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ICE: src/librustc/middle/region.rs:1037: Encountered greater count 28 #69307

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Kumassy opened this issue Feb 20, 2020 · 10 comments · Fixed by #70367
Closed

ICE: src/librustc/middle/region.rs:1037: Encountered greater count 28 #69307

Kumassy opened this issue Feb 20, 2020 · 10 comments · Fixed by #70367
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A-async-await AsyncAwait-Triaged C-bug glacier I-ICE P-high T-compiler

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@Kumassy
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@Kumassy Kumassy commented Feb 20, 2020

Code

use tokio::prelude::*;
use tokio::runtime::Runtime;
use tokio::sync::mpsc;

fn main() {
    let mut rt = Runtime::new().unwrap();
    let mut sum = 0;
    sum += rt.block_on(async {
        let (tx, mut rx) = mpsc::unbounded_channel();
        tx.send(1).unwrap();

        while let Some(res) = rx.recv().await {
            println!("{:?}", res);
        }
        1
    });
}

Playground Link

Meta

rustc --version --verbose:

rustc 1.41.0 (5e1a79984 2020-01-27)
binary: rustc
commit-hash: 5e1a799842ba6ed4a57e91f7ab9435947482f7d8
commit-date: 2020-01-27
host: x86_64-unknown-linux-gnu
release: 1.41.0
LLVM version: 9.0

Same issue still exists in rustc +beta --version --verbose:

rustc 1.42.0-beta.3 (86f329b41 2020-02-07)
binary: rustc
commit-hash: 86f329b419dbac59da59e2ac7d6e21e5eb679ec7
commit-date: 2020-02-07
host: x86_64-unknown-linux-gnu
release: 1.42.0-beta.3
LLVM version: 9.0

and also in rustc +nightly --version --verbose:

rustc 1.43.0-nightly (7760cd0fb 2020-02-19)
binary: rustc
commit-hash: 7760cd0fbbbf2c59a625e075a5bdfa88b8e30f8a
commit-date: 2020-02-19
host: x86_64-unknown-linux-gnu
release: 1.43.0-nightly
LLVM version: 9.0

Error output

error: internal compiler error: src/librustc/middle/region.rs:1037: Encountered greater count 28 at span src/main.rs:13:31: 13:46 - expected no greater than 12

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:905:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

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 1.41.0 (5e1a79984 2020-01-27) running on x86_64-unknown-linux-gnu

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

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

error: aborting due to previous error
Backtrace

error: internal compiler error: src/librustc/middle/region.rs:1037: Encountered greater count 28 at span src/main.rs:13:31: 13:46 - expected no greater than 12

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:905:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:84
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1025
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1426
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:193
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:475
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc::ty::context::tls::with_opt::{{closure}}
  17: rustc::ty::context::tls::with_opt
  18: rustc::util::bug::opt_span_bug_fmt
  19: rustc::util::bug::bug_fmt
  20: rustc::middle::region::resolve_expr
  21: <rustc::middle::region::RegionResolutionVisitor as rustc::hir::intravisit::Visitor>::visit_stmt
  22: <rustc::middle::region::RegionResolutionVisitor as rustc::hir::intravisit::Visitor>::visit_block
  23: rustc::middle::region::resolve_expr
  24: <rustc::middle::region::RegionResolutionVisitor as rustc::hir::intravisit::Visitor>::visit_body
  25: rustc::middle::region::region_scope_tree
  26: rustc::ty::query::__query_compute::region_scope_tree
  27: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::region_scope_tree>::compute
  28: rustc::dep_graph::graph::DepGraph::with_task_impl
  29: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  30: rustc_typeck::check::generator_interior::resolve_interior
  31: rustc_typeck::check::FnCtxt::resolve_generator_interiors
  32: rustc::ty::context::tls::with_context::{{closure}}
  33: rustc_typeck::check::typeck_tables_of
  34: rustc::ty::query::__query_compute::typeck_tables_of
  35: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  36: rustc::dep_graph::graph::DepGraph::with_task_impl
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  38: rustc::ty::query::__query_compute::typeck_tables_of
  39: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  40: rustc::dep_graph::graph::DepGraph::with_task_impl
  41: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  42: rustc_typeck::collect::type_of
  43: rustc::ty::query::__query_compute::type_of
  44: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
  45: rustc::dep_graph::graph::DepGraph::with_task_impl
  46: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  47: rustc::hir::intravisit::walk_expr
  48: rustc::hir::intravisit::walk_expr
  49: rustc::hir::intravisit::walk_expr
  50: rustc::hir::intravisit::walk_block
  51: rustc::hir::intravisit::Visitor::visit_fn
  52: rustc::hir::intravisit::walk_item
  53: <rustc_typeck::collect::CollectItemTypesVisitor as rustc::hir::intravisit::Visitor>::visit_item
  54: rustc::hir::map::Map::visit_item_likes_in_module
  55: rustc_typeck::collect::collect_mod_item_types
  56: rustc::ty::query::__query_compute::collect_mod_item_types
  57: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_mod_item_types>::compute
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  61: rustc_typeck::check_crate::{{closure}}::{{closure}}
  62: rustc::util::common::time
  63: rustc_typeck::check_crate
  64: rustc_interface::passes::analysis
  65: rustc::ty::query::__query_compute::analysis
  66: rustc::dep_graph::graph::DepGraph::with_task_impl
  67: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  68: rustc::ty::context::tls::enter_global
  69: rustc_interface::interface::run_compiler_in_existing_thread_pool
  70: std::thread::local::LocalKey<T>::with
  71: scoped_tls::ScopedKey<T>::set
  72: syntax::with_globals
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.41.0 (5e1a79984 2020-01-27) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [region_scope_tree] processing `main`
#1 [typeck_tables_of] processing `main`
#2 [typeck_tables_of] processing `main::{{closure}}#0`
#3 [type_of] processing `main::{{closure}}#0`
#4 [collect_mod_item_types] collecting item types in top-level module
#5 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

@Kumassy Kumassy added C-bug I-ICE T-compiler labels Feb 20, 2020
@pnkfelix
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@pnkfelix pnkfelix commented Feb 20, 2020

T-compiler triage: P-high. Leaving nomination label in place, since I don't want to disrupt WG-async-await workflow.

@pnkfelix pnkfelix added the P-high label Feb 20, 2020
@LeSeulArtichaut
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@LeSeulArtichaut LeSeulArtichaut commented Feb 20, 2020

This does already ICE on 1.39.0

@Kumassy
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@Kumassy Kumassy commented Feb 20, 2020

I could further simplify the code as:

use tokio::runtime::Runtime;

fn main() {
    let mut rt = Runtime::new().unwrap();
    let mut sum = 0;
    sum += rt.block_on(async {
        (async { }).await;
        1
    });
}

Playgrond Link

error: internal compiler error: src/librustc/middle/region.rs:1037: Encountered greater count 20 at span src/main.rs:7:9: 7:26 - expected no greater than 12

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:905:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

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 1.41.0 (5e1a79984 2020-01-27) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

error: aborting due to previous error

@Kumassy
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@Kumassy Kumassy commented Feb 20, 2020

However, this code does not cause ICE:

use tokio::runtime::Runtime;

fn main() {
    let mut rt = Runtime::new().unwrap();
    let mut sum = 0;
    sum = sum + rt.block_on(async {
        (async { }).await;
        1
    });
}

Playground Link

@Centril Centril added the E-needs-mcve label Feb 21, 2020
@Centril
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@Centril Centril commented Feb 21, 2020

If you can reproduce this without depending on tokio that would be great.

@Kumassy
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@Kumassy Kumassy commented Feb 21, 2020

How abot this?

use futures::executor::block_on;

fn main() {
    let mut sum = 0;
    sum += block_on(async {
        (async { }).await;
        1
    });
}

Playground Link

error: internal compiler error: src/librustc/middle/region.rs:1037: Encountered greater count 20 at span src/main.rs:6:9: 6:26 - expected no greater than 8

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:905:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

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 1.41.0 (5e1a79984 2020-01-27) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

error: aborting due to previous error

@Centril
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@Centril Centril commented Feb 21, 2020

Minimized:

fn block_on<F>(_: F) -> usize {
    0
}

fn main() {
    let mut sum = 0;
    sum += block_on(async {
        (async {}).await;
        1
    });
}

@Centril Centril removed the E-needs-mcve label Feb 21, 2020
@rust-lang-glacier-bot rust-lang-glacier-bot added the glacier label Feb 21, 2020
@tmandry tmandry added AsyncAwait-OnDeck AsyncAwait-Triaged E-needs-mentor labels Feb 25, 2020
@tmandry tmandry added this to To do in wg-async work via automation Feb 25, 2020
@pnkfelix
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@pnkfelix pnkfelix commented Mar 12, 2020

Discussed in T-compiler meeting. Keeping as P-high but removing nomination.

@nikomatsakis
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@nikomatsakis nikomatsakis commented Mar 24, 2020

OK so I've been investigating this a bit. I am not quite able to write-up mentoring instructions yet because I don't really understand what's going on, but I can leave a few notes.

First off, the ICE occurs in the code that is attempting to approximate what values may be live across an await. It occurs specifically when you have a foo += async { ... x.await ... } structure. The nested async blocks etc are not really needed. For example, this also fails in the same way;

fn block_on<F>(_: F) -> usize {
    0
}

fn main() {
    let mut sum = 0;
    sum += block_on(async {
        bar().await;
    });
}

async fn bar() { }

The ICE occurs in this match arm:

hir::ExprKind::AssignOp(_, ref left_expr, ref right_expr) => {

It appears to be related to some logic that is attempting to figure out a "worst case" execution order for += instructions:

// If the actual execution order turns out to be right-to-left,
// then we're fine. However, if the actual execution order is left-to-right,
// then we'll assign too low a count to any `yield` expressions
// we encounter in 'right_expression' - they should really occur after all of the
// expressions in 'left_expression'.

I confess I don't quite follow this logic anymore, but the problem has to do with entering a distinct async block. This code for example does not trigger the failure:

async fn bar() {
    let mut sum = 0;
    sum += block_on(async {
        baz().await;
    });
}

async fn baz() {
}

@nikomatsakis
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@nikomatsakis nikomatsakis commented Mar 24, 2020

Ah, I think maybe I see the problem here actually -- I suspect the problem is that we need to clear (and then restore) the pessimistic_yield flag when we recurse into a closure body.

@nikomatsakis nikomatsakis removed the E-needs-mentor label Mar 24, 2020
@nikomatsakis nikomatsakis self-assigned this Mar 24, 2020
@tmandry tmandry moved this from To do to In progress in wg-async work Mar 30, 2020
@bors bors closed this as completed in ba50bc5 Apr 9, 2020
wg-async work automation moved this from In progress to Done Apr 9, 2020
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