Index: lld/trunk/test/wasm/cxx-mangling.ll
===================================================================
--- lld/trunk/test/wasm/cxx-mangling.ll
+++ lld/trunk/test/wasm/cxx-mangling.ll
@@ -1,8 +1,8 @@
 ; RUN: llc -filetype=obj %s -o %t.o
 ; RUN: wasm-ld --export=_Z3fooi --demangle -o %t_demangle.wasm %t.o
-; RUN: obj2yaml %t_demangle.wasm | FileCheck %s
+; RUN: obj2yaml %t_demangle.wasm | FileCheck --check-prefixes=CHECK,DEMANGLE %s
 ; RUN: wasm-ld --export=_Z3fooi --no-demangle -o %t_nodemangle.wasm %t.o
-; RUN: obj2yaml %t_nodemangle.wasm | FileCheck %s
+; RUN: obj2yaml %t_nodemangle.wasm | FileCheck --check-prefixes=CHECK,MANGLE %s
 
 target triple = "wasm32-unknown-unknown"
 
@@ -58,9 +58,11 @@
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Name:            __wasm_call_ctors
 ; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         Name:            'undefined function bar(int)'
+; DEMANGLE-NEXT:      Name:            'undefined function bar(int)'
+; MANGLE-NEXT:        Name:            undefined function _Z3bari
 ; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Name:            'foo(int)'
+; DEMANGLE-NEXT:      Name:            'foo(int)'
+; MANGLE-NEXT:        Name:            _Z3fooi
 ; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Name:            _start
 ; CHECK-NEXT: ...
Index: lld/trunk/wasm/Driver.cpp
===================================================================
--- lld/trunk/wasm/Driver.cpp
+++ lld/trunk/wasm/Driver.cpp
@@ -310,10 +310,8 @@
 
     // Add a synthetic dummy for weak undefined functions.  These dummies will
     // be GC'd if not used as the target of any "call" instructions.
-    Optional<std::string> SymName = demangleItanium(Sym->getName());
-    StringRef DebugName =
-        Saver.save("undefined function " +
-                   (SymName ? StringRef(*SymName) : Sym->getName()));
+    std::string SymName = toString(*Sym);
+    StringRef DebugName = Saver.save("undefined function " + SymName);
     SyntheticFunction *Func =
         make<SyntheticFunction>(Sig, Sym->getName(), DebugName);
     Func->setBody(UnreachableFn);
Index: lld/trunk/wasm/Symbols.h
===================================================================
--- lld/trunk/wasm/Symbols.h
+++ lld/trunk/wasm/Symbols.h
@@ -349,6 +349,7 @@
 // Returns a symbol name for an error message.
 std::string toString(const wasm::Symbol &Sym);
 std::string toString(wasm::Symbol::Kind Kind);
+std::string maybeDemangleSymbol(StringRef Name);
 
 } // namespace lld
 
Index: lld/trunk/wasm/Symbols.cpp
===================================================================
--- lld/trunk/wasm/Symbols.cpp
+++ lld/trunk/wasm/Symbols.cpp
@@ -226,10 +226,14 @@
 void LazySymbol::fetch() { cast<ArchiveFile>(File)->addMember(&ArchiveSymbol); }
 
 std::string lld::toString(const wasm::Symbol &Sym) {
+  return lld::maybeDemangleSymbol(Sym.getName());
+}
+
+std::string lld::maybeDemangleSymbol(StringRef Name) {
   if (Config->Demangle)
-    if (Optional<std::string> S = demangleItanium(Sym.getName()))
+    if (Optional<std::string> S = demangleItanium(Name))
       return *S;
-  return Sym.getName();
+  return Name;
 }
 
 std::string lld::toString(wasm::Symbol::Kind Kind) {
Index: lld/trunk/wasm/Writer.cpp
===================================================================
--- lld/trunk/wasm/Writer.cpp
+++ lld/trunk/wasm/Writer.cpp
@@ -554,8 +554,7 @@
   for (const Symbol *S : ImportedSymbols) {
     if (auto *F = dyn_cast<FunctionSymbol>(S)) {
       writeUleb128(Sub.OS, F->getFunctionIndex(), "func index");
-      Optional<std::string> Name = demangleItanium(F->getName());
-      writeStr(Sub.OS, Name ? StringRef(*Name) : F->getName(), "symbol name");
+      writeStr(Sub.OS, toString(*S), "symbol name");
     }
   }
   for (const InputFunction *F : InputFunctions) {
@@ -564,8 +563,7 @@
       if (!F->getDebugName().empty()) {
         writeStr(Sub.OS, F->getDebugName(), "symbol name");
       } else {
-        Optional<std::string> Name = demangleItanium(F->getName());
-        writeStr(Sub.OS, Name ? StringRef(*Name) : F->getName(), "symbol name");
+        writeStr(Sub.OS, maybeDemangleSymbol(F->getName()), "symbol name");
       }
     }
   }