ICE from ZSTs not at the start of structs during codegen for unsizing coercions

[Kixiron]

Code

#![feature(coerce_unsized)]

use std::ops::CoerceUnsized;

#[repr(C)]
pub struct BoxWithZstTail<T: ?Sized>(Box<T>, ());

impl<S: ?Sized, T: ?Sized> CoerceUnsized<BoxWithZstTail<T>> for BoxWithZstTail<S>
    where Box<S>: CoerceUnsized<Box<T>>
{}

pub fn noop_dyn_upcast_with_zst_tail(b: BoxWithZstTail<dyn Send + Sync>) -> BoxWithZstTail<dyn Send> {
    b
}

Meta

rustc --version --verbose:

rustc 1.63.0-nightly (ebbcbfc23 2022-05-27)
binary: rustc
commit-hash: ebbcbfc236ced21d5e6a92269edb704692ff26b8
commit-date: 2022-05-27
host: x86_64-pc-windows-msvc
release: 1.63.0-nightly
LLVM version: 14.0.4

Backtrace

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `16`,
 right: `0`', /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/compiler/rustc_codegen_ssa/src/base.rs:219:17
stack backtrace:
   0:     0x7f078e0bb24d - std::backtrace_rs::backtrace::libunwind::trace::h5ecf6d3c2f2dbed3
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f078e0bb24d - std::backtrace_rs::backtrace::trace_unsynchronized::h1f34ec78f43478d1
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f078e0bb24d - std::sys_common::backtrace::_print_fmt::h5eb133ec83ff86d3
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f078e0bb24d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc8814d47922b5f5b
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f078e116fec - core::fmt::write::h871772ca8ace1475
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/core/src/fmt/mod.rs:1196:17
   5:     0x7f078e0ac9e1 - std::io::Write::write_fmt::he514622e09de3df5
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/io/mod.rs:1654:15
   6:     0x7f078e0bdf35 - std::sys_common::backtrace::_print::hd629e2d6c07b6e79
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f078e0bdf35 - std::sys_common::backtrace::print::h6bddafb613b6308d
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f078e0bdf35 - std::panicking::default_hook::{{closure}}::hf8d6097c4866d273
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/panicking.rs:295:22
   9:     0x7f078e0bdc56 - std::panicking::default_hook::h44331fd67f31aee4
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/panicking.rs:314:9
  10:     0x7f078e8946b1 - rustc_driver[7b89ea061d8aedc7]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f078e0be60a - std::panicking::rust_panic_with_hook::h51126dbc27bfe5a6
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/panicking.rs:702:17
  12:     0x7f078e0be447 - std::panicking::begin_panic_handler::{{closure}}::ha0ed88016ebdcd1e
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/panicking.rs:588:13
  13:     0x7f078e0bb704 - std::sys_common::backtrace::__rust_end_short_backtrace::h05a84a7ce4d2e529
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys_common/backtrace.rs:138:18
  14:     0x7f078e0be179 - rust_begin_unwind
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/panicking.rs:584:5
  15:     0x7f078e083443 - core::panicking::panic_fmt::hc7f457b7c7e09a46
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/core/src/panicking.rs:142:14
  16:     0x7f078e113d98 - core::panicking::assert_failed_inner::hc6fe9441630b9e22
  17:     0x7f078e9a2d6c - core[c8091fc9dea0c6cf]::panicking::assert_failed::<u64, u64>
  18:     0x7f0790a8c3a5 - rustc_codegen_ssa[3777d9370248289c]::base::unsize_ptr::<rustc_codegen_llvm[7635d7a996797e4d]::builder::Builder>
  19:     0x7f078fc0fd37 - <rustc_codegen_ssa[3777d9370248289c]::mir::FunctionCx<rustc_codegen_llvm[7635d7a996797e4d]::builder::Builder>>::codegen_rvalue_operand
  20:     0x7f078fbf3dfc - rustc_codegen_ssa[3777d9370248289c]::mir::codegen_mir::<rustc_codegen_llvm[7635d7a996797e4d]::builder::Builder>
  21:     0x7f078fbaa9b3 - rustc_codegen_llvm[7635d7a996797e4d]::base::compile_codegen_unit::module_codegen
  22:     0x7f0790ab3e16 - <rustc_query_system[a1cbf340ec6d6f93]::dep_graph::graph::DepGraph<rustc_middle[c4bb946b42085c78]::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle[c4bb946b42085c78]::ty::context::TyCtxt, rustc_span[c774ced8c61a5d44]::symbol::Symbol, rustc_codegen_ssa[3777d9370248289c]::ModuleCodegen<rustc_codegen_llvm[7635d7a996797e4d]::ModuleLlvm>>
  23:     0x7f0790ab3929 - rustc_codegen_llvm[7635d7a996797e4d]::base::compile_codegen_unit
  24:     0x7f0790a9e38a - <rustc_codegen_llvm[7635d7a996797e4d]::LlvmCodegenBackend as rustc_codegen_ssa[3777d9370248289c]::traits::backend::CodegenBackend>::codegen_crate
  25:     0x7f0790a5aac7 - <rustc_session[d1b76e352c1a3b5b]::session::Session>::time::<alloc[6f618ff12e561101]::boxed::Box<dyn core[c8091fc9dea0c6cf]::any::Any>, rustc_interface[94703aee012e7483]::passes::start_codegen::{closure#0}>
  26:     0x7f0790a85c2a - <rustc_interface[94703aee012e7483]::passes::QueryContext>::enter::<<rustc_interface[94703aee012e7483]::queries::Queries>::ongoing_codegen::{closure#0}::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<alloc[6f618ff12e561101]::boxed::Box<dyn core[c8091fc9dea0c6cf]::any::Any>, rustc_errors[ae611370a546922c]::ErrorGuaranteed>>
  27:     0x7f0790a79f0f - <rustc_interface[94703aee012e7483]::queries::Queries>::ongoing_codegen
  28:     0x7f0790a2e382 - <rustc_interface[94703aee012e7483]::interface::Compiler>::enter::<rustc_driver[7b89ea061d8aedc7]::run_compiler::{closure#1}::{closure#2}, core[c8091fc9dea0c6cf]::result::Result<core[c8091fc9dea0c6cf]::option::Option<rustc_interface[94703aee012e7483]::queries::Linker>, rustc_errors[ae611370a546922c]::ErrorGuaranteed>>
  29:     0x7f0790a57d3f - rustc_span[c774ced8c61a5d44]::with_source_map::<core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>, rustc_interface[94703aee012e7483]::interface::create_compiler_and_run<core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>, rustc_driver[7b89ea061d8aedc7]::run_compiler::{closure#1}>::{closure#1}>
  30:     0x7f0790a2f1e2 - <scoped_tls[a35f89285f520bf3]::ScopedKey<rustc_span[c774ced8c61a5d44]::SessionGlobals>>::set::<rustc_interface[94703aee012e7483]::interface::run_compiler<core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>, rustc_driver[7b89ea061d8aedc7]::run_compiler::{closure#1}>::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>>
  31:     0x7f0790a4493f - std[f19dd7bb03296d5c]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[94703aee012e7483]::util::run_in_thread_pool_with_globals<rustc_interface[94703aee012e7483]::interface::run_compiler<core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>, rustc_driver[7b89ea061d8aedc7]::run_compiler::{closure#1}>::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>>::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>>
  32:     0x7f0790a44a99 - <<std[f19dd7bb03296d5c]::thread::Builder>::spawn_unchecked_<rustc_interface[94703aee012e7483]::util::run_in_thread_pool_with_globals<rustc_interface[94703aee012e7483]::interface::run_compiler<core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>, rustc_driver[7b89ea061d8aedc7]::run_compiler::{closure#1}>::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>>::{closure#0}, core[c8091fc9dea0c6cf]::result::Result<(), rustc_errors[ae611370a546922c]::ErrorGuaranteed>>::{closure#1} as core[c8091fc9dea0c6cf]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  33:     0x7f078e0c8533 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb3d14b8461bee867
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/alloc/src/boxed.rs:1951:9
  34:     0x7f078e0c8533 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h528c1f598bc32c8b
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/alloc/src/boxed.rs:1951:9
  35:     0x7f078e0c8533 - std::sys::unix::thread::Thread::new::thread_start::h9efddab2b9d9a6d4
                               at /rustc/a6b8c6954829669a5c4fa320c3e6132edf04fcfc/library/std/src/sys/unix/thread.rs:108:17
  36:     0x7f078dfee609 - start_thread
  37:     0x7f078df11133 - clone
  38:                0x0 - <unknown>

error: internal compiler error: unexpected panic

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 1.63.0-nightly (a6b8c6954 2022-06-03) running on x86_64-unknown-linux-gnu

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:
end of query stack