[SystemZ] `UNREACHABLE executed at llvm/lib/CodeGen/ValueTypes.cpp:252!` due to call with `type { i128 }` argument

[alexrp]

target datalayout = "E-m:e-i1:8:16-i8:8:16-i64:64-f128:64-v128:64-a:8:16-n32:64"
target triple = "s390x-unknown-linux6.12.43-gnu2.41.0"

%main.U128 = type { i128 }

define ccc void @"main.test.C ABI integers"() {
Entry:
  call void null(%main.U128 zeroinitializer)
  ret void
}

❯ llc --version | head -n2
LLVM (http://llvm.org/):
  LLVM version 21.1.0
❯ llc reduced.ll
Unknown type!
UNREACHABLE executed at /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/ValueTypes.cpp:252!
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: llc reduced.ll
1.      Running pass 'Function Pass Manager' on module 'reduced.ll'.
2.      Running pass 'SystemZ DAG->DAG Pattern Instruction Selection' on function '@"main.test.C ABI integers"'
 #0 0x0000772e5e391af0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/alexrp/Source/llvm-project/llvm/lib/Support/Unix/Signals.inc:838:3
 #1 0x0000772e5e38e9b4 llvm::sys::RunSignalHandlers() /home/alexrp/Source/llvm-project/llvm/lib/Support/Signals.cpp:104:20
 #2 0x0000772e5e38f1e9 SignalHandler(int, siginfo_t*, void*) /home/alexrp/Source/llvm-project/llvm/lib/Support/Unix/Signals.inc:426:14
 #3 0x0000772e5cc458d0 (/lib/x86_64-linux-gnu/libc.so.6+0x458d0)
 #4 0x0000772e5cca49bc __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x0000772e5cca49bc __pthread_kill_internal ./nptl/pthread_kill.c:89:10
 #6 0x0000772e5cca49bc pthread_kill ./nptl/pthread_kill.c:100:10
 #7 0x0000772e5cc4579e raise ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x0000772e5cc288cd internal_signal_block_all ./stdlib/../sysdeps/unix/sysv/linux/internal-signals.h:81:3
 #9 0x0000772e5cc288cd __abort_lock_wrlock ./stdlib/abort.c:58:3
#10 0x0000772e5cc288cd abort ./stdlib/abort.c:81:3
#11 0x0000772e5e2a543e (/opt/llvm-21/bin/../lib/libLLVM.so.21.1+0xea543e)
#12 0x0000772e5ec0ed9b (/opt/llvm-21/bin/../lib/libLLVM.so.21.1+0x180ed9b)
#13 0x0000772e5ec0ee6c llvm::EVT::getEVT(llvm::Type*, bool) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/ValueTypes.cpp:302:40
#14 0x0000772e626fb2e4 llvm::SystemZTargetLowering::LowerCall(llvm::TargetLowering::CallLoweringInfo&, llvm::SmallVectorImpl<llvm::SDValue>&) const /home/alexrp/Source/llvm-project/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp:2284:37
#15 0x0000772e5eebcf27 llvm::SmallVectorBase<unsigned int>::size() const /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/SmallVector.h:79:32
#16 0x0000772e5eebcf27 llvm::SmallVectorImpl<llvm::SDValue>::operator=(llvm::SmallVectorImpl<llvm::SDValue> const&) /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/SmallVector.h:1012:28
#17 0x0000772e5eebcf27 llvm::SmallVector<llvm::SDValue, 4u>::operator=(llvm::SmallVector<llvm::SDValue, 4u> const&) /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/SmallVector.h:1243:34
#18 0x0000772e5eebcf27 llvm::TargetLowering::LowerCallTo(llvm::TargetLowering::CallLoweringInfo&) const /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:11255:16
#19 0x0000772e5eec7c3b llvm::SelectionDAGBuilder::lowerInvokable(llvm::TargetLowering::CallLoweringInfo&, llvm::BasicBlock const*) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:8841:3
#20 0x0000772e5eede236 llvm::SelectionDAGBuilder::LowerCallTo(llvm::CallBase const&, llvm::SDValue, bool, bool, llvm::BasicBlock const*, llvm::TargetLowering::PtrAuthInfo const*) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:8988:3
#21 0x0000772e5ef083b8 llvm::SelectionDAGBuilder::visitCall(llvm::CallInst const&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:9603:16
#22 0x0000772e5ef08774 llvm::Value::getValueID() const /home/alexrp/Source/llvm-project/llvm/include/llvm/IR/Value.h:544:12
#23 0x0000772e5ef08774 llvm::Instruction::getOpcode() const /home/alexrp/Source/llvm-project/llvm/include/llvm/IR/Instruction.h:312:49
#24 0x0000772e5ef08774 llvm::Instruction::isTerminator() const /home/alexrp/Source/llvm-project/llvm/include/llvm/IR/Instruction.h:315:50
#25 0x0000772e5ef08774 llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:1338:22
#26 0x0000772e5ef8c171 llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, true, false, void, true, llvm::BasicBlock>, false, true>, llvm::ilist_iterator_w_bits<llvm::ilist_detail::node_options<llvm::Instruction, true, false, void, true, llvm::BasicBlock>, false, true>, bool&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:854:17
#27 0x0000772e5ef8ccac llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1891:33
#28 0x0000772e5ef8e3d9 llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:605:22
#29 0x0000772e5ef85137 llvm::OptLevelChanger::~OptLevelChanger() /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:267:11
#30 0x0000772e5ef85137 llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:373:1
#31 0x0000772e5ef85137 llvm::SelectionDAGISelLegacy::runOnMachineFunction(llvm::MachineFunction&) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:345:6
#32 0x0000772e5e8d947b llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (.part.0) /home/alexrp/Source/llvm-project/llvm/lib/CodeGen/MachineFunctionPass.cpp:108:30
#33 0x0000772e5e54cd34 llvm::FPPassManager::runOnFunction(llvm::Function&) /home/alexrp/Source/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1408:7
#34 0x0000772e5e54cf45 llvm::ilist_detail::node_base_prevnext<llvm::ilist_node_base<true, void>, true>::getNext() const /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/ilist_node_base.h:42:38
#35 0x0000772e5e54cf45 llvm::ilist_node_impl<llvm::ilist_detail::node_options<llvm::Function, true, false, void, false, void>>::getNext() /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/ilist_node.h:119:66
#36 0x0000772e5e54cf45 llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Function, true, false, void, false, void>, false, false>::operator++() /home/alexrp/Source/llvm-project/llvm/include/llvm/ADT/ilist_iterator.h:187:25
#37 0x0000772e5e54cf45 llvm::FPPassManager::runOnModule(llvm::Module&) /home/alexrp/Source/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1443:22
#38 0x0000772e5e54d75b runOnModule /home/alexrp/Source/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:1520:7
#39 0x0000772e5e54d75b llvm::legacy::PassManagerImpl::run(llvm::Module&) /home/alexrp/Source/llvm-project/llvm/lib/IR/LegacyPassManager.cpp:531:55
#40 0x000058f6f43ec16d compileModule(char**, llvm::LLVMContext&) /home/alexrp/Source/llvm-project/llvm/tools/llc/llc.cpp:761:34
#41 0x000058f6f43e04cf main /home/alexrp/Source/llvm-project/llvm/tools/llc/llc.cpp:404:35
#42 0x0000772e5cc2a578 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#43 0x0000772e5cc2a63b call_init ./csu/../csu/libc-start.c:128:20
#44 0x0000772e5cc2a63b __libc_start_main ./csu/../csu/libc-start.c:347:5
#45 0x000058f6f43e1aa5 _start (/opt/llvm-21/bin/llc+0x14aa5)

[uweigand]

Hi @JonPsson1, looks like you added this code here: https://reviews.llvm.org/D97514

The problem is that

        EVT OrigArgVT = getValueType(MF.getDataLayout(), OrigArgType);

doesn't work if the original argument type is a struct like in this case.

Maybe we should avoid looking at the original type after all, and simply compute the required space from the list of parts (we know where we're going to store them, so we should be able to just track the space requirements).

Can you have a look?

[JonPsson1]

I see in the ABI:

• Structures with a size of 1, 2, 4, or 8 bytes which are not equivalent to a floating
point type are passed as integral values.
• All other structures are passed by reference. If needed, the called function makes a
copy of the value.

If I can compile a C program and pass a struct containing just an __int128, clang emits that argument as a pointer (per above), both in the declaration of called function and at the call site.

So I actually wonder if the test case is legal - meaning if so that the backend would have the responsibility of converting everything to match the ABI, which would be really awkward given that this also includes transforming function declarations etc. I don't see in the lang-ref ('call' instruction) anything that specifies this, though.

[alexrp]

It is true that Zig doesn't handle the s390x ABI correctly here, and that's a bug in Zig.

However, that's actually immaterial to this issue; LLVM IR is not C, and it's expected that calls involving types not covered by the C ABI are still lowered to something semantically sensible, even if that doesn't match the C ABI. It's then the frontend's responsibility not to rely on that at C ABI boundaries (again, that aspect is a bug in Zig).

Note that this crash also occurs if you change ccc to fastcc.

[JonPsson1]

Patch proposed.

[JonPsson1]

@alexrp Does this resolve your issue regarding this?

[alexrp]

Judging by the test case added, I believe so. Thank you!