ICE: "Got a scalar pair where a scalar was expected" -Zmir-opt-level=4 --emit=mir

[matthiaskrgr]

Code

// run-rustfix
#![allow(unused)]
fn a() -> usize { 0 }
//~^ ERROR return types are denoted using `->`

fn bar(_: u32) {}

fn baz() -> *const dyn Fn(u32) { unimplemented!() }

fn foo() {
    match () {
        _ if baz() == &bar as &dyn Fn(u32) => (),
        () => (),
    }
}

fn main() {
}

Meta

rustc --version --verbose:

rustc 1.62.0-nightly (878c7833f 2022-04-16)
binary: rustc
commit-hash: 878c7833f6c1ff10e2fd89074e5bd4ef5ff15936
commit-date: 2022-04-16
host: x86_64-unknown-linux-gnu
release: 1.62.0-nightly
LLVM version: 14.0.0

Error output

Backtrace

error: internal compiler error: /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/compiler/rustc_const_eval/src/interpret/operand.rs:77:42: Got a scalar pair where a scalar was expected

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/compiler/rustc_errors/src/lib.rs:1349:9
stack backtrace:
   0:     0x7f0edf49d7fd - std::backtrace_rs::backtrace::libunwind::trace::h533af29c806df9d1
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f0edf49d7fd - std::backtrace_rs::backtrace::trace_unsynchronized::hdb4c2ff88b52ef66
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f0edf49d7fd - std::sys_common::backtrace::_print_fmt::h68495a06222c4efb
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f0edf49d7fd - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h91043f683408357d
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f0edf4f8eec - core::fmt::write::hcc15453d8963f001
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/core/src/fmt/mod.rs:1194:17
   5:     0x7f0edf48ef51 - std::io::Write::write_fmt::h5217846c280e1260
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/io/mod.rs:1655:15
   6:     0x7f0edf4a0515 - std::sys_common::backtrace::_print::h88be4bfce1061450
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f0edf4a0515 - std::sys_common::backtrace::print::he017a6566e010988
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f0edf4a0515 - std::panicking::default_hook::{{closure}}::hb793c4d82607bce7
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/panicking.rs:295:22
   9:     0x7f0edf4a0189 - std::panicking::default_hook::hc3c558385f484fdc
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/panicking.rs:314:9
  10:     0x7f0edfcd1421 - rustc_driver[19d608e2c8daf1f4]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f0edf4a0ce6 - std::panicking::rust_panic_with_hook::h28c3b2fc9e3a60cd
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/panicking.rs:702:17
  12:     0x7f0ee0d28881 - std[cd658a55527ed977]::panicking::begin_panic::<rustc_errors[9417c7ccc58903d8]::ExplicitBug>::{closure#0}
  13:     0x7f0ee0d27d96 - std[cd658a55527ed977]::sys_common::backtrace::__rust_end_short_backtrace::<std[cd658a55527ed977]::panicking::begin_panic<rustc_errors[9417c7ccc58903d8]::ExplicitBug>::{closure#0}, !>
  14:     0x7f0ee0cbddef - std[cd658a55527ed977]::panicking::begin_panic::<rustc_errors[9417c7ccc58903d8]::ExplicitBug>
  15:     0x7f0ee0c6f166 - std[cd658a55527ed977]::panic::panic_any::<rustc_errors[9417c7ccc58903d8]::ExplicitBug>
  16:     0x7f0ee0c6afe5 - <rustc_errors[9417c7ccc58903d8]::HandlerInner>::bug::<&alloc[c0e4610846cb0c5f]::string::String>
  17:     0x7f0ee0c6ad50 - <rustc_errors[9417c7ccc58903d8]::Handler>::bug::<&alloc[c0e4610846cb0c5f]::string::String>
  18:     0x7f0ee0d314bd - rustc_middle[77cffc0d0a9caf4f]::ty::context::tls::with_opt::<rustc_middle[77cffc0d0a9caf4f]::util::bug::opt_span_bug_fmt<rustc_span[ae9ba53627e4b7a2]::span_encoding::Span>::{closure#0}, ()>
  19:     0x7f0ee0d33f46 - rustc_middle[77cffc0d0a9caf4f]::util::bug::opt_span_bug_fmt::<rustc_span[ae9ba53627e4b7a2]::span_encoding::Span>
  20:     0x7f0ee0d33eb3 - rustc_middle[77cffc0d0a9caf4f]::util::bug::bug_fmt
  21:     0x7f0edfebeecf - <rustc_const_eval[2c45cfb8cbd0596a]::interpret::operand::Immediate>::to_scalar
  22:     0x7f0ee10cd5e2 - <rustc_mir_transform[30431bd415c4c272]::const_prop::ConstPropagator as rustc_middle[77cffc0d0a9caf4f]::mir::visit::MutVisitor>::visit_body
  23:     0x7f0ee10c9264 - <rustc_mir_transform[30431bd415c4c272]::const_prop::ConstProp as rustc_middle[77cffc0d0a9caf4f]::mir::MirPass>::run_pass
  24:     0x7f0ee110903e - rustc_mir_transform[30431bd415c4c272]::pass_manager::run_passes
  25:     0x7f0ee10f43de - rustc_mir_transform[30431bd415c4c272]::optimized_mir
  26:     0x7f0ee16f4720 - rustc_query_system[f27402853dfb6133]::query::plumbing::try_execute_query::<rustc_query_impl[604497a8fc516067]::plumbing::QueryCtxt, rustc_query_system[f27402853dfb6133]::query::caches::DefaultCache<rustc_span[ae9ba53627e4b7a2]::def_id::DefId, &rustc_middle[77cffc0d0a9caf4f]::mir::Body>>
  27:     0x7f0ee17e6d0e - <rustc_query_impl[604497a8fc516067]::Queries as rustc_middle[77cffc0d0a9caf4f]::ty::query::QueryEngine>::optimized_mir
  28:     0x7f0ee1bd753d - <rustc_middle[77cffc0d0a9caf4f]::ty::context::TyCtxt>::instance_mir
  29:     0x7f0ee0c9998f - rustc_middle[77cffc0d0a9caf4f]::mir::pretty::write_mir_pretty
  30:     0x7f0edff0bd10 - rustc_mir_transform[30431bd415c4c272]::dump_mir::emit_mir
  31:     0x7f0ee1d29b86 - <rustc_interface[c2767953942b9161]::queries::Queries>::ongoing_codegen
  32:     0x7f0ee1cf02fb - <rustc_interface[c2767953942b9161]::interface::Compiler>::enter::<rustc_driver[19d608e2c8daf1f4]::run_compiler::{closure#1}::{closure#2}, core[9a854ec5d686c1fc]::result::Result<core[9a854ec5d686c1fc]::option::Option<rustc_interface[c2767953942b9161]::queries::Linker>, rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>
  33:     0x7f0ee1d18ecf - rustc_span[ae9ba53627e4b7a2]::with_source_map::<core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>, rustc_interface[c2767953942b9161]::interface::create_compiler_and_run<core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>, rustc_driver[19d608e2c8daf1f4]::run_compiler::{closure#1}>::{closure#1}>
  34:     0x7f0ee1cf0ee7 - <scoped_tls[673d87c3fad674a0]::ScopedKey<rustc_span[ae9ba53627e4b7a2]::SessionGlobals>>::set::<rustc_interface[c2767953942b9161]::interface::run_compiler<core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>, rustc_driver[19d608e2c8daf1f4]::run_compiler::{closure#1}>::{closure#0}, core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>
  35:     0x7f0ee1d062ff - std[cd658a55527ed977]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[c2767953942b9161]::util::run_in_thread_pool_with_globals<rustc_interface[c2767953942b9161]::interface::run_compiler<core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>, rustc_driver[19d608e2c8daf1f4]::run_compiler::{closure#1}>::{closure#0}, core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>::{closure#0}, core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>
  36:     0x7f0ee1d06439 - <<std[cd658a55527ed977]::thread::Builder>::spawn_unchecked_<rustc_interface[c2767953942b9161]::util::run_in_thread_pool_with_globals<rustc_interface[c2767953942b9161]::interface::run_compiler<core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>, rustc_driver[19d608e2c8daf1f4]::run_compiler::{closure#1}>::{closure#0}, core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>::{closure#0}, core[9a854ec5d686c1fc]::result::Result<(), rustc_errors[9417c7ccc58903d8]::ErrorGuaranteed>>::{closure#1} as core[9a854ec5d686c1fc]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x7f0edf4aab93 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::ha55af26f35189599
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/alloc/src/boxed.rs:1866:9
  38:     0x7f0edf4aab93 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h6a841b0f36efd076
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/alloc/src/boxed.rs:1866:9
  39:     0x7f0edf4aab93 - std::sys::unix::thread::Thread::new::thread_start::h4d154f7a3783bf9b
                               at /rustc/878c7833f6c1ff10e2fd89074e5bd4ef5ff15936/library/std/src/sys/unix/thread.rs:108:17
  40:     0x7f0edf2835c2 - start_thread
  41:     0x7f0edf308584 - __clone
  42:                0x0 - <unknown>

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 1.62.0-nightly (878c7833f 2022-04-16) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=4

query stack during panic:
#0 [optimized_mir] optimizing MIR for `foo`
end of query stack
error: aborting due to previous error

[matthiaskrgr]

Also reproducible in miri:

use std::fmt::Debug;
use std::ptr;

fn main() {
    let a: *const dyn Debug = &1 as &dyn Debug;
    let b: *const dyn Debug = &1 as &dyn Debug;
    let _ = a < b;
}

[RalfJung]

The second one looks very different from the first. That looks like a bug in the Miri implementation of <, which is not prepared for wide pointers.

[RalfJung]

I cannot reproduce the original example any more. And in fact main is empty so I don't think Miri even did anything. The backtrace points to ConstProp, which would make this a rustc bug, not a Miri bug. Not sure if there is anything actionable here.

The second one still ICEs.

[RalfJung]

@bjorn3 do you know the codegen behavior of < on wide pointers? Does it do anything with the metadata?
(==/!= also compares the metadata, as far as I know).

[RalfJung]

Actually testing indicates that it is... lexicographic?!?

[bjorn3]

Indeed. This is the actual implementation:

rust/compiler/rustc_codegen_ssa/src/mir/rvalue.rs

Lines 625 to 639 in 5b8cf49

	mir::BinOp::Le | mir::BinOp::Lt | mir::BinOp::Ge | mir::BinOp::Gt => {
	// a OP b ~ a.0 STRICT(OP) b.0 | (a.0 == b.0 && a.1 OP a.1)
	let (op, strict_op) = match op {
	mir::BinOp::Lt => (IntPredicate::IntULT, IntPredicate::IntULT),
	mir::BinOp::Le => (IntPredicate::IntULE, IntPredicate::IntULT),
	mir::BinOp::Gt => (IntPredicate::IntUGT, IntPredicate::IntUGT),
	mir::BinOp::Ge => (IntPredicate::IntUGE, IntPredicate::IntUGT),
	_ => bug!(),
	};
	let lhs = bx.icmp(strict_op, lhs_addr, rhs_addr);
	let and_lhs = bx.icmp(IntPredicate::IntEQ, lhs_addr, rhs_addr);
	let and_rhs = bx.icmp(op, lhs_extra, rhs_extra);
	let rhs = bx.and(and_lhs, and_rhs);
	bx.or(lhs, rhs)
	}

[matthiaskrgr]

Example #1 still crashes with -Zmir-opt-level=4 as noted in the title, reopening.