internal compiler error

[wolfiestyle]

Got this error while trying to compile a simple program (https://gist.github.com/darkstalker/c8c605ddc56aa4d31fc8). It uses the num 0.1.24 crate.

  error: internal compiler error: Impl DefId { krate: 2, node: 24906 } was matchable against Obligation(predicate=Binder(TraitPredicate(core::ops::Mul<_>)),depth=1) but now is not
  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: run with `RUST_BACKTRACE=1` for a backtrace
  thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:209

The stack trace and rustc version are here: https://gist.github.com/darkstalker/f4ce878d18a4f5c489d7

[arielb1]

duplicate of #22645.