f16 usage triggers a compiler internal error, despite good error messages

[pictographer]

Code

fn main() {
    println!("Hello, world!");
    let a: f16 = 1.0;
    let b = 3.0;
    let c = a / b * 3.0;
    println!("{:?}", c);
    println!("{:?}", c == 1.0);
}

Meta

rustc --version --verbose:

rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: x86_64-unknown-linux-gnu
release: 1.80.1
LLVM version: 18.1.7

Note, the compiler doesn't crash on nightly. cargo +nightly run -Z unstable-options behaves as expected.

Error output

pictographer@pictorus-old-xps13:~/fmath$ cargo run
   Compiling fmath v0.1.0 (/home/pictographer/fmath)
error[E0658]: the type `f16` is unstable
 --> src/main.rs:3:12
  |
3 |     let a: f16 = 1.0;
  |            ^^^
  |
  = note: see issue #116909 <https://github.com/rust-lang/rust/issues/116909> for more information

thread 'rustc' panicked at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/compiler/rustc_const_eval/src/interpret/operator.rs:365:37:
not implemented: f16_f128
stack backtrace:
   0:     0x74d6eb885f05 - std::backtrace_rs::backtrace::libunwind::trace::h23054e327d0d4b55
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1:     0x74d6eb885f05 - std::backtrace_rs::backtrace::trace_unsynchronized::h0cc587407d7f7f64
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x74d6eb885f05 - std::sys_common::backtrace::_print_fmt::h4feeb59774730d6b
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x74d6eb885f05 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd736fd5964392270
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x74d6eb8d6c4b - core::fmt::rt::Argument::fmt::h105051d8ea1ade1e
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/fmt/rt.rs:165:63
   5:     0x74d6eb8d6c4b - core::fmt::write::hc6043626647b98ea
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/fmt/mod.rs:1168:21
   6:     0x74d6eb87abdf - std::io::Write::write_fmt::h0d24b3e0473045db
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/io/mod.rs:1835:15
   7:     0x74d6eb885cde - std::sys_common::backtrace::_print::h62df6fc36dcebfc8
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x74d6eb885cde - std::sys_common::backtrace::print::h45eb8174d25a1e76
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x74d6eb888719 - std::panicking::default_hook::{{closure}}::haf3f0170eb4f3b53
  10:     0x74d6eb8884ba - std::panicking::default_hook::hb5d3b27aa9f6dcda
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:298:9
  11:     0x74d6e82150c1 - std[fba9fafec3bdacf8]::panicking::update_hook::<alloc[a325a9cea6fa5e89]::boxed::Box<rustc_driver_impl[ce01f96e2e949677]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x74d6eb888e4b - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h2026a29033a1b9f6
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/alloc/src/boxed.rs:2077:9
  13:     0x74d6eb888e4b - std::panicking::rust_panic_with_hook::h6b49d59f86ee588c
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:799:13
  14:     0x74d6eb888b8b - std::panicking::begin_panic_handler::{{closure}}::hd4c2f7ed79b82b70
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:656:13
  15:     0x74d6eb8863c9 - std::sys_common::backtrace::__rust_end_short_backtrace::h2946d6d32d7ea1ad
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x74d6eb8888f7 - rust_begin_unwind
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/panicking.rs:652:5
  17:     0x74d6eb8d31e3 - core::panicking::panic_fmt::ha02418e5cd774672
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/core/src/panicking.rs:72:14
  18:     0x74d6eaba9857 - <rustc_const_eval[964325fd78f4b8e1]::interpret::eval_context::InterpCx<rustc_const_eval[964325fd78f4b8e1]::const_eval::dummy_machine::DummyMachine>>::binary_op.cold
  19:     0x74d6e6ba2453 - <rustc_mir_transform[e8632467688ea17a]::known_panics_lint::ConstPropagator as rustc_middle[ecc07153edf3c281]::mir::visit::Visitor>::visit_assign
  20:     0x74d6e9dc9173 - <rustc_mir_transform[e8632467688ea17a]::known_panics_lint::ConstPropagator as rustc_middle[ecc07153edf3c281]::mir::visit::Visitor>::visit_body
  21:     0x74d6e6f12ac0 - <rustc_mir_transform[e8632467688ea17a]::known_panics_lint::KnownPanicsLint as rustc_mir_transform[e8632467688ea17a]::pass_manager::MirLint>::run_lint
  22:     0x74d6e960194d - rustc_mir_transform[e8632467688ea17a]::pass_manager::run_passes_inner
  23:     0x74d6e70b2a48 - rustc_mir_transform[e8632467688ea17a]::mir_drops_elaborated_and_const_checked
  24:     0x74d6e975a7f9 - rustc_query_impl[c1633093ec927e0e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[c1633093ec927e0e]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ecc07153edf3c281]::query::erase::Erased<[u8; 8usize]>>
  25:     0x74d6e975d24d - rustc_query_system[b257ee99c2874caa]::query::plumbing::try_execute_query::<rustc_query_impl[c1633093ec927e0e]::DynamicConfig<rustc_query_system[b257ee99c2874caa]::query::caches::VecCache<rustc_span[4d50fd03223eefaa]::def_id::LocalDefId, rustc_middle[ecc07153edf3c281]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[c1633093ec927e0e]::plumbing::QueryCtxt, true>
  26:     0x74d6e9a7b3b2 - rustc_query_impl[c1633093ec927e0e]::query_impl::mir_drops_elaborated_and_const_checked::get_query_incr::__rust_end_short_backtrace
  27:     0x74d6ea093987 - rustc_interface[c31201428b712578]::passes::analysis
  28:     0x74d6ea093025 - rustc_query_impl[c1633093ec927e0e]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[c1633093ec927e0e]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[ecc07153edf3c281]::query::erase::Erased<[u8; 1usize]>>
  29:     0x74d6ea339ef5 - rustc_query_system[b257ee99c2874caa]::query::plumbing::try_execute_query::<rustc_query_impl[c1633093ec927e0e]::DynamicConfig<rustc_query_system[b257ee99c2874caa]::query::caches::SingleCache<rustc_middle[ecc07153edf3c281]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[c1633093ec927e0e]::plumbing::QueryCtxt, true>
  30:     0x74d6ea339b38 - rustc_query_impl[c1633093ec927e0e]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  31:     0x74d6ea21224d - rustc_interface[c31201428b712578]::interface::run_compiler::<core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>, rustc_driver_impl[ce01f96e2e949677]::run_compiler::{closure#0}>::{closure#1}
  32:     0x74d6ea347869 - std[fba9fafec3bdacf8]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[c31201428b712578]::util::run_in_thread_with_globals<rustc_interface[c31201428b712578]::interface::run_compiler<core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>, rustc_driver_impl[ce01f96e2e949677]::run_compiler::{closure#0}>::{closure#1}, core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>>
  33:     0x74d6ea34766a - <<std[fba9fafec3bdacf8]::thread::Builder>::spawn_unchecked_<rustc_interface[c31201428b712578]::util::run_in_thread_with_globals<rustc_interface[c31201428b712578]::interface::run_compiler<core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>, rustc_driver_impl[ce01f96e2e949677]::run_compiler::{closure#0}>::{closure#1}, core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[1a380081440346cb]::result::Result<(), rustc_span[4d50fd03223eefaa]::ErrorGuaranteed>>::{closure#2} as core[1a380081440346cb]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  34:     0x74d6eb892e3b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hdf5fcef8be77a431
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/alloc/src/boxed.rs:2063:9
  35:     0x74d6eb892e3b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8e8c5ceee46ee198
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/alloc/src/boxed.rs:2063:9
  36:     0x74d6eb892e3b - std::sys::pal::unix::thread::Thread::new::thread_start::hb85dbfa54ba503d6
                               at /rustc/3f5fd8dd41153bc5fdca9427e9e05be2c767ba23/library/std/src/sys/pal/unix/thread.rs:108:17
  37:     0x74d6e4e94ac3 - start_thread
                               at ./nptl/pthread_create.c:442:8
  38:     0x74d6e4f26850 - __GI___clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
  39:                0x0 - <unknown>

error: 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 1.80.1 (3f5fd8dd4 2024-08-06) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `main`
#1 [analysis] running analysis passes on this crate
end of query stack
For more information about this error, try `rustc --explain E0658`.
error: could not compile `fmath` (bin "fmath") due to 1 previous error

Backtrace

See above.

[tgross35]

This was a known unimplemented! in const eval that has been fixed. The fix has made it to beta so will be stable pretty soon., trying with beta or nightly won't have the ICE.

Originally reported at #122587