[Debug-Info][DBX] DW_AT_noreturn should not be generated when dwarf version is not 5

[shchenz]

Summary

As discussed in D99250 , we added a new tuning debugger DBX(D99400) to add some debug info customizations for DBX on AIX.

This is part of the customizations, not generating DWARF infos not matching the DWARF version.

This patch is for attribute DW_AT_noreturn which is introduced in DWARF 5.

Now for DBX, we only generate this attribute when DWARF version is 5 or higher.

[shchenz]

1: use strict dwarf flag instead of DBX debugger

[shchenz]

we use a new way in D101024, so this is not needed

[aprantl]

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

1281

Should we factor out a FlagSupported(attribute) function? I think Dwarf.def already stores the version in which an attribute was introduced, so we don't need to duplicate this in the code here?

[shchenz]

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

1281

Thanks Adrian, @aprantl . Great minds think alike, haha. All of you, including @probinson and @dblaikie have the same opinions for this change. I have added the function in D101125 and abandoned related patches including this one.

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCSection.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MachineLocation.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetLoweringObjectFile.h"
+#include "llvm/Target/TargetMachine.h"
 #include <cassert>
 #include <cstdint>
 #include <string>
 #include <utility>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "dwarfdebug"
void DwarfUnit::applySubprogramAttributes(const DISubprogram *SP, DIE &SPDie,
   }
 
   if (SP->isLValueReference())
     addFlag(SPDie, dwarf::DW_AT_reference);
 
   if (SP->isRValueReference())
     addFlag(SPDie, dwarf::DW_AT_rvalue_reference);
 
-  if (SP->isNoReturn())
+  // DW_AT_noreturn was introduced in DWARF 5, in strict DWARF mode, only
+  // generate this attribute when DWARF version is not smaller than 5.
+  if (SP->isNoReturn() &&
+      (!Asm->TM.Options.DebugStrictDwarf || DD->getDwarfVersion() >= 5))
     addFlag(SPDie, dwarf::DW_AT_noreturn);
 
   if (SP->isProtected())
     addUInt(SPDie, dwarf::DW_AT_accessibility, dwarf::DW_FORM_data1,
             dwarf::DW_ACCESS_protected);
   else if (SP->isPrivate())
     addUInt(SPDie, dwarf::DW_AT_accessibility, dwarf::DW_FORM_data1,
             dwarf::DW_ACCESS_private);

llvm/test/DebugInfo/PowerPC/noreturn.ll

+; RUN: llc -filetype=obj -mtriple=powerpc64le-unknown-linux-gnu < %s | \
+; RUN:   llvm-dwarfdump -debug-info - | FileCheck %s
+; RUN: llc -filetype=obj -mtriple=powerpc64le-unknown-linux-gnu \
+; RUN:   -strict-dwarf=true < %s | llvm-dwarfdump -debug-info - | \
+; RUN:   FileCheck %s --check-prefix=STRICT
+
+; CHECK: DW_AT_noreturn
+; STRICT-NOT: DW_AT_noreturn
+
+; Function Attrs: noreturn
+define dso_local void @_Z1fv() #0 !dbg !7 {
+  call void @_Z4exitv() #2, !dbg !10
+  unreachable, !dbg !10
+}
+
+; Function Attrs: noreturn
+declare void @_Z4exitv() #1
+
+attributes #0 = { noreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 13.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "noreturn.cpp", directory: "./")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 13.0.0"}
+!7 = distinct !DISubprogram(name: "f", linkageName: "_Z1fv", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagNoReturn, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 3, column: 3, scope: !7)