ICE when attempting to return inside a "do catch" block (with #![feature(catch_expr)])

[mrwright]

It seems like a return in a do catch {} block can sometimes cause an ICE.

catch.rs:

#![feature(catch_expr)]

fn main() {
    let _: Result<(), ()> = do catch {
        let _ = Err(())?;
        return;
    };
}

I'm using rustc 1.22.0-nightly (150b625a0 2017-10-08). Compiling with rustc catch.rs results in

error: internal compiler error: broken MIR in NodeId(4) (_1 = ()): bad assignment (! = ()): Sorts(ExpectedFound { expected: !, found: () })
 --> catch.rs:3:11
  |
3 |   fn main() {
  |  ___________^
4 | |     let _: Result<(), ()> = do catch {
5 | |         let _ = Err(())?;
6 | |         return;
7 | |     };
8 | | }
  | |_^

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 1.22.0-nightly (150b625a0 2017-10-08) running on x86_64-unknown-linux-gnu

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:439:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.

The error does not occur with Err(()) in place of the return;. It also does not occur if a return; is added after the do catch {} block (and in that case the compiler correctly warns that the newly-added return is unreachable).

The backtrace (from RUST_BACKTRACE=full):

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:439:8
stack backtrace:
   0:     0x7ff89f268e13 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h6586f2a9393de1d1
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x7ff89f263560 - std::sys_common::backtrace::_print::h3dec927d50ceb107
                               at /checkout/src/libstd/sys_common/backtrace.rs:71
   2:     0x7ff89f276313 - std::panicking::default_hook::{{closure}}::h83ba37abaee4af2a
                               at /checkout/src/libstd/sys_common/backtrace.rs:60
                               at /checkout/src/libstd/panicking.rs:381
   3:     0x7ff89f27601a - std::panicking::default_hook::h84414cfb51346d66
                               at /checkout/src/libstd/panicking.rs:391
   4:     0x7ff89f2767d7 - std::panicking::rust_panic_with_hook::hc5becc315f665cab
                               at /checkout/src/libstd/panicking.rs:577
   5:     0x7ff89d931888 - std::panicking::begin_panic::h91a4272b15139aac
   6:     0x7ff89d92dce3 - rustc_errors::Handler::span_bug::h818a6980a83a0d6a
   7:     0x7ff89d9f5556 - rustc_mir::transform::type_check::TypeChecker::typeck_mir::hc75985338c64e28b
   8:     0x7ff89d9f841a - <rustc_mir::transform::type_check::TypeckMir as rustc::mir::transform::MirPass>::run_pass::he658866152be9628
   9:     0x7ff89da2084d - rustc_mir::transform::run_suite::h64c28382bd0fe488
  10:     0x7ff89da1fc55 - rustc_mir::transform::mir_const::h826db401d1b4585a
  11:     0x7ff89c00858f - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::compute_result::h24cb204ad2b3e092
  12:     0x7ff89bda732c - rustc::dep_graph::graph::DepGraph::with_task::hd124f2b55ca71aab
  13:     0x7ff89c009060 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::force::h45ea49524d78dcc8
  14:     0x7ff89c0098c1 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_const<'tcx>>::try_get::hc8452aa8ca69f794
  15:     0x7ff89c111c5a - rustc::ty::maps::TyCtxtAt::mir_const::h042b99b5fe2977e6
  16:     0x7ff89c10edd3 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_const::h180dddd540d106f8
  17:     0x7ff89d9ea182 - rustc_mir::transform::check_unsafety::unsafety_violations::h19de821f0076c27e
  18:     0x7ff89c012dbb - rustc::ty::maps::<impl rustc::ty::maps::queries::unsafety_violations<'tcx>>::force::hb7a64ac3b3461f98
  19:     0x7ff89c0139f2 - rustc::ty::maps::<impl rustc::ty::maps::queries::unsafety_violations<'tcx>>::try_get::hedb73960c75f9cac
  20:     0x7ff89c11210d - rustc::ty::maps::TyCtxtAt::unsafety_violations::h17300d0ec2153f7b
  21:     0x7ff89c10ee9a - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::unsafety_violations::h2cc24c67b69a9521
  22:     0x7ff89da20448 - rustc_mir::transform::mir_validated::h794c515d623ed355
  23:     0x7ff89c00a6bf - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::compute_result::h59f785e0d7f50f2b
  24:     0x7ff89bda732c - rustc::dep_graph::graph::DepGraph::with_task::hd124f2b55ca71aab
  25:     0x7ff89c00b190 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::force::ha0c601a999645f2f
  26:     0x7ff89c00b9f1 - rustc::ty::maps::<impl rustc::ty::maps::queries::mir_validated<'tcx>>::try_get::h99efb5915f3ac297
  27:     0x7ff89c111d8a - rustc::ty::maps::TyCtxtAt::mir_validated::he85faea6b924ec31
  28:     0x7ff89c10ee03 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_validated::h89fb2c8b26d004dc
  29:     0x7ff89dc9d209 - rustc_borrowck::borrowck::borrowck::h257816007c121805
  30:     0x7ff89c0275ef - rustc::ty::maps::<impl rustc::ty::maps::queries::borrowck<'tcx>>::compute_result::h11aa284fc5f2689d
  31:     0x7ff89bda3b12 - rustc::dep_graph::graph::DepGraph::with_task::h6efbdc4d292292cb
  32:     0x7ff89c02806d - rustc::ty::maps::<impl rustc::ty::maps::queries::borrowck<'tcx>>::force::h0643799d9432c62c
  33:     0x7ff89c02887d - rustc::ty::maps::<impl rustc::ty::maps::queries::borrowck<'tcx>>::try_get::he08acc9dd96b1547
  34:     0x7ff89c1129ce - rustc::ty::maps::TyCtxtAt::borrowck::h607458e61f03edd5
  35:     0x7ff89c10f063 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::borrowck::hccbf7a762d6ad734
  36:     0x7ff89dc9d067 - rustc_borrowck::borrowck::check_crate::hf8e143db5104f5f9
  37:     0x7ff89f5a4960 - rustc::ty::context::TyCtxt::create_and_enter::hcabbdde20fa10fc4
  38:     0x7ff89f618acb - rustc_driver::driver::compile_input::h9793286a10a505ce
  39:     0x7ff89f63477e - rustc_driver::run_compiler::h51c96efa7b2ea675
  40:     0x7ff89f553607 - std::sys_common::backtrace::__rust_begin_short_backtrace::h19cb26897b35d05c
  41:     0x7ff89f2b0bac - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:99
  42:     0x7ff89f58c630 - <F as alloc::boxed::FnBox<A>>::call_box::h4157afcb57e5a63b
  43:     0x7ff89f2751db - std::sys::imp::thread::Thread::new::thread_start::h41d0f90599fa7590
                               at /checkout/src/liballoc/boxed.rs:736
                               at /checkout/src/libstd/sys_common/thread.rs:24
                               at /checkout/src/libstd/sys/unix/thread.rs:90
  44:     0x7ff89a14c493 - start_thread
  45:     0x7ff89ef44abe - __clone
  46:                0x0 - <unknown>

Output of rustc --version --verbose:

$ rustc --version --verbose         
rustc 1.22.0-nightly (150b625a0 2017-10-08)
binary: rustc
commit-hash: 150b625a07f135d0a5e1693adf2b14315709779e
commit-date: 2017-10-08
host: x86_64-unknown-linux-gnu
release: 1.22.0-nightly
LLVM version: 4.0