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
@@ -29,7 +29,7 @@
   demangle_success = 0,
 };
 
-char *itaniumDemangle(const char *mangled_name, char *buf, size_t *n,
+char *itaniumDemangle(std::string_view mangled_name, char *buf, size_t *n,
                       int *status);
 
 enum MSDemangleFlags {
@@ -65,7 +65,7 @@
 /// demangling occurred.
 std::string demangle(const std::string_view MangledName);
 
-bool nonMicrosoftDemangle(const char *MangledName, std::string &Result);
+bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result);
 
 /// "Partial" demangler. This supports demangling a string into an AST
 /// (typically an intermediate stage in itaniumDemangle) and querying certain
diff --git a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp b/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
--- a/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
+++ b/llvm/lib/DebugInfo/Symbolize/Symbolize.cpp
@@ -679,7 +679,7 @@
 LLVMSymbolizer::DemangleName(const std::string &Name,
                              const SymbolizableModule *DbiModuleDescriptor) {
   std::string Result;
-  if (nonMicrosoftDemangle(Name.c_str(), Result))
+  if (nonMicrosoftDemangle(Name, Result))
     return Result;
 
   if (!Name.empty() && Name.front() == '?') {
@@ -700,7 +700,7 @@
     std::string DemangledCName(demanglePE32ExternCFunc(Name));
     // On i386 Windows, the C name mangling for different calling conventions
     // may also be applied on top of the Itanium or Rust name mangling.
-    if (nonMicrosoftDemangle(DemangledCName.c_str(), Result))
+    if (nonMicrosoftDemangle(DemangledCName, Result))
       return Result;
     return DemangledCName;
   }
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
@@ -20,10 +20,10 @@
   std::string Result;
   const char *S = MangledName.data();
 
-  if (nonMicrosoftDemangle(S, Result))
+  if (nonMicrosoftDemangle(MangledName, Result))
     return Result;
 
-  if (S[0] == '_' && nonMicrosoftDemangle(S + 1, Result))
+  if (S[0] == '_' && nonMicrosoftDemangle(MangledName.substr(1), Result))
     return Result;
 
   if (char *Demangled = microsoftDemangle(S, nullptr, nullptr)) {
@@ -43,14 +43,15 @@
 
 static bool isDLangEncoding(std::string_view S) { return starts_with(S, "_D"); }
 
-bool llvm::nonMicrosoftDemangle(const char *MangledName, std::string &Result) {
+bool llvm::nonMicrosoftDemangle(std::string_view MangledName,
+                                std::string &Result) {
   char *Demangled = nullptr;
   if (isItaniumEncoding(MangledName))
     Demangled = itaniumDemangle(MangledName, nullptr, nullptr, nullptr);
   else if (isRustEncoding(MangledName))
-    Demangled = rustDemangle(MangledName);
+    Demangled = rustDemangle(MangledName.data());
   else if (isDLangEncoding(MangledName))
-    Demangled = dlangDemangle(MangledName);
+    Demangled = dlangDemangle(MangledName.data());
 
   if (!Demangled)
     return false;
diff --git a/llvm/lib/Demangle/ItaniumDemangle.cpp b/llvm/lib/Demangle/ItaniumDemangle.cpp
--- a/llvm/lib/Demangle/ItaniumDemangle.cpp
+++ b/llvm/lib/Demangle/ItaniumDemangle.cpp
@@ -365,16 +365,17 @@
 
 using Demangler = itanium_demangle::ManglingParser<DefaultAllocator>;
 
-char *llvm::itaniumDemangle(const char *MangledName, char *Buf,
-                            size_t *N, int *Status) {
-  if (MangledName == nullptr || (Buf != nullptr && N == nullptr)) {
+char *llvm::itaniumDemangle(std::string_view MangledName, char *Buf, size_t *N,
+                            int *Status) {
+  if (MangledName.empty() || (Buf != nullptr && N == nullptr)) {
     if (Status)
       *Status = demangle_invalid_args;
     return nullptr;
   }
 
   int InternalStatus = demangle_success;
-  Demangler Parser(MangledName, MangledName + std::strlen(MangledName));
+  Demangler Parser(MangledName.data(),
+                   MangledName.data() + MangledName.length());
   Node *AST = Parser.parse();
 
   if (AST == nullptr)
diff --git a/llvm/lib/ProfileData/GCOV.cpp b/llvm/lib/ProfileData/GCOV.cpp
--- a/llvm/lib/ProfileData/GCOV.cpp
+++ b/llvm/lib/ProfileData/GCOV.cpp
@@ -339,7 +339,7 @@
       if (Name.startswith("_Z")) {
         int status = 0;
         // Name is guaranteed to be NUL-terminated.
-        char *res = itaniumDemangle(Name.data(), nullptr, nullptr, &status);
+        char *res = itaniumDemangle(Name, nullptr, nullptr, &status);
         if (status == 0) {
           demangled = res;
           free(res);
diff --git a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
--- a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
+++ b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
@@ -71,10 +71,10 @@
 }
 
 static std::string demangle(const std::string &Mangled) {
-  const char *DecoratedStr = Mangled.c_str();
+  std::string_view DecoratedStr = Mangled;
   if (StripUnderscore)
     if (DecoratedStr[0] == '_')
-      ++DecoratedStr;
+      DecoratedStr.remove_prefix(1);
 
   std::string Result;
   if (nonMicrosoftDemangle(DecoratedStr, Result))
@@ -86,9 +86,10 @@
   if (Types)
     Undecorated = itaniumDemangle(DecoratedStr, nullptr, nullptr, nullptr);
 
-  if (!Undecorated && strncmp(DecoratedStr, "__imp_", 6) == 0) {
+  if (!Undecorated && DecoratedStr.substr(6) == "__imp_") {
     Prefix = "import thunk for ";
-    Undecorated = itaniumDemangle(DecoratedStr + 6, nullptr, nullptr, nullptr);
+    Undecorated =
+        itaniumDemangle(DecoratedStr.substr(6), nullptr, nullptr, nullptr);
   }
 
   Result = Undecorated ? Prefix + Undecorated : Mangled;
diff --git a/llvm/tools/llvm-nm/llvm-nm.cpp b/llvm/tools/llvm-nm/llvm-nm.cpp
--- a/llvm/tools/llvm-nm/llvm-nm.cpp
+++ b/llvm/tools/llvm-nm/llvm-nm.cpp
@@ -639,7 +639,7 @@
 
 static std::optional<std::string> demangle(StringRef Name) {
   std::string Demangled;
-  if (nonMicrosoftDemangle(Name.str().c_str(), Demangled))
+  if (nonMicrosoftDemangle(Name, Demangled))
     return Demangled;
   return std::nullopt;
 }
diff --git a/llvm/tools/llvm-opt-report/OptReport.cpp b/llvm/tools/llvm-opt-report/OptReport.cpp
--- a/llvm/tools/llvm-opt-report/OptReport.cpp
+++ b/llvm/tools/llvm-opt-report/OptReport.cpp
@@ -340,7 +340,7 @@
             if (!NoDemangle) {
               int Status = 0;
               char *Demangled =
-                itaniumDemangle(FuncName.c_str(), nullptr, nullptr, &Status);
+                  itaniumDemangle(FuncName, nullptr, nullptr, &Status);
               if (Demangled && Status == 0) {
                 OS << Demangled;
                 Printed = true;