3 files changed, 46 insertions, 3 deletions
diff --git a/llvm/include/llvm/Demangle/Demangle.h b/llvm/include/llvm/Demangle/Demangle.h
index df7753f23b8..27340b77aa2 100644
--- a/llvm/include/llvm/Demangle/Demangle.h
+++ b/llvm/include/llvm/Demangle/Demangle.h
@@ -27,8 +27,10 @@ enum : int {
 
 char *itaniumDemangle(const char *mangled_name, char *buf, size_t *n,
                       int *status);
+
+enum MSDemangleFlags { MSDF_None = 0, MSDF_DumpBackrefs = 1 << 0 };
 char *microsoftDemangle(const char *mangled_name, char *buf, size_t *n,
-                        int *status);
+                        int *status, MSDemangleFlags Flags = MSDF_None);
 
 /// "Partial" demangler. This supports demangling a string into an AST
 /// (typically an intermediate stage in itaniumDemangle) and querying certain
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
index 04575818422..9cf7c4bb127 100644
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -878,6 +878,8 @@ public:
   // True if an error occurred.
   bool Error = false;
 
+  void dumpBackReferences();
+
 private:
   Type *demangleVariableEncoding(StringView &MangledName);
   Type *demangleFunctionEncoding(StringView &MangledName);
@@ -2046,12 +2048,43 @@ void Demangler::output(const Symbol *S, OutputStream &OS) {
   Type::outputPost(OS, *S->SymbolType);
 }
 
+void Demangler::dumpBackReferences() {
+  printf("%d function parameter backreferences\n",
+         (int)FunctionParamBackRefCount);
+
+  // Create an output stream so we can render each type.
+  OutputStream OS = OutputStream::create(nullptr, 0, 1024);
+  for (size_t I = 0; I < FunctionParamBackRefCount; ++I) {
+    OS.setCurrentPosition(0);
+
+    Type *T = FunctionParamBackRefs[I];
+    Type::outputPre(OS, *T);
+    Type::outputPost(OS, *T);
+
+    printf("  [%d] - %*s\n", (int)I, (int)OS.getCurrentPosition(),
+           OS.getBuffer());
+  }
+  std::free(OS.getBuffer());
+
+  if (FunctionParamBackRefCount > 0)
+    printf("\n");
+  printf("%d name backreferences\n", (int)BackRefCount);
+  for (size_t I = 0; I < BackRefCount; ++I) {
+    printf("  [%d] - %*s\n", (int)I, (int)BackReferences[I].size(),
+           BackReferences[I].begin());
+  }
+  if (BackRefCount > 0)
+    printf("\n");
+}
+
 char *llvm::microsoftDemangle(const char *MangledName, char *Buf, size_t *N,
-                              int *Status) {
+                              int *Status, MSDemangleFlags Flags) {
   Demangler D;
   StringView Name{MangledName};
   Symbol *S = D.parse(Name);
 
+  if (Flags & MSDF_DumpBackrefs)
+    D.dumpBackReferences();
   OutputStream OS = OutputStream::create(Buf, N, 1024);
   if (D.Error) {
     OS << MangledName;
diff --git a/llvm/tools/llvm-undname/llvm-undname.cpp b/llvm/tools/llvm-undname/llvm-undname.cpp
index 2124ec16945..31d0590af2d 100644
--- a/llvm/tools/llvm-undname/llvm-undname.cpp
+++ b/llvm/tools/llvm-undname/llvm-undname.cpp
@@ -26,12 +26,20 @@
 
 using namespace llvm;
 
+cl::opt<bool> DumpBackReferences("backrefs", cl::Optional,
+                                 cl::desc("dump backreferences"), cl::Hidden,
+                                 cl::init(false));
 cl::list<std::string> Symbols(cl::Positional, cl::desc("<input symbols>"),
                               cl::ZeroOrMore);
 
 static void demangle(const std::string &S) {
   int Status;
-  char *ResultBuf = microsoftDemangle(S.c_str(), nullptr, nullptr, &Status);
+  MSDemangleFlags Flags = MSDF_None;
+  if (DumpBackReferences)
+    Flags = MSDemangleFlags(Flags | MSDF_DumpBackrefs);
+
+  char *ResultBuf =
+      microsoftDemangle(S.c_str(), nullptr, nullptr, &Status, Flags);
   if (Status == llvm::demangle_success) {
     outs() << ResultBuf << "\n";
     outs().flush();