incremental compilation test-case regression: llvm/shift_right_plus_left

[andrewrk]

Reproduction:

First, revert 1b1c70c.

$ stage3/bin/zig build test-cases -Denable-llvm
compiler [669/1112] llvm/shift_right_plus_left (llvm, x86_64-linux) [2/2] update [2/3] ... panic: attempt to unwrap error: GenericPoison
/home/andy/dev/zig/src/type.zig:31:23: 0x30257b4 in zigTypeTagOrPoison (test)
        switch (ty.tag()) {
                      ^
/home/andy/dev/zig/lib/std/debug.zig:311:22: 0x2eeb341 in panicExtra__anon_43896 (test)
    std.builtin.panic(msg, trace);
                     ^
/home/andy/dev/zig/lib/std/builtin.zig:851:25: 0x2d13163 in panicUnwrapError (test)
    std.debug.panicExtra(st, "attempt to unwrap error: {s}", .{@errorName(err)});
                        ^
/home/andy/dev/zig/src/type.zig:27:37: 0x2e13ad3 in zigTypeTag (test)
        return ty.zigTypeTagOrPoison() catch unreachable;
                                    ^
/home/andy/dev/zig/src/type.zig:775:33: 0x3068920 in eql (test)
                if (b.zigTypeTag() != .ErrorUnion) return false;
                                ^
/home/andy/dev/zig/src/type.zig:643:25: 0x3068014 in eql (test)
                if (!eql(a_info.return_type, b_info.return_type, mod))
                        ^
/home/andy/dev/zig/src/Module.zig:4471:44: 0x3109144 in semaDecl (test)
                type_changed = !decl.ty.eql(decl_tv.ty, mod);
                                           ^
/home/andy/dev/zig/src/Module.zig:4035:38: 0x2f8b104 in ensureDeclAnalyzed (test)
    const type_changed = mod.semaDecl(decl_index) catch |err| switch (err) {
                                     ^
/home/andy/dev/zig/src/Compilation.zig:3033:38: 0x2f892d9 in processOneJob (test)
            module.ensureDeclAnalyzed(decl_index) catch |err| switch (err) {
                                     ^
/home/andy/dev/zig/src/Compilation.zig:2894:30: 0x2ec0519 in performAllTheWork (test)
            try processOneJob(comp, work_item);
                             ^
/home/andy/dev/zig/src/Compilation.zig:2234:31: 0x2ebdac1 in update (test)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/andy/dev/zig/src/test.zig:1599:28: 0x2cfca91 in runOneCase (test)
            try comp.update();
                           ^
/home/andy/dev/zig/src/test.zig:1314:33: 0x2ce4e56 in workerRunOneCase (test)
        case.result = runOneCase(
                                ^
/home/andy/dev/zig/src/ThreadPool.zig:77:9: 0x2ce4d54 in spawn__anon_4852 (test)
        @call(.{}, func, args);
        ^
/home/andy/dev/zig/src/test.zig:1271:43: 0x2ce5831 in run (test)
                try case_thread_pool.spawn(workerRunOneCase, .{
                                          ^
/home/andy/dev/zig/src/test.zig:65:16: 0x2ce748f in test_0 (test)
    try ctx.run();
               ^
/home/andy/dev/zig/lib/test_runner.zig:79:28: 0x2ce81ab in main (test)
        } else test_fn.func();
                           ^
/home/andy/dev/zig/lib/std/start.zig:566:22: 0x2ce9336 in main (test)
            root.main();
                     ^
error: the following test command crashed:
/home/andy/dev/zig/zig-cache/o/2b9ea9978f70417a3e719f74c7395c37/test /home/andy/dev/zig/build-release/stage3-release/bin/zig