ICE: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after InstCombine in phase Optimization) at bb0[2]: Operand::Copy with non-Copy type &i32

[chengniansun]

Code

#![feature(no_core, lang_items)]
#![no_core]
#[lang = "sized"]
trait Sized {}
#[lang = "copy"]
trait Copy {}
#[no_mangle]
fn test() {
    &1;
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (9d78d1d02 2020-11-05)
binary: rustc
commit-hash: 9d78d1d02761b906038ba4d54c5f3427f920f5fb
commit-date: 2020-11-05
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly

Error output

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after InstCombine in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after ConstProp in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyBranches-after-const-prop in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after EarlyOtherwiseBranch in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyComparisonIntegral in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyArmIdentity in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyBranchSame in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after DestinationPropagation in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyBranches-final in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after RemoveNoopLandingPads in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after SimplifyCfg-final in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:3 ~ reduced_mutant[8787]::test), const_param_did: None }) (after RenameReturnPlace in phase Optimization) at bb0[2]:
`Operand::Copy` with non-`Copy` type &i32
 --> reduced_mutant.rs:9:5
  |
9 |     &1;
  |     ^^
  |
  = note: delayed at compiler/rustc_mir/src/transform/validate.rs:171:36

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:974:13
note: run with `RUST_BACKTRACE=1` environment variable to display a 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 1.49.0-nightly (9d78d1d02 2020-11-05) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=1 -Z new-llvm-pass-manager=yes -Z unsound-mir-opts=yes -Z verify-llvm-ir=yes -Z validate-mir=yes -Z polonius=yes -Z polymorphize=yes -C debuginfo=2 -C opt-level=1 --crate-type staticlib

query stack during panic:
end of query stack

Backtrace

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:974:13
stack backtrace:
   0: rust_begin_unwind
             at /rustc/9d78d1d02761b906038ba4d54c5f3427f920f5fb/library/std/src/panicking.rs:495:5
   1: std::panicking::begin_panic_fmt
             at /rustc/9d78d1d02761b906038ba4d54c5f3427f920f5fb/library/std/src/panicking.rs:437:5
   2: rustc_errors::HandlerInner::flush_delayed
   3: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   4: core::ptr::drop_in_place
   5: core::ptr::drop_in_place
   6: <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop
   7: core::ptr::drop_in_place
   8: rustc_span::with_source_map
   9: rustc_interface::interface::create_compiler_and_run
  10: rustc_span::with_session_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

NOTE: The bug is found by our work-in-progress compiler testing tool Kira, and the test program is reduced/minimized by Perses

[tmiasko]

The InstCombine transformation operates under assumption that &T will implement Copy trait. The code example uses a custom core (#![no_core] feature) which does not provide such implementation, which is subsequently detected by MIR validator -Zvalidate-mir. I would consider this to be essentially an unsupported configuration and not a bug.

I would recommend generating test cases without #![no_core] or #[lang = ...], those are implementation details of standard library that will likely lead to bugs of limited practical significance.

[camelid]

Also: @chengniansun I am not able to reproduce this ICE on the latest nightly. What command are you running, and can you still reproduce this?

EDIT: Oops, I missed that this was explicitly running the MIR validator. It would be great if you could mention that in the summary in the future!

[camelid]

Note that the MIR validator only fails with #[no_mangle], which seems pretty bizarre.

[jonas-schievink]

#[no_mangle] triggers codegen, which requests the optimized MIR

[jonas-schievink]

This is #9307, so closing in favor of that

[camelid]

In case anyone's curious, this is the bisection:

---

searched nightlies: from nightly-2020-01-01 to nightly-2020-11-09
regressed nightly: nightly-2020-11-02
searched commits: from 4f7612a to b202532
regressed commit: a6403b0

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-apple-darwin
Reproduce with:

cargo bisect-rustc --preserve --regress=ice --start=2020-01-01 --end=2020-11-09 -- rustc -- -Zvalidate-mir 

---

However, the "regressed commit" is actually just a new MIR validation that was catching an existing bug, so it doesn't mean anything.

[chengniansun]

Thanks, everyone, for the analysis.

I have disabled the validation of mir on my end in the future testing.

[camelid]

Well the MIR validator will still help you catch bugs, it's just that this particular bug is not significant because the code is somewhat bizarre.

[jonas-schievink]

Yes, I'd rather suggest not using #[lang] attributes, since they often just lead to #9307 again, especially with automated testing.

[chengniansun]

Thanks, @camelid and @jonas-schievink .

I will enable this flag later. Currently my testing infrastructure has some problems with extracting crash signatures from stderr. This mainly because the ICE message usually contains some details about the program under compilation, and I rely on crash signatures to cluster duplicates.

Moreover, sometimes, the ICE message and the panic message contains absolute paths of the source files in the rust compiler, such as /rustc/<hash code>/......./sty.rs.

When I address the problem above, I will enable this flag again.

Thank you for your advices. I learned something new today.