ICE: ../src/librustc_trans/mir/operand.rs:82: impossible case reached while using inline assembly

[sethdusek]

So I was messing around with inline assembly and sse, when I tried doing this

#![feature(asm)]

fn xor_buf(buf: [u32; 4], buf2: [u32; 4]) {
    let res: [u32; 4];
    unsafe { asm!("
        movaps xmm0, 1
        xorps xmm0, 2
        movaps 1, xmm0":"=r"(res):"a"(buf), "b"(buf):"xmm0":"intel") };
}

And instead of the expected result I got this

error: internal compiler error: ../src/librustc_trans/mir/operand.rs:82: impossible case reached

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 'Box<Any>', ../src/librustc_errors/lib.rs:655
note: Run with `RUST_BACKTRACE=1` for a backtrace.

You can run it yourself here https://is.gd/VmN4SF

[nagisa]

stack backtrace:
   1:     0x7fd8d02ee03f - std::sys::backtrace::tracing::imp::write::h22f199c1dbb72ba2
   2:     0x7fd8d02fd59d - std::panicking::default_hook::{{closure}}::h9a389c462b6a22dd
   3:     0x7fd8d02fa9c6 - std::panicking::default_hook::h852b4223c1c00c59
   4:     0x7fd8d02fb0a8 - std::panicking::rust_panic_with_hook::hcd9d05f53fa0dafc
   5:     0x7fd8cc746657 - std::panicking::begin_panic::h2f463d37998ebeba
   6:     0x7fd8cc756578 - rustc_errors::Handler::bug::haca77c19c882b432
   7:     0x7fd8cd7b934a - rustc::session::opt_span_bug_fmt::{{closure}}::hfeb850fbe828b399
   8:     0x7fd8cd6f2ee5 - rustc::session::opt_span_bug_fmt::h46e45438a860a75e
   9:     0x7fd8cd6f2d22 - rustc::session::bug_fmt::hde22f071bf5a80ea
  10:     0x7fd8cee95910 - <collections::vec::Vec<T> as core::iter::traits::FromIterator<T>>::from_iter::hc5cbb62358ceb057
  11:     0x7fd8cef3b64f - rustc_trans::mir::rvalue::<impl rustc_trans::mir::MirContext<'bcx, 'tcx>>::trans_rvalue::h2a14de75e2fd4285
  12:     0x7fd8cef29969 - rustc_trans::mir::block::<impl rustc_trans::mir::MirContext<'bcx, 'tcx>>::trans_block::he67d3259f79e4177
  13:     0x7fd8cef27c58 - rustc_trans::mir::trans_mir::h2fb44ecb31cfdffa
  14:     0x7fd8ceec7b83 - rustc_trans::base::trans_closure::h941de14309416d66
  15:     0x7fd8cef47cd4 - rustc_trans::trans_item::TransItem::define::h2e690ccd1ee22f95
  16:     0x7fd8ceecb07a - rustc_trans::base::trans_crate::h9b06de31ed8799d1
  17:     0x7fd8d06827ed - rustc_driver::driver::phase_4_translate_to_llvm::hc3883ea2c4750179
  18:     0x7fd8d06ba8b5 - rustc_driver::driver::compile_input::{{closure}}::h9162a2fa292aeb3f
  19:     0x7fd8d06b1bb7 - rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}::h1928c4704cfe9c61
  20:     0x7fd8d0680224 - rustc_driver::driver::phase_3_run_analysis_passes::he578df6b8805151c
  21:     0x7fd8d0667bfb - rustc_driver::driver::compile_input::h5b63ccd49eeeb98b
  22:     0x7fd8d06931da - rustc_driver::run_compiler::h98c7274e7cb1d11d
  23:     0x7fd8d05cfe0b - std::panicking::try::do_call::h99ed0da044e497c3
  24:     0x7fd8d0305496 - __rust_maybe_catch_panic
  25:     0x7fd8d05ed951 - <F as alloc::boxed::FnBox<A>>::call_box::hbdd5a14cd8e33b97
  26:     0x7fd8d02f9420 - std::sys::thread::Thread::new::thread_start::h50b05608a499d2b2
  27:     0x7fd8c85e2453 - start_thread
  28:     0x7fd8cffc97de - __GI___clone
  29:                0x0 - <unknown>

[cbiffle]

I believe this is the same issue as #37433, which happens when a non-scalar is passed as an input operand. You probably want to be passing pointers instead of buf and res directly, e.g. &buf as *const u32.

[aidanhs]

Small example with same error as top comment (yes, this is invalid):

#![feature(asm)]
fn main() {
    unsafe { asm!("" : : "i"("hello")) };
}

[istankovic]

Still reproducible with rustc 1.26.0-nightly (adf2135ad 2018-03-17).

[levex]

No longer reproduces:

$ rustc +nightly -vV
rustc 1.31.0-nightly (77af31408 2018-10-11)
binary: rustc
commit-hash: 77af314083e5acabf9ba5335e47271f35eef2e99
commit-date: 2018-10-11
host: x86_64-unknown-linux-gnu
release: 1.31.0-nightly
LLVM version: 8.0
$ rustc +nightly 37437.rs 
error[E0669]: invalid value for constraint in inline assembly
 --> 37437.rs:4:14
  |
4 |     unsafe { asm!("" : : "i"(hello)) };
  |              ^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0669`.

[estebank]

There's already a similar test for this case. CC #53787.