ICE: evaluation of constant value failed | #[inline] causes compiler panic when bench-marking

[DzenanJupic]

I'm currently experimenting with a bunch of sorting algorithms. To reduce boilerplate, I made use of the const_trait_impl feature.

It seems like this feature breaks when benchmarking an #[inline] function. It however works well when not using #[inline], or when not benchmarking.

Minimal example:

Code

Cargo.toml

[package]
name = "temp"
version = "0.1.0"
edition = "2018"

[[bench]]
name = "counting_sort"

// lib.rs
#![feature(const_trait_impl)]
#![allow(incomplete_features)]

pub trait UsizeConversions {
    fn into_usize(self) -> usize;
}

impl const UsizeConversions for u8 {
    fn into_usize(self) -> usize {
        self as usize
    }
}

pub trait CountingSort {
    fn sort(&mut self);
}

impl CountingSort for [u8] {
    #[inline] // when this is removed, everything works well
    fn sort(&mut self) {
        let _counts = [0usize; u8::MAX.into_usize() + 1];
    }
}

#[test]
fn works_in_tests() {
    let mut data = vec![5, 2, 8, 10];
    CountingSort::sort(&mut *data);
}

benches/counting_sort.rs

#![feature(test)]

extern crate test;

use temp::CountingSort;
use test::Bencher;

#[bench]
fn counting_sort(b: &mut Bencher) {
    b.iter(|| {
        let mut data = vec![5, 2, 8, 10]; 
        CountingSort::sort(&mut *data);
    });
}

Meta

rustc --version --verbose:

rustc 1.53.0-nightly (07e0e2ec2 2021-03-24)
binary: rustc
commit-hash: 07e0e2ec268c140e607e1ac7f49f145612d0f597
commit-date: 2021-03-24
host: x86_64-pc-windows-msvc
release: 1.53.0-nightly
LLVM version: 12.0.0

Command

 cargo bench

Error output

error[E0080]: evaluation of constant value failed
  --> C:\Users\info\Code\Rust\temp\src\lib.rs:21:32
   |
21 |         let _counts = [0usize; u8::MAX.into_usize() + 1];
   |                                ^^^^^^^^^^^^^^^^^^^^ calling non-const function `<u8 as UsizeConversions>::into_usize`

error: internal compiler error: compiler\rustc_codegen_llvm\src\context.rs:793:17: failed to get layout for `[usize; _]`: the type `[usize; _]` has an unknown layout

Backtrace

thread 'rustc' panicked at 'Box<Any>', /rustc/07e0e2ec268c140e607e1ac7f49f145612d0f597\library\std\src\panic.rs:59:5
stack backtrace:
   0:     0x7ffa437d77ee - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h62553bb33d269d2e
   1:     0x7ffa438027cc - core::fmt::write::h187a24ff0c56237d
   2:     0x7ffa437cb208 - <std::io::IoSlice as core::fmt::Debug>::fmt::h7a51133a1941366b
   3:     0x7ffa437dba02 - std::panicking::take_hook::ha7af702674468c4c
   4:     0x7ffa437db4da - std::panicking::take_hook::ha7af702674468c4c
   5:     0x7ffa2f61b057 - rustc_driver::report_ice::h530a14ca8f015ece
   6:     0x7ffa437dc1e5 - std::panicking::rust_panic_with_hook::hffdabf0e02906eb3
   7:     0x7ffa33682720 - <rustc_errors::emitter::FileWithAnnotatedLines as core::fmt::Debug>::fmt::h138bd76935548e4c
   8:     0x7ffa33681df9 - <rustc_errors::emitter::FileWithAnnotatedLines as core::fmt::Debug>::fmt::h138bd76935548e4c
   9:     0x7ffa339008b1 - rustc_query_system::query::job::report_cycle::h78ff372fa02cb0ad
  10:     0x7ffa3364d5a0 - <rustc_feature::builtin_attrs::AttributeType as core::fmt::Debug>::fmt::h4d81e9bb6564882a
  11:     0x7ffa336541b5 - rustc_errors::HandlerInner::err_count::h836eba26b76f283e
  12:     0x7ffa33651d52 - rustc_errors::Handler::bug::h64fb55725578e531
  13:     0x7ffa335135f8 - <rustc_middle::ty::consts::int::ScalarInt as core::fmt::UpperHex>::fmt::he313431e7a456270
  14:     0x7ffa33513410 - <rustc_middle::ty::consts::int::ScalarInt as core::fmt::UpperHex>::fmt::he313431e7a456270
  15:     0x7ffa33513359 - <rustc_middle::ty::consts::int::ScalarInt as core::fmt::UpperHex>::fmt::he313431e7a456270
  16:     0x7ffa33513529 - <rustc_middle::ty::consts::int::ScalarInt as core::fmt::UpperHex>::fmt::he313431e7a456270
  17:     0x7ffa338f9a17 - rustc_middle::util::bug::bug_fmt::hf44d9914e298ce88
  18:     0x7ffa2f87067a - <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::hbcc603c5009aff0b
  19:     0x7ffa2f87052c - <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::hbcc603c5009aff0b
  20:     0x7ffa2f8fe279 - <rustc_codegen_llvm::back::archive::LlvmArchiveBuilder as rustc_codegen_ssa::back::archive::ArchiveBuilder>::build::ha5a74b8a3be08753
  21:     0x7ffa2f81591f - rustc_codegen_llvm::llvm_::diagnostic::Diagnostic::unpack::ha6027da799128368
  22:     0x7ffa2f8eede9 - <rustc_codegen_llvm::back::archive::LlvmArchiveBuilder as rustc_codegen_ssa::back::archive::ArchiveBuilder>::build::ha5a74b8a3be08753
  23:     0x7ffa2f8799f2 - <rustc_codegen_llvm::back::lto::ThinLTOKeysMap as core::fmt::Debug>::fmt::h267b43b08cde10bf
  24:     0x7ffa2f8a2a56 - <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::link::h1ca676796a6dc6ab
  25:     0x7ffa2f8cb91f - <rustc_codegen_llvm::base::ValueIter as core::iter::traits::iterator::Iterator>::next::h76a924d7c4d8667e
  26:     0x7ffa2f87bc3e - <rustc_codegen_llvm::back::lto::ThinLTOKeysMap as core::fmt::Debug>::fmt::h267b43b08cde10bf
  27:     0x7ffa2f8cb1c2 - <rustc_codegen_llvm::base::ValueIter as core::iter::traits::iterator::Iterator>::next::h76a924d7c4d8667e
  28:     0x7ffa2f88b3ec - <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate::h8a4e9bbd19201980
  29:     0x7ffa2f762dd8 - rustc_interface::passes::BoxedResolver::to_resolver_outputs::h26a866d2af02ca21
  30:     0x7ffa2f76f0b6 - rustc_interface::queries::Queries::ongoing_codegen::h23da4f767055d06d
  31:     0x7ffa2f632c53 - <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt::h898edfdbf8c7dbdf
  32:     0x7ffa2f6916bc - <rustc_driver::args::Error as core::fmt::Debug>::fmt::h54d0345b5b43328e
  33:     0x7ffa2f6351eb - <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt::h898edfdbf8c7dbdf
  34:     0x7ffa2f624034 - rustc_driver::pretty::print_after_hir_lowering::h04bf553be4aa75de
  35:     0x7ffa2f63745f - <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt::h898edfdbf8c7dbdf
  36:     0x7ffa2f65676d - <rustc_hir::intravisit::ErasedMap as rustc_hir::intravisit::Map>::foreign_item::he23d70bdee5d6fd3
  37:     0x7ffa437eb16a - std::sys::windows::thread::Thread::new::h485ded1a10d2ce17
  38:     0x7ffaaac07034 - BaseThreadInitThunk
  39:     0x7ffaac242651 - RtlUserThreadStart

Edit:

rustc note

note: compiler flags: -C opt-level=3 -C embed-bitcode=no
note: some of the compiler flags provided by cargo are hidden

[JohnTitor]

Triage: it now works with the latest nightly, I guess #86166 fixed it. Marking as E-needs-test, it'd be great if we could add a test somehow.

[tmiasko]

A slight modification is required to reproduce the original issue:

--- a/src/lib.rs
+++ b/src/lib.rs
@@ -19,7 +19,8 @@ pub trait CountingSort {
 impl CountingSort for [u8] {
     #[inline] // when this is removed, everything works well
     fn sort(&mut self) {
-        let _counts = [0usize; u8::MAX.into_usize() + 1];
+        let _counts = [0usize; u8::MAX.into_usize() * 0];
+        &_counts;
     }
 }

[tmiasko]

Constness of associated functions is encoded & decoded without looking at constness of impl. Encoding a result of is_const_fn_raw query in encode_info_for_impl_item could be sufficient for now:

rust/compiler/rustc_metadata/src/rmeta/encoder.rs

Line 1226 in b6f3cb9

constness: sig.header.constness,

Duplicate of #84846.

[fee1-dead]

Fixed by #86750.