[ICE] in const eval when when storing Simd<_, 3>

[bend-n]

Code

#![feature(portable_simd, core_intrinsics)]
use core::intrinsics::simd::SimdAlign;
use std::{ptr::null, simd::prelude::*};

const _: () = {
    let c = Simd::from_array([0; 3]);
    unsafe {
        core::intrinsics::simd::simd_masked_store::<_, _, _, { SimdAlign::Element }>(
            c,
            null::<i32>(),
            c,
        )
    };
    // inlined v so i can report on rl/r instead of rl/miri.
    // and store_sel isnt const for some reason
    // c.store_select(&mut [], Mask::from_bitmask(0));
};
fn main() {}

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (39052daf9 2026-01-22)
binary: rustc
commit-hash: 39052daf937d46373ac29778e1b8853c52c0cc25
commit-date: 2026-01-22
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Error output

assertion `left matches right` failed

Backtrace

thread 'rustc' (195017) panicked at /rustc-dev/39052daf937d46373ac29778e1b8853c52c0cc25/compiler/rustc_const_eval/src/interpret/intrinsics/simd.rs:832:9:
assertion `left matches right` failed
  left: Memory { sized: true }
 right: BackendRepr::SimdVector { .. }
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_matches_failed::<rustc_abi::BackendRepr>
   4: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::check_simd_ptr_alignment
   5: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::eval_simd_intrinsic
   6: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::eval_intrinsic
   7: <rustc_const_eval::const_eval::machine::CompileTimeMachine as rustc_const_eval::interpret::machine::Machine>::call_intrinsic
   8: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::init_fn_call
   9: rustc_const_eval::const_eval::eval_queries::eval_to_allocation_raw_provider
      [... omitted 3 frames ...]
  10: rustc_const_eval::const_eval::eval_queries::eval_to_const_value_raw_provider
      [... omitted 3 frames ...]
  11: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}
  12: rustc_data_structures::sync::parallel::par_slice::par_rec::<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>
  13: rustc_thread_pool::join::join_context::<rustc_thread_pool::join::join::call<(), rustc_data_structures::sync::parallel::par_slice::par_rec<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}>::{closure#0}, rustc_thread_pool::join::join::call<(), rustc_data_structures::sync::parallel::par_slice::par_rec<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#2}>::{closure#0}, (), ()>::{closure#0}
  14: rustc_data_structures::sync::parallel::par_slice::par_rec::<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>
  15: rustc_thread_pool::join::join_context::<rustc_thread_pool::join::join::call<(), rustc_data_structures::sync::parallel::par_slice::par_rec<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#1}>::{closure#0}, rustc_thread_pool::join::join::call<(), rustc_data_structures::sync::parallel::par_slice::par_rec<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>::{closure#2}>::{closure#0}, (), ()>::{closure#0}
  16: rustc_data_structures::sync::parallel::par_slice::par_rec::<&rustc_span::def_id::LocalDefId, rustc_data_structures::sync::parallel::par_for_each_in<&rustc_span::def_id::LocalDefId, &[rustc_span::def_id::LocalDefId], <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners<rustc_hir_analysis::check_crate::{closure#2}>::{closure#0}>::{closure#0}::{closure#0}>
  17: rustc_hir_analysis::check_crate
  18: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  19: <rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
  20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  21: <rustc_thread_pool::job::StackJob<rustc_thread_pool::latch::LatchRef<rustc_thread_pool::latch::LockLatch>, <rustc_thread_pool::registry::Registry>::in_worker_cold<<rustc_thread_pool::thread_pool::ThreadPool>::install<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#5}::{closure#0}::{closure#1}::{closure#0}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()> as rustc_thread_pool::job::Job>::execute
  22: <rustc_thread_pool::registry::WorkerThread>::wait_or_steal_until_cold
  23: <rustc_thread_pool::registry::ThreadBuilder>::run
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: the compiler unexpectedly panicked. this is a bug.

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: please attach the file at `/home/os/rlly/rustc-ice-2026-01-23T12_18_03-195014.txt` to your bug report

note: rustc 1.95.0-nightly (39052daf9 2026-01-22) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED] -C target-cpu=native -Z macro-backtrace -Z threads=32

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

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `_`
#1 [eval_to_const_value_raw] simplifying constant for the type system `_`
#2 [analysis] running analysis passes on crate `rlly`
end of query stack

[folkertdev]

relevant line of code:

rust/compiler/rustc_const_eval/src/interpret/intrinsics/simd.rs

Lines 830 to 834 in d222ddc

	alignment: SimdAlign,
	) -> InterpResult<'tcx> {
	assert_matches!(vector_layout.backend_repr, BackendRepr::SimdVector { .. });
	let align = match alignment {

That assert is inconsistent with the actual (current) layout calculation of vector types:

rust/compiler/rustc_abi/src/layout.rs

Lines 1508 to 1513 in d222ddc

	// Non-power-of-two vectors have padding up to the next power-of-two.
	// If we're a packed repr, remove the padding while keeping the alignment as close
	// to a vector as possible.
	VectorKind::PackedFixed if !count.is_power_of_two() => {
	(BackendRepr::Memory { sized: true }, Align::max_aligned_factor(size))
	}

[enthropy7]

@rustbot claim