Unexplained errors applying `-Z instrument-coverage` to some rustc `ui` tests

[richkadel]

When experimentally adding -Zinstrument-coverage to the set of ui tests in the Rust source tree, most tests still pass; of those that don't, almost all failures can be explained, and some improvements have been made to surface known incompatibilities between -Zinstrument-coverage and other compiler options (see #79958 (comment)).

However, there are 4 3 tests that still fail with -Zinstrument-coverage that I don't understand.

I'm hoping someone(s) that understand these tests and/or compiler options can take a look, explain why they are expected to fail, or clarify what the bug might be, if they should not fail.

---

Fixed via #80072

$ ./x.py test --rustc-args="-Zinstrument-coverage" src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs

Failure due to:
error[E0493]: destructors cannot be evaluated at compile-time
--> /usr/local/google/home/richkadel/rust/src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs:15:25
|
LL | pub const fn unwrap(self) -> T {
| ^^^^ constant functions cannot evaluate destructors
(this error is printed twice)

---

$ ./x.py test --rustc-args="-Zinstrument-coverage" src/test/ui/issues/issue-33287.rs

Failure due to:
   stderr:
   ------------------------------------------
   error: this operation will panic at runtime
     --> /usr/local/google/home/richkadel/rust/src/test/ui/issues/issue-33287.rs:7:17
      |
   LL |     let range = A[1]..;
      |                 ^^^^ index out of bounds: the length is 1 but the index is 1
      |
      = note: `#[deny(unconditional_panic)]` on by default

---

$ ./x.py test --rustc-args="-Zinstrument-coverage" src/test/ui/print_type_sizes/niche-filling.rs

Failure due to additional lines in the compiler output:
   +       print-type-size type: `std::option::Option<std::num::NonZeroU32>`: 4 bytes, alignment: 4 bytes
   +       print-type-size     variant `Some`: 4 bytes
   +       print-type-size         field `.0`: 4 bytes
   +       print-type-size     variant `None`: 0 bytes

---

$ ./x.py test --rustc-args="-Zinstrument-coverage" src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs

Failure due to:
   error: internal compiler error:
   compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32:
   could not fully normalize `std::option::Option<<i32 as std::iter::Iterator>::Item>`

[richkadel]

@tmandry @wesleywiser

I created this issue for the 4 tests that created errors or output that I can't explain.

[richkadel]

I don't know if any of these issues are actually bugs in -Z instrument-coverage, or acceptable incompatabilities. In case there are bugs, they might affect the tracking issue: #79121

[tmandry]

unstable-precise-live-drops-in-libcore.rs emits unused code warnings, but only if -Zinstrument-coverage is not specified:

> rustc +stage1 src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs
warning: enum is never used: `Either`
 --> src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs:7:6
  |
7 | enum Either<T, S> {
  |      ^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: associated function is never used: `unwrap`
  --> src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs:15:18
   |
15 |     pub const fn unwrap(self) -> T {
   |                  ^^^^^^

warning: 2 warnings emitted

Backtrace:

Details

> 
RUST_BACKTRACE=1 rustc +stage1 -Zinstrument-coverage -Ztreat-err-as-bug src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs
error[E0493]: destructors cannot be evaluated at compile-time
  --> src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs:15:25
   |
15 |     pub const fn unwrap(self) -> T {
   |                         ^^^^ constant functions cannot evaluate destructors

thread 'rustc' panicked at 'aborting due to `-Z treat-err-as-bug=1`', compiler/rustc_errors/src/lib.rs:990:27
stack backtrace:
   0: std::panicking::begin_panic
             at ./library/std/src/panicking.rs:519:12
   1: rustc_errors::HandlerInner::panic_if_treat_err_as_bug
             at ./compiler/rustc_errors/src/lib.rs:990:27
   2: rustc_errors::HandlerInner::bump_err_count
             at ./compiler/rustc_errors/src/lib.rs:980:9
   3: rustc_errors::HandlerInner::emit_diagnostic
             at ./compiler/rustc_errors/src/lib.rs:796:13
   4: rustc_errors::Handler::emit_diagnostic
             at ./compiler/rustc_errors/src/lib.rs:715:9
   5: rustc_errors::diagnostic_builder::DiagnosticBuilder::emit
             at ./compiler/rustc_errors/src/diagnostic_builder.rs:101:9
   6: rustc_mir::transform::check_consts::post_drop_elaboration::CheckLiveDrops::check_live_drop
             at ./compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs:59:9
   7: <rustc_mir::transform::check_consts::post_drop_elaboration::CheckLiveDrops as rustc_middle::mir::visit::Visitor>::visit_terminator
             at ./compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs:93:21
   8: <rustc_mir::transform::check_consts::post_drop_elaboration::CheckLiveDrops as rustc_middle::mir::visit::Visitor>::visit_basic_block_data
             at ./compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs:72:9
   9: rustc_middle::mir::visit::Visitor::super_body
             at ./compiler/rustc_middle/src/mir/visit.rs:259:21
  10: rustc_middle::mir::visit::Visitor::visit_body
             at ./compiler/rustc_middle/src/mir/visit.rs:78:17
  11: rustc_mir::transform::check_consts::post_drop_elaboration::check_live_drops
             at ./compiler/rustc_mir/src/transform/check_consts/post_drop_elaboration.rs:40:5
  12: rustc_mir::transform::mir_drops_elaborated_and_const_checked
             at ./compiler/rustc_mir/src/transform/mod.rs:341:5
  13: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_drops_elaborated_and_const_checked>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  14: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  15: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:200:9
  16: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:608:17
  17: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  18: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  19: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  20: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  21: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  22: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  23: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  24: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  25: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  26: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  27: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  28: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  29: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  30: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  31: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  32: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  33: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  34: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  35: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  36: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
  37: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  38: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  39: rustc_query_system::query::plumbing::ensure_query_impl
  40: rustc_query_system::query::plumbing::ensure_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:749:5
  41: rustc_middle::ty::query::TyCtxtEnsure::mir_drops_elaborated_and_const_checked
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:404:17
  42: rustc_interface::passes::analysis::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:865:17
  43: rustc_data_structures::profiling::VerboseTimingGuard::run
             at ./compiler/rustc_data_structures/src/profiling.rs:570:9
  44: rustc_session::utils::<impl rustc_session::session::Session>::time
             at ./compiler/rustc_session/src/utils.rs:9:9
  45: rustc_interface::passes::analysis
             at ./compiler/rustc_interface/src/passes.rs:860:5
  46: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  47: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  48: rustc_query_system::dep_graph::graph::DepGraph<K>::with_eval_always_task
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:334:9
  49: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:600:17
  50: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  51: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  52: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  53: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  54: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  55: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  56: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  57: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  58: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  59: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  60: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  61: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  62: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  63: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  64: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  65: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  66: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  67: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  68: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  69: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
  70: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  71: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  72: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
  73: rustc_middle::ty::query::TyCtxtAt::analysis
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
  74: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::analysis
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
  75: rustc_driver::run_compiler::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:440:59
  76: rustc_interface::passes::QueryContext::enter::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:725:42
  77: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  78: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  79: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  80: rustc_interface::passes::QueryContext::enter
             at ./compiler/rustc_interface/src/passes.rs:725:9
  81: rustc_driver::run_compiler::{{closure}}::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:440:13
  82: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
             at ./compiler/rustc_interface/src/queries.rs:413:19
  83: rustc_driver::run_compiler::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:341:22
  84: rustc_interface::interface::create_compiler_and_run::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:196:13
  85: rustc_span::with_source_map
             at ./compiler/rustc_span/src/lib.rs:765:5
  86: rustc_interface::interface::create_compiler_and_run
             at ./compiler/rustc_interface/src/interface.rs:190:5
  87: rustc_interface::interface::run_compiler::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:212:12
  88: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:152:13
  89: scoped_tls::ScopedKey<T>::set
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137:9
  90: rustc_span::with_session_globals
             at ./compiler/rustc_span/src/lib.rs:94:5
  91: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:150:9
  92: rustc_interface::util::scoped_thread::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:125:24
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z instrument-coverage -Z treat-err-as-bug

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `Either::<T, T>::unwrap`
#1 [analysis] running analysis passes on this crate
end of query stack

The error happens during drop elaboration. I'm guessing -Zinstrument-coverage somehow marks the code as used; perhaps the unreachable function handling is involved somehow?

cc @ecstatic-morse

[tmandry]

issue-33287.rs: Using -Ztreat-err-as-bug again we can see that the covered_file_name query is causing optimized_mir to be evaluated for the test function, when it wasn't before.

Details

> 
RUST_BACKTRACE=1 rustc +stage1 -Zinstrument-coverage -Ztreat-err-as-bug src/test/ui/issues/issue-33287.rs
error: this operation will panic at runtime
 --> src/test/ui/issues/issue-33287.rs:7:17
  |
7 |     let range = A[1]..;
  |                 ^^^^ index out of bounds: the length is 1 but the index is 1
  |
  = note: `#[deny(unconditional_panic)]` on by default

thread 'rustc' panicked at 'aborting due to `-Z treat-err-as-bug=1`', compiler/rustc_errors/src/lib.rs:990:27
stack backtrace:
   0: std::panicking::begin_panic
             at ./library/std/src/panicking.rs:519:12
   1: rustc_errors::HandlerInner::panic_if_treat_err_as_bug
             at ./compiler/rustc_errors/src/lib.rs:990:27
   2: rustc_errors::HandlerInner::bump_err_count
             at ./compiler/rustc_errors/src/lib.rs:980:9
   3: rustc_errors::HandlerInner::emit_diagnostic
             at ./compiler/rustc_errors/src/lib.rs:796:13
   4: rustc_errors::Handler::emit_diagnostic
             at ./compiler/rustc_errors/src/lib.rs:715:9
   5: rustc_errors::diagnostic_builder::DiagnosticBuilder::emit
             at ./compiler/rustc_errors/src/diagnostic_builder.rs:101:9
   6: rustc_mir::transform::const_prop::ConstPropagator::report_assert_as_lint::{{closure}}
             at ./compiler/rustc_mir/src/transform/const_prop.rs:522:13
   7: core::ops::function::FnOnce::call_once{{vtable.shim}}
             at ./library/core/src/ops/function.rs:227:5
   8: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at ./library/alloc/src/boxed.rs:1328:9
   9: rustc_middle::lint::struct_lint_level::struct_lint_level_impl
             at ./compiler/rustc_middle/src/lint.rs:362:9
  10: rustc_middle::lint::struct_lint_level
             at ./compiler/rustc_middle/src/lint.rs:364:5
  11: rustc_middle::ty::context::TyCtxt::struct_span_lint_hir
             at ./compiler/rustc_middle/src/ty/context.rs:2575:9
  12: rustc_mir::transform::const_prop::ConstPropagator::report_assert_as_lint
             at ./compiler/rustc_mir/src/transform/const_prop.rs:519:9
  13: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_terminator
             at ./compiler/rustc_mir/src/transform/const_prop.rs:1216:29
  14: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_body
             at ./compiler/rustc_mir/src/transform/const_prop.rs:1050:13
  15: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
             at ./compiler/rustc_mir/src/transform/const_prop.rs:150:9
  16: rustc_mir::transform::run_passes::{{closure}}
             at ./compiler/rustc_mir/src/transform/mod.rs:186:9
  17: rustc_mir::transform::run_passes
             at ./compiler/rustc_mir/src/transform/mod.rs:202:13
  18: rustc_mir::transform::run_optimization_passes
             at ./compiler/rustc_mir/src/transform/mod.rs:446:5
  19: rustc_mir::transform::inner_optimized_mir
             at ./compiler/rustc_mir/src/transform/mod.rs:486:5
  20: rustc_mir::transform::optimized_mir
             at ./compiler/rustc_mir/src/transform/mod.rs:462:25
  21: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::optimized_mir>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  23: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
  24: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  25: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  26: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  27: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  28: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  29: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  30: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  31: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  32: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  33: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  34: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  35: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  36: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  37: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  38: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  39: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  40: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  41: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  42: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  43: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
  44: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  45: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  46: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
  47: rustc_middle::ty::query::TyCtxtAt::optimized_mir
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
  48: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::optimized_mir
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
  49: rustc_mir::transform::coverage::query::covered_file_name
             at ./compiler/rustc_mir/src/transform/coverage/query.rs:132:20
  50: rustc_mir::transform::coverage::query::provide::{{closure}}
             at ./compiler/rustc_mir/src/transform/coverage/query.rs:14:49
  51: core::ops::function::FnOnce::call_once
             at ./library/core/src/ops/function.rs:227:5
  52: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::covered_file_name>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  53: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  54: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
  55: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  56: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  57: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  58: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  59: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  60: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  61: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  62: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  63: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  64: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  65: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  66: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  67: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  68: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  69: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  70: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  71: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  72: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  73: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  74: <rustc_query_system::query::caches::ArenaCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:198:13
  75: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  76: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  77: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
  78: rustc_middle::ty::query::TyCtxtAt::covered_file_name
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
  79: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::covered_file_name
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
  80: rustc_codegen_llvm::coverageinfo::mapgen::add_unreachable_coverage
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs:292:49
  81: rustc_codegen_llvm::coverageinfo::mapgen::finalize
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs:51:5
  82: rustc_codegen_llvm::coverageinfo::<impl rustc_codegen_ssa::traits::coverageinfo::CoverageInfoMethods for rustc_codegen_llvm::context::CodegenCx>::coverageinfo_finalize
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs:46:9
  83: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
             at ./compiler/rustc_codegen_llvm/src/base.rs:149:17
  84: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  85: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:200:9
  86: rustc_codegen_llvm::base::compile_codegen_unit
             at ./compiler/rustc_codegen_llvm/src/base.rs:104:9
  87: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::compile_codegen_unit
             at ./compiler/rustc_codegen_llvm/src/lib.rs:106:9
  88: rustc_codegen_ssa::base::codegen_crate
             at ./compiler/rustc_codegen_ssa/src/base.rs:642:38
  89: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
             at ./compiler/rustc_codegen_llvm/src/lib.rs:267:18
  90: rustc_interface::passes::start_codegen::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:996:9
  91: rustc_data_structures::profiling::VerboseTimingGuard::run
             at ./compiler/rustc_data_structures/src/profiling.rs:570:9
  92: rustc_session::utils::<impl rustc_session::session::Session>::time
             at ./compiler/rustc_session/src/utils.rs:9:9
  93: rustc_interface::passes::start_codegen
             at ./compiler/rustc_interface/src/passes.rs:995:19
  94: rustc_interface::queries::Queries::ongoing_codegen::{{closure}}::{{closure}}
             at ./compiler/rustc_interface/src/queries.rs:282:20
  95: rustc_interface::passes::QueryContext::enter::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:725:42
  96: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  97: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  98: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  99: rustc_interface::passes::QueryContext::enter
             at ./compiler/rustc_interface/src/passes.rs:725:9
 100: rustc_interface::queries::Queries::ongoing_codegen::{{closure}}
             at ./compiler/rustc_interface/src/queries.rs:273:13
 101: rustc_interface::queries::Query<T>::compute
             at ./compiler/rustc_interface/src/queries.rs:35:28
 102: rustc_interface::queries::Queries::ongoing_codegen
             at ./compiler/rustc_interface/src/queries.rs:271:9
 103: rustc_driver::run_compiler::{{closure}}::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:446:13
 104: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
             at ./compiler/rustc_interface/src/queries.rs:413:19
 105: rustc_driver::run_compiler::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:341:22
 106: rustc_interface::interface::create_compiler_and_run::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:196:13
 107: rustc_span::with_source_map
             at ./compiler/rustc_span/src/lib.rs:765:5
 108: rustc_interface::interface::create_compiler_and_run
             at ./compiler/rustc_interface/src/interface.rs:190:5
 109: rustc_interface::interface::run_compiler::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:212:12
 110: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:152:13
 111: scoped_tls::ScopedKey<T>::set
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137:9
 112: rustc_span::with_session_globals
             at ./compiler/rustc_span/src/lib.rs:94:5
 113: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:150:9
 114: rustc_interface::util::scoped_thread::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:125:24
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z instrument-coverage -Z treat-err-as-bug

query stack during panic:
#0 [optimized_mir] optimizing MIR for `test`
#1 [covered_file_name] retrieving the covered file name, if instrumented, for `test`
end of query stack

This indicates a possible performance issue with that query; maybe there's a way we can implement it that doesn't demand optimized MIR. EDIT: The fact that this is causing new errors might also mean that it isn't correct to rely on that query, but that is less clear to me.

Also, I feel like this function should be getting called by main in the test to make sure we're exercising all the code paths the original regression test was meant to exercise.

cc @wesleywiser

[tmandry]

..skipping the layout one for now..

trivial-bounds-inconsistent.rs: This again seems to be happening during drop elaboration, but this time it's happening as a direct result of the covered_file_name query, so sort of a combination of the last two.

Details

> RUST_BACKTRACE=1 rustc +stage1 -Zinstrument-coverage src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs
warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:14:19
   |
14 | enum E where i32: Foo { V } //~ WARNING trivial_bounds
   |                   ^^^
   |
   = note: `#[warn(trivial_bounds)]` on by default

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:16:21
   |
16 | struct S where i32: Foo; //~ WARNING trivial_bounds
   |                     ^^^

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:18:20
   |
18 | trait T where i32: Foo {} //~ WARNING trivial_bounds
   |                    ^^^

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:20:20
   |
20 | union U where i32: Foo { f: i32 } //~ WARNING trivial_bounds
   |                    ^^^

warning: where clauses are not enforced in type aliases
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:22:14
   |
22 | type Y where i32: Foo = ();
   |              ^^^^^^^^
   |
   = note: `#[warn(type_alias_bounds)]` on by default
help: the clause will not be checked when the type alias is used, and should be removed
   |
22 | type Y  = ();
   |       --

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:22:19
   |
22 | type Y where i32: Foo = ();
   |                   ^^^

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:26:28
   |
26 | impl Foo for () where i32: Foo { //~ WARNING trivial_bounds
   |                            ^^^

warning: Trait bound i32: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:34:19
   |
34 | fn f() where i32: Foo { //~ WARNING trivial_bounds
   |                   ^^^

warning: Trait bound &'static str: Foo does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:41:28
   |
41 | fn g() where &'static str: Foo { //~ WARNING trivial_bounds
   |                            ^^^

warning: Trait bound str: Sized does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:55:37
   |
55 | struct TwoStrs(str, str) where str: Sized; //~ WARNING trivial_bounds
   |                                     ^^^^^

warning: Trait bound for<'a> Dst<(dyn A + 'a)>: Sized does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:57:51
   |
57 | fn unsized_local() where for<'a> Dst<dyn A + 'a>: Sized { //~ WARNING trivial_bounds
   |                                                   ^^^^^

warning: Trait bound str: Sized does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:61:35
   |
61 | fn return_str() -> str where str: Sized { //~ WARNING trivial_bounds
   |                                   ^^^^^

warning: Trait bound String: Neg does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:65:46
   |
65 | fn use_op(s: String) -> String where String: ::std::ops::Neg<Output=String> {
   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: Trait bound i32: Iterator does not depend on any type or lifetime parameters
  --> src/test/ui/trivial-bounds/trivial-bounds-inconsistent.rs:70:25
   |
70 | fn use_for() where i32: Iterator { //~ WARNING trivial_bounds
   |                         ^^^^^^^^

error: internal compiler error: compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32: could not fully normalize `std::option::Option<<i32 as std::iter::Iterator>::Item>`

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
stack backtrace:
   0: std::panicking::begin_panic
             at ./library/std/src/panicking.rs:519:12
   1: rustc_errors::HandlerInner::bug
             at ./compiler/rustc_errors/src/lib.rs:958:9
   2: rustc_errors::Handler::bug
             at ./compiler/rustc_errors/src/lib.rs:675:9
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
             at ./compiler/rustc_middle/src/util/bug.rs:33:34
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1798:40
   5: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
   6: rustc_middle::ty::context::tls::with_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1798:9
   7: rustc_middle::util::bug::opt_span_bug_fmt
             at ./compiler/rustc_middle/src/util/bug.rs:29:5
   8: rustc_middle::util::bug::bug_fmt
             at ./compiler/rustc_middle/src/util/bug.rs:14:5
   9: rustc_traits::normalize_erasing_regions::normalize_generic_arg_after_erasing_regions::{{closure}}
             at ./compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32
  10: rustc_infer::infer::InferCtxtBuilder::enter
             at ./compiler/rustc_infer/src/infer/mod.rs:583:9
  11: rustc_traits::normalize_erasing_regions::normalize_generic_arg_after_erasing_regions
             at ./compiler/rustc_traits/src/normalize_erasing_regions.rs:22:5
  12: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  13: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
  14: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  15: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  16: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  17: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  18: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  19: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  20: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  21: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  22: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  23: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  24: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  25: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  26: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  27: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  28: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  29: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  30: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  31: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  32: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  33: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
  34: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  35: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  36: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
  37: rustc_middle::ty::query::TyCtxtAt::normalize_generic_arg_after_erasing_regions
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
  38: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::normalize_generic_arg_after_erasing_regions
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
  39: <rustc_middle::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_middle::ty::fold::TypeFolder>::fold_ty
             at ./compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:97:9
  40: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::fold_with
             at ./compiler/rustc_middle/src/ty/structural_impls.rs:969:9
  41: rustc_middle::ty::normalize_erasing_regions::<impl rustc_middle::ty::context::TyCtxt>::normalize_erasing_regions
             at ./compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:37:13
  42: rustc_middle::ty::util::<impl rustc_middle::ty::TyS>::needs_drop
             at ./compiler/rustc_middle/src/ty/util.rs:766:30
  43: rustc_mir::dataflow::drop_flag_effects::on_all_drop_children_bits::{{closure}}
             at ./compiler/rustc_mir/src/dataflow/drop_flag_effects.rs:156:12
  44: rustc_mir::dataflow::drop_flag_effects::on_all_children_bits::on_all_children_bits
             at ./compiler/rustc_mir/src/dataflow/drop_flag_effects.rs:126:9
  45: rustc_mir::dataflow::drop_flag_effects::on_all_children_bits
             at ./compiler/rustc_mir/src/dataflow/drop_flag_effects.rs:138:5
  46: rustc_mir::dataflow::drop_flag_effects::on_all_drop_children_bits
             at ./compiler/rustc_mir/src/dataflow/drop_flag_effects.rs:150:5
  47: rustc_mir::transform::elaborate_drops::find_dead_unwinds
             at ./compiler/rustc_mir/src/transform/elaborate_drops.rs:116:9
  48: <rustc_mir::transform::elaborate_drops::ElaborateDrops as rustc_mir::transform::MirPass>::run_pass
             at ./compiler/rustc_mir/src/transform/elaborate_drops.rs:41:32
  49: rustc_mir::transform::run_passes::{{closure}}
             at ./compiler/rustc_mir/src/transform/mod.rs:186:9
  50: rustc_mir::transform::run_passes
             at ./compiler/rustc_mir/src/transform/mod.rs:202:13
  51: rustc_mir::transform::run_post_borrowck_cleanup_passes
             at ./compiler/rustc_mir/src/transform/mod.rs:372:5
  52: rustc_mir::transform::mir_drops_elaborated_and_const_checked
             at ./compiler/rustc_mir/src/transform/mod.rs:340:5
  53: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_drops_elaborated_and_const_checked>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  54: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  55: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:200:9
  56: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:608:17
  57: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  58: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  59: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  60: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  61: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  62: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  63: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  64: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  65: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  66: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  67: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  68: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  69: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
  70: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
  71: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
  72: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
  73: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
  74: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
  75: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
  76: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
  77: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
  78: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
  79: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
  80: rustc_middle::ty::query::TyCtxtAt::mir_drops_elaborated_and_const_checked
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
  81: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::mir_drops_elaborated_and_const_checked
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
  82: rustc_mir::transform::inner_optimized_mir
             at ./compiler/rustc_mir/src/transform/mod.rs:485:20
  83: rustc_mir::transform::optimized_mir
             at ./compiler/rustc_mir/src/transform/mod.rs:462:25
  84: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::optimized_mir>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
  85: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
  86: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
  87: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
  88: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
  89: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
  90: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
  91: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
  92: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
  93: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
  94: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
  95: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
  96: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
  97: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
  98: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
  99: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
 100: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
 101: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
 102: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
 103: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
 104: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
 105: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
 106: <rustc_query_system::query::caches::DefaultCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:114:79
 107: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
 108: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
 109: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
 110: rustc_middle::ty::query::TyCtxtAt::optimized_mir
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
 111: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::optimized_mir
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
 112: rustc_mir::transform::coverage::query::covered_file_name
             at ./compiler/rustc_mir/src/transform/coverage/query.rs:132:20
 113: rustc_mir::transform::coverage::query::provide::{{closure}}
             at ./compiler/rustc_mir/src/transform/coverage/query.rs:14:49
 114: core::ops::function::FnOnce::call_once
             at ./library/core/src/ops/function.rs:227:5
 115: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::covered_file_name>::compute
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:377:17
 116: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
 117: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}::{{closure}}
 118: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:74
 119: stacker::maybe_grow
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/stacker-0.1.12/src/lib.rs:55:9
 120: rustc_data_structures::stack::ensure_sufficient_stack
             at ./compiler/rustc_data_structures/src/stack.rs:16:5
 121: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:73:17
 122: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
 123: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
 124: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
 125: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:72:13
 126: rustc_middle::ty::context::tls::with_related_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1777:13
 127: rustc_middle::ty::context::tls::with_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1761:40
 128: rustc_middle::ty::context::tls::with_context_opt
             at ./compiler/rustc_middle/src/ty/context.rs:1750:22
 129: rustc_middle::ty::context::tls::with_context
             at ./compiler/rustc_middle/src/ty/context.rs:1761:9
 130: rustc_middle::ty::context::tls::with_related_context
             at ./compiler/rustc_middle/src/ty/context.rs:1774:9
 131: rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:61:9
 132: rustc_query_system::query::plumbing::force_query_with_job::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:598:9
 133: rustc_query_system::query::plumbing::with_diagnostics
             at ./compiler/rustc_query_system/src/query/plumbing.rs:302:18
 134: rustc_query_system::query::plumbing::force_query_with_job
             at ./compiler/rustc_query_system/src/query/plumbing.rs:597:51
 135: rustc_query_system::query::plumbing::try_execute_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:426:16
 136: rustc_query_system::query::plumbing::get_query_impl::{{closure}}
             at ./compiler/rustc_query_system/src/query/plumbing.rs:645:23
 137: <rustc_query_system::query::caches::ArenaCache<K,V> as rustc_query_system::query::caches::QueryCache>::lookup
             at ./compiler/rustc_query_system/src/query/caches.rs:198:13
 138: rustc_query_system::query::plumbing::try_get_cached
             at ./compiler/rustc_query_system/src/query/plumbing.rs:379:5
 139: rustc_query_system::query::plumbing::get_query_impl
             at ./compiler/rustc_query_system/src/query/plumbing.rs:637:5
 140: rustc_query_system::query::plumbing::get_query
             at ./compiler/rustc_query_system/src/query/plumbing.rs:739:5
 141: rustc_middle::ty::query::TyCtxtAt::covered_file_name
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:487:17
 142: rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::covered_file_name
             at ./compiler/rustc_middle/src/ty/query/plumbing.rs:448:17
 143: rustc_codegen_llvm::coverageinfo::mapgen::add_unreachable_coverage
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs:292:49
 144: rustc_codegen_llvm::coverageinfo::mapgen::finalize
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs:51:5
 145: rustc_codegen_llvm::coverageinfo::<impl rustc_codegen_ssa::traits::coverageinfo::CoverageInfoMethods for rustc_codegen_llvm::context::CodegenCx>::coverageinfo_finalize
             at ./compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs:46:9
 146: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
             at ./compiler/rustc_codegen_llvm/src/base.rs:149:17
 147: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:301:14
 148: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
             at ./compiler/rustc_query_system/src/dep_graph/graph.rs:200:9
 149: rustc_codegen_llvm::base::compile_codegen_unit
             at ./compiler/rustc_codegen_llvm/src/base.rs:104:9
 150: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::compile_codegen_unit
             at ./compiler/rustc_codegen_llvm/src/lib.rs:106:9
 151: rustc_codegen_ssa::base::codegen_crate
             at ./compiler/rustc_codegen_ssa/src/base.rs:642:38
 152: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
             at ./compiler/rustc_codegen_llvm/src/lib.rs:267:18
 153: rustc_interface::passes::start_codegen::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:996:9
 154: rustc_data_structures::profiling::VerboseTimingGuard::run
             at ./compiler/rustc_data_structures/src/profiling.rs:570:9
 155: rustc_session::utils::<impl rustc_session::session::Session>::time
             at ./compiler/rustc_session/src/utils.rs:9:9
 156: rustc_interface::passes::start_codegen
             at ./compiler/rustc_interface/src/passes.rs:995:19
 157: rustc_interface::queries::Queries::ongoing_codegen::{{closure}}::{{closure}}
             at ./compiler/rustc_interface/src/queries.rs:282:20
 158: rustc_interface::passes::QueryContext::enter::{{closure}}
             at ./compiler/rustc_interface/src/passes.rs:725:42
 159: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at ./compiler/rustc_middle/src/ty/context.rs:1733:50
 160: rustc_middle::ty::context::tls::set_tlv
             at ./compiler/rustc_middle/src/ty/context.rs:1717:9
 161: rustc_middle::ty::context::tls::enter_context
             at ./compiler/rustc_middle/src/ty/context.rs:1733:9
 162: rustc_interface::passes::QueryContext::enter
             at ./compiler/rustc_interface/src/passes.rs:725:9
 163: rustc_interface::queries::Queries::ongoing_codegen::{{closure}}
             at ./compiler/rustc_interface/src/queries.rs:273:13
 164: rustc_interface::queries::Query<T>::compute
             at ./compiler/rustc_interface/src/queries.rs:35:28
 165: rustc_interface::queries::Queries::ongoing_codegen
             at ./compiler/rustc_interface/src/queries.rs:271:9
 166: rustc_driver::run_compiler::{{closure}}::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:446:13
 167: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
             at ./compiler/rustc_interface/src/queries.rs:413:19
 168: rustc_driver::run_compiler::{{closure}}
             at ./compiler/rustc_driver/src/lib.rs:341:22
 169: rustc_interface::interface::create_compiler_and_run::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:196:13
 170: rustc_span::with_source_map
             at ./compiler/rustc_span/src/lib.rs:765:5
 171: rustc_interface::interface::create_compiler_and_run
             at ./compiler/rustc_interface/src/interface.rs:190:5
 172: rustc_interface::interface::run_compiler::{{closure}}
             at ./compiler/rustc_interface/src/interface.rs:212:12
 173: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:152:13
 174: scoped_tls::ScopedKey<T>::set
             at /usr/local/google/home/tmandry/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137:9
 175: rustc_span::with_session_globals
             at ./compiler/rustc_span/src/lib.rs:94:5
 176: rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:150:9
 177: rustc_interface::util::scoped_thread::{{closure}}
             at ./compiler/rustc_interface/src/util.rs:125:24
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z instrument-coverage

query stack during panic:
#0 [normalize_generic_arg_after_erasing_regions] normalizing `std::option::Option<<i32 as std::iter::Iterator>::Item>`
#1 [mir_drops_elaborated_and_const_checked] elaborating drops for `use_for`
#2 [optimized_mir] optimizing MIR for `use_for`
#3 [covered_file_name] retrieving the covered file name, if instrumented, for `use_for`
end of query stack
error: aborting due to previous error; 14 warnings emitted

Here we're generating MIR for a function which can never be called, due to its where i32: Iterator clause. So this might indicate that it's a bug to run the optimized_mir query on a function which couldn't be called. Or that the normalization code is too brittle somehow.

cc @matthewjasper

[tmandry]

I haven't looked into the layout issue yet but it looks like the coverage code is causing a layout to be computed that wasn't before. Unclear to me if that's actually a problem or not; the test is relying on the side effectful outputs of a query computed on demand so that's not going to be super robust.

[richkadel]

perhaps the unreachable function handling is involved somehow?

I can't think of a reason the "unreachable function handling" would mark anything as used. It also seems "late" in the process (well after MIR processing is done). But in any case, it doesn't (at least not intentionally) actually use the code. It just gets the spans for unused functions, and adds code regions for those spans to the coverage map for a function that is used (being codegenned).

But outside of that, if an unused function (as reported by these errors) is still going through codegen anyway, the coverage map variables (generated by LLVM) may add references to those functions' symbols that could mark functions "used" (perhaps only indirectly) in LLVM IR.

Are the errors generated based on an assessment of used or not used, from an LLVM perspective? Or just from MIR? If only from MIR, then I don't think the coverage map generation would play a role in marking them used; and I would look at the InstrumentCoverage pass instead. It's inserting additional statements and occasionally additional BasicBlocks with Goto terminators (to count some branches).

[tmandry]

LLVM [IR] won't affect any compiler messages emitted by rustc.

I also can't think of how the unreachable code handling would affect this, just throwing out ideas. It does seem that without coverage enabled the functions are marked unused, and with coverage they are considered used, and I'm not sure why.

[ecstatic-morse]

The regression in the first case is legitimate and not related to unused functions. If you look at the MIR after SimplifyCfg-elaborate-drops, you'll see that drop elaboration is no longer able to remove the frivolous drops in the presence of code coverage statements. IIRC, I looked for a very specific pattern when determining whether a SwitchInt terminator is a switch on an enum discriminant or not:

rust/compiler/rustc_mir/src/dataflow/impls/mod.rs

Lines 680 to 717 in 4031f7b

	/// Inspect a `SwitchInt`-terminated basic block to see if the condition of that `SwitchInt` is
	/// an enum discriminant.
	///
	/// We expect such blocks to have a call to `discriminant` as their last statement like so:
	///
	/// ```text
	/// ...
	/// _42 = discriminant(_1)
	/// SwitchInt(_42, ..)
	/// ```
	///
	/// If the basic block matches this pattern, this function returns the place corresponding to the
	/// enum (`_1` in the example above) as well as the `AdtDef` of that enum.
	fn switch_on_enum_discriminant(
	tcx: TyCtxt<'tcx>,
	body: &'mir mir::Body<'tcx>,
	block: &'mir mir::BasicBlockData<'tcx>,
	switch_on: mir::Place<'tcx>,
	) -> Option<(mir::Place<'tcx>, &'tcx ty::AdtDef)> {
	match block.statements.last().map(|stmt| &stmt.kind) {
	Some(mir::StatementKind::Assign(box (lhs, mir::Rvalue::Discriminant(discriminated))))
	if *lhs == switch_on =>
	{
	match &discriminated.ty(body, tcx).ty.kind() {
	ty::Adt(def, _) => Some((*discriminated, def)),
	// `Rvalue::Discriminant` is also used to get the active yield point for a
	// generator, but we do not need edge-specific effects in that case. This may
	// change in the future.
	ty::Generator(..) => None,
	t => bug!("`discriminant` called on unexpected type {:?}", t),
	}
	}
	_ => None,
	}
	}

We used to have a bespoke terminator for that operation, but it was refactored away. To fix the test, modify that function to skip over code coverage statements when looking for a discriminant read or put the code coverage statements elsewhere.

[richkadel]

@tmandry - I currently inject the Coverage statement in the last bb of the bcb, and I push it to the end of the statements vec. But looking at this example, I think that looks weird, since Terminators are sort of a special case of a Statement, and in this case, one logically flows into the other. Adding the Coverage statement oddly breaks up that pair.

I think I will try injecting the statement at the front of the statements vec, and in the first (leader) bb of the bcb. A slight performance hit with the vec insert(0, cov_stmt) vs. the push(), but I think it's negligible.

I'll see if that resolves it. Who knows, maybe it will help with other issues.

[richkadel]

$ ./x.py test --rustc-args="-Zinstrument-coverage" src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs

Now passes, with #80072

[richkadel]

1 down, 3 to go.

The fix in #80072 did not fix tests 2, 3, and 4 above.