rustc panic with divide by zero

[bpa]

thread 'rustc' panicked at 'attempt to divide by zero', librustc_trans/abi.rs:430:26

Stripped down version of code to reproduce

mod a {
    pub trait A {}
}

mod b {
    pub struct Builder {}

    pub fn new() -> Builder {
        Builder {}
    }

    impl Builder {
        pub fn with_a(&mut self, _a: fn() -> ::a::A) {}
    }
}

pub use self::b::new;

Meta rustc --version --verbose:

rustc 1.26.0 (a77568041 2018-05-07)
binary: rustc
commit-hash: a7756804103447ea4e68a71ccf071e7ad8f7a03e
commit-date: 2018-05-07
host: x86_64-unknown-linux-gnu
release: 1.26.0
LLVM version: 6.0

stack backtrace:

   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:207
   3: std::panicking::default_hook
             at libstd/panicking.rs:223
   4: core::ops::function::Fn::call
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:403
   6: std::panicking::begin_panic_fmt
             at libstd/panicking.rs:349
   7: rust_begin_unwind
             at libstd/panicking.rs:325
   8: core::panicking::panic_fmt
             at libcore/panicking.rs:72
   9: core::panicking::panic
             at libcore/panicking.rs:51
  10: rustc_trans::abi::CastTarget::llvm_type
  11: rustc_trans::abi::FnType::llvm_type
  12: <rustc::ty::layout::TyLayout<'tcx> as rustc_trans::type_of::LayoutLlvmExt<'tcx>>::llvm_type
  13: rustc_trans::abi::FnType::llvm_type
  14: rustc_trans::declare::declare_fn
  15: rustc_trans::trans_item::predefine_fn
  16: rustc_trans::trans_item::MonoItemExt::predefine
  17: rustc_trans::base::compile_codegen_unit
  18: rustc::dep_graph::graph::DepGraph::with_task_impl
  19: rustc_errors::Handler::track_diagnostics
  20: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  21: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::force
  22: rustc::ty::maps::<impl rustc::ty::maps::queries::compile_codegen_unit<'tcx>>::try_get
  23: rustc::ty::maps::TyCtxtAt::compile_codegen_unit
  24: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::compile_codegen_unit
  25: rustc_trans::base::trans_crate
  26: <rustc_trans::LlvmTransCrate as rustc_trans_utils::trans_crate::TransCrate>::trans_crate
  27: rustc::util::common::time
  28: rustc_driver::driver::phase_4_translate_to_llvm
  29: rustc_driver::driver::compile_input::{{closure}}
  30: <std::thread::local::LocalKey<T>>::with
  31: <std::thread::local::LocalKey<T>>::with
  32: rustc::ty::context::TyCtxt::create_and_enter
  33: rustc_driver::driver::compile_input
  34: rustc_driver::run_compiler_impl
  35: syntax::with_globals

[nikomatsakis]

Pending fix in #50819. Assigned to the current reviewer ( @michaelwoerister ).