ICE encountered in 1.37 stable borrowck

[spacejam]

reproduction branch:
https://github.com/spacejam/sled/tree/tyler_ice_ice_baby

the last commit is the one-line-change that induces the panic

rustc 1.37.0 (eae3437 2019-08-13) running on x86_64-unknown-linux-gnu

λ cargo build --verbose
       Fresh unicode-xid v0.2.0
       Fresh semver-parser v0.7.0
       Fresh autocfg v0.1.6
       Fresh scopeguard v1.0.0
       Fresh nodrop v0.1.13
       Fresh smallvec v0.6.10
       Fresh lazy_static v1.4.0
       Fresh cfg-if v0.1.9
       Fresh semver v0.9.0
       Fresh lock_api v0.3.1
       Fresh proc-macro2 v1.0.3
       Fresh rustc_version v0.2.3
       Fresh libc v0.2.62
       Fresh crossbeam-utils v0.6.6
       Fresh byteorder v1.3.2
       Fresh arrayvec v0.4.11
       Fresh crc32fast v1.2.0
       Fresh quote v1.0.2
       Fresh crossbeam-channel v0.3.9
       Fresh fxhash v0.2.1
       Fresh fs2 v0.4.3
       Fresh log v0.4.8
       Fresh syn v1.0.5
       Fresh serde_derive v1.0.100
       Fresh memoffset v0.5.1
       Fresh parking_lot_core v0.6.2
       Fresh serde v1.0.100
       Fresh crossbeam-epoch v0.7.2
       Fresh parking_lot v0.9.0
       Fresh bincode v1.1.4
       Fresh serde_bytes v0.11.2
       Fresh pagecache v0.19.3 (/home/t/src/sled/crates/pagecache)
   Compiling sled v0.27.0 (/home/t/src/sled/crates/sled)
     Running `rustc --edition=2018 --crate-name sled /home/t/src/sled/crates/sled/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata,link -C debuginfo=2 --cfg 'feature="default"' -C metadata=2acb3c3e0ff06fc3 -C extra-filename=-2acb3c3e0ff06fc3 --out-dir /home/t/src/sled-debug/target/debug/deps -C incremental=/home/t/src/sled-debug/target/debug/incremental -L dependency=/home/t/src/sled-debug/target/debug/deps --extern log=/home/t/src/sled-debug/target/debug/deps/liblog-4e901f1a3fefb1b6.rlib --extern pagecache=/home/t/src/sled-debug/target/debug/deps/libpagecache-f5439c50a69613b4.rlib --extern parking_lot=/home/t/src/sled-debug/target/debug/deps/libparking_lot-bca2b5a814139bef.rlib --extern serde=/home/t/src/sled-debug/target/debug/deps/libserde-9bd90558114cf56f.rlib --extern serde_bytes=/home/t/src/sled-debug/target/debug/deps/libserde_bytes-1a92f9f5462d075a.rlib`
thread 'rustc' panicked at 'assertion failed: self.bccx.region_scope_tree.scopes_intersect(old_loan.kill_scope,
                                             new_loan.kill_scope)', src/librustc_borrowck/borrowck/check_loans.rs:493:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:200
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:214
   6: rustc::util::common::panic_hook
   7: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:481
   8: std::panicking::begin_panic
   9: rustc_borrowck::borrowck::check_loans::CheckLoanCtxt::report_error_if_loans_conflict
  10: rustc_borrowck::dataflow::DataFlowContext<O>::each_bit_on_entry
  11: <rustc_borrowck::borrowck::check_loans::CheckLoanCtxt as rustc::middle::expr_use_visitor::Delegate>::borrow
  12: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  13: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  14: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  15: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  16: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  17: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  18: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  19: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  20: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  21: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  22: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  23: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  24: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  25: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  26: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  27: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  28: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  29: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  30: rustc::middle::expr_use_visitor::ExprUseVisitor::walk_expr
  31: rustc::middle::expr_use_visitor::ExprUseVisitor::consume_expr
  32: rustc_borrowck::borrowck::check_loans::check_loans
  33: rustc_borrowck::borrowck::borrowck
  34: rustc::ty::query::__query_compute::borrowck
  35: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::borrowck>::compute
  36: rustc::dep_graph::graph::DepGraph::with_task_impl
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  38: rustc_mir::borrow_check::do_mir_borrowck
  39: rustc::ty::context::GlobalCtxt::enter_local
  40: rustc_mir::borrow_check::mir_borrowck
  41: rustc::ty::query::__query_compute::mir_borrowck
  42: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::mir_borrowck>::compute
  43: rustc::dep_graph::graph::DepGraph::with_task_impl
  44: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  45: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  46: rustc::util::common::time
  47: rustc_interface::passes::analysis
  48: rustc::ty::query::__query_compute::analysis
  49: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::analysis>::compute
  50: rustc::dep_graph::graph::DepGraph::with_task_impl
  51: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  52: rustc::ty::context::tls::enter_global
  53: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  54: rustc_interface::passes::create_global_ctxt::{{closure}}
  55: rustc_interface::interface::run_compiler_in_existing_thread_pool
  56: std::thread::local::LocalKey<T>::with
  57: scoped_tls::ScopedKey<T>::set
  58: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
query stack during panic:
#0 [borrowck] processing `<iter::Iter as std::iter::Iterator>::next`
#1 [mir_borrowck] processing `<iter::Iter as std::iter::Iterator>::next`
#2 [analysis] running analysis passes on this crate
end of query stack

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 1.37.0 (eae3437df 2019-08-13) running on x86_64-unknown-linux-gnu

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 `sled`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name sled /home/t/src/sled/crates/sled/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata,link -C debuginfo=2 --cfg 'feature="default"' -C metadata=2acb3c3e0ff06fc3 -C extra-filename=-2acb3c3e0ff06fc3 --out-dir /home/t/src/sled-debug/target/debug/deps -C incremental=/home/t/src/sled-debug/target/debug/incremental -L dependency=/home/t/src/sled-debug/target/debug/deps --extern log=/home/t/src/sled-debug/target/debug/deps/liblog-4e901f1a3fefb1b6.rlib --extern pagecache=/home/t/src/sled-debug/target/debug/deps/libpagecache-f5439c50a69613b4.rlib --extern parking_lot=/home/t/src/sled-debug/target/debug/deps/libparking_lot-bca2b5a814139bef.rlib --extern serde=/home/t/src/sled-debug/target/debug/deps/libserde-9bd90558114cf56f.rlib --extern serde_bytes=/home/t/src/sled-debug/target/debug/deps/libserde_bytes-1a92f9f5462d075a.rlib` (exit code: 101)

edit: confirmed this works without target-cpu=native, edited that out of the text above

[memoryruins]

It also emits ICE for me on stable 1.37.0. The assert message is the same that occurred in #62107 and #63932. Trying on beta and nightly, it no longer produces an ICE

error[E0596]: cannot borrow `guard` as mutable, as it is not declared as mutable
   --> crates/sled/src/iter.rs:118:21
    |
92  |         let (mut pid, mut node, guard) =
    |                                 ----- help: consider changing this to be mutable: `mut guard`
...
118 |                     guard.repin();
    |                     ^^^^^ cannot borrow as mutable

rustc 1.38.0-beta.5 (d097af105 2019-09-03) / rustc 1.39.0-nightly (0b36e9dea 2019-09-09)

[jonas-schievink]

Closing as fixed then.

[hellow554]

Related: #64453