EarlyOtherwiseBranch introduces access to a dead local variable #159618

#![feature(custom_mir, core_intrinsics)]
use std::intrinsics::mir::*;
#[custom_mir(dialect = "runtime")]
fn main() {
    mir! {
        let a: u64;
        let b: u64;
        { a = 1; StorageDead(b); match a { 0 => bb1, _ => bb3 }}
        bb1 = { match b { 0 => bb1, _ => bb3 } }
        bb2 = { Goto(bb4) }
        bb3 = { Goto(bb4) }
        bb4 = { Return() }
    }
}

fn main() -> () {
    let mut _0: ();
    let mut _1: u64;
    let mut _2: u64;
    let mut _3: bool;
    let mut _4: bool;

    bb0: {
        _1 = const 1_u64;
        StorageDead(_2);
        _3 = Ne(copy _1, copy _2); // undefined behavior: _2 is dead
        switchInt(move _3) -> [0: bb3, otherwise: bb2];
    }

    bb1: {
        _4 = Ne(copy _2, copy _2);
        switchInt(move _4) -> [0: bb4, otherwise: bb2];
    }

    bb2: {
        return;
    }

    bb3: {
        switchInt(copy _1) -> [0: bb1, otherwise: bb2];
    }

    bb4: {
        switchInt(copy _2) -> [0: bb1, otherwise: bb2];
    }
}