niche optimization cannot be applied to non-power-of-two-sized int

[anderspapitto]

I'd like to be able to apply niche optimizations to irregular integer sizes, e.g. u24 (or [u8;3]), where the niche is the zero pattern for all bytes. That's led me to this ICE.

Code

#![feature(rustc_attrs)]

#[rustc_layout_scalar_valid_range_start(1)]
#[rustc_nonnull_optimization_guaranteed]
struct Foo(pub u8, pub u8, pub u8);
fn foo1() -> Option<Foo> { Some(unsafe { Foo(0, 0, 0) }) }

Meta

rustc --version --verbose:

1.75.0-nightly (2023-10-16 49691b1f70d71dd7b834)

(via rust playground https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=c68c4d3734c44fdb16f959686c5d61be)

Error output

Compiling playground v0.0.1 (/playground)
warning: the feature `rustc_attrs` is internal to the compiler or standard library
 --> src/lib.rs:1:12
  |
1 | #![feature(rustc_attrs)]
  |            ^^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

thread 'rustc' panicked at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/compiler/rustc_abi/src/layout.rs:281:22:
nonscalar layout for layout_scalar_valid_range type: Layout {
    size: Size(3 bytes),
    align: AbiAndPrefAlign {
        abi: Align(1 bytes),
        pref: Align(8 bytes),
    },
    abi: Aggregate {
        sized: true,
    },
    fields: Arbitrary {
        offsets: [
            Size(0 bytes),
            Size(1 bytes),
            Size(2 bytes),
        ],
        memory_index: [
            0,
            1,
            2,
        ],
    },
    largest_niche: None,
    variants: Single {
        index: 0,
    },
    max_repr_align: None,
    unadjusted_abi_align: Align(1 bytes),
}
stack backtrace:
   0:     0x7ff382386fbc - std::backtrace_rs::backtrace::libunwind::trace::h52e21b6d54f4efe1
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7ff382386fbc - std::backtrace_rs::backtrace::trace_unsynchronized::ha6bdebc0b682a39e
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7ff382386fbc - std::sys_common::backtrace::_print_fmt::h23ab7873c0a83148
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7ff382386fbc - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h83da7f60cc7c7cd3
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7ff3823eea50 - core::fmt::rt::Argument::fmt::h695747813e9a4377
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/core/src/fmt/rt.rs:142:9
   5:     0x7ff3823eea50 - core::fmt::write::h8167ebd23b9a1080
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/core/src/fmt/mod.rs:1117:17
   6:     0x7ff38237a2ff - std::io::Write::write_fmt::hbb584c40957aadf3
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/io/mod.rs:1762:15
   7:     0x7ff382386da4 - std::sys_common::backtrace::_print::h0771a24c55f9a845
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7ff382386da4 - std::sys_common::backtrace::print::h0a0146f60845778a
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7ff382389bd7 - std::panicking::default_hook::{{closure}}::h5c829ccf7ff10dcf
  10:     0x7ff38238991a - std::panicking::default_hook::h0b7592f4ae109148
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/panicking.rs:292:9
  11:     0x7ff384f4434a - std[c698645e906a989e]::panicking::update_hook::<alloc[bb531d63f2d8c501]::boxed::Box<rustc_driver_impl[a565de00d2c1816a]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7ff38238a378 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h1edc5bec4ce090d5
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/alloc/src/boxed.rs:2021:9
  13:     0x7ff38238a378 - std::panicking::rust_panic_with_hook::h9275c70e8cb8097f
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/panicking.rs:735:13
  14:     0x7ff38238a0d1 - std::panicking::begin_panic_handler::{{closure}}::h5946c93671f604d2
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/panicking.rs:609:13
  15:     0x7ff3823874d6 - std::sys_common::backtrace::__rust_end_short_backtrace::h782a9a422ef9d5aa
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys_common/backtrace.rs:170:18
  16:     0x7ff382389e02 - rust_begin_unwind
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/panicking.rs:597:5
  17:     0x7ff3823eb075 - core::panicking::panic_fmt::hdde6b669b056f39d
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/core/src/panicking.rs:72:14
  18:     0x7ff3868be253 - rustc_ty_utils[69d546cb106a7340]::layout::layout_of_uncached
  19:     0x7ff3868b304e - rustc_ty_utils[69d546cb106a7340]::layout::layout_of
  20:     0x7ff3868b2fd1 - rustc_query_impl[40da232d0ce86907]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[40da232d0ce86907]::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 16usize]>>
  21:     0x7ff3868b27e4 - rustc_query_system[e3e293bd174804eb]::query::plumbing::try_execute_query::<rustc_query_impl[40da232d0ce86907]::DynamicConfig<rustc_query_system[e3e293bd174804eb]::query::caches::DefaultCache<rustc_middle[cf52819fa178b5a6]::ty::ParamEnvAnd<rustc_middle[cf52819fa178b5a6]::ty::Ty>, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 16usize]>>, false, true, false>, rustc_query_impl[40da232d0ce86907]::plumbing::QueryCtxt, false>
  22:     0x7ff3868b24de - rustc_query_impl[40da232d0ce86907]::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
  23:     0x7ff38621e192 - <core[8466deefe4bf88b6]::iter::adapters::GenericShunt<core[8466deefe4bf88b6]::iter::adapters::by_ref_sized::ByRefSized<core[8466deefe4bf88b6]::iter::adapters::map::Map<core[8466deefe4bf88b6]::slice::iter::Iter<rustc_middle[cf52819fa178b5a6]::ty::VariantDef>, rustc_ty_utils[69d546cb106a7340]::layout::layout_of_uncached::{closure#8}>>, core[8466deefe4bf88b6]::result::Result<core[8466deefe4bf88b6]::convert::Infallible, &rustc_middle[cf52819fa178b5a6]::ty::layout::LayoutError>> as core[8466deefe4bf88b6]::iter::traits::iterator::Iterator>::next
  24:     0x7ff3868b4c3f - rustc_ty_utils[69d546cb106a7340]::layout::layout_of_uncached
  25:     0x7ff3868b304e - rustc_ty_utils[69d546cb106a7340]::layout::layout_of
  26:     0x7ff3868b2fd1 - rustc_query_impl[40da232d0ce86907]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[40da232d0ce86907]::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 16usize]>>
  27:     0x7ff3868b27e4 - rustc_query_system[e3e293bd174804eb]::query::plumbing::try_execute_query::<rustc_query_impl[40da232d0ce86907]::DynamicConfig<rustc_query_system[e3e293bd174804eb]::query::caches::DefaultCache<rustc_middle[cf52819fa178b5a6]::ty::ParamEnvAnd<rustc_middle[cf52819fa178b5a6]::ty::Ty>, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 16usize]>>, false, true, false>, rustc_query_impl[40da232d0ce86907]::plumbing::QueryCtxt, false>
  28:     0x7ff3868b24de - rustc_query_impl[40da232d0ce86907]::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7ff386b9b3ce - <rustc_mir_transform[c1d87982e12de6b0]::const_prop::CanConstProp>::check
  30:     0x7ff386148a5d - <rustc_mir_transform[c1d87982e12de6b0]::const_prop_lint::ConstPropLint as rustc_mir_transform[c1d87982e12de6b0]::pass_manager::MirLint>::run_lint
  31:     0x7ff38615b286 - rustc_mir_transform[c1d87982e12de6b0]::run_analysis_to_runtime_passes
  32:     0x7ff383cd9836 - rustc_mir_transform[c1d87982e12de6b0]::mir_drops_elaborated_and_const_checked
  33:     0x7ff38613bb75 - rustc_query_impl[40da232d0ce86907]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[40da232d0ce86907]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 8usize]>>
  34:     0x7ff38613bdac - rustc_query_system[e3e293bd174804eb]::query::plumbing::try_execute_query::<rustc_query_impl[40da232d0ce86907]::DynamicConfig<rustc_query_system[e3e293bd174804eb]::query::caches::VecCache<rustc_span[8b3ee959687609c3]::def_id::LocalDefId, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[40da232d0ce86907]::plumbing::QueryCtxt, false>
  35:     0x7ff38613b6d0 - rustc_query_impl[40da232d0ce86907]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7ff3869b476b - rustc_interface[bf8842423122044e]::passes::analysis
  37:     0x7ff3869b3e6f - rustc_query_impl[40da232d0ce86907]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[40da232d0ce86907]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 1usize]>>
  38:     0x7ff386c08c26 - rustc_query_system[e3e293bd174804eb]::query::plumbing::try_execute_query::<rustc_query_impl[40da232d0ce86907]::DynamicConfig<rustc_query_system[e3e293bd174804eb]::query::caches::SingleCache<rustc_middle[cf52819fa178b5a6]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[40da232d0ce86907]::plumbing::QueryCtxt, false>
  39:     0x7ff386c08a55 - rustc_query_impl[40da232d0ce86907]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  40:     0x7ff386cf2a92 - std[c698645e906a989e]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[bf8842423122044e]::util::run_in_thread_with_globals<rustc_interface[bf8842423122044e]::interface::run_compiler<core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>, rustc_driver_impl[a565de00d2c1816a]::run_compiler::{closure#1}>::{closure#0}, core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>>
  41:     0x7ff386cf1d73 - <<std[c698645e906a989e]::thread::Builder>::spawn_unchecked_<rustc_interface[bf8842423122044e]::util::run_in_thread_with_globals<rustc_interface[bf8842423122044e]::interface::run_compiler<core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>, rustc_driver_impl[a565de00d2c1816a]::run_compiler::{closure#1}>::{closure#0}, core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[8466deefe4bf88b6]::result::Result<(), rustc_span[8b3ee959687609c3]::ErrorGuaranteed>>::{closure#1} as core[8466deefe4bf88b6]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  42:     0x7ff3823952f5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h65ed97a99699e110
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/alloc/src/boxed.rs:2007:9
  43:     0x7ff3823952f5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7496a8683d4f5253
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/alloc/src/boxed.rs:2007:9
  44:     0x7ff3823952f5 - std::sys::unix::thread::Thread::new::thread_start::h3cc99d3e71f64c79
                               at /rustc/49691b1f70d71dd7b8349c332b7f277ee527bf08/library/std/src/sys/unix/thread.rs:108:17
  45:     0x7ff38225e609 - start_thread
  46:     0x7ff382181133 - clone
  47:                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: please attach the file at `/playground/rustc-ice-2023-10-17T04:38:35.260903133Z-116.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

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

query stack during panic:
#0 [layout_of] computing layout of `Foo`
#1 [layout_of] computing layout of `core::option::Option<Foo>`
#2 [mir_drops_elaborated_and_const_checked] elaborating drops for `foo1`
#3 [analysis] running analysis passes on this crate
end of query stack
warning: `playground` (lib) generated 1 warning
error: could not compile `playground` (lib); 1 warning emitted

[Noratrieb]

ICEs with internal features are expected, think of them like errors.
That said, I can see the use case for supporting this, so I won't close the issue.

[scottmcm]

Per rust-lang/compiler-team#620, this is not a bug.

Personally, I think it should just be closed, since pattern types are the way forward, not these attributes, and thus there's no need to add maintenance burden to support this.

(Though TBH I'd personally like rust to just have u24 and u40 and such natively. But that's a wish, not something to be tracked in an issue.)

[Noratrieb]

sounds good