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Bit casting packed struct gives LLVM Error #991

Hejsil opened this Issue May 6, 2018 · 4 comments


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Hejsil commented May 6, 2018

pub const LevelUpMove = packed struct {
    move_id: u9,
    level: u7,

test "" {
    var move = LevelUpMove { .move_id = 0, .level = 1 };
    var v = @bitCast(u16, move);
Invalid bitcast
  %2 = bitcast %LevelUpMove* %move to i16, !dbg !622
LLVM ERROR: Broken module found, compilation aborted!

@Hejsil Hejsil added the bug label May 6, 2018

@andrewrk andrewrk added this to the 0.3.0 milestone May 7, 2018


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tgschultz commented Jun 8, 2018

Ran into this recently, with the @bitCast going in the opposite direction:

@bitcast(PackedStruct, [16]u8);

I got a different error from LLVM and I'm logging it here just in case it helps at all.

LLVM ERROR: Cannot select: 0x1e1174dc2a8: i32 = bitcast FrameIndex:i64<1>
  0x1e117214c08: i64 = FrameIndex<1>
In function: BufferReader_peekReadRaw

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dbandstra commented Jun 14, 2018

I tried to bitcast a primitive value (e.g. u8) to a packed struct and got errors as well.

// stripped down example
const Attributes = packed struct {
  contents: u8,

test "asdf" {
  const byte: u8 = 0;
  const attributes = @bitCast(Attributes, byte);

This gives the compile error:

TODO buf_read_value_bytes struct type

If you change const byte: u8 = 0; to var byte: u8 = 0;, then the compile error becomes:

zig: /home/dbandstra/zig/src/codegen.cpp:1779: LLVMOpaqueValue* gen_assign_raw(CodeGen*, LLVMValueRef, TypeTableEntry*, LLVMValueRef): Assertion `LLVMGetTypeKind(LLVMTypeOf(value)) == LLVMPointerTypeKind' failed.

The same errors happen if the struct is not packed.


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kevinw commented Jun 26, 2018

I hit a variant of this with @ptrCast here:

const b_ptr = @ptrCast([*]const c.sg_buffer_desc, &buffer_desc);

The full LLVM traceback is in the README of that repository.


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kevinw commented Jun 26, 2018

I ran a zig debug build on the above error and got this assertion:

Assertion failed: (LLVMGetTypeKind(LLVMTypeOf(value)) == LLVMPointerTypeKind), function gen_assign_raw, file /Users/kevin/src/zig/src/codegen.cpp, line 1769.

The backtrace in lldb:

(lldb) bt
* thread #1, queue = '', stop reason = signal SIGABRT
  * frame #0: 0x00007fff59533b6e libsystem_kernel.dylib`__pthread_kill + 10
    frame #1: 0x00007fff596fe080 libsystem_pthread.dylib`pthread_kill + 333
    frame #2: 0x00007fff5948f1ae libsystem_c.dylib`abort + 127
    frame #3: 0x00007fff594571ac libsystem_c.dylib`__assert_rtn + 320
    frame #4: 0x00000001000479b2 zig`gen_assign_raw(g=0x000000010600b400, ptr=0x000000010945a3d8, ptr_type=0x000000010945e630, value=0x000000010945e5e0) at codegen.cpp:1769
    frame #5: 0x000000010003e1e0 zig`ir_render_decl_var(g=0x000000010600b400, executable=0x0000000109109f58, decl_var_instruction=0x000000010b3e7550) at codegen.cpp:2834
    frame #6: 0x000000010003d2b7 zig`ir_render_instruction(g=0x000000010600b400, executable=0x0000000109109f58, instruction=0x000000010b3e7550) at codegen.cpp:4767
    frame #7: 0x000000010003b9b2 zig`ir_render(g=0x000000010600b400, fn_entry=0x0000000109109e00) at codegen.cpp:4938
    frame #8: 0x000000010003349b zig`do_code_gen(g=0x000000010600b400) at codegen.cpp:5922
    frame #9: 0x0000000100031741 zig`codegen_build(g=0x000000010600b400) at codegen.cpp:7601
    frame #10: 0x00000001000c3fb4 zig`main(argc=25, argv=0x00007ffeefbff708) at main.cpp:903
    frame #11: 0x00007fff593e3015 libdyld.dylib`start + 1
    frame #12: 0x00007fff593e3015 libdyld.dylib`start + 1
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