diff --git a/llvm/include/llvm/ADT/STLArrayExtras.h b/llvm/include/llvm/ADT/STLArrayExtras.h
new file mode 100644
--- /dev/null
+++ b/llvm/include/llvm/ADT/STLArrayExtras.h
@@ -0,0 +1,35 @@
+//===- llvm/ADT/STLArrayExtras.h - additions to <array> ---------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains some templates that are useful if you are working with the
+// STL at all.
+//
+// No library is required when using these functions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_STLARRAYEXTRAS_H
+#define LLVM_ADT_STLARRAYEXTRAS_H
+
+#include <cstddef>
+
+namespace llvm {
+
+//===----------------------------------------------------------------------===//
+//     Extra additions for arrays
+//===----------------------------------------------------------------------===//
+
+/// Find the length of an array.
+template <class T, std::size_t N>
+constexpr inline size_t array_lengthof(T (&)[N]) {
+  return N;
+}
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_STLARRAYEXTRAS_H
diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -18,6 +18,7 @@
 
 #include "llvm/ADT/identity.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/STLArrayExtras.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/iterator.h"
@@ -1410,7 +1411,7 @@
 }
 
 //===----------------------------------------------------------------------===//
-//     Extra additions for arrays
+//     Extra additions to <algorithm>
 //===----------------------------------------------------------------------===//
 
 // We have a copy here so that LLVM behaves the same when using different
@@ -1430,12 +1431,6 @@
   }
 }
 
-/// Find the length of an array.
-template <class T, std::size_t N>
-constexpr inline size_t array_lengthof(T (&)[N]) {
-  return N;
-}
-
 /// Adapt std::less<T> for array_pod_sort.
 template<typename T>
 inline int array_pod_sort_comparator(const void *P1, const void *P2) {
@@ -1563,10 +1558,6 @@
   llvm::sort(adl_begin(C), adl_end(C), Comp);
 }
 
-//===----------------------------------------------------------------------===//
-//     Extra additions to <algorithm>
-//===----------------------------------------------------------------------===//
-
 /// Get the size of a range. This is a wrapper function around std::distance
 /// which is only enabled when the operation is O(1).
 template <typename R>
diff --git a/llvm/lib/Support/ARMAttributeParser.cpp b/llvm/lib/Support/ARMAttributeParser.cpp
--- a/llvm/lib/Support/ARMAttributeParser.cpp
+++ b/llvm/lib/Support/ARMAttributeParser.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/ARMAttributeParser.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLArrayExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/ScopedPrinter.h"
 
diff --git a/llvm/lib/Support/Signals.cpp b/llvm/lib/Support/Signals.cpp
--- a/llvm/lib/Support/Signals.cpp
+++ b/llvm/lib/Support/Signals.cpp
@@ -15,7 +15,7 @@
 
 #include "DebugOptions.h"
 
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLArrayExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/CommandLine.h"
diff --git a/llvm/lib/Support/Triple.cpp b/llvm/lib/Support/Triple.cpp
--- a/llvm/lib/Support/Triple.cpp
+++ b/llvm/lib/Support/Triple.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/Triple.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLArrayExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
diff --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp
--- a/llvm/lib/Support/raw_ostream.cpp
+++ b/llvm/lib/Support/raw_ostream.cpp
@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLArrayExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/Compiler.h"