Compiler segfault/infinite loop when @splat used with scalar type

[Pyrolistical]

Zig Version

0.11.0-dev.4246+71dfce31b

Steps to Reproduce and Observed Behavior

Env:

$ sw_vers
ProductName:            macOS
ProductVersion:         13.4
BuildVersion:           22F66

$ uname -a
Darwin My-MacBook-Air.local 22.5.0 Darwin Kernel Version 22.5.0: Mon Apr 24 20:53:44 PDT 2023; root:xnu-8796.121.2~5/RELEASE_ARM64_T8103 arm64

Given repo.zig

pub fn main() void {
    const segfaults: u8 = @splat(0);
    _ = segfaults;
}

Run zig build-exe repo.zig

Sometimes it segfaults, sometimes bus error, sometimes works correctly, sometimes goes into infinite loop:

$ zig build-exe repo.zig
zsh: segmentation fault  zig build-exe repo.zig
$ zig build-exe repo.zig
zsh: bus error  zig build-exe repo.zig
$ zig build-exe repo.zig
repo2.zig:2:27: error: expected vector type, found 'u8'
    const segfaults: u8 = @splat(0);
                          ^~~~~~~~~
referenced by:
    callMain: zig/lib/std/start.zig:598:17
    initEventLoopAndCallMain: zig/lib/std/start.zig:542:34
    remaining reference traces hidden; use '-freference-trace' to see all reference traces
$ zig build-exe repo.zig
^C

Expected Behavior

Compiler error:

$ zig build-exe repo.zig
repo2.zig:2:27: error: expected vector type, found 'u8'
    const segfaults: u8 = @splat(0);
                          ^~~~~~~~~
referenced by:
    callMain: zig/lib/std/start.zig:598:17
    initEventLoopAndCallMain: zig/lib/std/start.zig:542:34
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

[xdBronch]

heres a stack trace

thread 431559 panic: reached unreachable code
Analyzing a.zig: a.zig:main
      %6 = dbg_block_begin()
      %7 = dbg_stmt(2, 5)
    > %8 = elem_type_index(@InternPool.Index.u8_type, 0)
      %9 = as_node(%8, @InternPool.Index.zero)
      %10 = splat(@InternPool.Index.u8_type, %9)
      %11 = as_node(@InternPool.Index.u8_type, %10)
      %12 = dbg_var_val(%11, "a")
      %13 = dbg_stmt(3, 5)
      %14 = ensure_result_non_error(%11)
      %15 = dbg_block_end()
      %16 = restore_err_ret_index(%5, %4294967211)
      %17 = break(%5, @InternPool.Index.void_value)
    For full context, use the command
      zig ast-check -t a.zig

  in a.zig: a.zig:main
    > %5 = block({%6..%17})

/home/user/zig/lib/std/debug.zig:344:14: 0x37f889c in assert (zig)
    if (!ok) unreachable; // assertion failure
             ^
/home/user/zig/src/Sema.zig:7713:11: 0x3fecffc in zirElemTypeIndex (zig)
    assert(indexable_ty.isIndexable(mod)); // validated by a previous instruction
          ^
/home/user/zig/src/Sema.zig:1020:71: 0x3d1f046 in analyzeBodyInner (zig)
            .elem_type_index              => try sema.zirElemTypeIndex(block, inst),
                                                                      ^
/home/user/zig/src/Sema.zig:5725:34: 0x467bef9 in resolveBlockBody (zig)
        if (sema.analyzeBodyInner(child_block, body)) |_| {
                                 ^
/home/user/zig/src/Sema.zig:5708:33: 0x40c0063 in zirBlock (zig)
    return sema.resolveBlockBody(parent_block, src, &child_block, body, inst, &label.merges);
                                ^
/home/user/zig/src/Sema.zig:1543:49: 0x3d2fca0 in analyzeBodyInner (zig)
                    break :blk try sema.zirBlock(block, inst, tags[inst] == .block_comptime);
                                                ^
/home/user/zig/src/Sema.zig:881:30: 0x3f79e28 in analyzeBody (zig)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
/home/user/zig/src/Module.zig:5323:21: 0x3cfd3b4 in analyzeFnBody (zig)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
/home/user/zig/src/Module.zig:3922:40: 0x3ae08a6 in ensureFuncBodyAnalyzed (zig)
            var air = mod.analyzeFnBody(func_index, sema_arena) catch |err| switch (err) {
                                       ^
/home/user/zig/src/Compilation.zig:3207:42: 0x3ade960 in processOneJob (zig)
            module.ensureFuncBodyAnalyzed(func) catch |err| switch (err) {
                                         ^
/home/user/zig/src/Compilation.zig:3144:30: 0x394067d in performAllTheWork (zig)
            try processOneJob(comp, work_item, main_progress_node);
                             ^
/home/user/zig/src/Compilation.zig:2067:31: 0x393c031 in update (zig)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/user/zig/src/main.zig:3864:24: 0x396bd10 in updateModule (zig)
        try comp.update(main_progress_node);
                       ^
/home/user/zig/src/main.zig:3285:17: 0x399afd8 in buildOutputType (zig)
    updateModule(comp) catch |err| switch (err) {
                ^
/home/user/zig/src/main.zig:277:31: 0x37fac75 in mainArgs (zig)
        return buildOutputType(gpa, arena, args, .run);
                              ^
/home/user/zig/src/main.zig:213:20: 0x37f7d05 in main (zig)
    return mainArgs(gpa, arena, args);
                   ^
/home/user/zig/lib/std/start.zig:608:37: 0x37f775e in main (zig)
            const result = root.main() catch |err| {
                                    ^
???:?:?: 0x7f22b5bde84f in ??? (libc.so.6)
[1]    431559 IOT instruction (core dumped)  zig/build/stage4/bin/zig run a.zig

[Pyrolistical]

@mlugg I found another segfault. Is this crash the same issue?

pub fn main() void {
    _ = @mulAdd(f32, @splat(0), undefined, undefined);
}

[alichraghi]

yes. because Result type (f32) is not indexable