ICE: Slice pattern matching with constant slice and slice literal

[Brekcel]

Attempting to pattern match a slice with a constant value and THEN a slice literal causes an ICE.

Simple test case:

fn main() {
	let s = &[0x00; 4][..]; //Slice of any value
	const MAGIC_TEST: &[u8] = b"TEST"; //Const slice to pattern match with
	match s {
		MAGIC_TEST => (),
		[0x00, 0x00, 0x00, 0x00] => (),
		_ => ()
	}
}

However simply changing the order to test the slice literal and then the const slice compiles fine:

//Compiles fine
fn main() {
	let s = &[0x00; 4][..]; //Slice of any value
	const MAGIC_TEST: &[u8] = b"TEST"; //Const slice to pattern match with
	match s {
		[0x00, 0x00, 0x00, 0x00] => (), // Only thing changes was the order of these 2
		MAGIC_TEST => (), // Only thing changes was the order of these 2
		_ => ()
	}
}

Error message:

B:\slice_ice>cargo run --verbose
   Compiling slice_ice v0.1.0 (B:\slice_ice)
     Running `rustc --crate-name slice_ice src\main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=f42f6a124a503700 -C extra-filename=-f42f6a124a503700 --out-dir B:\slice_ice\target\debug\deps -C incremental=B:\slice_ice\target\debug\incremental -L dependency=B:\slice_ice\target\debug\deps`
error: internal compiler error: librustc_mir\hair\pattern\_match.rs:1679: unexpected const-val Const { ty: &[u8], val: ScalarPair(Ptr(Pointer { alloc_id: AllocId(1), offset: Size { raw: 0 } }), Scalar(Bits { size: 8, bits: 4 })) } with ctor Slice(4)
 --> src\main.rs:5:3
  |
5 |         MAGIC_TEST => (),
  |         ^^^^^^^^^^

thread 'main' panicked at 'Box<Any>', librustc_errors\lib.rs:525:9
stack backtrace:
   0: <std::sys::windows::args::Args as core::ops::drop::Drop>::drop
   1: <std::ffi::os_str::OsString as std::sys_common::IntoInner<std::sys::windows::os_str::Buf>>::into_inner
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: <rustc::ty::sty::Binder<rustc::ty::ProjectionPredicate<'tcx>> as rustc::ty::ToPredicate<'tcx>>::to_predicate
   5: std::panicking::rust_panic_with_hook
   6: <rustc_mir::build::scope::BreakableScope<'tcx> as core::fmt::Debug>::fmt
   7: <rustc_mir::dataflow::graphviz::Edge as core::fmt::Debug>::fmt
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: <unknown>
  12: <rustc_mir::dataflow::graphviz::Edge as core::fmt::Debug>::fmt
  13: <rustc_mir::dataflow::graphviz::Edge as core::fmt::Debug>::fmt
  14: rustc_mir::hair::pattern::_match::split_grouped_constructors::range_borders
  15: <unknown>
  16: <rustc_mir::hair::pattern::_match::Matrix<'a, 'tcx> as core::fmt::Debug>::fmt
  17: <unknown>
  18: <rustc_mir::hair::pattern::_match::Matrix<'a, 'tcx> as core::fmt::Debug>::fmt
  19: <rustc_mir::hair::pattern::_match::Matrix<'a, 'tcx> as core::fmt::Debug>::fmt
  20: <unknown>
  21: <rustc_mir::hair::pattern::_match::Matrix<'a, 'tcx> as core::fmt::Debug>::fmt
  22: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
  23: <rustc_mir::hair::pattern::_match::Matrix<'a, 'tcx> as core::fmt::Debug>::fmt
  24: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
  25: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
  26: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
  27: rustc_mir::hair::pattern::check_match::check_crate
  28: rustc::ty::query::on_disk_cache::__ty_decoder_impl::<impl serialize::serialize::Decoder for rustc::ty::query::on_disk_cache::CacheDecoder<'a, 'tcx, 'x>>::read_str
  29: rustc::ty::context::tls::track_diagnostic
  30: rustc::dep_graph::graph::DepGraph::assert_ignored
  31: rustc::ty::context::tls::track_diagnostic
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  34: rustc::ty::query::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::check_match
  35: <rustc_mir::dataflow::move_paths::abs_domain::AbstractOperand as core::fmt::Debug>::fmt
  36: rustc_mir::dataflow::impls::MaybeUninitializedPlaces::new
  37: rustc_mir::hair::pattern::check_match::check_crate
  38: <unknown>
  39: <rustc_driver::pretty::IdentifiedAnnotation<'hir> as rustc_driver::pretty::HirPrinterSupport<'hir>>::sess
  40: <rustc_driver::CompilationFailure as core::fmt::Debug>::fmt
  41: rustc_driver::driver::compile_input
  42: rustc_driver::run_compiler
  43: <env_logger::filter::inner::Filter as core::fmt::Display>::fmt
  44: rustc_driver::run_compiler
  45: <env_logger::filter::inner::Filter as core::fmt::Display>::fmt
  46: _rust_maybe_catch_panic
  47: rustc_driver::profile::dump
  48: rustc_driver::main
  49: <unknown>
  50: std::panicking::update_panic_count
  51: _rust_maybe_catch_panic
  52: std::rt::lang_start_internal
  53: <unknown>
  54: <unknown>
  55: BaseThreadInitThunk
  56: RtlUserThreadStart
query stack during panic:
#0 [check_match] processing `main`
end of query stack
error: aborting due to previous error


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

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.30.1 (1433507eb 2018-11-07) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

error: Could not compile `slice_ice`.

Caused by:
  process didn't exit successfully: `rustc --crate-name slice_ice src\main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=f42f6a124a503700 -C extra-filename=-f42f6a124a503700 --out-dir B:\slice_ice\target\debug\deps -C incremental=B:\slice_ice\target\debug\incremental -L dependency=B:\slice_ice\target\debug\deps` (exit code: 101)

rustc version:

B:\slice_ice>rustc --version --verbose
rustc 1.30.1 (1433507eb 2018-11-07)
binary: rustc
commit-hash: 1433507eba7d1a114e4c6f27ae0e1a74f60f20de
commit-date: 2018-11-07
host: x86_64-pc-windows-msvc
release: 1.30.1
LLVM version: 8.0

[oli-obk]

So... I do have a fix for byte slices, but that just exposed that we have the same ICE for other slices:

fn main() {
	let s = &[0x00; 4][..]; //Slice of any value
	const MAGIC_TEST: &[u32] = &[1, 2, 3, 4]; //Const slice to pattern match with
	match s {
		MAGIC_TEST => (),
		[0x00, 0x00, 0x00, 0x00] => (),
		_ => ()
	}
}

This can be fixed, too, but I need to wait for #55915 to be merged before being able to do this in a reasonable way.