Crash during CBE codegen of inline else prong switching on union

[kcbanner]

Zig Version

0.11.0-dev.3790+95a94ac23

Steps to Reproduce and Observed Behavior

Found this via the CI on #15823 (somehow this branch keeps crashing the compiler :D)

Reduction:

fn InstructionType() type {
    const InstructionOperands = @Type(.{
        .Struct = .{
            .layout = .Auto,
            .fields = &.{},
            .decls = &.{},
            .is_tuple = false,
        },
    });

    return struct {
        const Self = @This();
        operands: InstructionOperands,

        pub fn read() !Self {
            var operands: InstructionOperands = undefined;
            return .{ .operands = operands };
        }
    };
}

pub const Instruction = union(enum) {
    nop: InstructionType(),

    fn readOperands(self: *Instruction) !void {
        switch (self.*) {
            inline else => |*inst| inst.* = try @TypeOf(inst.*).read(),
        }
    }
};

pub fn main() !void {
    var inst = Instruction{ .nop = undefined };
    try inst.readOperands();
}

c:\cygwin64\home\kcbanner\temp>zig-debug build-exe inline_else_crash.zig -fno-LLVM -fno-LLD -ofmt=c -lc -target x86_64-linux -mcpu x86_64 --zig-lib-dir c:\cygwin64\home\kcbanner\kit\zig\lib
thread 39780 panic: reached unreachable code
Analyzing inline_else_crash.zig: inline_else_crash.zig:Instruction.readOperands
      %87 = dbg_block_begin()
      %88 = dbg_var_val(%86, "inst")
      %89 = dbg_stmt(3, 36)
      %90 = validate_deref(%86) node_offset:27:36 to :27:42
      %91 = dbg_stmt(3, 45)
      %92 = typeof_builtin({
        %93 = validate_deref(%86) node_offset:27:57 to :27:63
        %94 = load(%86) node_offset:27:57 to :27:63
        %95 = break_inline(%92, %94)
      }) node_offset:27:49 to :27:64
      %96 = ref(%92) token_offset:27:49 to :27:56
      %97 = dbg_stmt(3, 64)
      %98 = dbg_stmt(3, 69)
      %99 = field_call(.auto, %96, "read", []) node_offset:27:49 to :27:71
    > %100 = try(%99, {
        %101 = err_union_code(%99) node_offset:27:45 to :27:71
        %102 = dbg_stmt(3, 45)
        %103 = ret_node(%101) node_offset:27:45 to :27:71
      }) node_offset:27:45 to :27:71
      %104 = store_node(%86, %100) node_offset:27:36 to :27:71
      %105 = dbg_block_end()
      %106 = break(%86, @InternPool.Index.void_value)
    For full context, use the command
      zig ast-check -t inline_else_crash.zig

  in inline_else_crash.zig: inline_else_crash.zig:Instruction.readOperands
    > %86 = switch_block_ref(%80,
        by_ref inline else => {%87..%106}) node_offset:26:9 to :26:15
  in inline_else_crash.zig: inline_else_crash.zig:Instruction.readOperands
    > %81 = block({%82..%110}) node_offset:25:47 to :25:48
  in inline_else_crash.zig: inline_else_crash.zig:main
    > %136 = try(%135, {%137..%139}) node_offset:34:5 to :34:28
  in inline_else_crash.zig: inline_else_crash.zig:main
    > %118 = block({%119..%143}) node_offset:32:21 to :32:22
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMain
    > %2958 = is_non_err(%2957)
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMain
    > %2960 = block({%2954..%2959})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMain
    > %2951 = block({%2952..%3096})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMain
    > %2861 = switch_block(%2859,
        else => {%3099..%3105},
        %2862 => {%2863..%2875},
        %2876 => {%2877..%2895},
        by_val %2896 => {%2897..%2948},
        %2949 => {%2950..%3098})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMain
    > %2845 = block({%2846..%3109})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:initEventLoopAndCallMain
    > %2566 = builtin_call(%2564, %2565, @InternPool.Index.empty_struct)
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:initEventLoopAndCallMain
    > %2413 = block({%2414..%2574})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMainWithArgs
    > %2189 = call(.auto, %2187, [])
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:callMainWithArgs
    > %2152 = block({%2153..%2197})
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:main
    > %2348 = builtin_call(%2336, %2337, %2347)
  in c:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig: start.zig:main
    > %2219 = block({%2220..%2356})

C:\cygwin64\home\kcbanner\kit\zig\lib\std\debug.zig:272:14: 0x7ff6e7216317 in assert (zig.exe.obj)
    comptime format: []const u8,
             ^
C:\cygwin64\home\kcbanner\kit\zig\src\InternPool.zig:3581:19: 0x7ff6e72cff35 in get (zig.exe.obj)
            assert(ip.isIntegerType(int.ty));
                  ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:6673:31: 0x7ff6e736bdfd in intern (zig.exe.obj)
    return mod.intern_pool.get(mod.gpa, key);
                              ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:6867:25: 0x7ff6e75cf1f2 in intValue_u64 (zig.exe.obj)
    const i = try intern(mod, .{ .int = .{
                        ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:6851:60: 0x7ff6e77a19bb in intValue__anon_119455 (zig.exe.obj)
    if (std.math.cast(u64, x)) |casted| return intValue_u64(mod, ty, casted);
                                                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\codegen\c.zig:5664:71: 0x7ff6e842b506 in airErrUnionPayloadPtrSet (zig.exe.obj)
        try f.object.dg.renderValue(writer, error_ty, try mod.intValue(error_ty, 0), .Other);
                                                                      ^
C:\cygwin64\home\kcbanner\kit\zig\src\codegen\c.zig:3042:73: 0x7ff6e7fb560b in genBodyInner (zig.exe.obj)
            .errunion_payload_ptr_set    => try airErrUnionPayloadPtrSet(f, inst),
                                                                        ^
C:\cygwin64\home\kcbanner\kit\zig\src\codegen\c.zig:2754:25: 0x7ff6e7fb6935 in genBody (zig.exe.obj)
        try genBodyInner(f, body);
                        ^
C:\cygwin64\home\kcbanner\kit\zig\src\codegen\c.zig:2795:20: 0x7ff6e79c15ce in genBodyResolveState (zig.exe.obj)
        try genBody(f, body);
                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\codegen\c.zig:2616:28: 0x7ff6e79c06ff in genFunc (zig.exe.obj)
    try genBodyResolveState(f, undefined, &.{}, main_body, false);
                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\link\C.zig:136:20: 0x7ff6e79c23bb in updateFunc (zig.exe.obj)
    codegen.genFunc(&function) catch |err| switch (err) {
                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\link.zig:574:77: 0x7ff6e771e7d4 in updateFunc (zig.exe.obj)
            .c     => return @fieldParentPtr(C,     "base", base).updateFunc(module, func_index, air, liveness),
                                                                            ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:4215:37: 0x7ff6e7539dab in ensureFuncBodyAnalyzed (zig.exe.obj)
            comp.bin_file.updateFunc(mod, func_index, air, liveness) catch |err| switch (err) {
                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30201:36: 0x7ff6e80c3019 in ensureFuncBodyAnalyzed (zig.exe.obj)
    sema.mod.ensureFuncBodyAnalyzed(func) catch |err| {
                                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:33965:40: 0x7ff6e7b051d9 in resolveInferredErrorSet (zig.exe.obj)
        try sema.ensureFuncBodyAnalyzed(ies.func);
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30529:53: 0x7ff6e7ad2209 in analyzeIsNonErrComptimeOnly (zig.exe.obj)
                    try sema.resolveInferredErrorSet(block, src, ies_index);
                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:17979:60: 0x7ff6e7ad1064 in zirTry (zig.exe.obj)
    const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
                                                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1641:67: 0x7ff6e774b156 in analyzeBodyInner (zig.exe.obj)
                if (!block.is_comptime) break :blk try sema.zirTry(block, inst);
                                                                  ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:10150:45: 0x7ff6e8036926 in resolveProngComptime (zig.exe.obj)
                return sema.resolveBlockBody(spa.parent_block, src, child_block, prong_body, spa.switch_block_inst, merges);
                                            ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:11439:40: 0x7ff6e7a1ce70 in zirSwitchBlock (zig.exe.obj)
        return spa.resolveProngComptime(
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1011:69: 0x7ff6e773d860 in analyzeBodyInner (zig.exe.obj)
            .switch_block_ref             => try sema.zirSwitchBlock(block, inst, true),
                                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:5551:21: 0x7ff6e771caad in analyzeFnBody (zig.exe.obj)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:4149:40: 0x7ff6e7539425 in ensureFuncBodyAnalyzed (zig.exe.obj)
            var air = mod.analyzeFnBody(func_index, sema_arena) catch |err| switch (err) {
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30201:36: 0x7ff6e80c3019 in ensureFuncBodyAnalyzed (zig.exe.obj)
    sema.mod.ensureFuncBodyAnalyzed(func) catch |err| {
                                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:33965:40: 0x7ff6e7b051d9 in resolveInferredErrorSet (zig.exe.obj)
        try sema.ensureFuncBodyAnalyzed(ies.func);
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30529:53: 0x7ff6e7ad2209 in analyzeIsNonErrComptimeOnly (zig.exe.obj)
                    try sema.resolveInferredErrorSet(block, src, ies_index);
                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:17979:60: 0x7ff6e7ad1064 in zirTry (zig.exe.obj)
    const is_non_err = try sema.analyzeIsNonErrComptimeOnly(parent_block, operand_src, err_union);
                                                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1641:67: 0x7ff6e774b156 in analyzeBodyInner (zig.exe.obj)
                if (!block.is_comptime) break :blk try sema.zirTry(block, inst);
                                                                  ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:5551:21: 0x7ff6e771caad in analyzeFnBody (zig.exe.obj)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:4149:40: 0x7ff6e7539425 in ensureFuncBodyAnalyzed (zig.exe.obj)
            var air = mod.analyzeFnBody(func_index, sema_arena) catch |err| switch (err) {
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30201:36: 0x7ff6e80c3019 in ensureFuncBodyAnalyzed (zig.exe.obj)
    sema.mod.ensureFuncBodyAnalyzed(func) catch |err| {
                                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:33965:40: 0x7ff6e7b051d9 in resolveInferredErrorSet (zig.exe.obj)
        try sema.ensureFuncBodyAnalyzed(ies.func);
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30529:53: 0x7ff6e7ad2209 in analyzeIsNonErrComptimeOnly (zig.exe.obj)
                    try sema.resolveInferredErrorSet(block, src, ies_index);
                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:30557:56: 0x7ff6e80149ca in analyzeIsNonErr (zig.exe.obj)
    const result = try sema.analyzeIsNonErrComptimeOnly(block, src, operand);
                                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:17863:32: 0x7ff6e7a0952b in zirIsNonErr (zig.exe.obj)
    return sema.analyzeIsNonErr(block, src, operand);
                               ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:987:66: 0x7ff6e773c3b1 in analyzeBodyInner (zig.exe.obj)
            .is_non_err                   => try sema.zirIsNonErr(block, inst),
                                                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:10129:45: 0x7ff6e8036642 in resolveProngComptime (zig.exe.obj)
                return sema.resolveBlockBody(spa.parent_block, src, child_block, prong_body, spa.switch_block_inst, merges);
                                            ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:11356:52: 0x7ff6e7a1b610 in zirSwitchBlock (zig.exe.obj)
                    return spa.resolveProngComptime(
                                                   ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1010:69: 0x7ff6e773d77e in analyzeBodyInner (zig.exe.obj)
            .switch_block                 => try sema.zirSwitchBlock(block, inst, false),
                                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:7013:33: 0x7ff6e7ffc218 in analyzeCall (zig.exe.obj)
                sema.analyzeBody(&child_block, fn_info.body) catch |err| switch (err) {
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:22760:28: 0x7ff6e7a5dc29 in zirBuiltinCall (zig.exe.obj)
    return sema.analyzeCall(block, func, func_ty, func_src, call_src, modifier, ensure_result_used, resolved_args, null, null);
                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1060:69: 0x7ff6e774026e in analyzeBodyInner (zig.exe.obj)
            .builtin_call                 => try sema.zirBuiltinCall(block, inst),
                                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:7013:33: 0x7ff6e7ffc218 in analyzeCall (zig.exe.obj)
                sema.analyzeBody(&child_block, fn_info.body) catch |err| switch (err) {
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:6533:32: 0x7ff6e79f7f43 in zirCall__anon_134522 (zig.exe.obj)
        return sema.analyzeCall(block, func, func_ty, callee_src, call_src, modifier, ensure_result_used, resolved_args, bound_arg_src, call_dbg_node);
                               ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:944:62: 0x7ff6e7739e74 in analyzeBodyInner (zig.exe.obj)
            .call                         => try sema.zirCall(block, inst, .direct),
                                                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:7013:33: 0x7ff6e7ffc218 in analyzeCall (zig.exe.obj)
                sema.analyzeBody(&child_block, fn_info.body) catch |err| switch (err) {
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:22760:28: 0x7ff6e7a5dc29 in zirBuiltinCall (zig.exe.obj)
    return sema.analyzeCall(block, func, func_ty, func_src, call_src, modifier, ensure_result_used, resolved_args, null, null);
                           ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1060:69: 0x7ff6e774026e in analyzeBodyInner (zig.exe.obj)
            .builtin_call                 => try sema.zirBuiltinCall(block, inst),
                                                                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5629:34: 0x7ff6e809f884 in resolveBlockBody (zig.exe.obj)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:5612:33: 0x7ff6e7ad5ab9 in zirBlock (zig.exe.obj)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:1486:49: 0x7ff6e774d0cf in analyzeBodyInner (zig.exe.obj)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
C:\cygwin64\home\kcbanner\kit\zig\src\Sema.zig:823:30: 0x7ff6e7997a4e in analyzeBody (zig.exe.obj)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:5551:21: 0x7ff6e771caad in analyzeFnBody (zig.exe.obj)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
C:\cygwin64\home\kcbanner\kit\zig\src\Module.zig:4149:40: 0x7ff6e7539425 in ensureFuncBodyAnalyzed (zig.exe.obj)
            var air = mod.analyzeFnBody(func_index, sema_arena) catch |err| switch (err) {
                                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\Compilation.zig:3143:42: 0x7ff6e75372a4 in processOneJob (zig.exe.obj)
            module.ensureFuncBodyAnalyzed(func) catch |err| switch (err) {
                                         ^
C:\cygwin64\home\kcbanner\kit\zig\src\Compilation.zig:3080:30: 0x7ff6e73c1f34 in performAllTheWork (zig.exe.obj)
            try processOneJob(comp, work_item, main_progress_node);
                             ^
C:\cygwin64\home\kcbanner\kit\zig\src\Compilation.zig:2029:31: 0x7ff6e73be2df in update (zig.exe.obj)
    try comp.performAllTheWork(main_progress_node);
                              ^
C:\cygwin64\home\kcbanner\kit\zig\src\main.zig:3839:24: 0x7ff6e73ec451 in updateModule (zig.exe.obj)
        try comp.update(main_progress_node);
                       ^
C:\cygwin64\home\kcbanner\kit\zig\src\main.zig:3274:17: 0x7ff6e72675d2 in buildOutputType (zig.exe.obj)
    updateModule(comp) catch |err| switch (err) {
                ^
C:\cygwin64\home\kcbanner\kit\zig\src\main.zig:269:31: 0x7ff6e71fcd41 in mainArgs (zig.exe.obj)
        return buildOutputType(gpa, arena, args, .{ .build = .Exe });
                              ^
C:\cygwin64\home\kcbanner\kit\zig\src\main.zig:213:20: 0x7ff6e71fa93e in main (zig.exe.obj)
    return mainArgs(gpa, arena, args);
                   ^
C:\cygwin64\home\kcbanner\kit\zig\lib\std\start.zig:507:80: 0x7ff6e71fa601 in main (zig.exe.obj)
    return @call(.always_inline, callMainWithArgs, .{ @intCast(usize, c_argc), @ptrCast([*][*:0]u8, c_argv), envp });
                                                                               ^
???:?:?: 0x7ff6e913afb5 in ??? (zig.exe)
???:?:?: 0x7ff6e913b01b in ??? (zig.exe)
???:?:?: 0x7ffe5cb37613 in ??? (KERNEL32.DLL)
???:?:?: 0x7ffe5e7426f0 in ??? (ntdll.dll)

Expected Behavior

No crash.

[kcbanner]

Oops, that isn't actually the reduction - my stdlib is causing the crash. Fixed reduction.

[kcbanner]

Further reduced to this:

const InstructionType = struct {
    operands: void,

    pub fn read() !InstructionType {
        return .{ .operands = {} };
    }
};

pub fn main() !void {
    var inst: InstructionType = undefined;
    (&inst).* = try InstructionType.read();
}

It wasn't anything to do with inline else, but a bug with airErrUnionPayloadPtrSet.