ICE with match on non-const functions in constant definitions

[K900]

enum Thing { This, That }

fn non_const() -> Thing {
    Thing::This
}

pub const Q: i32 = match non_const() {
    Thing::This => 1,
    Thing::That => 0
};

error: internal compiler error: /checkout/src/librustc_mir/build/mod.rs:534: no terminator on block 10

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: rustc 1.24.0-nightly (0077d128d 2017-12-14) running on x86_64-unknown-linux-gnu

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:448:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.

(playground)

This ICEs on nightly/beta, but produces a correct error on stable.

Originally reported on Reddit here.

[eddyb]

cc @arielb1 @nikomatsakis Did anything change in pattern-matching between stable and beta?

[K900]

I'm bisecting as I'm writing this, but it's taking a while on my dual-core laptop :(

[eddyb]

cc @Mark-Simulacrum

[Mark-Simulacrum]

cc @est31 -- Is there a chance you could run bisect? We should really get playground to be capable of doing it...

[est31]

@Mark-Simulacrum not today, sorry. Maybe on friday...

[Deewiant]

I decided to bisect this myself and found 5b1cc1d (or #45821 as a whole) to be the cause, and created #46877 to fix it.