Crash during codegen for target OS PS3

[e820]

Zig Version

0.16.0-dev.1446+947301105

Steps to Reproduce and Observed Behavior

I'd like to preface this with the fact that this is not an issue that can be triggered with the current upstream compiler. I was experimenting with the powerpc64-ps3(-ilp32) target and extended lib/std/Target.zig:cTypeBitSize with the following prong to get rid of the initial panic when using the target:

.ps3 => switch (c_type) {
    .char => return 8,
    .short, .ushort => return 16,
    .int, .uint, .float, .long, .ulong => return 32,
    .longlong, .ulonglong, .double => return 64,
    .longdouble => return 128,
},

Which matches the clang behavior. Running the patched compiler however crashes due to a segfault:

0x00007fffeb3d1765 in llvm::MachineRegisterInfo::addRegOperandToUseList(llvm::MachineOperand*) () from /usr/lib/libLLVM.so.21.1
#0  0x00007fffeb3d1765 in llvm::MachineRegisterInfo::addRegOperandToUseList(llvm::MachineOperand*) () from /usr/lib/libLLVM.so.21.1
#1  0x00007fffeb31d1f0 in llvm::MachineInstr::addOperand(llvm::MachineFunction&, llvm::MachineOperand const&) () from /usr/lib/libLLVM.so.21.1
#2  0x00007fffef1c3c29 in ?? () from /usr/lib/libLLVM.so.21.1
#3  0x00007fffef1cae7f in ?? () from /usr/lib/libLLVM.so.21.1
#4  0x00007fffeb64de68 in llvm::TargetInstrInfo::lowerCopy(llvm::MachineInstr*, llvm::TargetRegisterInfo const*) const () from /usr/lib/libLLVM.so.21.1
#5  0x00007fffeb184650 in ?? () from /usr/lib/libLLVM.so.21.1
#6  0x00007fffeb18472c in ?? () from /usr/lib/libLLVM.so.21.1
#7  0x00007fffeb310b75 in llvm::MachineFunctionPass::runOnFunction(llvm::Function&) () from /usr/lib/libLLVM.so.21.1
#8  0x00007fffeaf050a3 in llvm::FPPassManager::runOnFunction(llvm::Function&) () from /usr/lib/libLLVM.so.21.1
#9  0x00007fffeaf05283 in llvm::FPPassManager::runOnModule(llvm::Module&) () from /usr/lib/libLLVM.so.21.1
#10 0x00007fffeaf045a2 in llvm::legacy::PassManagerImpl::run(llvm::Module&) () from /usr/lib/libLLVM.so.21.1
#11 0x00000000064c0c40 in ZigLLVMTargetMachineEmitToFile (targ_machine_ref=0x7fff85482050, module_ref=0x7fff841c6cc0, error_message=0x7fff8c41a640, options=0x7fff8c41a790)
    at /home/lauree/Developer/zig/src/zig_llvm.cpp:411
#12 0x00000000021fb976 in codegen.llvm.Object.emit (o=0x7fff84002ff8, pt=..., options=...)
#13 0x0000000002033a5c in Compilation.flush (comp=0x7fff84000d20, arena=..., tid=main)
#14 0x0000000001f2788c in Compilation.update (comp=0x7fff84000d20, main_progress_node=...)
#15 0x00000000033aa806 in Compilation.updateSubCompilation (parent_comp=0x6f6b300, sub_comp=0x7fff84000d20, misc_task=compiler_rt, prog_node=...)
#16 0x0000000002d162b4 in Compilation.buildOutputFromZig (comp=0x6f6b300, src_basename=..., root_name=..., output_mode=Lib, link_mode=static, misc_task_tag=compiler_rt, prog_node=..., options=...,
    out=0x6f6b950)
#17 0x0000000002883344 in Compilation.buildRt (comp=0x6f6b300, root_source_name=..., root_name=..., output_mode=Lib, link_mode=static, misc_task=compiler_rt, prog_node=..., options=..., out=0x6f6b950)
#18 0x0000000002364211 in Thread.WaitGroup.spawnManager__anon_207123.Manager.run (wg_inner=0x6f6b6c0, args_inner=...)
#19 0x0000000002d1494b in Thread.callFn__anon_326024 (f=<optimized out>, args=...)
#20 0x0000000002882d22 in Thread.PosixThreadImpl.spawn__anon_254921.Instance.entryFn (raw_arg=...)
#21 0x00007ffff7c9698b in start_thread (arg=<optimized out>) at pthread_create.c:448
#22 0x00007ffff7d1a9cc in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

I realize this is probably not a priority issue, given that the target isn't even strictly supported in the compiler, but I thought I'd put it out there and then see if I can get to the bottom of it when I get the time.

Expected Behavior

No segfault.

[alexrp]

Have you built LLVM with either -DCMAKE_BUILD_TYPE=Debug or -DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_ASSERTIONS=ON? (Recommend the latter as Debug LLVM is very slow.) If not, I strongly suggest doing that before even trying to investigate this.

[e820]

Yeah, trying to compile the LLVM IR emitted by Zig using a debug build of llc aborts with the following assertion failure:

llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp:1354: void {anonymous}::SelectionDAGLegalize::LegalizeOp(llvm::SDNode*): Assertion `(Res.getValueType() == Node->getValueType(0) || Node->getValueType(0) == MVT::Glue) && "Type mismatch for custom legalized operation"' failed.

Considering ISEL is very much outside of my area of expertise I doubt I'll be able to make much sense of this, but I'll see what I can do.

[alexrp]

I suggest grabbing the LLVM IR that's causing that assertion to get hit and running it through llvm-reduce. By the end of that, it should be much easier to determine what the root cause is.

[e820]

llvm-reduce leaves me with the following:

target datalayout = "E-m:e-p:32:32-Fi64-i64:64-i128:128-n32:64"
target triple = "ppc64-unknown-lv2-unknown"

@__anon_1820 = external constant [7 x i8]

define { ptr, i64 } @__ubsan_handle_add_overflow() {
Entry:
  ret { ptr, i64 } { ptr @__anon_1820, i64 6 }
}

Fwiw, running release llc on the reduced IR crashes with a different error from the one initially observed, but maybe they're related:

LLVM ERROR: Cannot select: 0x55a235378dd0: i64 = any_extend 0x55a2353790e0
  0x55a2353790e0: i64,ch = PPCISD::TOC_ENTRY<(load (s64) from got)> TargetGlobalAddress:i32<ptr @__anon_1820> 0, Register:i64 $x2
In function: __ubsan_handle_add_overflow

[alexrp]

Well, I think you're out of luck here; it doesn't look like this target is well-tested in LLVM at all.

❯ bat test.c
int x;
int main() { return x; }
❯ clang --target=powerpc64-lv2 test.c -c
clang: /home/alexrp/Source/llvm-project/llvm/lib/Target/PowerPC/PPCFastISel.cpp:2047: llvm::Register {anonymous}::PPCFastISel::PPCMaterializeGV(const llvm::GlobalValue*, llvm::MVT): Assertion `VT == MVT::i64 && "Non-address!"' failed.

[e820]

Interestingly your example doesn't reproduce for me, tried it with a debug clang 21 as well as on compiler explorer.