[NFC] refactor demangle of llvm-nm

[DiggerLin]

Summary

refactor demangle of llvm-nm .

[MaskRay]

llvm::demangle is used by a lot of ELF tools to assume ELF style mangling where there is no extra prefix. I think many don't expect demangling ._Zxxxx symbols.
If XCOFF needs ., I think separate functions are needed. You can add a new utility function or extending demangle with an optional parameter about XCOFF.

[DiggerLin]

In D159539#4649765, @MaskRay wrote:

llvm::demangle is used by a lot of ELF tools to assume ELF style mangling where there is no extra prefix. I think many don't expect demangling ._Zxxxx symbols.

I tried in gnu-c++filt in linux which is elf format in linux OS. it demangle ._Zxxxx symbols.

bash> /opt/at15.0/bin/powerpc64le-linux-gnu-c++filt ._ZL5func0v
.func0()

[jhenderson]

This patch should have been created using a GitHub Pull Request. See the big red notice at the top of the page...

llvm/lib/Demangle/Demangle.cpp

std::string llvm::demangle(std::string_view MangledName) {
 
   if (nonMicrosoftDemangle(MangledName, Result))
     return Result;
 
   if (starts_with(MangledName, '_') &&
       nonMicrosoftDemangle(MangledName.substr(1), Result))
     return Result;
 
+  if (starts_with(MangledName, '.') &&
+      nonMicrosoftDemangle(MangledName.substr(1), Result))
+    return "." + Result;
+
   if (char *Demangled = microsoftDemangle(MangledName, nullptr, nullptr)) {
     Result = Demangled;
     std::free(Demangled);
   } else {
     Result = MangledName;
   }
   return Result;
 }

llvm/tools/llvm-nm/llvm-nm.cpp

static void darwinPrintStab(MachOObjectFile *MachO, const NMSymbol &S) {
 
   outs() << format(" %02x %04x ", NSect, NDesc);
   if (const char *stabString = getDarwinStabString(NType))
     outs() << format("%5.5s", stabString);
   else
     outs() << format("   %02x", NType);
 }
 
-static std::optional<std::string> demangle(StringRef Name) {
-  std::string Demangled;
-  if (nonMicrosoftDemangle(Name, Demangled))
-    return Demangled;
-  return std::nullopt;
-}
-
-static std::optional<std::string> demangleXCOFF(StringRef Name) {
-  if (Name.empty() || Name[0] != '.')
-    return demangle(Name);
-
-  Name = Name.drop_front();
-  std::optional<std::string> DemangledName = demangle(Name);
-  if (DemangledName)
-    return "." + *DemangledName;
-  return std::nullopt;
-}
-
-static std::optional<std::string> demangleMachO(StringRef Name) {
-  if (!Name.empty() && Name[0] == '_')
-    Name = Name.drop_front();
-  return demangle(Name);
-}
-
 static bool symbolIsDefined(const NMSymbol &Sym) {
   return Sym.TypeChar != 'U' && Sym.TypeChar != 'w' && Sym.TypeChar != 'v';
 }
 
 static void writeFileName(raw_ostream &S, StringRef ArchiveName,
                           StringRef ArchitectureName) {
   if (!ArchitectureName.empty())
     S << "(for architecture " << ArchitectureName << "):";
static void printSymbolList(SymbolicFile &Obj,
   }
 
   for (const NMSymbol &S : SymbolList) {
     if (!S.shouldPrint())
       continue;
 
     std::string Name = S.Name;
     MachOObjectFile *MachO = dyn_cast<MachOObjectFile>(&Obj);
-    if (Demangle) {
-      function_ref<std::optional<std::string>(StringRef)> Fn = ::demangle;
-      if (Obj.isXCOFF())
-        Fn = demangleXCOFF;
-      if (Obj.isMachO())
-        Fn = demangleMachO;
-      if (std::optional<std::string> Opt = Fn(S.Name))
-        Name = *Opt;
-    }
+    if (Demangle)
+      Name = llvm::demangle(Name);
 
     if (PrintFileName)
       writeFileName(outs(), ArchiveName, ArchitectureName);
     if ((OutputFormat == just_symbols ||
          (UndefinedOnly && MachO && OutputFormat != darwin)) &&
         OutputFormat != posix) {
       outs() << Name << "\n";
       continue;