layout decided on a larger discriminant type (I32) than typeck (I16)

[piegamesde]

Code

#![no_std]
#![no_main]

extern crate panic_halt;

#[repr(C)]
enum Foo {
	Bar
}

#[arduino_uno::entry]
fn main() -> ! {
	loop {
	}
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (38d911dfc 2020-10-09)
binary: rustc
commit-hash: 38d911dfc55a7a1eea1c80139113ed2ff0151087
commit-date: 2020-10-09
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly
LLVM version: 11.0

Error output

error: internal compiler error: compiler/rustc_middle/src/ty/layout.rs:1076:21: layout decided on a larger discriminant type (I32) than typeck (I16)

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:945:9

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 (38d911dfc 2020-10-09) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z unstable-options -C opt-level=s -C panic=abort -C lto -C debuginfo=2 -C debug-assertions=on -C incremental --crate-type bin

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

query stack during panic:
#0 [layout_raw] computing layout of `Foo`
#1 [lint_mod] linting top-level module
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error; 1 warning emitted

Backtrace

stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt
   6: rustc_middle::util::bug::opt_span_bug_fmt
   7: rustc_middle::util::bug::bug_fmt
   8: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached
   9: rustc_middle::ty::layout::layout_raw
  10: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::layout_raw>::compute
  11: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  12: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  13: rustc_data_structures::stack::ensure_sufficient_stack
  14: rustc_query_system::query::plumbing::get_query_impl
  15: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of
  16: <rustc_lint::types::VariantSizeDifferences as rustc_lint::passes::LateLintPass>::check_item
  17: <rustc_lint::BuiltinCombinedModuleLateLintPass as rustc_lint::passes::LateLintPass>::check_item
  18: rustc_hir::intravisit::Visitor::visit_nested_item
  19: rustc_lint::late::late_lint_mod
  20: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::lint_mod>::compute
  21: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  23: rustc_data_structures::stack::ensure_sufficient_stack
  24: rustc_query_system::query::plumbing::get_query_impl
  25: rustc_query_system::query::plumbing::ensure_query_impl
  26: rustc_data_structures::sync::join
  27: rustc_session::utils::<impl rustc_session::session::Session>::time
  28: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  29: rustc_session::utils::<impl rustc_session::session::Session>::time
  30: rustc_interface::passes::analysis
  31: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  32: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_query_system::query::plumbing::get_query_impl
  36: rustc_interface::passes::QueryContext::enter
  37: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  38: rustc_span::with_source_map
  39: rustc_interface::interface::create_compiler_and_run
  40: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[jonas-schievink]

MCVE:

#![no_std]
#![no_main]

#[repr(C)]
pub enum Foo {
    Bar,
}

And then use cargo +nightly build -Zbuild-std=core --target avr-unknown-gnu-atmega328 to build.

[jonas-schievink]

Bug is presumably here:

rust/compiler/rustc_middle/src/ty/layout.rs

Lines 108 to 117 in 790d19c

	if repr.c() {
	match &tcx.sess.target.target.arch[..] {
	// WARNING: the ARM EABI has two variants; the one corresponding
	// to `at_least == I32` appears to be used on Linux and NetBSD,
	// but some systems may use the variant corresponding to no
	// lower bound. However, we don't run on those yet...?
	"arm" => min_from_extern = Some(I32),
	_ => min_from_extern = Some(I32),
	}
	}

I believe this should use the size of a C int instead, which on AVR is 16 bits.

[jonas-schievink]

Heh, also happens when targeting msp430-none-elf (our other 16-bit target)