Index: llvm/include/llvm/Demangle/Demangle.h
===================================================================
--- llvm/include/llvm/Demangle/Demangle.h
+++ llvm/include/llvm/Demangle/Demangle.h
@@ -60,6 +60,9 @@
 // Demangles a Rust v0 mangled symbol. The API follows that of __cxa_demangle.
 char *rustDemangle(const char *MangledName, char *Buf, size_t *N, int *Status);
 
+// Demangles a D mangled symbol.
+char *dlangDemangle(const char *MangledName);
+
 /// Attempt to demangle a string using different demangling schemes.
 /// The function uses heuristics to determine which demangling scheme to use.
 /// \param MangledName - reference to string to demangle.
Index: llvm/lib/Demangle/CMakeLists.txt
===================================================================
--- llvm/lib/Demangle/CMakeLists.txt
+++ llvm/lib/Demangle/CMakeLists.txt
@@ -4,6 +4,7 @@
   MicrosoftDemangle.cpp
   MicrosoftDemangleNodes.cpp
   RustDemangle.cpp
+  DLangDemangle.cpp
 
   ADDITIONAL_HEADER_DIRS
   "${LLVM_MAIN_INCLUDE_DIR}/llvm/Demangle"
Index: llvm/lib/Demangle/DLangDemangle.cpp
===================================================================
--- /dev/null
+++ llvm/lib/Demangle/DLangDemangle.cpp
@@ -0,0 +1,56 @@
+//===--- DLangDemangle.cpp ------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file defines a demangler for D programming language as specified in the
+/// ABI specification, available at:
+/// https://dlang.org/spec/abi.html#name_mangling
+///
+//===----------------------------------------------------------------------===//
+//
+// Ported from libiberty library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Demangle/Demangle.h"
+#include "llvm/Demangle/MicrosoftDemangleNodes.h"
+#include "llvm/Demangle/Utility.h"
+
+#include <cassert>
+#include <cctype>
+#include <cstdlib>
+#include <cstring>
+#include <limits.h>
+
+using namespace llvm;
+using llvm::itanium_demangle::OutputString;
+
+char *llvm::dlangDemangle(const char *MangledName) {
+  OutputString Decl;
+  char *Demangled = nullptr;
+
+  if (MangledName == nullptr || *MangledName == '\0')
+    return nullptr;
+
+  if (strncmp(MangledName, "_D", 2) != 0)
+    return nullptr;
+
+  initializeOutputString(nullptr, nullptr, Decl, 1024);
+
+  if (strcmp(MangledName, "_Dmain") == 0) {
+    Decl << "D main";
+  }
+
+  if (Decl.getCurrentPosition() > 0) {
+    Decl << '\0';
+    Decl.setCurrentPosition(Decl.getCurrentPosition() - 1);
+    Demangled = Decl.getBuffer();
+  }
+
+  return Demangled;
+}
Index: llvm/lib/Demangle/Demangle.cpp
===================================================================
--- llvm/lib/Demangle/Demangle.cpp
+++ llvm/lib/Demangle/Demangle.cpp
@@ -21,6 +21,11 @@
 
 static bool isRustEncoding(const char *S) { return S[0] == '_' && S[1] == 'R'; }
 
+static bool isDLangEncoding(const std::string &MangledName) {
+  return MangledName.size() >= 2 && MangledName[0] == '_' &&
+         MangledName[1] == 'D';
+}
+
 std::string llvm::demangle(const std::string &MangledName) {
   std::string Result;
   const char *S = MangledName.c_str();
@@ -47,6 +52,8 @@
     Demangled = itaniumDemangle(MangledName, nullptr, nullptr, nullptr);
   else if (isRustEncoding(MangledName))
     Demangled = rustDemangle(MangledName, nullptr, nullptr, nullptr);
+  else if (isDLangEncoding(MangledName))
+    Demangled = dlangDemangle(MangledName);
 
   if (!Demangled)
     return false;
Index: llvm/test/Demangle/dlang.test
===================================================================
--- /dev/null
+++ llvm/test/Demangle/dlang.test
@@ -0,0 +1,10 @@
+RUN: llvm-cxxfilt -n  < %s | FileCheck --match-full-lines %s
+
+; Full test suite for dlang demangling at
+; llvm/unittests/Demangle/DLangDemangleTest.cpp
+
+CHECK: D main
+       _Dmain
+
+CHECK: _DDD
+       _DDD
Index: llvm/unittests/Demangle/CMakeLists.txt
===================================================================
--- llvm/unittests/Demangle/CMakeLists.txt
+++ llvm/unittests/Demangle/CMakeLists.txt
@@ -5,6 +5,7 @@
 
 add_llvm_unittest(DemangleTests
   DemangleTest.cpp
+  DLangDemangleTest.cpp
   ItaniumDemangleTest.cpp
   OutputStringTest.cpp
   PartialDemangleTest.cpp
Index: llvm/unittests/Demangle/DLangDemangleTest.cpp
===================================================================
--- /dev/null
+++ llvm/unittests/Demangle/DLangDemangleTest.cpp
@@ -0,0 +1,35 @@
+//===------------------ DLangDemangleTest.cpp -----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Testing input ported from libiberty library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Demangle/Demangle.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include <cstdlib>
+#include <utility>
+
+class DLangDemangleTestFixture
+    : public testing::TestWithParam<std::pair<const char *, const char *>> {
+protected:
+  char *Demangled;
+
+  virtual void SetUp() { Demangled = llvm::dlangDemangle(GetParam().first); }
+
+  virtual void TearDown() { std::free(Demangled); }
+};
+
+TEST_P(DLangDemangleTestFixture, DLangDemangleTest) {
+  EXPECT_STREQ(Demangled, GetParam().second);
+}
+
+INSTANTIATE_TEST_SUITE_P(DLangDemangleTest, DLangDemangleTestFixture,
+                         testing::Values(std::make_pair("_Dmain", "D main")));
Index: llvm/unittests/Demangle/DemangleTest.cpp
===================================================================
--- llvm/unittests/Demangle/DemangleTest.cpp
+++ llvm/unittests/Demangle/DemangleTest.cpp
@@ -22,6 +22,7 @@
   EXPECT_EQ(demangle("?foo@@YAXH@Z"), "void __cdecl foo(int)");
   EXPECT_EQ(demangle("foo"), "foo");
   EXPECT_EQ(demangle("_RNvC3foo3bar"), "foo::bar");
+  EXPECT_EQ(demangle("_Dmain"), "D main");
   EXPECT_EQ(demangle("__RNvC3foo3bar"), "foo::bar");
 
   // Regression test for demangling of optional template-args for vendor