true, _ => false };
}

fn main() {
    foo(&[Enum::A]);
}

backtrace:

error: internal compiler error: /checkout/src/librustc/mir/tcx.rs:187: Rvalue::Discriminant on Lvalue of type <usize as std::slice::SliceIndex<[Enum]>>::Output

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 1.23.0-nightly (ee2286149 2017-11-07) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:507:8
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:69
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:58
             at /checkout/src/libstd/panicking.rs:381
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:391
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:577
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::bug
   7: <std::thread::local::LocalKey<T>>::with
   8: rustc::ty::context::tls::with_opt
   9: _ZN5rustc7session16opt_span_bug_fmt17h28653ab0ad5ebc6eE.llvm.80CEBD21
  10: rustc::session::bug_fmt
  11: rustc::mir::tcx::<impl rustc::mir::Rvalue<'tcx>>::ty
  12: _ZN11rustc_trans3mir6rvalue76_$LT$impl$u20$rustc_trans..mir..MirContext$LT$$u27$a$C$$u20$$u27$tcx$GT$$GT$20trans_rvalue_operand17hb51fa7a56ff80228E.llvm.42CB1140
  13: rustc_trans::base::trans_instance
  14: rustc_trans::trans_item::TransItemExt::define
  15: _ZN11rustc_trans4base20compile_codegen_unit17ha4116c55c0998339E.llvm.42CB1140
  16: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::compute_result
  17: _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h65fbb140f0b6ef1aE.llvm.828C6C6A
  18: rustc_errors::Handler::track_diagnostics
  19: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  20: _ZN5rustc2ty4maps80_$LT$impl$u20$rustc..ty..maps..queries..compile_codegen_unit$LT$$u27$tcx$GT$$GT$5force17had4524b73e79c5fbE.llvm.6336F49B
  21: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::try_get
  22: rustc::ty::maps::TyCtxtAt::compile_codegen_unit
  23: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::compile_codegen_unit
  24: rustc_trans::base::trans_crate
  25: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::trans_crate
  26: rustc::util::common::time
  27: rustc_driver::driver::phase_4_translate_to_llvm
  28: _ZN12rustc_driver6driver13compile_input28_$u7b$$u7b$closure$u7d$$u7d$17hb5bec2b4d6fc98bbE.llvm.5ECE37CB
  29: <std::thread::local::LocalKey<T>>::with
  30: <std::thread::local::LocalKey<T>>::with
  31: rustc::ty::context::TyCtxt::create_and_enter
  32: rustc_driver::driver::compile_input
  33: rustc_driver::run_compiler

rustc --version --verbose:

rustc 1.23.0-nightly (ee2286149 2017-11-07)
binary: rustc
commit-hash: ee2286149a5f0b148334841d4f067dc819dcca3b
commit-date: 2017-11-07
host: x86_64-unknown-linux-gnu
release: 1.23.0-nightly
LLVM version: 4.0

[arielb1]

Sounds like someone (I bet inlining) is not normalizing after substituting.