Index: lld/COFF/CMakeLists.txt
===================================================================
--- lld/COFF/CMakeLists.txt
+++ lld/COFF/CMakeLists.txt
@@ -30,6 +30,7 @@
   DebugInfoCodeView
   DebugInfoMSF
   DebugInfoPDB
+  Demangle
   LibDriver
   LTO
   MC
Index: lld/COFF/Symbols.cpp
===================================================================
--- lld/COFF/Symbols.cpp
+++ lld/COFF/Symbols.cpp
@@ -12,6 +12,7 @@
 #include "lld/Common/Memory.h"
 #include "lld/Common/Strings.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -26,26 +27,25 @@
               "symbols should be optimized for memory usage");
 
 // Returns a symbol name for an error message.
-static std::string demangle(StringRef symName) {
+static std::string maybeDemangleSymbol(StringRef symName) {
   if (config->demangle) {
-    if (Optional<std::string> s = demangleMSVC(symName))
-      return *s;
-    if (config->mingw) {
-      StringRef demangleInput = symName;
-      std::string prefix;
-      if (demangleInput.consume_front("__imp_"))
-        prefix = "__declspec(dllimport) ";
-      if (config->machine == I386)
-        demangleInput.consume_front("_");
-      if (Optional<std::string> s = demangleItanium(demangleInput))
-        return prefix + *s;
-    }
+    std::string prefix;
+    StringRef demangleInput = symName;
+    if (demangleInput.consume_front("__imp_"))
+      prefix = "__declspec(dllimport) ";
+    if (config->machine == I386)
+      demangleInput.consume_front("_");
+    std::string demangled = demangle(demangleInput);
+    if (demangled != demangleInput)
+      return prefix + demangled;
   }
   return symName;
 }
-std::string toString(coff::Symbol &b) { return demangle(b.getName()); }
+std::string toString(coff::Symbol &b) {
+  return maybeDemangleSymbol(b.getName());
+}
 std::string toCOFFString(const Archive::Symbol &b) {
-  return demangle(b.getName());
+  return maybeDemangleSymbol(b.getName());
 }
 
 namespace coff {
Index: lld/Common/Strings.cpp
===================================================================
--- lld/Common/Strings.cpp
+++ lld/Common/Strings.cpp
@@ -36,23 +36,6 @@
   return s;
 }
 
-Optional<std::string> lld::demangleMSVC(StringRef name) {
-  std::string prefix;
-  if (name.consume_front("__imp_"))
-    prefix = "__declspec(dllimport) ";
-
-  // Demangle only C++ names.
-  if (!name.startswith("?"))
-    return None;
-
-  char *buf = microsoftDemangle(name.str().c_str(), nullptr, nullptr, nullptr);
-  if (!buf)
-    return None;
-  std::string s(buf);
-  free(buf);
-  return prefix + s;
-}
-
 StringMatcher::StringMatcher(ArrayRef<StringRef> pat) {
   for (StringRef s : pat) {
     Expected<GlobPattern> pat = GlobPattern::create(s);
Index: lld/include/lld/Common/Strings.h
===================================================================
--- lld/include/lld/Common/Strings.h
+++ lld/include/lld/Common/Strings.h
@@ -20,7 +20,6 @@
 // Returns a demangled C++ symbol name. If Name is not a mangled
 // name, it returns Optional::None.
 llvm::Optional<std::string> demangleItanium(llvm::StringRef name);
-llvm::Optional<std::string> demangleMSVC(llvm::StringRef s);
 
 std::vector<uint8_t> parseHex(llvm::StringRef s);
 bool isValidCIdentifier(llvm::StringRef s);
Index: lld/test/COFF/undefined-symbol-itanium-i386.s
===================================================================
--- lld/test/COFF/undefined-symbol-itanium-i386.s
+++ lld/test/COFF/undefined-symbol-itanium-i386.s
@@ -7,6 +7,7 @@
 # NODEMANGLE: error: undefined symbol: __Z3fooi
 # NODEMANGLE: error: undefined symbol: __Z3barPKc
 # NODEMANGLE: error: undefined symbol: __imp___Z3bazv
+# NODEMANGLE: error: undefined symbol: _Z3fooi
 
 # CHECK: error: undefined symbol: foo(int)
 # CHECK-NEXT: >>> referenced by {{.*}}.o:(_main)
@@ -17,6 +18,9 @@
 # CHECK-NEXT: >>> referenced by {{.*}}.o:(_f1)
 # CHECK-EMPTY:
 # CHECK-NEXT: error: undefined symbol: __declspec(dllimport) baz()
+# CHECK-NEXT: >>> referenced by {{.*}}.o:(_f2)
+# CHECK-EMPTY:
+# CHECK-NEXT: error: undefined symbol: _Z3fooi
 # CHECK-NEXT: >>> referenced by {{.*}}.o:(_f2)
 
         .section        .text,"xr",one_only,_main
@@ -34,3 +38,4 @@
 .globl _f2
 _f2:
 	call	*__imp___Z3bazv
+	call	_Z3fooi
Index: lld/test/COFF/undefined-symbol.s
===================================================================
--- lld/test/COFF/undefined-symbol.s
+++ lld/test/COFF/undefined-symbol.s
@@ -7,6 +7,7 @@
 # NODEMANGLE: error: undefined symbol: ?foo@@YAHXZ
 # NODEMANGLE: error: undefined symbol: ?bar@@YAHXZ
 # NODEMANGLE: error: undefined symbol: __imp_?baz@@YAHXZ
+# NODEMANGLE: error: undefined symbol: __imp_undecorated
 
 # CHECK: error: undefined symbol: int __cdecl foo(void)
 # CHECK-NEXT: >>> referenced by {{.*}}.obj:(main)
@@ -17,6 +18,9 @@
 # CHECK-NEXT: >>> referenced by {{.*}}.obj:(f1)
 # CHECK-EMPTY:
 # CHECK-NEXT: error: undefined symbol: __declspec(dllimport) int __cdecl baz(void)
+# CHECK-NEXT: >>> referenced by {{.*}}.obj:(f2)
+# CHECK-EMPTY:
+# CHECK-NEXT: error: undefined symbol: __imp_undecorated
 # CHECK-NEXT: >>> referenced by {{.*}}.obj:(f2)
 
         .section        .text,"xr",one_only,main
@@ -34,3 +38,4 @@
 .globl f2
 f2:
 	callq	*"__imp_?baz@@YAHXZ"(%rip)
+	callq	*__imp_undecorated(%rip)