"fatal error: unknown codeview register H1" when using `@llvm.dbg.value` on a half float parameter on aarch64-windows

[andrewrk]

Repro

Tested with 14.0.6.

$ ~/local/llvm14-release/bin/clang-14 reduced.ll -target aarch64-windows-gnu
fatal error: error in backend: unknown codeview register H1
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /home/andy/local/llvm14-release/bin/clang-14 -c test2.ll -target aarch64-windows-gnu
1.	Code generation
2.	Running pass 'Function Pass Manager' on module 'test2.ll'.
3.	Running pass 'AArch64 Assembly Printer' on function '@test2.isNan__anon_222'
 #0 0x0000000002f2bd20 PrintStackTraceSignalHandler(void*) Signals.cpp:0:0
 #1 0x0000000002f29c5c llvm::sys::CleanupOnSignal(unsigned long) (/home/andy/local/llvm14-release/bin/clang-14+0x2f29c5c)
 #2 0x0000000002e67b84 llvm::CrashRecoveryContext::HandleExit(int) (/home/andy/local/llvm14-release/bin/clang-14+0x2e67b84)
 #3 0x0000000002f2226e llvm::sys::Process::Exit(int, bool) (/home/andy/local/llvm14-release/bin/clang-14+0x2f2226e)
 #4 0x0000000000a5b123 (/home/andy/local/llvm14-release/bin/clang-14+0xa5b123)
 #5 0x0000000002e6e5c2 llvm::report_fatal_error(llvm::Twine const&, bool) (/home/andy/local/llvm14-release/bin/clang-14+0x2e6e5c2)
 #6 0x0000000002af595c llvm::MCRegisterInfo::getCodeViewRegNum(llvm::MCRegister) const (/home/andy/local/llvm14-release/bin/clang-14+0x2af595c)
 #7 0x0000000003c7415a llvm::CodeViewDebug::calculateRanges(llvm::CodeViewDebug::LocalVariable&, llvm::SmallVector<llvm::DbgValueHistoryMap::Entry, 4u> const&) (/home/andy/local/llvm14-release/bin/clang-14+0x3c7415a)
 #8 0x0000000003c89fbc llvm::CodeViewDebug::collectVariableInfo(llvm::DISubprogram const*) (/home/andy/local/llvm14-release/bin/clang-14+0x3c89fbc)
 #9 0x0000000003c8a111 llvm::CodeViewDebug::endFunctionImpl(llvm::MachineFunction const*) (/home/andy/local/llvm14-release/bin/clang-14+0x3c8a111)
#10 0x0000000003c23677 llvm::DebugHandlerBase::endFunction(llvm::MachineFunction const*) (/home/andy/local/llvm14-release/bin/clang-14+0x3c23677)
#11 0x0000000003c1e591 llvm::AsmPrinter::emitFunctionBody() (/home/andy/local/llvm14-release/bin/clang-14+0x3c1e591)
#12 0x0000000000a6a6f8 (anonymous namespace)::AArch64AsmPrinter::runOnMachineFunction(llvm::MachineFunction&) AArch64AsmPrinter.cpp:0:0
#13 0x00000000021cdb14 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/home/andy/local/llvm14-release/bin/clang-14+0x21cdb14)
#14 0x0000000002638a00 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/andy/local/llvm14-release/bin/clang-14+0x2638a00)
#15 0x0000000002638b6c llvm::FPPassManager::runOnModule(llvm::Module&) (/home/andy/local/llvm14-release/bin/clang-14+0x2638b6c)
#16 0x000000000263a4f1 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/andy/local/llvm14-release/bin/clang-14+0x263a4f1)
#17 0x000000000325f2e1 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::StringRef, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) (/home/andy/local/llvm14-release/bin/clang-14+0x325f2e1)
#18 0x0000000003f6d0f8 clang::CodeGenAction::ExecuteAction() (/home/andy/local/llvm14-release/bin/clang-14+0x3f6d0f8)
#19 0x000000000391b219 clang::FrontendAction::Execute() (/home/andy/local/llvm14-release/bin/clang-14+0x391b219)
#20 0x00000000038aba6b clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/home/andy/local/llvm14-release/bin/clang-14+0x38aba6b)
#21 0x00000000039cb820 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/home/andy/local/llvm14-release/bin/clang-14+0x39cb820)
#22 0x0000000000a5c51c cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/home/andy/local/llvm14-release/bin/clang-14+0xa5c51c)
#23 0x0000000000a59479 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) driver.cpp:0:0
#24 0x00000000037325a5 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#25 0x0000000002e67a13 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) (/home/andy/local/llvm14-release/bin/clang-14+0x2e67a13)
#26 0x0000000003732904 clang::driver::CC1Command::Execute(llvm::ArrayRef<llvm::Optional<llvm::StringRef> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, bool*) const (.part.0) Job.cpp:0:0
#27 0x0000000003705556 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&) const (/home/andy/local/llvm14-release/bin/clang-14+0x3705556)
#28 0x0000000003705f09 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) const (/home/andy/local/llvm14-release/bin/clang-14+0x3705f09)
#29 0x0000000003715409 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*> >&) (/home/andy/local/llvm14-release/bin/clang-14+0x3715409)

reduced.ll

define internal fastcc i1 @test2.isNan__anon_222(half %0) !dbg !33 {
Entry:
  call void @llvm.dbg.value(metadata half %0, metadata !40, metadata !DIExpression()), !dbg !42
  %1 = fcmp une half 0xH0000, %0, !dbg !43
  ret i1 %1
}

; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
declare void @llvm.dbg.value(metadata, metadata, metadata) #0

attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }

!llvm.module.flags = !{!0, !1, !2}
!llvm.dbg.cu = !{!3}

!0 = !{i32 2, !"Debug Info Version", i32 3}
!1 = !{i32 2, !"CodeView", i32 1}
!2 = !{i32 7, !"PIC Level", i32 2}
!3 = distinct !DICompileUnit(language: DW_LANG_C99, file: !4, producer: "zig 0.10.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !5, globals: !27)
!4 = !DIFile(filename: "test2", directory: ".")
!5 = !{!6, !21}
!6 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "builtin.CompilerBackend", scope: !7, file: !7, line: 1222, baseType: !8, size: 64, align: 64, elements: !9)
!7 = !DIFile(filename: "builtin.zig", directory: "/home/andy/dev/zig/lib/std")
!8 = !DIBasicType(name: "u64", size: 64, encoding: DW_ATE_unsigned)
!9 = !{!10, !11, !12, !13, !14, !15, !16, !17, !18, !19, !20}
!10 = !DIEnumerator(name: "other", value: 0)
!11 = !DIEnumerator(name: "stage1", value: 1)
!12 = !DIEnumerator(name: "stage2_llvm", value: 2)
!13 = !DIEnumerator(name: "stage2_c", value: 3)
!14 = !DIEnumerator(name: "stage2_wasm", value: 4)
!15 = !DIEnumerator(name: "stage2_arm", value: 5)
!16 = !DIEnumerator(name: "stage2_x86_64", value: 6)
!17 = !DIEnumerator(name: "stage2_aarch64", value: 7)
!18 = !DIEnumerator(name: "stage2_x86", value: 8)
!19 = !DIEnumerator(name: "stage2_riscv64", value: 9)
!20 = !DIEnumerator(name: "stage2_sparc64", value: 10)
!21 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "builtin.OutputMode", scope: !7, file: !7, line: 533, baseType: !22, size: 8, align: 8, elements: !23)
!22 = !DIBasicType(name: "u2", size: 2, encoding: DW_ATE_unsigned)
!23 = !{!24, !25, !26}
!24 = !DIEnumerator(name: "Exe", value: 0)
!25 = !DIEnumerator(name: "Lib", value: 1)
!26 = !DIEnumerator(name: "Obj", value: 2)
!27 = !{!28, !31}
!28 = !DIGlobalVariableExpression(var: !29, expr: !DIExpression())
!29 = distinct !DIGlobalVariable(name: "zig_backend", linkageName: "builtin.zig_backend", scope: !30, file: !30, line: 5, type: !6, isLocal: true, isDefinition: true)
!30 = !DIFile(filename: "builtin.zig", directory: "zig-cache/o/dad7b6fae1ca78a1c1cb52547270f805")
!31 = !DIGlobalVariableExpression(var: !32, expr: !DIExpression())
!32 = distinct !DIGlobalVariable(name: "output_mode", linkageName: "builtin.output_mode", scope: !30, file: !30, line: 9, type: !21, isLocal: true, isDefinition: true)
!33 = distinct !DISubprogram(name: "isNan__anon_222", linkageName: "test2.isNan__anon_222", scope: !34, file: !34, line: 32, type: !35, scopeLine: 32, flags: DIFlagStaticMember, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition, unit: !3, retainedNodes: !39)
!34 = !DIFile(filename: "test2.zig", directory: ".")
!35 = !DISubroutineType(types: !36)
!36 = !{!37, !38}
!37 = !DIBasicType(name: "bool", size: 1, encoding: DW_ATE_boolean)
!38 = !DIBasicType(name: "f16", size: 16, encoding: DW_ATE_float)
!39 = !{!40}
!40 = !DILocalVariable(name: "x", arg: 1, scope: !41, file: !34, line: 32, type: !38)
!41 = distinct !DILexicalBlock(scope: !33, file: !34, line: 32, column: 1)
!42 = !DILocation(line: 32, column: 31, scope: !41)
!43 = !DILocation(line: 33, column: 5, scope: !44)
!44 = distinct !DILexicalBlock(scope: !41, file: !34)

[llvmbot]

@llvm/issue-subscribers-bug

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

[llvmbot]

@llvm/issue-subscribers-debuginfo

[DavidSpickett]

Still present on main as of 00797b88e0113aeea03045b18b3f63332f850dfe.

Picking H1 makes sense because half float is 16 bit. Then we're trying to get the codeview register number for that. Except codeview only has the 32 bit (S) and and 64 bit (D) registers. (llvm/include/llvm/DebugInfo/CodeView/CodeViewRegisters.def)

It's the same over in Microsoft's repo https://github.com/microsoft/microsoft-pdb/blob/master/include/cvconst.h#L1603. Though there's always a chance that isn't up to date I suppose.

I looked for half float support in msvc but I don't think it has it beyond https://docs.microsoft.com/en-us/windows/win32/dxmath/half-data-type but even if you use that I don't know that it would put it in a float register. None of the type names listed in https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point work either.

But regardless it seems like it'd be fine to use the number for S1 instead. Any debugger would know the type of the variable anyway, just like if you have a uint16_t in a 64 bit register.

x86 puts the value in an XMM register which is along the same lines (maybe there is some special name for XMM as 16 bit elements but I don't know it).

Only problem is that the codeview mappings are put into a case statement in one place, so it'll need some refactoring to avoid duplicate values in that.

[majnemer]

ISTM that Microsoft has mappings for the half precision registers here.

[DavidSpickett]

Thanks! Also now I see from microsoft/microsoft-pdb#51 that that repo isn't up to date.

I'll fix the H registers at least. There's also B register mappings but I'm not sure I can get clang to emit them so I'll probably leave them out.