Bug with non-trivial usage of unnamed struct, optional types and switch over tagged union

[sivukhin]

Zig Version

0.9.0-dev.1815+20e19e75f

Steps to Reproduce

Try to compile following code (godbolt link: https://godbolt.org/z/8MqKo6P9W):

const std = @import("std");
const Two = struct { a: ?i32, b: i32 };
const Complex = union(enum) { two: Two };

fn get() Complex {
    return Complex{ .two = Two{ .a = null, .b = 1 } };
}

pub fn main() void {
    const x = get();
    switch (x) {
        Complex.two => |two| std.debug.print("{}\n", .{two.a orelse two.b}),
    }
}

Expected Behavior

Code is perfectly valid and should output string 1

Actual Behavior

Zig compiler crashes with the following error:

broken LLVM module found: Instruction does not dominate all uses!
  %9 = getelementptr inbounds %"struct:12:55", %"struct:12:55"* %0, i32 0, i32 0, !dbg !16575
  store i32 %11, i32* %9, align 4, !dbg !16574

This is a bug in the Zig compiler.thread 11096 panic: 
Unable to dump stack trace: debug info stripped

[iacore]

Zig version 0.10.0-dev.40+303bad998, can reproduce.

When I changed the type of b to ?i32, it broke more.

const std = @import("std");
const Two = struct { a: ?i32, b: ?i32 };
const Complex = union(enum) { two: Two };

fn get() Complex {
    return Complex{ .two = Two{ .a = null, .b = 1 } };
}

pub fn main() void {
    const x = get();
    switch (x) {
        .two => |two| std.debug.print("{}\n", .{two.a orelse two.b}),
    }
}

broken LLVM module found: Instruction does not dominate all uses!
  %9 = getelementptr inbounds %"struct:12:48", %"struct:12:48"* %0, i32 0, i32 0, !dbg !17078
  %14 = getelementptr inbounds %"?i32", %"?i32"* %9, i32 0, i32 1, !dbg !17077
Instruction does not dominate all uses!
  %9 = getelementptr inbounds %"struct:12:48", %"struct:12:48"* %0, i32 0, i32 0, !dbg !17078
  %15 = getelementptr inbounds %"?i32", %"?i32"* %9, i32 0, i32 0, !dbg !17077

This is a bug in the Zig compiler.thread 5194 panic: 
Unable to dump stack trace: debug info stripped

[cryptocode]

Quick note that this can be further reduced to:

const std = @import("std");

const Wrapper = struct { val: ?u8};
pub fn get() Wrapper {
    return .{ .val = null };
}

pub fn main() u8 {
    const x = get();
    var b = @as(u8,1);
    return .{x.val orelse b}[0];
}

Introducing a temporary for the array item "solves" the issue, which may give some indication as to where the culprit is.

var tmp = x.val orelse b;
return .{tmp}[0];

[Vexu]

Duplicate of #3882