diff --git a/libcxxabi/src/cxa_demangle.cpp b/libcxxabi/src/cxa_demangle.cpp
--- a/libcxxabi/src/cxa_demangle.cpp
+++ b/libcxxabi/src/cxa_demangle.cpp
@@ -386,15 +386,12 @@
 
   int InternalStatus = demangle_success;
   Demangler Parser(MangledName, MangledName + std::strlen(MangledName));
-  OutputBuffer O;
-
   Node *AST = Parser.parse();
 
   if (AST == nullptr)
     InternalStatus = demangle_invalid_mangled_name;
-  else if (!initializeOutputBuffer(Buf, N, O, 1024))
-    InternalStatus = demangle_memory_alloc_failure;
   else {
+    OutputBuffer O(Buf, N);
     assert(Parser.ForwardTemplateRefs.empty());
     AST->print(O);
     O += '\0';
diff --git a/libcxxabi/src/demangle/Utility.h b/libcxxabi/src/demangle/Utility.h
--- a/libcxxabi/src/demangle/Utility.h
+++ b/libcxxabi/src/demangle/Utility.h
@@ -69,7 +69,9 @@
 
 public:
   OutputBuffer(char *StartBuf, size_t Size)
-      : Buffer(StartBuf), CurrentPosition(0), BufferCapacity(Size) {}
+      : Buffer(StartBuf), BufferCapacity(Size) {}
+  OutputBuffer(char *StartBuf, size_t *SizePtr)
+      : OutputBuffer(StartBuf, StartBuf ? *SizePtr : 0) {}
   OutputBuffer() = default;
   // Non-copyable
   OutputBuffer(const OutputBuffer &) = delete;
@@ -77,12 +79,6 @@
 
   operator StringView() const { return StringView(Buffer, CurrentPosition); }
 
-  void reset(char *Buffer_, size_t BufferCapacity_) {
-    CurrentPosition = 0;
-    Buffer = Buffer_;
-    BufferCapacity = BufferCapacity_;
-  }
-
   /// If a ParameterPackExpansion (or similar type) is encountered, the offset
   /// into the pack that we're currently printing.
   unsigned CurrentPackIndex = std::numeric_limits<unsigned>::max();
@@ -198,21 +194,6 @@
   ScopedOverride &operator=(const ScopedOverride &) = delete;
 };
 
-inline bool initializeOutputBuffer(char *Buf, size_t *N, OutputBuffer &OB,
-                                   size_t InitSize) {
-  size_t BufferSize;
-  if (Buf == nullptr) {
-    Buf = static_cast<char *>(std::malloc(InitSize));
-    if (Buf == nullptr)
-      return false;
-    BufferSize = InitSize;
-  } else
-    BufferSize = *N;
-
-  OB.reset(Buf, BufferSize);
-  return true;
-}
-
 DEMANGLE_NAMESPACE_END
 
 #endif
diff --git a/llvm/include/llvm/Demangle/Utility.h b/llvm/include/llvm/Demangle/Utility.h
--- a/llvm/include/llvm/Demangle/Utility.h
+++ b/llvm/include/llvm/Demangle/Utility.h
@@ -69,7 +69,9 @@
 
 public:
   OutputBuffer(char *StartBuf, size_t Size)
-      : Buffer(StartBuf), CurrentPosition(0), BufferCapacity(Size) {}
+      : Buffer(StartBuf), BufferCapacity(Size) {}
+  OutputBuffer(char *StartBuf, size_t *SizePtr)
+      : OutputBuffer(StartBuf, StartBuf ? *SizePtr : 0) {}
   OutputBuffer() = default;
   // Non-copyable
   OutputBuffer(const OutputBuffer &) = delete;
@@ -77,12 +79,6 @@
 
   operator StringView() const { return StringView(Buffer, CurrentPosition); }
 
-  void reset(char *Buffer_, size_t BufferCapacity_) {
-    CurrentPosition = 0;
-    Buffer = Buffer_;
-    BufferCapacity = BufferCapacity_;
-  }
-
   /// If a ParameterPackExpansion (or similar type) is encountered, the offset
   /// into the pack that we're currently printing.
   unsigned CurrentPackIndex = std::numeric_limits<unsigned>::max();
@@ -198,21 +194,6 @@
   ScopedOverride &operator=(const ScopedOverride &) = delete;
 };
 
-inline bool initializeOutputBuffer(char *Buf, size_t *N, OutputBuffer &OB,
-                                   size_t InitSize) {
-  size_t BufferSize;
-  if (Buf == nullptr) {
-    Buf = static_cast<char *>(std::malloc(InitSize));
-    if (Buf == nullptr)
-      return false;
-    BufferSize = InitSize;
-  } else
-    BufferSize = *N;
-
-  OB.reset(Buf, BufferSize);
-  return true;
-}
-
 DEMANGLE_NAMESPACE_END
 
 #endif
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
@@ -548,9 +548,6 @@
     return nullptr;
 
   OutputBuffer Demangled;
-  if (!initializeOutputBuffer(nullptr, nullptr, Demangled, 1024))
-    return nullptr;
-
   if (strcmp(MangledName, "_Dmain") == 0) {
     Demangled << "D main";
   } else {
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
@@ -375,15 +375,12 @@
 
   int InternalStatus = demangle_success;
   Demangler Parser(MangledName, MangledName + std::strlen(MangledName));
-  OutputBuffer OB;
-
   Node *AST = Parser.parse();
 
   if (AST == nullptr)
     InternalStatus = demangle_invalid_mangled_name;
-  else if (!initializeOutputBuffer(Buf, N, OB, 1024))
-    InternalStatus = demangle_memory_alloc_failure;
   else {
+    OutputBuffer OB(Buf, N);
     assert(Parser.ForwardTemplateRefs.empty());
     AST->print(OB);
     OB += '\0';
@@ -427,9 +424,7 @@
 }
 
 static char *printNode(const Node *RootNode, char *Buf, size_t *N) {
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
   RootNode->print(OB);
   OB += '\0';
   if (N != nullptr)
@@ -472,9 +467,7 @@
     return nullptr;
   const Node *Name = static_cast<const FunctionEncoding *>(RootNode)->getName();
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
  KeepGoingLocalFunction:
   while (true) {
@@ -525,9 +518,7 @@
     return nullptr;
   NodeArray Params = static_cast<FunctionEncoding *>(RootNode)->getParams();
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
   OB += '(';
   Params.printWithComma(OB);
@@ -543,9 +534,7 @@
   if (!isFunction())
     return nullptr;
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
   if (const Node *Ret =
           static_cast<const FunctionEncoding *>(RootNode)->getReturnType())
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -246,7 +246,10 @@
 
 StringView Demangler::copyString(StringView Borrowed) {
   char *Stable = Arena.allocUnalignedBuffer(Borrowed.size());
-  std::memcpy(Stable, Borrowed.begin(), Borrowed.size());
+  // This is not a micro-optimization, it avoids UB, should Borrowed be an null
+  // buffer.
+  if (Borrowed.size())
+    std::memcpy(Stable, Borrowed.begin(), Borrowed.size());
 
   return {Stable, Borrowed.size()};
 }
@@ -970,9 +973,6 @@
   // Render this class template name into a string buffer so that we can
   // memorize it for the purpose of back-referencing.
   OutputBuffer OB;
-  if (!initializeOutputBuffer(nullptr, nullptr, OB, 1024))
-    // FIXME: Propagate out-of-memory as an error?
-    std::terminate();
   Identifier->output(OB, OF_Default);
   StringView Owned = copyString(OB);
   memorizeString(Owned);
@@ -1283,11 +1283,6 @@
 
   EncodedStringLiteralNode *Result = Arena.alloc<EncodedStringLiteralNode>();
 
-  // Must happen before the first `goto StringLiteralError`.
-  if (!initializeOutputBuffer(nullptr, nullptr, OB, 1024))
-    // FIXME: Propagate out-of-memory as an error?
-    std::terminate();
-
   // Prefix indicating the beginning of a string literal
   if (!MangledName.consumeFront("@_"))
     goto StringLiteralError;
@@ -1446,9 +1441,6 @@
 
   // Render the parent symbol's name into a buffer.
   OutputBuffer OB;
-  if (!initializeOutputBuffer(nullptr, nullptr, OB, 1024))
-    // FIXME: Propagate out-of-memory as an error?
-    std::terminate();
   OB << '`';
   Scope->output(OB, OF_Default);
   OB << '\'';
@@ -2311,8 +2303,6 @@
 
   // Create an output stream so we can render each type.
   OutputBuffer OB;
-  if (!initializeOutputBuffer(nullptr, nullptr, OB, 1024))
-    std::terminate();
   for (size_t I = 0; I < Backrefs.FunctionParamCount; ++I) {
     OB.setCurrentPosition(0);
 
@@ -2339,7 +2329,6 @@
                               char *Buf, size_t *N,
                               int *Status, MSDemangleFlags Flags) {
   Demangler D;
-  OutputBuffer OB;
 
   StringView Name{MangledName};
   SymbolNode *AST = D.parse(Name);
@@ -2364,9 +2353,8 @@
   int InternalStatus = demangle_success;
   if (D.Error)
     InternalStatus = demangle_invalid_mangled_name;
-  else if (!initializeOutputBuffer(Buf, N, OB, 1024))
-    InternalStatus = demangle_memory_alloc_failure;
   else {
+    OutputBuffer OB(Buf, N);
     AST->output(OB, OF);
     OB += '\0';
     if (N != nullptr)
diff --git a/llvm/lib/Demangle/MicrosoftDemangleNodes.cpp b/llvm/lib/Demangle/MicrosoftDemangleNodes.cpp
--- a/llvm/lib/Demangle/MicrosoftDemangleNodes.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangleNodes.cpp
@@ -119,7 +119,6 @@
 
 std::string Node::toString(OutputFlags Flags) const {
   OutputBuffer OB;
-  initializeOutputBuffer(nullptr, nullptr, OB, 1024);
   this->output(OB, Flags);
   StringView SV = OB;
   std::string Owned(SV.begin(), SV.end());
diff --git a/llvm/lib/Demangle/RustDemangle.cpp b/llvm/lib/Demangle/RustDemangle.cpp
--- a/llvm/lib/Demangle/RustDemangle.cpp
+++ b/llvm/lib/Demangle/RustDemangle.cpp
@@ -157,9 +157,6 @@
     return nullptr;
 
   Demangler D;
-  if (!initializeOutputBuffer(nullptr, nullptr, D.Output, 1024))
-    return nullptr;
-
   if (!D.demangle(Mangled)) {
     std::free(D.Output.getBuffer());
     return nullptr;