internal compiler error: src/librustc_mir/interpret/place.rs:41: expected wide pointer extra data (e.g. slice length or trait object vtable)

[bjorn3]

#![feature(unsized_fn_params)]

pub fn take_unsized_slice(s: [u8]) {
    s[0];
}

(Playground)

Errors:

error: internal compiler error: src/librustc_mir/interpret/place.rs:41: expected wide pointer extra data (e.g. slice length or trait object vtable)

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:882:9
stack backtrace:
   0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
   1: core::fmt::write
   2: std::io::Write::write_fmt
   3: std::panicking::default_hook::{{closure}}
   4: std::panicking::default_hook
   5: rustc_driver::report_ice
   6: std::panicking::rust_panic_with_hook
   7: std::panicking::begin_panic
   8: rustc_errors::HandlerInner::bug
   9: rustc_errors::Handler::bug
  10: rustc::util::bug::opt_span_bug_fmt::{{closure}}
  11: rustc::ty::context::tls::with_opt::{{closure}}
  12: rustc::ty::context::tls::with_opt
  13: rustc::util::bug::opt_span_bug_fmt
  14: rustc::util::bug::bug_fmt
  15: rustc_mir::interpret::eval_context::InterpCx<M>::size_and_align_of
  16: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::force_allocation_maybe_sized
  17: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpCx<M>>::eval_rvalue_into_place
  18: <rustc_mir::transform::const_prop::ConstPropagator as rustc::mir::visit::MutVisitor>::visit_statement
  19: <rustc_mir::transform::const_prop::ConstProp as rustc_mir::transform::MirPass>::run_pass
  20: rustc_mir::transform::run_passes
  21: rustc_mir::transform::run_optimization_passes
  22: rustc_mir::transform::optimized_mir
  23: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::optimized_mir>::compute
  24: rustc::dep_graph::graph::DepGraph::with_task_impl
  25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  26: rustc::ty::<impl rustc::ty::context::TyCtxt>::instance_mir
  27: rustc_mir::monomorphize::collector::collect_items_rec
  28: rustc_mir::monomorphize::collector::collect_items_rec
  29: rustc_session::utils::<impl rustc_session::session::Session>::time
  30: rustc_mir::monomorphize::collector::collect_crate_mono_items
  31: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  32: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute::{{closure}}
  33: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::dep_graph::graph::DepGraph::with_eval_always_task
  37: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::force_query_with_job::{{closure}}::{{closure}}
  38: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}
  39: rustc::ty::context::tls::enter_context::{{closure}}
  40: rustc::ty::context::tls::set_tlv
  41: rustc::ty::context::tls::enter_context
  42: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::start_query::{{closure}}
  43: rustc::ty::context::tls::with_related_context::{{closure}}
  44: rustc::ty::context::tls::with_context::{{closure}}
  45: rustc::ty::context::tls::with_context_opt
  46: rustc::ty::context::tls::with_context
  47: rustc::ty::context::tls::with_related_context
  48: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::force_query_with_job::{{closure}}
  49: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  50: rustc_codegen_cranelift::driver::codegen_cgus
  51: rustc_codegen_cranelift::driver::run_aot
  52: rustc_codegen_cranelift::driver::codegen_crate
  53: <rustc_codegen_cranelift::CraneliftCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  54: rustc_session::utils::<impl rustc_session::session::Session>::time
  55: rustc_interface::passes::QueryContext::enter
  56: rustc_interface::queries::Queries::ongoing_codegen
  57: rustc_interface::interface::run_compiler_in_existing_thread_pool
  58: scoped_tls::ScopedKey<T>::set
  59: 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 1.42.0-nightly (c2d141df5 2020-01-24) running on x86_64-apple-darwin

[JohnTitor]

Triage: This now occurs on unsized_fn_params.

[DutchGhost]

Triage: This now occurs on unsized_fn_params.

Also still with unsized_locals:

#![feature(unsized_locals)]

struct Bug {
    V1: [(); {
        let f: [u8];
        f.len()
    }],
}

fn main() {}

[ouz-a]

This doesn't ICE anymore

[bjorn3]

#![feature(unsized_fn_params)]

pub fn take_unsized_slice(s: [u8]) {
    s[0];
}

now crashes with

thread 'rustc' panicked at 'const-prop encountered formatting error: unsized locals are not supported', compiler/rustc_mir_transform/src/const_prop_lint.rs:463:17

cc @RalfJung I think this is caused by your PR to remove unsized locals support from miri.

[RalfJung]

Hm yeah seems related -- but shouldn't that code be rejected? It has an unsized local, not just an unsized argument, so the unsized_fn_params feature flag is not enough.

[bjorn3]

Where is the unsized local? s is an unsized argument, not an unsized local and s[0] evaluates to a sized value.

[RalfJung]

Ah you are right. The problem is again ConstProp violating some interpreter invariants.

The fix is fairly easy though: add a new UnsizedLocal variant here

rust/compiler/rustc_middle/src/mir/interpret/error.rs

Line 407 in 27b7b3d

pub enum UnsupportedOpInfo {

and then throw that instead of a free-form string here

rust/compiler/rustc_const_eval/src/interpret/place.rs

Line 976 in 38b7215

throw_unsup_format!("unsized locals are not supported");

That should entirely get rid of the ICE.

[matthiaskrgr]

This now crashes with error: internal compiler error: /rustc/28a29282f6dde2e4aba6e1e4cfea5c9430a00217/compiler/rustc_const_eval/src/interpret/place.rs:274:13: OpTy of type [u8] was immediate when it was expected to be an MPlace