truncate to a u0 with a variable causes a compiler error

[winksaville]

For example, this code:

const std = @import("std");
const assert = std.debug.assert;

test "truncate.u0.literal" {
    var z = @truncate(u0, 0);
    assert(z == 0);
}

test "truncate.u0.const" {
    const c0: usize = 0;
    var z = @truncate(u0, c0);
    assert(z == 0);
}

test "truncate.u0.var" {
    var d: u8 = 2;
    var z = @truncate(u0, d);
    assert(z == 0);
}

Causes the compiler to generate an error:

$ zig test truncate-u0.zig 
Trunc only produces integer
  trunc i8 %1 to void, !dbg !664
LLVM ERROR: Broken module found, compilation aborted!

But If I comment out test "truncate.u0.var" the first two tests for literal and const work:

$ zig test truncate-u0.zig 
Test 1/2 truncate.u0.literal...OK
Test 2/2 truncate.u0.const...OK
All tests passed.

[winksaville]

The actual source is here.