Broken MIR in async fn generation

[mtnmts]

Hey, This code attempts to increment a integer behind a tokio RwLock by 1, This causes a compiler error.

Minimized example that reproduces the ICE:

use tokio::sync::RwLock;
use std::io;

#[tokio::main]
async fn main() ->  io::Result<()> {
    State::default().crash_compiler().await; Ok(())
}

#[derive(Default)]
struct State {
    value: RwLock<u64>,
}

impl State {
    async fn crash_compiler(&mut self) {
        let i : u64 = 1;
        *self.value.write().await = *self.value.read().await + i;
    }
}

But, making this very small modification makes the code not break the compiler

...
        let v = *self.value.read().await + i;
        *self.value.write().await = v;
...

my Cargo.toml contains tokio = {version = "0.2.21", features=["full"] } as a dependency.

This code does not compile, and generates the following error (full backtrace in bottom of the issue)

   Compiling compiler_bug v0.1.0 (/home/martin/code/compiler_bug)
error: internal compiler error: src/librustc_mir/transform/generator.rs:715:13: Broken MIR: generator contains type (u64, bool) in MIR, but typeck only knows about for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}
  --> src/main.rs:15:40
   |
15 |       async fn crash_compiler(&mut self) {
   |  ________________________________________^
16 | |         let i : u64 = 1;
17 | |         *self.value.write().await = *self.value.read().await + i;
18 | |     }
   | |_____^

thread 'rustc' panicked at 'Box<Any>', /rustc/f455e46eae1a227d735091091144601b467e1565/src/libstd/macros.rs:13:23
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 1.46.0-nightly (f455e46ea 2020-06-20) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -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

error: could not compile `compiler_bug`.

Meta

rustc --version --verbose

rustc 1.46.0-nightly (f455e46ea 2020-06-20)
binary: rustc
commit-hash: f455e46eae1a227d735091091144601b467e1565
commit-date: 2020-06-20
host: x86_64-unknown-linux-gnu
release: 1.46.0-nightly
LLVM version: 10.0

also breaks the same way on stable (the traces attached are from nightly ^)

rustup run stable rustc --version -v

rustc 1.44.1 (c7087fe00 2020-06-17)
binary: rustc
commit-hash: c7087fe00d2ba919df1d813c040a5d47e43b0fe7
commit-date: 2020-06-17
host: x86_64-unknown-linux-gnu
release: 1.44.1
LLVM version: 9.0

Backtrace (RUST_BACKTRACE=1)

 Compiling compiler_bug v0.1.0 (/home/martin/code/compiler_bug)
error: internal compiler error: src/librustc_mir/transform/generator.rs:715:13: Broken MIR: generator contains type (u64, bool) in MIR, but typeck only knows about for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}
  --> src/main.rs:15:40
   |
15 |       async fn crash_compiler(&mut self) {
   |  ________________________________________^
16 | |         let i : u64 = 1;
17 | |         *self.value.write().await = *self.value.read().await + i;
18 | |     }
   | |_____^

thread 'rustc' panicked at 'Box<Any>', /rustc/f455e46eae1a227d735091091144601b467e1565/src/libstd/macros.rs:13:23
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:217
  10: rustc_driver::report_ice
  11: <alloc::boxed::Box<F> as core::ops::function::Fn<A>>::call
             at /home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc/boxed.rs:1090
  12: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}
             at /home/martin/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:318
  13: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  14: std::panicking::begin_panic
  15: rustc_errors::HandlerInner::span_bug
  16: rustc_errors::Handler::span_bug
  17: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
  18: rustc_middle::ty::context::tls::with_opt::{{closure}}
  19: rustc_middle::ty::context::tls::with_opt
  20: rustc_middle::util::bug::opt_span_bug_fmt
  21: rustc_middle::util::bug::span_bug_fmt
  22: <rustc_mir::transform::generator::StateTransform as rustc_mir::transform::MirPass>::run_pass
  23: rustc_mir::transform::run_passes
  24: rustc_mir::transform::run_optimization_passes
  25: rustc_mir::transform::optimized_mir
  26: 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
  27: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  28: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  29: rustc_data_structures::stack::ensure_sufficient_stack
  30: rustc_query_system::query::plumbing::get_query_impl
  31: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  32: rustc_middle::ty::layout::layout_raw
  33: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  34: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  35: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  36: rustc_data_structures::stack::ensure_sufficient_stack
  37: rustc_query_system::query::plumbing::get_query_impl
  38: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  39: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  40: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  41: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  42: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  43: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  44: rustc_middle::ty::layout::layout_raw
  45: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  46: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  47: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  48: rustc_data_structures::stack::ensure_sufficient_stack
  49: rustc_query_system::query::plumbing::get_query_impl
  50: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  51: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  52: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  53: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  54: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  55: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  56: rustc_middle::ty::layout::layout_raw
  57: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  58: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  59: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  60: rustc_data_structures::stack::ensure_sufficient_stack
  61: rustc_query_system::query::plumbing::get_query_impl
  62: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  63: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  64: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
  65: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  66: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  67: rustc_middle::ty::layout::layout_raw
  68: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  69: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  70: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  71: rustc_data_structures::stack::ensure_sufficient_stack
  72: rustc_query_system::query::plumbing::get_query_impl
  73: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  74: <core::iter::adapters::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold
  75: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::try_fold
  76: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  77: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
  78: rustc_middle::ty::layout::layout_raw
  79: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  80: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  81: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  82: rustc_data_structures::stack::ensure_sufficient_stack
  83: rustc_query_system::query::plumbing::get_query_impl
  84: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  85: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_statement
  86: <rustc_mir::transform::const_prop::ConstPropagator as rustc_middle::mir::visit::MutVisitor>::visit_body
  87: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  88: rustc_mir::transform::run_passes
  89: rustc_mir::transform::run_optimization_passes
  90: rustc_mir::transform::optimized_mir
  91: 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
  92: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  93: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  94: rustc_data_structures::stack::ensure_sufficient_stack
  95: rustc_query_system::query::plumbing::get_query_impl
  96: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::instance_mir
  97: rustc_mir::monomorphize::collector::collect_neighbours
  98: rustc_data_structures::stack::ensure_sufficient_stack
  99: rustc_mir::monomorphize::collector::collect_items_rec
 100: rustc_mir::monomorphize::collector::collect_crate_mono_items
 101: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
 102: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
 103: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
 104: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
 105: rustc_data_structures::stack::ensure_sufficient_stack
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 1.46.0-nightly (f455e46ea 2020-06-20) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [optimized_mir] optimizing MIR for `State::crash_compiler::{{closure}}#0`
#1 [layout_raw] computing layout of `[static generator@src/main.rs:15:40: 18:6 self:&mut State for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}]`
#2 [layout_raw] computing layout of `std::future::from_generator::GenFuture<[static generator@src/main.rs:15:40: 18:6 self:&mut State for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}]>`
#3 [layout_raw] computing layout of `std::mem::ManuallyDrop<std::future::from_generator::GenFuture<[static generator@src/main.rs:15:40: 18:6 self:&mut State for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}]>>`
#4 [layout_raw] computing layout of `std::mem::MaybeUninit<std::future::from_generator::GenFuture<[static generator@src/main.rs:15:40: 18:6 self:&mut State for<'r, 's, 't0, 't1, 't2, 't3, 't4, 't5, 't6> {std::future::ResumeTy, &'r mut State, u64, State, &'s tokio::sync::rwlock::RwLock<u64>, tokio::sync::rwlock::RwLock<u64>, impl std::future::Future, (), &'t2 tokio::sync::rwlock::RwLockReadGuard<'t3, u64>, tokio::sync::rwlock::RwLockReadGuard<'t4, u64>, impl std::future::Future}]>>`
#5 [layout_raw] computing layout of `[static generator@src/main.rs:4:1: 4:15 for<'r, 's> {std::future::ResumeTy, &'r mut State, State, impl std::future::Future, ()}]`
#6 [optimized_mir] optimizing MIR for `main`
#7 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error

error: could not compile `compiler_bug`.

[mtnmts]

Confirmed this also breaks the same way on stable

[hellow554]

MCVE:

struct S<T>(std::marker::PhantomData<T>);

impl<T> std::ops::Deref for S<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        todo!()
    }   
}
impl<T> std::ops::DerefMut for S<T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        todo!()
    }   
}

async fn new() -> S<u64> {
    todo!()
}

async fn crash() {
    *new().await = 1 + 1;
}

fn main() {
    let _ = crash();
}

Fun fact: changing 1+1 to 2 doesn't ICE. Also I can't inline an S instance into the crash function. It has to be created outside?!. Weird stuff somtimes.

Also it would be nice to get rid of the deref, but I couldn't figure out how. So it's on this currently.

Also worth mentioning: this needs cargo build. check isn't sufficient.

@rustbot modify labels: -E-needs-mcve +E-needs-bisection

[hellow554]

The bisection doesn't emit anything useful. This panics like forever. I went back to 2019-01-01 (with the old await! API and stuff) and it still ICEs there, so I guess it was like this forever.

Feel free to add the tag again, but I'll remove it.

@rustbot modify labels: -E-needs-bisection