intrinsicck is broken in the presence of associated types

[fizyk20]

The compiler told me to report it, so here goes ;)

I tried to compile this code using cargo build: https://gist.github.com/fizyk20/4cf1665a18ff800584f1

This is the only file in the crate. Cargo.toml looks like this:

name = "peano-array"
version = "0.1.0"
authors = ["Bartłomiej Kamiński <fizyk20@gmail.com>"]

So, nothing really unusual.

What I got is posted below:

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/blob/master/CONTRIBUTING.md#bug-reports
thread 'rustc' panicked at 'assertion failed: `(left == right)` (left: `64`, right: `128`)', src/librustc_trans/trans/intrinsic.rs:193

stack backtrace:
   1:     0x7f57f242266e - sys::backtrace::write::ha67a6a2049d22fadIvs
   2:     0x7f57f242ad55 - panicking::on_panic::hfa4bf0215983f759lzx
   3:     0x7f57f23eb94e - rt::unwind::begin_unwind_inner::ha1b5da93bdf7e8ffC0w
   4:     0x7f57f23ec6b6 - rt::unwind::begin_unwind_fmt::hac9e09b20e42a51cIZw
   5:     0x7f57f12574c5 - trans::intrinsic::trans_intrinsic_call::h7041dfce108605fd2dH
   6:     0x7f57f126509e - trans::callee::trans_call_inner::h1312425629985073641
   7:     0x7f57f12c35af - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
   8:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
   9:     0x7f57f122a213 - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  10:     0x7f57f12c2b4f - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  11:     0x7f57f12c1733 - trans::expr::trans_unadjusted::h842ed4ea995ab4beb2B
  12:     0x7f57f1209589 - trans::expr::trans::h0a46d0057de341dfLuB
  13:     0x7f57f129b7d5 - trans::expr::trans_into::hd80da72fd88f78b0voB
  14:     0x7f57f1309cf0 - trans::_match::mk_binding_alloca::h8933109284487913883
  15:     0x7f57f12148d4 - trans::base::init_local::h05162f2d49649b99pOh
  16:     0x7f57f1229ec6 - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  17:     0x7f57f1228fd6 - trans::base::trans_closure::h5ba05285462a4747sDi
  18:     0x7f57f122a808 - trans::base::trans_fn::h05022c5934c7e8c7fNi
  19:     0x7f57f12645e8 - trans::monomorphize::monomorphic_fn::hb8352eb2d7d26c23DHL
  20:     0x7f57f125420e - trans::callee::trans_fn_ref_with_substs::hfc6b0bc3f78e159eGBo
  21:     0x7f57f1268d6d - trans::meth::trans_method_callee::hb526dbe08959880cHJK
  22:     0x7f57f12e2a09 - trans::callee::trans_call_inner::h5390986988460394530
  23:     0x7f57f12cb0e6 - trans::expr::trans_index::hac54b3447ae4d077bgC
  24:     0x7f57f12c18ab - trans::expr::trans_unadjusted::h842ed4ea995ab4beb2B
  25:     0x7f57f1209589 - trans::expr::trans::h0a46d0057de341dfLuB
  26:     0x7f57f129b526 - trans::expr::trans_to_lvalue::hac83b8b50acc99b6k1B
  27:     0x7f57f12c5674 - trans::expr::trans_rvalue_stmt_unadjusted::h1b8ea36ec1927e36fsC
  28:     0x7f57f129bcf5 - trans::expr::trans_into::hd80da72fd88f78b0voB
  29:     0x7f57f129b4a2 - trans::controlflow::trans_stmt_semi::haea6d90b71002e6cy0v
  30:     0x7f57f1229e9a - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  31:     0x7f57f12c2b4f - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  32:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
  33:     0x7f57f1301d8b - trans::_match::trans_match_inner::h74c561c52dd5299ftcK
  34:     0x7f57f12c2b19 - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  35:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
  36:     0x7f57f122a213 - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  37:     0x7f57f12c69f5 - trans::expr::trans_rvalue_stmt_unadjusted::h1b8ea36ec1927e36fsC
  38:     0x7f57f129bcf5 - trans::expr::trans_into::hd80da72fd88f78b0voB
  39:     0x7f57f1301d8b - trans::_match::trans_match_inner::h74c561c52dd5299ftcK
  40:     0x7f57f12c2b19 - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  41:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
  42:     0x7f57f1309cf0 - trans::_match::mk_binding_alloca::h8933109284487913883
  43:     0x7f57f12148d4 - trans::base::init_local::h05162f2d49649b99pOh
  44:     0x7f57f1229ec6 - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  45:     0x7f57f12c2b4f - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  46:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
  47:     0x7f57f129b4a2 - trans::controlflow::trans_stmt_semi::haea6d90b71002e6cy0v
  48:     0x7f57f1229e9a - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  49:     0x7f57f1228fd6 - trans::base::trans_closure::h5ba05285462a4747sDi
  50:     0x7f57f122a808 - trans::base::trans_fn::h05022c5934c7e8c7fNi
  51:     0x7f57f12645e8 - trans::monomorphize::monomorphic_fn::hb8352eb2d7d26c23DHL
  52:     0x7f57f125420e - trans::callee::trans_fn_ref_with_substs::hfc6b0bc3f78e159eGBo
  53:     0x7f57f1252ca2 - trans::callee::trans_fn_ref::h557d599d56e051cd2qo
  54:     0x7f57f124ea18 - trans::callee::trans::hfc3e2da0f1482e8bNgo
  55:     0x7f57f1264e28 - trans::callee::trans_call_inner::h1312425629985073641
  56:     0x7f57f12c35af - trans::expr::trans_rvalue_dps_unadjusted::h0c5c402374fadccbRyC
  57:     0x7f57f129bbc8 - trans::expr::trans_into::hd80da72fd88f78b0voB
  58:     0x7f57f1309cf0 - trans::_match::mk_binding_alloca::h8933109284487913883
  59:     0x7f57f12148d4 - trans::base::init_local::h05162f2d49649b99pOh
  60:     0x7f57f1229ec6 - trans::controlflow::trans_block::h712a0dbbff7e0feau1v
  61:     0x7f57f1228fd6 - trans::base::trans_closure::h5ba05285462a4747sDi
  62:     0x7f57f122a808 - trans::base::trans_fn::h05022c5934c7e8c7fNi
  63:     0x7f57f122d928 - trans::base::trans_item::hd3ac3af06c93993fPdj
  64:     0x7f57f123a40c - trans::base::trans_crate::h14e6ea6d455593f8i0j
  65:     0x7f57f29912f4 - driver::phase_4_translate_to_llvm::h8ce7c7bfb0fd9b185Oa
  66:     0x7f57f298b885 - driver::phase_3_run_analysis_passes::closure.16542
  67:     0x7f57f2985ab1 - middle::ty::ctxt<'tcx>::create_and_enter::h9578579149294230291
  68:     0x7f57f2980991 - driver::phase_3_run_analysis_passes::h8415522514568150077
  69:     0x7f57f2964a90 - driver::compile_input::h52c7dafd49963360Tba
  70:     0x7f57f2a4aa63 - run_compiler::h473c62e00f865fa9A7b
  71:     0x7f57f2a484de - boxed::F.FnBox<A>::call_box::h10713159552398332324
  72:     0x7f57f2a47e09 - rt::unwind::try::try_fn::h16887904248528792425
  73:     0x7f57f242a84d - __rust_try
  74:     0x7f57f24158f7 - rt::unwind::try::inner_try::hafffff77ddacfa5fvWw
  75:     0x7f57f2a48028 - boxed::F.FnBox<A>::call_box::h5417278073590676257
  76:     0x7f57f2429991 - sys::thread::Thread::new::thread_start::h29dca2a2cf2294b535v
  77:     0x7f57eccc94a3 - start_thread
  78:     0x7f57f208713c - clone
  79:                0x0 - <unknown>

Meta

rustc --version --verbose:

rustc 1.3.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 1.3.0

(I'm on Arch Linux)

Backtrace is above, so I won't be pasting it here again ;)

[apasel422]

Reduced:

trait Bar {
    type Bar;
}

struct ArrayPeano<T: Bar> {
    data: T::Bar,
}

fn foo<T>(a: &ArrayPeano<T>) -> &[T] where T: Bar {
    unsafe { std::mem::transmute(a) }
}

impl Bar for () {
    type Bar = ();
}

fn main() {
    let x: ArrayPeano<()> = ArrayPeano { data: () };
    foo(&x);
}

[apasel422]

It appears that &ArrayPeano<()> is being treated as a fat pointer in rustc_trans::trans::intrinsic::check_intrinsics.

[apasel422]

More specifically, rustc_trans::trans::type_of::sizing_type_of is reporting:

DEBUG:rustc_trans::trans::type_of: sizing_type_of &ArrayPeano<isize>
DEBUG:rustc_trans::trans::type_of: --> mapped t=&ArrayPeano<isize> to llsizingty={ i8*, i8* }

[apasel422]

Weirdly, implementing the trait for isize (independent of what the associated type Bar is set to) results in the expected error.

[apasel422]

This debug output is also concerning:

DEBUG:rustc::middle::ty::util: Ty::impls_bound(ArrayPeano<isize>, Sized) = false

It seems that because isize doesn't implement Bar, <isize as Bar>::Bar is not known to be Sized. This is impossible, because Bar::Bar is not declared ?Sized. This manifests as this ICE because transmute restrictions are tested with isize.

[arielb1]

How did the isize get there? Trying to compute ArrayPeano<isize>: Sized causes a trait error, which makes impls_bound return false. Why are we asking for it?

[arielb1]

intrinsicck tries to use the types isize and [isize] for checking sizedness. This is, like, totally nonfunctional when associated types are involved.

I can't really see how intrinsicck can survive with associated types.

[arielb1]

intrinsicck should really be replaced with an unreachable + generating an rust-lang/rfcs#1229 warning.

[dylanede]

Just bumped into this problem when trying to transmute a reference into a * const (). Is there a known workaround?

Edit: For anyone else wondering, the workaround for transmute is to just use transmute_copy instead, and potentially forget the original if necessary.

[eddyb]

This has been fixed, @apasel422's reduction produces a transmute size mismatch error.