[DWARF][M68k] Add new DW_CC for the new M68kRTD calling convention

[myhsu]

Summary

Add DW_CC_LLVM_M68kRTD to model the new llvm::CallingConv::M68kRTD (see D149864 and D149867).

To my best understanding since DW_CC_LLVM_* are considered vendor extensions, we can just add it to LLVM without being ratified or even adding into GCC/GDB. Please let me know if I'm wrong.

[aprantl]

LGTM, is it easy to add a test that runs llvm-dwarfdump on some yaml2obj or llc output?

[myhsu]

Add a llc test to check if DW_CC_LLVM_M68kRTD is printed correctly in llvm-dwarfdump.

llvm/include/llvm/BinaryFormat/Dwarf.def

 HANDLE_DW_CC(0xc4, LLVM_AAPCS_VFP)
 HANDLE_DW_CC(0xc5, LLVM_IntelOclBicc)
 HANDLE_DW_CC(0xc6, LLVM_SpirFunction)
 HANDLE_DW_CC(0xc7, LLVM_OpenCLKernel)
 HANDLE_DW_CC(0xc8, LLVM_Swift)
 HANDLE_DW_CC(0xc9, LLVM_PreserveMost)
 HANDLE_DW_CC(0xca, LLVM_PreserveAll)
 HANDLE_DW_CC(0xcb, LLVM_X86RegCall)
+HANDLE_DW_CC(0xcc, LLVM_M68kRTD)
 // From GCC source code (include/dwarf2.h): This DW_CC_ value is not currently
 // generated by any toolchain.  It is used internally to GDB to indicate OpenCL
 // C functions that have been compiled with the IBM XL C for OpenCL compiler and
 // use a non-platform calling convention for passing OpenCL C vector types.
 HANDLE_DW_CC(0xff, GDB_IBM_OpenCL)
 
 // Line Number Extended Opcode Encodings
 HANDLE_DW_LNE(0x01, end_sequence)

llvm/lib/DebugInfo/DWARF/DWARFTypePrinter.cpp

case CallingConvention::DW_CC_LLVM_PreserveMost:
       OS << " __attribute__((preserve_most))";
       break;
     case CallingConvention::DW_CC_LLVM_PreserveAll:
       OS << " __attribute__((preserve_all))";
       break;
     case CallingConvention::DW_CC_LLVM_X86RegCall:
       OS << " __attribute__((regcall))";
       break;
+    case CallingConvention::DW_CC_LLVM_M68kRTD:
+      OS << " __attribute__((m68k_rtd))";
+      break;
     }
   }
 
   if (Const)
     OS << " const";
   if (Volatile)
     OS << " volatile";
   if (D.find(DW_AT_reference))

llvm/test/DebugInfo/M68k/calling-convention.ll

+; RUN: llc --mtriple=m68k -filetype=obj %s -o %t
+; RUN: llvm-dwarfdump -v %t | FileCheck %s
+
+; CHECK-LABEL: DW_TAG_subprogram
+; CHECK: DW_AT_calling_convention [DW_FORM_data1]        (DW_CC_LLVM_M68kRTD)
+define m68k_rtdcc void @foo() !dbg !3 {
+entry:
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 17.0.0 (https://github.com/llvm/llvm-project.git)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "foo.c", directory: "/path/to/file")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = distinct !DISubprogram(name: "foo", scope: !4, file: !4, line: 4, type: !5, scopeLine: 4, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !7)
+!4 = !DIFile(filename: "./foo.c", directory: "/path/to/file")
+!5 = !DISubroutineType(cc: DW_CC_LLVM_M68kRTD, types: !6)
+!6 = !{null}
+!7 = !{}

llvm/test/DebugInfo/M68k/lit.local.cfg

+if not "M68k" in config.root.targets:
+    config.unsupported = True