[llvm-nm] Demangle Rust symbols

[tmiasko]

Summary

Add support for demangling Rust v0 symbols to llvm-nm by reusing
nonMicrosoftDemangle which supports both Itanium and Rust mangling.

[dblaikie]

Looks good

[jhenderson]

LGTM.

I had some concern about this now meaning some names getting demangled when they shouldn't be, but at the same time, such names would only come from C code, and those names are reserved by the compiler. I guess in such a situation, the user could just not use the --demangle option.

Perhaps worth a release note?

llvm/test/tools/llvm-nm/X86/demangle.ll

entry:
   ret i32 1
 }
 
 define float @_Z3barf(float) #0 {
 entry:
   ret float 0.000000e+00
 }
 
+define i32 @_RNvC1a3baz(i32) #0 {
+entry:
+  ret i32 1
+}
+
+; MANGLED:       0000000000000020 T _RNvC1a3baz
 ; MANGLED:       0000000000000010 T _Z3barf
 ; MANGLED:       0000000000000000 T _Z3fooi
 
+; MACHO-MANGLED: 0000000000000020 T __RNvC1a3baz
 ; MACHO-MANGLED: 0000000000000010 T __Z3barf
 ; MACHO-MANGLED: 0000000000000000 T __Z3fooi
 
+; COFF-MANGLED:          00000020 T _RNvC1a3baz
 ; COFF-MANGLED:          00000010 T _Z3barf
 ; COFF-MANGLED:          00000000 T _Z3fooi
 
+; DEMANGLED:     0000000000000020 T a::baz
 ; DEMANGLED:     0000000000000010 T bar(float)
 ; DEMANGLED:     0000000000000000 T foo(int)
 
+; COFF-DEMANGLED:        00000020 T a::baz
 ; COFF-DEMANGLED:        00000010 T bar(float)
 ; COFF-DEMANGLED:        00000000 T foo(int)

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 Optional<std::string> demangle(StringRef Name, bool StripUnderscore) {
-  if (StripUnderscore && !Name.empty() && Name[0] == '_')
-    Name = Name.substr(1);
-
-  if (!Name.startswith("_Z"))
-    return None;
-
-  int Status;
-  char *Undecorated =
-      itaniumDemangle(Name.str().c_str(), nullptr, nullptr, &Status);
-  if (Status != 0)
-    return None;
-
-  std::string S(Undecorated);
-  free(Undecorated);
-  return S;
+static Optional<std::string> demangle(const std::string &Name,
+                                      bool StripUnderscore) {
+  const char *Mangled = Name.c_str();
+  if (StripUnderscore && Mangled[0] == '_')
+    Mangled = Mangled + 1;
+
+  std::string Demangled;
+  if (nonMicrosoftDemangle(Mangled, Demangled))
+    return Demangled;
 }
 
 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) {