ICE: translating unsupported cast: fn() -> u64 (cast_pointer) -> f32 (cast_float)

[gmorenz]

Code:

fn f() -> u64 {
    0
}

fn main() {
    let n = f as f32;
}

Error with backtrace:

src/main.rs:6:9: 6:10 warning: unused variable: `n`, #[warn(unused_variable)] on by default
src/main.rs:6     let n = f as f32;
                      ^
error: internal compiler error: translating unsupported cast: fn() -> u64 (cast_pointer) -> f32 (cast_float)
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libsyntax/diagnostic.rs:163

stack backtrace:
   1:     0x7f6e5389ced0 - rt::backtrace::imp::write::h3e02102493c7a1b79Hp::v0.11.0.pre
   2:     0x7f6e538a3a00 - failure::on_fail::h73803e3fd7728138o3p::v0.11.0.pre
   3:     0x7f6e55a06ef0 - unwind::begin_unwind_inner::h66e3981eb8555b96cZd::v0.11.0.pre
   4:     0x7f6e54e4a4e0 - unwind::begin_unwind::h14114372353668361027::v0.11.0.pre
   5:     0x7f6e54e4ae80 - diagnostic::Handler::bug::h163e51ddd1a017c2Dgc::v0.11.0.pre
   6:     0x7f6e562f9520 - driver::session::Session::bug::h09f59f7b6f35750fdsr::v0.11.0.pre
   7:     0x7f6e5637cbf0 - middle::trans::expr::trans_imm_cast::h261d15fd2f6453feLQh::v0.11.0.pre
   8:     0x7f6e5636e380 - middle::trans::expr::trans_unadjusted::h37391b28c8fd0d0b60f::v0.11.0.pre
   9:     0x7f6e5632a310 - middle::trans::expr::trans_into::hdc05c03d27b262d4JDf::v0.11.0.pre
  10:     0x7f6e56434000 - middle::trans::_match::store_local::closure.85655
  11:     0x7f6e56433cf0 - middle::trans::_match::mk_binding_alloca::h16257314354832004452::v0.11.0.pre
  12:     0x7f6e563eaa70 - middle::trans::_match::store_local::h71f3ff230e537ab6JEu::v0.11.0.pre
  13:     0x7f6e563297e0 - middle::trans::base::init_local::he8478d5bef2cef9cOZp::v0.11.0.pre
  14:     0x7f6e56328d40 - middle::trans::controlflow::trans_stmt::h77aa44239cd8a9d8Mdc::v0.11.0.pre
  15:     0x7f6e5632a940 - middle::trans::controlflow::trans_block::hf4faa65f79a4fae52ic::v0.11.0.pre
  16:     0x7f6e563f0850 - middle::trans::base::trans_closure::hbab3416264edbe7aauq::v0.11.0.pre
  17:     0x7f6e562fa790 - middle::trans::base::trans_fn::hd7d1d11484c269ccbCq::v0.11.0.pre
  18:     0x7f6e562f3230 - middle::trans::base::trans_item::h40a4f8eccf6f8e7eCSq::v0.11.0.pre
  19:     0x7f6e564011b0 - middle::trans::base::trans_crate::h470bfcf3cac093e1JMr::v0.11.0.pre
  20:     0x7f6e56c06570 - driver::driver::phase_4_translate_to_llvm::h2fa30f4b120cdb579Aq::v0.11.0.pre
  21:     0x7f6e56bfd2b0 - driver::driver::compile_input::h1d313b682f9ead2bDeq::v0.11.0.pre
  22:     0x7f6e56cca0c0 - driver::run_compiler::hcc8540f7b478ad28b0s::v0.11.0.pre
  23:     0x7f6e56cc9fd0 - driver::main_args::closure.117522
  24:     0x7f6e56cdf0f0 - task::TaskBuilder<S>::try_future::closure.118663
  25:     0x7f6e56cded10 - task::TaskBuilder<S>::spawn_internal::closure.118640
  26:     0x7f6e55d5c590 - task::spawn_opts::closure.7462
  27:     0x7f6e55a5f290 - rust_try
  28:     0x7f6e55a03500 - unwind::try::h800fde6f36f3558bBNd::v0.11.0.pre
  29:     0x7f6e55a031e0 - task::Task::run::hf743f122a6385418XYc::v0.11.0.pre
  30:     0x7f6e55d5c350 - task::spawn_opts::closure.7408
  31:     0x7f6e55a05da0 - thread::thread_start::hd9510588dd47efddvld::v0.11.0.pre
  32:     0x7f6e53311060 - start_thread
  33:     0x7f6e556cd489 - __clone
  34:                0x0 - <unknown>

[steveklabnik]

Triage: same ICE

This is now rejected:

test.rs:4:13: 4:21 error: illegal cast; cast through an integer first: `fn() -> u64 {f}` as `f64`
test.rs:4     let n = f as f64;

However:

fn f() -> u64 { 0 }

fn main() {
    let n = f as u64 as f64;
}

now segfaults at compile-time:

(lldb) run ./test.rs
Process 52461 launched: '/usr/local/bin/rustc' (x86_64)
test.rs:4:9: 4:10 warning: unused variable: `n`, #[warn(unused_variables)] on by default
test.rs:4     let n = f as u64 as f64;
                  ^
Process 52461 stopped
* thread #2: tid = 0x126ff8, 0x00000001024efc59 librustc_llvm-4e7c5e5c.dylib`llvm::TypeFinder::run(llvm::Module const&, bool) + 73, name = 'rustc', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
    frame #0: 0x00000001024efc59 librustc_llvm-4e7c5e5c.dylib`llvm::TypeFinder::run(llvm::Module const&, bool) + 73
librustc_llvm-4e7c5e5c.dylib`llvm::TypeFinder::run(llvm::Module const&, bool) + 73:
-> 0x1024efc59:  movq   0x8(%rbx), %rsi
   0x1024efc5d:  testq  %rsi, %rsi
   0x1024efc60:  je     0x1024f0070               ; llvm::TypeFinder::run(llvm::Module const&, bool) + 1120
   0x1024efc66:  movzbl 0x8(%rsi), %eax
(lldb) bt
* thread #2: tid = 0x126ff8, 0x00000001024efc59 librustc_llvm-4e7c5e5c.dylib`llvm::TypeFinder::run(llvm::Module const&, bool) + 73, name = 'rustc', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
  * frame #0: 0x00000001024efc59 librustc_llvm-4e7c5e5c.dylib`llvm::TypeFinder::run(llvm::Module const&, bool) + 73
    frame #1: 0x00000001023b4192 librustc_llvm-4e7c5e5c.dylib`llvm::TypePrinting::incorporateTypes(llvm::Module const&) + 34
    frame #2: 0x00000001023c430c librustc_llvm-4e7c5e5c.dylib`llvm::Value::printAsOperand(llvm::raw_ostream&, bool, llvm::Module const*) const + 364
    frame #3: 0x0000000101d42bfa librustc_llvm-4e7c5e5c.dylib`llvm::AsmPrinter::lowerConstant(llvm::Constant const*) + 1610
    frame #4: 0x0000000101d45842 librustc_llvm-4e7c5e5c.dylib`emitGlobalConstantImpl(llvm::Constant const*, llvm::AsmPrinter&) + 2498
    frame #5: 0x0000000101d3dfcb librustc_llvm-4e7c5e5c.dylib`llvm::AsmPrinter::EmitGlobalVariable(llvm::GlobalVariable const*) + 1899
    frame #6: 0x0000000101d418f0 librustc_llvm-4e7c5e5c.dylib`llvm::AsmPrinter::doFinalization(llvm::Module&) + 80
    frame #7: 0x00000001024cd523 librustc_llvm-4e7c5e5c.dylib`llvm::FPPassManager::doFinalization(llvm::Module&) + 83
    frame #8: 0x00000001024cdafd librustc_llvm-4e7c5e5c.dylib`llvm::legacy::PassManagerImpl::run(llvm::Module&) + 1421
    frame #9: 0x00000001013b68c7 librustc_llvm-4e7c5e5c.dylib`LLVMRustWriteOutputFile(Target=<unavailable>, PMR=0x0000000103f05e70, M=0x0000000103f05e70, path=<unavailable>, FileType=CGFT_ObjectFile) + 503 at PassWrapper.cpp:211
    frame #10: 0x00000001005a34ff librustc_trans-4e7c5e5c.dylib`back::write::write_output_file::hdb56d5084c63bc86v6b + 223
    frame #11: 0x00000001005a601f librustc_trans-4e7c5e5c.dylib`back::write::optimize_and_codegen::closure.38410 + 1327
    frame #12: 0x00000001005b0cb9 librustc_trans-4e7c5e5c.dylib`back::write::execute_work_item::hd8db7afca5e1ebc8nZc + 6345
    frame #13: 0x00000001005a7af4 librustc_trans-4e7c5e5c.dylib`back::write::run_passes::hd2f044ab61edb7b9cFc + 6468
    frame #14: 0x0000000100029e1a librustc_driver-4e7c5e5c.dylib`driver::phase_5_run_llvm_passes::hb3416b462f92d001dOa + 362
    frame #15: 0x00000001000055db librustc_driver-4e7c5e5c.dylib`driver::compile_input::heef3a8983ecc9746Iba + 5339
    frame #16: 0x00000001000d644f librustc_driver-4e7c5e5c.dylib`run_compiler::h09dbb9820b7ec68bF5b + 4159
    frame #17: 0x00000001000d3808 librustc_driver-4e7c5e5c.dylib`thunk::F.Invoke$LT$A$C$$u20$R$GT$::invoke::h10490261994158956019 + 600
    frame #18: 0x00000001000d2350 librustc_driver-4e7c5e5c.dylib`rt::unwind::try::try_fn::h10082179094849837244 + 192
    frame #19: 0x0000000103a67089 libstd-4e7c5e5c.dylib`rust_try_inner + 9
    frame #20: 0x0000000103a67076 libstd-4e7c5e5c.dylib`rust_try + 6
    frame #21: 0x00000001000d2b89 librustc_driver-4e7c5e5c.dylib`thunk::F.Invoke$LT$A$C$$u20$R$GT$::invoke::h16026492124957986721 + 1433
    frame #22: 0x00000001039d06f3 libstd-4e7c5e5c.dylib`sys::thread::thread_start::hb52a23d4ffceb69312E + 179
    frame #23: 0x00007fff865272fc libsystem_pthread.dylib`_pthread_body + 131
    frame #24: 0x00007fff86527279 libsystem_pthread.dylib`_pthread_start + 176

FWIW, the error message is also misleading: it should suggest casting through usize.

[steveklabnik]

This is now fixed. It suggests casting through usize, then actually compiles and runs just fine.