diff --git a/lldb/source/Core/Mangled.cpp b/lldb/source/Core/Mangled.cpp
--- a/lldb/source/Core/Mangled.cpp
+++ b/lldb/source/Core/Mangled.cpp
@@ -164,7 +164,7 @@
   return demangled_cstr;
 }
 
-static char *GetDLangDemangledStr(const char *M) {
+static char *GetDLangDemangledStr(std::string_view M) {
   char *demangled_cstr = llvm::dlangDemangle(M);
 
   if (Log *log = GetLog(LLDBLog::Demangle)) {
@@ -263,7 +263,7 @@
         demangled_name = GetRustV0DemangledStr(m_mangled);
         break;
       case eManglingSchemeD:
-        demangled_name = GetDLangDemangledStr(mangled_name);
+        demangled_name = GetDLangDemangledStr(m_mangled);
         break;
       case eManglingSchemeNone:
         llvm_unreachable("eManglingSchemeNone was handled already");
diff --git a/llvm/include/llvm/Demangle/Demangle.h b/llvm/include/llvm/Demangle/Demangle.h
--- a/llvm/include/llvm/Demangle/Demangle.h
+++ b/llvm/include/llvm/Demangle/Demangle.h
@@ -58,7 +58,7 @@
 char *rustDemangle(std::string_view MangledName);
 
 // Demangles a D mangled symbol.
-char *dlangDemangle(const char *MangledName);
+char *dlangDemangle(std::string_view MangledName);
 
 /// Attempt to demangle a string using different demangling schemes.
 /// The function uses heuristics to determine which demangling scheme to use.
diff --git a/llvm/lib/Demangle/DLangDemangle.cpp b/llvm/lib/Demangle/DLangDemangle.cpp
--- a/llvm/lib/Demangle/DLangDemangle.cpp
+++ b/llvm/lib/Demangle/DLangDemangle.cpp
@@ -14,6 +14,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Demangle/Demangle.h"
+#include "llvm/Demangle/StringViewExtras.h"
 #include "llvm/Demangle/Utility.h"
 
 #include <cctype>
@@ -22,6 +23,7 @@
 
 using namespace llvm;
 using llvm::itanium_demangle::OutputBuffer;
+using llvm::itanium_demangle::starts_with;
 
 namespace {
 
@@ -541,20 +543,20 @@
   return parseMangle(Demangled, this->Str);
 }
 
-char *llvm::dlangDemangle(const char *MangledName) {
-  if (MangledName == nullptr || strncmp(MangledName, "_D", 2) != 0)
+char *llvm::dlangDemangle(std::string_view MangledName) {
+  if (MangledName.empty() || !starts_with(MangledName, "_D"))
     return nullptr;
 
   OutputBuffer Demangled;
-  if (strcmp(MangledName, "_Dmain") == 0) {
+  if (MangledName == "_Dmain") {
     Demangled << "D main";
   } else {
 
-    Demangler D = Demangler(MangledName);
-    MangledName = D.parseMangle(&Demangled);
+    Demangler D(MangledName.data());
+    const char *M = D.parseMangle(&Demangled);
 
     // Check that the entire symbol was successfully demangled.
-    if (MangledName == nullptr || *MangledName != '\0') {
+    if (M == nullptr || *M != '\0') {
       std::free(Demangled.getBuffer());
       return nullptr;
     }
diff --git a/llvm/lib/Demangle/Demangle.cpp b/llvm/lib/Demangle/Demangle.cpp
--- a/llvm/lib/Demangle/Demangle.cpp
+++ b/llvm/lib/Demangle/Demangle.cpp
@@ -46,6 +46,9 @@
 }
 
 bool llvm::nonMicrosoftDemangle(const char *MangledName, std::string &Result) {
+  if (!MangledName)
+    return false;
+
   char *Demangled = nullptr;
   if (isItaniumEncoding(MangledName))
     Demangled = itaniumDemangle(MangledName);
diff --git a/llvm/tools/llvm-dlang-demangle-fuzzer/llvm-dlang-demangle-fuzzer.cpp b/llvm/tools/llvm-dlang-demangle-fuzzer/llvm-dlang-demangle-fuzzer.cpp
--- a/llvm/tools/llvm-dlang-demangle-fuzzer/llvm-dlang-demangle-fuzzer.cpp
+++ b/llvm/tools/llvm-dlang-demangle-fuzzer/llvm-dlang-demangle-fuzzer.cpp
@@ -13,7 +13,7 @@
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
   std::string NullTerminatedString((const char *)Data, Size);
-  char *Demangled = llvm::dlangDemangle(NullTerminatedString.c_str());
+  char *Demangled = llvm::dlangDemangle(NullTerminatedString);
   std::free(Demangled);
   return 0;
 }
diff --git a/llvm/unittests/Demangle/DLangDemangleTest.cpp b/llvm/unittests/Demangle/DLangDemangleTest.cpp
--- a/llvm/unittests/Demangle/DLangDemangleTest.cpp
+++ b/llvm/unittests/Demangle/DLangDemangleTest.cpp
@@ -11,10 +11,11 @@
 #include "gtest/gtest.h"
 
 #include <cstdlib>
+#include <string_view>
 #include <utility>
 
 struct DLangDemangleTestFixture
-    : public testing::TestWithParam<std::pair<const char *, const char *>> {
+    : public testing::TestWithParam<std::pair<std::string_view, const char *>> {
   char *Demangled;
 
   void SetUp() override { Demangled = llvm::dlangDemangle(GetParam().first); }
@@ -29,9 +30,8 @@
 INSTANTIATE_TEST_SUITE_P(
     DLangDemangleTest, DLangDemangleTestFixture,
     testing::Values(
-        std::make_pair("_Dmain", "D main"), std::make_pair(nullptr, nullptr),
-        std::make_pair("_Z", nullptr), std::make_pair("_DDD", nullptr),
-        std::make_pair("_D88", nullptr),
+        std::make_pair("_Dmain", "D main"), std::make_pair("_Z", nullptr),
+        std::make_pair("_DDD", nullptr), std::make_pair("_D88", nullptr),
         std::make_pair("_D8demangleZ", "demangle"),
         std::make_pair("_D8demangle4testZ", "demangle.test"),
         std::make_pair("_D8demangle4test5test2Z", "demangle.test.test2"),